1" l’tAl.’l‘|uoII‘lv H‘ n ‘I I l : llflhuui r 11!. - 41.11.}; ’ . I o 0v . o t I: I O - . ’I - u |. . \‘ .l'l. I v lb‘lt‘lnnl‘i .- - u ‘i‘." ‘ I \d‘lo. O ‘ II\ I {Ii} . . I .Iotl‘illllll. ' \‘ytu .Uau n - .y lafllalltfilt - x a 1.! u . nmmm 3 129 3900 891 1419 This is to certify that the dissertation entitled Boiiing Incipience and Heat Transfer on Smooth and Enhanced Surfaces presented by Saleem Shakir has been accepted towards fulfillment ofthe requirements for Ph.D Mechanical Engineering degree in ahedwe M ajor professor Date Amt?) , [2‘ (63 :‘Z MSU is an Affirmative Ac!ion.’EquaI Opportunity Instituthm 0— 12771 MSU RETURNING MATERIALS: Place in book drop to LJBRAfiJES remove this checkout from .—:_—_ your record. FINES will be charged if book is returned after the date stamped below. Etc f: 4 1995 BOILING INCIPIENCE AND HEAT TRANSFER ON SMOOTH AND ENHANCED SURFACES By Saleem Shakir A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSPHY Department of Mechanical Engineering 1987 ABSTRACT BOILING INCIPIENCE AND HEAT TRANSFER ON SMOOTH AND ENHANCED SURFACES BY Saleem Shakir A comprehensive experimental study in nucleate pool boiling of binary mixtures was carried out to investigate the effects of mixture composition on boiling incipient and deactivation superheats and heat transfer coefficients. All experiments were performed at a pressure of 1.01 bar on conventional smooth surfaces and an enhanced surface (High Flux of Union Carbide Corp.). Contact angles were also measured for the same mixtures on the smooth surfaces of brass and copper. The incipience and deactivation of boiling sites on the enhanced surface occurred at much lower wall superheats than on the smooth ones. For the mixture systems investigated, the incipient superheats were observed to be higher than the corresponding deactivation superheats. The classical boiling nucleation criterion was found to be inadequate in predicting the measured incipient superheats. The variation in the measured contact angles was not sufficient to explain the maximum in the incipient superheats observed at intermediate mixture compositions. Several new factors were identified for boiling nucleation in mixtures Which could qualitatively explain these maxima in incipient superheats observed for the mixtures. The boiling heat transfer coefficients obtained on the smooth surafces showed a deterioration when compared with the values obtained from a simple linear mixing law between the single component values. The enhanced surface heat transfer coefficients for boiling of the same mixtures showed both positive and negative deviations from the linear udxing law between the pure component values. The heat transfer coefficients on the enhanced surface showed appreciable augmentation when compared to those obtained on conventional smooth surfaces under similar conditions. The Schluender correlation was tested against the observed values of heat transfer coefficients and reasonable agreement was Observed for only two of the four mixture systems tested on smooth surfaces. Enhanced surface heat transfer coefficients could not be satisfactorily correlated by the Schluender correlation. I dedicate this Dissertation in memory of my father, Shakir Ali Thanvi iv ACKNOWLEDGEMENTS I would like to express my sincere appreciation to Dr..J.R. Thome for providing me with the opportunity to design and construct the Boiling Heat Transfer facility and for offering support throughout this endeavor. I vnnxld also like to express my gratitude to Dr. J.R. Lloyd for his valuable suggestions and guidance. In addition, I would also like to thank Dr. J.V. Beck and Dr. J.J. McCrath for their encouragement and help throughout this work. To RHEL Rose for all the help he offered in the laboratory instrumentation. Thanks to my friends S.K. Ali and M. Usman for helping me with the computer facilities. Finally, I wish to acknowledge the efforts of my parents for their contributions and support in more ways than they will ever know. To Seema my wife for her understanding and patience under difficult conditions. It would not be possible without their encouragement. TABLE OF CONTENTS LIST OF TABLES . IJST OF FIGURES NOMENCLATURE . 1. INTRODUCTION . 2. LITERATURE SURVEY 2.1 BOILING CURVE 2.2 INCEPTION OF BOILING 2.2.1 Superheat Requirement for Vapor Nucleation 2.2.2 Boiling Incipience in Binary Mixtures . 2.3 NUCLEATE POOL BOILING IN BINARY MIXTURES 2.3.1 Bubble growth dynamics 2.3.2 Bubble Departure from the Surface 2.4 HEAT TRANSFER COEFFICIENTS IN NUCLEATE POOL BOILING 2.4.1 Predictive Methods for Boiling Heat Transfer Coefficients of Mixtures on Smooth Surfaces 2.5 ENHANCED SURFACES 3!. EXPERIMENTAL FACILITIES AND PROCEWURES 3.1 BOILING FACILITY 3.1.1 Boiling Vessel and Attachments 3.1.2 Equipment and Instrumentation vi Page ix xi xviii 10 l6 19 22 27 29 33 41 46 46 46 49 3.2 TEST SECTIONS 3.3 CONTACT ANGLE FACILITY AND MEASUREMENTS 3.4 MIXTURE PREPARARTION 3.5 EXPERIMENTAL PROCEDURE PHASE EQUILIBRIUM.AND MIXTURE PROPERTIES . 4.1 VAPOR-LIQUID PHASE EQUILIBRIUM 4.2 MIXTURE PROPERTIES . 4.2.1 Generalized Corresponding States Method 4.2.2 Method of Calculation for Binary Mixtures BOILING INCIPIENCE IN BINARY MIXTURES 5.1 BOILING INCIPIENCE RESULTS AND DISCUSSIONS 5.2 FACTORS INFLUENCING BOILING INCIPIENT SUPERHEATS . 5.2.1 Condensation Effect 5.2.2 Contact Angle Effect 5.2.3 Surface Tension Effect . 5.3 TRENDS IN THE OBSERVED EXPERIMENTAL INCIPIENT SUPERHEATS . 5.3.1 Ethanol-benzene mixtures 5.3.2 Aqueous-alcohol mixtures 5.3.3 Enhanced Surface 5.4 SUMMARY OF EFFECTS IDENTIFIED FOR BOILING INCIPIENCE ON A SMOOTH SURFACE . BOILING HEAT TRANSFER COEFFICIENTS . 6.1 EXPERIMENTAL RESULTS AND DISCUSSION 6.2 SMOOTH SURFACE 6.2.1 Prediction of Smooth Surface Results 6.3 ENHANCED SURFACE . vii 51 57 60 6O 62 62 74 75 78 93 93 113 113 115 117 119 119 120 122 123 124 124 125 125 146 7. CONCLUSIONS 7.1 BOILING INCIPIENCE AND DEACTIVATION 7.2 CONTACT ANGLES 7.3 HEAT TRANSFER COEFFICIENTS RECOMMENDATIONS APPENDIX.A COMPUTER PROGRAMS AND MIXTURE PROPERTIES APPENDIX B CALCULATIONS TO OBTAIN WALL SUPERHEATS AND HEAT TRANSFER COEFFICIENTS AKPPENDIX.C EXPERIMENTAL DATA OBTAINED ON SMOOTH AND ENHANCED SURFACES IIIIST OF REFERENCES viii 156 156 157 157 159 161 176 184 216 Table 2.1. 2.2. 4.1. AA.1. 11.1. 1k.1. 1&.12. 15.-2. 13.,2, A-3. LIST OF TABLES Shock's data for the onset of nucleate boiling in flow boiling of ethanol-water mixtures. Numerical values of A0. Binary interaction coefficients (6..) for mixture 1J properties [67]. . . . Summary of mixture systems studied on different surfaces. Comparision of experimental and predicted [Eq. (6.6)] superheats for the Enhanced Surface. Listing of Computer Program MIXPR1.FOR. Listing of CRIDAT.MX1. Listing of CONDAT.MX1. Listing of Computer Program MIXPR2.FOR. Listing of CRIDAT.MX2. Listing of CONDAT.MX2. Mixture Propperties from MIXPR1.FOR and MIXPR2.FOR. . . . . . . . Experimental data for methanol-water mixtures Enhanced Tube-High Flux. Experimental data for methanol-water mixtures Smooth Tube. Experimental data for ethanol-water mixtures Enhanced Tube-High Flux. Experimental data for ethanol-water mixtures Smooth Tube. ix 19 35 92 93 155 161 167 167 168 173 173 174 185 188 191 194 C.2. C.3. C.3. C.4. C.4. 3. 1. 2. l. 2. Experimental data for ethanol-water mixtures Polished Tube. Experimental data for n-propanol-water mixtures Enhanced Tube—High Flux. Experimental data for n-propanol-water mixtures Smooth Tube. Experimental data for ethanol-benzene mixtures Smooth Tube. Experimental data for ethanol-benzene mixtures Smooth Disk. 198 201 204 208 212 LIST OF FIGURES P601 boiling curve. (a) Vapor nuclei trapped in pits and cracks in a surface; (b) liquid front advancing towards a conical cavity; (c) formation of bubbles from a conical cavity. . Hsu's criterion for inception of boiling [26]. Vapor trapping mechanism as envisioned by Lorenz et a1. [34]. Phase equilibrium diagram, surface tension, and slope of saturation curve for ethanol-water by Shock [52]. Contact angle data for ethanol- water mixtures against nitrogen at 25° C by Eddington and Kenning [16]. . . . . . . . . Boiling incipience data for nitrogen-argon mixtures by Thome et a1. [72]. (a) Activation superheats; (b) deactivation superheats. . . The effect of prepressurization on boiling activation superheats for nitrogen- argon mixtures at 1.55 bar [75]. (Legend: +, 0.2 bar; x, 0.4 bar; 0, 0.7 bar of prepressurization). . . . . Bubble growth model of Van Stralen [89] for a spherical bubble growing in a superheated binary mixture. (a) Temperature and concentration profiles; (b) process shown on a phase-equilibrium diagram. Differing definitions of linear mixing law for an azeotropic mixture system. . . . Maximum rise in local boiling point by Thome [74]. Comparision of ethanol-water data at 1.0 bar with four predictive methods. 2 Legend: (0) Valent and Afgan [85] at 300 kW/m ; xi 13 15 17 18 20 21 24 32 39 3.1. (x) Valent and Afgan [85] at 190 kW/mzé (o) Tolubiskiy and Ostrovskiy [78] at 116 kW/m ; (+) Grigorev et al. [21] at 232 kW/mz; (A) Bonilla and Perry [6] at 95 kW/mz; (V) Cichelli and Bonilla [10] at 221 kW/mz; (I) Preusser [45] at 200 kW/mz; (0) present work at 200 kW/mz. Nucleate pool boiling rig (not to scale). Legend: 1-boiling vessel, 2-test boilng surface, 3-bu1k liquid thermocouple, 4—temperature controller thermocouple, 5-immersion heater, 6- sight glass window, 7-liquid feed line, 8- condenser, 9-degassing line, lO-safety relief valve line, ll-pressure gage tap. . . . . Nucleate pool boiling rig. (a) Electrical circuit for the immersion heater to heat the bulk liquid; (b) Electrical circuit for supplying power to the test section. . . . . (a) Smooth disk test surface; (b) Smooth disk test section. Legend: 1-test boiling surface, 2-electrical heater, 3-support section, 4-bottom cover plate, S-thermocouple holes, 6-power input leads. (Dimensions in mm). Smooth copper tube test section. Legend: l-test boiling surface, 2-cartridge heater, 3-stain1ess steel sleeve to hold boiling surface, 4-holes for thermocouple leads, S-power input leads, 6-stainless steel end plug. (Dimensions in mm). . . . . . . . . RMS surface measurement for the smooth disk (R2). (a) near the center; (b) away from the center. (Units: x-axis - micrometer, y-axis - KiloAngstrom) RMS surface measurement for the smooth tube (R1). (a) near the center; (b) away from the center. (Units: x-axis - micrometer, y-axis - kiloAngstrom) . High Flux test boiling tube (not to scale). Legend: 1-High Flux tube, 2-surface coating, 3- copper sleeve, 4-teflon plug, S-epoxy, 6-sleeve to hold boiling surface, 7-thermocoup1e leads, 8- cartridge heater, 9-power input leads, lO-holes for thermocouple leads, ll-thermocouple junction” (Dimensions in mm). Contact angle measurement apparatus. xii 4O 47 48 50 52 53 54 55 56 59 4.1. 4.2. Phase equilibrium diagram for a binary mixture system. (a) Ideal mixture; (b) azeotropic mixture. Phase equilibrium diagram showing the maximum decrease in the local mole fraction of the volatile component. Phase equilirium diagram for methanol-water at 1.01 bar. . . . . . . . . . . . . . . . . . . . . . Difference in the vapor and liquid mole fractions for methanol-water at l.01_bar; (a) Equilibrium conditions; (b) local conditions. . . . Phase equilirium diagram for ethanol-water at 1.01 bar. Difference in the vapor and liquid mole fractions for ethanol-water at 1.01 bar; (a) Equilibrium conditions; (b) local conditions. . . . . . . Phase equilirium diagram for n-propanol-water at 1.01 bar. . . . Difference in the vapor and liquid mole fractions for n-propanol-water at 1.01 bar; (a) Equilibrium conditions; (b) local conditions. . . . . . . . Phase equilirium diagram for ethanol-benzene at 1.01 bar. Difference in the vapor and liquid mole fractions for ethanol-benzene at 1.01 bar; (a) Equilibrium conditions; (b) local conditions. . . . . . . . Variation in liquid thermal conductivity with composition at saturation conditions. . . . . Variation in liquid viscosity with composition at saturation conditions. . . . . . . . . . . Variation in liquid heat capacity with composition at saturation conditions. . . . . . . Variation in surface tension with composition at saturation conditions. (a) Generalized Corresponding States Method; (b) Eq. (4.27). Variation in liquid density with composition at saturation conditions. . . . . . . . . . . . Variation in vapor density with composition at saturation conditions. . . . . . . . . . . . . Variation in heat of vaporization with composition at saturation conditions. . . xiii 64 65 66 67 68 69 70 71 72 73 79 81 82 84 86 88 91 5.1. 5.2. Variation in measured superheats for methanol-water mixture system on smooth tube: (a) boiling incipient superheats; (b) boiling deactivation superheats. . . . . . . . . . . . . . . . . Variation in measured superheats for methanol-water mixture system on enhanced tube: (a) boiling incipient superheats; (b) boiling deactivation superheats. . . . . . . . . . . . Variation in measured superheats for ethanol-water mixture system on smooth tube: (a) boiling incipient superheats; (b) boiling deactivation superheats. . . . . . . . . . . . . . . . . . Variation in measured superheats for ethanol-water mixture system on polished tube: (a) boiling incipient superheats; (b) boiling deactivation superheats. . . . . . . . . . . . . . . . . Variation in measured superheats for ethanol-water mixture system on smooth disk: (a) boiling incipient superheats; (b) boiling deactivation superheats. . . . . . . . . . . . . . . . . Variation in measured superheats for ethanol-water mixture system on enhanced tube: (a) boiling incipient superheats; (b) boiling deactivation superheats. . . . . . . . . . . . . . . . . . Variation in measured superheats for n-propanol- water mixture system on smooth tube: (a) boiling incipient superheats; (b) boiling deactivation superheats. . . . . . . . . . . Variation in measured superheats for n-propanol- water mixture system on enhanced tube: (a) boiling incipient superheats; (b) boiling deactivation superheats. . . . . . . . . . . Variation in measured superheats for ethanol- benzene mixture system on smooth tube: (a) boiling incipient superheats; (b) boiling deactivation superheats. . . . . . . . . . . . .Variation in measured superheats for ethanol- benzene mixture system on smooth disk: (a) boiling incipient superheats; (b) boiling deactivation superheats. . . . . . . . . . . . . . . . . . . (a) Variation in the slope of the saturation curve . __L__ at 1.01 bar, (b) variation in (dP/dT)sat with composition. xiv 94 95 96 97 98 99 . 100 . 101 . 102 . 103 . 105 5.112. 5.1:3 . SQle-. 5.1.55 Variation in measured contact angles for methanol- water mixture system at 1.01 bar against nitrogen gas at 25°C. . . . . . Variation in measured contact angles for ethanol- water mixture system at 1.01 bar against nitrogen gas at 25°C. . . . . Variation in measured contact angles for n-propanol -water mixture system at 1.01 bar against nitrogen gas at 25°C. Variation in measured contact angles for ethanol- benzene mixture system at 1.01 bar against nitrogen gas at 25°C. . Vapor trapping mechanism at the point of bubble break-off. (a) bubble detaching from the surface; (b) vapor trapped in the cavity. . . . . . . Condensation effect illustrated on a phase equilibrium diagram. Variation in contact angle data reported by Ponter and Peier [43] under conditions of equilibrium and total reflux: (a) methanol-water; (b) n-propanol- water. . . . . . . . . . . . . . . Variation in surface tension reported by Ponter and Peier [43] under conditions of equilibrium and total reflux: (a) methanol-water; (b) n-propanol- water. . . . . . . . . Wall superheats for methanol-water mixtures boiling on smooth tube (for decreasing heat flux data). Wall superheats for ethanol-water mixtures boiling on smooth tube (for decreasing heat flux data). Wall superheats for ethanol-water mixtures boiling on polished tube (for decreasing heat flux data). Wall superheats for n-propanol-water mixtures boiling on smooth tube (for decreasing heat flux data). . . . . . . . . . . Wall superheats for ethanol-benzene mixtures boiling on smooth tube (for decreasing heat flux data). . . . . . . . . . . . . . . . . Wall superheats for ethanol-benzene mixtures boiling on smooth disk (for decreasing heat flux data). . . . . . . . . . . . . . . . . . . . . . . XV . 106 . 107 . 108 . 109 . 112 . 114 . 116 . 118 . 126 . 127 . 128 . 129 . 130 . 131 Experimental and predicted (Eq. 6.3) wall superheats for methanol-water mixtures boiling on smooth tube. Comparision of experimental and predicted (Eq. 6.1) boiling heat transfer coefficients using entire data for methanol-water mixtures boiling on smooth tube. Experimental and predicted (Eq. 6.3) wall superheats for ethanol-water mixtures boiling on smooth tube. Comparision of experimental and predicted (Eq. 6.1) boiling heat transfer coefficients using entire data for ethanol-water mixtures boiling on smooth tube. Experimental and predicted (Eq. 6.3) wall superheats for ethanol-water mixtures boiling on polished tube. Comparision of experimental and predicted (Eq. 6.1) boiling heat transfer coefficients using entire data for ethanol-water mixtures boiling on polished tube. . . . . . . . . . . Experimental and predicted (Eq. 6.3) wall superheats for n-propanol-water mixtures boiling on smooth tube. Comparision of experimental and predicted (Eq. 6.1) boiling heat transfer coefficients using entire data for n—propanol-water mixtures boiling on smooth tube. Experimental and predicted (Eq. 6.3) wall superheats for ethanol-benzene mixtures boiling on smooth tube. Comparision of experimental and predicted (Eq. 6.1) boiling heat transfer coefficients using entire data for ethanol-benzene mixtures boiling on smooth tube. Experimental and predicted (Eq. 6.3) wall superheats for ethanol-benzene mixtures boiling on smooth disk. Comparision of experimental and predicted (Eq. 6.1) boiling heat transfer coefficients using data for ethanol-benzene mixtures boiling on smooth disk. Wall superheats for methanol-water mixtures boiling on enhanced tube (for decreasing heat flux data). xvi . 134 . 135 . 136 . 137 . 138 . 139 . 140 . 141 . 142 . 143 . 144 . 145 . 147 6“2(). 6.221.. 6.2222 . 6.2535 . Wall superheats for ethanol-water mixtures boiling on enhanced tube (for decreasing heat flux data). Wall superheats for n-propanol-water mixtures boiling on enhanced tube (for decreasing heat flux data). . . . . . . . . . . . . . . . . Comparision of enhanced surface wall superheats to the smooth tube for methanol-water mixtures. Comparision of enhanced surface wall superheats to the smooth tube for ethanol-water mixtures. Comparision of enhanced surface wall superheats to the smooth tube for n-propanol-water mixtures. Comparision of experimental and predicted (Eq. 6.1) boiling heat transfer coefficients using entire data for n-propanol-water mixtures boiling on enhanced surface. xvii . 148 . 149 . 150 . 151 . 152 p 0 w 0 u h 0. "0 fl’WD‘D‘Hv cm as ’4 *TFi n rtrraa z” €005 €01 1 lex’xd 4’ 4 x NOMENCLATURE empirical parameter empirical scaling parameter J 1 kg K liquid specific heat [ 2 mass diffusion coefficient [22;] bubble departure diameter [m] bubble departure frequency [sec—1] mass diffusion shell thickness [m] thermal boundary layer thickness [m] pressure [bars] heat flux [3%] m power [W] radius of vapor bubble embryo [m] N-m universal gas constant [-————-] kg mol Scriven number time [sec] bubble growth time [sec] bubble waiting time [sec] temperature [°C] saturation temperature [°C] wall temperature [°C] a s ecific volume m- p [kg] 3 __J£___ molar volume [kg-mole] 3 volume [m ] mass fraction of liquid mole fraction of liquid liquid mole fraction of component 1 (volatile) liquid mole fraction of component 2 (non-volatile) xviii (31reaek Symbols (.2 ‘12 6 8 <2 bulk liquid mole fraction of volatile component local liquid mole fraction of volatile component vapor mole fraction of component 1 (volatile) vapor mole fraction of component 2 (non-volatile) bulk vapor mole fraction local vapor mole fraction compressibility factor slope of saturation curve heat transfer coefficient [ 5w ] m K contact angle [degrees] liquid mass transfer coefficient [E] 2 mass diffusion coefficient [EEZT porous coating thickness [mm] J 1. mole] or [kg] temperature difference [K] ideal wall superheat [K] (-Tw-TS) wall superheat [K] heat of vaporization [ boiling range [K] wall superheat of component 1 at given heat flux [K] wall superheat of component 2 at given heat flux [K] cavity half angle [deg.] density [m°%es] or [3%] liquid thermal conductivity [SHE] liquid viscosity [N 2°C] m surface tension [E] m 2 liquid thermal diffusion coefficient [Egg] acentric factor xix Subscripts as: b c 431:]; g. icl. ‘Lfll: 2 1. n1 [>rrdad Maura“ P d S‘Jtperscripts I) E: azeotrope bulk critical experimental gas ideal incipience liquid local mixture predicted reduced saturation saturation vapor wall volatile component non-volatile component departure excess XX CHAPTERI INTRODUCTION The exchange of heat between a heated surface and the liquid surrounding it is one of the most common phenomena employed in the design of heat exchange equipment. When the temperature difference be tween the heated surface and the surrounding liquid (wall superheat) exceeds a certain minimum the mode of heat exchange progresses from a Single-phase to a two-phase convection process. The two-phase process, when accompanied by the formation of vapor bubbles on the heated Surface is referred to as nucleate boiling. When the medium surrounding ‘tllee heated surface is a quiescent pool of stagnant liquid the two-phase Process is called "Nucleate pool boiling." The nucleate pool boiling reignime is bounded by the inception of boiling on the heated surface at 10w heat flux and by the departure from nucleate boiling at the peak l'1€2‘at flux. These two special points are referred to as the "Onset of Nucleate Boiling" (ONE) and "Departure from Nucleate Boiling" (DNB), re3&3pectively. Boiling heat transfer is a two-phase convection process of SjLég‘nif'icant practical importance. Knowledge of the characteristics of t‘\1osed heat flux is lowered is of significance since it specifies the Inirrimum possible wall superheat to sustain boiling during normal oI>er'ation. Previous studies on boiling nucleation have been directed towards single component liquids. The only published data for the onset of boiling in liquid mixtures, to the author's knowledge, is for the forced convective boiling of ethanol-water and ethanol-cyclohexane mixtures inside heated tubes. The second parameter of the present study was to investigate the effects of mixture composition on heat transfer coefficients. The b(“filling heat transfer coefficients for mixtures generally show degradation as compared to their pure component values. Thus, the 1)x’ediction of heat transfer coefficients for binary mixtures becomes important from an economic and reliability standpoint. A pool boiling facility was designed and developed in the present study to investigate the nucleate pool boiling of binary mixtures. Boiling incipience/activation and deactivation superheatsanmlheat transfer coefficients have been experimentally obtained for the binary mixture systems of methanol and water, ethanol and water, n-propanol and water, and ethanol and benzene. All experiments were performed at a pressure of 1.01 bar. Test surfaces studied included smooth surfaces (a roughened disk, a polished tube and a smooth tube), and one enhanced surface (High Flux of Union Carbide Corporation, U.S.A). Since the wetting process was expected to be one of the contributing factors in boiling incipience, contact angles were also measured forzflj.four mixture systems. Mixture physical properties have also been estimated based on the generalized corresponding states method. CHAPTER 2 LITERATURE SURVEY The process of boiling can be divided into two main categories, nucleate pool boiling and flow boiling. In convective boiling, the heat exchange process between the heated wall and the liquid is Obtained in the presence of either an external force (other than gravity) that is applied to make the fluid flow past the surface or due to buoyancy forces created by the boiling process. This type of boiling occurs for evaporation of a liquid flowing inside a tube or over a bank of tubes. 0n the other hand, in pool boiling the heat transfer takes place in a pool of otherwise quiescent liquid surrounding the heated surface. The liquid motdxnn is only due to the natural convection currents created by the heat transfer process itself. A general discussion of boiling will be presented before proceeding to nucleate pool boiling in binary mixtures. 2.1 BOILING CURVE The phenomenon of boiling can be easily understood by considering the boiling curve, as shown in Fig. 2.1. The temperature difference between the heated wall and the liquid surrounding it is plotted on the abscissa. This temperature difference will be referred to as the "wall superheat." The heat flux passing through the heated surface is ‘plotted on the ordinate. A typical curve that is obtained by boiling water is shown in Fig. 2.1. The boiling curve can be divided into four distinct regions: HEAT FLUX q [MW/m2] 1.25 I II In 1! NATURAL g o ruusmou FILM couvscnou 3 2 REGION aouuuo :3 E a O z a 1.00 ' 0.75 0.50 0.25 I 1 L Figure 2.1. Pool boiling curve. The first region, AB, is that of single-phase liquid natural convection heat transfer occurring at small wall superheats. The second region, ED, is that of nucleate pool boiling. Discrete vapor bubbles form and depart from the heated surface. As the wall superheat is increased, the bubble population increases. This portion, BD, can be further subdivided into two regions. In the lower part, BC, only discrete bubbles are observed. A small portion of the surface experiences bubble generation while the rest of the surface still is in the natural convection mode. With further increase in the wall superheat, the process slowly enters the second portion, CD, of fully developed nucleate boiling. In this portion bubbles from neighboring sites on the surface coalesce and the whole surface experiences vigorous boiling. Heat transfer from the surface continues to improve as the process moves along the curve BD. Portion DE on the boiling curve is called the Transition regime. Eventually the vapor bubble generation becomes very intense and starts to restrict the liquid from reaching the heated surface. This results in a deterioration in heat transfer due to the very little contact between the surface and the liquid. Point D represents such a transition. The heated surface is partially covered with patches of vapor and partially with liquid. The portion EF is the Film boiling regime. A stable film of vapor is formed between the heated surface and the surrounding liquid. As the wall temperature is increased, the radiant component of heat transfer becomes dominant. The upper limit of this region is usually the melting point of the material of the heated surface or the electrical heater burns out. The boiling curve shown in Fig. 2.1 is realized if the temperature of the surface can be independently controlled e.g. as can be done by condensing steam for the heat source. For the case where the surface is heated by an electric heater, heat flux becomes the independent parameter.2hntflds situation it is not possible to obtain the transition zone, DE, and the wall temperature suddenly increases to a large value if the heat flux is increased beyond point D. Hence, [naint D is also referred to as the ‘Burnout' point, ‘Critical Heat Flux,’ and also the point from which 'Departure from Nucleate Boiling' takes place. It is to be noted that the boiling curve for different surface- 1iquid combinations remains similar to that shown in Fig. 2.1. However, the position of the curve may shift. The importance of the nucleate boiling regime is obvious. Fairly high heat transfer coefficients are obtained at relatively low wall superheats. The majority of the processes involving two-phase flow are designed toltake place in this portion. The nucleate boiling regime is bounded.by the inception of boiling on the heated surface at a relatively low heat flux and the departure from nucleate boiling at the peak heat flux (point D in Fig. 2.1). Therefore, the lower and upper bounds of the nucleate boiling regime are of significant practical importance. A knowledge of these two points is desired to take advantage of the augmentation in heat transfer coefficients as compared to single-phase natural convection. 2.2 INCEPTION 0F BOILING The process of nucleate pool boiling to be considered here involves the transfer of heat from a solid surface to the surrounding liquid. It is now a well established fact that the process of boiling initiates on the solid surface in the form of bubble streams emanating from tiny pits and scratches on the surface. Such imperfections are microscopic in size and are found on any engineering surface. Experimental studies of Clark et. a1. [11] confirmed that bubbles did form only in small pits and scratches on an otherwise smooth surface. It was postulated that bubbles emerge from cavities on a surface in which a gas or vapor nucleus preexists. As the surface is heated, the vapor nucleus grows and a bubble emerges and detaches from the surface. After the bubble departs some vapor is left behind in the cavity, which becomes a source for the next bubble. The mechanism of trapping of vapor in such cavities is thus very fundamental to the bubble nucleation from a heated surface. Bankoff [3] considered the spreading of liquid over a surface containing grooves and cavities. As a simple case, consider the geometry as shown in Fig. 2.2 in which a semi-infinite liquid front advances unidirectionally over the surface. Different situations can be realized depending upon the contact angle B and the cavity half angle 1. If the contact angle 8 is greater than the angle 21, the advancing liquid front will first strike the opposite wall of the cavity before reaching the bottom of the cavity. The condition for gas entrapment by this approach is: B > 21 (2.1) If the liquid wets the cavity walls, then the remaining vapor pressure will be insufficient to balance the surface tension forces leading to the complete penetration of the liquid to the base of the crevice. (0) GAS LIQUID soup 2" (b) c) L - uomo ( v - upon L L Figure 2.2. (a) Vapor nuclei trapped in pits and cracks in a surface; (b) liquid front advancing towards a conical cavity; (c) formation of bubbles from a conical cavity. 10 Cole [12] has shown that steep, narrow cracks and crevices that are poorly wetted by the liquid are the potential sites for nucleation. Experimental evidence that nucleation indeed results from gas or vapor trapped in such cavities is very promising [32]. 2.2.1 Superheat Rgggirement for Vapor Nucleation Consider the mechanical equilibrium of a spherical vapor nucleus in a liquid at constant temperature T2 and pressure P2 . The pressure difference across the interface can be expressed as: l 1 Pv - P2 - 0(r1+ r2) (2.2) where Pv is the vapor pressure inside the nucleus and P1 is the imposed liquid pressure corresponding to its saturation temperature. r1 and r2 are the principal radii of curvature of the vapor. For r1=r2=r, Eq. (2.2) becomes AP = Pv - P2 = 3% (2.3) Equathn1(2.3) is known as the Laplace equation. For thermal equilibrium, the saturation temperature of the vapor must be equal to that of the surrounding liquid. This implies that the surrounding liquid must be superheated above its saturation temperature Tsat' Curvature of the interface fractionally lowers the vapor pressure, P v, inside the nucleus compared to that above a planar interface, Pm, for the same liquid temperature. This is given by the Kelvin equation P -203 20; Exaexpl: ~£]z[1- f] (2.4) w rRT rP v v From Eqs. (2.3) and (2.4), a :1; P00 - P2 - r [1 + G ] (2.5) 11 To calculate the liquid superheat (TV-T ) corresponding to the sat pressure difference (130$ng the Clausius-Clapeyron equation can be used __ _ ____X___ (2.6) Assuming ideal gas behavior for the vapor (va=RT) and GV >> 5,, the above equation can be written as QB Ahv dT T(RT/P) Ahv __ _ :_; dT (2.7) RT "U'U If the vapor is assumed to be at the normal saturation state, Eq. (2.7) may be integrated between (Pfi’Tsat) and (Pm,TV) Pco TV I __13 __Ath _d_T P ~ 2 R T P2 Tsat P Ah 1n(§2) = - ‘jx (% - % ) 2 R v sat Pco Ahv ln(-—) - + (T - T ) Pi fi T T v sat v sat fiTstat Pco Tv - Tsat = _—Zh;__ 1n(§;) (2.8) Substituting Eq. (2.5) into Eq. (2.8), fiTstat a G2 Tv - Tsat - _—Zh_—_ ln[1 + P—f (l + :-)] (2.9) v £ v v If G > G and —2£ < 1, then Eq. (2.9) can be rewritten as: v 2 Pfir RT2 g_ sat TV - Tsat - ATsat - r P Ah (2'10) 12 The condition along the saturation curve is given by the Clapeyron equation: Ah P d [5%] _ ~v2 (2.11) sat RT Equation (2.11) can be written as 20 AT _ (2.12) sat rc(dP/dT)sat To maintain equilibrium, the superheat of the liquid needed is a function of the surface tension, cavity radius and the slope of the vapor-pressure curve. It should be noted that Eq. (2.12) has been derived for the case of a uniformly superheated liquid. In nucleate pool boiling, the process of nucleation takes place on the heated surface which is surrounded by liquid at its saturation temperature or just below its saturation temperature (as in the case of subcooled boiling). A real engineering surface has an abundance of cavities with a large variation in size and shape. The problem is therefore to model and predict the superheat requirement for the vapor nucleus to grow under such conditions. The criterion (Eq. (2.12)) for the formation of a bubble does not. hold when only the solid surface is hot. This was experimentally verified by Griffith and Wallis [20]. The discrepancy has been attributed to the nature of the temperature field of the liquid in the immediate vicinity of the surface. Hsu [26] proposed a model for the incipience of boiling from a bubble site on a heated surface. A transient one-dimensional heat conduction model was assumed in the liquid layer adjacent to the surface. A hemispherical bubble growing out of a cavity, as shown in Fig. 2.3, was considered. Hsu postulated that the criterion for nucleation from this site is that the temperature of the liquid at the A ‘gkr Isotherm at lbubbie temperature ::'_-_— _..:E§:.' 5:— ‘ _.'.: Figure 2. 3. 13 I I 1 Bubble equilibrium g/Eq. (2.10) \ Liquid temperature profiles with . increasing heat flux q \\\\\\ Hsu's criterion for inception of boiling [26] . '1 re, ("1. (4‘ Av. ‘5. ~..v “A CAL. r. a. U) '~i.‘ (7" (h . ‘ a. e 14 bubble cap is equal to or greater than the bubble interior temperature. This criterion is diagrammatically represented in Fig. 2.3. If the line representing the temperature profile (of the liquid near the surface) intersects the equilibrium bubble curve, then nucleation occurs. The first possible site to be activated corresponds to the point of tangency between the equilibrium bubble curve and the liquid temperature profile. If an.active site of size rc does not exist, then the wall temperature must be increased to a point where active cavities do exist. Hence, a size range of cavities is predicted by Hsu's criterion” Hsu.assumed.that the location of the isotherm corresponding to the temperature Tv is 2rc. The assumption regarding the location of the isotherm has led to various modifications of this criterion. Han and Griffdtfli [22] suggested the location of the isotherm should be at 1.5rc. Howell and Siegel [25] argued that only a favorable heat balance is required for the bubble to grow and that it is not necessary that the thermal layer surrounding the bubble embryo be hotter'dunithe bubble embryo itself at all distances. Lorenz, Mikic and Rohsenow [34] developed a model to account for the wettability of the surface and the geometrical shape of the cavity. Contact angles were used as a measure of the wettability and the geometry of the cavity was represented by the radius of its mouth and its included angle, Fig. 2.4. A simple vapor trapping mechanism was considered.fOr the idealized case of a conical cavity. Once the vapor is trapped by the liquid front, the interface readjusts to form an embryo with radius of curvature reff' Conservation of volume requires reff to be a function of B and 1. The model is useful in the sense that if the size range of cavities is known for one liquid, then the equivalent value of reff for other liquids with different contact lS ADVANCING ADVANCING LIQUID : LIQUID ¢———— ‘— souo SOLID CONICAL CAVITY CYLINDRICAI. CAVITY Vapor hopped iip>27 Vapor trappedioroil pip“) "Gum LIQUID VAPOR A sous 50m “'0“ Figure 2.4. Vapor trapping mechanism as envisioned by Lorenz et a1. [34]. 16 angles can be obtained. An important aspect of their analysis was that the effective radius reff may not necessarily be the same as the cavity mouth radius and that reff is a function of liquid contact angle and geometrical factors of the cavity. 2,2,2 Boiling Incipience in Binarngixtures Very few experimental studies have investigated the functional dependence of boiling incipient superheats on the mixture composition. Shock [51] obtained some results for the onset of nucleate boiling for fIOW'boiling of ethanol-water mixtures inside a heated tube. These temperatures were obtained by observing changes in the heated tube's axial temperature profile. He noted that the trends in.arand (dP/dT)sat at 1.01 bar, Fig. 2.5, predict a decrease in the superheat required for nucleation, Eq. (2.12). Only three mole fractions were tested by Shock, Table 2.1. The increase in the superheat was attributed to the drastic change in the contact angle with increasing composition of ethanol. See the contact angle data of Eddington and Kenning [16] for the ethanol-water mixtures shown in Fig. 2.6, for instance. Shock [52] concluded that for low contact angle fluids it may not be realistic to assume that bubbles on the point of nucleation are hemispheres at the mouth of cavities with circular entrances of radius lay Fbr such cases rC is not equal to reff' With low contact angle fluids, theznumber of sites that trap vapor are smaller in number, and in cavities where vapor is trapped, the volume of the vapor is greatly reduced. The critical nucleus in such conditions may no longer be at the cavity mouth, but deep within the cavity with reff < rc. This decrease in r may be responsible for the greater superheats required for the stability of the nucleus. l7 4200 1!] 4000 » ‘- i ‘1’ m 3000 - N [tribe] 3600 - - 60 - 50 1 40 «rt-4s] Figure 2.5. Phase equilibrium diagram, surface tension, and slope of saturation curve for ethanol-water by Shock [52] . 18 100 I I I y I l I I I 8 0 Brass . I Stainless steel - '3? o -l 1’. e1 - q 0 l j l 1 a a a a n 00 0.2 0.4 06 08 10 xethanol Figure 2.6. Contact angle data for ethanol-water mixtures against nitrogen at 25°C by Eddington and Kenning [16] . 19 Table 2.1. Shock's data for the onset of nucleate boiling in flow boiling of ethanol-water mixtures x Tw ATsat reff P ethanol (°C) (°C) (pm) (bar) 0.0 138.2 9.9 1.05 2.61 0.058 143.2 26.6 0.23 2.59 0.197 145.0 36.7 0.095 2.47 Thome et al. [72] reported on incipient superheats in pool boiling for the cryogenic mixture system nitrogen-argon at 1.0 bar. The activation and deactivation of the same boiling site was obtained for fourteen compositions in the range 0.04-1.0 mole fraction of nitrogen. No effect of composition on the superheats was observed, Fig. 2.7, even though Eq. (2.12), the solid curve in Fig. 2.7(a), predicts a monotonic decrease. The site activated and deactivated at the same wall superheat. Contact angle variation with composition for this mixture system is not known, but the values are assumed to be small. Mercier (in [75]) looked at the effect of prepressurization on the activation superheats for the nitrogen-argon mixture, Fig. 2.8. For this case a maximum was observed. Prepressurization is believed to cause partial or complete condensation of the vapor nuclei, resulting in higher incipient superheats. 2.3 NUCLEATE POOL BOILING HEAT TRANSFER IN BINARY LIQUID MIXTURES Experimental investigations on nucleate pool boiling of binary mixtures have established that the boiling heat transfer coefficients of the mixtures, at a given heat flux, can be considerably lower than would be expected for an "ideal" single-component liquid with the same physical properties as the mixture. To understand the deterioration in the heat transfer coefficients of mixtures, it is necessary to consider the important boiling parameters and their functional dependence on 20 1* a 0 l i 1 l i l l l i 0 02 04 0.6 08 10 (O) initrogen 2 - .. Ideact bi . . 2 I Y i . 1. AU] 1 f i 0? ii 0 0. 2 0.4 0. 6 0. 8 1.0 i b ) i nitrogen Figure 2.7. Boiling incipience data for nitrogen-argon mixtures by Thome et a1. [72] . (a) Activation superheats; (b) deactivation superheats. A1'inc [K] Figure 2 . 8 . 21 22 , , , . . . . . . 20 - I . x - e t + t 3 . x O 18 . x g . + + e 16 - : g 9 '1 l4 .. ii 12 ~ .. 10 - .. 3 - Prepressurization (bars) " 0 _ '1' 0.2 _, x 0.4 3’ 4 - . 0 0.7 2 - q o 1 L l l 1 l L l 1 0.0 0.2 0.4 0.0 0.0 1.0 ' 2nitrogen The effect of prepressurization on boiling activation superheats for nitrogen-argon mixtures at 1.55 bar [75] . 22 mixture composition. Various mechanisms that contribute to the augmentation in the heat transfer process in nucleate boiling will also be discussed. 2 1 Bubble Growth ice The process of nucleate boiling is identified by the generation of vapor bubbles on the heated surface. Hence, the mechanics of bubble growth is a key to understanding the nucleate boiling process. The growth of a bubble begins once the vapor nucleus attains a size greater than that for stable equilibrium. Stated differently, once the wall superheat exceeds the equilibrium value, the bubble starts to grow. Most of the earlier models of the bubble growth process were developed to describe single component fluids. The same ideas were then extended to explain the bubble growth dynamics for mixtures of fluids. Bubble growth in a single component fluid can be divided into two periods [19] . The first period of growth is dominated by hydrodynamic and surface tension forces. This early stage of growth, which is relatively short, is hydrodynamically controlled by the imparting of inertia to the surrounding liquid. The inertial stresses rise rapidly after nucleation and then decrease proportional to l/r2 as the bubble enters the second period of growth, known as the "asymptotic" period. The growth is then limited by the rate at which heat can diffuse from the superheated liquid surrounding the bubble to the bubble interface thus providing the latent heat of vaporization needed to vaporize the liquid. The growth rate of the bubble is therefore governed by the conduction of heat to the bubble interface. In a binary mixture the phenomenon of vapor bubble growth is much more complex. In general, the composition of the volatile component in the vapor phase, 37, is greater than in the liquid phase, 32. During the 23 growth of a vapor bubble, the different volatilities of the two components cause a depletion of the volatile component very near the bubble interface. This is due to the fact that the volatile component 'vaporizes nwme readily. This results in a local concentration gradient around the bubble. The local value of El decreases and the bubble point rises. Figure 2.9 shows the thermal and concentration gradient around a bubble. The bubble point at the interface reaches its maximum value when the rate of diffusion of the volatile component to the interface balances the rate of its excess evaporation at the interface. The rate of evaporation of the volatile component at the interface is proportional to the composition difference between the vapor phase and the liquid phase G-SE). This was first explained by Van Wijk et a1. [96]. Due to the rise in the local boiling point, the driving force to supply latent heat to the bubble is reduced to Tw-Tsat,loca1' This causes a decrease in the bubble growth rate in mixtures as compared.to a single-component liquid with physical properties the same as those of the mixture. Such a hypothetical fluid can also be referred to as an "equivalent pure fluid." Several theoretical and experimental studies have concentrated oni bubble growth models. These studies can be separated into two categories, those 'for bubbles growing homogeneously in a superheated liquid i.e. remote from a heated surface, and those growing heterogeneously at a heated wall. Spherical bubble growth remote from a heated surface. Scriven [49] and Van Stralen [87-93] extended the theory for spherically symmetric bubble growth for single component liquids to binary mixtures. Scriven concluded that the rate of bubble growth, dr/dt, in the asymptotic 24 1“) x---- .1--- Diffusion 4}, shall -- ---_3f Thermal ' ei boundary ‘ it." : i layer : E A0 I i AT : E ATeff 1 Tact (‘5) i i i d' s r T re Iu (0 l A L TW 1 Tat """""""" ISOLO -------------- i ....... g ' .t L i (b) Figure 2.9. Bubble growth model of Van Stralen [89] for a spherical bubble growing in a superheated binary mixture. (a) Temperature and concentration profiles; (b) process shown on a phase-equilibrium diagram. 25 stage in a binary mixture is always slower than that of an equivalent pure fluid. The expression for the radius is given in the form: r = 2312;? (2.13) where B is the bubble growth coefficient and as shown below is a function of the composition of the fluid as well as the wall superheat. 737; AT (pV/p,>[1-(y-x>J~,/6 (cpg/Ahv>
oon Hoouu muoaaaaouim .Houwon empauuuaoim .ooawuom wcHHwon umou-H "viewed .aofiuoom umou onou Hoodoo euooam 320* .m.n assume n.0mw ill. a‘ mn/vm/VL/vm/VAV vzvmwmywxvm/m Iwmymxvmnu IAHV @00 .L fiwn N - s \\\\.\\\\\VU 9'92 \\\\\\ \\\\\ 5dr 54 r 1‘ 5 03-0." 1445 ii! 8 I; :i ' l :I U ........................................................ n:- R U. 20:: . ; : ii "R 24 49"" L ........................ '. ..... I'!’ ........ "W“ : - ujtuq ,, l: . ., 11111;} R .... il.|_.,Il.l“l ........ -....l ...... a .......... 3 .......... 1..-. ..... ,. ................... b o . - l. l ; . .. FIngLe "1'9 5 [l | j. '2; scan new i g l E} w 31w _wi .................................................................................................. .5; -2- .. 5 .35 stage” 5 25 ,5 t ....................... ........................ ............ , ............ :' ............ , ............. :i Eggs—.3 -..0 c0 ' 500 ' 1000 1500 um STI'LUS 2109 U 2000» LEUEL (a) 03/07 i.e.-.48 kFl . . , . . . 2 . "g; ID 0 l‘ ' i .3 °. *1 ..................... 3! p 0. a 20'; ............................................................................... .- I]. H k 875. Fl fl . - I. g , I M!- ; l 'I "1 , E . , Ra 3 . 65013! 0 Ella . :‘tilmfiwfuhd milil'nilli .Ll. . . ”Tani . . . . 1. . i . . It‘ll. Jijuh'li'l 31“! l-Wffii.wo 1.11....g ,r . I I Figure 3.6. RMS surface measurement for the smooth disk (R2). (a) near the center; (b) away from the center. (Units: x- axis - micrometer, y-axis - kiloAngstrom). e- 410. a TIR 11 2-un 1. 1201.9 Re- L 0. OUum R 2000.un RngLe NIH SCH" HEHU 1 UI 5fum -2 III 400 1 S 80 S 25 SCH" t=40sec DIR.-n> ST?LU3 21mg 0 ZOODUM LEUEL .03/07 14-57 ID 1' L, 0. 9 R ' 0. fl ' _. 909- 125. H TIR 10.1?kfl Ra 925. R E 0.00um R '2000 um SE8" t-40scc DIR -—> STYLUS 21mg 0 2000Un LEUEL Figure 3.7. 55 .1.’ I. coco-Io-g CO — . 1 00...... -—..—. .... ............................................................................................ wit-.2: -0. my ------------------------------------------------------------------- l _. - - . C.....O.... C... : . . O . . U . 0 O . . . . . C . . I O . . . O O O O O O 0 O O O . . C . I . O . C . . O O O O O . O . . . C . . . . . . . I O . . . . . . . . . . . O O . O . O . C C . . I . . l . . . O U C . O . : . _t'::_::‘ TEHCDR INSTRUMENTS “2E ......................... 1 E .................. i ............................. ........................ oEfiflfir‘th‘ MAL'?‘ pm... . .. El . 1.11 .E: _.1 ....................... ........................ , ........................ , ....................... ' 1 TEWCCP [HSTRUMEHTE RMS surface measurement for the smooth tube (R1). (a) near the center; (b) away from the center. (Units: axis - micrometer, y- -axis - kiloAngstrom). X- 56 .AEE SH mcoamcoafivv .coaquSH oan:ooofiuo£u-aa .mvuoH oaflfioooahoSu you moHo£-OH .mvon wanna H03091m .Houoon owouuuuo01m .muooH mamaoooauonu-n .oocMHSm wcaaaon vac: ou o>oon1o .hxono1m .mnaa coamou1c .o>ooam Honnoo-n .mcauuoo ooomuam-u .onau stm £mH=1H ”vcowoa .Aoawom cu uosv ondu mafiawon umou RSHh an“: .w.m ousmfim .: L L . n.«- 1.": 1 n «— I'll] I'IIII-nlu. .s!!!taol.‘l'lfl"l.li‘nn’!arovvalI . 57 vessel. Four thermocouples were inserted axially in the wall of the tube and the temperature of the surface was extrapolated from their readings. Details of the calculations are given in Appendix B. The heater inside the copper tube was powered by an a.c. variac. All four mixture systems, i.e. methanol-water, ethanol-water, propanol-water and ethanol-benzene, were tested on this surface. The surface of this tube was also treated with a 400 grade emery paper. A polished tube (mirror finish) of the same geometry was also used to test only the ethanol— water mixture system. RMS surface roughness measurements of the disk and the tube (after being roughened with emery paper) are shown in Figs. 3.6 and 3.7. These measurements were taken at University of Notre Dame. The third test section was an enhanced tube made out of High Flux tubing, Fig. 3.8. Methanol-water, ethanol-water and propanol-water mixture systems were tested on this surface. The ethanol-benzene mixture system was already investigated by Ali and Thome [2] on the same surface and was not repeated. 3.3 CONTACT ANGLE FACILITY AND MEASUREMENTS Contact angles were measured for all four binary mixture systems investigated in this work. Measurements were made on smooth surfaces of brass and copper. The sessile drOp method was employed using a NRL (Naval Research Laboratory) Contact Angle Goniometer Model 100 manufactured by Rame Hart, USA. This model is comprised of an optical bench on which are mounted a microscope assembly with a magnification of 23X, a specimen stage and a variable intensity illuminator. Two independently rotatable cross hairs are provided in the goniometer head to allow direct reading of the contact angle in degrees. 58 A stainless steel chamber (similar to that in Fig. 3.1) was specifically fabricated to obtain the controlled conditions (temperature, pressure and composition ) required for contact angle measurements of mixtures. The test surface was made by soldering two semi-circular pieces of brass and copper to form a circular disk 50 mm in diameter and 2 mm thick. It was first thoroughly cleaned with acetone and then with double distilled water before placing on a spool inside the chamber. The chamber was placed on the stage between the light source and the microscope. Using fine adjustment screws the test surface was positioned perfectly horizontal. High quality optical flats (faces parallel to one-millionth of an inch, "Van-Keuren," USA) were mounted on the chamber for viewing purposes. Figure 3.9 shows a picture of the assembly. The chamber was first sealed, then evacuated using the vacuum pump and finally filled with nitrogen gas. The temperature inside the chamber was maintained at 25°C by using a very small heater (75 watts). Two thermocouples were placed very near the surface to measure the gas temperature. A sensitive diaphragm pressure regulator was used in the nitrogen line to maintain the pressure at 1.01 bar. Any excessive pressure was released manually through a vent valve. A micrometer syringe assembly (2.0 ml capacity) was mounted on the top of the chamber to introduce a liquid droplet of 0.002 ml on the test surface. When observed on the microscope, the droplet appears as a silhouette against a soft green background. The liquid/solid interface is aligned with the horizontal cross hair, and the contact angle is determined by rotating the read-out crosshair to tangency with the drop profile at its base. The value of the contact angle is directly read on the goniometer scale which is calibrated in l-degree increments. For each mixture composition an average of 36 measurements were made. The 59 Figure 3.9. Contact angle measurement apparatus. 60 error in measurement was $0.5 degrees and the reproducibility of the readings was better than i2 degrees. 3.4 MIXTURE PREPARATIONS The binary mixtures were prepared on a weight basis using a sensitive balance. Double distilled water and reagent grades of methanol, ethanol, propanol, and benzene were used to prepare the mixtures. The density of a sample of each mixture was determined before and after each experiment to check if any changes in the mixture composition took place due to degassing of the system. The results showed negligible variation (within the error of the measurement of density) . 3.5 EXPERIMENTAL PROC-URE The vessel was first evacuated using an Edwards two-stage vacuum pump to a pressure between 0.1 and 0.0 psia. The mixture was then fed in to the vessel through the liquid feed line with all other openings completely closed. As the liquid reached the desired level, 8 to 10 cm above the test section, the valve on the feed line was closed. The set point on the temperature controller was moved to a point corresponding to the saturation temperature of the mixture. Power to the temperature controller and hence to the immersion heater was then turned on. Once the pressure inside the vessel exceeded 1.01 bar the valve on the degassing line was slowly opened at discrete intervals until saturation conditions, temperature and corresponding pressure (1.01 bar), were . reached. Power to the test section was then supplied. The heat flux was slowly increased to a moderately high value, approximately 175-200 kW/mz, and the surface was allowed to vigorously boil for 15 to 20 minutes. The saturation conditions were maintained by manually 61 controlling the coolant flow rate to the condenser. The heat flux to the test section.was then slowly decreased to zero and the surface was 1allowed.to come to thermal equilibrium with the saturated bulk liquid. Extra care was taken during this cool-down to maintain the pressure at its saturation value (1.01 bar in this case) to avoid any affect of pre-pressurization on the subsequent process. The heat flux was then increased in small increments after steady state was achieved at each step until a single boiling site was observed to be activated or complete surface activation occurred. The temperature readings from the thermocouples embedded in the wall of the test surface were displayed on the temperature readout devices and were recorded at each heat flux setting. The power to the surface was obtained from the voltage and current measurements. Complete surface activation was accompanied by a sudden drop in the surface temperature. After activation occurrrui, the heat flux was gradually increased to its operating maximum and then lowered to its minimum to obtain the boiling curve and the wall superheat of boiling deactivation on the test surface. This process was repeated at least twice for obtaining heat transfer coefficients and a minimum of three times for incipience and deactivation superheats. CHAPTER4 PHASE EQUILIBRIUM AND lflXTURE PHYSICAL PROPERTIES 4.1 VAPOR-LIQUID PHASE EQUILIBRIUM The process of mixture boiling requires an understanding of the thermodynamics of vapor-liquid phase equilibria. Only a summary is given here. The factor that makes thermodynamics of mixtures different . from that of pure substances is the differing compositions in the liquid and vapor phase that may still be in equilibrium with each other. The pertinent parameters for mixtures are then pressure, temperature and composition of every component in each phase.Conservation of mass requires E ii - 1.0 1 = 1,2, ------ ,n (4.1) 1 E 3:1 = 1.0 i = 1,2, ------ ,n (4.2) 1 here 5&1 and §i are the mole fractions of component i in the liquid and vapor phases, respectively. For a binary mixture, i=2. The number of independent variables to completely specify the state of the system can be determined from the phase rule for non-reactive components. Consider a system containing C distinct components and let P be the number of phases in which each of the components is present. The degree of freedom of the system, F, i.e. the number of variables that can be independently chosen, is given by: F=C+2-P (11.3) 62 63 In a binary mixture system existing in liquid and vapor phases the value for F-2+2-2-2. If pressure and liquid composition are chosen, then the vapor composition and saturation temperature are uniquely defined. The relationship between these parameters is very conveniently expressed in the form of a Phase-Equilibrium diagram. Figure 4.1 is an example of such a diagram for a binary mixture system at any constant pressure. In this diagram the mole fraction of the more volatile component (the one with the lower boiling point) is plotted as the abscissa and the temperature as the ordinate. A constant temperature line, T will intersect the bubble point line and the dew point line sat’ at two distinct points, labelled as L and V in Fig. 4.1(a). Point L corresponds to the composition of the more volatile component in the liquid phase and point V corresponds to the composition of the same component in the vapor phase. It is noted here that at any intermediate composition the volatile component is above and the non-volatile component is below its boiling point. This results in a vapor phase which is richer in the volatile component since it vaporizes more readily. Some binary mixture systems exhibit a behavior called "azeotropy," as shown in Fig. 4.1(b). The point where the mole fraction of component i is same in both phases is the azeotropic composition. Hence, at an azeotrope the mixture system behaves as a single component. Most mixture systems are non-ideal in their behaviour. The measure of ideality of mixtures is determined by Raoult's law. It states that the partial pressure (Pi) of component i is related to its mole fraction (£1) and the vapor pressure of pure component 1 (Pi) at the same temperature 1 i 1 (4'4) 64 4K Eh P: constant e ____________________________ .5. 7“" 1 2 i : O 1 ' O. 1 ' E : i 1! : ' | I : I E 5 I I : I I 5. i xi yi (0) Vapor Liquid Mole Fraction \ _ P = constant I h» N Temperature I I I I I I I I I I I I I zp—-------- lb-----—-— "1 ’1 (b) Vapor Liquid Mole Fraction Figure 4.1. Phase equilibrium diagram for a binary mixture system. (a) Ideal mixture; (b) azeotropic mixture. 65 I C lllllllllllllllllllllllllll .2 .m nu ® In." mm m» ...... n" 1.. o x, 1.0 ~ rxb ~V1 9.22035; ~YW '0 ~x Phase equilibrium diagram showing the maximum decrease in the local mole fraction of the volatile component. Figure 4.2. 66 00 ‘\ II’CI m 0.20 0.40 0.80 0.80 we Figure 4.3. Phase equilirium diagram for methanol-water at 1.01 bar. 67 0.50 0.40; _ see-3 u _ 1 I? u — " 0.20-1 040-: ”~90 IIIFIIIIIHIHII]!lllllllllllllllllllllITEIlHEIlll 0.00 0.20 0.40 0.80 0.90 m (0) imetbanol 0.50 .4 :1 0.40: u—E _-1 nae—'3 1x I‘. 1 _ l> - " 020—: 2.10—E ”~90 ITIIlllllllilIITITIIIIH]llllllllllllllllllllIllI 0.00 0.20 0.40 0.60 0.90 m (b) imethanol Figure 4.4. Difference in the vapor and liquid mole fractions for methanol-water at 1.01 bar; (a) Equilibrium conditions; (b) local conditions. 68 991—3 . E. 3 .52 1- : i .1. i 1 i 7“ TIII[IIHIIHTEHIIIIHIIIIHEIIIIIIIIIEHIIIIIH 0.” 0.20 0.40 0.. 0.80 m Figure 4.5. iethanol Phase equilirium diagram for ethanol-water at 1.01 bar. 69 0.40 52 I o. 0.00 HI]IIIIIIIIIITIIIIIHIIIIIIFIIIIIIIIIIII 0.00 0.20 0.40 0.60 0.30 m (0) iethanol 0.40 0.30— : : u ._ I 0.20—- e- .. 110—: 2.00 IIHEIIIIIHIIIHHIHIIIHIIIHIIIIIIIIT 0.” 0.20 0.40 0.60 0.80 1..” ('3’ 2ethanol Figure 4.6. Difference in the vapor and liquid mole fractions for ethanol-water at 1.01 bar; (a) Equilibrium conditions; (b) local conditions. Tl'cl 70 m— : AZ 911—: i : s .1 ‘ : :1 E n i 85 IIIIIIIIIIIIIIIIIITIIIIIIIIIIFIIIIIIIIIIIIIIIIII m 0.20 0. 40 0.60 0.80 i.“ xpropanol Figure 4.7. Phase equilirium diagram for n-propanol-water at 1.01 bar . 7l 0.30 q I 0.20 -: 1; I I I I). I- 0.10 .. 2 101MB EIIIIIIIEIIIIIIIIIWIIIIIIIll‘IIIIEIIIIIIIIIIIIIIIIIIIIII 0.00 0.20 0.40 0.60 0.90 00) xfluopand 0.30 .1 0.20 —: -0 -I 1x I ' I z>- «- 0.10 i 0.00 -: 0.” 0.20 0.40 0.60 0.90 we (b) xprepanoI Figure 4.8. Difference in the vapor and liquid mole fractions for n- propanol-water at 1.01 bar; (a) Equilibrium conditions; (b) local conditions. T [’c1 72 “ \I , N \I llllllllJTllIlIllllTllLllll b ---- 8’1 TIIIIIIIII[IIIIIIIIIIITIIIITIIIIIIIIITIIIIIIIIIII am 0.20 0.40 ' 0.90 0.90 m iethatoI Figure 4.9. Phase equilirium diagram for ethanol-benzene at 1.01 bar. 73 0.30 0.20 a? I 1)- 0.1.0 0.00 (a) 0.30 0.20 1; I 1)- 0.1.0 0.00 (b) Figure 4 . IIIIJIJJJIJIIILIIIIIIIIIJ am 0.20 0.40 0.60 0.90 we LlllIJlllIIlllJIlllIlllJlllJI IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII'ITIIIIITT] am 0.20 0.40 0.“ 0.90 1..” xethanol 10. Difference in the vapor and liquid mole fractions for ethanol-benzene at 1.01 bar; (a) Equilibrium conditions; (b) local conditions. 74 This is only true for large values of i In a vapor mixture the 1' partial pressure of a component is also expressed as Pi - yi P (4.5) where P is the system total pressure. Combining Eqs. (4.4) and (4.5) "UI'U H-o ) §i (4.6) ii = < Using Eq. (4.6), the phase equilibrium diagram for an ideal mixture system can be easily obtained. However, for mixtures that do not obey Raoult's law, i.e. non-ideal mixtures, the methods for predicting equilibrium states is fairly complicated [44]. The phase equilibrium data for all the mixture systems investigated in this work are well documented at 1.01 bar, the pressure 1at which all experiments were carried out. Figures 4.3 - 4.10 show the phase-equilibrium data for all four binary mixture systems. The data has been obtained from [9,31,77] . The difference between the vapor and liquid mole fractions at equilibrium and local conditions can be interpreted with the help of Fig. 4.2. 4.2 MIXTURE PROPERTIES The need for systematically determined and reasonably accurate mixture properties for use in mixture boiling cannot be overemphasized. Most of the existing sources either report values at temperatures other than saturation or correlations have to be used that have a limited range of applicability. A generalized corresponding states method , proposed by Teja [62,63], has been used to predict binary mixture physical properties. 75 4 er 112 d Cortes 1 States ethod A pure fluid with critical parameters Tc’ PC, 1‘70 and molecular weight M is defined to be in corresponding states with a reference fluid if the compressibility Z and the reduced property of the two substances at the same reduced temperature, Tr’ and reduced pressure, Pr’ are given by z a z(°) (4.7) and (An) - (Afl)(°) (4.8) where superscript '0' refers to the reference fluid, A is a property and (A0) is the reduced property. 0 is a function of critical parameters and is defined for each property. The method proposed by Teja for estimating mixture properties is based on the known prOperties of the two reference fluids and requires the critical properties and the acentric factors of the pure components that form the mixture. The reference fluids can be the pure component themselves. Very accurate predictions (well within the accuracy of the experimental data) were reported for mixtures. Only one adjustable coefficient to characterize each binary system is required. The method is very simple to use and can be very easily extended to multicomponent mixtures. The principle which is extended by Teja was originally proposed by Pitzer et al. [41]. The new proposed equation has the form (rl) (rl) w - w (r2) (r1) where Z is the compressibility factor, 1.12 is the acentric factor and superscripts rl and r2 refer to the two reference fluids which are chosen so that they are similar to the pure component of interest, or in the case of mixtures to the key components of interest. The reduced property (A0) of any (non-spherical) fluid (with critical parameters 76 T , P , vc, acentric factor 4) and molecular weight M) may be obtained C C from a knowledge of the reduced properties (Afl)(r1) and (Afl)(r2) of two reference substances (rl) and (r2) at the same reduced temperature Tr and reduced pressure Pr by means of the relationship (r1) (rl) w - w (r2) (r1) An '3 (AD) + w(r2)- w(r1) [(Afl) ' (An) ] (ii-10) Equation (4.10) may be extended for mixtures using van der Waals one— ~ fluid model to replace Tc’ vc, M and w of a pure fluid by the pseudo- critical properties Tcm’ R? , Mm and com of a hypothetical equivalent CID. substance: “ =E E 321;. T a; (4.11) cm cm 1 J Ci. Ci' 1 j J J vcm - E E x1 xj vci. (4-12) 1 j J wm= E x1 col (4.13) i Mm = E xi .1 (4.14) i The one fluid model can be used to obtain the properties of mixtures provided the cross parameters Tc and Ge (i=j) are specified. The ij ij mixing rules for this purpose are as follows: Tcij - gij JTii~iiTjj~jj (4.15) 3 6C - E E 661/3 + G 1/3] (4.16) 11 °jj where aij is a binary interaction coefficient which has to be calculated from experimental data. This coefficient, independent of temperature and composition, is sufficient to characterize each binary mixture. For the case when the two pure components in each binary 77 mixture are used as the reference fluids, this coefficient in part reflects the inability of representing the intermolecular forces via Eqs. (4.10) - (4.16). However, for non-aqueous mixtures, the use of aiJ-l.0 has been claimed to yield good agreement between calculated and experimental values. For binary mixture systems, the simplified forms of Eqs. (4.11) - (4.16) can be written as: ~ ~2 ~ .. ~ .. ..2 .. v = x1 T v + 2x1x2T v + x2 T v (4.17) cm cm C11 C11 C12 C12 C22 c22 ~ ~2 2 2~ ~ ~ ~2 ~ - x v + x x v + x v (4 18) 1 1 2 2 - cm C11 C12 C22 Mm — §,M, + izm, (4.20) The second term on the right side of Eq. (4.10) can also be simplified in the following manner ~ ~ r1 w _ w(rl) x,w, + x2w2 - w( ) w_ w = w Since w (r1>_ w. w ”(1)2 and§1=1';2, (r1) w - w ~ - x2 (4.21) w(r2)- w(r1) Substituting Eq. (4.21) in Eq. (4.10) yields An — (A0)(r1) + §,[(An)(r2) - (Afl)(rl)] (r2) An - E, (Afl)(r1) + £2 (A9) (4.22) Herme, the acentric factor for the pure components need not be eStimated. The reduced property (A0) of the pure components has to be obtained from any suitable equation or correlation and Eq. (4.22) is t1len used to estimate the mixture property at any desired composition. 78 4.2.2 Method of Calculation for Bina£1.Mixtures. Given Tc’ 6C and M for each component, the calculation of physical properties will proceed as follows: 1. Calculate pseudocritical quantities T , G and M using Eqs. cm cm m (4.17), (4.18) and (4.20). The value of the binary interaction coefficient Eij may be set initially equal to 1.0. 2. Calculate T - —I‘. r T cm 3. Calculate the reduced properties (A0) of the pure components at T . r 4. Calculate A0 for the given mixture system from Eq. (4.22). 5. Calculate 0 (using mixture pseudocritical parameters Mm, 3 cm and Tcm) and obtain the property A. 6. If some experimental data are available, the coefficient zij can be varied until the difference between the calculated and experimental value is minimized. No iterations are required. The correlations used for pure components and expressions for C2 are given below for each property. The binary interaction coefficients obtained from Ref. [67] are listed in Table 4.1 at the end of the chapter. Thermal conductivity-liguid.phase. The correlation used for estimating thermal conductivity of pure components is [65]: 3 _ 2/3 _ 4/3 _ -3 J A20 A + 3(1 Tr) + C(l Tr) [A£]—10 S m K (4.23) ~ - ~ 3 and n = M1/2 v 2/3 T 1/2 [v 1 - m , [T 1 - K C C C C kmol Constants A, B and C for the pure components of interest are [67]: 79 ., W7“; A METHANOL-WATER '° T,“ a ETHANOL-WATER .66 . ‘ 0 PROPANOL‘WATER : \ v ETHANOL-BENZENE 500-5 409—3 0! _- .< ._ EXI3-2: 200—} 1.00: 11minIIIIIIIIIIIWIH‘HIllmlllmflrmlml am ‘ 220 me use 0.90 X: Figure 4.11. Variation in liquid thermal conductivity with composition at saturation conditions. 80 HETHANOL ETHANOL PROPANOL BENZENE WATER A 5.39498 6.33533 11.6854 1.39874 -9.67795 B 11.94140 15.55490 12.7422 3.22771 100.5070 C 0.0 0.0 0.0 0.0 95.6611 For thermal conductivity of aqueous mixtures Teja [65,67] suggests the 'use of mass fractions instead of mole fractions. Figure 4.11 shows the predicted variation in thermal conductivity with liquid composition for the mixtures. The points on the graphs of physical properties (Figs. 4.11-4.17) represent calculated values and are joined by straight line only for illustrative purposes. Viscosity-liguid phase. The correlation used for estimating the liquid viscosity of pure components is [64]: ln(n£0) - A + —%— [”3] = cP - 10'3 E;% (4.24) r m 3 -1/2 ~ m c [Vc] - kmol and 0 - M-l/2 6C2/3 T Constants A and B for the pure components of interest are [46]: HETHANOL ETHANOL PROPANOL BENZENE WATER A -11.19289 -11.49610 11.68540 ~12.87967 -1l.94228 B 2.49172 3.06256 4.07907 2.23317 2.34154 The predicted variations in the values of viscosity are shown in Fig. 4.12. fleat capacity-liguid phase. The heat capacities of the pure components were obtained from the following correlation [66]: P3 B J 1n[ -— ] - A - -‘ [C ] - —- (4.25) R Tr p2 kg J kmol-K R is the gas constant (- 8314.0 ), and the constants are [67]: 81 4a.: :1 A METHANOL-WATER IO _. Tni' .. a ETHANOL WATER 800-: o PROPANOL-WATER v ETHANOL-BENZENE 6.00 0.20 0.40 05$ 0.80 L00 Figure 4.12. Variation in liquid viscosity with composition at saturation conditions. 82 5.0 A METHANOL-WATER Id 0 ETHANOL-WATER MK 0 PROPANOL-WATER ‘ v ETHANOL-BENZENE 4.. 1 . : \-\\.: _ : \\ - .4 ' - : \\ _ : 3 t 2.0-3 :1 3 1'9 lllillllllIIIIHIIIIIIIIIIIIIIHHWITIHIIHIIVW was 0.26 6.46 0.80 0.80 .196 ~ X: Figure 4.13. Variation in liquid heat capacity with composition at saturation conditions. 83 METHANOL ETHANOL PROPANOL BENZENE WATER A 2.8410 4.2453 3.6893 3.3498 2.2178 B 0.3315 0.9565 0.4673 0.2985 0.0065 The predicted variations of heat capacity with composition are shown in Fig. 4.13. Surface tension. The reduced surface tension of the reference fluids [47] was correlated by means of the equation: -3 E 00 - A - B Tr [a] - 10 m (4.26) 5C2/3 m3 and 0 - Tc [vc] = kmol Constants A and B were obtained from the data in Ref. [29]: HETHANOL ETHANOL PROPANOL BENZENE WATER A 0.020955 0.027218 0.031569 0.048187 0.026642 B 0.018424 0.024993 0.028329 0.052465 0.021925 Figure 4.14(a) shows the variations in surface tension obtained using Eq. (4.26). The surface tension values for aqueous mixture systems were also obtained by the method of Tamura, Kurata and Odani [given in Ref. 46]. The final correlation is given in the form: 3 1:1 m a - s a ' + s a ' [a] - 10' (4.27) where subscript w and 0 refer to water and organic compound, respectively. 5* is the superficial volume fraction in the surface layer. Figure 4.14(b) shows the surface tension variation using Eq. (4.27) for aqueous mixture systems. It should be noted that Fig. 4.14(b) predicts a drastic drop in surface tension values of aqueous Mixtures with the addition of small amounts of an organic to water. 84 _, 7w 2 A METHANOL-WATER IO -%- o ETHANOL-WATER , , o PROPANOL-WATER " (x v EYHANOL-BENZENE 55 b 4., 39 2 1F|IIHIIHIIIHIIHIIIHIIIIIIIIIIIIIIIHIHHIIIH 0.00 020 0.40 05” 0.80 L00 (0) 32, 7 A METHANOL-WATER 16’3“; 4 a ETHANOL-WATER . - o PROPANOL-WATER 6 v ETHANOL-BENZENE 59 44 b 35 2 1W IIIIIIIHIIIIIIIHIIIIIIIIIIHIIIIIIIIIIIIIIIIIIII . 0.00 0.20 0.40 0.60 0.80 1.00 (b) in Figure 4.14. Variation in surface tension with composition at saturation conditions. (a) Generalized corresponding states method; (b) Eq. (4.27). 85 Liguid densig. The equation proposed for estimating liquid densities of binary mixtures is [61]: cm ~ Zérl) ~ ZérZ) [Tr ] = x1 (r1) + x2 (r2) (4.28) pr pr where Z =- E32. Z i = 1,2 cm 1 c 1 The reduced saturated liquid densities, pfirl) and p 121.2,) of the reference fluids were obtained using the Modified Rackett equation [54]: RT g kg 1_ __c_. n __ _ -3 __ [p ] - [ P ] ZRA [ps] 3 — 10 3 (4.29) s c cm cm 2/7 3 . atm-cm where n = [1 + (1-Tr) ] and R is the gas constant (=82.06 gmol-K ) ZRA is a specified constant for each compound: METHANOL ETHANOL PROPANOL BENZENE WATER ZRA 0.23230 0.25041 0.25272 0.26967 0.24091 The predicted variations in liquid density are shown in Fig. 4.15. Egpgg_ggg§1§y. In this case the density values correspond to the vapor mole fraction that is in equilibrium with the liquid. The Teja-Patel equation of state [39] was used to estimate vapor density of binary mixtures. This equation of state is cubic in nature and requires the cmitical temperature and pressure and two additional parameters to characterize each particular fluid. Patel and Teja [39] demonstrated that their equation not only reproduced many of the good features of the Soave [53] and Pang-Robinson [40] equations for non-polar fluids, [Muzalso overcomes some of their limitations for polar fluids. The Teja-Patel equation of state is of the form: 86 A METHANOL-WATER D ETHANOL-WATER 0. PROPANOL'WATER V ETHANOL-BENZENE 1000‘ lo :5- Ei30bj: of“ : fl 800—: 7% 0.00 Figure 4.15. [III[IITIIIWIIIIHIHIIIHIIHHIIFHIIIIHIHH 0.20 0.40 0.80 0.80 .100 ~ X: Variation in liquid density with composition at saturation conditions. 87 P — RT - §(T) (4.30) v - b 3(3 + b) + a(G - b) where R is the universal gas constant, and a,b and c are given by: ~2T2 c a(T) - Wa[ P ] T(Tr) (4.31) c ~TC b = "([7] (4.32) c RTC c - WC[—§—] (433) c where W = 1 - 3W (4.34) c c 2 2 Nb = 3W0 + 3(1-2\IIC)Wb + Wb + l - 3WC (4.35) and Wb is the smallest positive root of: 3 2 2 2 Wb + (2 - 300) Wb + 30c Wb - We - 0 (4.36) We is the predicted value of the critical compressibility factor. For T(Tr), the form of the expression is: __ 2 T(Tr) - [1 + F(1 - JTr)] (4.37) The optimum values of We and F correspond to the minimum deviation in saturated liquid densities and the equilibrium condition of equality of fugacities. For the fluids of interest, the values of ‘IIC and F are given as follows [39]: HETHANOL ETHANOL PROPANOL BENZENE WATER We 0.272 0.300 0.303 0.310 0.269 F 0.972708 1.2303395 1.241347 0.704657 0.689803 Compared with other equations of state, the Teja-Patel equation gave JSubstantially better predictions of saturated liquid and vapor densities (for the compounds above, the maximum deviation is reported ‘t<> be 3.27%). Equation (4.30) can be used for the estimation of mixture 88 3-0 A METHANOL-WATER a ETHANOL-WATER kg 0 PROPANOL-WATER 735' I . _ _ _ v ETHANOL-BENZENE 2.0 —: a: : 1.0 {3 ”9 llllIllllllHl'lIHIlllllllllllllllllllllllllllll 0.00 0.20 0.40 0.80 0.80 1.00 ~ 7‘: 1[igure 4.16. Variation in vapor density with composition at saturation conditions. 89 properties if a, b and c are replaced by the mixture constants am, bIn and cm as follows [39]: am -E E xi jaij (4.38) i j bm - E xibi (4.39) 1 cm -§ xi c, (4.40) i where aij - éij/aiiajj (41-41) The predicted variation in vapor density are shown in Fig. 4.16 (these are plotted against the liquid mole fraction). Enthalpy of vaporization. The enthalpy of a mixture of constant composition is a function of both temperature and pressure. At any temperature, T, and pressure, P, the enthalpy of a mixture, Hm(T,P), can be represented as: .. o D Hm(T,P) -§ xiHi(T’0) - Hm(T,P) i - 1,2, ------ ,n (4.42) i where all H:(T,0) refer to the same reference state, and the term H:(T,P), which is known as the isothermal departure, relates the mixture enthalpy at some pressure, P, to the enthalpy of a mixture of ideal gases at zero pressure. To calculate the enthalpy of vaporization Of a binary mixture (differential latent heat, i.e. vapor and liquid Phase that are in equilibrium with each other) it is necessary to Calculate the enthalpy of the mixture corresponding to the vapor and liquid mole fractions separately. For integral latent heat (i.e. vapor and liquid phases corresponding to the same composition), it is Sufficient to determine the isothermal enthalpy departures, since the 90 first term in Eq. (4.42) cancels out. Only differential latent heats are of interest when equilibrium is considered. The ideal gas enthalpy H:(T,0) is estimated by integrating Cp from 0 K to the saturation temperature. A fourth order polynomial in T was used for CI) and constants for each pure component were obtained from Ref. [46] . The isothermal enthalpy departure is calculated using Teja-Patel equation of state, Eq. (4.30). From classical thermodynamics the following relation can be obtained: dH = d(Pv) + [T(%% - P] dT (4.43) v T Integration of Eq. (4.43) from zero pressure to the pressure of interest, P, (i.e from infinite volume to volume K7) gives the isothermal enthalpy departure D ~ G 8P ~ H a RT - Pv + [P - T( ) - P] dv (4.44) m 6T v T (I) Now using Eq. (4.30), the enthalpy departure may be computed by performing the integration in Eq. (4.44). The resulting expression is: (H - H0) = f {RT(Z-1) - [T(%%) -a][§% 1n(%f%)]} (4.45) where f is a conversion factor, and M - [939 - n]% (4.46) N = [be + (b—gc-fr's (4.47) Q - [Egg + N]§E (4.48) For mixtures a, b and 0 need to be replaced by am, bm and cm given by Eqs. (4.38)-(4.40) . The predicted values of enthalpy of vaporization are plotted in Fig. 4.17. 91 2344 A METHANOL-WATER _fl _1 \ n ETHANOL-WATER kg 1 e o PROPANOL-WATER : v ETHANOL-BENZENE 1800-: 5. . 5’ 1322—3 :1 = — = :. _ : e , > V_ _ _ 3% IllllllllllllIllIIIIIIHIIHIIIIIIIIIIIIIHIIIIII 0.00 0.20 0.40 0.80 0.80 1.00 ~ X: Figure 4.17. Variation in heat of vaporization with composition at saturation conditions . 92 Two computer programs were developed to predict the binary mixture properties. The first program, MIXPRl, estimates thermal conductivity, viscosity, heat capacity, surface tension and liquid density. The second program, MIXPR2, is based on the equation of state, Eq. (4.30), and predictions of vapor density and enthalpy of evaporation are obtained from it. Pure component critical data are obtained from [24]. A listing of the computer programs along with the input data files are given in Appendix A. Table A.3 lists all the properties obtained. Table 4.1. Binary Interaction coefficients (éij) for mixture properties [67] A1 ”2 Cp£ a pv Ahv HETHANOL4HATER 1.0 1.34 1.0 1.0 1.083 1.083 ETHANOLPUAIER 1.4 1.36 1.0 1.0 1.075 1.075 PROPANOL4HATER 1.4 1.37 1.0 1.0 1.0 1.0 ETHANOL-BENZENE 1.0 1.0 1.0 1.0 1.0 1.0 CHAPTER 5 BOILING INCIPIENCE IN BINARY MIXTURES 5.1 BOILING INCIPIENCE RESULTS AND DISCUSSION Boiling incipient (activation) and deactivation superheats were experimentally measured to investigate their variation with mixture composition. Table 5.1 lists the binary mixture systems studied on different surfaces. The rms roughness measurements for the surfaces are given in Chapter 3. The boiling activation and deactivation superheats, Figs. 5.1-5.10, were observed to be complex functions of composition. 'The superheats were observed to be much smaller for the enhanced (High Flux) surface than for the plain smooth surfaces. Also, for smooth surfaces the activation superheats were much higher than their corresponding deactivation superheats and the two exhibit different trends in their behavior. Table 5.1 Summary of mixture systems studied on different surfaces Mixture System Surface Roughness Methanol-water Smooth tube R1 Enhanced tube -- Ethanol-water Smooth disk R2 Smooth tube R1 Polished tube -- Enhanced tube -— n-Propanol-water Smooth tube R1 Enhanced tube -- Ethanol-benzene Smooth disk R2 Smooth tube R1 93 0:. mg 5.4 94 K i I] q ‘ .3 A 20—3 ‘ ‘ ‘ '1 t .2 .1 '3 : A A .4 we ‘ ‘ A l t ajlfillllllllllllplllllllllll[llllllllllillilllllll 0.00 0.20 0.40 0.80 0.8.1.00 inn-Ml (0) Lu 1"}: - w—Z .3 .. V ' v v 3 + ‘ V g... - V V 4 51 o—1TI‘IIIIIIIIIIHIIIIIIIIIIIHITIIIIIIIIllllllllllll 0.00 0.20 0.40 0.80 0.9.1.00 imammal (b) FIgure 5.1. Variation in measured superheats for methanol-water mixture system on smooth tube: (a) boiling incipient superheats; (b) boiling deactivation superheats. 95 4.0 [Kl i 3.0 ‘ g A r—g 2.0 ‘ ‘ 3 d ‘ ‘ 4 A a 1.0 w—llllllllllllllllllllIllIIIlHllllW'llllIlllllllll 0.00 0.20 0.40 0.80 I.B0 1.00 imotl-mmol (a) 20 V [K] V ; v v x , , V v ' 3 w ¥ v + .— 4 M 1|IllI“”[IIHIIIIIIHIIIIIHIllllllllllllllllill 0.00 I20 0.40 0.80 I.80 1N indium! (b) Figure 5.2. Variation in measured superheats for methanol-water mixture system on enhanced tube: (a) boiling incipient superheats; (b) boiling deactivation superheats. 96 fill ‘9? [K] I I A 5 15—] E " A I — ‘ I A I I! d a g F. 10'—‘ A I < — A = : . . It I 5‘1 .j. 0 IIII IIII IIII IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII I I I 0.00 0.20 0.40 0.80 0.80 1.00 it«hone: (0) [K1 _. , I a v I 3 ‘ ' a I o- 5: : ' I ' v I 4 I A} ‘5 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I II I I I II I I II I III ILI I I I I 0.00 0.20 0.40 0.60 I.80 m iomnmfl (b) Figure 5.3. Variation in measured superheats for ethanol-water mixture system on smooth tube: (a) boiling incipient superheats; (b) boiling deactivation superheats. 97 30 IKI DD A‘I’mc I. D. D at 111111 0 IIIIIIIIIIIIIIIIIIIIIIIIIIIIIITIIIIIIIIIIIIIIIII 000120 0.40 0.80 0.80 we i«I'm-sol (a) LEF— (Kl , 15 ' V : I [.3 V ' V Y 4 55-: ' ' A:Z = I % IIIIIIIIIIIIIIIIIIIIIIIIITIIIIIIIIIIIIIIIIII'IIIII m 0.20 0.40 0.60 0.80 m 'xothonol (b) Figure 5.4. Variation in measured superheats for ethanol-water mixture system on polished tube: (a) boiling incipient superheats; (b) boiling deactivation superheats. 98 50 [K] . A 4 . A : . i ‘ : 8 g ‘ ‘ ‘ ‘ b [A Z A ‘ I" # 2o 5 1" A: 0.00 0.20 0.40 0.80 I30 1.00 iownmfl (0) 20 7 V K I I v ' g V I 18; V V W I F? I V v I' '4 A} 0.00 0.20 0.40 0.60 0.8I1.00 icfiund (b) Figure 5.5. Variation in measured superheats for ethanol-water mixture system on smooth disk: (a) boiling incipient superheats; (b) boiling deactivation superheats. 99 12.0 - [K] A : A I ‘ I A I as 5 9 E : k .- A I d I 4.0 I . g ‘ : ‘ A} M qIIIFIIIIIIIIIIIIITIIIITTIIIIIIIIIIITIIIIIFIIlIIIII m 0.20 0.40 0.60 0.80 1.00 1mm» (a) 6.0 [x] , ._ 4.9 I 3 A2 '5- 2.0 E ' V 3 ' v I V ,V 0.0 1 IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII 0.20 0.40 0.60 0.80 ism (b) Figure 5.6. Variation in measured superheats for ethanol-water mixture system on enhanced tube: (a) boiling incipient superheats; (b) boiling deactivation superheats. 100 32.L A [K13 ‘ : .A _4 24—2: . :1 s .g 16': g 3 '3 1 z i d g A I ._. ‘ g E 3 s . B—~ '0 . A 0 . .;. ' i 0.00 0.20 0.40 0.60 0.80 1.00 ipumomfl (a) s -1 [K1 : 3 8; E V v § ‘ v z : ¥ ' V V .’ V V ' A'l am 9120 0.40 {3.60 0.80 we ifmmrwl (b) Figure 5.7. Variation in measured superheats for n-propanol-water mixture system on smooth tube: (a) boiling incipient superheats; (b) boiling deactivation superheats. 101 8.0 [K] . s A I 6.0 5 i u i ‘ ‘ g A C 1 0-3" 4.0 4 d ‘ E i s 2.0 i ~11 0.0 . ' 0.00 0.20 0.40 0.60 0.80 1.00 immw (a) 4.0 [K1 3 2.0 i ' ' .5 ' Azz ' +' 0.0 0.00 0.20 0.40 0.80 0.80 1.00 xptownoi (b) Figure 5.8. Variation in measured superheats for n-propanol-water mixture system on enhanced tube: (a) boiling incipient superheats; (b) boiling deactivation superheats. 102 is: [K] : . -: E : g ‘ i 1.2—- . E ‘ i i . P- ' ‘ ‘ < :3 Q A ‘ . I : 9': E I A'l -‘ 1 4 TTTTlHHlIIHIIIllIIILHIHIFPIHIHH[IIHIHII 0.00 0.20 0.40 0.60 0.60 xwflumfl (0) 12.0 [x] v ' : v v 3 a0: ' < : .' ' J, ": A'z : i 2 shows the dese in composition of the volatile component. Point 2' is the local vapor mole fraction §L that is in equilibrium with local liquid mole fraction E In the extreme L' situation” the composition of the vapor in the last bubble leaving the surface can be assumed to be at §L and therefore the vapor that is left behind will also be of the same composition. When the last bubble departs from a cavity on the surface, the residual vapor (mole fraction §L) left in it is surrounded by the bulk liquid (mole fraction i) which 114 X. 1.0 ~ '~ 0 X5 V... :1 ~Y ~v1 35 ~x 22209.3... n-Yn Condensation effect illustrated on a phase equilibrium diagram . Figure 5.17. 115 rushes to the surface. It can be seen from the phase-equilibrium diagram in Fig. 5.17 that these two phase are not in equilibrium with each other. A possible mechanism that can lead to a state of equilibrium is the condensation of the non-volatile component in the vapor phase. This process of condensation, shown by 2' -* 1' in Fig. 5.17, continues until the vapor phase comes to equilibrium with the surrounding liquid phase. Another possible mechanism that would result in the same net effect can be the evaporation of the non-volatile component at the interface. This evaporation process is unlikely to occur since the heat of vaporization is required for evaporation of any amount of liquid and cannot be provided by the surface as it is no longer heated. If condensation in the vapor phase is assumed to be the mechanism for achieving equilibrium, then its effect would be to reduce the volume of the trapped vapor in the cavity. A reduction in volume will be accompanied by a decrease in the radius r of the vapor nucleus. This decrease in volume of the vapor is proportional to the distance between points 2' and 1' which is the difference between the vapor and bulk liquid compositions, yb-ib. Hence, for pure components and at azeotropic compositions this mechanism will not occur as (§b-§b)-o for such cases. 5,2,2 Contact mle Effect Experimental data on contact angles obtained by Ponter and Peier [43], shown in Fig. 5.18, suggest that the two can be different when measured under equilibrium and total reflux conditions. Equilibrium refers to the situation when the liquid and vapor are in phase equilibrium with each other. Total reflux corresponds to the case where the vapor and liquid in contact have the same composition. The two situations are represented in Fig. 5.17 by points 1 and 1 and by 1 and 50 4O 30' 2O 10- Contact angle I DEG) 116 A Equiluibrium a Total reflux (0) 24 20 16 12 Contact angle (DEG) I I 52L I In I I 10 20 30 40 so so 70 so 90 100 Bull: liquid composition I mole% ) A Equilibrium a Total reflux azeotrope Al. (b) Figure 5.18. 10 20304050 60708090100 Bulk liquid composition I mole % ) Variation in contact angle data reported by Ponter and Peier [43] under conditions of equilibrium and total reflux: (a) methanol-water; (b) n-propanol-water. 117 I 2 , respectively. The variation in contact angle values during the process 2 -r 1 will probably have some effect on the radius r. During the present investigation attempts to measure the contact angles under these two conditions proved unsuccessful. The bottom of the vessel specifically designed for measuring contact angles was filled with a liquid mixture to produce vapor of the desired composition. However, when saturation conditions were reached, the condensation on the inside of the optical flats made it impossible to view the surface inside the vessel. This problem was solved by blowing hot air on the outside of the optical flats. The second problem encountered was the difficulty in keeping the test surface dry. A thin film of condensate tended to cover the surface, making it impossible to take any measurements. A heater was provided to heat the surface and evaporate the liquid film from it. However, the slightly higher surface temperature caused the liquid droplet (used for measuring the contact angle) to vaporize when introduced on the surface for measurement. If the temperature of the surface was allowed to decrease, then the liquid film reappeared on it. This heating and cooling process also made it very difficult to maintain the pressure at the desired level. Thus, due to lack of proper conditions, it was not possible to obtain data. In fact, it is not clear if the Ponter and Peier data [43] are reliable since they may have had a problem with a liquid film without knowing it. 5,2,3 figfgce Tension Effect Ponter and Peier [43] also obtained surface tension values corresponding to equilibrium and total reflux conditions and shown in Fig. 5.19. Their data for methanol-water and n-propanol-water mixtures, which are limited to small mole fractions, suggest that surface tension at total reflux can be much smaller than that corresponding to the (0) (b) Surface tension I dynes/cm ) Surface tension Idynes/ cm ) 118 ml 60 A Equilibrium a Total reflux 50 I 40. 30- 20- ”L nm/ 0 1 A L 4 s O 2 4 6 6 1O 12 14 16 16 20 22 L A A A L .l L Composition I mole% ) 70 A Equilibrium a Total reflux l» 1o. 00 2 4 6 6 1O 12 14 16 16 20 22 Composition I mo|e% I Figure 5.19. Variation in surface-tension reported by Ponter and Peier [43] under conditions of equilibrium and total reflux: (a) methanol-water; (b) n-propanol-water. box‘h‘ 119 equilibrium condition. The surface tension of the vapor-liquid interface during the process 2 4 1 will therefore change. It is also probable that a change in value of a, due to either the temperature gradient over the bubble interface or due to a local change in composition, will have an effect on the height, h, and hence on the radius r. 5.3 TRENDS IN THE OBSERVED EXPERIMENTAL INCIPIENT SUPERHEATS 5,3,1 Ethanol—benzene mixtures Of all the mixture systems investigated in this work, the ethanol- benzene mixture system shows the least variation in physical properties, especially surface tension, and measured contact angle. Hence, it can be used as a starting point for testing the validity of the suggested mechanisms and factors influencing boiling incipience. The experimentally measured incipient superheats for this mixture system, Figs. 5.9 and 5.10, which were obtained on two different smooth surfaces show a maximum on either side of the azeotrope. On the left of the azeotrope the maximum, on each surface, is in the vicinity of the maximum in (§b-§b) which occurs at mole fraction 0.15 of the volatile component, Fig. 4.10. On the right of the azeotrope the two surfaces exhibit maxima at different mole fractions which are fairly close to a mole fraction of 0.8 where the maximum in Gb-SEb) occurs on the right of the azeotrope. As the decrease in radius r is proportional to (yb- Eb), the ethanol-benzene results seem to follow the suggested trend to a fair degree, i.e. the effect of condensation on the trapped vapor nucleus. The nature of initiation of boiling on the two surfaces was observed to be different from each other. On the tubular test surface boiling initiated with the emergence of discrete sites whose density increased with heat flux. On the other hand, the initiation of boiling 120 on the disk was generally observed at relatively higher wall superheats with the sudden boiling of the entire surface accompanied by a rapid temperature drop. This type of vapor seeding mechanism is assumed to be associated with the difference in the microgeometry of the surfaces. 5,3,2 Agggous-alcohol gixggeg Among the three aqueous mixture systems ethanol-water was the most extensively investigated. Three different smooth surfaces were used for measuring the incipient and deactivation superheats as a function of composition, as shown in Figs. 5.3-5.5. The maximum in the incipient superheat on each surface was observed at a different mole fraction. For the polished tube the maximum in incipient superheat, Fig.5.4, coincided with that in (§b-§b), Fig. 4.6(a), and for the smooth disk, Fig. 5.5, it coincided with that in GL-SZ Fig. 4.6(b). The maximum L). in the incipient superheat for the smooth tube was observed between these two mole fractions, as shown in Fig. 5.3. Ethanol-water is an azeotropic mixture system with the azeotrope occurring at 0.89 mole fraction, as shown in Fig. 4.5. Methanol-water is a non-azeotropic mixture system and the peak in the the incipient superheats, shown in Fig.5.1, coincided with that in (yrs: Fig. 4.4(b). It should be L). noted that the trend in (§L-§L) versus liquid mole fraction Eb is identical to that in (§b-§b) versus vapor mole fraction yb. The n- propanol-water mixture system is also an azeotropic mixture system with a maximum in (§b-§b) on either side of the azeotrope, as shown in Fig. 4.8. The observed incipient superheats for n-propanol-water mixtures form a maximum, which coincides with that observed in 6b-; to the b) 1 left of the azeotrope; to the right of the azeotrope no such maximum was observed. This mixture system was repeated in order to confirm the large maximum in the incipient superheats. No difference in the results 121 was observed. For mixture systems which exhibit a maximum in (yb-ib) on either side of the azeotrope, e.g. n-propanol-water, phase equilibrium dictates that the difference (§b-§b) be negative to the right of azeotrope, Fig. 5.17. This implies that the equilibrium concentration of the volatile component in the vapor phase is smaller than that in the liquid phase. The magnitude of depletion of the volatile component is therefore much smaller as compared to the situation when (§b-§b) is positive. The decrease in the radius due to condensation is proportional to the level of depletion. This means that to the right of the azeotrope the decrease in radius to achieve equilibrium will be relatively smaller. The argument regarding the decreased amount of depletion of volatile component for the case when (§b-§b) is negative is further strengthened by looking at the boiling wall superheats on either side of the azeotrope. For the n-propanol-water mixture system, Fig. 6.4, the difference in the boiling wall superheats (AT-AT id) is smaller on the right than on the left of the azeotrope. For mixture compositions to the right of the azeotrope, once vapor is trapped in the cavity it is the volatile component that should condense out of the vapor phase to achieve equilibrium. Such a process may result in a liquid layer rich in the volatile component in the immediate vicinity of the vapor nucleus. Since the heat of vaporization for the volatile component in aqueous mixtures is much smaller than that of water, a relatively smaller wall superheat may be required to vaporize this liquid layer to aid the vapor bubble in its initial nucleation and growth. On the other hand, to the left of the azeotrope, the non-volatile component is condensed out to attain equilibrium. A liquid layer rich in the non-volatile component would require a relatively higher superheat to vaporize. Hence, for azeotropic aqueous mixtures to the right of the azeotrope, the decreased level of 122 depletion and the lower heat of vaporization of the volatile component seem to be the probable cause for smaller incipient superheats observed. The scatter in data in the measured superheats leads one to question the consistency of the surface. It is observed that the wall superheats required to sustain boiling are much smaller than those required to initiate boiling on the same surface. Once the vapor is trapped in a cavity, then according to the suggested mechanism of condensation, the decrease in volume may be enough to completely deactivate that particular cavity size. In general a particular size range of cavities may be completely snuffed out and the next size range may require higher wall superheats. As the microgeometry of any one surface is usually different from that of any other surface, the same mixture system may exhibit differing incipient superheats. 5.3.; Enhanced Surface The incipient superheats on the enhanced surface were measured for the following reasons: (1) to compare its performance with smooth surfaces, and (2) to look for any similarity between the trends in: the data. It was observed that the wall superheats required to initiate boiling on the enhanced surface are much lower than on the smooth surface. The incipient superheats were generally observed bo‘be higher than the corresponding deactivation superheats. For any mixture system, the trend in the incipient superheats for the enhanced surface was different from that observed on the smooth surface. The mechanism of boiling on enhanced surfaces needs to be further explored and more data on incipient superheats may be required before any comprehensive explanation can be presented. 123 5.4 SUHHARY OF EFFECTS IDENTIFI- FOR BOILING INCIPIENCE ON A SMOOTH SURFACE The following,effects on.boiling incipience in binary mixtures on smooth surfaces have been identified and reviewed above: 1. The vapor trapping mechanism at the point of deactivation of boiling sites. Condensation of the non-volatile component within a trapped vapor nucleus. Physical properties, especially surface tension and the heat of vaporization. The contact angle effect. The surface microgeometry effect on the vapor trapping process. A generalized model of incipience in binary mixtures is a very complex function of some or all of the above factors. The microgeometry of the surface is less amenable to any sort of mathematical formulation since the dimensions of critical importance, e.g. the cavity radii, etc., are on the order of microns. Future investigations may reveal the factors that are dominant under a particular set of conditions. CHAPTER6 BOILING HEAT TRANSFER COEFFICIENTS 6.1-ERIHENTAL RESULTS AND DISCUSSION Nucleate pool boiling data for all four binary mixture systems on smooth and enhanced surfaces are tabulated in Appendix C. The ideal wall superheats at any heat flux have been obtained using the linear molar mixing law: Eqs. (2.18) and (2.19) for the azeotropic mixture systems and Eq. (2.17) for the non-azeotropic systems. The ideal heat transfer coefficients are then obtained from the ideal wall superheats. The results on smooth and enhanced surfaces are discussed separately and the performances of the two are compared in regard to mixture boiling. The values tabulated in Appendix C were obtained from the boiling curves for the decreasing heat flux, as this is more representative of the boiling process. The measurements were taken by first increasing the heat flux to the test surface and then by decreasing it. This procedure was repeated more than once. The reproducibility of the results was very satisfactory, within the accuracy of the measurement errors. For a discussion on the calculations and errors associated with measurements, see Appendix B. In the fully developed boiling regime the wall superheats for the increasing and decreasing heat flux were very close to each other. However, in the lower part of the boiling curve, values of wall superheats for the decreasing heat flux were generally lower than those obtained for the increasing heat flux. This discrepancy is due to the greater number of boiling sites that remain 124 125 active when the heat flux is decreased once it has reached a moderately high heat value. This phenomenon, commonly referred to as hysteresis, is generally observed in boiling. 6.2 SMOOTH SURFACE The variation in the wall superheat as a function of composition at four different heat flux levels is shown in Figs. 6.1-6.6 for all four mixture systems tested. The linear mixing law line, not shown for clarity, is a straight line connecting the pure component 2 (ail-0.0) , the azeotropic composition (if one exists) and the pure component 1 (32,-1.0) at the same heat flux. It is observed that, at any constant heat flux, the experimental wall superheats are above their corresponding linear values. This trend implies a deterioration in mixture heat transfer coefficients when compared with the values obtained from linear mixing law. Only one exception is at the 0.30 mole fraction of n-propanol in water, shown in Fig. 6.4. At this point the experimental wall superheat is observed to be lower than the corresponding value from linear mixing law. A similar effect was reported by Calus and Leonidoplous [8] for the same mixture system boiling on a 0.3 mm diameter horizontal wire of nickel-aluminum. The influence of differing surface roughness is reflected in the results of ethanol-water (Figs. 6.2 and 6.3) and ethanol-benzene (Figs. 6.5 and 6.6). It is observed that the wall superheats generally decrease with increasing roughness of the surface. 6,2,1 Prediction of Smooth Surface Results The semi-empirical correlation recently developed by Schluender [48] to predict mixture heat transfer coefficients in pool boiling has not been widely tested against experimental data. However, Uhlig and 126 : HEAT flux lKl : A :10 kW/m' ‘2 a 143 u : '1' 70 n "‘ 21 u 230—: ° F ~ .l <1 29 -_- .. 1, IIIIIIIIIIIIFIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII 0.00 I.2I 0.40 0.80 0.60 1.00 imetiwl'tol Figure 6.1. Wall superheats for methanol- water mixtures boiling on smooth tube (for decreasing heat flux data). 127 3r : HEAT FLUX [Kl " A 218 kW/m’ .2 a 144 n - + 95 .. : 0 45 u .—i -l l - | r- —-+ _ i 4 -1 “ i g -1 s ‘ A ‘L r ‘ - T 1 .I r \+ r i j 1 c t I I I 5 IIIIIIIIIIIITITIIIIIIIIIIIIIITITIIIIIIITIIIIIIIIII 0.” 0.20 0.40 0.60 _ I.60 1.00 ietiumol Figure 6.2. Wall superheats for ethanol-water mixtures boiling on smooth tube (for decreasing heat flux data). 128 42% "" . HEAT FLUX [Kl I A 217 kW/m’ " a 144 u '2 + 04 u "‘ O 70 N 3 - '- .: q -+ .~ 11? 1W IIIIIIIIIIIIIIIIIllllillllIIIIIIIIIIIIIIIIIIIIIIII 0.00 0.20 0.40 0.60 - 0.60 1.00 xethanoi Figure 6.3. Wall superheats for ethanol-water mixtures boiling on polished tube (for decreasing heat flux data). 129 2% -* HEAT FLUX lKl _. A 217 kW/«? "' D 143 '0 ‘-' + 94 n 20'“ O 46 n -E i .. 5 2 .. g. - l- < 1 l : M . i p - g j I l '1 AZ E 4 E 4 a 5 HillITIIPIIIIIIIIIILIIIIIIIIIIIIIIIIII[IIIIIIIII 0.00 0.20 0.40 0.60 0.60 1.00 xpropanol Figure 6.4. Wall superheats for n-propanol-water mixtures boiling on smooth tube (for decreasing heat flux data). 130 2.; _1 . HEAT FLUX [Kl A 144 mm” "‘ . D 64 u — : + 70 u l O 46 u U l " l AZ - a d a A 15—'1 --E Y A : v i - I l " l a— I I l w IIIIIIIIIIIITIEFIIIlIITIlIIIIIIIIIIIIIIIIIIIIIIIII 0.00 0.20 0.40 0.80 0.8I ~ xethanol Figure 6.5. Wall superheats for ethanol-benzene mixtures boiling on smooth tube (for decreasing heat flux data). 131 HEAT FLUX 234 IlW/m1 199 n 135 u 44 u O+D> AT T IllllllIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII 0.00 0.20 0.40 0.60 0.60 1.00 iethanol Figure 6.6. Wall superheats for ethanol-benzene mixtures boiling on smooth disk (for decreasing heat flux data). 132 Thome [84] have reported good agreement, within 320%, between their experimental results and those predicted by the Schluender correlation for the acetone-water mixture system. The experiments were performed on a horizontal tube of 19.05 mm diameter at 1.01 and 3.03 bars. The Schluender correlation is attractive because it incorporates the functional dependence of the degradation of the heat transfer coefficient on heat flux (the experimental observations do indeed confirm this dependence). The Schluender correlation for azeotropic mixture systems is: a l aid 8 ll -r-aid( ><~ ” > 1 —B°a (6.1) ' + T -T yl-x1 [ -exp[- ]]} q 52 s1 pifliAhv T - T 52 Saz ~ ~ where T -T =- —_ x1 < x (6.2a) $2 31 ~ az az T - T saz SI ~ ~ and T - T - ————————— x1 > x (6.2b) . $2 51 1 _ i az az In terms of wall superheat (since a-q/AT), Eq. (6.1) can be rewritten as: ATi: - 1 ' AT aid ~ ~ Boq {1 + THE-T320140[l-expl- ——.,p,d,ll} .. .. 3,5. AT = ATid + (T82- Tsl)(y1-x1)[l-exp[- ZZEZZE;]] (6.3) (Ts - TS ) and (§,-§,) are always of the same sign and their product is 2 1 therefore positive. The second term on right hand side of Eq. (6.3) is the amount by which the actual superheat, AT, is different from its . The difference AT - AT. , referred id id to as ”excess superheat," A8, is generally positive as the observed linear value (or ideal value), AT 133 superheats are always above their corresponding linear values in mixture boiling. As the heat flux approaches its critical value, qcr, the exponential term in Eq. (6.3) approaches zero. Hence, for this condition Eq. (6.3) can be written as: Ao—(T -T )(§-§) asq-rq (6.4) 52 S1 C1? Thome (Eq. (2.38)), using the phase equilibrium diagram expresses the excess superheat at this condition as: A0 - Apr as q 4 qcr (6.5) The variation in the mass transfer coefficient, fil,vfith composition is generally not known. In the absence of any data, 61 has been assumed by Schluender to be 2 x 10-4 m/s (this value corresponds to the metyhylethylketone-toluene mixture system at 1.0 bar [48]). The factor Bo, according to Schluender, includes all the improbabilities and has to be adjusted to experimental results. In general Bo depends upon heat flux and pressure. Schluender [48] reports B0 to be of the order unity and obtains good agreement between the experimental and predicted values using BO-l. Uhlig and Thome [84] (acetone-water mixtures) and Bier et al. [5] (binary mixtures of sulfurhexafloride and refrigerants) obtained reasonable agreement using Bo-l. Hence, Bd-l is taken to be unity in Schluender correlation. The experimental and predicted values from Schluender correlation are compared in Figs. 6.7-6.18 at three different heat flux levels for each mixture system and the overall deviations for the entire data are also shown. The correlation works very well for ethanol-benzene, Fig. 6.15-18, and reasonably well for the n-propanol-water mixture system, shown in Figs. 6.13 and 6.14. The deviations between the experimental and predicted values are quite large for the methanol- water, Figs. 6.7 and 6.8, and ethanol-water mixture systems, shown in 134 _ FRED. EXP. HEAT FLUX [K] (i) A 210 kW/m’ ® a 143 n ® 0 27 u 3' “OO‘ ......... ‘- OOOOOOOOO ‘M.... I"" ..--o~.. .-..*§ oooooo 6‘..-" ----§. “ S 0" ..’a-- fl‘T‘: .‘T‘s a" 0“". k i. A ,B' r- o ." d f, I” { '0‘...‘.-.-...- ‘- u-“_.__¢.-' ‘ gran-n4 .-'O'“* 'l ‘ ..... *.‘ 0 so" 0 0.00 0.20 0.40 0.60 0.60 1.00 xmethanol Figure 6.7. Experimental and predicted (Eq. 6.3) wall superheats for methanol-water mixtures boiling on smooth tube. aexp Figure 6.8. 135 Comparision of experimental and predicted (Eq. 6.1) boiling heat transfer coefficients using entire data for methanol-water mixtures boiling on smooth tube. 136 AT 3" PRED. EXP. HEAT FLUX [Kl I: G) A 210 kW/m’ -‘ ® a 144 n '2 @ o 40 u : 1“. 25 — é’l Te“ .. : " : .1. I'm-L. l -I ' l s‘ ..... I “ :‘l’ “ .0 "“A. E 1;; ‘s --------- «13.-.... ‘~ ‘ g 3" 9 Mun"-.- -- | 1 ,0.“ ”J. _________ “'13- --------- a--- : or" "‘9' """ “~-.. 3 “w" . t O 8 All i i 5Illll'lillllilillllfllilllllllIlllllllillTFlllllll 0.00 0.20 0.I4 I50 I.90 1.00 iethanol Figure 6.9. Experimental and predicted (Eq. 6.3) wall superheats for ethanol-water mixtures boiling on smooth tube. 137 .zE .iJTITITITIiIl’Ii 14 Figure 6.10. Comparision of experimental and predicted (Eq. 6.1) boiling heat transfer coefficients using entire data for ethanol-water mixtures boiling on smooth tube. TAT 138 Figure 6.11. +0—— PRED. EXP. HEAT FLUX [Kl (D A 211 kW/m’ ® a 144 n ® 0 70 u A. ’, a; ““e 0’ ‘ w..o"* ‘1’ I e )‘5‘. .I)‘ ,.: ' 4': a... 0 ’0' "’.--q.--.." I 'o e m IInIrlIIIlIIIllrIrIIIflrlIIIIIIIIIFWIIIIIIIIIII 0.00 0.20 0.40 0.60 0.30 1.00 xethanol Experimental and predicted (Eq. 6.3) wall superheats for ethanol-water mixtures boiling on polished tube. an X a... Figure 6.12. 139 I I ’1’” ’,fl 6"" I - ,’ + 1’ ’ .0 I I / I, /’ _l ’I’ III I l I ’ _ I I I I I I I ,’ I I I I 2—t I I I ,’ / I I ’l I’ ’ I 1’ _ I ’ I I I aprecl Comparision of experimental and predicted (Eq. boiling heat transfer coefficients using entire data for ethanol-water mixtures boiling on polished tube. 140 q PRED. EXP. HEAT FLUX “‘1 2 (D A 217 kW/m’ -4 ® a 143 u 25— ® 0 45 u d 4 Z 5". d i : 20"" in ‘\ : - ' : *- " i : 4 fl: 0.- ““9““ : ”i "I a... ......... *---.- ' --”*...‘ ® . ' ' 4. 5 [HITTFITTIIII IIHIFII'IIIIHIIIFIITTIHIIIITTIIIII am 020 0.40 0.90 0.9a m iwmml Figure 6.13 Experimental and predicted (Eq. 6.3) wall superheats for n-propanol-water mixtures boiling on smooth tube. aexp Figure 6.14. 141 is“ [If --1 ,1 -} ‘6?!” '1 A“ I, I I’ll 12—’ ’I’J I,’ .. IE [4+ _ [I’D - I’ I x’. ” —} I’I w 9’! e-n I” a ’1’ _ II. o’,’ q 4__. 1 wilfllilllrlllll 0 4- B 12 16 apred ##K Comparision of experimental and predicted (Eq. 6.1) boiling heat transfer coefficients using entire data for n-propanol-water mixtures boiling on smooth tube. 142 . Z‘r : FRED. EXP. HEAT FLUX [K]- E A 144 le/IIIa - : o a u .. _ E @ 0 46 u 4 E i .- I ‘ - A? { 1.5— -J I ........ ..' ..... -. ‘s ' I ‘s ‘ i 11%IIIFIIITFIHIIIIlllllllllllfll[Ullllllllllllllll] m 0.29 0.40 0.50 6.90 flaw Figure 6.15. Experimental and predicted (Eq. 6.3) wall superheats for ethanol-benzene mixtures boiling on smooth tube. 143 QJITITlTITlg I1 I IT I I ll 2 4 6 8 1.0 “pm! furl—2 Figure 6.16. Comparision of experimental and predicted (Eq. 6.1) boiling heat transfer coefficients using entire data for ethanol-benzene mixtures boiling on smooth tube. ' llIlI ‘1 _ FRED. EXP. HEAT FLUX [K] _ g G) A 234 kW/m’ : ® 0 199 n "T 5 ® 0 44 n " ,A. ”k A12 _ I: ~.~‘~~ ® E -. ‘A‘ : .- 1 ‘ l’p. .a.‘-.‘ “s E d I’ .-‘a.... ‘s‘u : I cc," . ~ I @‘~~‘D:.~“ I 0‘ V -' ' ------- «a. ....... i I " E - a 3 IIIIIIIHIlllqllflifillllllIIIIIHIIIHIHHPIH 0.00 0.20 0.46 0.60 6.80 1.06 ~ xothonol Figure 6.17. Experimental and predicted (Eq. 6.3) wall superheats for ethanol-benzene mixtures boiling on smooth disk. 145 2 g 3:! P IIIJTIIIJ @3. “exp L111T11|1$ I; a‘fIITIrIIIFIIFIrIIIII 0 5 m 15 20 “mod 31% . Figure 6.18. Comparision of experimental and predicted (Eq. 6.1) boiling heat transfer coefficients using data for ethanol-benzene mixtures boiling on smooth disk. 146 Figs. 6.9-6.12. However, the scatter in the data is small and better agreement can be obtained using higher values of 30' 80-2 yielded much better predictions, within $2525. There is no rationale for choosing a different value of B0 for each particular mixture system since data would be needed to determine the best value of B0 and the correlation would be more difficult to apply and less general in form. 6 . 3 ENHANCED SURFACE RESULTS Experimentally observed variations in wall superheats for the boiling of methanol-water, ethanol-water and n-propanol-water mixture systems on High Flux are shown in Figs. 6.19-6.21 at four different heat flux levels. The linear molar mixing law lines are again not shown for clarity. For the methanol-water mixture system, the observed wall superheats, shown in Fig. 6.19, exhibit positive deviations (hence negative deviation in a) from those predicted using the linear mixing law approach. The other two mixture systems show both positive and negative deviations in wall superheats, as shown in Figs. 6.20 and 6.21. This implies that for boiling on an enhanced surface the heat transfer coefficients can be higher or lower than expected from a linear mixing law approach. It should be kept in mind that the linear mixing law does not incorporate any non-linear variations in mixture physical properties. To demonstrate the augmentation in heat transfer on the enhanced surface (High Flux) as compared to a conventional smooth surface, experimental wall superheats from the two surfaces under the same conditions are plotted in Figs 6.22-6.24 for methanol- water, ethanol-water and n-propanol-water mixture systems, respectively. The enhancement is obtained for both the pure components and the mixtures. In general a 2 to ZI--fold increase in heat transfer coefficients is observed. These results support the earlier 147 a0 HEAT FLUX [K] A 99 kW/m' 0 56 n + 40 .. 6.0 _f 0 21 H 2 w ' + : A 3 0 ; -+ ,. 2.0 0U3 |llllll|1|lllll [[llllllll IllllillllllllIllllllllllIlllll m .20 0.40 0 .80 0. 90 m imethanol Figure 6.19. Wall superheats for methanol-water mixtures boiling on enhanced tube (for decreasing heat flux data). 148 7.0 HEAT FLUX "‘1 A 99 ItW/IIIa D 75 " + 50 N O 25 n 5.0 .— d 3.01 ' _T : d k : -1 v_ - ¢ '4 I “fl : - Al '" I : s m IIIIIIITT[IIIIITIITIIIIll”IIIIIIIIIIIIIIIHIIIIII 0.00 0.20 0.40 0.80 0.8.1.00 xothonol Figure 6.20. Wall superheats for ethanol-water mixtures boiling on enhanced tube (for decreasing heat flux data). 149 8.0 HEATFLUX [K] A 99ltW/III2 U 66 n + 40 u 6.0 o 21 .. '2 4.0 2.0 .3. 0.. KIITIIIWIIIIIIIIIITIIILIllll'llllll[[Illlllllllllll am 0.20 we 0.60 0.8.1.00 xpfoponol Figure 6.21. Wall superheats for n-propanol-water mixtures boiling on enhanced tube (for decreasing heat flux data). 150 3 lJLllllll HEAT FLUX A 94 ltW/III2 a 45 u 20': P _- < _. r HEAT FLUX ' A 99 kW/m’ 0 40 n 0 IIIHIIIIIIl”Illlllllllllrllllllllllllllllllllllll 0.20 0.40 0.80 0.80 m iIIIoII'IcII'Io' Figure 6.22. Comparision of enhanced surface wall superheats to the smooth tube for methanol-water mixtures. lSl 2... q [Kl - d ‘1 m 20— HEAT FLUX : A 95 llW/III2 .. o «I .. 15...... .. AT AZ 0 IIIIIIITTIIIIIIIIlllllllllllIIIHIIIIIIIITIIIEIIITII 0.40 0.80 0.80 xothanl Figure 6.23. Comparision of enhanced surface wall superheats to the smooth tube for ethanol-water mixtures. 152 20 - EMQQLLH. [Kl .. HEAT FLUX , .. A 94 kW/m2 E J 46 u g 15— g .. I ._ I , I 9 ’ Al I HEAT FLUX E A 99 IEW/II‘Iz E D 50 n g I I d . 0 ITIIIIIHIHIIIIlllllflllIIIIIIIIIIIIIIIIIIII[fill 0.00 0.20 0.40 0.80 0.30 ipropcII'IoI Figure 6.24. Comparision of enhanced surface wall superheats to the smooth tube for n-propanol-water mixtures. 153 observations made by Ali and Thome [2] and Uhlig and Thome [84] for boiling of mixtures on the High Flux surface. The enhanced surface shows a reduced "mixture effect," as the deviation between the actual and linear mixing law predictions is much smaller on the enhanced surface than on the conventional smooth surface. The mixture boiling results obtained on the enhanced surface were used to test the validity of Eq. (2.39) derived by Webb [98] for pure components and tested on refrigerants only. Eq. (2.39) is: 2 <1 q T -T = 0.044—9— + 9166“ w sat A2 6C dp(dP/dT)sat (2.39) where 6c is the porous layer thickness and dp is the particle size used for time coating. For High Flux tubing 6c- 0.25 mm and dp- 0.042 mm are reported [37,98]. Webb [98] also reports in-line cubic packing for High Flux surface. Shakir et al. [50] have compared the experimental and predicted values of wall superheats using Eq. (6.6) , and the results are shown in Table 6.1. It is obvious from the predicted wall superheats that even with mixture properties the correlation is far from being satisfactory when used for mixture boiling. It is not surprising since the mass transfer effects are not taken in to consideration in Eq. (6.6). Also, the nucleation superheat term in Eq. (6.6) is too dominant, such that (Tw - Tsat) is only a slight function of the heat flux 9- Schluender correlation was also tested for mixture boiling on enhanced surfaces. Fig. 6.25 compares the results for the n-propanol- water mixture system data to the predicted results. The deviations are observed to be higher than those obtained for the same mixture system boiling on smooth surfaces (Fig. 6.14) using the same Bo and fig. 154 ac , Z / ‘3 — *” gK o” —:. :7 l3 -4 ,I : I/a % . 29—3 Ix“ E. '5' .. [Its a El x/q. a. - I, I” ’ g - ’Im gfi a l,’ —-: ,” B an ,I” 6 __ [[3 gm a a III -—I ’ a I’ c—J ” % a ’I” W' I”5 a a B’I” : Ara flaw/ .1 a ‘3?!’ —:' I’I%’$I :: ,9 Z 'IIII[IIIIIIIIIITIIIFIIIIITIII 0 .10 20 31w— 30 “PT“ In K Figure 6.25. Comparision of experimental and predicted (Eq. 6.1) boiling heat transfer coefficients using entire data for n-propanol-water mixtures boiling on enhanced surface. 155 Thome [76] has recently considered the nature in which mixture boiling on enhanced surfaces differs from that on a conventional smooth surface. The reduced mixture effect observed on enhanced surfaces is explained on the basis of a superposition boiling, model. The model proposed by Thome comprises contributions from boiling heat transfer and boiling induced liquid-phase convection. Thome suggests that due to the depletion of the more volatile component a deterioration in boiling heat transfer occurs, as is true for boiling on a conventional smooth surface. The factor that augments heat transfer on an enhanced surface is the liquid-phase convection induced by the special geometry of such surfaces. Thome draws an analogy between the convective boiling inside of tubes and that in the narrow passages of the enhanced surface. A qualitative analysis shows very promising results. Future efforts, according to Thome, for modeling boiling on enhanced surfaces should include both the mass transfer and the augmented liquid-phase convection effects. Table 6.1. Comparison of experimental and predicted [Eq. (6.6)] wall superheats for the enhanced surface AT (K) at a (kW/m2) xme ll 01 99 81 52 a E a E a E 0.00 3.5 3.9 3.1 3.9 2.5 3.9 0.05 6.2 3.2 5.6 3.2 4.7 3.2 0.25 6.0 2.1 5.4 2.1 4.3 2.0 0.55 5.6 1.5 5.1 1.5 4.1 1.4 0.85 5.7 1.3 5.2 1.3 4.0 1.2 1.00 4.6 1.2 4.3 1.2 3.7 1.2 CHAPTER7 CONCIBSIONS 7 .1 BOILING INCIPIENCE AND DEACI'IVATION 1. 0n smooth surfaces, the incipient superheats for the mixtures were larger than is predicted from a simple linear mixing law between the single components values. The corresponding incipient and deactivation superheats on the enhanced surface showed both positive and negative deviations from the linear mixing law. The incipient and deactivation superheats for all four mixture systems investigated were strong, non-linear functions of mixture composition. Deactivation superheats for boiling on smooth surfaces were much smaller on value than the corresponding incipient superheats on the same surface. The incipient and deactivation superheats for any mixture system showed a different trend for boiling on the same surface. On smooth surfaces, the incipient superheats exhibit a maximumfor azeotropic and non azeotropic aqueous mixture systems. Forthe ethanol-benzene mixture system, a maximum was observed onboth sides of the azeotrope. The incipient superheats were observed to vary with the type of surface finish and enhancement. The incipient superheats on the enhanced surface (High Flux) were much lower than for the smooth. surfaces. The maximum in the incipient superheat was observed to shift with the type of surface. 156 157 20 The classical boiling nucleation equation ATinc - r(dP/dT)sat was demonstrated to be inadequate for predicting incipientsuperheats for mixtures. Several new factors were identified forboiling nucleation on smooth surfaces which could qualitativelyexplain the maxima in incipient superheats observed for themixtures. 7.2 CONTACT ANGLES 1. The contact angles for the pure organic components were observed to be much smaller than for pure water. The‘contact angles foraqueous mixtures showed a non-linear variation with the mixture composition and were smaller than the linear mixing law prediction. The material of the surface showed a negligible effect on the contact angles for the same mixture system. 7.3 HEAT TRANSFER COEFFICIENTS 1. The wall superheats (and heat transfer coefficients) for boiling of mixtures on smooth and enhanced surfaces were observed to be non-linear function of mixture composition. 0n smooth surfaces the wall superheats were observed to be much higher than expected from a linear mixing law. This implies a deterioration in mixture heat transfer coefficients when compared to the pure component values. Fbr boiling of mixtures on the enhanced surface, the wall superheats showed both positive and negative deviations from the linear mixing law. 158 4. The enhanced surface results show appreciable augmentation of the heat transfer coefficients for the mixtures compared to those for the smooth surface. RECOMMENDATIONS Suggestions for future work.in the area of nucleate pool boiling of mixtures and for further advancement of the experimental facility are as follows: 1. The experimental studies be extended to other enhanced surfaces, e.g. Thermoexcel, Gewa-T, etc. The experiments may be designed to obtain: (a) boiling nucleation and decativation superheats as a function of mixture composition; (b) nucleate pool boiling heat transfer coefficients as a function of mixture composition and heat flux; an peak nucleate heat flux as a function of mixture composition; (d) functional dependence of (a), (b) and (c) on pressure and subccooling will also be of interest. The experimental results thus obtained may help explain the mechanism of boiling on enhanced surfaces and eventually lead to the development of a physical model in the form of a empirical or semi-empirical correaltion. The results may also help in determining the suitability of enhanced surfaces to multicomponent mixture boiling. 159 2. 160 A data acquisition acquisition system should be interfaced with the existing instrumentation to record and process the experimental data. this will also aid in creating a data bank of all the research work carried out in the laboratory. A flow boiling facility be designed to study forced convective boiling inside tubes. APPENDIX A APPENDIX.A COMPUTER PROGRAMS AND MIXTURE PROPERTIES Table A.l.1. Listing of Program MIXPR1.FOR OOOOOO v-l :1: H U! l l 100 4 1 C 7 PROGRAM MIXPRl PROGRAM CALCULATES THE PROPERTIES OF BINARY MIXTURES LOGICAL*1 FNAME(15),FTAME(15),FMAME(15),FPAME(15) DIMENSION X(15),T(15),Y(15,10),STRO(16),C1(5),C2(5),C3(5), C4(5),C5(5),C6(5),D1(5),D2(5),D3(5),D4(5),D5(5),D6(5),D7(5), D8(5),D9(5),W11(15) TYPE *,'ENTER THE MIXTURE SYSTEM' ACCEPT 4,(STRO(L),L—l,l6) FORMAT(16A1) OPEN(UNIT-2,NAME-'CRIDAT.MX1',TYPEa'OLD',FORM-'FORMATTED') DO 1 MM=1,5 M-MM READ(2,*)C1(M),C2(M),C3(M),C4(M),C5(M),C6(M) CONTINUE CLOSE(UNIT=2) 0PEN(UNIT-2,NAME='CONDAT.MX1',TYPE='OLD',FORM='FORMATTED') D0 7 KK-1,5 . K—KK READ(2,*)D1(K),D2(K),D3(K),D4(K),DS(K),D6(K),D7(K),D8(K),D9(K) CONTINUE CLOSE(UNIT-2) TYPE *,'l-METHANOL, 2-ETHANOL, 3-PROPANOL, 4-BENZENE, S-WATER' TYPE *,' ' TYPE *,’ENTER THE # FOR THE VOLATILE COMPONENT' ACCEPT *,1 TYPE *,'ENTER THE # FOR THE NON-VOLATILE COMPONENT' ACCEPT *,J WMl-Cl(I) WM2-C1(J) C WM IS THE MOLECULAR WEIGHT PC1-C2(I) PC2-C2(J) C PC IS THE CRITICAL PRESSURE IN BARS 161 162 TCl-C3(I) TC2-C3(J) C TC IS THE CRITICAL TEMPERATURE IN DEG K DCl—C4(I) DC2-C4(J) C DC IS THE CRITICAL DENSITY IN KG/CU-M ZCl-CS(I) ZC2-C5(J) C ZC IS THE CRITICAL COMPRESSIBILITY FACTOR ZRAl-C6(I) ZRA2-C6(J) C ZRA IS THE CONSTANT IN MODIFIED RACKETT EQ. FOR LIQUID DENSITY c ******************************************************************** CALL GTLIN(FTAME,'ENTER INPUT FILENAME FOR X-TSAT') OPEN(UNIT-2,NAME-FTAME,TYPE-'OLD',FORMs'FORMATTED’) READ(2,11)MF 11 FORMAT(IZ) DO 12 KK-1,MF K-KK READ(2,13)X(K),T(K) 13 FORMAT(2(F7.3)) 12 CONTINUE CLOSE(UNIT-2) c ******************************************************************** PRINT 18,(STRO(L),L—1,16) 18 FORMAT(1H1,16Al,//) PRINT 19 19 FORMAT(3X,'X1',5X,'TSAT',7X,'TCOND',8X,'VIS',9X, 1 'SP HT',7X,'S TEN',5X,'LIQ DEN',/) C ****5%*************************************************************** F1-1.0/3.0 F2-2.0/3.0 F3-4.0/3.0 F4-2.0/7.0 R-82.06 C R IS UNIVERSAL GAS CONSTANT IN ATM-(CU CM)/GMOL-K VC1-WM1/DC1 vc2-WM2/Dcz 0 VC IN CU-M/KG MOL VC12-(((VCl**F1)+(VC2**F1))**3.0)/8.0 ATClZ-(SQRT(TCl*VC1*TC2*VC2))/VC12 C 3%******************************************************************* TYPE *,'DO YOU WANT TO CALCULATE THERMAL CONDUCTIVITY?’ TYPE *,'Y OR N' ACCEPT 21,IANS 21 FORMAT(A1) IF(IANS.EQ.'N')GO TO 31 C 3%******************************************************************* TYPE *,'CALCULATION OF THERMAL CONDUCTIVITY Now BEGINS' TYPE *,'ENTER THE BINARY INTERACTION CONSTANT PAR' ACCEPT *,PAR A1-D1(I) A2-D1(J) 31-02(1) BZ-D2(J) CCl-D3(I) CC2-D3(J) TYPE *,’AQUEOUS MIXTURE - Y OR N' 163 ACCEPT 21,IANS IF(IANS.EQ.'N')GO TO 28 C CHANGE MOLE FRACTION TO MASS FRACTION FOR AQUEOUS MIXTURES 23 28 24 29 DO 23 KK-1,MF W11(KK)-(X(KK)*WM1)/(X(KK)*WM1+(1.0-X(KK))*WM2) CONTINUE GO TO 29 DO 24 KK—1,MF W11(KK)-X(KK) CONTINUE CONTINUE DO 22 K-1,MF w1-w11(R) w2-1.0-w1 WMM-W1*WM1+W2*WM2 TClZ-PAR*ATC12 VCM-(W1*W1*V01)+(2.0*W1*W2*V012)+(W2*W2*V02) TCM-((W1*W1*TC1*VC1)+(2.0*W1*W2*TC12*V012)+ (W2*W2*TC2*VC2))/VCM PM—(SQRT(WMM/TCM))*(VCM**F2) TR-(T(K)+273.15)/TCM TKPl—A1+Bl*((1.0-TR)**F2)+CC1*((1.0-TR)**F3) TKP2-A2+BZ*((1.0-TR)**F2)+CC2*((1.0-TR)**F3) TK-((W1*TKP1+W2*TKP2)/PM)*0.001 Y(K,1)-TK*1000.0 C THE VALUE OF THERMAL CONDUCTIVITY HAS BEEN MULTIPLIED BY 1000.0 C Y(I,1) IS IN 0.001*W/M-K 22 CONTINUE GO TO 33 C ******************************************************************** 31 32 33 34 DO 32 K-1,MF Y(K,1)-0.0 CONTINUE TYPE *,'DO YOU WANT TO CALCULATE LIQUID DYNAMIC VISCOSITY?’ TYPE *,'Y OR N' ACCEPT 34,1ANS PORMAT(A1) IF(IANS.EQ.'N')GO TO 42 C ******************************************************************** TYPE *,'CALCULATION OF LIQUID DYNAMIC VISCOSITY Now BEGINS' TYPE *,'ENTER THE BINARY INTERACTION CONSTANT PAR' ACCEPT *,PAR A1-D4(I) A2-D4(J) Bl—D5(I) BZ-D5(J) DO 35 K-1,MF X1-X(K) x2-1.o-x1 WMM-X1*WM1+X2*WM2 TClZ-PAR*AT012 VCM-(X1*X1*VC1)+(2.0*X1*X2*VC12)+(X2*X2*VC2) TCM-((X1*X1*TC1*VC1)+(2.0*X1*X2*TC12*VC12)+ (X2*X2*TC2*VCZ))/VCM PM-(VCM**F2)/(SQRT(TCM*WMM)) TR-(T(K)+273.15)/TCM VISl-A1+(Bl/TR) VIsz-A2+(Ez/TR) 164 C VISl - ALOG(VISl*P1) AND VISZ - ALOG(VISZ*P2) VISM—(EXP((X1*VISl)+(X2*VISZ)))/PM C VISM IS THE VISCOSITY OF THE MIXTURE IN CENTI POISE Y(K,2)-VISM*1000.0 C Y(K,2) IS THE LIQUID DYNAMIC VISCOSITY IN E-06*(N-S/SQ M) 35 CONTINUE GO TO 44 c ******************************************************************** 42 DO 43 K-1,MF Y(K,2)-0.0 43 CONTINUE 44 TYPE *,'DO YOU WANT TO CALCULATE LIQUID HEAT CAPACITY?’ TYPE *,'Y OR N' ACCEPT 4S,IANS 45 FORMAT(A1) IF(IANS.EQ.'N')GO TO 53 C ******************************************************************** TYPE *,'CALCULATION OF HEAT CAPACITY NOW BEGINS' TYPE *,'ENTER THE BINARY INTERACTION CONSTANT PAR' ACCEPT *,PAR A1-D6(I) A2-D6(J) B1-D7(I) B2-D7(J) TC12-PAR*ATC12 DO 46 K-1,MF X1—X(K) x2-1.o-x1 WMM-X1*WM1+X2*WM2 TC12-PAR*ATC12 VCM—(X1*X1*VCI)+(2.0*X1*X2*VC12)+(X2*X2*VC2) TCM—((X1*X1*TC1*VC1)+(2.0*X1*X2*TC12*VC12)+ 1 (X2*X2*TC2*VC2))/VCM TR-(T(K)+273.15)/TCM RR—8314.0 C RR IS CAS CONSTANT IN J/KMOL-K CP1-(RR/WM1)*(EXP(A1-(Bl/TR))) CP2-(RR/WM2)*(EXP(A2-(BZ/TR))) CP-X1*CP1+X2*CP2 C CP IS THE SPECIFIC HEAT IN J/KG-K Y(K,3)-CP/1000.0 C Y(K,3) Is SPECIFIC HEAT IN 1000.0*J/KG-K 46 CONTINUE GO TO 55 53 DO 54 K-1,MF Y(R,3)-O.O 54 CONTINUE C ******************************************************************** 55 TYPE *,'DO YOU WANT TO CALCULATE SURFACE TENSION' TYPE *,'Y OR N' ACCEPT 56,IANS 56 FORMAT(A1) IF(IANS.EQ.'N')GO TO 64 c ******************************************************************** TYPE *,'CALCULATION OF SURFACE TENSION NOW BEGINS' TYPE *,'ENTER THE BINARY INTERACTION CONSTANT PAR' ACCEPT *,PAR TClZ-PAR*ATC12 165 Al-D8(I) A2-D8(J) B1-D9(I) B2-D9(J) DO 57 K-1,MF x1-x))/WMM H12-((A(J)*(TA-TREF))+((B(J)/2.0)*((TA**2)-(TREF**2)))+ 1 ((C(J)/3.0)*((TA**3)-(TREF**3)))+ 1 ((D(J)/4.0)*((TA**4)-(TREF**4))))/WMM ENT-DELTA1*(H11-H12)+HLL-HVV PRINT 61,DELTA1,HII,HI2 172 61 FORMAT(5X,F7.3,3X,F9.4,3X,F9.4) C ENTHALPY IN KJ/KG TYPE S4,PX1,PX2,TT,DLL,DVV,ENT 54 FORMAT(2X,2(2X,F5 3),3X,F7 3,5X,F8 3,3X,F8 5,3X,F9.4,/) PRINT 55,PX1,PX2,TT,DLL,DVV,ENT 55 FORMAT(1X,2(3X,F5.3),3X,F7.3,3X,F8.3,3X,F8.5,3X,F9.4,/) 75 CONTINUE c ******************************************************************** TYPE *,'DO YOU WANT TO CONTINUE FOR ANOTHER MIXTURE SYSTEM?’ TYPE *,'Y OR N' ACCEPT 114,IANS 114 FORMAT(A1) IF(IANS.EQ.'Y')GO TO 100 140 STOP END 173 Table A.2.2. Listing of CRIDAT.MX2 kg M Pc(bars) Tc (K) c ‘3) W m 1. 32.0000 79.50000 513.150 275.0000 0.2720 0 2. 46.1000 63.90000 516.250 280.0000 0.3000 1 3. 60.1000 50.50000 536.850 273.0000 0.3030 1 4. 78.1080 49.24000 562.600 301.6000 0.3100 0 5. 18.0156 221.29000 647.300 315.0000 0.2690 0 Table A.2.3. Listing of CONDAT.MX2 (Constants for estimating Cp [46]). U‘IJ-‘UJNH U'IbLONH .2155779E+02 .9015913E+01 .2470687E+01 .3392378E+02 .3224874E+02 OOOOO Methanol Ethanol n Propanol Benzene Water B 0.7093802E-01 0.2141122E+00 0.3325796E+00 0.4744556E-01 0.1924204E-02 C 0.2587521E-04 -0 -0.8391960E-04 -0.1855528E-03 -0.3017588E-03 0.1055695E-04 - 0000 F W5 .972708 0.0660761744 .230395 0.0753109306 .241347 0.0763160884 .704657 0.0786728710 .689803 0.0651030242 .2852177E-07 .1373534E-08 .4296482E-07 .7131491E-07 .3597152E-08 174 Table A.3. Mixture Preperties from MIXPR1.FOR and MIXPR2.FOR. , -3 J [Tsat] - C [AI] = 10 s m K -6 N s 3 J {41-10 -; [01-10-— 2 m pg kg K -3 .1‘1 . 15g [0] - 10 m [92 . pv1= 3 m 3 LI— [Ahv] - 10 kg ETHANOL-WATER x1 x2 Tsat 2! ”l Cpl 0 pl 'v 0.000 1.000 100.00 669.5 275.0 4.192 61.06 948.7 0.594 0.050 0.950 92.80 594.1 342.2 4.108 57.50 941.4 0.629 0.100 0.900 87.90 533.8 405.7 4.024 54.00 932.3 0.662 0.250 0.750 80.10 407.9 548.2 3.781 44.55 900.3 0.751 0.400 0.600 75.60 329.2 607.9 3.549 37.01 868.4 0.837 0.550 0.450 72.60 275.9 587.4 3.326 30.98 838.0 0.920 0.700 0.300 69.80 238.1 517.0 3.110 26.16 810.2 1.005 0.850 0.150 67.20 210.1 422.7 2.899 22.24 784.7 1.090 1.000 0.000 64.50 188.8 326.6 2.690 19.01 761.5 1.178 ETHANOL4WAIER ‘1 *2 Tsar: ‘1 "1 Cpl " ”1 Pv 0.000 1.000 100.00 669.5 275.0 4.192 61.06 948.7 0.594 0.050 0.950 90.10 546.2 369.9 4.102 56.51 941.4 0.658 0.100 0.900 86.00 467.5 451.9 4.016 51.95 929.1 0.714 0.200 0.800 83.20 371.3 580.5 3.865 44.07 901.8 0.818 0.350 0.650 81.20 288.8 701.0 3.674 35.38 864.9 0.971 0.500 0.500 79.90 237.7 733.6 3.513 29.21 833.3 1.124 0.650 0.350 79.00 202.5 695.0 3.371 24.64 806.0 1.278 0.800 0.200 78.20 176.8 613.4 3.240 21.15 782.5 1.432 0.890 0.110 78.00 164.4 552.2 3.167 19.41 769.5 1.524 1.000 0.000 78.35 151.5 471.3 3.088 17.53 754.2 1.634 2260. 2065. 1907. 1572. 1383. 1274. 1210. 1174. 1155. 2260. 1964. 1735. 1423. 1159. 1019. 940. 894. 876. 859. WNJ-‘PONOWO PNUONOJ-‘OChWO Table A.3. (continued) n PROPANOLrWAIER I-‘OOOOOOOOO l—‘OOOOOOOOOO .000 .060 .150 .300 .430 .550 .650 .770 .900 .000 .000 .070 .140 .250 .350 .450 .550 .700 .800 .900 .000 OOOOOOOOOH OOOOOOOOOOH .000 .940 .850 .700 .570 .450 .350 .230 .100 .000 .000 .930 .860 .750 .650 .550 .450 .300 .200 .100 .000 100. 89. 88. 88. 87 87 89 97 00 60 50 10 .70 .60 88. 45 .60 92. 90 .00 sat 80. 71. 69. 68. 68. 68 00 70 50 90 50 .50 68. 69. 70. 72. 78. 50 30 50 80 30 669. 464. 340. 251. 212. 189. 174. 162. 150. 143. 20. 26. 33. 43. 54. 66. 78. 100. 116. 133. 151. \JQOQI—‘J-‘VNOU‘ mbtémomoxooomw 275. 401. 539. 712. 792. 805. 767. 691. 569. 465. 308. 348. 371. 395. 417. 437. 456. 480. 490. 491. 471. 175 \o~qL»~Jqu>¢~>rd<> O‘NND—‘mWUIVNOH NMWWWWWWJ-‘b DJNNNNNNNHHH .192 .089 .948 .728 .546 .381 .248 .088 .926 .811 .885 .925 .980 .080 .177 .281 .392 .577 .716 .877 .088 61. .08 .00 35. 29. 26. 23. 21. 19. 17. 54 45 21. 21. 21. 21 19 18 06 17 73 12 71 39 23 72 12 83 74 .25 20. 20. 81 34 .90 19. 22 .75 18. 17. 24 54 948. 934. 902. 857. 827. 804. 786. 767. 746. 729. 829. 834. 831. 823. 817. 809. 801. 789. 780. 769. 754. mpkflUIUTCnOOP-‘V NWHJ—‘QU’IOQPOO POPJh‘P‘P‘H‘HHO be at the saturation value. This assumption, in the case of enhanced surface is justified for the following reasons: (1) the wall superheats are very small, (2) very vigorous boiling was observed.on.the main surface above the heater resulting in very high heat transfer coefficients, and (3) the unheated length of the tube experiences natural convection even at the highest heat flux. t. ' L...- . g ' I'. r """"" ‘ i: —[. o_o——T3 EOT. h.- o l I ‘- _________ . Fig B.3 1 _3 _3 _3 _3 r. - 4.8x10 m, r - 6.6x10 m, r - 8.5x10 m, r‘ - 9.3x10 m, 1 t c o _3 Lb - 0.152 m, L - 12.5x10 m, L - Lb + L nc no 2 Ab - 2xroLb, Anc - 2nroan [m ] .14. _LL Ac (copper) - 391 m-K , Ae (enhanced) - 242 m-K Tsat - % (T1 + T2) , Tt - % (T2+T3+T5+T6) [°C] (T - T ) Q = 1 r ‘3 S—lt r [W] .2 .2 (2nA Lb) 1n(rt) + (2MA Lb) 1n(re) T - T [ 1 1 (:9) + 1 1 (39)] °C (B 3 1) t'Q 21rALbnr 2111eran [] '° AT = Tw - Tsat [K] (B.3.2) a = .271: [ g ] (B.3.3) m K where ('1 = Eg—Lb [W—zl O m For the natural convection regime it was assumed that the entire surface was at the uniform temperature, Tw' As a first approximation with Q=VI in Eq. (B.3.l), AT and a were obtained from Eqs. (B.3.2) and (B.3.3). The losses from area Anc were then estimated from the value of a from from Eq. (B.3.3) QL - aAnCATm [W] (B.3.4) (T -T ) [K] where AT = m w sat NIH A new value of Q-—-VI-QL was then substituted in Eq. (B.3.l) to obtain AT and a from Eqs.(B.3.2) and (B.3.3). When boiling started on the heated length, the unheated length remained in the natural convection mode. To estimate losses from the unheated length, an, the value of a used in Eq. (B.3.4) was obtained by extrapolating the heat transfer coefficients in natural convection to the mean temperature ATm. From this estimate of losses a new value of Q-VI-QL was substituted in Eq. (8.3.1) and AT and or obtained from Eqs. (B.3.2) and (B.3.3), respectively. 183 4 Est tion of Errors in erinental Data The experimental error in the wall superheats measured are estimated to be iD.2 K” The error in the heat flux is estimated to be i6%. The error in the heat transfer coefficients thus range from 125% to i8% in going from low end of the enhanced surface boiling curve to the top end of the smooth surface boiling curve. APPENDIX C APPENDIX.C EXPERIMENTAL DATA OBTAINED ON SMOOTH AND ENHANCED SURFACES Q heat flux Pgfl m Tsat saturation temperature [ C] Tw wall temperature [°C] ATid ideal wall superheat, Eqs. (2.18) and (2.19) [K] AT wall superheat (-Tw - Tsat) [K] .. _‘L kW a heat transfer coefficient (= 2 AT m -K .. q kW a. ideal heat transfer coefficient (= ) 2 1d AT id m -K AT. Ratio = "3%g - ;g_ id 184 185 Table C.l.1. Methanol-water mixtures - Enhanced tube (High Flux) METHANOLrWATER ENHANCED'TUBE 99. 82. 66. 52. 40. 29. 21. 13. METHANOL.WATER 98. 81. 66. 52. 40. 29. 20. 13. METHANOL‘HATER 98. 81. 66. 52. 40. 29. 20. 13. «'1 Uia‘O‘OOJ-‘NJ-‘OH no J-‘O‘WOQWUJONW A. bmmaxoowr-‘oww AT 0 4.6 21.5 4.3 18.9 4.0 16.7 3.7 14.3 3.4 12.0 3.1 9.8 2.9 7.2 2.4 5.6 2.1 3.6 1.3 2.6 ENHANCED TUBE Arid AT 4.5 6.2 4.3 5.6 3.9 5.1 3.6 4.7 3.3 4.3 3.0 3.9 2.9 3.5 2.4 3.1 2.1 2.6 1.3 1.6 ENHANCED TUBE Arid AT 4.5 6.2 4.2 5.7 3.9 5.0 3.6 4.6 3.2 4.1 3.0 3.6 2.8 3.2 2.3 2.8 2.0 2.5 1.3 1.8 MOLE FR. - 0.00 (PURE WATER) MOLE FR. — 0.05 aid a 21.6 15.8 19.1 14.4 16.8 13.0 14.4 11.2 12.2 9.3 9.9 7.6 7.3 6.0 5.6 4.2 3.6 2.8 2.6 2.1 MOLE FR. = 0.10 aid a 21.9 15.8 19.4 14.3 17.0 13.1 14.6 11.4 12.4 9.9 10.1 8.2 7.4 6.3 5.6 4.6 3.7 3.0 2.6 1.9 T sat T sat 100.0'C = 92.6’C Ratio OOOOOOOOOO sat .73 .75 .77 .78 .76 .77 .82 .76 .79 .81 = 87.8'C Ratio 0000000000 .72 .74 .77 .78 .80 .81 .86 .83 .82 .72 Table C.l.1. (continued) 186 METHANOLrWATER ENHANCED TUBE 99. 81. 66. 52. 40. 29. 20. 13. a. WO‘WQQWU‘NU‘H E: H. D. METHANOLrHAIER 98. 81. 66. 52. 40. 29. 20. 13. A. J-‘O‘WVQUJWOU‘0 HETHANOLPHAIER 98. 81. 66. 52. 40. 29. 20. 13. a. U10L‘NQWUOUTUD Paranananauauauaknb U9K>h30\aih‘¢“fl<0(fl HHNNNNQHWW» moor-dbouomuaoov—I HHHNNNWWW“ NNQNJ-‘VOPO‘O 5 hanahauauauaaubtm1>W®b\lb0\l AT1d AT 17.1 17.2 16.6 16.6 15.3 15.3 13.7 13.9 12.6 13.0 11.4 11.7 9.6 10.2 7.8 8.5 5.5 5.9 SMOOTH TUBE ATid AT 17.4 17.3 16.9 16.8 15.6 15.4 14.0 14.0 13.0 13.1 11.8 12.1 10.2 10.7 8.5 9.1 6.1 6.2 SMOOTH TUBE AT a 17.6 12.4 17.1 11.3 15.8 9.1 14.2 6.7 13.3 5.3 12.1 3.8 10.6 2.6 8.9 2.1 6.5 1.4 MOLE FR. — 0.65 "id 12.7 12. 11.7 11. 9.4 9. 6.9 6 5.6 5 4.0 3 2.9 2 2.3 2 1.7 1. MOLE FR. = 0.80 aid 12.5 12. 11.5 11. 9.3 9 6.8 6 5.4 5 3.9 3 2.7 2 2.1 2 1.5 1 MOLE FR. - 0.89 (AZEOTROPE) oxmxnoboowat T sat T sat = 79.0'C Ratio .99 .00 .00 .98 .97 .97 .94 .92 .93 000000t-‘l-‘0 0000HHHHH c> o = 78.0°C 197 Table C.2.2. (continued) ETHANOLJHATER SMOOTH TUBE MOLE FR. - 1.00 Tsat = 78.3'C (PURE ETHANOL) q AT a 218.8 16.8 13.0 194.5 16.2 12.0 144.6 15.0 9.6 95.1 13.7 6.9 70.7 12.9 5.5 46.1 11.8 3.9 27.8 10.4 2.7 18.5 8.9 2.1 9.3 6.5 1.4 198 Table C.2.3. Ethanol-water mixtures - Polished tube. ETHANOLrWATER POLISHED TUBE MOLE FR, - 0.00 Tsat - 100.6'C (PURE WATER) q AT a 217.3 16.9 12.8 193.2 16.1 12.0 144.5 14.6 9.9 94.6 12.5 7.6 70.7 10.9 6.5 27.3 7.5 3.6 ETHANOL4WATER POLISHED TUBE MOLE FR. - 0.14 Tsat = 85.0'C q ATid AT aid a Ratio 217.4 18.3 32.7 11.8 6.6 0.56 192.8 17.4 30.6 11.1 6.3 0.57 145.0 15.8 24.4 9.2 5.9 0.65 95.7 13.6 18.8 7.0 5.1 0.72 71.1 12.1 17.3 5.9 4.1 0.70 ETHANOL-WATER POLIS- TUBE MOLE FR. = 0.25 Tsat = 82.7°C q ATid AT aid a Ratio 216.1 19.5 28.0 11.1 7.7 0.70 192.2 18.5 26.9 10.4 7.1 0.69 143.9 16.7 22.8 8.6 6.3 0.73 94.6 14.5 18.8 6.5 5.0 0.77 70.1 13.0 16.9 5.4 4.1 0.77 ETHANOL4HATER POLISHED TUBE MOLE FR. = 0.35 T - 81.4'C sat & AT1d AT aid a Ratio 216.4 20.5 28.8 10.6 7.5 0.71 192.7 19.5 27.5 9.9 7.0 0.71 144.4 17.6 25.3 8.2 5.7 0.70 94.7 15.3 22.1 6.2 4.3 0.69 70.5 13.9 19.7 5.1 3.6 0.70 Table C.2.3. ETHANOLrWATER 216.7 192.4 143.2 94.5 70.2 ETHANOLPWAIER 215.9 193.1 143.1 93.7 69.6 ETHANOLFUATER 216.6 192.4 143.2 93.8 69.6 ETHANOL4HATER 216.2 191.8 143.0 94.0 69.5 (continued) 199 POLISHED TUBE ATid 22.0 20.9 18.9 16.5 15.2 AT 29.3 28.2 25.7 22.7 21.0 POLISHED TUBE ATid 23.6 22.4 20.2 17.7 16.4 POLISHED ATid 25.1 23.8 21.5 19.0 17.7 AT 27.7 26.6 24.5 22.2 20.6 TUBE AT 26.0 25.1 23.0 21.1 19.8 POLISHED TUBE AT 26.0 24.7 22.3 19.7 18.5 w-baxxloo ooooboow MOLE FR. - 0. id «PU‘VQO O‘NONNQ MOLE FR. - 0. id L‘UIVQO NWHO‘N MOLE FR. = 0. 1d 0001050000 \OOO‘H0 MOLE FR. - 0. (AZEOTROPE) 50 Tsat - 80. a Ratio 7.4 0.75 6.8 0.74 5.6 0.74 4.1 0.73 3.3 0.72 65 Tsat - 79. a Ratio 7.8 0.85 7.2 0.84 5.8 0.82 4.2 0.80 3.4 0.80 80 Tsat - 78 0 Ratio 8.3 0.96 7.7 0.95 6.2 0.94 4.4 0.90 3.5 0.89 89 Tsat = 78. 1°C 3°C .4’C 2°C Table C.2.3. ETHANOL4HATER 216. 192. 142. 93. 69. 45. 26. 17. ooxoxobboxooou-a (continued) 200 POLISHED'TUBE AT 26. 24. 22. 20. 19. 17. 15. 12. 8. H0000O‘O‘CDN HHHNWJ-‘ONm HDQUTU'UIWQN MOLE FR“ - 1.00 (PURE ETHANOL) T sat - 78.6“C 201 Table C.3.1. Propanol-water mixture - Enhanced tube (High Flux). PROPANOLwWATER ENHANCED TUBE MOLE FR. - 0.00 Tsat - 100.3°C (PURE WATER) q AT 0 99.1 4.6 21.5 82.0 4.3 19.0 66.4 4.0 16.7 52.7 3.7 14.3 40.4 3.4 12.0 29.9 3.1 9.8 21.0 2.9 7.2 13.6 2.4 5.6 7.6 2.1 3.6 3.5 1.3 2.6 PROPANOL4HATER ENHANCED TUBE MOLE FR. — 0.06 Tsat - 89.3°C 9 ATid AT aid o Ratio 98.8 4.4 5.9 22.2 16.8 0.76 81.7 4.1 5.0 19.7 16.2 0.82 66.4 3.8 4.3 17.3 15.3 0.89 52.5 3.5 3.8 14.8 13.8 0.93 40.4 3.2 3.3 12.6 12.2 0.97 29.8 2.9 2.8 10.2 10.5 1.03 20.9 2.8 2.5 7.5 8.4 1.11 13.4 2.3 2.3 5.8 5.9 1.03 7.6 2.0 1.9 3.7 4.1 1.09 3.5 1.3 1.4 2.6 2.4 0.93 PROPANOL4HATER ENHANCED TUBE MOLE FR. = 0.15 T - 88.5'C sat & ATid AT aid 0 Ratio 98.6 4.2 4.2 23.4 23.3 0.99 81.5 3.9 3.7 20.9 22.3 1.07 66.4 3.6 3.2 18.4 20.6 1.12 52.5 3.3 2.9 15.9 18.1 1.14 40.3 3.0 2.6 13.6 15.7 1.16 29.8 2.7 2.3 11.0 13.1 1.19 20.7 2.5 2.0 8.2 10.1 1.24 13.4 2.2 1.7 6.2 8.0 1.28 7.5 1.9 1.5 3.9 4.9 1.23 3.4 1.3 1.3 2.6 2.7 1.03 Table C.3.1. PROPANOLrWATER ENHANCED TUBE £0 98. 81. 66. 52. 40. 29. 20. 13. ¥~onbxocnc~\nuana~ (continued) 5 PROPANOL4WATER <1 bLflWQQbU’INNO‘ PROPANOL4NATER 99. 81. 66. 52. 40. 29. 20. 13. a. pQWQOUIUINLDN P‘P‘FHQIQ'OrOQDLDUJ UJ\J¢>h‘UJO\KDhJU1Gi P‘H‘HHHEOFOPGBDUWUJ I.“ a. E: wmuooomason-b E: p. a. HHHHNNNWWW unmoosomkoor-ibu 202 5 HHHNNNNNWU’ OOCMNHNO‘HO‘ HHNNNWWUkL‘ MVHUNHWO-D‘m \IGDOJ-‘LDUIVONp ENHANCED TUBE ENHANCED TUBE E: MOLE FR. o: 1 QWHNNNOJ-‘WO - 0.30 Ol-‘OQI-‘WNCDNCD MOLE FR. - 0.43 (AZEOTROPE) MOLE FR. = 0.60 aid a 26.7 20.6 24.1 18.5 21.3 16.9 19.0 14.9 16.7 13.2 13.6 11.2 10.7 9.0 7.4 6.5 4.6 4.3 2.3 2.2 sat = 87.7'C Ratio c>c>cnorardhahahahl sat sat .11 .08 .12 .10 .04 .91 .99 .91 .77 - 87.8'C = 88.1’C BE ('1' H 0 0000000000 Table C.3.1. (continued) 203 PROPANOLrWATER ENHANCED TUBE 98. 81. 66. 52. 40. 29. 20. 13. a. WO‘POOWNNCDQ PROPANOLrHATER 98. 81. 66. 52. 40. 29. 20. 13. no muabxoooJ-‘oxmoxox ATid AT 4.0 6.1 3.6 5.7 3.3 5.3 2.9 4.5 2.6 4.0 2.4 3.5 2.1 3.1 1.9 2.7 1.8 2.3 1.6 2.1 ENHANCED TUBE ATid AT 4.2 6.3 3.8 5.7 3.4 5.2 3.1 4.7 2.7 4.3 2.5 3.9 2.2 3.4 2.1 3.1 1.9 3.0 1.8 2.5 PROPANOLPUAIER 98. 81. 66. 52. 40. 29. 20. 13. an. PO‘UTOQWO‘NUIU‘ Ea l—‘NMMNNWW-L‘k WOHNO‘ONUIOU 22. 20. 18. 16. 14. oooowwwr-‘axouaoo 1" H4300!“ ENHANCED TUBE MOLE FR. "id 24. 22. 20. 17. 15. 12. 10. 6. 4. 2. “i 23. 21. 19. 17. 14. \DQU'IOQVH‘PUJO‘ 11 9. 6 3 l HMOHWWONU’10 MOLE FR. 9- 16. 14. 12. 11. H HUDU‘O‘CDO 0.77 O‘WONbHNO‘kH 0.90 15. 14. 12. .buaLoLakhbro~ac~a~ H HNbO‘VOH MOLE FR. - 1.00 (PURE PROPANOL) sat - 89.6'C Ratio 0000000000 0000000000 sat .65 .64 .62 .65 .65 .67 .67 .72 .78 .78 .66 .67 .65 .66 .64 .65 .63 .66 .64 .71 - 96.8'C 204 Table C.3.2. Propanol-water mixture - Smooth tube. PROPANOLrHATER SMOOTH TUBE MOLE FR. - 0.00 Tsat - 100.6'C (PURE WATER) q AT a 216.9 14.9 14.5 192.3 14.8 13.0 143.7 13.7 10.5 94.3 12.3 7.6 69.9 11.1 6.3 46.5 9.0 5.2 27.6 6.4 4.3 18.5 4.6 4.0 9.5 2.7 3.6 PROPANOL4HATER SMOOTH TUBE MOLE ER. - 0.06 T - 89.6'C sat & ATid AT aid o Ratio 216 7 15.2 24.1 14.2 9.0 0.63 192.2 15.0 22.5 12.8 8.5 0.67 143.5 13.9 19.7 10.3 7.3 0.70 94.2 12.6 17.4 7.5 5.4 0.72 69.9 11.4 15.7 6.1 4.4 0.72 45.8 9.5 13.9 4.8 3.3 0.68 27.5 7.1 9.8 3.9 2.8 0.72 18.3 5.3 6.6 3.4 2.8 0.81 9.3 3.1 3.7 3.0 2.5 0.84 PROPANOL:WATER SMOOTH TUBE MOLE FR. = 0.15 Tsat - 88.5'C & ATid AT aid 0 Ratio 218 5 15.6 16.6 14.0 13.2 0.94 193.9 15.3 16.3 12.7 11.9 0.93 144 5 14.2 15.5 10.2 9.3 0.92 94.7 12.9 15.0 7.3 6.3 0.86 70.2 11.8 14.4 5.9 4.9 0.82 45.8 10.2 13.1 4.5 3.5 0.78 27.5 8.1 10.8 3.4 2.5 0.75 18.3 6.4 7.3 2.9 2.5 0.88 10.1 3.8 4.1 2.7 2.4 0.92 205 Table C.3.2. (continued) PROPANOLPHAIER SMOOTH TUBE MOLE FR. - 0.30 Tsat - 88.1'C q AT1d AT aid 0 Ratio 218.9 16.2 15.1 13.5 14.4 1.07 194.2 15.7 14.8 12.3 13.1 1.06 144.4 14.7 14.1 9.8 10.2 1.04 95.2 13.5 13.5 7.1 7.1 1.00 70.2 12.6 13.3 5.5 5.3 0.95 45.9 11.5 12.8 4.0 3.6 0.90 27.4 9.8 11.8 2.8 2.3 0.84 18.3 8.2 9.8 2.2 1.9 0.83 9.2 4.9 5.4 1.9 1.7 0.92 PROPANOL-WATER SMOOTH TUBE MOLE FR. - 0.43 T - 87.7'C (AZEOTROPE) sat q AT a 218.3 16.8 13.0 192.9 16.2 11.9 143.6 15.1 9.5 94.4 14.0 6.8 69.6 13.3 5.2 45.6 12.6 3.6 27.7 11.3 2.4 18.5 9.7 1.9 9.3 5.9 1.6 PROPANOLAWATER SMOOTH TUBE MOLE FR. - 0.55 Tsat - 87.6'C a ATid AT aid a Ratio 217.6 17.1 18.2 12.7 12.0 0.94 192.8 16.4 17.6 11.7 10.9 0.93 143.8 15.3 16.1 9.4 8.9 0.95 93.7 14.2 14.9 6.6 6.3 0.96 69.6 13.6 14.2 5.1 4.9 0.96 45.7 12.8 13.2 3.6 3.5 0.97 27.2 11.5 11.8 2.3 2.3 0.97 18.0 9.9 10.2 1.8 1.8 0.97 9.1 6.2 6.7 1.4 1.3 0.93 Table C.3.2. 206 (continued) PROPANOL4HATER SMOOTH TUBE 217.5 192.9 143.5 94.0 69.5 45.3 26.7 17.9 9.2 PROPANOL#HATER 217.6 193.2 143.9 94.3 69.8 45.2 27.0 18.1 8.9 PROPANOL4HATER 218.1 193.3 143.5 94.4 69.5 45.6 27.3 18.1 9.2 AT1d AT 17.3 17.9 16.6 17.4 15.5 16.3 14.4 15.1 13.8 14.2 13.0 13.1 11.6 11.7 10.1 9.9 6.5 6.8 SMOOTH TUBE AT1d AT 17.5 19.2 16.9 18.7 15.8 17.4 14.7 16.0 14.0 15.0 13.2 13.8 11.8 12.3 10.3 10.7 6.8 7.1 SMOOTH TUBE ATid AT 17.8 19.4 17.1 18.7 16.0 17.7 15.0 16.4 14.3 15.7 13.4 14.6 12.0 13.1 10.5 11.4 7.1 7.4 MOLE FR. - 0.65 T H N 9 [do 9. H HHNWU‘IO‘QH bCDUJU‘OU‘NO‘O‘ MOLE ER. H N p. O- H rdrdhauaUIOnord UJ\JUJ¢‘C>C‘P‘UMP MOLE HR. wwwbowxoww sat 12. 000000»onme HI—‘NU’P - 0.77 T sat WNNWO‘OWWM - 0.90 T sat FHA uwa>cna h>O\P‘HMb¢Dr4LBLD l-‘l-‘pr - 88.45'C Ratio .97 .96 .95 .96 .97 .99 .00 .02 .95 0HH000000 - 89.6“C Ratio .91 .90 .91 .92 .93 .96 .97 .96 000000000 000000000 \0 H 207 Table C.3.2. (continued) PROPANOL4HATER SMOOTH TUBE MOLE FR.1- 1.00 Tsat - 97.0'C (PURE PROPANOL) q AT 0 217.7 18.0 12.1 193.2 17.3 11.1 143.3 16.2 8.8 94.0 15.2 6.2 69.3 14.5 4.8 45.3 13.6 3.3 26.9 12.1 2.2 17.9 10.7 1.7 9.0 7.4 1.2 208 Table C.4.1. Ethanol-benzene mixture - Smooth tube. ETHANOL-BENZENE SMOOTH TUBE MOLE FR. - 0.00 Tsat — 80.0'C (PURE BENZENE) q AT a 217.4 23.4 9.3 193.2 21.9 8.8 143.8 20.1 7.2 94.3 18.5 5.1 69.6 17.6 4.0 45.7 16.6 2.8 27.2 14.9 1.8 18.2 13.4 1.4 8.3 8.6 1.0 ETHANOLPBENZENE SMOOTH TUBE MOLE FR. - 0.07 Tsat a 71.7'C q ATid AT aid a Ratio 143.9 19.5 23.2 7.4 6.2 0.84 93.9 18.0 20.9 5.2 4.5 0.86 69.6 17.1 19.7 4.1 3.5 0.87 45.5 16.2 18.3 2.8 2.5 0.88 27.2 14.6 16.3 1.9 1.7 0.89 18.2 13.1 14.6 1.4 1.2 0.90 9.1 8.6 9.3 1.1 1.0 0.92 ETHANOL-BENZENE SMOOTH TUBE MOLE FR. = 0.14 T t = 69.5“C q AT1d AT aid a Ratio 143.2 18.9 22.5 7.6 6.4 0.84 94.2 17.5 19.7 5.4 4.8 0.89 69.5 16.7 18.7 4.2 3.7 0.89 45.6 15.8 17.6 2.9 2.6 0.90 27.0 14.3 16.0 1.9 1.7 0.89 18.2 12.8 14.6 1.4 1.2 0.88 9.1 8.5 9.9 1.1 0.9 0.86 Table C.4.1. ETHANOL-BENZENE 144. 94. 70. 45. 27. 18. ETHANOL-BENZENE 144. 94. 70. 46. 27. 18. ETHANOL-BENZENE 144. 94. 70. 45. 27. 18. NWWONNN WWWVONH WHWQONN (continued) 209 SMOOTH TUBE AT1d AT 18.1 19.3 16.7 17.5 15.9 16.6 15.2 15.8 13.8 14.4 12.3 12.7 8.4 8.5 SMOOTH TUBE ATid AT 17.2 17.5 15.9 16.2 15.3 15.5 14.6 14.7 13.3 13.5 11.9 12.1 8.3 8.2 SMOOTH TUBE AT 0 16.4 8.8 15.2 6.2 14.6 4.8 14.0 3.3 12.9 2.1 11.5 1.6 8.2 1.1 MOLE ER. — 0. p.» D- HHNWJ—‘U‘m Hmoox-‘wo MOLE FR. = 0. H. G. l-‘l-‘NUJbLfim l—‘UIOHO‘OFP MOLE FR. = 0. (AZEOTROPE) 25 HHI—‘NJ—‘U‘V HPOONPU’I 35 HHNU§UIQ HU'Ol-‘UIWN 45 Tsat T — 68.9'C E ff p. O sat 0000000 .93 .95 .96 .96 .96 .99 - 68.5“0 if ('1‘ p. O sat H000000 .98 .98 .99 .98 .99 — 68.5'C 210 Table C.4.1. (continued) ETHANOL-BENZENE SMOOTH TUBE & AT1d AT 144.4 16.1 16.5 95.3 14.9 15.5 70.4 14.3 14.8 45.6 13.7 14.0 27.4 12.5 12.8 18.2 11.2 11.7 9.3 8.2 8.3 ETHANOL-BENZENE SMOOTH TUBE & AT1d AT 144.2 15.6 16.7 94.3 14.4 15.4 69.6 13.8 14.8 45.7 13.1 13.7 27.3 12.0 12.3 18.2 10.7 11.1 9.2 8.2 8.3 ETHANOL-BENZENE SMOOTH TUBE q Arid AT 94.0 14.1 15.4 69.8 13.5 14.7 45.6 12.7 13.7 27.3 11.6 12.2 18.2 10.4 11.0 9.2 8.2 8.9 MOLE FR. 9 H0 O- MOLE FR. MOLE HHNWL‘O‘O HO‘NWOPO HHNWU‘IO‘O HVU’U‘OU’IN HHNWU’IO‘ id id HVU’O‘NO‘ - 0. — 0 55 HHNWJ-‘Chm i—‘O‘HNNHV .70 HHNWJ—‘O‘m HO‘NU’NHO‘ HHNWPO‘ OQNUJNH T sa 0000000 0000000 .92 .92 .93 .95 .95 .92 211 Table C.4.1. (continued) ETHANOL-BENZENE SMOOTH TUBE a ATid AT 143.6 15.0 18.3 94.4 13.8 16.0 70.0 13.1 15.0 45.6 12.3 14.2 27.4 11.3 12.7 18.2 10.1 11.6 9.1 8.2 9.1 ETHANOL-BENZENE SMOOTH TUBE q AT 0 217.2 16.2 13.4 192.1 15.8 12.2 143.5 14.7 9.8 94.1 13.5 6.9 69.9 12.8 5.4 45.7 11.9 3.8 27.2 10.9 2.5 18.0 9.8 1.8 9.3 8.1 1.1 MOLE FR. - 0.90 aid a 9.6 7.8 6.8 5.9 5.3 4.6 3.7 3.2 2.4 2.1 1.8 1.6 1.1 1.0 MOLE FR. - 1.00 (PURE ETHANOL) T sat T sat - 72.8'C Ratio 0000000 .82 .86 .87 .87 .88 .87 .90 - 78.3“C 212 Table 0.4.2. Ethanol-benzene mixture - Smooth disk. ETHANOL-BENZENE SMOOTH DISK MOLE FR. - 0.00 Tsat - 80.3'C (PURE BENZENE) q AT a 238.0 15.7 15.2 201.3 15.4 13.1 168.4 15.0 11.2 138.1 14.4 9.6 110.6 13.9 8.0 83.1 13.2 6.3 64.4 12.6 5.1 44.3 11.8 3.7 30.3 10.3 2.9 ETHANOL-BENZENE SMOOTH DISK MOLE FR. - 0.05 Tsat — 74.0°C 4 ATid AT aid a Ratio 234.2 15.5 18.6 15.1 12.6 0.83 199.0 15.2 17.5 13.1 11.4 0.87 165.9 14.7 17.1 11.3 9.7 0.86 136.3 14.3 16.5 9.5 8.2 0.86 108.9 13.8 16.2 7.9 6.7 0.85 84.4 13.4 15.8 6.3 5.3 0.85 62.9 12.7 15.1 5.0 4.2 0.84 44.7 11.9 14.5 3.7 3.1 0.82 29.6 10.3 12.5 2.9 2.4 0.82 ETHANOL-BENZENE SMOOTH DISK. MOLE FR. = 0.12 T t - 70.4'C q ATid AT aid a Ratio 234.2 15.2 18.0 15.4 13.0 0.85 199.0 14.9 17.3 13.4 11.5 0.86 166.1 14.5 16.7 11.5 9.9 0.87 136.1 14.1 16.1 9.6 8.4 0.87 108.6 13.6 15.9 8.0 6.8 0.86 84.4 13.3 15.4 6.3 5.5 0.86 62.9 12.7 15.0 5.0 4.2 0.84 44.3 11.8 14.4 3.7 3.1 0.82 29.3 10.3 13.0 2.8 2.3 0.80 Table C.4.2. ETHANOL-BENZENE 234. 199. 166. 136. 109. 84. 63. 44. ETHANOL-BENZENE 234. 198. 164. 133. 105. 80. 58. 41. 27. ETHANOL-BENZENE 238. 199. 168. 135. 108. 85. 63. 44. 29. NpOLfiWO‘Wt-‘w WDOWOWWHU‘I m-PO‘Nvl-‘UIVHQ (continued) SMOOTH Ho 9- 14. 14. 14. 13. 13. 13. 12. womeoonw 10. SMOOTH AT H0 O- 14. 14. 13. 13. 13. 13. 11. 10. wwmoubooow SMOOTH H w #000Hw000 213 DISK H # \ONNNONUQO DISK H w l—‘PEWOHNU‘N DISK 17. 14. 12. H mwmaxooo \DVHO‘WN‘PU‘C MOLE FR. -=- 0.24 G H- 9. 15. 13. Nwmmooxo ONOEHOQNO MOLE FR. 10 O\O\\JNWN\O\DMJ$‘ p. Q. 14. 12. 16. 13. NWPWN UiNl-‘VWQVWH NW‘PUIV \lw-l-‘\OO\U'|O\O\O = 0.35 MOLE FR. - 0.45 (AZEOTROPE) 000000000 - 68.3'C sat Ratio H00000000 sat .97 .97 .97 .95 .98 .94 .94 .93 .02 = 68.3“C Table C.4.2. (continued) 214 ETHANOL-BENZENE SMOOTH DISK 236. 200. 167. 137. 110. 85. 64. 45. 30. wOANVNJ-‘WHO 13. 13. 13. 12. 12. 12. 11. 11. 10. ETHANOL-BENZENE 234. 198. 165. 134. 107. 82. 60. 43. 28. GAVQUFHOQUI AT 12. 12. 12. 12. 11. 11. 11. 10. ETHANOL-BENZENE 235. 198. 165. 135. 107. 82. 42. 27. pHmNJ-‘OO‘FFO AT 12. 12. 12. 12. 11. 10. 10. 10. mummoobwouo HONOUIHOWO‘ H0 D- OFWNWOHNO‘ AT 14. 13. 13. 13. 12. 12. 11. 11. 10. OWOWQNU'IQUI SMOOTH DISK pa. D- SMOOTH [do 0.. AT 14. 13. 13. 12. 12. 11. 11. 10. GGWQPOOQH DISK 14. 13. 13. 12. 12. 11. 11. 10. bur-daiwun—abo E MOLE FR. — 0.57 17. 15. 12. H WDU‘NQO P a. oopoooxioomm H 16. 14. 12. H WPUVQO bbbowbbbb MOLE FR. = 0.70 18. 15. 13. MOLE FR. H 9 H- a. 0HbHHQJ-‘NH “id 18. 16. 13. 11. WbLflV‘O ONNWWNNHO‘ 16. 14. 12. H (Ari-‘UIO‘QO 00w00¥>HON = 0.80 16. 14. 12. H NbU‘leo 9 \OOUIHNWO‘QQ Tsat - 68.3'C E n p. O l-‘I-‘t-‘000000 sat .94 .95 .97 .98 .98 .99 .00 .01 .00 - 69.0'C Ratio H00000000 sat .92 .93 .91 .96 .95 .97 .97 .99 .00 - 70.4°C Ratio 000000000 .90 .92 .92 .96 .94 .94 .97 .95 .97 Table C.4.2. ETHANOL-BENZENE 234. 198. 165. 135. 107. 83. 62. 30. ETHANOL-BENZENE 240. 203. 167. 137. 110. 86. 64. 46. 30. 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