Séhéififfiflfi 0%" BMW Dfififfi 8F REE Rem: far the fiagma at M. S. MECrHiGM STATE. UWERSHY NGUE’EN m CHAN 19??» IHIHHIIHIIllllllHHHIHIHIIHIIIIHHllllllfllllllllllfl 31293 01719 7827 LIBRARY Michigan State Unlverslty PLACE IN REI'URN BOX to remove this checkout from your record. To AVOID FINB retum on or before date due. MAY BE RECALLED with earlier due date if requested. DATE DUE DATE DUE DATE DUE 1/98 macs-m4 ABSTRACT SIMULATION OF BATCH DRYING 0F RICE By Nguyen Kim Chan Knowledge of the drying parameters is essential in the design and evaluation of a grain dryer. Most designs, however, are based on a limited number of experimental results which are slow and expensive to obtain. The computer simulation of grain drying has been studied by many researchers. The results of these studies revealed that simula- tion provides an accurate, fast and inexpensive tool for grain dryer design. An attempt was made in this work (using the existing fixed bed Hichigan State University corn drying model) to simulate the drying of rice. ApprOpriate changes were made in the basic MSU model to account for the differences in physical and thermal properties and in drying characteristics between the rice and corn. Chancellor's semi—empirical thin layer drying equation was used to describe the thin-layer drying behavior of rice. Henderson's equation provided the necessary equi- librium moisture content, after the two constants for rice were 1 Nguyen Kim Chan found. These equations, along with the MSU fixed bed program and related subroutines, constitutes the deep bin rice drying model. The results were obtained for a number of runs and were plotted on a WANG 2200 computer to investigate the validity of the model and to analyze the influence of a drying parameter upon the drying rate. It was found that the model can be used to predict fixed bed drying of rice. Though the accuracy of results obtained is still questionable because of questionable values used for the physical parameter, the methodology is valid. This means that rice drying can now be satis- factorily simulated on an electronic computer. Approved: fiL-Z’L/é j: glow/K Major Profeigdr Department Chairman SIMULATION OF BATCH DRYING 0F RICE By Nguyen Kim Chan A RESEARCH REPORT Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Agricultural Engineering 1976 ACKNOWLEDGEMENTS To Dr. Merle L. Esmay I express my gratitude for his guidance and encouragement throughout my graduate program. Gratitude is also expressed to Dr. Fred w. Bakker Arkema for his support and guidance which made this work possible. Appreciation is extended to Mr. Lloyd E. Lerew and Mr. Shehab Sokhansanj for their assistance with various aspects of this study. This work is dedicated to my wife, Nguyen Bao Ngan, and to my son, Nguyan Kim Khanh. Their personal sacrifice during this long absence is recognized and deeply appreciated. ii TABLE OF CONTENTS Page LIST OF TABLES. . . ...................... V LIST OF FIGURES ........................ vi LIST OF SYMBOLS ........................ viii INTRODUCTION. ......................... l REVIEW OF LITERATURE ...................... 4 Rice Drying Methods .................... 4 Rice Drying Thin-Layer Equations .............. 6 Physical and Thermal Properties of Rice .......... 10 Physical Properties .................. ll Thermal Properties ................... l5 Thermal Diffusivity .................. l7 Drying Simulation of Other Cereal Grains .......... l7 THEORY ............................. l9 Theoretical Thin—Layer Drying Equations .......... 2l Fixed Bed Model ...................... 23 Modification of the Michigan State University Model . . . . 26 TABLE OF CONTENTS (cont‘d.) RESULTS AND DISCUSSION ..................... CONCLUSION ........................... SUGGESTIONS FOR FURTHER STUDY ................. BIBLIOGRAPHY .......................... iv Page 36 68 69 7O Table LIST OF TABLES Page PHYSICAL PROPERTIES OF ROUGH RICE ............. l2 THERMAL PROPERTIES OF MEDIUM GRAIN ROUGH RICE ....... l6 PHYSICAL BED AND DRYING AIR PARAMETER VALUES USED IN THE RICE DRYING MODEL .................... 34 EFFECT OF SPECIFIC SURFACE AREA .............. 67 Figure l. 2. 10. ll. 12. I3. 14. LIST OF FIGURES Page Subroutine LAYEQ ...................... 27 Subroutine CREADY ..................... 28 Function Subprogram CMC .................. 32 Listing of a sample output ................. 39 Result of simulation vs. experimental data for drying of 1 ft of short grain rice ................. 43 Result of simulation vs. experimental data of a thin layer drying of IR 8 Rice . . . . . . . . . .......... 44 Equilibrium moisture content equation vs. data ....... 45 Drying rate in a fixed rice bed at three locations ..... 46 Moisture content vs. depth at three time intervals ..... 48 Grain temperature vs. depth at three time intervals during fixed bed drying of rice ............. 49 Absolute humidity vs. depth at three time intervals during fixed bed drying of rice ............. 50 Relative humidity vs. time at three locations during fixed bed drying of rice ................. 5l Effect of temperature on drying rate of a fixed bed of rice ......................... 52 Effect of temperature on moisture gradient during drying of a fixed bed of rice, when MCav first dropped below 13% 53 vi LIST OF FIGURES (cont'd.) Figure 15. l6. l7. l8. I9. 20. 21. 22. 23. 24. 25. Grain temperature vs. depth at three inlet air temperatures, when MCav first drops below l3% . . . . Effect of airflow on drying rate of a fixed bed of rice Effect of airflow on moisture gradient during drying of a fixed bed of rice when MCav first drops below l3% . Grain temperature vs. depth at three airflow rates, when MCav first drops below 13% ........... Effect of absolute humidity on drying rate of a fixed bed of rice ..................... Drying rate in a 2 ft rice depth bed at 3 locations . . Effect of bed depth on drying efficiency ........ Relative humidity of air in a 2 ft grain bed ...... Grain temperature distribution within a fixed bed of rice after various drying periods .......... Properties of drying air in a grain bed after 6 hours . Properties of rice in a drying bed ........... vii Page 54 55 56 57 58 59 6O 61 64 65 66 SYMBOLS Specific product surface area, ftz/ft3 Specific heat, BTU/lb °F Convective heat transfer coefficient, BTU/hr ft2 °F Heat of vaporization, BTU/lb Relative humidity, decimal time, hours constant Constant Diffusion coefficient, ftZ/hr Flow rate, lb of dry product/hr ft2 Humidity ratio Phenomenological coefficient Length, ft Local or average moisture content, decimal, dry basis Moisture ratio (M - Meq) / (Min - Meq)’ dimensionless Pressure, psia Gas constant, ft lb/lb Cross sectional bed area, ft2 viii abs Air temperature, °F Absolute air temperature, °R -—Subscripts-- Air Equilibrium Inlet At time t = 0 Product Saturated vapor At time t Vapor Hater ix INTRODUCTION Rice is the most important crop in the world today and provides staple food for hundreds of millions of people in Asia. The increase of rice production and improvement of rice quality are two of the major world agricultural needs of today. Rice is a biological product with hygroscopic properties. High moisture content profoundly accelerates fungus growth, development of insects and mites, deterioration of starch and loss of nutrients. In order to maintain high quality over a long period of time rice must be dried. The harvest moisture content of 20 to 24 per cent wet basis must be reduced T3 to 14 per cent wet basis for safe storage (Esmay l970). Sun drying of high moisture content rice has been practiced for centuries. The grain is spread on concrete or a hard earth floor. The drying process takes place by an exchange of moisture and heat between the grain and the surrounding atmospheric air. Even under the most favorable conditions it has been found that considerable cracking re- sults. For large scale production or for early maturing varieties of rice for which more than one harvest a year is possible, artificial drying is preferred. Unlike most cereal grains, rice is consumed primarily in the whole kernel form so that the market premium for unbroken kernels is much greater. Therefore, to avoid cracked kernels, more care is re- quired for drying rice than for other cereal grains. Stress crack development depends on the rate of migration of moisture from the inside to the outside of the kernel. As the rice is dried, the outer portion shrinks, resulting in stress and strain. When too much moisture is removed too rapidly, checking or shattering of the kernel results. To reduce this effect, rice is dried with air at 100 to T30 degrees Farenheit in two or more passes through the dryer. Between passes through the dryer, the grain is held in a bin to allow moisture to equilibriate throughout the individual kernels. This tempering relieves stress (Nasserman 1957) and strain and facil- itates drying in the next passes. Though rice drying is a complicated process, the design of a rice dryer is based largely on a limited number of laboratory and field experiments. There has been little or no use of a powerful new tool for experimentation called simulation. In simulation the designer represents his dryer design by a number of equations of which the solu- tions predict the drying behavior of the equipment. Simulation models are usually solved on electronic computers; today's technology makes this type of solution possible. An advantage of computer simulation is that when a model satisfactorily predicts grain drying behavior, the effect of various parameters influencing this behavior can be in- vestigated (Bakker-Arkema et al. 1973). Rather than return to the laboratory for more testing, answers can be obtained in minutes from the computer resulting in faster, better and less espensive design. Grain drying simulation model has been available for corn but there is no existing model for rice. The purpose of this study is to employ an existing corn drying model for the drying of rice. Changes were made to make the simula- tion model applicable. The resulting output from the computer has been compared with experimental data. Various drying parameters have been analyzed and discussed. It is the hope of the author that this work will contribute to the existing literature in the field of rice drying and provide a good model for rice drying simulation and rice dryer design. REVIEW OF LITERATURE Rice Drying Methods For the proper drying of rice, moisture must be removed from inside the grain kernel. To prevent internal checking or breaking of the kernel from drying too rapidly, drying is usually done in three to five stages or passes. In each stage, the rice passes through the dryer and then is tempered in a bin so that the kernel moisture will equilibriate. Esmay and Chancellor (l970) found that for batch drying of rice at a temperature above lOO of deg. Far. tends to cause overdrying and thus a lower head yield of milled rice. Smith and others (l959) reported on early research on artifi- cial drying of rice in Arkansas and Texas concluded that a drying temperature of l20 deg. F could.be used without injuring the rice if the moisture content was reduced only about 2 per cent at each drying operation and the rice was allowed to remain in storage l2 to 24 hours between drying periods. However, when necessary to dry a given lot of rice in one continuous operation, the drying air and temperature should not exceed llO deg° F. Stahel (1949) showed that a moisture content of 15 per cent is critical for crack formation, drying or wetting of the rice which passes this point increasing the internal cracks. From experiments with combined rice, MacNeal (1949) concluded that in most cases head rice yield was increased and the total drying time was decreased as the number of drying passes was increased from one to four in the temperature range from lOO to 150 deg. F. The tempering between drying was important since it gave the moisture in the grain an opportunity to equalize and thereby reduce the drying time. To increase dryer's efficiency Calderwood and Hutchinson (l96l) conducted a series of experiments in Beaumont, Texas, and found a significant drop in moisture content in rice cooled by aera- tion following a pass through the dryer. According to Hutchinson and Hillms (1962) the practice of aerating is in widespread use in the Southwest of the United States. They indicated that aeration is used to: I) maintain the quality of undried grain until it can be moved through the dryer, 2) remove harvest or dryer heat, 3) remove small amounts of moisture (l to 2 per cent), and 4) maintain the quality of rice during storage. Infrared drying of rice has not been found to be of practical importance. However, Wratten and Faulkner (l966) found that infrared energy could be used as a source of heat to preheat the rice before the drying operation. Rice Drying Thin-layer Equations The theory of drying of biological products has been treated by many workers and has been adapted to many cereal grains and drying systems in use. Henderson and Perry (l966) reported that the moisture removal of thin layers of grain during the falling rate is inversely propor- tional to the moisture to be removed: d _ dt - -K (M - Me) (I) Where: M : Moisture content, per cent t : Time, hours Me : Equilibrium moisture content, per cent K : Drying constant, hr"1 Solution of equation (l) yields: The constant K is determined by the characteristics of the grain. Equation (2) forms the basis for much thin-layer drying theory. Thompson (l967) simulated the process of drying a deep bed of grain by consecutively calculating the changes that occur during short increments of time in thin layers of the bed. For thin-layer drying of corn Thompson's equation is: t = A ln (MR) + 8 ln (MR)2 Where: t : drying time, hours M - M e M - M o e MR : MO : Initial moisture content, per cent dry basis M : Moisture content, per cent dry basis A : l,86l7 + 0.0048843 9 For rice, Allen (l960) developed an equation for shallow bed drying: c e (4) =$10910 (M -M) 0 e 0 Where: M : Moisture content at the end of the constant rate drying period, decimal O : Time, hours m : Dimensional Drying Rate Constant, hr-1 Me : Equilibrium Moisture Content, decimal. For intermittent system of drying rice in a shallow bed, Faulkner and Wratten (l967) developed the following equation: - nl _ _ . ) n2 n3 R I T E N 1 _ eC2(TE/TG) (Vt/L) (5) M : Moisture removed in time t, per cent dry basis M. : Initial moisture, per cent dry basis T : Dry bulb temperature of entering air, deg. R. E Tw : Wet bulb temperature of entering air, deg. R. TG : Initial grain temperature, deg. R. V : Air velocity, ft./min. L : Length of air passage through the grain, ft. t : Time, min. Ramarao and Wratten (T969) developed a generalized equation to predict moisture removal from the Dawn variety of rice in the Louisiana State University model dryer. This equation is: MR = (73.109 - 59.8l9TE/Tw) (37 167 - 32-068TE/TG) (Mi - Me) (TE - TL) 0.592 Tw -l.l08 l.45(R )-0.438 (Te/TN) (5 e-7.963(Vt/X) e ] .. v Where: Re : modified Reynolds number - pV/u MR : Moisture removed at any time t, per cent dry basis T : Dry bulb temperature of inlet air, deg. R. T : Wet bulb temperature of inlet air, deg. R. V : Velocity of air flow, ft./min. X : Characteristic length of dryer, ft. Equation (6) has not been tested for other dryer types or other varieties of rice. Only limited data for air, grain temperature were used to develop the equation. More work is therefore needed to verify its usefulness and accuracy. Chancellor (l967) developed the following thin-layer equation for heated air drying of short grain rice. G9 4G0 -960) (7) M - Me _ _ = 0.735 (e + l/4 e + l/9 e Mo- Mw Where: 9 : time, hours G : constant. l0 Chancellor determined experimentally that the value of G increases with an increase in grain temperature. This relationship is expressed as: - 6l47 T G = 8860 Where: T : grain temperature, deg. R. Consequently, based on experimental results, the empirical thin-layer equation by Chancellor can be used to represent the char- acteristics of drying of rice. Of all the various equation forms presented above, all have some limitation to a fixed bed grain dryer, besides their forms do not lend themselves to the application in the Michigan State Univer- sity grain dryer model. Chancellor's equation was thought to be best suited for the model. Hence this study primarily uses this thin- layer equation. Physical and Thermal Properties of Rice Prerequisite to an accurate engineering design of the machines and equipment for processing rice is knowledge of the true values of the physical as well as thermal properties of the rice itself. It is ll these properties that distinguish the rice drying process from that of other cereal grains. The magnitude of physical and thermal properties of rice must be evaluated as a function of moisture content (Wratten 1969). Rice will often range from a high of 22 to 24 per cent moisture at harvest time, down to a low of ID to l2 per cent for safe storage. Rice varieties divided by grain size and shape fall into three types: short, medium and long grain. The type must be considered when evaluating the physical and thermal properties of rice (Wratten l970). Some of the physical and thermal properties of rice have been determined by various authors but only at specific levels of moisture content and most properties determined pertained to bulk condition. Only limited information on thermal properties of rice is available. The work by Wratten et al. (l968) is found to be more general and complete, therefore their values are used in this simulation model. The results of their findings are presented below. Physical Properties The values of length, width, thickness, volume, density, spe- cific gravity and porosity for medium and long grain rice at a mois- ture content ranging from l2 to l8 per cent wet basis are shown in Table 1. 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Q'u‘l‘UN.’ as: :3 Us 4 2'. 2?;IZQHUC O IN‘O OCIIZ< 0X2 C L: >- m '1; 00C?! Ceanx cza' coxovn m 5 m D h rtrwdddwo.u4vrun:unu: a 1X1whhqvmox4uloohfl>UPo Z C({‘>.<1¢1¢1L._II "Vet—II; 9'1 r:-—-) -I.' w ‘cuuuucmquohoxxaxoxom I I 6 b It I o I o s I t I t t G O 6 D 9 H N o I o s s I s o o o o o o o u» o o o t o o o o o as o o o 0 . CLCUUCCCUQ 1n 0 m D m o .4 '4 N N n . C‘( It? , , lbL-UQQ-l‘u ' NHJWOKQ NNN NNNN ZZZZZZZ DUO UUUQ ..)1'TI :XPIko‘GIO.1111’EXPI9.0’GI) f “C,TH,RH,CELT,CF*.XMO.KAB 6 O .76" ON I o 6—6 ”A \L‘) .v NIL a .:x H .4!“ O- \D" V} X II ”yxvm (\XC.” I/\xr~ CHAN! O (in... . 21—1 0X Ca\\t))< Subroutine LAYEQ. 1 Flg. 28 wax A: zaxo mzxocthure a m we quo ox "crxp : m: 2410 m C.» cc 3: zero ozxuczx» n m: zaxo :.:.n.oxxuozx.uh N N: 2410 a vac: « «a ZGIU « « NTExTuxVVCH o: 2410 uncecca on quo .1» x23u23u-:x mm qum .mq 4:.0 um.zmo.p4wo.x..z :p.urx\zwazxzcrrru N ZdI nNu—LX. UQ QOCH “1x val—1.0 CZXPV >OdV~uQ IZHPZCPP... .. U mode .oo.ao.«o. mnxflfixma «uhao ocmauo.m> z»; memo um .o >qumo u7upsoam3m 29 (2) Check absorption flag; if it is not set, compute the equivalent time, add the time increment and compute the new moisture content. (3) Use the Del-Guidice equation to simulate absorption if the absorption flag is set. In the drying process, the conditions at a particular position change with each time step. Each set of new conditions specifies a new dry- ing curve. The amount of drying must be transferred to the new curve before solving for moisture content at the end of the current time step. This correction is made by solving the thin-layer equation for time using the current moisture content. This is referred to as the equivalent drying time (Thompson 1967). The Chancellor equation in its original form cannot be solved for time, so the root finding technique is employed using the subrou- tine ZEROIN, which is available in the Fortran Psychrometric package (SYCHART). [2] A function subprogram for the equilibrium moisture content of rice had to be written. Wratten (1969) extrapolated data obtained by Karon and Adam (1949) by the use of the following equation of Strohman and Yoerger (l967): RH = (e Where: RH M P s a, b, c, d Though the 30 DM ae 1n PS + CedM) Relative humidity, decimal. Moisture content, decimal DB. Saturation vapor pressure of water, lb per sq. ft = Constants results obtained by this equation are believed to have small errors (Wratten, 1969), values for the constants are not available. The Henderson equation for predicting equilibrium moisture l - Pv/va = exp (-aT Where: 3 Pv/va content of cereal grains is used. Its general form is: b absM ) : Equilibrium moisture content, per cent DB. : Relative Humidity, decimal. a, b : Product constants. Based on data in the book by Brooker et a1. (1974), the values for a and b were calculated to be: 31 0.3438 x 10'5 9| 1| 0' 11 2.377 The change in equilibrium moisture content with respect to relative humidity is more considerable, so for simplification purposes, a and b were assumed to be independent of temperature. Henderson's equation with constants for rice as discussed above, was used in subroutine CMC to calculate the equilibrium mois- ture content at each time step. A listing of function subprogram CMC is shown in Figure 3. [3] Appropriate values for the physical and thermal properties. Tables 1 and 2 give the values for rice. Table 3 shows a summary of the physical properties of the bed and drying parameters for use in the rice drying model._ The heat of evaporation, hfg’ and properties of the air, are assumed to be the same as in the corn drying model. The specific surface area which is the area of the rice kernel surfaces per unit bed volume is calculated as follows: Total surface area of rice ft2 =———§-:ft Volume of rice ft -1 Sa 1 PAGE 12/11/75 .01g00596. =1 CDC 6500 FTN VJo0-P380 OPT CMC FUNCTION 32 O‘OflNMJm LO mnnnmnmm ZZZZZZZZ d<<<<<<< IIIIIIII 00000000 0 D O H \ A A N LL \ H v O Q A (’1 m d p— 0". OH OK 0 .v R N\ '- IA ‘ I 1” A1 «M @l VJ 090 CM ova EU .0- U” GOO Q moo ZUNJII...‘ ouN‘Cd H 0").- 0.2 POOHIVy L‘ I macs u 2 Z 11 ll CVUD-o Tufirk*~“ ukurhodfi Fig. 3 Function Subprogram CMC 1 PAGE 12/11/75 501.00.86- =1 CDC 6500 FTN V3.0-P380 OPT BLOCK DATA 33 v-{NM 4'1.an mmmmmmm ZZZZZZZ «(ddddd IIIIIII 0000000 CA.CP.CV,CN,RP, HFG 34 TABLE 3. PHYSICAL BED AND DRYING AIR PARAMETER VALUES USED IN THE RICE DRYING MODEL Parameter Units Values References a ft 324 Wratten et al. (1970) Ca BTU/le 0.242 Threlkel (1970) Cp BTU/le -0.632 Wratten et a1. (1970) h BTU/hr ft F same as in Bakker Arkema et al. (1974) corn model hfg BTU/1b Pa lb/ft pp 1b/ft 47.67 Wratten et a1. (1970) CV BTU/le 0.45 Threlkel (1970) Cw BTU/le 1.0 " Area of one grain : 0.0658 in2 (Wratten, 1968) Volume of one grain : 1.152 x 10-3 in3/grain Weight of one grain : . 3 3 1.152 x 10'3 lFETE’ x 85.54 ‘b3 x ft 3 9 ft 1728 in _ -5 . — 5.71 x 10 1b/gra1n 85.54 1b/ft3 = true density of rice (Wratten 1958). 35 Number of grain per cubic foot: 40.49 1b/ft3 _5 = 7.1 x 105 grain/ft3 5.71 x 10 1b/grain 40.49 1b/ft3 bulk density. Surface area : 7.1 x 105 grain/ft3 x 0.0558 inz/grain x ft2/144 in2 2 = 324553- = 324 ft- ft 1 RESULTS AND DISCUSSION The simulation model describing fixed bed drying of rice con- sists of four equations and four unknowns. The system can be solved simultaneously by numerical integration using finite difference tech- niques. An expression required for the equilibrium moisture content of rice has been obtained as discussed earlier. A model of the ther- modynamic chart for calculating the humidity and other harmodynamic properties of the drying air, to check for possible condensation is also available. The four subroutines which finm1the fixed bed rice dryer model are: (1) The thin-layer rice drying process (Subroutine LAYEQ); (2) The equilibrium moisture content (Subroutine CREADY, function subprogram CMC); (3) The dry air-water vapor relationship (SYCHART package); and (4) The main MSU fixed bed drying model. 36 37 The model will need the following input to provide the desired output: - Initial moisture content, product temperature, drying air tem- perature, humidity ratio of the air, and airflow rate (First card); - Depth of bed, number of nodes between printout and depth incre- ment (Second card); - Maximum drying time, time increment between printout, and final moisture content (Third card). The relationship between airflow and depth increment is critical in the fixed bed program and has to be observed strictly to insure sta- bility. If the depth increment is too large with respect to airflow, the equation will diverge or oscillate from the true solution. If too small, the solution requires excessive computer time. After the rice drying model had been operated properly, a num- ber of runs were made to simulate the drying behavior as described by the thin—layer equation and the equilibrium moisture content equation. Drying parameters were also investigated using as standard run: 28.2 per cent moisture content, DB (=24% wb) 100 deg. F, drying air temperature 38 30 CFM per sq. ft. air flow rate 1 ft., bed depth A complete listing of the output is provided in Figure 4. To test the accuracy of the Chancellor's equation, data obtained from the computer output were plotted against experimental results for the same drying condition. Figure 5 shows that the fixed bed rice drying simulation model agrees very well with the experimental curve by Soemangat and Esmay for the H20 removed. It should be noted that the Chancellor thin-layer equation and the Soemangat data were developed from the same variety of rice. In Figure 2 are plotted drying rate data for IR.8 rice obtained experimentally by Kachru (1970) and calculated by the thin-layer Chancellor equation. A fairly good fit results. The properties for IR.8 variety of rice have not been determined. The values calculated from the equilibrium moisture content equa- tion and the experimental data are plotted in Figure 7. The good fit is due to the fact that both were developed from data obtained by Hogan and Karn (1955). Typical results of deep bed drying are presented in Figure 8 for a 1 ft bed depth. 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"a". mm“. as“. and. and. m~«. mud. co“. “a“. mom. mo oz :mc... 5mm... m5”... «.u.co mmo.«¢ m«~.n¢ md5..c amfl.¢o o«m.~c Nat..a ¢”~.oo orUP coca sow... 000.0. no”... omo.oo 4.0.«m n-.na ~N5..a cwfl.oo -m.~o «my... o,m.uo« arm» «Ha mo.«5o u owzmdxshm ofi.5 n ow>ozmm o~x o~.N.~m ujhaazH >oamzm cfimfi. u oz moqamaq DN. u onbaaommq hzmoamm mo. u on—qmzwczoo bzhuwua «q.u« u .7.» 2 f . A. ~ mnooo. .om5oo. om5ao. «~5oo. 3.09:. osoao. cacao. samuo. nmmca. mwmuo. uumuo. :2: mm: noNMn. :5oou. ”.moN. mo~.~. nw5aw. ammo“. omo5u. ~momd. No.3”. a:«n«. magma. :3: 4m¢ m5“. «5“. no“. mm“. 5:“. on“. and. MN“. 0”". no“. Ned. we or a moo.mo omn.mo oefi.5o moo... «05.0o a5:.~ . «~3..o 5o5.m¢ -~.5c www.cc 00¢.oo arm» coma. mam.ne ¢5n.mo oofl.5c noc.oo o55.oo o0..~c ¢~«.:o :05.m¢ c-.5o «cc.mo ooo.oo« arm» «a. 3o.«no n omxmdxnpm . m5.o u ou>ozux ow: .«.maam u PanzH >om02m ”0:“. u oz moqaw>< NN. n onkaaommq hzuoamq on. . u onhqmzunzoo hzmuoma «u.a u wry» 05.99. ”noon. «okoo. om5oo. ca5oa. «Nona. among. swmuo. Nomom. onmao. cumuo. 2:: mm. _ ocean. c.5Nn. oomww. 55dgw. omnnN. 5o5o~. ammo“. n5moa. mnc.d. “Nana. o~o~«. :2: 40¢ _ «m3. ~o3. .5“. mo”. 5m“. 0... a... ~na. .~«. ma“. ca“. mo u: _ 50c.mo «oo.¢o ~oe.m. «55.5o :a5.¢o nmm.«o m...no oc«.um ~5c.oa «x:.mo muc.om azup coma N c5o.~e «we... Noo.ma «n5.5o .d5.oo 5mm.«a :N:.n¢ on“.mo o5c.em cm:.mc ouo.oo« .zm» «H. 0 c..~m~ u ouxmaxaum on.. u om>ozmm ow: oc.aoc: n pnazu >oamzw co.~. u or uuqau>< m mw. u onhamomma pzmoama so. u zouquzmozou hzmoama 09.. u 01“» 43 mum. DH .moflu samuw uuosm 00 um H 00 wcwmuv now mumv HmucmEHumaxm m> coHumHDEHm mo uasmmm .0 000 A05 0 \@ 00v umw4m5wom an cofiumfisaflm * A . mumo fifl1. 0 d m N 800 on m. 00 , Ad 0 paAomal OZH 44 mp: umxma easy a we mumv Hmucmafiummxm m> cowumaasam mo uasmmm .0 000 .muwp 0 0H 00 wcwhuc c m N 4 F. *j’yn 4”/ I!” :oAumHaEHm . . fienmflv unsung an mung ¥ . Emu 00 0. «ma OH 00 ON mm on N00 'gq ‘nuanuoo QJHJSION 45 mm N ooH .mumv m> aoflumsvm ucmucou musumHoE Eswunflawsvm .5 000 00 00 05 00 on 00 on ON 00 M v v ; mumm— .II . ceflumsvm uZm ¢nu* 00 0H ON Nmm gq nuanuoo alnnsgow 46 .mcoHumooH mmucu um vmn mowu 00x00 a G0 wumu mcwzuo .0 000 3m S m m N o n e m N 0 . 0H\QH 000. 0 5 m f ./ E. on . m. ooH :IIIllul #IJUV ma a. «H .v IIIIIII.T ON _~‘ M‘ mm N00 30 nuanuoa axnnsxow 47 exhibit quite distinctive characteristics. It is interesting to note that 2 hours of drying (1 ft bed) have passed before any decrease in moisture takes p1ace in the upper 1ayers. However, it does not mean no drying in the bed occurs since the average moisture content of the grain bed decreases steadily. Effect of time on moisture content, product temperature and abso1ute humidity distribution in the bed are shown from Figures 9 through 11. The comp1ex nature of re1ative humfidity of the drying air in the bed is investigated in Figure 12 (1 ft bed depth). It can be seen that the re1ative humidity in the bottom of the bed is that of the in- 1et air whi1e in the upper 1ayers, the re1ative humidity stays con- stant for a certain period of time before decreasing. Figures 13 to Figure 15 show the effect of drying air tempera- ture on drying rate (average moisture content), on moisture content distribution and on rice temperature within the bed. The effects of airf1ow on drying rate, on moisture content and on grain temperature are shown in Figures 16 to 18. The resu1ts of the effect of in1et air humidity are p1otted on Figure 19; it is c1ear that higher humidity decreases drying rate. Figures 20, 21, and 22 investigate the characteristics of a 2 ft bed depth. It can be seen that at higher bed depths drying is more 48 .m~m>umucfl wEwu mounu um sumov m> ucmucou wuaumwoz .0 000 um H 0. w. 5. 0. 0. Q. n. N. H. O _ nH\aH moo. EMU Om . be cod “1qu \JT\ 0.— L..\T \...\ \.\0 \.T\\ 0\0 .+\.;. .\ mum OH \ \:\ \ 0 \. \M i \A \M \1 "av ON mum O \ mum M \\ \ \ N00 °ga JUBJUOO alnustou 49 .ouwu mo wcwmuv won vexww 0cwusv mHm>umucH mswu mmusu um summv m> musumummsmu samuo .00 000 ab 0. 0. 5. 0. 0. q. n. N. a. o 0 00 .0 » W 00 a mu: m . O5 naxna 000. c mum 0 Emu on m. OOH 00 mum OH 00 OOH '30 ‘alnnaladmaa utezs 50 mHE O." mum 0 mu: 0 .oofiu mo wcamuu con 00x00 wcwuav me>uoucw mEHu wounu um nuamv m> zuwvwEDL ou3H0mn< .00 000 H m. me No on no 0‘. no N. H0 1 : w v v w _ W nH\3H 000. 0 a Emu on J mo OOH w r ._ \J _ .T\. \ W \.“\\:\ \l r\# A \ L \1 coo. moo. 0H0. 000. '119 519 J0 qt/ozH J0 QT ‘AnIpImnq anntosqv 51 mum 5% o 3. 60 NH .mowu mo wcfizun con 00x00 wagusv mcofiumooH mouzu um mafia m> muHUHE:; m>wum~o0 .00 mam 0H N 0 3 m 1H 11% u “ . o i I. " .Tllltyaf. .w / . / v/ : .TIIIIII .IIIIIII E + 0" / V/ 0" m +/ /. , /+ Ill/Ir . L _ [IF : nH\£H moo. " EMU on + i m. 000 II, A ; ; _ 0 .fl . _ III/Ill 0 W - PI.“ ON 00 o0 00 NOOH 'Knipimnq 34139138 52 mg: 00 0 0 5 0 m a 0 N o 00 a. o: /.. __ _ m. 03 /_. m. cm //_. a: H moo. /“ / / HENU on fl+ IIIIIIII ON / / / . N00 '33 ‘nuanuoo alnaston 53 ab 0.00 moooH mooHH . o .00 300mg maouv umuww >woz cwza meg» 00 non wmxwm m 0 wadxuc weausv ucmanmuw musumwoe co muzumumasmu mo uumwum .00 000 54 O H 0. 0. 5. 0. 0. q. 0. N 0 TJ 11‘ q %1 4| 0 w J 0 _ “3.: moo. \+ \i\ 0 So on \K '4? NON '80 ‘Juanuoo alnnstou 54 oO\0MH.3OHUD map“? UWHHN >Q u: can; .musuwumemu uwm uchH mmusu um suamw m> wuauwuomeu :«muo .mH mam 0. 0. 5. 0. 0. 0. . m. N. H. o 0 m" 0V _ 0 A, m. m. nH\pH mac. _, Emu on 0 y/. / 0/ ”f/uT/u / : .. “n _ / luv/:1 f /V/ I .T/.. ././ 0 M v/..:- ./ M /./ l./: ./.7/ [.rur on O0 O5 00 om ooH OHH ‘alnneladman utels ado 55 . GOA“ 00 won waxwm a mo mama wazuv co zofiuuwm 00 uuowmm .00 000 (5 ‘0 Ln \1’ m N H O my: 00 0 0 00 ,E u . , u o. f nH\nH moo. ./ $5.0 on [III/IIWHWIIIII a. 000 i m a ewe ON a . . III/11+ w , lllllllr IIIIIII.IIIIILI ? /.r “W cm 7v- 0N _‘k ‘_ Non 'gq ‘afiezane nuaauoo axnnstow 56 um Emu oq Emu on 500 oN a . .xmfi sodas ago». a...“ > oz cans .mu.» mo can aaxflu a mo wcwmpv wcwusn acmwvmum musumHoE so 3oH0uHm mo uowmwm .5H me 0. 0. 5. 0. 0. c. m. N. H. o A H1 H‘ 1H H1 H HI m H w 0 0 w w n 0 W m m DH\DH moo. ” mo OOH « \NW 3 \.\ «mmmmmmmw\\\\\\\+ “ + .i\ m \\\\\\|HummM““v » + . wu““““\. \\\\\\\ ».mH - m»--m--» .\° 0 N '80 ‘3uanuoa alnastow 57 uhH 800 ON Emu om Emu oq w'v- .oumu onmuHm omusu um cummv m> unnuwuomsmu sauna .0H 0H0 0. 5. .umH aoHon amouv umuHu >woz case \0 0. q. n o No a: AH 000. m. 00H / - / / // /.// ///.. ./.. 00 00 00 00 oooH ‘91n3813dm83 utexg 0J0 GO 5 mum nH\nH moo. nH\nH NHo. nH\nH 0H0. .ouHu 00 won vmxHu a 00 oumu wcH5u0 co 5quwazs wusHOmnm mo uumwmm .mH mam 7 / A! / / F... on ma OCH *7 —' / // // ./, CM OH O N N00 '30 ‘aSeJaAe auaauoo aznnstow 59 .mcoHumooH mmucu um won cumwv onu um N m cH oumu wcquo .ON 0H0 mum OH 0 w 5 0 0 q 0 N H o 0 A M _ .. . ” £H\DH moo. _ 0 M Em. on u _ mo OOH E o 0 “Til/“w OH .0 /L/ m” _ 1 v M” /1f 0 llIIIIJTIIIIII. 0 0 0 0.0 H . _ A /L t _ _ /. / . 0 / “w _ v 0N AIIIIIII , M /.v A. um N IIIIIII T‘ IT! 1" IA .Nom 'gq ‘Juanuoo axonstou 60 .5ucmHonwm 0CH5H0 so nummv can mo.uomwwm .HN mHm .Nom -L‘h—‘- some. van on H 00 'v—v—v’ on —v— O0 05 o0 L T some. can an N H Flu? o0 ;ka‘~ «Jana-unkxoofi ‘Jte naIJno aqa go Antptmnq antnetau 61 .umn cflaum umN . a. .0. mo Nowe029: w>wuaflmm .NN w.m mum OH 0 0 0 0 .0 m N H o m .50 m 0, .cH 0. w 7 1‘th ON .cH NH ./ /.... A A n M /.: .. /.. / / o.» _" . /in #0 0 .5 0H M, M 40/ 2 L T _ A / / 00 0" /T 4/. 0.. _ _ M . .152 / ow : 0 M7 .1 . _ Lu/nT I'lL : H aAIJBIau ‘Kniptmn °/. 62 efficient. Since the relative humidity of the outlet air is higher, more water is removed from the grain. A number of observations can be made: (1) An increase in the drying air temperature, increases the drying rate of a rice bed (Figure 13). (2) The average moisture content decrease of a fixed bed of rice is constant for a certain period of time (Figure 13). (3) The bottom layer of a fixed bed of rice overdries at high inlet air temperature (Figure 13). (4) An increase in the airflow rate increases the drying rate (Figure 16). (5) At higher inlet air temperature (same airflow) or lower airflow (same temperature) the moisture gradient in the bed is higher (Figures 14 and 17). (6) Relative humidity of the outlet air increases and grain temperature decreases as the depth of bed increases (Figures 12, 21, and 22). (7) The drying rate decreases as inlet humidity increases (Figure 20). 63 (8) The effect of specific surface area on drying rate is small (Table 4). Figure 23 shows the grain temperature distribution within a fixed bed of rice after various drying periods. Figure 24 shows the temperature and relative humidity profile of the drying air in the grain bed. The rice temperature and moisture content distribution are shown in Figure 25. It would be difficult and time consuming to obtain data required to plot Figures 23 through 25 from physical experiments. A large number of tests would have to be conducted to obtain the necessary data. Simu- lation, on the other hand, furnishes this information rapidly and at little cost. Of course, simulation results can only be trusted if the mathematical models represent the physical system satisfactorily. ‘64 .«vofluma wcwxuc macaum> nouww mod» «0 can umxfim m awsuwz coflusnfluumwv quUmquEmu samuw .mm mam mum 0H m w n o m c m N 14, q .4 114 in a1 a J 1 com .aEwH cwmuw W So on s v .2: .959 5:. fix _ $9 2“. o : o! $ .é» r m 0 av)“ @ . Q1) 1 7 coo coda 65 .muso; o uwuum econ cflmuw a Ca uwm wcfixuv mo mmfluummoum .Gfl mam “HRH m. w. No Q. m. <0 m. N. H. o J a _ J H A . l. . _ )4 + + 1- Ewu 0m + x m 000." + 1 + 92 aw , é). ; 7)"? ‘T o . + 6%? _ o) w m?» M + sT . c : + ,r _ 3 . a. + T « _ : .. u + « 1 i 0 9% hauw « _ thEmu h i .1 wV , k. as x3 ow cm ".7 I. 1 cc 3 a m d a J on n n l 8 a“. 8 / v0 3 I E n In A 8 m om m In D. 7;. 1+ rA omml NOOH 66 Grain Moisture content, ‘7. D.B No 0H m ....4 Nmm um H _.L .uwn wcHauc mnu CH moHu mo moHuummoum .mm.me 1 mo 4+ Om +2 % om r mm _. om w mm do alnnaladman UIBJS 67 1 TABLE 4. EFFECT OF SPECIFIC SURFACE AREA Time 56:324 ft" Sa=400 ft-1 Hrs MC RH MC RH % % % % 0 28.0 82.3 28.0 82 3 1 26.4 72.1 26.4 72 3 2 24.6 53.8 24.6 53.9 3 22.8 42.5 22.8 42.5: 4 21.0 35.3 21.0 35.3 5 19.4 30.7 19.5 30.7 6 18.1 27.5 18.1 27.5 7 16.8 15.2 16.8 23.2 8 15.7 23.3 15.7 23.3 9 14.7 21.7 14.7 21 7 10 13.8 20.4 13.8 20 4 1Temperature: 100°F; bed depth: 1 ft; absolute humidity: .005 lb/lb. CONCLUSIONS The rice drying model used in this study is capable of predict- ing the performance of a fixed bed rice dryer. The accuracy of the re- sults obtained 15 questionable because of unverified input values for: l) the rice thin—layer equation, 2) the rice equilibrium moisture con- tent equation at relative humidity higher than 90 per cent, and 3) the physical and thermal properties of rice. Although the exact prediction for a fixed bed rice dryer by the modified MSU simulation model may at present not be possible, the pro- cedure is valid and a comparative performance study on parameter sen- sitivity can be made with confidence. It is to be emphasized that throughout this work, the methodology, not the numerical results, is of primary importance. The substantial saving in time and cost thus justifies the use of simulation in rice dryer design. 68 SUGGESTIONS FOR FURTHER STUDY In this study the two constants for the equilibrium moisture con- tent equation is evaluated as a function of relative humidity only. For better accuracy, an equation which incorporates both relative humidity and temperature should be developed. Better physical parameters for rice and a more accurate rice dry- ing equation should be developed. Other models such as the MSU concurrent flow and counterflow models should be applied to rice. Apply the newly developed USOLAR model (Bakker-Arkema and Roth 1975) to fixed bed rice drying simulation. The saving in com- puter time and core memory will be considerable. 69 BIBLIOGRAPHY Allen, J. R. (1960) Application of grain drying theory to the drying of maize and rice. Journal of Ag. Egr. Research 5(4)363. Bakker-Arkema, F. w.. J. R. Rosenau and w. H. Clifford (1969) Measure- ment of grain surface area and its effect on the heat and mass transfer rates in fixed and moving beds of Biological products. ASAE paper No. 69-356, also Trans. ASAE l4(5)864. Bakker-Arkema, F. N., L. E. Lerew, S. F. DeBoer and M. G. Roth (1974) Grain Dryer Simulation. Ag. Exp. Station, Michigan State Uni- versity Research Report No. 224. Biswas, D., F. T. Wratten and M. D. Faulkner (1969) Effect of high temperature and moisture for pre-conditioning rice for milling. Paper presented at Southwest Region ASAE Meeting. March 27, 1969. Brooker, D. B., F. w. Bakker-Arkema and C. N. 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Agr. ng. Serv. Report No. 467. Smith, H. D. and w. M. Hurst (1930) Artificial drying of rice on the farm. U.S. Dept. of Agriculture Cir. No. 292. Spencer, H. B. (1969) A mathematical simulation of grain drying. Journ. of Ag. Egr. Research 14(3)226. Strohman, R. D. and R. R. Yoerger (1967) A new equilibrium moisture content equation. Trans. ASAE 10(5)675. Thompson, T. L. (1968) Simulation for optimal dryer design. Trans. ASAE 13(6)844. 72 Thompson, T. L., R. M. Peart and G. H. Foster (1967) Mathematical simulation of corn drying. A new model. Trans. ASAE 11 (4)582. Wratten, F. T. and G. P. Bal (1973) High temperature and treatment effects on physical properties of rough rice. Paper pre- sented at Southwest Region ASAE Meeting, April 5, 1973. Wratten, F. T., J. L. Chesness and M. D. Faulkner (1969) An analyt- ical and experimental study of radiant heating of rice grain. ASAE paper no. 69-391, also Trans. ASAE l3(5)644. Wratten, F. T. and M. D. Faulkner (1966) A new system for rice dry- ing. Paper presented at Southwest Region ASAE Meeting, March 31, 1966. Wratten, F. T., w. 0. Poole, J. L. Chesness, S. Bal and V. Ramarao (1968) Physical and thermal properties of rough rice. Trans ASAE 12(6)801. Simulation of Batch Drying of Rice (Nguyen Din Chan, M.S. . L976 NSTRTE lllllllllIlllllllllllllllllllllllllllllllllllllllllllllllll