"\""‘“0IIIV'VIVI-ffi>" ,‘f'k'r ‘N 4‘; "fl iT-Z, "I?" \\';I., ~.‘ ("$1”) '.‘ h.) fin? “m- '\W~-u mm ,3..' ..\‘-I.|u’ " L 'LN. ‘ ‘_ ru"""1.$ . KN.“ ‘ t It. defin- 'L ‘ ..; \"’ V" 9»? P‘b WM JV n33%szs\-I1 #55353; .. Ag? 1"? “i:{ J‘ '15: 35mm} { ,-T.v .' . can. , . ffitmmn €9.41 ‘ L '. .:3 - < "1.1+ Jg ‘ m ‘45-; , \l ‘ ‘W'M‘rl "g ‘llllllllll lllllllllllllllllllil ’Wmmu... martian? ' téiemaan fitate ‘ Untfersity i ‘ ~09 0-." ‘ .THESI? This is to certify that the thesis entitled LOU/Urge Flow Loam/6 0f cog/u presented by oswy WAL nefa< be sot/24 has been accepted towards fulfillment of the requirements for M' 5’ degree in [3/3. 51;, //@%//W Major professor z/é/Zt 0-7639 MSU is an AI]? rrrrr ' v9 Action/Equal O ppppppppp ' ty Institution }V1ESI_J RETURNING MATERIALS: Place in book drop to LJBRARJES remove this checkout from .—3_.. your record. FINES_ will — » be charged if book is returned after the date stamped below. *- -.-h...‘ ' [AUG 153???§ COUNTERFLOW COOLING OF CORN BY Osny Waltrick de Souza A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Agricultural Engineering 1984 ABSTRACT COUNTERFLOW COOLING OF CORN BY Osny Waltrick de Souza Cooling of grain after drying is a necessary practice in the United States as‘well as in Brazil. Inadequate and non-uniform cooling is a frequent problem. Bleptimizing the cooling of grain, the overall energy efficiency of the dryer and the quality of the end-product are improved. A laboratory-scale counterflow cooling unit was em- ployed to cool corn at different conditions of grain temper- ature, grain and air flow rate, grain moisture content, and bed depth. The outlet grain temperature from the cooler was de- creased by: (l) decreasing the inlet grain temperature, (2) increasing the air flow rate, (3) increasing the inlet grain moisture content, (4) decreasing the air flow rate, (5) increasing the bed depth. The lack of adequate information about the cooling of grain requires further studies under typical United States and Brazilian conditions. Major Professor _/f§2é/é? - /v/£yéa4l ACKNOWLEDGMENTS The author wishes to acknowledge the encouragement and guidance of Dr. Fred W. Bakker-Arkema, his support and understanding throughout the deve10pment of this study. Appreciation is expressed to Dr. Roger G. Brook and Dr. Robert P. Ruppel for serving on the guidance committee. The financial support by Companhia Paranaense de Silos e Armazens--Copasa, Curiba, Parana, Brazil, was greatly appreciated. Special thanks goes to my family and friends, for their support. Special gratitude is expressed to my wife, Nilceia T. C. Souza, for her love, support and understanding. ii LIST TABLE OF CONTENTS OF TABLES O O O O O O O O O O O O O O O O O O O 0 LIST OF FIGURES O O O O O O O O O O O O O O O O O O 0 LIST I. II. III. OF SYMBOLS O O O O O O O O O O O O C O O O O O O INTRODUGION O O O O O O O O O O O O O O O O O I OBJEGIVES O O O O O O O O C O O O O O O O O O 0 LITERATURE REVIEW 0 O O O O O O O O O O O O O O 3.1 DOWN huh) 3.5 www o o a couch 3.9 Grain Production . . . . . . . . . . . . . Grain quality 0 O O O O O I O I O O Equilibrium Moisture Content . . . . Moisture Adsorption and Desorption of grain O O I O O O I O O O O O O O O O O 0 0 3.4.1 Hysteresis Effect . . . . . . . . . . Cooling Theory . . . . . . . . . . . . . . 3.5.1 Types of Coolers . . . . . . . . . . Grain Moisture Content Before Harvesting . Cooling Immediately Before Drying . . . . . Cooling Immediately After Drying . . . . 3.8.1 Tempering Between Drying and Cooling. 3.8.2 Dryeration . . . . . . . . . . . . . Cooling in Storage . . . . . . . . . . . . iii Page vi xii GNO‘ OS 10 11 17 17 18 24 26 29 31 IV. Page EXPERIMENTAL O O O O O O O O O O O O O O O O O O 3 3 4.1 COOling After DrYing O O O O 0 O O O O O O 33 4.1.1 C0019: O O O O O O O O O O O O O O O 34 4.1. 2 Grain I O O O O O O O O O O O O O O 34 4.1.3 Grain Flow Rate . . . . . . . . . . . 34 4.1.4 Temperatures O O O O O O O O O O O O 36 40105 Air Flow Rate 0 O O O O O O O O O O O 37 4.1.6 Moisture Content . . . . . . . . . . 37 4.2 Procedure I O O O O O O O O O O O O O O 39 4.3 Auxiliary Equations . . . . . . . . . . . . 40 4.3.1 Heat and Mass Transfer Equations . . 40 4.3.1.1 Latent heat of vaporization . 40 4.3.1.2 Specific heat - For the specific heat of the air . . . . . 41 - For the specific heat of the corn 0 O O O O O O O O 41 4.3.2 Airflow Rate Calculation 4.3.3 Moisture Removed . . . . 4.3.4 Beat Balance . . . . 4.3.5 Latent/Total Beat Ratio . 3 RESULTS AND DISCUSS ION O O O O O O O O O O O O O 46 5.1 Experiment 1 O O O O O I O O O O O O O O O 48 5.1.1 Comments on Experiment 1 . . . . . . 48 5.2 Experiment 2 O O O O O O O O O O O O O O O 57 5.2.1 Comments on Experiment 2 . . . . . . 58 5.3 Experiment 3 O I O O O O O O O O O O O O O 66 5.3.1 Comments on Experiment 3 . . . . . . 74 5.4 Experiment 4 O O O O O O O O O O O O O O O 75 5.4.1 Comments on Experiment 4 . . . . . . 83 S O 5 Exwr iment 5 O O O O O O O O O O O O 0 O O 84 5.5.1 Comments on Experiment 5 . . . . . . 92 iv 5.6 Experiment 6 5.6.1 Comments on Experiment 6 5.7 Comments on Experiments 1-6 . VI. VII. REFERENCES . CONCLUSIONS SUGGESTIONS FOR FURTHER STUDIES Page 94 94 106 110 112 113 Table 7A 10 11 LIST OF TABLES Average monthly dry bulb temperature (°C) and relative humidity (%) in four states of Southern Brazil during 1979 . . . . . . . . . . Production of cereal grain in the world, United States, and Brazil during the period of 1973 to 1982 C O O O O O O O O O O O C O O O C O O 0 Comparison of rate of moisture adsorption by grains initially at different moisture contents before being subjected to approximately the same pressure increases . . . . . . . . . . . . . . . Drying and rewetting of soft red winter wheat . Desorption and adsorption EMC (% w.b.) of shelled corn at 72°F . . . . . . . . . . . . . . Safe corn storage period (days) . . . . . . . . Effect of tempering rice followed by cooling by aeration upon the amount of moisture removed during the cooling and upon the milling Yield 0 O O O O O O 0 O I O O O O O O 0 Corn and air temperatures for drying at 100 cfm/bu, followed by 4 hours tempering, and cooling at 20 cfm/bu . . . . . . . . . . . . . . Table of experiments with experimental conditions 0 I O O I O O O O O I O O O O O O O O Inlet and outlet air conditions in experiment 1 in which the Ga/Gp ratio values are 0.18 , 0.19 , and 0.19 w.b., respectively, during the first, second and third pass of the corn through the dryer/cooler system . . . . . . . . . . . . Experimental bed temperature in the cooling bed and calculated outlet grain temperature in experiment 1 . . . . . . . . . . . . . . . . Air and grain inlet and outlet temperatures in experiment 1 O O O O O O O O I O O O O O O O O 0 vi Page 13 15 16 25 28 30 47 49 50 52 Table Page 12 Experimental grain moisture content and moisture removed (MR) per hour in experiment 1 . 53 13 Heat balance in experiment 1 with Ga/Gp ratios of 0.18 , 0.19 , and 0.19 respectively during the 1,2, and 3 hours Of operation . . . . . . . 54 14 Inlet and outlet air conditions in experiment 2 in which the Ga/Gp ratio values are 0.29, 0.19, and 0.18 w.b., respectively, during the three hours of operation . . . . . . . . . . . . 59 15 Experimental bed temperatures in the cooling bed and calculated outlet grain temperature in exmr 1ment 2 O O O O I O O O O O O O O O O O O O 60 16 Experimental air and grain inlet and outlet temperatures in experiment 2 . . . . . . . . . . 62 17 Experimental grain moisture content and moisture removed (MR) per hour in experiment 2 . 63 18 Beat balance in experiment 2 with GA/Gp ratios Of 0.29, 0.19, and 0.18, respectively during the l, 2, and 3 hours Of Operation . . . . . . . 64 19 Inlet and outlet air conditions in experiment 3 in which the Ga/Gp ratio values are 0.67, 0.45, and 0.41 w.b., respectively, during the three hours Of Operation . . . . . . . . . . 67 20 Experimental bed temperature in the cooling bed and calculated outlet grain temperature in experiment 3 . . . . . . . . . . . . . . . . 68 21 Experimental air and grain inlet and outlet temperatures in experiment 3 . . . . . . . . . . 70 22 Experimental grain moisture content and moisture removed (MR) per hour in experiment 3 . 71 23 Heat balance in experiment 3 with Ga/Gp ratios of 0.67, 0.45, and 0.41, respectively during the 1, 2, and 3 hours Of Operation . . . . . . . . . 72 24 Inlet and outlet air conditions in experi- ment 4 in which the Ga/Gp ratio value is 0.25 w.bO I O I O O O O O O O O O O O I O O O O 76 25 Experimental bed temperature in the cooling bed and calculated outlet grain temperature in experiment 4 . . . . . . . . . . . . . . . . 77 vii Table Page 26 Experimental air and grain inlet and outlet temperatures in experiment 4 . . . . . . . . . . 79 27 Temperature at the same level (4.7 inches (12.0 cm)) from tOp Of the cooler in experi- ment 4 I I I I I I I I I I I I I I I I I I I I I 80 28 Experimental grain moisture content and moisture removed (MR) per hour in experiment 4 . 81 29 Heat balance in experiment 4 with a (Ga/Gp) wet ratio of 0.25, during the 2-hour cooling Operation . . . . . . . . . . . . . . . . . . . 82 30 Inlet and outlet air conditions in experi- ment 5 in which the Ga/Gp ratio value is OI43 WIbI I I I I I I I I I I I I I I I I I I I 85 31 Experimental bed temperature in the cooling bed and calculated outlet grain temperature in experiment 5 I I I I I I I I I I I I I I I I I I 86 32 Experimental air and grain inlet and outlet temperature in experiment 5 . . . . . . . . . . 88 33 Temperature at the same level (4.7 inches (12.0 cm)) from top Of the cooler in experi- ment 5 I I I I I I I I I I I I I I I I I I I I I 89 34 Experimental grain moisture content and moisture removed per hour in experiment 5 . . . 90 35 Heat balance in experiment 5 with a Ga/Gp ratio value of 0.43 w.b., during the 2-hour cooling operation I I I I I I I I I I I I I I I I I I I 91 36 Inlet and outlet air conditions in experi- ment 6 in which the Ga/Gp ratio value is 0I34 WIbI I I I I I I I I I I I I I I I I I I I 95 37 Experimental bed temperature in the cooling bed and calculated outlet grain temperature in experiment 6 I I I I I I I I I I I I I I I I 96 38 . Experimental air and grain inlet and outlet temperatures in experiment 6 . . . . . . . . . . 99 39 Moisture content changes during the cooling process in experiment 6 with a Ga/Gp ratio of 0I34 WIbI I I I I I I I I I I I I I I I I I I I 100 viii Table 40 41 42 Page Experimental grain moisture content and moisture removed (M.R.) per hour in experiment 6 . . . . 102 Heat balance in experiment 6 with a Ga/Gp ratio value Of 0I34 WIbI I I I I I I I I I I I I I I I 103 Major results of tests 1-6 . . . . . . . . . . . 107 ix Figure 01:th 6A 10 11 12 13 14 15 LIST OF FIGURES Concurrent flow grain cooling system Counter flow grain cooling system . . . . . Cross flow grain cooling system . . . . . . Mixing flow grain cooling system . . . . . . Block diagram of concurrent flow dryer with counter flow cooler . . . . . . . . . . . . Schematic of the pilot-scale concurrent flow dryer and counter flow cooler showing the thermocouple locations (dots). . . . . . . . Thermocouple positions at the 4.7 inch (12.0 cm) level from the inlet of the cooler Temperature profile in the cooling bed during cooling in experiment 1 . . . . . . . . . . Latent/total heat ratio vs time during cooling in experiment 1 . . . . . . . . . . . . . . Temperature profile in the cooling bed during cooling in experiment 2 . . . . . . . . . . Latent/total heat ratio vs time during cooling in experiment 2 . . . . . . . . . . . . . . Temperature profile in the cooling bed during cooling in experiment 3 . . . . . . . . . . Latent/total heat ratio vs time during cooling in experiment 3 . . . . . . . . . . . . . . Temperature profile in the cooling bed during cooling in experiment 4 . . . . . . . . . . Temperature profile in the cooling bed during cooling in experiment 5 . . . . . . . . . . Temperature profile in the cooling bed during cooling in experiment 6 . . . . . . . . . . X Page 19 19 19 19 35 38 38 51 55 61 65 69 73 78 87 98 Figure 16 17 Grain moisture content and temperature profiles during a specific cooling period in experiment 6 I I I I I I I I I I I I I I I I 101 Latent/total heat ratio vs time during cooling in experiment 6 I I I I I I I I I I I I I I I I 104 xi MF MO MR MRp SP 0) LIST OF SYMBOLS Bed depth, ft. Specific heat of the air, BTU/1b°F. Specific heat of the product, BTU/lb°P. Air flow rate, lb/h ft2. Grain flow rate, lb/h ft2. Latent heat of vaporization, BTU/1b. Average moisture content, decimal dry basis. Moisture content, percent dry basis or otherwise specified. Final moisture content, percent dry basis or other- wise specified. Initial moisture content, percent dry basis or otherwise specified. Moisture removed, lb/h. Moisture removed from or to the air, lb/h. Moisture removed from or to the product, lb/h. Relative humidity, percent. Static pressure due to airflow inches of water. Cooling air temperature, °F or otherwise specified. Humidity ratio, lb water/lb dry air. Grain temperature, °F or otherwise specified. Density of the air, 1b/ft3. xii CHAPTER 1 INTRODUCTION Providing an adequate food reserve is possible in two ways. The first one is through production, in which a lot of effort is made in a short period of time (3-5 months in the case of grain). The second is through conservation, which can take a few days or years. Each time the grain storage period increases, the more complex it becomes to manage a storage facility and maintain quantity and quality of the stored-grain. There are major problems when dealing with grain stor- age: moisture content, insects and mold. In order to solve moisture content problems, the cheapest way is drying. When drying, the grain is usually heated to increase the water vapor pressure in the grain to facilitate moisture removal. Cooling is required after drying, because high temperatures can cause deterioration during the storage period. When cooling takes place in a drying process, many factors are important. This process can cause serious dam- age to the grain kernels. Fissuring and breakage can occur as well as rewetting of the kernels. The main purpose is to take the water out of the grain during the drying and cooling stages. Depending on the 2 climatic and grain conditions, the grain can lose or gain water during the cooling period. To improve the overall energy efficiency of the drying process, it is recommended that some drying be carried out during the cooling process. Many efforts have been con- ducted to overcome unfavorable climatic conditions; addi- tional studies are necessary'to supply necessary informa- tion. Cooling is an Operation necessary to maintain grain quality, and to improve drying efficiency. It is not only used after drying, but also during the storage period in order to protect grain against insects, mold, and deteriora- tion. Another use for cooling is before the grain.is dried. Grain can be kept at a high moisture content for a short period of time when properly ventilated, even when the climatic conditions are unfavorable. To deal with high moisture content grain, insects, and molds is not an easy task, especially not in Southern Brazil where the climatic conditions are unfavorable for grain storage. As shown in Table 1, grain in Brazil is harvested during hot and humid seasons. This requires special care in the control of the grain moisture content, the insects, and the mold growth. Cooling plays a very important role also in Brazil, because cooling helps to improve the quality of the harvested crOp. Countries, like Brazil, which are increasing agricul- tural production very fast, need not only to develop their Table‘h. Average monthly dry bulb temperature (°C) and relative humidity (i) in four states of Southern Brazil during 1979. States Sao Paulo Parana S. Catarina R.G. Sul. Months T (°C) 88(1) T (°C) 88(1) T (°C) RH(S) T (°C) RH(%) January 12.4 80 17.8 81 22.9 75 23.2 63 february' 24.0 80 20.3 79 24.7 79 24.4 73 March. 20.4 77 18.1 82 22.4 81 21.6 75 Hpril' 18.7 79 16.2 82 20.6 81 18.6 81 May. 17.9 76 14.1 80 17.2 80 14.9 79 June 15.6 75 12.0 80 14.4 83 12.4 80 E July 15.0 73 11.7 78 15.0 82 13.5 78 f $ugust 18.0 79 15.1 80 17.8 84 16.2 83 S September. 17.2 81 14.2 84 17.3 81 15.8 74 1 October. ‘ 20.4 79 17.5 82 20.6 84 19.1 82 i ovember' 19.9 81 17.1 81 21.0 80 20.4 71 ecember 21.7 83 19.6 82 23.7 79 22.9 75 kverages 18.4 79 16.1 81 19.8 81 18.6 75 ' Harvest season in Southern Brazil. Note: Meteorological observations were taken at the capital city of each state. 4 production technology, but also to improve their conserva- tion techniques. This involves training of personnel and development of appropriate physical facilities. To be successful in a modern grain storage operation, it is important to employ up-to-date technology over the total storage period. CHAPTER 2 OBJECTIVES The main purpose of this research is to analyze the counterflow cooling of shelled corn after the drying pro- cess. The specific objectives are: (1) To collect data on the cooling rate of shelled corn in a pilot-scale counterflow cooler. (2) To measure the effects of inlet air temperature and the inlet grain temperature on the cooling rate of the grain. (3) To measure the moisture content change (adsorption or desorption) of the grain during the cooling process. (4) To measure the effects of grain flow rate and air flow rate on grain cooling. (5) To measure the effects of bed depth changes on the grain cooling process. CHAPTER 3 LITERATURE REVIEW 3.1 EBAIN_RBQDQQIIQE Wheat is the most produced grain crop in the world, followed by rice. Corn is the leading grain crOp in the United States; Brazil is the largest producer of coffee in the world (FAG, 1978-1982). Grains are the major source of food for humans and for animals. The above cited grains are important as well as barley, oats, rye, sorghum and soy- beans. Grain production has increased rapidly, largely as a result of new varieties, fertilizers, and weed and insect control measures. The increase in production, as shown in Table 2, necessitates continued emphasis on postharvest operations in order to economically preserve the crop pro- duced. Grain production is periodic, while the need for food occurs throughout the year. So storage is a necessity to ensure proper distribution and a stable price to the con- sumer. This can be accomplished by establishing a network of storage facilities, adequately distributed over the pro- duction and consumption areas. Such facilities should be equipped with drying, cleaning, handling, and cooling Table 2. Production of cereal grain* in the World, United States, and Brazil during the period of 1973 to 1982. P ODUCTION,(1.000.0 0 MT) Year World United States Brazil 1973 ‘ 1,377.1 237.6 ‘ 23.6 1974 1,334.9 204.4 27.3 1975 1,359.2 249.1 26.2 1976 1,479.9 258.1 31.2 1977 1,471.0 265.8 30.9 1978 1,601.9 276.5 24.0 1979 1,553.9 302.9 27.2 1980 1,565.0 269.6 _ 33.2 1981 1,653.4 333.5 ‘ 32.1 1982 1,695.1 338.9 34.0 Sources: -United States Department of Agriculture (1983) —Food and Agriculture Organization (1978-1982) -Anuario Estatistico do Brasil (1980) MT = metric ton. * Includes corn, rice, oats, barley, rye, and sorghum. 8 equipment to ensure the quality of grain during the storage period. 3-2 GRAIN_QQALIIX Grains are classified in different grades according to visual and physiological criteria. Grain moisture content and percentage of foreign materials are among the criteria largely used in U.S. grain standards. Germination capabili- ty is used in the seed market. In Brazil, test weight is one of the major criteria in the wheat market. The visual condition refers to the external appearance of a kernel such as a crack in the seed coat, a broken kernel, or separated cotyledones. Many factors can affect the quality of grains such as: climatic conditions in the field, harvesting, handling, drying, cooling, storage and milling. In a processing plant, all previous operations are important because the damage will appear at the end of the process as a summation of the damage that occurred in each step. Drying is one of the most important steps in a process- ing plant, not only because it can cause serious damage to the grains, but also because it is one of the most expensive operations in the grain processing system. Since heated air drying is the usual procedure, cooling will be necessary. Damage occurs when the hot grain kernels are suddenly cooled. Fissuring during cooling is directly related to the moisture and temperature gradients between the grain and the air. 9 Henderson (1954) studied short grain rice and concluded that fissuring during fast drying was due to an increase in temperature rather than a decrease in moisture in portions near the surface of the kernel. It was found that fissuring was also caused by a rapid increase in moisture which occurs in the field if dew accumulates on the kernels. Kunze (1965) reported that cracking occurred when brown rice, equilibrated at a particular humidity, was subjected to a high moisture environment. The degree of cracking is dependent on the magnitude of the change in relative humidi- ty. Kunze hypothesized that adsorptive fissures are caused when external cells expand by adsorbing moisture, producing compressive stress in the surface layers. Wasserman (1972) concluded that when high moisture content air is used in a fixed bed dryer, rewetting of some of the grain occurs causing serious quality deterioration. Wasserman made the following recommendations to overcome the problem of rewetting: (1) use supplemental heat when the relative humidity is above 75% for a prolonged period, and (2) provide enough energy to raise the air temperature about 12.001:- (6.7°C). Normally, damage caused to grain kernels during drying and cooling is not measured separately. Therefore, it is hard to distinguish which damage to attribute to drying and which to cooling. Further studies are necessary in the cooling stage, in order to determine the cause of the damage to the grain kernels. 10 In Brazil, broken kernels and separated cotyledones are considered damaged kernels and cannot be more than 1.0 percent when summed with foreign materials. Fissuring is not considered damage in the Brazilian grain market, except in the case of rice. Germination capability is also used in the seed market only. 3.3 EQUILIBRIUH_HQISIHBE_QQNIENI The equilibrium moisture content (EMC) refers to the quantity of moisture in the product when it is in equilib- rium with the surrounding environment, usually air. The EMC of grain depends on the air temperature and humidity, the grain variety, the maturity and the previous history. In addition, the EMC will depend on whether or not the grain adsorbed or desorbed moisture to achieve equilibrium. The EMC achieved by desorption is higher than that achieved by adsorption. This phenomenon is referred to as the “hystere- sis effect.‘ The relative humidity of the air surrounding the grain in equilibrium with its environment is called the equilibrium relative humidity. Several EMC equations are available for grains. Some are specific for grains while others can predict the EMC for different agricultural products, by varying one or more coefficients in the equations. Variations in the EMC values reported for one product at the same relative humidity and temperature are common. Some of the causes responsible for the variation are: ll (1) a difference in moisture equilibrium determination: (2) an experimental error in the EMC determination, result- ing from difficulties in maintaining and measuring the relative humidity and temperature while a sample equi- librates; (3) inaccurate measurement of the moisture content and relative humidity: and (4) the grains are of different varieties and have differ— ent histories. One of the best known relationships for predicting the EMC of grains is the semi-empirical model prOposed by Henderson (1952): 1 - (Pv/va) = Exp (-hTab8Mi) (1) where M is the moisture equilibrium content (%dde and h and i are product constants: Pv andPvs are vapor pressure of the surrounding air and vapor pressure at the saturation point, respectively; Tabs is the absolute temperature. Other EMC equations can be found in the literature (Brooker et al., 1974). 3-4 MQIEIflBE_ADEQB2IIQH_AND_D§§QBRIIQN;QE_§BAIH Grain is a living organism. It is hygrosc0pic and adsorbs or desorbs moisture as the temperature and humidity conditions change. Many studies have been conducted on the drying (desorption of moisture) of grain, but only a second- ary interest has been shown in the wetting process (adsorption of moisture). 12 Moisture adsorption and desorption by grain kernels has been reported to cause cracking and fissuring damage to the grains (Kunze and Hall, 1967): no quantitative data was reported by these authors on the amount and rate of adsorp- tion or desorption, which is necessary to produce damaged grains. However, it is known that the damage starts at the surface and can reach the center if the variations in tem— perature and moisture are great and take enough time. Kunze and Hall (1967) studied moisture adsorption char- acteristics of brown rice. The highest adsorption rate occurred immediately after the grains were exposed to the more humid atmosphere. Fissuring did not start until after the period of peak adsorption, thus indicating that there was a lag between the highest rate of moisture adsorption and grain damage. It was also observed by the authors that the grains with the higher moisture content adsorbed mois- ture much faster than those with the low moisture content. The results are shown in Table 3. Literature on grain drying has long indicated that moisture removal from low moisture grain is more difficult than from a high moisture grain (Kunze and Hall, 1967). Free water vapor in the atmosphere experiences a similar difficulty in being absorbed by dry grain. Thus, higher moisture-content grain will adsorb moisture more readily than will dry grain subjected to the same vapor pressure change at the same temperature (Kunze and Hall; 1967). l3 Table 3. Comparison of rate of moisture adsorption by brown rice ini- tially at different moisture contents before being subjected to approximately the same vapor pressure increases. H20 Initial Final adsorbed RH Initial RH VP in 23 h. Variety Percent EMC (db) Percent (PSI) grams Ratio. . 38°F ortuna 59.6 15.2 86.7 0.030 0.0388 10.5 to 1 [ortuna 11.2 9.4 34.8 0.027 0.0037 Century 59.6 15.2 86.7 0.030 0.0324 11.6 to 1 Century 11.2 9.4 34.8 0.027 0.0028 ortuna 59.6 15.2 100.0 0.045 0.0552 3.7 to 1 ortuna 11.2 9.4 59.6 0.055 0.0149 entury 59.6 15.2 100.0 0.045 0.0506 4.3 to 1 entury 11.2 9.4 59.6 0.055 0.0118 . 68°F ortuna I 54.9 13.9 86.6 0.107 0.0682 9.2 to 1 ortuna 11.2 7.8 33.6 0.077 0.0074 Century 54.9 13.9 86.6 0.107 0.0522 9.3 to 1 Century 11.2 7.8 33.6 0.077 0.0056 ortuna 54.9 13.9 100.0 0.151 0.1230 4.3 to 1 ortuna 11.2 7.8 54.9 0.150 0.0286 entury 54.9 13.9 100.0 0.151 0.0971 4.9 to 1 entury 11.2 7.8 54.9 0.150 0.0198 Source: Kunze and Hall (1967). Grain moisture (db) x 10"3 Grain moisture (db) - humidity ratio ' Ratio = 14 Fortes et a1. (1981) studied drying and rewetting (de- sorption and adsorption) of soft red winter wheat. The wheat was hand harvested from the very early stages of maturity (84 percent moisture content, dd») until the wheat moisture content had decreased to about 30 percent. Drying tests were performed on the day of harvesting. The condi- tions in which this experiment was conducted are shown in Table 4. Drying refers to desorption conditions and rewet— ting refers to adsorption conditions. Table 5 shows the difference between the desorption and adsorption isotherms for corn at 72.0°F (22.2°C). A number of theories have been advanced to explain the hysteresis effect in grains. The 'ink bottle“ theory is probably the best-known (Brooker et al., 1981). 3.4-1 Hrsteresis.fiffect Chung and Pfost (1967) conducted a series of tests of adsorption and desorption of water vapor at 122.0°F (50.0°C) using freshly harvested wheat. After three cycles of ad- sorption and desorption, the hysteresis loop disappeared. This phenomenon was explained by the concepts of shrinkage and crack formation. Cracks might be increased only during the first three adsorption-desorption cycles. Consequently, the availability of sorptive sites inside the grain kernels is changed only during these cycles and not subsequently. 15 Table 4. Drying and rewetting conditions of soft red winter wheat. M.C. at Air Harvest Dry Bulb Relative Harvest Velocity Date Temp. (°C) Humidity (8) (decimal, db) (m/s) .DRXING_EX@EBIMENTS 59 June 47.0 33.8 0.864 1.50 1 July 47.0 33.8 0.667 1.50 5 July 47.0 33.8 0.341 1.50 6 July 47.0 33.8 0.292 1.50 7 July 67.5 13.3 0.256 1.61 7 July 47.0 33.8 0.211 1.50 7 July 47.0 33.8 0.200 1.50 7 July 26.7 41.2 0.211 1.40 7 July 87.0 5.6 0.211 1.71 Wmnsms --- 26.1 96.2 0.120 1.40 --- 26.1 91.3 0.123 1.40 --- 37.8 84.8 0.125 1.50 Source: Egrtgs et a1. (1981). 16 Table 5. Desorption and adsor tion EMC (% WJL) of shelled corn at 72.0°F (22.2 C). LB (%) Desorption Adsorption 88.5 24.2 23.4 67.6 16.5 15.2 46.5 12.9 11.5 125.8 9.8 8.0 9.4 7.0 5.6 Source: Chung and Pfost (1967). 17 3.5 CQQLIH§_IHEQEX The cooling of a moist material involves the simul- taneous processes of heat and mass transfer. During the cooling of grain, air is used to carry heat from the grains and sometimes moisture. Heat, which comes with grain, is used to evaporate moisture from the kernels: moisture trans- fer of water occurs within the kernels and on the grain surfaces. Grain and air conditions are the driving forces of the cooling process: relative temperatures and moisture contents determine the direction of the heat and moisture flow. 3-5-1 W Basically, grains are cooled inside closed compart- ments. Sometimes open space, as on a floor, can be safely used when the amount of grain to be cooled is small. In most cases, a cooler can be defined as an extension of the dryer. A cooler can be a silo, a bin, a portion of the dryer, or another compartment adapted for this function. A grain mass can be cooled in three ways: (1) moving the grains through the air; (2) moving the air through the grains: and (3) moving both the air and the grains. Based on the relative direction of the air and the grain, coolers can be classified in four categories: 18 (1) concurrent flow: (2) counterflow: (3) crossflow; and (4) mixed flow. These types of coolers are called continuous flow and are commonly used after drying, because they are attached to the dryer, forming a single processing unit. The four types of coolers are illustrated in Figures 1, 2, 3, and 4. The air flow/grain flow (Ga/Gp) ratio is one way to evaluate cooler efficiency. For example, a commercial crossflow dryer has a Ga/Gp ratio in the cooler of about 2.5 in order in removing 5.0 percentage points of moisture from corn (e.g., from 20-15 percent) (Bakker-Arkema et al., 1979). However, a commercial concurrent flow dryer, has a Ga/Gp ratio of about 0.4 for the same grain conditions (Bakker-Arkema, 1984). In Brazil, cascade dryers are the most widely used with two-thirds of a typical unit used for the drying section and one-third for cooling section. The Ga/Gp ratio in the cooler of such dryers is about 0.6 for the same conditions above cited. 3.6 GBAIN_MQI5IHBE_QQUIENI_BEEQBE_EAB¥ESIING Even in the field, where weather is the primary influ- ence on the plants, grain kernels are subjected to stresses, which may cause formation of small fissures. 19 Exhaust ( 7' Grain )7 Counter flow grain Figure 1. Concurrent flow grain Figure 2. cooling system. cooling system. we: Grain In / JA' 10101 2.. .rAirOuflet A A M -1 G M EAJ'NE‘IWE .a-Ouflet a-Wi' a ., 1,52; am”. ‘3' 0071.7 Dry Grain Out Figure 3. Cross flow grain Figure 4. Mixing flow grain cooling system. cooling system. 20 Climatic conditions cannot be managed. However, there are some growth factors which can be managed such as: seed- time, length of growing period, and harvest time. From the drying and storage point of view, all the above cited factors are important, because in one way or another they will affect the subsequent operations. For example, harvest time is closely related to moisture content of grains, which may vary greatly from plant to plant, and sometimes on one plant. Chau and Kunze (1982) studied medium grain rice in the field and concluded that the range in moisture content of grains in mature panicles was less than 10 percent (w.b.) when the average field moisture control of the rice was 22 percent. A variation up to 46 percent moisture content was observed among grains in immature panicles. Variation among grain kernels has several reasons. The top of a plant matures faster than the bottom. Also, draught conditions after seeding causes some seeds to remain dormant until it rains. And thus, plants will germinate at different times, resulting in different maturation time and different moisture contents during the harvesting period. There are other sources of non-uniform maturation such as: fertilizer distribution, weeds, tapography, soil, quality of seed, etc. (Brooker et al., 1974). When the harvesting operation is delayed and the mois- ture in the air increases to a level whereby the grain is rewetted, serious damage may result to the grain. 21 3.7 QQQLIflGiIHMEQIATELX_BEEQBE_DBXIHQ Between harvesting and storage drying is required to prepare the crop for safe storage. Frequently the drying capacity is lower than the harvesting capacity. Drying of grain can be done 24 hours a day. However, harvesting of the same crOp is possible in 12 hours or less per day. On some days, it is impossible to harvest because of the weather and other factors that affect the Operation. So, it is a common procedure to have a certain amount of wet grain waiting to be dried. If the waiting exceeds 24 hours, cooling should take place in order to maintain the grain free of insects and molds, and to maintain the temperature at an acceptable level to prevent deterioration due to the respiration process. This cooling/drying process is often called aeration. Cooling of wet grain does not only keep the grain temperature at an acceptable level and prevent insect and mold development, but also helps the subsequent operations. During the cooling period, the moisture from one grain kernel will ndgrate to another through the air, which will result in equalization of the moisture content among the kernels. At the same time, the average grain moisture content decreases or increases slightly, depending upon the air and grain conditions. Grain with a moisture content above an average of 18 percent usually loses moisture during cooling. Converse et a1. (1973) studied cooling of high moisture corn in Kansas 22 and concluded that storage conditions for the first few days are critical with regard to mold invasion. Delays in cool- ing increased mold invasion and the amount of deterioration in quality; Cooling as an adjunct to drying, to maintain quality during short-term storage, had to be started im- mediately after harvest. Thompson (1972) studied the drying/cooling of high moisture shelled corn using ambient air. He concluded that under certain conditions the amount of grain deterioration is: (1) doubled each time the airflow'rate is halved, in the range of 0.5 to 2.0 cfm per bu (0.5 to 1.9 mom/ton): (2) halved for each 15 days delay in date of harvest: (3) doubled for each 2 percent increase in moisture con- tent, in the range of 20 to 25 percent: ' (4) dependent upon the grain temperature and date of harvest. Hodges et a1. (1971) stored moist shelled corn in a bin at 35.0-40.0°F (1.6-4.4°C) for periods of 2, 4, and 8 days. To prevent mold growth, corn with 26 to 28 percent moisture content and an initial temperature of 70.0-90.0°F (21.0- 32.0°C) should be cooled within 2 days. Biological activity was low for corn at 20 percent moisture content. High temperatures permitted rapid growth of mil“: films, whereas extensive growth of Pgnigillinm an occurred in corn held at 25-28 percent moisture content. 23 Calderwood (1966) conducted research using aeration to aid heated-air drying of rice» A series Of aeration tests using small-sized bins showed a wide variation in the time rice could be maintained at its initial grade. The moisture content, ambient temperature, and airflow rate each affected the safe storage time. The use Of aeration for additional drying, by cooling rice after one pass through the drier, reduced the dryer operating time. The heat absorbed by the rice was utilized more efficiently for drying when it was dissipated by1aeration than when it was retained for pre- heating of rice for the next dryer pass. Souza (1978) conducted research in cooling of wheat while holding the crop in a silo before drying. He con- cluded that wheat initially at 14-22 percent moisture con- tent, reached an overall average moisture content about 17J) ;t]u0 percent after 22 hours Of aeration using natural air (58.0 percent average relative humidity and 71.6°F (22.0°C) average temperature), 1.0 percent less than initially. The grain temperature sometimes fell as low as 10.0°F (5.5°C) below ambient, maintaining the grain cool enough to protect it from spoilage during aeration period.‘ Cooling with natural air before drying can remove some water from the grain, equalize moisture content and reduce the temperature to levels below the ambient, because heat of vaporization takes place. SO, it is a recommended procedure since it will aid the subsequent Operations and will improve 24 the final quality of the grain. Table 6 shows the safe corn storage period, relating moisture content and temperature. 3.8 CQQLIHG_IMHEDIAIELX_AEIEB_DBXIN§ Storage Of grain is possible for short or long periods, given certain conditions. One of the main factors affecting the grain during storage is the moisture content, which can be reduced to acceptable levels by drying the product. This can be accomplished with unheated air or with heated air. When natural unheated air is used, it is readyfor safe storage as soon as the grain reaches the desirable level of moisture content. When heat is used to raise the tempera- ture of the inlet air, subsequent cooling must take place, because the grain cannot be safely stored at high tempera- ture levels. High temperatures can cause deterioration of the agricultural crOp in a short period of time by respira- tion, insects, molds, etc. Thus, cooling plays a crucial role in many grain production systems. Cooling after drying is usually assumed to remove some water from the grain, helping the drying process. (Common values in the literature are between 0.5 to 1.0 percent of moisture (Brooker et al., 1974). In order to have any removal of water from the grain, the inlet air conditions should be favorable. The Opposite will happen and the grain will absorb water, if the air conditions are not favorable. Absorption followed by desorption during cooling may cause fissuring and cracking of the grain kernels. 25 Table 6. Safe corn storage periods (days). torage air 0 Percent corn moisture content (w.b.) emperature, C 15 20 25 30 23.9 116.0 12.1 4.3 2.6 21.1 155.0 16.1 5.8 3.5 18.3 207.0 21.5 7.8 4.6 15.6 259.0 27.0 9.6 5.8 12.8 337.0 35.0 12.5 7.5 10.0 466.0 48.0 17.0 10.0 7.2 725.0 75.0 27.0 16.0 4.4 906.0 94.0 34.0 20.0 1.7 1,140.0 118.0 42.0 25.0 Source: U.S.D.A. (1968). 26 Sabbah et al‘. (1972) studied cooling of shelled corn after drying. As the cooling air passed through the hot grain, heat was transferred from the grain to the air in two forms, as sensible heat and as latent heat. .As the air flow rate increased, cooling attributed to moisture removal de- creased. The air flow rate reached a level where the addi- tional amount of moisture removed became insignificant: beyond that level, cooling occurred as a result of sensible heat transfer only. 3.8.1 WW3 Tempering of grain is a practice used between drying and cooling and between passes during drying. Tempering is practiced to improve the energy,efficiency of the grain drying process and to Obtain a dried product of better quality. Gustafson et a1. (1983) studied the effect of tempering of corn before cooling on the breakage suscepti- bility'and moisture removal rate during cooling, and con- cluded that short-term tempering reduces the breakage sus- ceptibility of grain. In addition, tempering causes more water to be removed during cooling, thereby improving the efficiency of the drying process. In a thin layer of corn, the breakage susceptibility decreased by 67 percent after 15 minutes of tempering and by 96 percent after 30 minutes. Approximately 50 percent of the improvement in moisture content removal occurred in the first 15 minutes Of temper- ing and 70 percent during the first 30 minutes. 27 Steffe et al. (1979) studied the effects of tempering between dryer passes in rice, and concluded that tempering between dryer passes aids in removing moisture and maintain- ing head yield. In drying high-moisture rice (31.1 percent d.b.) at 100.0017 (38.0°C) by 3.0 to 4.5 percent per pass during a 20-minute drying period, a 35-minute tempering time is sufficient. For a 35-minute drying period at 122.0°F (50.0°C), a 20-minute tempering time is satisfactory and shorter times may be adequate. The prevailing environmental conditions were 79.0°F (26.0°C) and 31 percent relative humidity. Calderwood and webb (1971) studied the effects of tem- pering on rice. They concluded that tempering rice for periods up to 12 hours at a high temperature (Table 7) following drying did not significantly change the amount Of moisture removed during a subsequent cooling cycle. The duration of the tempering period appeared to have no effect on the milling yield. Drying treatments, during which rice attained a maximum temperature of 122.0°F (50.0°C), appeared to have no adverse effects on the cooking quality. Table 7 shows the results of this research. Sabbah (1971) studied the drying of corn at 100 cfm/bu followed by 4 hours of tempering, and cooling at 20 cfm/bu. He concluded that tempering increases the moisture removed during the cooling process. As the inlet cooler grain temperature increased, the grain1was cooled faster due to 28 Table 7. Effect of tempering rice followed by cooling by aeration upon the amount of moisture removed during the cooling and upon the milling yield. Rice tempera— Heisture ture leaving removed Milling yield dryer (°C) during Tempering cooling control treated change Variety time h Ave. Max. 1 w.b. S 1 I Belle 0 83.9 88.8 1.0 52.6 88.7 -3.9 (Patna 0 45.6 48.3 1.2 50.6 88.9 -1.7 6 43.9 44.4 1.1 51.5 47.3 -4.2 6 - 46.1 47.2 0.5 49.4 49.2 -0.2 12 43.9 44.4 1.3 48.5 48.2 -0.3 12 45.6 47.2 0.8 49.7 46.0 -3.7 hate 0 45.0 85.6 1.0 66.8 67.1 +0.7 0 43.9 45.0 1.4 66.4 65.5 -0.9 6 43.9 46.1 1.2 65.4 64.0 -1.4 6 43.9 45.0 0.8 67.2 64.6 -2.6 12 43.9 44.4 1.4 65.3 64.0 -1.3 TP49 0 45.0 45.0 1.0 65.0 61.9 -3.1 0 41.1 43.9 1.4 62.4 62.1 -0.3 6 44.4 46.1 1.3 64.3 62.0 -2.3 6 41.1 43.3 1.2 62.5 64.5 +2.0 12 44.4 45.6 1.0 64.1 60.2 -3.9 12 42.2 43.9 1.1 63.0 63.2 +0.2 Source: Calderwood and Hebb (1971). 29 the increased mass transfer during the cooling process after tempering. The results are shown in Table 7A. 3.8.1.1 Dryeration Foster (1964) developed a new method of grain drying known as dryeration, which consists of three stages. Dryer- ation was developed to improve the quality of dried grain. The three stages are: (a) rapid drying with heated air to a moisture level two to three percentage points higher than the desired final moisture level: (b) tempering without air flow for a prescribed length of time, and; (c) cooling the grain slowly at a low air flow rate to remove the final two to three percentage points of moisture utilizing the heat in the grain. A field study by Thompson and Foster (1967) on dryera- tion of shelled corn showed that the amount of moisture removed during cooling increased as the tempering time in- creased. Under one set of drying conditions using heated air [187.0°F (86.0°C)], they found that the amount of mois- ture removed during the cooling process was higher after an 8-hour tempering period than after either a 2-4 hour or a 12-hour tempering period. Thus, there appears to be an Optimal length Of time for tempering. 30 Table 7A. Corn and air temperatures for drying at 100 cfm/bu, followed by 4 hours tempering, and cooling at 20 cfm/bu. TIME A1. 01" A2 02 ‘4 G4 A7 G7 A8 G8 START DRYING 0 47 47 47 47 47 47 47 47 47 47 10 151 151 136 134 118 113 67 67 67 67 77 168 168 165 165 162 161 140 139 135 133 STOP DRYING AND START TEMPERING 0 168 168 165 165 162 161 140 139 135 133 120 158 158 158 158 158 158 144 143 138 138 240 148 148 148 148 148 148 143 142 140 140 STOP TEMPERING AND START COOLING 0 148 148 148 148 148 148 143 142 140 140 5 113 115 121 121 122 122 121 121 120 120 10 90 91.5 105 108 113 114 114 114 113 113 20 71 71 78 80 92 93 98 99 100 100 30 64 64 66 66 71 73 94 94 94 94 40 63 63 63 63 64 65 87 88 88 88 60 63 63 63 63 63 63 63 70 73 74 80 63 63 63 63 63 63 63 63 64 65 STOP COOLING Source: Sabbah (1971) 9 Air temperature, °F 9' Grain temperature, °F 31 3-9 W In stored grain, insect infestation is a cyclic prob- lem. 'The repeated use Of insecticides has caused residue problems. The trend in government regulations has been to reduce chemical-residue tolerance in stored food and feed grains. A storage method which provides a low-temperature envi- ronment offers an alternative solution to insect and mold control and to decrease respiration rate. Aeration in which the dried grain is treated periodically with ambient air at a low flow rate, guarantees the low temperature environment. The air flow rate is between 0.1 and 0.01 cfm/bu depending on the size of the storage. Moisture losses during aeration are usually between 043 and 0.6 percent. The effect of aerating with air at rela- tive humidity not in equilibrium with the grain has been considered by Foster (1967). Grain at 12.0 percent moisture content and 80.0°F (l6.7°C) was cooled with air at 50.0°F (10.0°C) and 100 percent relative humidity. Upon entering the grain, the saturated air gave up moisture to the grain until equilibrium was reached. If the process proceeded adiabatically, heat released from the condensation of the moisture added to the grain would warm the air to 57.0°F (13.9°C). The grain between the cooling zone and the slower moving wetting zone cannot be cooled to below 57.0°F (13.9°C). Only the grain in contact with the entering air would be cooled to the entering temperature of 50.0°F 32 (10.0°C), since it would reach a moisture content in equili- brium with the saturated air. Thus, the amount of tempera- ture reduction possible in saturated air cooling is less than with air in moisture equilibrium with the grain due to condensation. The cooling times ranged from 17.5 hours at an airflow rate of 0.8 cfm/bu (0.9 MCM/ton) to 48 hours at an airflow rate of 0.2 cfm/bu (0.2 MCM/ton). The cooling time at 0.5 cfm/bu (0.5 MCM/ton) airflow rate averaged 23 hours. The cooling due to evaporation of moisture from the wheat was 54 percent of the total. The cooling air conditions were: air temperature 50.0°F (10.0°C) and relative humidity in moisture equilibrium. The initial grain temperature was 80.0°F (26.7°C). CHAPTER 4 EXPERIMENTAL 4.1 QQQLIN§_AEIEB_DBXIN§ During the fall Of 1983 and summer of 1984, corn was dried and cooled in a pilot-scale concurrent flow dryer located in the processing laboratory in the Agricultural Engineering Department at Michigan State University. The concurrent flow dryer consists of a single drying stage and a counterflow cooling stage. The overall dimensions are: a cross-sectional area of 1.0 21:2 (0.0929 m2) and a length or 1.0 £1: (0.3048 111 1. A bucket elevator carries the grain into the dryer and an auger, driven by a variable speed motor, transports the grain from the dryer. The variable speed auger controls the grain flow rate through the dryer. Liquid propane provides the fuel for the burner. The drying air temperature is measured by an iron-constantan thermocouple (type J) with an accuracy of j; 4.0°F (j; 2.2°C). The drying air is supplied by an 8.0 in. (20.3 cm) diameter fan driven by a 3/4 horsepower UL56 kw) electrical motor. The moisture content was Obtained by sampling the corn at 10-minute intervals as the dryer was being filled. 33 34 4.1.1 99521:; The counterflow cooler has a1cross-sectional area of 1.0 51:2 (0.0929 m2): the length is 3.0 ft (0.91 m). The cooler is not insulated. The connection between the dryer and the cooler consists of a 4.0 in. (10.2 cm) diameter auger. The grain is moved from the cooler by a 4.0 in. (10.2 cm) diameter auger. The natural air used to cool the grain was forced through the grain by a 2.0 Hp (1.49 kw) centrifugal fan. A schematic of the cooler/dryer system is shown in Figure 5. 4.1.2 Grain Corn of an unknown variety harvested in the fall of 1983 was used in the drying/cooling experiments. Two sources of corn were used. The first one was from the Michigan State University farm: it was used inexperi- ments 1, 4, 5, and 6. The second was from the Magg Farm-- Clinton County, Michigan: it was used in experiments 2 and 3. 4.1-3 GL§1n_EIQH_Bat§ A variable speed DC motor powers the auger from the outlet of the concurrent section of the dryer to the upper part of the cooler. It controls the grain flow rate in the system. Determination Of the grain flow rate was accom- plished by recording the weight of the grain over a measured time period. 35 GRAIN IN ‘il AIR IN AIR HEATING CONCURRENT FLOW DRYING [_, DRYING AIR OUT ‘7 COOLING AIR OUT ) f —V COUNTERFLOW COOLING Ll GRAIN OUT AIR IN Figure 5: Block diagram of concurrent flow dryer with counter flow cooler, 36 The cooler holds 2.9 51:3 (0.083 1113) of grain. In order to fill the dryer and the transfer auger, an additional ‘volume of 7.3 ft3 (0.207 m3) of grain is required. 4.1-4 Temperatures The cooling air temperatures were measured by copper- constantan thermocouples (type T) with an accuracy of 10.5 percent: the temperatures were recorded by means of a 10 channel digital recording unit (Omega Engineering Model 199) in experiments 1, 2, and 3, and by means of a 16 channel recording unit (Digistrip II) in experiments 4, 5, and 6. Three thermocouples were used as wet bulb thermometers. The inlet dry and wet bulb air temperatures were measured in two different positions. The first thermocouple measured the environmental temperature in the laboratory; it was placed close to the entrance of the air before the fan in such a way that no turbulence was present. The second point was located after the fan at the inlet air stream of the fan. The two thermocouples thus detected the rise in tem- perature in the fan. This rise was found to be, on the average, 1.0°F (0.5°C). The dry and wet bulb temperatures were also measured at the cooler outlet. By measuring these temperatures, it is possible to calculate the exit air relative humidity and, consequently, the amount of water removed from or added to the grain in the cooler. The dry bulb temperatures were also measured along the length Of the cooling section. In experiments 1, 2, and 3 the final temperature was evaluated 37 by inserting a mercury-in-glass thermometer into the grain mass as it left the cooler. In experiments 4, 5, and 6, a thermocouple was used. Figure 6 shows the dryer, the cool- er, and the thermocouple positions in the cooler. 4.1.5 Airflee_8ate In order to achieve two airflow rates, separate fans were placed at the inlet of the cooler. A 15.0 in. (38.1 cm) diameter fan attached to a 2.0 horsepower (1.49 kw) electri- cal motor produced an airflow rate of 206.8 lb/h ft2 (47.0 cfm/ftz) (8.7 kg/h m2) at 1.4 in. static pressure, an additional 18.0 in (45.7 cm) diameter fan attached to a 5.0 horsepower (3:7 kw) electrical motor produced a combined airflow rate of 484.0 lb/h ft? (110.0 cfm/ftz) (20.4 kg/h m2) at 9.4 in. static pressure. The connection between the fan and the cooler consists of a flexible plastic hose. A manometer was connected to the hose to read the static pressure required to calculate the airflow rate. 4.1-6 W The initial moisture content was obtained by sampling the grain as the dryer was being filled. Subsequent samples were taken during the tests by collecting cooled grain at regular time intervals. From those samples a small amount (1; 20 g) was taken to determine the moisture content. The difference between the inlet and outlet cooler grain mois- ture content was the value used to evaluate the efficiency Figure 6. Schematic of the pilot-scale concurrent flow dryer and counter flow cooler, showing the thermocouple locations (dots). - Bucket elevator - Grain storage hopper - Natural grain airlock - Heating air and grain boundary area Concurrent drying section - Dryer exhaust - Burner - Grain flow rate metering auger - DC motor 10 - Cooler exhaust 11 - Cooling section 12 - Cooling air entrance 13 - Cooling section discharge auger 14 - Cooler base. Legend: \DmNGLflnwal-J l 38 2 3 Figure 6A: Thermocouple positions at the (i 4.7 inch (12.0 cm) level from ' ‘ the inlet of the cooler. V19 1 a k // OlGlm Figure 6: Schematic of the pilot-scale concurrent flow dryer used in the laboratory, showing the thermocouple locations (dots). 39 of the cooler from the moisture removal point Of view. The moisture content was determined with an air oven heated to 217.0°F (102.7°C). Samples were kept in the oven for 72 hours. All samples were collected in plastic bags and were stored until the grain temperature equilibrated with the surrounding environment at 68.0°F (20.0°C). The moisture content was determined, using whole grain. A high accuracy scale was used to weigh the samples before and after placement in the oven. 4-2 RBQQEQHBE The grain from the field was stored in burlap bags at room temperature about 68.0°F (20.0°C) for five days before the tests were performed. The corn was heated (and partially dried) in the con- current flow drying section described in Chapter 4. A short period of time for tempering (110 min.) was allowed before cooling. The grain was fed by gravity through the cooler. The corn samples and temperatures were taken at 10- minute intervals. Several operating parameters were varied to study their effects on the cooling process: (1) grain flow rate--444, 480, 720, 840, 1065, 1100, and 1170 lb/h ft2 (18.7, 20.3, 30.7, 35.5. 45.0, 46.5, and 49.4 kg/h m2), (2) the airflow rate--206.8 and 484.0 1b/h ft2 (8.7 and 20.4 kg/h m2), and (3) the bed depth--2.0 and 3.0 ft (0.61 and 0.91 m). 40 The inlet grain temperature varied from approximately 90.0% (32.2%) to 150.0°F (65.5%), and the inlet grain moisture content from about 8.0 to 20.0 percent. The laboratory ambient temperature was approximately’ 70.0°F (21.1°C) for all tests: the relative humidity varied from about 15 percent to 80 percent. 4.3 AUXILIABX_EQHATIQN§ 4.3.1 Heat_and_Hass_Transfer_Eeuatiens The heat and mass transfer equations required for the cooling calculations were originally deve10ped for the drying of grain, but are equally acceptable for cooling calculations. 4.3.1.1 Latent Heat of vaporization The energy required to evaporate or condensate moisture in a product is called the latent heat of vaporization (or condensation). Rodrigues-Arias (1956) prOposed the follow- ing equation for the latent heat Of vaporization for corn in the temperature range of 40.0 to l40.0°F (4.4 to 60.0°C). hfg - (1,094.0 - 0.576) [1 + 4.35 Exp (-2,825.0 M)] (2) 6’. grain temperature (°F) M 2 average moisture content (decimal d.b.) Lerew (1972) proposed a simplified equation for the latent heat of vaporization of corn: hfg - 1,075.8965 - 0.56983 (T - 459.69) (3) 41 491.69 $,T s 609.69 Note: The temperature (T) is in degrees Rankine. 4.3.1.2 Specific Heat The specific can be treated as constant during the cooling process, since there are no great changes in the temperature during the cooling process. For the specific heat of air (Holman, 1981): Ca a 1.0057 xJ/xg°c (4) The specific heat of corn, is dependent on the tempera- ture and moisture content of the product. At 14.7 percent moisture content wet basis and a temperature of 54.0-83.8°F (12.2-28.8°C), the specific heat of corn is (Brooker et al., 1974): Cp a 0.484 BTU/lboF (4.187 KJ/Kg°C) (5) 4.3.2 Airflee_Bate_Qaleulatien Calculation of the airflow rate is based on of the static pressure which was measured during the cooling Opera- tion (Brooker et al., 1981): SP/BD a pressure drOp per foot of grain (inch H20) (6) where: SP - static pressure (inch H20) BD 2 bed depth (ft) Packing factor a 1.0 42 The pressure drop per foot of grain and the grain species are the parameters needed. Then: (CFM/ftz) x 60 x éf'a Airflow (lb/h ft2) (7) Whered‘is measured at the ambient temperature. The packing factor is related to the presence of foreign materials (FM) mixed with the grain. The PM tends, in general, to increase the resistance to air flow rate since the foreign material is usually of smaller equivalent diameter than that of the grain (Patterson, 1969). In this study, the packing factor is considered to be 1.0. If it had been 1.5, the air flow rate value Of 206.8 1b/h ft2 would have been 162.8 1b/h ftz, and 484.0 1b/h it2 would have been 440.1 1b/h ftz. The fans used for the experimental cooler were over- dimensioned for the hose connecting the fan and the cooler: this made it impossible to use the characteristic fan curves to calculate the airflows. 4.3.3 W During cooling, the grain kernel can absorb or lose water, depending upon the grain and air conditions. If evaporation takes place, the grain loses energy and the grain temperature decreases: if condensation takes place, the grain receives energy and the temperature increases. Sensible heat is the other form Of energy removal from the grain. 43 The amount of water removed is expressed by the follow- ing equation: MRp . Gp (MO - Mf) (8) where Mo and Mf a the initial and final moisture content, decimal d.b. Op 2 grain flow rate, lb per hour per square foot MRp =- moisture removed from the product, lb per hour per square foot. The moisture removed can also be calculated from the air inlet and outlet cooler conditions. The amount of water received or lost by the grain is the same as that lost or received by the air: MRa a Ca xAW (9) where MRa a moisture removed from the air, lb per hour per square foot. Ga - dry airflow rate, lb per hour per square foot. AW - humidity ratio difference, 1b of water per 1b dry air. 4.3.4 Heat_Balanee During the cooling process, the amount of energy ex- tracted from the grain is equal to that received by the air. It is equal to the sum of the latent and sensible heat. 44 Thus, Gp Cp 94 1: Gp hfg AMp + Ca Ca AT (10) In equation (10) the losses of energy by convection and conduction through the walls of the cooler to the surround- ing environment are assumed to be zero. Since the cooler is not insulated, a slight loss of sensible heat can take place. This is only significant when the air flow is very low. 4.3.5 W The latent/total heat ratio is a measure of the cooling efficiency. The ratio varies from -l.0 to +1.0. A positive ratio, form 0.0 to +1.0, means that evaporation takes place and water is removed from the grain to the air, drying the grain during the cooling processu A negative ratio, from —l.0 to 0.0, means that condensation takes place, and water is added to the grain during the cooling process. As cooling air passes through hot grain, heat is trans- ferred from the grain to air in the form of sensible and latent heat. The ratio of sensible and latent heat flow is governed by both internal and external resistances. The equation for the latent/total heat ratio is: latent heat Gp hfg.AMp total heat Ga Cp A9 Ratio - (11) where both the latent and sensible heat are calculated from the air conditions. 45 The amount of heat that can be removed during cooling is limited. As the air flow rate increases, cooling attri- buted to sensible heat transfer increases, and cooling at- tributed to moisture removal decreases. The air flow rate can reach a level where the amount of moisture removed becomes insignificant, and therefore, all cooling is due to sensible heat transfer. From the latent/total heat ratio, it is possible to evaluate whether or not the cooling process results in drying or rewetting of the grain. The ratio is also useful in analyzing the drying efficiency in the cooler and the final quality of the grain. A small absolute value of the latent heat/total heat ratio of close to zero means that no or little mass transfer occurred in the cooler. A large ratio close to +1 or -1 indicates that considerable mass transfer occurred during the cooling process. CHAPTER 5 RESULTS AND DISCUSSION The analysis of the cooling immediately after drying is based on the data acquired during the test runs in the laboratory in a counter flow cooler with a concurrent flow grain dryer. Six experiments (1, 2, 3, 4, 5, and 6) have been conducted; the results are discussed in the following sections. A summary Of the experimental conditions is shown in Table 8. Table 8 shows the air flow rate (lb/h ft2), the grain flow rate (lb/h ftz), the bed depth (ft), the inlet grain temperature (°F), and the inlet air temperature (°F) during cooling in the six experiments. Experiment 1 was conducted to investigate the moisture removal and temperature behavior during cooling of high moisture content grain after successive passes through the dryer without tempering between passes. Grain was cooled only once in experiments 2 through 6. The effect of a variation in air flow rate was investigated in experiments 2 and 3. Experiments 4 and 5 were conducted to investigate the effect of grain flow rate. The effect of bed depth was studied in experiment 6. 46 47 o.H mo souomm mconmm m mcHE=mmm * mm + OAm\m. u m e meom.o u um H .AmcoHuHccOO ucOHOEm any mum\5uo >N~.c n Nen\mm «cm.v u mum :\OH H hm.m m.no m.HMH o.m cm.o «we m.moH m om.oH m.mo o.va o.m mv.o one m.mo~ m cm.~H o.mm «.mmH o.~ m~.o com m.mc~ q hm.VH H.Hh «.mm o.~ Hw.o ohHH o.¢m¢ m om.eH >.Hb «.mm o.~ m¢.o mmoH o.vm¢ m ~H.¢H m.~h o.hm c.~ no.o emu o.¢mv m ~m.mH m.mm H.HcH c.~ mH.o ohHH m.oo~ m mH.mH o.Hh o.¢OH o.~ mH.o mwcH m.mo~ N em.¢H H.ow m.GOH c.~ a~.o an» m.mc~ N mo.MH m.¢m m.MHH o.~ mH.o mooH m.mo~ H mm.mH m.~m.o u a sxmm mom.a u an san F m mo bH .pont seHm .u:ootog .auHuHssn O>HamH0b .uoou season LOO Laos boa 2H .co>OsOb ObsunHoe .OOHLOO tsonum.m on» eo>o mandamusmmoa Hov me no Oneness so nH ossumcoesou comm .osHm> bousHsOHno as o nH LOO Loam: .mm + onm¢v u m H83: m 9H 9 3 mm m: "0902 “may best :oHe tee . em.m semo.o ~mmo.o o.es o.om e.so m.m.P mmoo.o o.ms e.mm m.=o m.oo~ m eo.m smmo.o osmo.o o.se s.mm s.mo m.mo. emoo.o o.s= e.~m a.se m.oo~ m m_.e oamo.o oemo.o o.ae m.mo o.oa m..o. seoo.o o.F= o.em o.ee m.oe~ . be e .n.o bH .o. a bHsb bHse sHso .n. a sHso oHsb mwlnn. 11m1mm ones: so: see .Ilmnmm so: see bH om: sH om: sH . om: bH . as: ee.=.m “may 3 .:.m Ahoy Nah aan ossumboaaoa ocsusbonsoa a: .3 ambaso amszH one an .aounhn LOHoooxtomec on» .3592» once on... NO name OLE» use scooon rant: on» $526 :HHoeeHaooenoe In... 36 can . 3.0 . 36 0.8 nosHm> OH»: .5ch 02.... no.3: sH — 303236 5 33338 .38 .6350 use SOHsH .¢ oHnma 50 Table 10. Experimental bed temperatures in the cooling bed and calcu- lated outlet grain temperature in experiment 1. Time TEMPERATURE (°F) AT1 A T2 J hour THERMOCOUPLES 1-5 1-out' 1 2 3 8 5 Out! 0.20 100.8 97.2 95.4 92.5 88.9 0.30 101.2 97.9 95.4 92.5 88.9 0.40 101.7 99.0 96.4 94.3 90.7 0.50 101.8 99.3 96.8 94.3 91.8 1.00 101.9 98.6 95.7 93.6 88.9 1:10 102.4 100.0 97.5 95.4 92.5 hverage 101.2 98.3 96.0 93.5 90.2 87.9 11.0 13.3 1:20 103.8 101.5 99.0 97.5 95.0 1:30 103.6 101.5 99.3 97.2 95.4 1:40 103.4 101.1 97.9 96.4 94.3 1:50 107.0 104.7 102.2 100.4 98.2 2:00 108.9 106.2 104.0 102.6 99.3 2:10 --- --- --- --- --- 2:20. --- -~- --- --- --- Average 105.3 103.0 100.5 98.8 96.8 89.8 8.9 15.5 2:30 102.0 97.9 93.6 92.5 92.1 2:40 110.5 108.0 105.1 102.9 100.0 2:50 116.5 112.6 108.7 106.2 100.0 3:00 113.0 110.1 106.9 105.4 103.3 3:10 115.4 113.4 111.9 109.8 108.0 3:20 117.5 115.2 113.4 112.3 109.4 3:30 119.4 117.7 115.9 114.8 112.6 Myerage 113.5 110.7 107.9 106.3 103.6 97.7 9.9 15.8 ' Calculated values. 9 F ==-— C 4- 32. 5 GRAIN TEMPERATURE ( 0F) 51 180- 130- 120- 110 - “N 100 90 FIN.“ P L 1 1 __________ 1 _________ J 0.0 4.7 9.4 14.2 18.9 outlet cooler' THERMOCOUPLE DISTANCE FROM THE INLET OF THE COOLER (inch) * Calculated value . Figure 7. 'Temperature profile in the cooling bed during cooling in experiment 1. 52 Table 11. Air and grain inlet and outlet temperatures in experiment 1. T s M P E R A T U R E (°F) Time Grain Air Grain Air hour out* in ATl in out ATZ 0:20 --- 77.0 100.8 100.8 0:30 --- 70.2 101.2 101.2 0:50 --- 66.9 101.8 101.8 1:00 --- 65.8 101.9 101.9 1:10 --- 65.8 102.4 102.4 Average 87.9 70.0 17.9 101.2 101.2 1:20 --- 65.1 103.8 103.8 1:30 --- 65.5 103.6 103.6 1:40 --- 65.1 103.4 103.4 2:00 --- 64.4 108.9 108.9 2:10 --- --- —-- --- 2:20 --- --- --- --- Average 89.8 64.9 24.9 105.3 105.3 2:30 --- 64.4 102.0 102.0 2:40 --- 64.8 110.5 110.5 2:50 --- 64.8 116.5 116.5 3:00 --- 64.0 113.0 113.0 3:10 --- 64.4 115.4 115.4 3:20 --- 64.8 117.5 117.5 3:30 --- 64.4 119.4 119.4 Average 97.7 64.5 33.2 113.5 113.5 ATu.means the difference between the laboratory ambient temperature and the outlet grain temperature (outlet grain - inlet air). Assumption: The outlet air temperature was assumed to be equal to the inlet grain temperature (4 T2 = 0) . 9 F=§C+32.' 53 .uoom Tucson mom uso m Loam . E n\mx Nom.v H OH eco>OEOu mu: m be e\bH H mHOE u m: ...n.c w. acoucoo OusumHoe chH uoHooo DOHusOIDOHcH memos uzq .mosHm> comuosomHa « em.m Ho.o em.MH ma.me sm.mH mace omono>< w«.H uN.HH NquH «H.«H “OOH omum me.o mm.~H mH.MH 111 mooH omum ~m.o mh.NH oo.mH om.mH mGOH OHum hm.o1 me.¢H mm.MH 111 mooH ooum ch25 mm. cm.~H m~.vH mm.mH mGOH omum om.o cH.¢H om.vH 111 mon ooum mm.o oa.vH mm.mH mm.mH mwcH omum .me.~ .am.e .em.oH mo.oH em.mH mooH omnbo>< ~m¢o1 «aN.WH audsH an.HH woOH omnm mo.H «me.qH wm.mH 111 mon QHAN mo.c1 «mo.mH mo.wH H¢.mH mGOH ooum mm.o hH¢.mH eh.mH 111 mmoH omuH ccoomm mm.c «Hh.mH om.hH mm.mH mon oouH NH.o «mh.hH hm.hH 111 mGOH omuH cm.c ho>.hH cm.mH em.mH mmoH omuH MH.o ms.o o~.aH mm.aH oe.- monum>¢ «m8o owde «mqu _wu4NN OHAH oo.o mo.mH mo.mH 111 oOHH couH mH.o h¢.mH mo.mH H¢.- oOHH omuo mm.H om.mH ~¢.om 111 coHH coho umqu om.o mm.mH m~.o~ Hv.- oOHH cmuo -.o mo.om om.c~ 111 OOHH omno mb.o o¢.mH mH.o~ om.m~ ooHH oHuo LOHOOO uoHOOO Homuc mum :\nH use DOHuso DOHcmhl uoHcH mum n\nH usoc whom m: ..b.c as ezmezoo mmoemHoz do oeHe .H ucOEHummxo cH boos mom «may co>oemu OusumHos can ucmucoo ousumHoe chum HmucmeHuomxm .NH oHnma 54 Table 13. Heat balance in experiment 1 with Ga/Gp ratios of 0.18 , 0.19 , and 0.19 respectively during the l, 2, and 3 hours of operation. Time HEAT (BTU/h) Latent/Totau (hour) Corn Air Heat Sensib1e* Sensib1e* Latent* Ratio* 1 7787.21 1548.52 6238.69 0.801 2 7966.50 2005.13 5961.39 0.748 3 8150.57 2431.97 5718.60 0.702 * Values derived from equation 10. l BTU/h = 0.293 w. 55 14)? H O \ H E a 0I5 - < H .4 1‘5. 8 E 0.0 b m a < .4 .0.5 .. .1,0 1 1 I 1.0 2.0 3.0 TIME (hour) Efigure 8. Latent/total heat ratio‘vs.timelduring cooling in experiment 1. 56 Table 10 and Figure 7 show the decrease in temperature as the grain flows through the cooler. Thermocouple 1 measured the inlet grain temperature, while thermocouple 5 measured the temperature at the position 18.9 inches (48.0 cm) from the inlet to the cooler. The outlet cooler grain temperature is a calculated value, based on equation 8. As the inlet grain temperature increased, the outlet grain temperature increased also. The difference between the inlet and calculated outlet grain temperature remained approximately constant during the second and third hour of the three-hour cooling period. The difference is due to the different inlet grain temperature. Table 11 shows the air and grain inlet and outlet temperatures during the course of the experiment. The de- sired outlet grain temperature was about 10°F (5~5°C) above the ambient temperature. Table 11 shows that the outlet grain temperature was well above the recommended value dur- ing this experiment. As the inlet grain temperature in- creased, the outlet grain temperature increased also. In Table 11 the inlet grain and the outlet air tempera- tures are assumed to be the same. lThe actual inlet grain temperature was not measured in this test. Table 12 shows the moisture content change of the corn in the cooler. The data shows that the grain lost water during the three-hour cooling period. 7As the inlet moisture content decreased, the moisture removed during the cooling process decreased also. The fact that no tempering occurred 57 between two passes, influenced this phenomenon. Since the measured moisture content values were erratic during the second hour of cooling, they were replaced with the calcu- lated values. Table 13 and Figure 8 show the heat balance and the latent/total heat ratio during the three hours of operation. The latent/total heat ratio was positive, which implies that evaporation took place during the whole period of cooling. Note that 70-80 percent of the cooling is due to evaporation during the cooling process, which implies an efficient cool- ing process. In conclusion, the ambient air and grain conditions are the main factors that affect the cooling process. .As the inlet grain temperature increased, the outlet grain tempera- ture increased also. ‘When the grain moisture content de- creased, the amount Of water removed during cooling de- creased also. The moisture content decrease from about 20- 13 percent caused a decrease in the value of the latent/ total heat ratio from about 0.8 to about 0.7. The value of experiment 1 is limited because Of the changing inlet grain condition. 5-2 EXREBIMENI_2 On December 12, 1983, corn, previously dried on the farm, was dried and cooled in a single pass Of the pilot- scale concurrent flow drier located in the laboratory. 58 The corn initial moisture content was about 14.0 per- cent and among the grains were around 15 percent of broken kernels plus foreign material. Three grain flow rates were studied (720, 1065, and 1170 lb/h £t2 (3,529.4, 5,520.6, and 5,735.3 Kg/h 1112)) to observe their effects on the cooling rate and moisture removed. Each grain flow rate took an hour of Operation. The results are shown in Tables 14, 15, 16, 17, and 18 and in Figures 9 and 10. 5.2.1 WW2 Table 14 shows the cooling air conditions. The air received water from the grain at 720, 1065 and 1170 1b/h ft2 (3,529.4, 5,520.6, and 5,735.0 Kg/h m2) of grain flow rate. In other words, the grain was dried in the cooler during the three-hour Operation. The amount of water removed at 1065 1b/h ft2 (54520.6 Kg/hmz) was the lowest in this exper- iment (Table 17); this may have been due to uncontrollable factors. The relative humidity (RH) and the humidity ratio (W) shown in Table 14 were calculated from psychrometric data (ASHRAE, 1981). Table 15 and Figure 9 show the temperature behavior during the cooling process. The inlet grain temperature remained almost constant. The slight variations noticed in the inlet temperature was also noticed in the outlet grain temperature. 59 .cOHnoa nson1m on» no>o mucoaonsnmos Hey me ho nomdno>m one monsumnoaaon HancoaHnonxo one .Amcowadvcoo unmanam umv Wuh\aho pmm.o u .LHm hep o nH non Lone: .n.o maxomm m o.ooo.. u .e.o beo a s\mu Nom.s u on eon P o on .oHeot seam .ncooeoa .huHOHasn O>HumHon .uoou chosen LOO neon non nH .uo>oeon onsnnHoe .mm + onmmav m bH P Has: 3 mm a: “ouoz .OsHa> OOnOHsOHso on Anew mama soHu Lad . .36 .mmd one nosHe> OH»: acxeo on» n03: 5" m uses—Heme: 5 2333.30 Ho 3320 one »OH:H m>.m ppmo.o mmmo.o o.oc c.~m m.pa p.—op oaoo.o o.om H.mm m.mm m.oo~ m m>.m om—o.o omNo.o 9.0m o.mm m.mm o.aop omcc.o o.pm 0.3m o.pb m.oom N mm.a NpNo.o o:~o.o o.aa N.mm —.mm m.cop omoc.c o.om h.mm p.05 Q.oom p «on s .n.o 2 .n.o 3 a £3 £3 33 .n... 3 a £3 33 use a): 26:. ence: no: has no: use pH on: pH own be em: pH on: no.2.m Amov 3 .=.¢ Ahoy soc OBHH oesnsnoaaOh onsumnocaoa a: 3Q. a m A a D O H m A 2 H .nogmnoao no meson can» on» 93.26 $323033.“ tni 36 use .:p OHan 60 Table 15. Experimental bed temperatures in the cooling bed and calcu- lated outlet grain temperature in experiment 2. TEMPERATURE (°F) Time THERMOCOUPLES A T1 ATZ (hour) 1 2 3 4 5 6 Out. 1-6 1-out' 0:10 103.0 100.0 96.0 94.0 91.0 85.0 0:20 103.0 100.0 97.0 95.0 92.0 84.0 0:30 109.0 107.0 101.0 98.0 94.0 84.0 0:40 108.0 106.0 102.0 99.0 97.0 83.5 0:50 107.0 101.0 98.0 94.0 92.0 84.0 1.00 111.0 105.0 101.0 99.0 95.0 84.0 4verage 106.8 103.2 99.2 96.5 93.5 84.1 88.6 22.7 18.2 1:10 101.0 99.0 97.0 93.0 90.0 83.3 1:20 103.0 102.0 99.0 96.0 92.0 86.0 1:30 104.0 102.0 100.0 97.0 95.0 86.0 1:40 104.0 102.0 100.0 98.0 95.0 86.9 1:50 106.0 102.0 100.0 98.0 97.0 86.9 2:00 106.0 105.0 101.0 98.0 95.0 86.0 fiverage 104.0 102.0 99.5 96.7 94.0 85.8 93.1 18.2 10.9 2:10 97.0 95.0 92.0 89.0 85.0 77.0 2:20 100.0 99.0 97.0 95.0 92.0 82.8 2:30 102.0 101.0 99.0 97.0 94.0 82.4 2:40 103.0 103.0 100.0 98.0 95.0 82.4 2:50 102.0 101.0 100.0 97.0 96.0 84.2 3:00 103.0 103.0 101.0 98.0 96.0 84.2 mverage 101.2 100.3 98.2 95.7 93.0 82.2 88.0 19.0 13.2 ' Calculated values of outlet grain temperature (°F). Note: Thermocouples 1-5 were placed 12.0 cm equidistant starting from top (grain entrance, T01) to the outlet of the cooler'(grain outlet, T05). was measured with a glass-tube thermometer. F = (9/5)C + 32- TC6 was located out of the cooler in a bucket. The temperature GRAIN TEMPERATURE ( OF) 140 "’ 130' 120 - 1101- 100 90 ALLA 61 l l L l L ---------- _ 0.0 4.7 9.4 14.2 18.9 23.6 outlet cooler* THERDDCOUPLE DISTANCE FROM THE INLET TO THE COOLER (inch) * Calculated value of outlet corn temperature. Figure 9. Temperature profile in the cooling bed during cooling in experiment 2. 62 Table 16. Experimental air and grain inlet and outlet temperatures in experiment 2. Time Gp ¥_f T E M P E a 5*? U R E (°F) ._ (hour) lb/ h Inlet Outlet AT1 Outlet Inlet A‘T2 air grain air grain 0:10 720 71.0 85.0 14.0 103.0 103.0 0:20 720 71.0 84.0 13.0 103.0 103.0 0:30 720 71.0 84.0 13.0 109.0 109.0 0:40 720 70.0 83.5 13.5 108.0 108.0 0:50 720 70.0 84.0 14.0 107.0 107.0 1:00 720 68.0 84.0 16.0 111.0 111.0 Average 720 70.2 84.1 13.9 106.8 106.8 1:10 1065 71.0 83.3 12.3 101.0 101.0 1:20 1065 71.0 86.0 15.0 103.0 103.0 1:30 1065 71.0 86.0 15.0 104.0 104.0 1:40 1065 71.0 86.9 15.9 104.0 104.0 1:50 1065 71.0 86.9 15.9 106.0 106.0 2:00 1065 71.0 86.0 15.0 106.0 106.0 Average 1065 71.0 85.8 14.8 104.0 104.0 2:10 1170 69.0 77.0 8.0 97.0 97.0 2:20 1070 69.0 82.8 13.2 100.0 100.0 2:30 1170 69.0 82.4 13.4 102.0 102.0 2:40 1170 70.0 82.4 12.4 103.0 103.0 2:50 1170 70.0 84.2 14.2 102.0 102.0 3:00 1170 70.0 84.2 14.2 103.0 103.0 Average 1170 69.5. 82.2 12.7 101.2 101.2 AT1 = the difference between the laboratory ambient temperature and the outlet grain temperature (outlet grain minus inlet air). Assumption: The outlet air temperature was assumed to be equal to the inlet grain temperature (ATZ = 0). 9 63 Table 17. Experimental grain moisture content and moisture removed (MR) per hour in experiment 2. Time Gp MOISTURE CONTENT ($ d.b.) MR (hour) lb/h rt2 inlet inlet outlet A ‘ lb/h rt2 dryer cooler cooler 0:10 720 16.47 15.09 14.82 0.27 0:20 720 16.40 15.50 14.59 0.91 0:30 720 16.14 14.34 13.61 0.73 0:40 720 16.14 14.93 14.14 0.79 0:50 122. 15155. 15482. lfllfll. 9235. .___. Average 720 16.34 14.94 14.33 0.61 4.39 1:00 1065 16.48 15.47 15.13 0.34 1:10 1065 16.35 14.97 14.90 0.07 1:20 1065 16.37 15.33 14.81 0.52 1:30 1065 16.47 15.38 15.05 0.33 1:40 1065 16.12 15.03 14.69 0.34 1:50 1965. 15.-.13. 1.4.3.5. 13.1.3.6. 1.5.2. .— Average 1065 16.15 15.19 14.84 0.35 3.73 2:00 1170 16.00 15.38 15.18 0.20 2:10 1170 16.08 15.15 14.74 0.41 2:20 1170 15.43 15.09 14.45 0.64 2:30 1170 14.89 15.29 14.70 0.59 2:40 1170 15.47 15.33 14.65 0.68 2:50 1119. 1§192. 15.55. 15123. 9113. ____. verage 1170 15.65 15.32 14.83 0.49 5.73 AMC means inlet-outlet cooler grain moisture content (S d.b.). MR = mois ure removed, lb per hour per square foot. 1 lb/h ft = 4.902 Kg/h m2. 64 Table 18. Heat balance in experiment 2 with Ga/Gp ratios of 0.29, 0.19, and 0.18, respectively during the l, 2, and 3 hours of operation. Time HEAT (BTU/h) Latent/Tbtal (hour) Corn Air Heat Sensible* Sensib1e* Latent* Ratio* 1 6510.30 1972.88 4537.42 0.717 2 5582.96 1637.50 3945.46 0.667 3 7453.21 1571.50 5880.71 0.789 * Values derived from equation 10. l BTU/h = 0.293 W. 65 1.0 " . / O z 0.5 - c: m {-0 c E i E 0.0 4' \ E .1 -005 _ -1.o 1 l ' 1.0 2.0 300 TIME (hour) Figure 10. Latent/total heat ratio vs. time during cooling in experiment 2. 66 Table 16 shows the difference between inlet air and outlet grain temperatures (AT1), the grain flow rate of 1065 lb/h ft2 (5,520.6 Kg/h m2). Outlet air and inlet grain temperatures ( T2) were assumed to be equal. Table 17 shows the moisture content of the grain and its variation during the three-hour cooling period. The moisture removed during cooling increased when the grain flow rate increased. Table 18 and Figure 10 show the latent/total heat ratio. All values shown are above positive 0.6, which means that evaporation of water from the grain took place during the three-hour operation. One of the most important factors in this particular test was the humidity of the air, which remained at low levels (Table 14) during the whole Opera- tion, making the drying process during the cooling more efficient. 5.3 lflflfifilflflfll4l On December 20, 1983, an experiment similar to experi- ment 2, was conducted. The air flow rate was increased in order to study its effects on cooling rate of grain. The procedure of experiment 3 was exactly the same as for experiment 2. The air and corn conditions and the results are shown in Tables 19, 20, 21, 22, and 23 and in Figures 11 and 12. 67 .Amcouaqomoo us0unac umv .sam use 0 pa son 50am: .mm + cam .e.e muxomz m o.ooo.P n .e.e esxo eE\aee emm.c u a axes ~oe.e u at e\eH F m we EH .oueet seem .uc00s0o .hufioaasa 0>auaa0n .uooh ohmsvn n0q noon 90a pa .c0>oaos ossunuoa .uoEon ssonnm 0:... s0>o 0305250003 3V wan uo 003.20.; 0.8 00252030» HmacoaasonE 05. .0sae> commasoamo no «8:: av u m m: nu P 3 mm m: "ouoz cadcv Ouflh IOHM LH¢ O om.m a—Po.o mmpo.o m.wm o.a> >.op ~.mm amco.o o.mp o.a: F.F> c.3m: m 0a.: Po—o.c mm—o.o o.mm a.~p o.—p ~.mm muco.o c.2P o.a: ~.F> o.=w= m :~.m socc.o smoo.o o.:~ o.mw >.os 0.5m omco.o o.mp m.m= m.~b c.2oa p mu» 3 .0.v AH .0.0 na a gang nasn nusn .0.o 9H a mass sass mun nxna Agsomv .nauun. seem: so: see at: sea as am: as em: as cm: as 3 .=.m Ahoy 3 .:.m Ahoy use made onsuasoqaoa onsumsoaaoa m: 36. a m A a a o a a A 2 H .couaasono Mo 0.32. 00.2.3 0:... 93.26 $31,300.32 tn... :6 use .m=.o .56 0.3 0030., oases 2:00 0.3 :03: 3 m anon—Eon: 5. 0:033:00 .50 .3330 new 63H .3 030a. 68 Table 20 . Experimental bed temperatures in the cool ing bed and calcu- lated outlet grain temperature in experiment 3. TEMPERATURE (°F) Time THERMOCOUPLES AT1 ATZ (hour) 1 2 3 4 5 6 Out' 1-6 1-out 0:05 98.0 97.0 92.0 89.0 86.0 81.5 0:10 96.0 93.0 91.0 88.0 86.0 81.5 0:15 96.0 93.0 89.0 87.0 85.0 81.5 0:20 95.0 93.0 87.0 85.0 84.0 81.5 0:25 98.0 93.0 88.0 85.0 83.0 81.5 0:30 99.0 96.0 91.0 86.0 83.0 81.5 Average 97.0 94.2 89.7 86.7 84.5 81.5 79.6 15.5 17.4 0:35 96.0 94.0 90.0 89.0 86.0 82.5 0:40 107.0 92.0 90.0 88.0 86.0 82.5 0:45 79.0 85.0 90.0 94.0 86.0 82.5 0:50 93.0 88.0 79.0 77.0 81.0 81.0 0:55 98.0 94.0 88.0 85.0 81.0 81.0 1:00 98.0 96.0 92.0 88.0 86.0 81.0 mverage 95.2 91.5 88.2 86 8 84.3 81.7 77.5 13.5 15.0 1:05 90.0 89.0 84.0 80.0 76.0 82.0 1:10 96.0 94.0 89.0 85.0 82.0 82.0 1:20 96.0 93.0 91.0 89.0 86.0 82.5 1:25 96.0 94.0 92.0 90.0 87.0 82.5 1:30 97.0 96.0 94.0 91.0 86.0 82.5 Average 95.2 93.3 90.0 87.0 83.8 82.2 80.3 13.0 14.9 ' Calculated values of outlet grain temperature (°F). Note: Thermocopules 1-5 were placed 12.0 cm equidistant, starting from top of the cooler (grain entrance, TC1) to the outlet of the cooler (grain outlet, T05). T06 was located out of the cooler in a bucket. The temperature was measured with a glass-tube thermometer. 9 F _.C + 2. 5 3 GRAIN TEMPERATURE ( °F) 2 r 69 130’ 120- d _s O l A“ A "V 1 l 1 l L________L______ 0.0 4.7 9.4 14.2 18.9 23.6 outlet cooler* THERMCOUPLE DISTANCE FROM TIE INLET OF TIE COOLER (inch) * Calculated value of outlet corn temperature. Figure 11. Temperature profile in the cooling bed during cooling in experiment 3. 70 Table 21. Experimental air and grain inlet and outlet temperatures in experiment 3. Time T E M P E R A T u R E (°F) (hour) Inlet Outlet A T1 Outlet Inlet A T2 air grain air grain 0:05 71.0 81.5 10.5 98.0 98.0 0:10 70.0 81.5 11.5 96.0 96.0 0:15 70.0 81.5 11.5 96.0 96.0 0:20 74.0 81.5 7.5 95.0 95.0 0:25 75.0 81.5 6.5 98.0 98.0 0:30 75.0 81.5 6.5 99.0 99.0 Average 72.5 81.5 .0 97.0 97.0 0:35 72.0 82.5 10.5 96.0 96.0 0:40 72.0 82.5 10.5 107.0 107.0 0:45 71.0 82.5 11.5 79.0 79.0 0:50 73.0 81.0 8.0 93.0 93.0 0:55 71.0 81.0 10.0 98.0 98.0 1:00 71.0 81.0 10.0 98.0 98.0 Average 71.7 81.7 10.0 95.2 95.2 1:05 73.0 82.0 9.0 90.0 90.0 1:10 71.0 82.0 11.0 96.0 96.0 1:15 71.0 82.0 11.0 96.0 96.0 1:20 71.0 82.5 11.5 96.0 96.0 1:25 71.0 82.5 11.5 96.0 96.0 1:30 71.0 82.5 11.5 97.0 97.0 Average 71.3 82.2 10.9 95.2 95.2 4T1 = the difference between the laboratory ambient temperature and the outlet grain temperature (outlet grain minus inlet air). Assumption: The outlet air temperature was assumed to be equal to the inlet grain temperature (4T2 = 0). F‘== 2-c:-+ 32. 5 71 Table 22. Experimental grain moisture content and moisture removed (MB) per hour in experiment 3. Time 0p MOISTURE CONTENT (Z d.b.) MR hour wet b/ inlet inlet outlet A M0 1b/ h ft2 h ft dryer cooler cooler 0:05 720 14.42 14.30 13.95 0.35 0:10 720 -- 14.16 13.58 0.58 0:15 720 15.49 14.09 13.71 0.38 0:20 720 -- 14.36 13.62 0.74 0:25 720 16.54 14.26 13.82 0.44 0:30 129. _:::_. 13151. 13135. lldfii ____. fverage 15.48 14.12 13.67 0.45 3.24 0:35 1065 15.77 14.26 13.56 0.70 0:40 1065 --- 13.95 13.89 0.06 0:45 1065 15.61 13.01. 14.42. -1.41* 0:50 1065 -- 15.50 13.80 1.70 0:55 1065 13.95 14.38 14.84 -0.46 1:00 1065. _:::_. 15132. 15199. 9133. .____ Average 15.11 14.50 14.04 0.46 4.90 1:05 1170 14.19 14.35 13.92 0.43 1:10 1170 -- 14.09 13.86 0.23 1:15 1170 ' 15.29 14.84 13.97 0.87 1:20 1170 --- 14.10 13.78 0.32 1:25 1170 14.93 14.34 13.80 0.54 1 :30 1.11.0. -- 1.4153. 13.-.19. 1.5.3. _— Average 14.80 14.37 13.90 0.47 5.50 = Discharage value. AMC = Inlet-outlet cooler grain moisture content (S d.b.). MR = Moisture removed, lb per hour per square foot. = Graig flow rate, 1b ger hour per square foot. 1 p1b/h ft :4. 902 Kg/h m . 72 Table 23. Heat balance in experiment 3 with Ga/Gp ratios of 0.67, 0.45, and 0.41, respectively during the 1, 2, and 3 hours of operation. Time HEAT (BTU/h) Latent/Total (hour) Corn Air Heat Sensib1e* Sensible* Latent* Ratio* 1 6233.50 2869.15 3364.35 0.540 2 7734.82 2729.76 5005.06 0.641 3 8417.51 2799.46 5618.05 0.667 * Values derived from equation 10. l BTU/h = 0.293 W. 1.0 LATENT/TOTAL HEAT RATIo .0 o o 0: I o e U‘ -1.0 Figure 12. Latent/total heat ratio vs. 73 l 1 1.0 2.0 TIME (hour) in experiment 3. 3J) time during cooling 74 5.3.1 WWI-.3. Experiment 3 was a repetition of experiment 2 except for changing the air flow rate from 206.8 lb/h ft2 to 484.0 1b/h ftz (1,013.7 Kg/h m2 to 2,372.5 Kg/h m2). The materials and method employed were the same. Table 19 shows the laboratory ambient air conditions. The relative humidity (RH) and humidity ratio (W) were very low, which helped the cooling process to be efficient, removing water from the grain during the whole period of operation. Table 20 and Figure 11 show the temperature decrease during the cooling period. There is no significant differ- ence among the three grain flow rates studied (720, 1065, and 1170 lb/h ft2 (3529.4, 5520.6, and 5735.3 Kg/h m2”. Table 21 shows the difference between inlet air and outlet grain temperature. A low ATl value means a good efficiency of the cooling process. The outlet grain temper- ature is lower than inlet air temperature, which means that evaporation took place. The difference between inlet air and outlet grain temperatures (AT1) is around 10°F (5.5°C), which means that the grain is cool enough to be safely stored. Table 22 shows the moisture content of the grain and its variation during the three-hour cooling period. The moisture removed during cooling increased when the grain flow rate increased. 75 Table 23 and Figure 12 show the heat balance. The latent/total heat ratio increased as the grain flow rate increased. Comparing experiment 3 (Ga 3 484.0 lb/h ft2 (2372.5 Kg/h m2)) and experiment 2 (Ga . 206.8 1b/h rt2 (1013.7 Kg/h m2)), the amount of water removed in experiment 2 is greater than that for experiment 3. However, the inlet grain tem- perature in experiment 2 was greater than in experiment 3 (Tables 15 and 20). The inlet grain temperature and mois- ture content and the laboratory ambient air were similar in both experiments. In conclusion, increasing the air flow rate does in- crease the amount of moisture removed from the grain. Under the specific conditions during which-the experiments were conducted, the increase in air flow rate decreased the amount of water removed.from the grain. Consequently, it decreased the drying efficiency during the cooling process and decreased the cooling rate. 5-4 EXRBBIMENI_1 Experiment 4 was conducted on July 24, 1984. Corn, originally approximately 14 percent moisture content, was dried to around 12 percent and cooled in a single pass. 'The number of thermocouples were increased to reach the bottom of the cooler. The air and corn conditions are shown in Tables 24, 25, 26, 27, 28, and 29 and in Figure 13. 76 .Annoanuvnoo anownsa new uuxauo >-.c u .naa use mo na non none: .nnoonon .mnaoaenn 0>un¢a0n .noou onusca n0q neon n03 na .u0>oe0n onsnnwos .uoanon nsonum on» 90>o unnoeonsneos Aoov.aunan ho n0m0n0>a 0L0 nonsnanoqson Hennoaanonuo one .mm + onmmav .e.e muxomm m o.oeo.. A .e.e en\o a an P we exme ~om.e u 0 pH .oauah 3a” m nu nxna — wean 3 3: 3: ”mac: .05Ha> nonmasonmo so Away 0am; 30H» nw< e tn... mud 3” 03.2: 039. 3:00 on» nown: n." a anon—.2093 5" 0.332500 .30 “.0330 one noanH m~.m om.o.o oomo.o o.om m.oa m.co. ~.eme oe.o.o c.3e p.~e o.oo m.eo~ m mo.a mepo.o smmo.o o.oa m.om m.po ..m~. ~m.o.e o.mm m._e e.em m.eo~ P at e .e.e an .e. u ease ease ease .e. a ease seen an axes Annexe m e ea seen: no: sea e en no: are m an am: an cw: an am: he eo3 no.3.m Ahoy 3 .3.3 Ahoy .05 made onsnanoqaoa onsnunoaaoa a: an. a m a a a o a m a 2 H .:N manna 77 m .Nm + U l H m m .0usnmu0memu :Hmum noauso nonmasoamo on: gonna amun0efiu0mx0 0nn :003u0n monouwmuep 0n» 0:005 fiafi .mousnmu0m60n :«mum Hmun0afiu0mx0 noauso 6:0 nods“ :003u0n monmuowmfip 0nn mnnme Heq .uoaooo 0nn mo uso mnmoe use .munoewusmm0e non mo monu0>m :0 we 0:Hm> musumu0380u nocm “muoz e AQOV muflnaMHmQEwu CMMHG uwHUSO HO mwsdm> CNUMHSUHMU a. «.ma H.mH m.oa~ H.~HH o.¢HH o.mHH H.maa n.5HH m.~NH m.m~m c.5ma ~.omH mmmH0>n m.HHH H.mHH m.mHH m.mHH n.5HH o.ama e.m- ~.h~H H.omH ocum m.~HH «.maa m.>HH m.maa «.3HH m.H~H h.m~H o.h~H H.omH cmua m.m~a m.mHH o.mHH o.maa m.mHH m.HNH H.¢~H m.>~a m.om~ ovni H.mHH m.eHH m.maa m.maa m.mHH m.-a m.vma >.h~H m.omH omui o.oaa m.maa e.haa m.~HH v.5HH N.H~H m.m~H H.5NH e.oma omud m.oaa c.mHH c.0HH m.oHH o.mHH m.mHH m.-H o.m~a «.mma oHuH >.¢H m.oa «.moa m.ooa m.moH m.oHH o.hoa m.oHH o.¢HH e.mHH m.o~H a.m~a 0mmu0>¢ o.moH o.HHH m.mHH o.HHH h.maa «.mHH m.ama s.m~a «.mma oouH m.eoa H.moH H.MHH H.moa >.maa c.maa ~.HNH «.mma m.m~a omuo «.ma m.ooa v.qoa m.mm m.moa o.HHH m.mHH ~.o~H m.vm~ oeuo v.mHH m.hoa «.moa m.mca d.aoa H.H¢H m.~oa «.moa m.~HH omuo n.3oa m.HHH n.naa h.~HH m.hHH o.o~a m.cma «.maa H.mHH omuo «.moa H.ooa m.oHH h.moa m.oHH ¢.¢HH c.5aa h.¢NH m.om~ can: Tysonfl nsola «use use a h m m v m N H nunonv we: 3.: mmaeaooozmmme we; 3% mmaenmmezme .v unmewuomxo :fi.0u:umu0m50n namum noauso pounasoamo on: non wnfiaooo 0n» ca mwusnnu0m50u con Hennmefiummxm .mm manna 78 1MD' 120 110 GRAIN TEMPERATURE ( OF) 90'- I 1 l1, 1 L, 1 L, #1 L___,L _________ 0.0 ”.7 9.14 1n.2 18.9 23.6 28.3 33.0 outlet cooler THERMOCOUPLE DISTANCE FROM THE INLET OF THE COOLER (inch) the first hour. the second hour. 1h 2h Figure 13. Temperature profile in the cooling bed during cooling in experiment 4. 79 outlet grain temperatures (grain out minus air in). .4T2 (grain in minus air out). 9 F ==4- C 4- 32. 5 Table 26. Experimental air and grain inlet and outlet temperatures in experiment A. Time T E §_P E R A r u R E (°F) ¥_ (hour) Grain Air A ‘1‘1 Grain Air A T2 out in in out 0:10 105.“ 8u.5 20.9 123.9 130.8 -6.9 0:20 107.3 88.5 22.8 120.5 113.1 11.A 0:30 116.“ 8A.? 31.7 113.9 112.5 1.0 0:50 10h.3 80.3 20.0 131.1 128.9 2.2 1:00 108.6 85.0 23.6 130.2 128.8 1.3 Average 106.8 8h.6 22.2 12A.2 123.1 1.0 1:10 11o.é 85.5 21.7 130.7 129.2 1.5 1:20 110.0 86.3 23.7 132.1 130." 1.7 1:30 115.1 86.1 29.0 13h.1 130.9 3.2 1:40 112.9 87.2 25.7 133.8 130.3 3.5 1:50 112.5 87.2 25.3 130.7 130.1 0.6 2:00 111.8 87.0 2A.8 131.1 130.1 1.0 Everage 112.1 86.6 25.5 132.1 130.2 1.9 .AT1 = the difference between the laboratory ambient temperature and the the difference between the inlet grain and outlet air temperatures Table 27. Temperature at the same level (4J7 inches (12.0 cm)) from the inlet of the cooler in exper- iment 4. Time T E M P E R A T U R E (°F) (hour) ‘Thermocouples‘ .AT 2 11 12 13 12-2 0:10 124.7 127.1 130.3 127.5 0:20 119.4 123.5 122.2 124.4 0:30 106.4 108.3 110.0 108.7 0:40 120.2 124.6 125.9 124.8 0:50 125.2 129.7 130.6 129.7 1:00 125.7 130.0 130.5 129.7 Average 120.3 123.9 124.9 124.1 4.6 1:10 126.0 130.3 130.6 '129.7 1:20 127.1 131.7 132.1 131.6 1:30 127.7 131.9 132.0 131.6 1:40 127.3 131.3 131.4 130.7 1:50 127.0 130.9 131.3 130.9 2:00 127.2 130.9 131.4 130.9 Average 127.0 131.2 '131.5 130.9 4.5 AT = the highest temperature variation at the same level. Note: Each temperature value is an average of ten (10) measurements. *thermocouple location--see Figure 6A. 9 F=-C+32. -5 81 Table 28. Experimental grain moisture content and moisture removed (MR) per hour in experiment 4. Time Gp MOISTURE CONTENT (1 d.b.) MR hour lb/h ftz inlet inlet outlet AMC lb/h rt?- dryer cooler cooler 0:10 840 14.93 14.05 12.17 1.88' 0:20 840 14.56 14.00 14.08 -0.08* 0:30 840 14.60 13.22 12.89 0.33 0:40 840 15.00 12.66 12.35 0.31 0:50 840 14.76 13.02 12.66 0.36 1:00 819. 15111. 13.25. 12132. 9193. _____ Average 14.77 13.04 12.56 0.48 4.03 1:10 840 14.73 13.25 12.52 0.73' 1:20 840 15.18 12.78 12.36 0.42 1:30 840 14.93 12.83 12.37 0.46 1:40 840 14.74 12.79 12.84 -0.05' 1:50 840 14.59 12.87 12.68 0.19 2:00 819. 15123. 13101. 12469. 0.51. ____. Average 14.78 12.89 12.50 0.39 3.28 ' = Discharge value. A140 2 Inlet minus outlet cooler grain moisture content (% d.b.). HR = Gp = Grai 1 lb/h ft Moisture removed, lb per hour per square foot. flow rate, wet lb per hour per square foot. = u.902 Kg/h m2. 82 Table 29. Heat balance in experiment 4 with a (Ga/Gp) wet ratio of 0.25, during the 2-hour cooling opera- tion. ime HEAT (BTU/h) Latent/Totah (hour) Corn Air Heat Sensible* Sensible* Latent* Ratio* 1 5966.01 1910.83 4055.18. 0.680 2 5445.53 2163.96 3281.57 0.603 * Values derived from equation 10. 1 BTU/h = 0.293 W. 83 5.4.1 WW Experiment 4 is similar to experiments 2 and 3. The main objective of this experiment was to study the adsorp- tion of water by the grain during cooling, based on the temperature and the position of the grain inside of the cooler. Other purposes of this experiment were to check the temperature variations at the same level (Table 27) and the temperature difference between inlet grain and outlet air. Table 24 shows the inlet and outlet air conditions. The inlet relative humidity (RH) decreased during the two- hour cooling operation. However, the humidity ratio (W) increased during the same period, which caused desorption of water during the two-hour cooling period. Table 25 and Figure 13 show the temperature profile during the two-hour cooling Operation. The temperature decreased until 23.6 inches (60.0 cm) from the inlet of the cooler. Adsorption took place between 23.6 inches (60.0 cm) and 28g3 inches (72.0 cm) because of the increase in temper- ature. Beyond the 2843 inch mark, the temperature decreased again, which means that desorption of*water took place in the last portions of the cooler. Table 26 shows the outlet grain temperature and the difference (AT1) when compared with the laboratory ambient air temperature. If ATl is greater than 10°? (5.5°C), the cooling process is not completed. In Table 26 a comparison between inlet grain and outlet air temperature showed that the inlet grain temperature was a few degrees warmer than 84 the surrounding air. Negative sign is due to instead state Operation of the dryer and therefore of the grain inlet temperature to the cooler. Table 27 shows the temperature at three locations at the same level (4.7 inches,(12.0 cm)) in the cooling bed. The slight variation is due to non-uniform airflow in the cooler. Table 28 shows the grain moisture content and moisture removed (HR) during the two-hour cooling operation. The amount of water removed during cooling at the first and second hour was shmilar and was about 4 lb per ft2 per hour. Table 29 shows the heat balance with a Ga/Gp ratio of 0.25 w.b. The latent/total heat ratio stayed positive (0.6),‘which means that sixty (60) percent of the cooling due to the evaporation process and forty (40) percent was due to sensible heat transfer. 5.5 EXREBIMENI_5 Experiment 5 was conducted on August 10, 1984. The same corn dried in experiment 4 was used in experiment 5; it was dried from about 12 percent moisture content to about 9 percent in a single pass through the dryer and cooler. The grain flow rate (Gp) 480 lb/h 131:2 (2348.6 Rg/h 1112) compared to 840 lb/h 131:2 (4117.6 Kg/h m2) in experiment 4. The air and corn conditions are shown in Tables 30, 31, 32, 33, 34, and 35 and in Figure 14. 85 .mm + ofimmmv .a.e ee\o~= e o.oeo.. u .a.e sH\o a EH . .Aueoeseeeoo seaweed soc sexaee e-.e u a exam ~ee.e u a» exea P .eam use mo nu toe some: we on .oaaas anamuasn 3 .ueoosoe .aawuaesn o>aamaou mm .uoou cannon son use: see AH .oo>osoe oesaaqoa u m: .cowsoe seesaw on» so>o naeoaonsnaoa.aoov.muuan no aomaso>m one eonsuacoesoa Haaeoaasoaxo one «one: .osae> cougasoauo a. .aacv came 30a» sa< - em.m memo.o mmeo.o o.om m.eo. e.~o. m.me. ~e.e.o m.mm e.ee e.mo o.oo~ m ea.e .emo.e Ppeo.o o.em o.ee. ..me o.em. oe.o.o o.em =.oe =.oo o.eo~ . ue e .a.e 8H .6. a page ease seen .8. a sage seen u« axed Assess m , e an eeuo: so: use e an so: use N an em: EH ow: ea em: an at: e-.:.z “boy 3 .=.m “hey can onus onsuueoeaoa ensuesoqsoa e: :< e e a a e o a u a 2 H 5.: mad 3" 0.53. 0.3.: eoxeo 23 cows: 5" m use—Susanne :« msoauwveoo new uoauso can boasn .om manna 86 .mm + U l m m .eusueuemeeu H m caeum ueause neueaseaeo use ueacfi amuseefluemxe one coezuee eeceeemuwc one memes New. .meusueuemeeu sebum deuceEeeemxe ueHuso one amaze :eezuen eoceuemmac ecu memes Hag. .ueaoeo on» me use momma poo .muceeeusmeee so» no emcee>e am we eeae> ousueueQEeu seem «euez .Ame. ousueuemeeu seeum ueause me mesae> peueasoamu « d.ae o.e~ e.eoa m.mHH «.mme m.oma H.HHH m.e~H «.mme e.eme «.mefi m.mea monum>¢ m.o~a m.m- m.e- m.oHH e.e~H «.mme o.~me o.mma m.~eH ooum o.m~e «.mme H.Hma m.eea m.mma H.omH m.mma «.mme «.mee omue m.o~H H.mme e.eea m.mea o.em~ H.ema ~.eme H.mme m.oea cone m.mHH o.mmH m.m~e m.HHH m.m~H m.~e~ H.meH e.HmH m.omH emud m.eea m.e- e.e~H d.aea e.m- m.m~H e.eme m.eee o.mmH eNAH e.mHH e.H~H m.m~H ~.oHH o.-~ e.e~H ~.HMH m.mmH e.mme cane Ten mém 1:: m4: «4.: flame 22: Ta: name came e52 e63 3363‘ m.mHH o.o~H e.e~e «.moe «.mma m.e- «.ome e.mma e.eme cone m.m~a e.o- H.m~H H.oHH o.o~e m.m~e e.m~H m.eme m.em~ omuc m.eHH e.o~H mammfl m.mea o.H~H m.m~e e.eme m.ome >.emfl oeuo m.eHH a.ma~ «.mNH e.eoe m.o~H m.e~H m.m~e e.mme H.8MH omuo a.aoa e.mHH m.~mH m.moH e.mHH ~.e~H m.m~e m.mme H.eMH cane c.5m e.eoe m.eHH ~.ooe «.maa H.-H ~.5~H H.~mH «.mma cane eso1H usoufl .use one a e e m e m m H Ausoev New Haw mmemaeoezmmme meme sees emceemmmzme .m uceefiuemxe ca eusumuemeeu sebum ueHuse oeueasoaee one pen mcflaeee ecu a“ meusueuemEeu pen Henceefiuemxm .Hm canes 87 130 120 110 GRAIN TEMPERATURE ( °E) 1OOF' L l i l 1 l A 1---.L-auu-a- 0.0 4.7 9.4 14.2 18.9 23.6 28.3 33.0 outlet cooler THERHOCOUPLE DISTANCE FROM THE INLET OF THE COOLER (inch) 1b a the first hour. 2h = the second hour. Figure 14. Temperature profile in the cooling bed during cooling in experiment 5. Table 32. Experimental air and grain inlet and outlet temperatures in experiment 5. 88 Time T E M P E R A T 0 R E (°F) (hour) Grain Air A T1 Grain Air 4 T2 out in in out 0:10 97.0 88.3 8.7 139.1 135.4 3.7 0:20 109.9 88.6 21.3 137.3 136.1 1.2 0:30 114.8 88.7 26.1 137.5 136.1 1.4 0:40 116.5 88.5 28.0 140.2 134.7 5.5 0:50 115.8 88.4 27.4 141.6 136.9 4.7 1:00 115.3 88.2 27.1 142.2 136.6 5.6 Average 111.5 88.4 23.1 139.6 136.0 3.7 1:10 115.6 88.9 26.7 141.9 138.7 3.2 1:20 116.9 89.4 27.5 158.3 158.0 0.3 1:30 118.3 88.8 29.5 161.7 150.5 11.2 1:40 120.5 88.9 31.6 143.8 140.9 2.9 1:50 125.0 88.1 36.9 142.4 142.2 0.2 2:00 120.6 88.2 32.4 152.0 142.8 9.2 Average 119.5 88.7 30.8 150.0 145.5 4.5 ‘AT1 = the difference between the laboratory ambient temperature and the outlet grain temperature (outlet grain minus inlet air). the difference between the inlet grain and outlet air temperatures (grain in minus air out). ' ‘ 9 F—§C+32. ATE 89 Table 33. Temperature at the same level (4:7 inches (12.0 cm)) from the inlet of the cooler in experiment 5. Time T E M P E R A T u R E (°F) (hour) Tiermocouples {AT 2 11 12 13 12-2 0:10 132.1 138.4 139.9 138.8 0:20 133.3 139.5 140.4 139.5 0:30 133.7 139.8 141.2 140.2 0:40 130.8 136.4 137.6 136.3 0:50 134.3 140.1 141.7 140.7 1:00 133.6 139.7 140.8 139.7 Average 133.0 139.0 140.3 139.2 7.3 1:10 135.8 142.5 143.7 142.5 1:20 146.8 153.1 158.9 154.9 1:30 151.6 164.9 163.5 164.2 1:40 139.1 145.2 146.0 145.0 1:50 139.2 145.5 146.5 145.8 2:00 135.0 141.4 142.8 141.8 bverage 141.2 148.1 150.2 149.0 9.0 AT = the highest temperature variation at the same level. Note: Each temperature value is an average of ten (10) mea SL1 rements e w A one C+32. 9O .sodeee one he cease one song “so o.m=w . a e\me ~om.= menace o.o. w uh n\aH P oaoee was peek onosco coo use: too ea .vo>oaos ossuoaos u m: .A.e.e 3 33:3 ossuoaoa :«osm noaeee uoaueo ensues node.“ n 02‘ 45.6 S acousoe ossuoeoa swoon soHeee uoaase oases 33 u mo: Q 4.96 3 acouseo oesuoaoa sfiosm soaoeo was oases mod: u 52‘ em.m -.. mo.o oe.o m~.e em.e e=.o. mo.~. one omeeoee 1111 _mmqq .qmqq .mmqqn "aqua .mqqaa .mmqaa umqma .qam cone pm.. mp.p mc.o em.op :=.P— mp.mp Po.mp om: omup mo.F Pm.o :>.o am.o m~.op mm.op o=.~— cm: can, am.p op.o mp.p o>.m om.m mm.m No.mp on: omnp am.— ao.o mo.o om.m =o.m m=.a Pp.mp om: omup mm.o a~.o om.o we.» mo.m .m.m Pm.mp om: opup 3a.: =o.. o=.o mm.o oo.o om.e mm.e m~.~. om: oememee .1111 .unqa .amqq .amqq “and. .quu. mung“ “mean. .qum eon. FN.P pm.o om.o mm.a mo.m mm.op Fm.mp om: omuo mm.F ma.o oa.o P>.o o..o mo.o— pp.mp on: case mm.o oe.o oo.o om.m mm.m mo.m >~.~P om: omuo mo.o m~.o mm.o oo.w mp.m m>.o mm.~— on: omuo p~.- m>.o mm.o mm.o oo.o- mm.op no... om: opuo ozfl Nozfi 52¢ noaoee LoHooe noaoee Lease a s New axed uoauso baa cease meem1 \e no: Ansenv e: A.e.e uv azmezoo meeamHoz ac came .m unoaasoqxo ca use: son Axxv oo>eaoe ossaoaoa use ecoucoo ossunaea semen Homeoaaeoexm .am edema 91 Table 35. Heat balance in experiment 5 with a Ga/Gp ratio value of 0.43 WJL' during the 2-hour cooling operation. Time HEAT (BTU/h) Latent/Total (hour) _Corn Air Heat Sensible* Sensible*‘Latent*‘ Ratio* 1 7346.49 2362.48 4984.01 0.678 2 8634.95 2820.00 5814.95 0.673 * values derived from equation 10. 1 BTU/h = 0.293 W. 92 5.5.1 WW Experiment 5 was conducted to observe possible water adsorption by the grain during cooling, when the grain flow rate is low. Compared to experiment 4, the inlet corn moisture was lower. Table 30 shows the inlet and outlet air conditions. The humidity ratio (W) increased during the two-hour cooling Operation, which means that the grain lost water to the air during the whole period based on inlet and outlet condi- tions. Table 31 and Figure 14 show the grain temperature profile during the two-hour operation. The temperature inside the cooler decreased until 23.6 inches (60.0 cm) from the inlet. From 23.6 inches (60.0 cm) until 28.3 inches (72.0 cm) the temperature increased, showing that adsorption of water by the grain took place. After that, the tempera- ture continued decreasing until the end of the cooling section, indicating desorption again. Table 32 shows the inlet and outlet air and grain temperatures. As the inlet grain temperature increases, the outlet grain temperature increases also. The difference between the outlet grain and ambient temperature is too large for safe storage, because ATl is greater than 10°F (5.5°C). The inlet grain temperature is a few degrees higher than the outlet air temperature, as shown in the1AT2 column in Table 32. 93 Table 33 shows the temperature variations at the same bed level (4:7 inches (12.0 cm)) from the inlet of the cooler. Non-uniform airflow in the cooler caused a maximum average temperature difference of 8.0°F (4.S°C). Table 34 refers to the moisture content of the grain at the inlet, at the 18.9 inch (48.0 cm) level and at the cooler outlet. 0f the total amount of moisture removed during cooling, half happened in the first 18.9 inches (18.0 cm). The total amount of water removed was greater in experiment 5 (Gp . 480 lb/h ft2 (2348.6 Kg/h m211 than in experiment 4 (Gp - 840 lb/h £t2 (4117.6 Kg/h m211 because of the longer time spent in the cooler by the grain. Table 35 shows the heat balance and the latent/total heat ratio. Even though the adsorption of water by the grain took place inside the cooler, the latent/total heat ratio remained positive. About 67 percent of the cooling was due to the evaporative process, and the remaining 33 percent due to the sensible heat transfer. In conclusion, increasing the inlet grain temperature increased the outlet grain temperature. Water absorption took place between 23.6-28.3 inches (60.0-72.0 cm) from the inlet of the cooler. Moisture removed during cooling increased when the inlet grain temperature was increased. The latent/total heat ratio was not significantly affected. Comparing experiment 5 with experiment 4, the tempera- ture behaviors are quite similar. In both cases, the 94 absorption occurred at the same interval (23.6-28.3 inches (60.0-72.0 cm) from the inlet of the cooler). 5.6 EXREBIMENI_§ Experiment 6 was conducted on August 25, 1984. Corn previously dried in experiments 4 and 5, was dried from approximately 11 percent to 8.0 percent in a single pass through the dryer and cooler. The bed depth of the cooler was increased from 2.0 ft (60.96 cm) to 3.0 ft (91.4 cm). The number of thermocouples was increased, maintaining the equidistance of 4.7 inches (12.0 cm). Sample holes were made along the cooling section, starting at 18.9 inch (48.0 cm) from the tep, at 4.7 inches (12.0 cm) distance interval. The air and corn conditions are shown in Tables 36, 37, 38, 39, 40, and 41 and in Figures 15, 16, and 17. 5.6.1 Comments.cn_flxneriment_§ The inlet and outlet air conditions are shown in Table 36. The humidity ratio (W) increased during the same test. The amount of water removed was greater during the first two-hour period than during the last two-hour period. This is due to the different drying temperature (400°F (204°C)) during the first and second hours of the test compared to the third and fourth hours (300°F (149°C)). This resulted in different inlet grain temperatures. Table 37 and Figure 15 show the temperature profile during cooling in experiment 6. 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GRAIN mammals: ( °F) 140 98 130 \ \ ‘x x \\ \\‘. 120 “\ \\\\. “3\~ .3”“~ ‘\\\\. ". “P““\ V IN‘ §::§o.. 110 - \ ‘~ “0 2h :.‘_ ______ 1‘1h ~~.~. 3h "c an 1M)- m)- 1 1 l L l L 1 1 _____________ 1 0.0 4.7 9.“ 1u.2 18.9 23-5 23-3 33.0 37.8 outlet cooler THERHOCOUPLE DISTANCE FROM THE INLET OF THE COOLER (inch) 1h, 2h, 3h, and 4h mean first, second, third and fourth hours reSpectively. At lst and 2nd hours, the air inlet drygr temperature was 400°F and at 3rd and 4th hours it was 300 F. Temperature profile in the cooling bed during cooling in experiment 6. Figure 15. 99 Table 38. Experimental air and grain inlet and outlet temperatures in experiment 6. Time T E M P E R A T u R E (°F) (hour) Grain Air A T1 Grain Air A T2 out in in out 0:10 --- 62.8 138.0 136.3 0:20 --- 62.5 1&2.1 135.9 0:30 106." 62.4 140.3 132.0 0:40 107.5 62.3 139.5 132.5 0:50 1oe.u 62.7 136.5 133.5 1:00 109.3 63.“ 136.0 127.5 Everage 107.9 62.7 #5.2 138.7 133.1 5.6 1:10 109.9 6u.0 133.9 128.3 1:20 111.0 6h.7 137.7 128.8 1:30 108.0 65.0 138.2 130.2 1:10 108.3 65.u 138.7 131.9 1:50 108.2 66.0 138.7 130.1 2:00 111.9 66.7 136.7 126.1 Average 109.6 65.3 hfl.3 137.3 129.2 8.1 2:10 112.8 67.3 129.8 121.1 2:20 111.“ 68.2 124.6 117.9 2:30 108.9 68.9 121.2 116.8 2:”0 107.0 69.8 120.2 117.8 2:50 101.8 71.0 118.8 118.3 3:00 101.1 71.7 121.7 121.8 Average 107.2 69.5 37.7 122.7 119.0 3.7 3:10 102.8 72.5 125.” 121.7 3:20 102.1 73.2 125.9 121.6 3:30 105.6 73.9 128.5 12u.3 3:10 106.9 71.2 --- --- Average 108.” 73.5 30.9 126.6 122.5 4.1 44T1 = the difference between the laboratory ambient temperature and the outlet grain temperature (outlet grain minus inlet air). ATZ 3 the difference between the inlet grain and outlet air temperatures (grain in minus air out). I? = 2-c:-+ 32, 5 Table 39. 100 Moisture content changes during the cooling process in experi- ment 6 with a Ga/Gp ratio of 0.311 w.b. Time M 0 I S T U R E C 0 N T E N T (f d.b.) (hour) _ Probe Positions Inlet 1 2 3 u 5 Outlet cooler cooler 0:30 7.u0 7.12 7.10 7.13 6.99 7.28 7.07 0:”0 8.76 7.49 7.89 7.62 7.62 7.21 7.58 0:50 9.3“ 8.6K 8.uh 8.65 8.23 7.85 8.un 1:00 7.22 7.06 6.65 6.86 7.23 7.86 7.33 3:10 8.81 8.5“ 8.75 9.19 9.35 9.19 9.u5 Probes 1-5 were placed equidistant 11.7 inches (12.0 cm) starting at 19.9‘ inches (48.0 cm) from the inlet of the cooler. 101 8.5 - mo 8.0 - ”5:130 Moisture Content A 7'5 -1 120 m ’7 f\\ ‘3. ‘3 \ 3 '0 \\ E a g \\ A 5 7.0 1— a ' 3110 \ / \ 8 \ a E Grain Temperature \‘ é \\ {J m \ 2 6.5 \\\ 100 ‘w 6.0 — - 90 7 l l J L 1 l L l_-_______J 0.0 11.7 9.11 111.2 18.9 23.6 28.3 33.0 37.8 outlet cooler PROBE AND THERHOCOUPLE POSITIONS (inch) Figure 16. Grain moisture content and temperature profile during a specific cooling period in experiment 102 Table 40. Experimental grain moisture content and moisture removed (MR) per hour in experiment 6. Time Gp MOISTURE CONTENT (5 d.b.) MR hour wet b/ inlet inlet outlet 21110 lb/h ftz h ft dryer cooler cooler 0:10 444 11.57 8.89 8.33 0.56 0:20 444 9.76 8.45 8.22 0.23 0:30 444 10.07 7.40 7.07 0.33 0:40 444 10.91 8.76 7.58 1.18 0:50 444 11.72 9.34 8.44 0.90 1:00 955. 9.52. 1.22. 1.33. :9.11. ____. Average 444 10.59 8.34 7.83 0.51 2.26 1:10 444 11.66 9.12 7.43 1.69 1:20 444 11.88 9.63 9.01 0.62 1:30 444 12.11 9.34 8.96 0.38 1:40 444 11.17 9.20 8.77 0.43 1:50 444 9.81 7.87 7.75 0.12 2 = 00 95.9. 19.95. 8.12. 1.8.4. 9.2.8. __ rverage 444 11.11 8.88 8.29 0.59 2.62 :10 444 11.43 9.16 .43 0.73 :20 444 9.41 8.65 9.01 -0.36 :30 444 12.06 9.33 8.34 0.99 :40 444 11.32 10.41 10.35 0.06 1 :50 nun 12.03 10.02 9.91 0.11 1 =00 999. 11.19. 9.98. .9.99. 9.29. ____. i verage nun 11.33 9.59 9.29 0.30 1.33 I I I 3:10 nun 10.07 8.81 9.15 -0.64 1 3:30 nun 9.70 9.03 8.43 0.50 1 3:30 111 9.57 8.69 8.72 -0.03 I 3:40 999. .11.83. 9.89. 8.29. 1.51. ____. ' kverage 444 10.24 9.08 8.72 0.36 1.60 ‘ AMC = Inlet minus outlet cooler grain moisture content (5 d.b.). MR: Gp = Graig 1 lb/h ft Moisture removed, lb per hour per square foot. flow rate, wetzlb per hour per square foot. 3 ”.902 Kglh m o 103 Table 41. Heat balance in experiment 6 with a Ga/Gp ratio value of 0.34 w.b. Time HEAT (BTU/h) Latent/Tbtafl (hour) ggorn Air Heat Sensible* Sensible* Latent* Ratio* 1 4771.38 2506.10 2265.28 0.475 2 4919.80 2294.27 2625.55 0.534 3 3120.03 1777.25 1342.78 0.430 4 3367.45 1759.30 1608.15 0.478 * Values derived from equation 10. 1 BTU/h = 0.293 W. 104 1.0” O E: 0.5— /\ ____. «z a: l- < E i g 0.0— E c.- ..J -O.5'- -1.0 L J l J 1.0 2.0 3.0 “.0 TIME (hour) Figure 17. Latent/total heat ratio vs. time during cooling in experiment 6. 105 the outlet grain temperature was higher than the temperature values of the third and fourth hours. Adsorption of water by the grain occurred from 18.9 inches (48.0 cm) to 23.6 inches (60.0 cm) and from 28.3 inches (72.0 cm) to 33.0 inches (84.0 cm) [both measured from the top of the cooler]. In the rest of the cooler, desorption of water took place. As stated previously» if the temperature decreases during the cooling process. evaporation occurs. If the temperature increases. condensation takes place. Table 38 shows the air and grain inlet and outlet temperatures. During the first two hours, ATl was greater than during the third and fourth hours. This was due to the higher inlet grain temperature. The difference between inlet grain and outlet air temperature is represented by 4T2, which is higher during the first two hours (6.9°P (3.9°C)) than during the third and fourth hours (3.9°F (2.2°C)). Again, this was due to the change in inlet grain temperature. The time that the grain was exposed to the air was not sufficient to reach the equilibrium temperature. This is the reason why the inlet grain temperature remains higher than the outlet air value (AT2). Table 39 and Figure 16 show the moisture content and temperature behavior during the cooling process. Both, temperature and grain samples were taken at the same posi- tion and at the same time. Both show the desorption and adsorption intervals. The temperature behavior occurred for reasons described previously; Adsorption of moisture by the 106 grain took place at the bottom 23.6 inches (60.0 cm)of the cooler. Table 40 shows that moisture content of the corn de- creased in the cooling process. During the first two hours, the moisture removed was greater than the values found for the next two-hour period. This was due to the higher inlet grain temperature during the first two hours. Table 41 and Figure 17 show the heat balance. The latent/total heat ratio was not greatly affected when the inlet grain temperature was changed. In conclusion, experiment 6, with a bed depth of 3.0 ft (91.0 cm) instead of 2.0 ft (61.0 cm) showed that the mois- ture removal rate decreased in the third foot. The moisture removal and temperature behavior during cooling in experiment 6 are quite similar to the values of the five previous experiments. The outlet grain temperature was greatly affected by the inlet grain temperature. The additional 1-foot.(30.5 cm) bed depth doubled the amount of energy transferred to the air. 5.7 QQflMENI§_QN_EXREBIMBNIE.12§ Table 42 shows a summary of the most important results obtained in experiments 1 to 6. Shown are the inlet and outlet grain temperature difference, the inlet.and