CHELZENG @F HECEH MG-{STUEE CQRN A Swami chhiam {Qopwi' for fine Degree of M. 5. MECEEGAN STATE UE‘EWEKSET‘E’ 340% ii farts E? mfizomo :c9 2967 gnaw: LIBRARY ' A Michigan State University CHILLING OF HIGH fiOISTURJ CORN An AB 811 Technical Problem Report MICHIGAN STATE UNIVdfivIPY Noedjijarto Pratomo 1967 ABSTRACT CHILLIRG OF HIGH MOISTURE CORN by Moedjijarto Pratomo The preservation of product quality during storage is a problem confronting all segments of today's agri- cultural industry. The losses or changes which may occur due to insect and mold deterioration in product quality during storage are not only of economic impor- tance. but can also have an influence on the safety and health of animals and humans. The growth of microflora and resultant deterioration of wet (high moisture) grain can be slowed or inhibited by holding the grain at low temperature (chilling). Cooling wet shelled corn to a temperature of 40 degree F immediately after harvest greatly increases the allowable storage time over that possible at higher tem- peratures. Increasing the holding time of wet (high moisture) corn is advantageous in any method of drying. since drying cost decreases as available drying time increases. This study concerns with the analysis of the cool- ing process in a deep granular bed in relation with the temperature and air flow as the parameters. A cooling bin was designed and connected with a refrigeration system which provided air down to 35 degree a‘ r. This chilled air was forced through a vertical column MOLDJIJARTO PBATOMO of high moisture corn starting with an initial uniform product temperature. The temperatures throughout the bed were measured at intervals of twenty minutes by sixteen c0pper-constantan thermocouples connected to a recording potentiometer through a multi-point con- tact connector. Interstitial air velocities of 0.67. 1.85. 1.95 and 12.35 ft/min were investigated. Plots of temperature-time curves from the expe- rimental temperature history data were presented and comparative plots between the highest and the lowest air velocities were drawn for the deep bed of high moisture corn (2? to 29 5 moisture. wet basis). The plots indicate that with the increasing airflow. the time required fro the cooling zone to move through the corn was reduced. Equations for predicting the cool- ing time was presented. Recommendations based on this study are proposed for improving the analysis. 7,, APPROVED : [QM 251'? -. @921 major Professor ///;"/776 (E) 6/7 CHILLING OF HIGH MOISTURE C RN BY hoedjijarto Pratomo A REPORT Submitted to Dr. Fred Wilte BakkernArkema in partial fulfillment of the requirements for A. E. 811 Department of Agricultural Sngineering Michigan State University 1967 ACKNOWLEDGEMENTS The author wishes to eXpress his sincere thanks and gratitude to Dr. Fred Wilte BakkeruArkema (Major Professor) for his counsel. suggestions and inspiration during the investigation and throughout this study. Grateful appreciation is due to Dr. W. G. Eickert (Agricultural Engineering) and Dr. S. T. Dexter (CrOp Science) for serving on the guidance committee. To Dr. Carl W. Hall. Head of the Department of Agri- cultural Engineering. for providing a department in which a pleasant and stimulating working atmosphere prevailed. the author is indeed grateful. An eXpression of gratitude is also extended to the Indonesian Government and the Center for DevelOpment Programs of the University of Kentucky who have made the research possible through a grant and aid. This work is dedicated to his mother Mrs. M. Pratomo and sister Mrs. S. M. Soetoto. Their encouragement. love and sacrifice have been a great asset to him. 11 TABLE OF CONTmNTS Page INTRODUCTION . . . . . . . . . . . . . 1 amVIsw OF LITgflATUBd . . . . . . . . . . 3 OBJsVTIVE . . . . . . . . . . . . . . 10 EKPEBIMdNTAL . . o . . . . . . . o . . 11 material . . . . . . . . . . . 11 Chilling bin and Refrigeration . . . . 12 EXperimental Difficulties . . . . . 20 .NALYSIS . . . . . . . . . . . . . . 23 fifidULTS AND DISCUSSION . . . . . . . . . . 25 1. The effect of airflow on cooling time 25 2. The.effect of mass transfer . . . . 33 SJMMAd‘ AND CONCLUbIONS . . . . . . . . . 36 .1‘...C0r’mi.jiJDATIONS o o o o o o o o o o o o 38 libi‘juiiJJCJD o o o o o o o o o o o o o 39 APPENDIX . . . . . . . . . . . . . '43 iii Table 1a 1b 1c 1d LIST OF TABLES Experimental Temperature Va a 0.67 ft/min EXperimental Temperature Va 3 1085 ft/min Experimental Temperature Va 2 1.95 ft/min EXperimental Temperature Grain Moisture Reduction iv History History History History Data Data Data Data Page #3 44 45 46 47 Figure 1 10 LIST OF FIGUCdS Allowable storage time for shelled Corn at Various Temperatures and moisture Contents Relations of Storage Temperature and Grain Moisture Content to Insect Heating. Fall in germination and Camp Grain (Fungal! Heating Equipments used Jeneral View of the EXperimental Set-up Diagram of the EXperimental Deep Bed of Chilling of Corn equipment Thermocouple Location in the Deep Bed of Corn Hot dire Anemometer Filament Calibration Chart Plots of EXperimental Temperature History Data. Va = 0.67 ft/min. x = 1. 2. 3 ft. respectively Plots of mXperimental Temperature History Data. Va 2 1.85 ft/min X a 1. 2. 3 ft. respectively Plots of EXperimental Temperature History Data. va a 1.95 ft/min A = 1. 2. 3 ft. respectively Plots of Emperimental Temperature History Data. Va = 12.35 ft/min X = 1. 2. 3 ft. respectively Comparative Plots of Temperature History Curves Between the Highest and Lowest Air Velocities. i z 1. 2. 3 ft. reSp. Plots of Cooling Time in Relation to Air Flow Page 14 14 15 17 21 26 27 28 29 30 I! I! ll 1! SYMBOLS temperature of the air. degree F initial temperature of the product. degree F proportionally constant product surface area per cubic foot. ft-1 particle diameter. ft interstitial air velocity. ft/min porosity of packed bed. dimensionless product density. lb/ft3 air density. lb/ft3 specific heat of the product. Btu/lb OF specific heat of the air. Etu/lb OF specific volume of the air. cu. ft/lb time. hours coordinate distance from air inlet. ft Biot number. a hL/K thermal conductivity. Btu/hr ft 0F convective heat transfer coefficient. Etu/hr f‘t2 F time for leading edge. hour time for trailing edge. hour air flow rate. CFm/bu Reynolds number base of natural logarithm vi INTRODUCTION During the past quarter of a century the increase in field culture mechanization and. cepecially the advent in the past decade of the pickeresheller. has forced the corn grower to look for s new means of harvesting and storing corn. This change in technology in general has led to an increasing amount of “high moisture" corn being harvested each year. By I'high moisture corn" is meant corn with a too much moisture content that it cannot be stored safely by conventional methods. The technological changes have not been limited to an increase in mechanization. The use of hybrid varieties with long growing seasons has increased the total corn production and made harvesting at high moisture content practically a ‘ necessity in many localities. Reports of work regarding storage. cooling and chilling of grains in this country indicate that little work has been done in this field and most of the work has cccured in Great Britain. The storage of moist grain by chilling has been practiced in Western Continental EurOpean countries for more than five years. but was not used in Great Britain until 1963. Since that time considerable interest has been shown by farmers. maltsters and corn merchants. Chilling is the lowering of the temperature of fresh produce to inhibit the growth of microorganisms and to preserve its quality. 9. Chilled high moisture shelled corn has an allowable storage time of several weeks. during which various conditi- oning or marketing options can be applied. These Options include 11) reducing the moisture contents of the corn by dehydrofrigidation. (2) arresting reSpiration and subsequent deterioration of the grain for longer storage by lowering the grain temperature to 32 degree F or below. (3) drying the corn at a more leisurely rate with conventional heated air drying equipment. (4) marketing the wet grain through regular marketing channel. and (5) selling and delivering wet. parti- ally dried. or dried corn to a grain processor. REVIEW OF LITERiTUHE The growth of microflora and resultant deterioration of wet (high moisture) grain can be slowed or inhibited by holding the grain at a low temperature (Shove. 1966). Increasing the holding time of wet corn is advantageous in any method of drying. since drying cost decreases as available drying time increases. In storing and drying wet grain it is important to know how long the grain can be held without excessive damage (dry matter loss). This information is particularly needed for in-storage drying. The time available for drying depends on the relation between the temperature of the grain and its moisture content (Beaty et al.. 1965). Net corn harvested and stored at 70 F must be dried in a few days to prevent deterioration (Figure 1). This relatively short drying period can create a bottleneck in the flow of corn at harvest time. As shown in Figure 1. the safe storage time for wet grain varies with moisture content and grain temperature. Corn harvested at 30 percent moisture and 80 F must be dried in about 2 days: however. if the same corn is harvested and stored at a temperature of 40 F. the drying time can be extended to 20 days. If 18 to 20 percent corn is harvested and stored at 30 to 40 F it can be kept 2 or 3 months. Shelled corn that is to be fed to livestock does not have to be dried if it is field-shelled when temperatures are low or is cooled after it is stored. However. it will have to be fed during the safe storage period (Figure 1) or dried to a OF GRAIN TEMPERATURE, ‘fifit l I‘Lfig o 10 20 3o 40 50 60 7o 80 9o ALLOWABLE STORAGE TIME, DAYS Figure 1. Allowable storage time for shelled corn at various temperatures and moisture con- tents. During this time the grain will lose % percent in dry matter, but will still be acceptable. Data are from the U.S. Department of Agriculture Grain Storage Research Laboratory, Ames, Iowa. moisture content of 12 to 13 percent for safe longer term storage (Beaty et al.. 1965). Grain deterioration is related to respiration of the grain itself and of the accompanying microorganisms. and the production of carbon dioxide is a product of this reSpiration (Steele et al.. 1962). Since the evolution of carbon dioxide can be measured readily. measurements of carbon dioxide were used by Steele et a1. (1962) as an index of deterioration. Such measurements can also be translated to loss in dry matter in the grain. For the purpose of their study. aerobic respi- ration with the complete oxidation of carbohydrates to carbon dioxide and water was assumed. The complete combustion of a typical carbohydrate is represented by the following equation: C6312 06 + 6 02 «.96 c0 2 + 6 320 + 677.2 Cal From this equation it may be computed that one percent loss in dry matter in the grain is accompanied by the evolution of 14.7 grams of C02 per 1.000 grams of grain dry matter (Steele et a1. 1962). Three ways of decreasing the respiration rate of grain according to Haugh (1964) are: (1) to decrease the moisture content of the grain. (2) to decrease the temperature. and (3) to decrease the available oxygen supply. These three factors. moisture. temperature and oxygen are all inter-related. hilthorpe et a1. (1948) reported that moisture content is the most critical of these three factors. In connection with the safe storage. insect heating. fall in germination and fungal heating. surges and Burrell (1964) produced a useful diagram (Figure 2) on the relatinn of storage temperature and grain moisture content. It was compiled from a large number of sources. Thus. at moisture contents up to about 22 3. grain can be stored safely for a reasonable time _ at temperatures of 41 F.or below. which can be obtained by refrigeration (chilling). Insects will not develop if the temperature is below 63 F. This is true of dry or wet grain. and therefore reduction to this temperature is a method of insect control. To control molds. bacteria and mites a much lower temperature must be used. dependent on the moisture content of the grain. A study of the effect of temperature on the radial growth of the fungus on agar by Tuite et al. (1966) revealed low tem- perature to be an importance limiting factor. Growth was markedly decreased at 12 C (53.6 F) and below.‘ DevelOpment of molds and insects in grain. and their control. can be related to three different levels of moisture content as follows (Hyde. 1965): Moisture content Insects and Micro-organisms of the grain controlled by a. Up to 15 percent Low moisture content: cooling with untreated air. b. 15 to 25 percent Drying; refrigeration (only up to 20-22 percent moisture content); ordinary airtight storage. c. 30-40 percent "Silage“ techniques (and unstable form of airtight storage). OF EQUILI?BBIL?JM §E%T;XE‘§9HU§I?IT¥ A; 32 F TO 77 F T0 T0 T0 T0 I‘O'I‘O T0 T0 T0 T0 53 51 6R 73 78 82 84 86 89 89 t 100. I 90” 80 - I O <§§g $$23§26 $333333: 0 0 $ 0 q; es 3% Egg co 4 T 4 I P t t 5 t t ‘5 b l $ €;’ 0 ‘3 ‘% ‘% ,4 cvbdt éflflflflf away» “3‘33: §&%%> VQflk» Vfifi? gfiflV wfiQ’ 503603 0990 Figure 2. SAFE INST HEAT 70 . m“ CI: :2 v 5: 00 ~ .(I it? soL 5 40 - 30 ....... i ......... 10 15 20 25 % MOISTURE Relations of storage temperature and grain moisture content to insect heating, fall in germination (to 95% in 35 weeks storage) and damp grain (fungal) heating. Broken lines indicate extrapolation. (Burges and Burrell. 1964). FUNGAL D HE: ATI AJG E] CT “ FALL IN a I iJG \ G ERMIE‘J "aTION EXperience so far suggests that different species of micro-organism are involved at the different moisture levels. Those growing at moisture contents up to 25 percent are mold fungi that require oxygen for growth. and die in its absence ”'(Semeniuk. in Anderson and AlcockJi954). The organisms (pro- bably bacteria) active at the higher moisture levels are less dependent on oxygen and flourish under acid conditions such as deve10p during the production of silage (Hyde. 1965). Four fungi grew in high moisture corn (23 - 28 %) stored in the presence of low oxygen and high carbon dioxide conceno : trations at 60 and 73 F (Tuite et a1.J1966). They were. in the order of their anaerobic abilityldYeast. mucor. Fusarium Moniliformae and Penicillium. Only the last two affect the feeding value although there are no specific studies on Mucor and the species of yeasts found in high moisture corn. Bacteria as observed by Burmeister et al. (1966) indicated 8 per gram) at their presence at substantial numbers (10 moisture contents of 28 Z and above. Mold will develOp on the surface of shelled corn when the temperature and humidity of the air in contact with the corn is favorable to mold growth (Dexter. 1957). Shelled corn. therefore. will keep without molding. regardless of its internal moisture content. so long as the grain is in an environment unfavorable to mold growth. Semeniuk (in Anderson and Alcock. 1954) found that a mini- mum relative humidity of 80 percent (at 85 F) in bulk bins is required for continued growth of molds. A relative humidity of 80 percent corresponds to an equilibrium moisture content of about 15.6 percent. wet basis. for corn at 77 F (Hall. 1957). In these tests. there was no evidence of mold. OEJdCTIVi In order to obtain quantitative information on the time required for a cooling zone to move through packed beds of agricultural grains. it was found necessary to undertake an eXperimental study. High moisture corn vere used in this investigation. The product temperature at difference longitudinal locations F‘W in a deep bed was measured at regular time intervals. EXperimental temperature-time curves were plotted and equations for predicting the time required for a cooling zone to move through corn grains were derived. From this preliminary study. it is heped that conclusions can be reached which will provide direction in the endeavor to improve the present analysis. 10 EX‘93IAENTAL "D ['1 Material The high moisture shelled corn used in this study had been harvested with a picker sheller. and was obtained from a local elevator in Mason. hichigan. It was cleaned of trash and small pieces of corn kernels which included some damaged kernels (less than 5 1) were removed. Moisture content at shelling was about 29 percent. wet basis. It was then placed in gunny bags (80 - 90 lbs weight) and stored without a preservative in a walk-in cold storage chamber maintained at 20 F until the time the grain was needed for chilling tests. Initial moisture contents were 27 to 29 percent for all tests. In this study it was necessary to rewet the grain until the average moisture content for all materials had reached 28%. Hukill et al. (1960) reported that rewetted grain dried some- what more rapidly than naturally wet grain. Findings by austrulid (1963) indicated that naturally moist corn. frozen and thawed kernels. and carefully remoistened kernels all had the same drying characteristics. The rewetting was done by carefully remoistening the kernels in a rotating drum for about 15 minutes. Preliminary work verified that after 15 minutes rotation the materials had been thoroughlywetted. After each thorough wetting. the mate- rials were put back in the freezer for a week before being used. At this time two bags of the frozen grain were removed out of the 20 degree F freezer. spread on a canvas and allowed to 11 12 thaw and warm to room temperature. As the corn was removed from cold storage. ice crystals were noticed on the grain surface. However. after the grain had come to room tempera- ture without any further exchange of air. there was no notice- able surface moisture. The moisture content of each sample of corn was determined before and at the end of each test by using a one stage oven procedure ( Figure 3 ). A 20-gram grain sample was weighed Lfli with an analytical Hettler balance. The balance was a fast- reading type with an accuracy of 3 0.05 mg. The samples of corn (four replications for each moisture level) were placed in the oven for 24 hours and the temperature of the oven was maintained at 200 degrees F. ghilligg Bin and Refrigeration Unit The deepobed chilling of high moisture corn was studied using a double-insulated column of dimensions: 1'! 1': U' deep ( Figures fl and 5 ). The column was filled with approx- imately 3.2 bushels of corn for each test. The bed was connected to a fan and refrigeration system which provided air down to 35 degree F. Chilled air was forced through the column of material. and temperatures thoughout the bed were measured at intervals of 4 minutes by 16 copper-constantan thermocouples. The refrigeration system was of the direct-eXpansion type. The condenser was of the air-cooled type and the compressor was totally enclosed. hermetic type. with the electric motor as an integral part of the compressor casing. The eXpansion 13 valve was thermostatically operated. Air was drawn over the evaporator from the room through door D1 ( Figure 5 ). After passing through the fan F2. this chilled air partially was exhausted through the deep bed into the room and partially was recirculated back over the evaporator from door D3 to door D2 thus repeat the cycle. This makes a considerable saving on the hersepower of the refrigeration plant. since the air drawn in from the plenum chamber is cooler than the air drawn in from the room. The centrifugal fan was placed after the evaporator in the chilled air duct. thus automatically reheating the air by 1 to 2 degrees F. This caused the chilled air to drop from a relative humidity of about 100 - 95 Percent to 85 - 80 per- cent relative humidity. A thermostatic eXpansion valve with its sensing bulb located in the air-stream Just after the evaporator was used to maintain a relatively constant air temperature during a given test ( Figure 5 ). At temperatures approaching freezing the evaporator coils in the chilling unit might freeze up. An automatic defrost system was installed to avoid this and operated for about three minutes per hour. A water collecting tray mounted beneath the cooling coil collects the water and allows it to drain away through a drain hose connection ( Figure 5 ). During the defrosting period the air from the evaporator was exhausted through fan F1 directly into the room rather than passing through the deep bed. The Operation of the defrost system can be described as follows: 14 mqu' , UFGRW -.;?§5:'.-'§:’:'E.' ’Zli. IULY|966 ooooooooooooooooo 00000000000 ............ oooooooooooo 000000000000 oooooooooooo on lot llClElSE visvtnaVUIE near! 100 f rolsrnct colvscr on llllfl DVEI hung: 3. ICE jigure 3. Equipments used. From left to right: A. mettler Ealance Model K—7T t. mettler Balance Model B-S C. Oven Figure 4. General View of the EXperimental Set-up. (Arrow indicates the direction of Airflow). ‘ \\\\\\\\\\\\\\\\\\\\\\\\\\V .\\\\\\\\\\\\\S \ Room Air Intake 15 Corn / VIIA' 'IIIII l—e Vl‘ Uri/III] _., FH‘ ~‘ 00 9 \\\\\\\\\\\\\\\\\\~’ k\\ n U! CID fl § sxxwxwxawx§§ . 00 U] / M \ ‘oo \ J D-H. Diagram of the EXperimental Deep Bed Chilling of Corn Equipment. 5. Figure 16 Figure 5. Diagram of the sXperimcntil Deep Red Chilling of Corn Equipuent Insulated Column ( 3/4" dtyroform Sheet and Glass Fibre on the inside ). Thermocouple Junction 91. 02, 03. 34, = sliding Doors PHI , ’1.) m n "U ll FBZ = Flexible Hose insulated with Glass Fibre on the outside. exhaust Fan Corn.Fan Lvaporitor Coil deter Tray mounted below the dvaporator Coil. Plenum Chinber oensing bulb ( fqermostatic 3Xpansion Valve ). 17 X T10 Ira FT y {,9 M .,3F1‘ M £92.}th 6 .. 2 FT 1 1 b 5 ll ’4' m, 1 FT H 3 H J Figure 6. Thermocouple Location in the Deep Bed of Corn. 18 Operation Corn Fan Exhaust Fan Hot Gas F2 F1 (Refrigerant) 1. Cooling ON OFF OFF 2. Start to defrost OFF ON ON 3. After 3 minutes OFF ON OFF Q. After 2 minutes ON OFF OFF The capacity of the refrigeration unit was one ton and the horsepower of the centrifugal fan was 0.5 HP. The temperature of the air entering the granular bed was to 0F 1 1 °F for all tests. To maintain this temperature throughout the test was not an easy Job. The initial corn temperatures were 80 °F 3 1 °? and moisture contents varied from 27 to 29 percent. wet basis. The cepper-constantan thermocouple Junctions were located every 6 inches along the vertical x-axis of the column. Four thermocouples were located in the middle of the column along the I-axis 1i ' appart. One was located Just before the chilled air entering the grain column and one each in the plenum chamber and after the corn fan. The remaining 9 ther- mocouples were installed along the vertical X-axis of the column as shown in the diagram ( Figures 5 and 6 ). The co-planar thermocouples were spaced to verify the assump- tion that there was no lateral temperature gradient within the deep bed. The thermocouples were connected to a 16-point re- cording potentiometer through a multipoint contact connector. During the tests. the temperature recorder made a continuous 19 record of the temperatures throughout the grain column for the first three hours. and then a time clock on the potentiometer was used to allow one complete cycle of points to be recorded each twenty minutes. The airflow was varied by sliding the control door D1. Doors D2 and D were employed to direct the air flow. Door Du was used to coitrol the incoming air flow to the test bin. Before starting a test and filling the bin. the whole unit has been cooled for about one hour to make sure that the bin and the ducts were at the cooling temperature. The chilled air was passed through the bin and out to the room by opening D4 until the thermocouple in the plenum chamber registered 40 degree F. Filling was then began. and interstitial air velocities of 0.21. 0.58. 0.61 and 3.86 CFM/bushel were in- vestigated. After the grain column had been filled. the air flow rate for each test was adjusted by changing the volume of the air until the proper amount of CFM was obtained. For each test. the mean interstitial velocity was deter- mined by two methods and the results averaged. One method was by direct measurement of mean air velocity (‘V ) before and after the grain column using a hot wire anemometer. The mean interstitial air velocity was then computed by the relation: Va 8 g/f where: Va 3 Interstitial Air Velocity. ft/min. '7 f I! mean Air Velocity. ft/min. porosity. dimensionless. where f is observedtx> ix? 0.00 (Thompson ans Isaacs. 1966). 20 The second method consisted of a chemical smoke tracer: the smoke was injected into the air stream at the bottom of the grain column. The time at which the first trace of smoke emerged frgm the tsp of the grain column was clocked with a stop watch. This method gave a direct value for Va. The hot-wire anemometer was calibrated in a wind tunnel using a pitot tube and a micro—manometer. Readings for zero ‘Nfi velocity or still air and for marina velocity were taken and the necessary calibration curve of I2 versus V% was drawn as shown in Figure 7. ggpggimental Difficulties ; a The difficulties in this form of experimentation are numerous. and most of them are not encountered in steady state measurements. 1. Care must be taken to ensure that the thermocouples are reading accurately. The thermocouples should be checked for accuracy by taking readings for ice at 32 degree F and for boiling water at 212 degree F. Accuracies for the thermocouples readouts should be at most 3 11 of the full scale. Considerable improvement in accuracy is achieved by careful calibration of the instrument in the Operating range. 2. Because of the small size of the corn kernels. it was not possible to locate the thermocouple Junctions inside the individual seeds. Instead. intergranular epace temperatures were measured. These measurements are at best bulk values 21 .pnmxo cofipmppfiamo pamsmafim gmpmfioaecm mpfiz pom AZHE\BL H >v ,> mm om mm om ma OH .m spam H CL. 11 _ _ _ — _ m on u manpmamaame MOH " em om 0000 0000 000m ooox ooom oomoa (w = I) 3. 22 for the air stream and grains and are inadmissible where the exclusive air or grain temperature is to be determined. Special care is needed to ensure a uniform air velocity dis- tribution in the bed. This is not an easy task. Furnas (1930). reports that even in beds of solids which were apparently uniform. it was virtually impractical to maintain a uniform fluid flow over the entire cross section. In beds of non-uniform products. this may lead to erratic errors. One of the procedural problems involved in analyzing the results of the laboratory tests was determining when the grain was cool. Theoretically. the time required to cool the grain exactly to cooling air temperature is infinite. As the cooling zone moves out of the corn. the rate of heat removal drops and the cooling time is increased proporti- onality. In these tests the corn was considered cooled when the top layer (thermocouple no. 10) had cooled two- thirds of the way from its initial temperature to the cooling air temperature . At this point. between 85 to 95 percent of possible cooling had been completed. 23 AJALYSIS figthesatigil Consideration of Cooling. When cool air is forced through a mass of grain. a cooling zone will develop and progress through the grain in the direction of airflow. The thickness of the zone and the Speed at which it can progress through the grain mass depends upon some function which describes the cooling rate of grain in relation to air Ff“ velocity. At any instant of time. Newton's law of cooling describes . the rate of change of grain temperature for any point in the mass (Hall. 1957). This is given by: d? = c}: (I: "' Ta) (1) dt where t = time. hrs. Tan air temperature. degree F *J T a grain temperature. degree x k = proportionality constant. .The solution of equation (1) is as follows: Q .31; T = cs + Ta when t = 0. T = initial grain temperlture. T1 so that T1 = c + Pa (3 =21 . Ta ~kt then T =(T1 - Ta) e + T This is recognized as the half-response equation 24 a sever. since it is impractical to supply the volume of air required to maintain the air temperature surrounding each kernel of grain at a constant level. equation (2) cannot be applied directly but must be related to airflow and air tem- perature. It appears that the effect of airflow rate or cooling time must be described by two different time periods (Sorenson et al.. 1966). The first period is the time for the leading Eh“ edge of the zone to move through corn grain ( TL ) and can be described as the time at which the air exhausted from the grain first starts to decrease in temperature. The second period. the trailing edge period. would be determined by the depth of the acne and the rate at which it moves. Under the conditions of this study. the author found.that the first period is closely approximated by: g -o.1495 where TL a time for leading edge to move through the grain. hours. Q a flow rate of air entering the grain. CFn/bu. The time indicated in Figure 10 for the trailing edge to move through the grain represents the total cooling time required. Jnder the conditions of these tests, this time can be expressed 35! l-Oo3214' where T H time for trailing edge to move through the grain. hours. Q a flow rate of air entering the grain. CFu/bu. RnbULSS AJ' JISCUSSION Ihe experimental data obtained for the packed bed are presented in fables 13 through 1d. Four different airflows were employed. and the cooling air temperature was 40 degree F for all tests. Initial grain temperature were 79 to 80 degree F and the moisture contents varied between 27 to 29 g wet basis. These data are plotted as temperature-time curves in Figures 83 through 8d. fhese curves indicate the tempe- ratures of shelled corn at different heights in the packed bed as a function of time. The correSponding temperature history curves between the highest airflow rate for this eXperinent. (12.35 ft/nin). are plotted along with the lowest airflow rate (0.67 ft/nin) for purposes of comparison (Figure 9). fhese conpmrutive curves and their significance will now be discussed. 1. The effect of air flow on cooling time: The temperature-tine curves were drawn at 3 ft. 2 ft and 1 ft from the inlet air. It is suspected that the somewhat erratic nature of some of the recorded data (Tables 1a. b. c. d) stems in part. from the irregularity of the grains. This irregularity makes the essage of air and the transfer of heat a very uncertain and changing process. To have any significance. it is necessary to obtain data which are the statistical averages of the temperature of an entire plane. Furnas (1930) suggests for example. that the only practical way to obtain an acceptable value for the temperature at any given position. is to force all the air passing a given plane in the bed through a smell 25 .mm>pso AHOpmHm mMSQmeQEmH HapCmSHHmQNm .mw mhsmfim mmbom . mw .mrHH NH 3 x o a m 26 GHQ mo soupon 809m Spmmv :Hmho mmmumm eggpmfioa :Hmpw HmeHcH m ZHE\B& Nmo.o H > om Oi om oo .05 on ‘WEDJVEWdVEJ C 889$ H 10 27 L): FR, ‘ t . I, . neflaln. .mm>hzo %L0pmfim.mpzpmmeEme amquEHthNm .Qx mpsmfim mmbom . 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O FUIO‘V 0.2 0.1 CORN GRAIN INITIAL GRAIN CONDITIONS: 79-50 F, 28-29% MOISTURE AIR ENTERING GRAIN: 40 F DRY BULB 37 F DEN POINT EQUATIONS FOR PREDICTING COOLING TIME: . “0015 TL = 0.45 Q -o.32 \ \ \ \ L \ | (L 1‘. 7\ I? o, i- x L V‘ “A ( \ E 13" a \ \ \ \ \ \ \ \ 0.5 0.7 1 2 3 45078910 20 IIEE REqUIRED EOE EDGE OE COOLING ZONE IO EOVE THROUGH GRAIN ..... HOURS Figure 10. Cooling Time in Relation to Air Flow. 31 32 orifice and measure the temperature of this air stream. fhe necessity for a uniform air velocity distribution in the bed has already been pointed out. Ihis is very diffi- cult to ensure. particularly for irregular beds. It is probable that the erratic nature of some of the data in Tables la. b. c. d may have resulted from a possible non-uniform interstitial air velocity in the stream. Cooling first occurs where the air enters the grain and I;“ proceeds through the grain in the direction of air flow. The thickness of the cooling zone and the Speed at which it can progress through the grain mass depends upon some function I it which describes the cooling rate of”: sin in relation to air *" velocity. After the front of the cooling zone has advanced through the grain. the air conditions leaving the grain will follow a definite pattern with time. depending upon the rate of air flow and the rate at which the temperature of the air surrounding the grain is changing. Cooling times were decreased with increasing air flow for all depths of the packed bed (Figures 8a. b. c. d and 9) and the following relationship between temperature and velocity of the cooling air is presented: L = 0.48 Q‘O°15 -O.324 where TL 2 time for leading edge to move through the grain. hours. time for trailing edge to move through the grain. hours. 5-: ll flow rate of air entering the grain, CPL/bu. I- N 33 The increasing agreenent between the curves at low air {1’1 flow rates is eXplained by the effect of Reynolds number on the heat transfer coefficient (Bakker and Eicxert. 1966). At low Reynolds number. 1.9.. at low air flow rates. the heat exchange process proceeds with considerable slowness. The air temperature change with time is therefore slowed down and may become negligible at very low values of Bey- nolds number. A definite correspondence in shape is observed between the highest and lowest curves. fhis is eXpected since the equations on which the curves are based are identical. The difference is observed to diminish with decreasinr air flow rates. but widens with increasing depths in the column. The aethod that has been described here can be used to correlate eXperimental data. and predicting the cooling time. As the agricultural product situation departs further from the ideal. the accuracy of predicting cooling rates become less precise and finally the ability of the method to correlate cooling data is effected. 2. The effect of mass transfer: Oven though the eXperinental moisture data (Table 2) indicate only an average moisture loss of 0.4; (wet basis) in each test. the equivalent heat energy required to accom- plish the transfer is substantial. This energy will be taken from the zair and the product. leading to evaporative cooling. 34 Cooling a wet product by convection. such as cooling grain by passing chilled air through it. removes some moisture from the product. Assuming that the system is ideally insula- ted. that is any source of external heat is excluded. the heat for evaporating the moisture and heat for increasing the temoe- rature of the air must come from the product. The moisture content of the product being cooled determines the dcgree of saturation of the air exhausted from the warm product. As an example. the equilibrium relative humidity is nearly 100 percent for shelled corn having a moisture content in excess of about 22 percent. wet basis: and air exhausted from the corn will be nearly saturated. The theoretical capacity of air for cooling and removing moisture can be obtained from a table of the prOperties of moist air or from psychrometric chart. Assuming a value of 0.55 btu/lb.OF (Shove. 1966) for the specific heat of wet shelled corn. a satisfactory quan- tity of air for cooling corn from harvest temperaturesof 60 to 80 OF would be one pound of chilled air per pound of shelled corn. Using a Specific volume of 12.5 cu.ft/lb of chilled air. the air flow rate for cooling shelled corn in a 24 hours period becomes: (1 lb chilled air/lb corn) (12.5 cu. ft[lb chilled air) . 1.440 minutes ” 3 0.00868 CFh/lb. corn or approximately % can of air per bushel to cool shelled corn from harvest temperatures to 30°F to 40 OF. The moisture content of the corn should be reduced by about one-half of one percent during the cooling period. 35 Moisture loss from the product during cooling increases the effective Nbiot number of the product slightly. because latent heat is absorbed from the product (Bakker and Bickert. 1966). The nature of the product will effect the rate of moisture loss. All the corn samples used in these tests under the different air flow rates maintained their physical and bio- logical appearances throughout the test. Corn quality is no different than when it was first loaded in the bin. This study has attempted to cover some fact in the chilling of high moisture corn. It must be well remembered that this particular application of refrigeration is compa~ ratively new and there is still a considerable amount of research to be done on the behaviour of corn when chilled at this low temperature. At this moment it appears that the greatest application for this method is where a farmer is using the grain for feeding. There are however indications that millers are interested in holding large quantities of grain at low tem- perature. drawing from store as and when they require it for drying. by this means the miller can keep the drying Opera- tion under his own control. bflnnnflY AND CJRCLUSIOHS Each year a greater amount of corn cores from the field in shelled form. Technological advances in harvesting. however. have ca-sed problems to farmers and elevator Opera- tors because the large amounts of wet shelled corn harvested rust be either dried or cooled quickly to prevent Spoilage. vet. chilled corn can be stored for several weeks (Figure 1) without deterioration. Insulated storage will decrease the ties that the refrigeration equipment will need to be Operated to maintain the grain at a low temperature. The following conclusions can be drawn free the study of the experimental temperature history data: 1. The fundamental irregularity in shape of agricultural grains together with the basic anisotrOpy of the bed constitute unavoidable sources of error in the analysis. 2. For agricultural products. the heating or cooling process is inevitably accompanied by mass transfer. 3. High moisture corns was cooled from 80 degree a to 40 de- gree F. The moisture content of corn. ambient temperature and airflow rate each affected the safe storage tine. Data from tests were used for preparing graphs to show the inter-relationships among these variables. 4. when cool air is forced through a mass of grain. a cooling zone will deveIOp and progress through the grain in the direction of airflow. The thickness of the zone and the speed at which it can progress through the grain mass 36 37 depends upon so?) function Which describes the cooling rate of grain in relation to air velocity. The.tine required to cool grain in storage is a function of the rate at which air is supplied through the grain. equations for predicting the time required for a cooling zone to move through corn grain are presented. 5. The effect of evaporative cooling are very beneficial in reducing the time required to move a cooling zone through grain and in reducing the refrigeration load requirements for cooling. Foster (1965) states that the heat to eva- porate the moisture comes from the grain and accounts for about half of the coolirr. He also found that the air required for cooling the grain is reduced preporti- anally. Even though the eXperimental moisture data (Table 2) indicate only an average moisture reduction of 0.4 % (wet basis) in each test. the moisture loss during cooling could be an advantage if the initial moisture content of the grain is higher than the desired final moisture content. bVen if moisture loss is undesirable from the standpoint of excessive loss in weight. it is not considered a problem when grain is stored for a reasonable period of time. Tests have shown that the average moisture content can be re-established after the grain has been cooled by controlling the relative humidity of the entering air at the proper level. 1. 2. nvnrumfmfliTIOJ“ LLLl‘udhéiLLJl‘J A s O From the eXperience gained. further study should be undertaxen to further develcp the relationship between cooling time. moisture content ratio. airflow. and tem- perature of cooling air and relative humidity with grains above 35 percent moisture content. wet basis. with picker sheller grains are harvested at higher P“ moisture content and work should be done on corn above 35 percent moisture content. a. Study the resistance to the airflow. F b. Shrinkage problems. i_ The constants ( Equations 3 for leading edge and 4 for trailing edge ) developed in this study should be inves- tigated further. dhile they were the fundamental rela- tionship describing the manner by which the cooling zone will move for Optimal airflow. they have not been yet correlated with quality factors in biological material. such as stress cracks in corn. EXperimental inventiga- tion should be made to determine if any correlation exists between the time required to cool a grain and the quality of the product resulting from the process. The author suggests for the next work to verify the importance of evaporative cooling. If the air tempera- ture is a true indication of grain temperature. then the heat of evaporative cooling (13H ) must be deteruined for the various conditions which are present in controlled storage environments for bulk grain. 38 1. 2. 3. 7. 9 .i? . |:\ ." RT“. ,' S 11 a.“ “511.11.! u 2.4 Anderson. J. A.and Alcock. A. W.. Storage of Cereal Grains and Their Products. American Association of Cereal Chemists. St. Paul. Minnesota. 1953. Eakker-Arkema. E. N.. and Eickert. W. E.."Daep Bed Sugar-beet Cooling." Paper No. 66-350. Annual meeting A.S.A.d.. University of Massachusetts. Ed June 26-29. 1966. Beaty. H. H.. et al.. ”Drying Shelled Corn". Circu- lar No. 916. Coop. Ext. Service. University of Illinois. 1965. ‘ Burmeister. H. 3.. Hartman. P. A.. Saul. R. A.. lMicrobiology of ansiled High moisture Corn". Applied microbilogy. Vol. 14. No. 1. 31-34. January. 1966. surges. H. 0.. and Burrell. N. J.. "Cooling Bulk of Grain in the British Climate to Control Storage Insects and to improve Keeping Quality". J. Sci. Food Agriculture. Vol. 15. January. p.32-50. 1964. Dexter. S. T.. "moisture Equilibrium Values in Rela- tion to Hold Formation of deeds of 3eve~al Grass and small-Seeded Legumes". Agronomy Journal. Vol. 49. No. 9. p. 485. 1957. Foster. G. H.. "Dryeration. A Corn Drying Process". Agr. Marketing service. No. 532. April. USDA. mashington DC. 1964. 39 9. 10. 11. 12. 13. 15. 16. 40 Foster. G. H.. ”Moisture Changes During Aeration of Grain". Paper No. 65-921. Winter meeting A.S.A.E.. Chicago. December 7-10. 1965. Furnas. C. C.. "Heat Transfer From a Gas Stream to a Bed of Broken Solids - I." Ind. Eng. Chem.. 22. 26. 1930. Furnas. C. C.. "Heat Transfer From a Gas Stream to a Bed of Broken Solids - II.” Ind. Eng. Chem.. 22. 721. 1930. Hall. Carl w.. Drying Farm Corps. Edward Brothers. Inc.. Ann Arbor. michigan. 336 pp.. 1957. Haugh. Gene C.. "Isothermal Diffusion of Oxygen within r Sealed Grain Storages". Unpublished Ph. D. Thesis. Purdue University. Lafayette. Indiana. 196#. hukill. N. V.. and Schmidt. J. L.. ”Drying Rate of Fully SXposed Grain nernels.” Trans. A.S.A.m.. Vol. 3. No. 2. p. 50. 1960. Hustrulid. Andrew. "Comparative Drying Rates of Natural- ly Moist. hemoistened. and Frozen Jheat." Transac- tions of the A.S.A.s.. 6. a. 304-308. 1963. Hustrulid. Andrew. "Basic Studies in Drying Shelled Corn." Minn. Farm and Home Sci.. Vol. 21. No. 1. p. 4. Agr. Exp. Sta.. University of Minnesota. St. Paul. Minnesota. Fall 1963. Huxsoll. C. C.. "Some Environmental Factors Influencing Deterioration of High Moisture Shelled Corn in Her- metic Storage." Unpublished M.S. Thesis. Purdue Uni- versity. Lafayette. Indiana. 1961. 41 17. Hyde. nary 5.. ”Principles of Wet Grain Conservation." J. and Proceedings of the Institution of Agricultu- ral Engineers. 21. 2. p. 75-82. London. 18. Kreith. F.. Principles of Heat Transfer. International Textbook Co.. Scranton. Pa.. 620. 1966. 19. nilthorpe. Joan. and Robertson. R. N.. "Respiration of Dry Grain. Insect nespiration and Teaperature and moisture Effects.” Australian Counsil Sci. Ind. Res. Bull.. No.237. p. 9-17. 1948. 20. nunday. G. D.. "Refrigerated Grain Storage." J. and Proc. of the Institution of Agric. Engineers. 21. 2. p. 65-79. London. 3 21. Olver. E. F.. et al.. ”Proceedings. Grain Conditioning Conference". Agricultural Engineering Department. University of Illinois. January 17-19. 1967. 22. Person. N. K.. Jr.. Sorenson. J.N.. Jr.. and McCune. N. E.. "Thermodynamic Considerations in the Design of Con- trolled Storage Environments for bulk Grain." Paper A.S.A.E.. 64-825. Winter meeting. New Orleans. La.. December 8-11. 196“. 23. Ross. I.J.. and Isaacs. G.w.. "Forces Acting in Stacks of Granular Materials." Transactions of the A.S.A.E.. 4! 1- P0 92-96. 977100. 1951. 7 24. Scheidegger. A. E.. The Physics of Flow Through Porous media. Haemillan. New York, 1960. 25. Shedd. C. K.. "Resistance of Grains and Seeds to Air Flow". Agro Engoo 34! p0 6160 19530 111nm. -. -. - 26. .27. 28. 29. 30. 31. 32. 33. 42 Shove. Gene C.. Associate Professor of Agricultural Engi- neering. University of Illinois. Urbana. Illinois. Personal CorreSpondence, November 18, 1965. Shove. Gene C.. ”Application of Dehydrofrigidation to Shelled Corn Conditioning.” Paper No..66-351. Annual meeting A.S.A.fi.. University of Massachusetts. June 26-29. 1966. Sorenson. J. w.. Jr.. Person. N. K.. Jr.. and McCune. W.E.. "Design Methods for Controlled Environment Storage of Grain”. Paper No. 66-417. Annual Meeting A.S.A.E.. University of Massachusetts. June 26-29. 1966. Steele. J. L.. and Saul. H. A.. ”Laboratory Measurements of the Rate of Deterioration of Grain during Drying". Paper presented at the Annual Meeting of the Mid-Cen- tral Section of the A.S.A.E.. Lincoln. Nebraska. March 30. 1962. Stoecker. N. F.. Refrigeration and Air Conditioning. p, 134, mcGraw Hill. New York. 1958. Thompson. a. A.. and Isaacs. G. J.. "Porosity determina- tions of Grains and Seeds with an Air Comparison Pyonometer." Paper No. 66-803. Minter Meeting A. S. A. E.. Chicago. December 6-9. 1966. Thompson. R. A.. and Poster. G. H.. "Stress Cracks and breakage in Artificially Dried Corn". mark. Res. Rep. Ho. 631. USDA. Washington. DC.. 1963. Tuite. J. F.. et al.. "Growth and Effects of holds in the Storage of High moisture Corn". Paper No. 66-415. Annual Meeting A.S.A.E.. University of nassachusetts. June 26-29. 1966. APPENDIX: 43 Table la. SXperinental Temperature History Data: Air Temperature a 40 F Va 2 0.21 GEN/bu = 0.67 ft/min Initial grain moisture = 27-2P 6 Depth of Bed 3 4 ft T333n0001P13 Ha0043113 ( OF 1 0135 x = 0 i = 6" x = 1' g a 1'-6" . = 2' (hrs) it 0 30.0 30.0 90.0 80.0 “0.0 1 40.0 53.0 68.0 73.0 77.0 2 40.0 40.0 52.0 63.0 71.0 3 40.0 40.0 44.0 53.0 65.0 0 40.0’ 40.0 40.0 46.0 51.0 5 40.0 40.0 40.0 41.0 43.0 6 40.0 40.0 40.0 40.0 40.5 7 40.0 40.0 40.0 40.0 40.0 8 40.0 40.0 40.0 40.0 40.0 9 40.0 40.0 40.0 40.0 40.0 10 40.0 ' 40.0 40.0 40.0 40.0 ** average of 5 recordings. K = Z'oé” X a 3' X a 3'-5' . . ’. 1‘ .f'!’ 4H".l'fl 30.0 80.0 80.0 77.5 78.0 78.0 74.0 76.0 77.0 72.0 74.0 74.0 60.0 70.0 72.0 56.0 62.0 69.0 45.0 49.0 56.0 41.0 43.0 54.0 40.0 42.0 43.0 40.0 40.0 40.0 40.0 40.0 40.0 44 ‘Table 1b. SXperimontal Temperature History Data: Air Temperature = 40 F V = a 0.58 CPA/bu = 1.85 ft/min Initial grain moisture a 27-283 Depth of Bed 4 ft ‘PHflRHQCOUPLZ RSCOEDIflG Lionl TIhi \ = 0 x a 6" X = 1' K = 1'-6" x = 2' (hrs) ** 0 80.0 80.0 80.0 80.0 90.0 1 42.0 44.0 64.0 70.0 77.0 2 40.0 43.0 48.0 61.5 66.0 3 40.0 40.0 41.0 43.0 57.0 4 40.0 40.0 40.0 41.0 49.0 5 40.0 40.0 40.0 40.0 43.0 6 40.0 40.0 40.0 40.0 40.0 7 40.0 40.0 40.0 40.0 40.0 8 40.0 40.0 40.0 40.0 40.0 9 40.0 40.0 40.0 40.0 40.0 ** average of 5 recordings K = 2'-6" A a 3' X = 3'~6' 80.0 30.0 00.0 78.0 79.0 79.5 70.0 77.0 78.0 03.0 71.0 72.0 54.0 66.0 67.0 47.0 50.0 59.0 44.0 50.0 51.5 42.0 45.0 54.5 40.0 41.0 41.0 40.0 40.0 40.0 45 Table 1°. £Xperinental Temperature History Data: Air Tenperature = 40 F Va = 0.61 CPA/bu = 1.95 ft/min Initial grain moisture = 28 4 Depth of Led a 4 ft r4.1100039L5 430‘13133 L021 K a 0 K = 6" K = 1'-0" A = 1'-6" A f*2’-0" 80.0 80.0 80.0 80.0 90.0 54.0 54.0 69.0 76.5 78.0 2 40.0 49.5 50.0 60.5 71.0 3 40.0 40.0 41.0 52.0 58.0 4 40.0 40.0 40.0 40.0 46.0 5 40.0 40.0 40.0 40.0 41.0 6 40.0 40.0 40.0 40.0 40.0 8 40.0 40.0 40.0 40.0 40.0 40.0 40.0 40.0 40.0 40.0 ** average of 5 recordings x - 2'-6~ x - 3' x a 3'-6' 80.0 80.0 80.0 78.0 78.0 70.0 73.0 75.0 78.0 61.5 68.0 72.0 50.0 61.0 61.0 44.0 53.0 53.5 42.0 47.0 49.0 40.0 40.0 40.0 40.0 40.0 40.0 46 Table 1d. EXperimental Temperature history Data: Air Temperature = 40 F V_ a 3.86 GEM/bu = 12.35 ft/min Initial grain moisture = 28-29 6 Depth of Eed z 4 ft TagamocoupLs RECORDING ( °F ) TIME X a 0 X c 6' X a 1' X a 1'-6' X a 2' (hrs) ** 0 80.0 80.0 79.5 80.0 80.0 1 40.0 40.0 69.0 70.0 70.0 2 40.0 40.0 50.0 54.0 60.0 3 . 40.0 40.0 41.0 51.0 54.0 4 40.0 40.0 40.0 48.0 49.0 5 40.0 40.0 40.0 43.0 45.0 6 40.0 40.0 40.0 40.0 41.0 7 40.0 40.0 40.0 40.0 40.0 8 40.0 40.0 40.0 40.0 40.0 9 40.0 40.0 40.0 40.0 40.0 ** average of 5 recordings I a 2'-6' X a 3' X a 3'-6' 80.0 80.0 80.0 74.0 77.0 78.0 70.0 74.0 75.0 66.0 8.0 71.0 52.0 57.0 63.0 47.0 49.0 53.0 43.0 44.0 46.0 41.0 42.0 42.0 40.0 40.0 40.0 40.0 40.0 40.0 aways m. mcsewww ow bmoowmwonu cows OSPHHpsm woman ,gonncso amazowwosv. 47 4H4 wwoi noowwsm pun now: deepenedCHo pmfiwnwos mew»: rcpmwswm wwwo Hosp. mmev AUH4 mcwdv «psottv Hensonpos OWE\US c.m. m Hawdpmw mwsww mHm. .m 2...... .0 W my o.mp 30.0 mm $0.0 $0.0 o o.u o.mm to.o cm mo.o $0.0 w 0.: 0.0» co.o mp mo.o $0.0 w 0.: w.mo to.o we ww.m $0.0 m o.m 4V wowedp