fl MW 1 \ W W H h IH WEI J 'Lffié WW1 LAYER DY .. \N3 CF GRAS'I‘x ‘9 EN STORAGE Thesis for fire Degree 0*." 911. D. EYE‘W'EG'” Sl‘i'ECE EI’VWVRsITY An and“ram“z1 .1. am urang Deshmukh 1958 .THEsrs Cl 0-169 This is to certify that the thesis entitled LAYER DRYING OF GRAIN IN STORAGE presented by Aflflflde P D‘ss‘m ash), has been accepted towards fulfillment of the requirements for Ph. D. degree in Agricultural Engineering 1343/. W Major professor Date December 1, 1958 LIBRARY Michigan State University LAYER DRYING OF GRAINS IN STORAGE by Anandrao Pandurang Deshmukh AN ABSTRACT Submitted to the School of Advanced Graduate Studies of Michigan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Agricultural Engineering 1958 (53¢ a @442 flaw/jig 2 ANANDRAO PANDURANG DESHMUKH ABSTRACT The objective was to study the velocity, depth, and relationship of the drying layer to the moisture content ratio, air flow and temperature of drying air for shelled corn and pea beans in a deep bin. Three different air temperatures and four different air flows were used to study the velocity of drying layer and to find the lowest possible air flow for drying pea beans and shelled corn for the controlled conditions in deep bins.l The air flows used were 2, 6, 10, and 14 cfm per bu. and drying temperatures were 58 - 60, 72 - 74, and 86 - 88 deg. F. One inch diameter holes were provided six inches apart along the height of the bin for sampling. The time required for drying shelled corn is less as compared to pea beans for a given initial and final moisture content. For shelled corn the lowest air flow that can be used for drying a bin of 6 feet is 3.5 cfm per bu. at 58 - 60 deg. F. The velocity of 15 per cent moisture layer depends on air flow and air temperature. The velocity of 15 per cent moisture content layer is 2 inches per hOur at 58-60 deg. F. and 6 cfm per bu. air flow, when the initial moisture content of the shelled corn was 35 per cent. The depth of drying layer was defined and depends on initial moisture content of the grain, air flow, and air temperature. 3 ANANDRAO PANDURANG DESHMUKH ABSTRACT The depth of drying layer was 31.2 per cent higher at 88 deg. F. than 74 deg. F., and 33.4 per cent higher at 74 deg. F. than at 60 deg. F. for shelled corn. Thus, at the higher air flow the temperature does not greatLy affect depth of drying layer. At a low air flow of 6 cfm per bu. the increase in depth was 23.1 per cent at 88 deg. F. as compared to an increase of 30 per cent at 72 deg. F. over 60 deg. F. for shelled corn. Thus, the temperature differ- ence is quite apparent at low air flows. The time required to dry a given depth of shelled corn can be calculated from the following formula: 9 173.8 - 1.39 (t) + 8 (m) + 35(d) - 13(q) O = time, hours t = air temperature, deg. F. M - Me Mo - Me d a depth factor, feet m = log q = air flow, lb. per sq. ft. LAYER DRYING OF GRAINS IN STORAGE by Anandrao Pandurang Deshmukh A THESIS Submitted to the School of Advanced Graduate Studies of Michigan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Agricultural Engineering 1958 ACKNOWLEDGMENTS The author wishes to express his sincere appreciation for the guidance and support of Dr. Carl W. Hall, who super- vised the investigation upon which this thesis is based. The author is greatful to Dr. Arthur W. Farrell and his staff for making materials, equipments, and facilities available for this research work. ‘Sincere thanks is expressed to the Stran Steel Corporation, Detroit, Michigan, for partial financial sup- port of the project. Special thanks is due Mr. Earl W. Anderson and Mr. Tap Collins for their interest and encouragement. The investigator also wishes to thank the other memf bers of the guidance committee, Dr. M. L. Esmay, Dr. W. Baten, and Professor Donald Renwick for their suggestions and guidance. Thanks is expressed to Mr. James Cawood, foreman of the Agricultural Engineering laboratory, and laboratory workmen for their valuable assistance. The patience and support of the author's parents are gratefully acknowledged. ii Anandrao Pandurang Deshmukh candidate for the degree of Doctor of Philosophy Final Examination: November 26, 1958, Agricultural Engineering Building, Room 218. Dissertation: Layer Drying of Grains in Storage Outline of Studies: Major Subject: Agricultural Engineering Minor Subjects: Mechanical Engineering Statistics Biographical Items: Born: January 19, 1929, Kuroli, Khatav, Satara, Bombay, India Undergraduate Studies: Agricultural College Poona, Bombay State, India, 1949-1952 Michigan State University, 1953-1955, East Lansing, Michigan Degrees: B.Sc. (Agri.) B.S. Agricultural Engineering Graduate Studies: Michigan State University, 1955-1956, M.S. 1956 Michigan State University, 1956-1958 Honors: Government of Bombay, merit scholar, l9A9-l952 B.Sc. Agri. with honors, second division Experiences: Graduate Research and Teaching Assistant March 1, l956-—December 31, 1958 Professional Societies: American Society of Agricultural Engineers 111 TABLE OF CONTENTS INTRODUCTION. OBJECTIVE. REVIEW OF LITERATURE THE INVESTIGATION Part I. Procedure Apparatus Discussion and Results. Conclusions Part II Apparatus Procedure Discussion and Results. Pea Beans. Shelled Corn. Statistical Analysis SUMMARY CONCLUSIONS Pea Beans. Shelled Corn. SUGGESTIONS FOR FURTHER STUDY REFERENCES APPENDIX iv 12 13 22 22 22 TABLE \Tl LIST OF TABLES Drying pea beans with different air flows. Depth of drying layer, inches, at various air flows on three different temperatures (pea beans) . . . . . . . . . . . . Drying shelled corn with different air flows. Depth of drying layer, inches, at various air flows on three different temperatures (shelled COI’I’l Relationship of obserVed and calculated values for drying time Page Al 42 SO 55 59 FIGURE la. lb. Aa. Ab. LIST OF FIGURES Filling the quonset bin with shelled corn through hatch openings. . . . . Supplemental heater used for drying shelled Corn. 0 0 O O 0 O O O O O O 0 Cross sectional view of quonset bin Schematic for layer drying of grains Principal apparatus used for procedure Moldy corn as compared to good corn Loss of water per bushel of beans from 20-10 per cent moisture content. . Velocity of 15 per cent moisture layer Depth of drying layer at various moisture contour lines. Velocity of 15 per cent moisture of shelled corn. Moisture content ratio at different depths vi Page 25 25 26 BO 35 35 an Z+5 58 6O DEFINITIONS constant coefficients of temperature and moisture content ratio depth of grain bin, inches depth of grain dried below 15 per cent moisture content, inches depth of drying zone, inches depth factor, feet coefficient of depth factor coefficient of air flow equilibrium moisture content of grain, wet basis, per cent initial moisture content of grain, wet basis logarithum of moisture content ratio air flow cfm per bu. lb. of air per sq. ft. temperature of drying air, deg. F. velocity of 15 per cent moisture layer, inches per hour drying time, hours vii INTRODUCTION The proper drying and storing of agricultural products is an important problem today. Natural field drying which has been used for centuries is no longer practical because of heavy field losses. The value of grain as food to human beings makes the problem one of world wide concern. ‘The request was made to the Food and Agricultural Organization, as a result of discussions at the International Meeting on Infestation of Foodstuffs held in London in August, 1947, to conduct a critical review of the methods of grain drying and storage in use in all parts of the world. This indi- cates the importance of the problem and is sure evidence of wOrldwide scope. In Michigan there continues to be a trend toward fewer but larger farms. Labor scarcity is increasing the rate of farm mechanization on many commercial farms. Mechanization has solved many of the problems of farm operation. With increased production and inadequate drying and storage facilities, the Michigan farmer is facing the difficulties of drying and storage of grain. The loss of production during harvesting is as high as 15 per cent in sorghum, 30 per cent in seeds of legumes; 8 per cent in storage of potatoes, sorghum 6 per cent, and storage loss as high as 45 per cent has been reported in 2 corn by Hall(l957j.Often weather prevents timely completion of harvest. When this happens, the farmer has to be very careful in operating a picker or combine. The harvesting loss of corn in October is 5 per cent as compared to that in November of 8.4 per cent and in December, 18.4 per cent. The estimated loss is $6.00 per acre in October, $10.00 in November, and $22.00 in December. Too much food value is lost when the crop is dried in the field exposed to the elements of nature. In the United States it has been estimated by Hall (1958) that the losses between harvest and consumption of grain and hay amounts to 25 per cent of the total production, and this loss in fruits and vegetables increases up to 35 per cent. Both harvesting and storage losses can be greatly minimized by adaptation and proper management of sound drying practices. In the United States 10 per cent of the grain produced does not reach the market because of losses during harvesting and storage. It is very important that the crops should be at proper moisture level in storage. This moisture content is much lower than the moisture content at harvest time. Recent studies have shown that crops harvested at a higher moisture content will have minimum field losses. For corn this moisture content is from 24 to 30 per cent; however, for safe storage of corn the moisture content should be below 13 per cent on wet basis. With higher moisture content the product has a higher rate of respiration and more heat is produced which is more harmful to grain. When' a product of high moisture level is stored there is a conden- sation problem formationci‘mold growth, and grain insects. Naturally a method of removal of excess moisture is neces- sary in order to take care of harvesting losses and assure safe storage after harvesting at high moisture levels. Hall (1957) has estimated that approximately 95 per cent of the total losses of both grain and hay could be prevented through proper storage and drying and that a possible saving of 75 per cent of the total losses which occur during harvesting and storage could be realized by combination of early harvest and subsequent drying. This leads, hence, to the importance of artificial drying. Today, high moisture grain is moved into the storage directly after harvest. In artificially dried hay as much as five times the amount of carotene is preserved as in sun dried hay. By frequent clipping from 40 to 60 per cent more protein can be obtained. A desirable combination would be frequent cutting of forage and subsequent drying. ‘. Storing wet hay may lead to spontaneous combustion. Hall (1957) has estimated losses of 23 million dollars from spontaneous combustion in the United States in 1953. Con- siderable damage occurs to the stored oat crop because excess moisture results in loss of vitality. L; For drying grain, fans and dryers are coming into use and the demand for this equipment will continue to increase. The acceptance of the picker—sheller gives assurance against losses of crop, but at the same time it brings the problem of high moisture corn. If real benefits of artificial drying are to be achieved, a fundamental understanding of the drying process and variables involved in drying is nec- essary. Most of the investigation today has been concerned with finding immediate solutions for the present problems. There is not much work which has been devoted to the theoretical analysis of these problems. As a result the present design practice concerning grain drying and farm processing has remained largely dependent on experience and empirical data. The design of duct and drying installation for specified performance requires a thorough knowledge of the drying profile, fan characteristics, and basic laws pertaining to air flows. The:use of heated air for drying in deep bins has generally been unsatisfactory because of over-drying of the grain which occurs where the heated air enters the grain. This over—drying reduces the value of the crop to the farmer. When the farmer sells the crop on 13 per cent moisture content, wet basis, a moisture content of the grain below 13 per cent results in, the farmer selling dry matter for the price of water. In the drying process, decrease in moisture content is controlled by the drying characteristics of the grain. These characteristics are moisture content of grain, temperature, and relative humidity of drying air. The knowledge of these character- istics is essential in the design and proper management of drying equipment and processes. The amount of heat energy required for the drying operation is essential to the knowl- edge of the economy and efficiency of the process. During the last few years the drying of crops has been forced to increase the efficiency of operation in order to save the cost of fuel and provide uniformity of drying to the desired moisture content. It is difficult to evaluate the drying efficiency of a drying system by other than the approach of adiabatic heat balance. Usually the amount of heat energy required to vaporize one pound of water from grain is more than the amount of energy required to vaporize one pound of free water. This is due to the resistance offered by the grain body to moisture movement. Very little work has been done to find out how much heat is required for drying various agricultural products. The pea bean is an important commercial crop in Michigan. In 1956, Michigan produced 5 million 103 lb. bags of pea beans which was 96.1 per cent of all pea beans produced in the United States and 9313 per cent of the beans of all kinds produced in Michigan. The value of the pea bean in Michigan in 1956 was 33.4 million dollars. Pea beans are stored in bulk, and safe storage moisture content is 15 per cent on wet basis. The climatic condi— tions during harvesting are such that harvesting is usually carried out with beans above 18 per cent moisture content. For edible condition the beans must be stored at safe moisture content. About 60 per cent of the 1957 beans were stored on the farm and the present trend of storing pea 'beans in bulk on the farm is increasing. However, rela- tively few on-the-farm drying systems for handling pea beans are availalbe. Commerical drying installations in use are designed primarily for drying small grains. The need for forded unheated air or supplemental heat for drying pea beans is definitely increasing, and very little information is available that can be used as a basis for design and selection of equipment for drying pea beans. For storage of pea beans, artificial drying is necessary; however, artificial drying is difficult because pea beans crack when heated air is used for rapid drying. Shelled corn is an important grain crop in the United. States. The total area of corn was 65.5 million acres in; 1957. The production of this crop in 1957 was 10 per cent higher than that of 1956. In 1957 U.S.A. produced 2330 million bushels of shelled corn and the net value of this crop was 4300 million dollars. Last year 69 per cent of the crop was stored-on-the farm whose net value was 3010 million dollars,’ Total area of corn in Michigan was 1.714 million acres in the year of 1957 and the total production of corn was 102 million bushels. More than 36 per cent of the total production of the corn was stored on the farm. The total value of this stored corn was 43 million dollars. Thus, a substantial amount of corn is stored on the farm and, hence, the need for the study of drying and storage of shelled corn is increasing to minimize the storage losses. The purpose of this work is to develop a more theoret— ical approach to the problems of grain drying. In order that a deep bin of grain may dry, heat must be transferred from the ambient air to the grain to supply the necessary latent heat for evaporation of the moisture. The moisture must diffuse out from the interior of the grain in liquid or in vapor. It is necessary to know the moisture gradient throughout the bin and air with respect to time. The work has been established that the higher the moisture content of the grain, the lower the temperature to which it can be safely exposed for a given purpose. Safe temperature is much lower for seed for germination than for grain for milling into flour. No theory has been advanced to explain the variation in the rate of drying with differing air and grain depth conditions and it was therefore decided to study this matter experimentally. This type of relation is found with a number of substances but not much in agricultural products. No correlation has yet been suggested to explain the influence of air temperature and humidity, initial moisture content and air flow, on the rate of drying. Such analysis must be made in terms of either moisture content ratio or vapor pressure and there has been doubt which of these two parameters correctly , describes the driving force for drying in the system. A rigorous analysis has been presented which shows that the moisture content ratio of the grain is the correct physical potential to employ. From the present investi- gation it appears that the need was to gather data on practical performance of deep layer drying with various air flows and different air temperatures. These data are necessary for the design of drying and storage installations and recommending optimum air flows for the most efficient drying. Time element is a factor in layer drying and hence should be determined with reasonable accuracy. If only drying is wanted, then the minimum air flow rate for different locali- ties and different grains should be established. Very little research work has been done on drying of pea beans and shelled corn in deep bins. More information is neces— sary for drying so that the drying systems may be properly designed for efficient and uniform drying. The movement of the drying layer has not been defined. The movement of the drying layer may serve as a basis for predicting the time required for drying a particular batch and the hazard due to overdrying and mold growth can be prevented. Food Situation in India In accordance with a booklet Indian Agriculture in .EELEE issued by the Economical and Statistical Adviser, Ministry of Agriculture Government of India (1957), total area of grain crops in India is 272.8 million acres and' the annual production of grain crops is 88.7 million tons. The net value of the grain crops is 96.5 thousand million rupees (one rupee is equal to approximately $0.20). To meet various emergencies about 20 to 25 per cent of grains are stored in Central and State Government warehouses;that is about 17 to 22 million tons of grains of 19 to 24 million rupees worth, are stored in these warehouses. In order to meet successfully the increasing demand, keeping an eye on the increasing population, much more stress has been put on agricultural development in the First and Second Five Year Plans. By the end of the Second Five Year Plan (1961) India hopes to achieve the agricul- tural production target of 104.5 million tons of grains. When this target will be reached more warehouses will be needed to store grains. Most of the present storages are not designed and constructed on scientific basis. This leads to the loss of about 20 per cent of total stored grains and fodder. At present government purchases the grain on weight basis and normally moisture content of the grain is not looked into. Obviously, therefore, the farmers try to sell their. 10 product as soon as it is harvested. Thus, storage of high moisture content grains leads to losses due to mold and insects. Besides the grains are kept inside the gunny bags of 164.4 pounds of weight, which also adds to the improper ventilation and thus at the end the total losses may exceed even 50 per cent or more. Most of these warehouses are ‘ ‘ semi-circular in shape and 200 x 100 x 30 feet in size. They have concrete floors, masonary walls, and corrugated sheet metal roof. These warehouses have provided one door only. Inside these warehouses the gunny bags with grain inside are piled one above the other and stored for a period of six to nine months. This gapping problem of putting an immediate stop to this loss to the national wealth has been receiving a serious consideration in the Ministry of Food and Agricul- ture. Thus, the principles of grain drying and storage is the only solution for this crying need of Indian Agricul— ture. By the use of the above principles 80 per cent of the annual losses in storages of grains and fodder can be saved. From the above discussion it is clear that proper design of ducts and adequate construction of warehouses is needed in India. This will save considerable amount of money and the products. In 1957 India has imported 3.5 million tons of grains, which amounts to 4 per cent of the total annual grain production. Thus proper design of ducts and the bins will not only save the national wealth but also it will suffice the acute need of food. 11 OBJECTIVES To study drying layer and its velocity and correlate the movement of drying layer, air flow and air temperature. Define the depth of drying layer or zone in terms of initial and equilibrium moisture content of grain. To find the minimum air flow for drying shelled corn and pea beans under the conditions studied. Derive an equation to predict the drying time for a given depth of bin for shelled corn at given air conditions. REVIEW OF LITERATURE Drying crops with solar heat is an ancient method. This method has been unchanged, since the crop was first grown, but for the last hundred years crop drying perfor— mance has been improved.~ This method depends on sunshine but many times the sun fails to shine when it is needed to do its part in drying. Then the farmer does little but watch the daily deterioration of his crop in the field while each successive rain or wind makes the situation more hopeless. This method is still largely used in under—developed countries like India. The use of solar energy offered con- siderable possibilities for drying agricultural products. Indian farmers are utilizing the solar energy for drying grains, turmeric, tea leaves, coffee beans, pepper, hay, fodder, fruits, vegetables, et cetera. Drying of the above agricultural products is done in thin layers and usually takes 4 to 6 days to dry during good drying season. Some- times 4 to 6 sunny days are not available for drying and the occurrence of rain or heavy wind storms during the drying period is quite frequent. Thus the farmer has to move the products from the drying yard to a shelter to protect them from rainfall and heavy wind. With intermittent l4 rainfall and sunshine, the operation of drying becomes laborious and time consuming. For drying grains, the Indian farmer prepares a drying yard on which many times he first threshes and follows with the drying. In preparing the threshing yard he selects a piece of land free from wind obstacles from East and West sides since his winnowing depends on the natural wind velocity. The loose surface soil of this piece of land is scraped off with a shovel and distributed around the edge of the yard. Then the yard is filled with water to a depth of 3 to 4 inches, and allowed to soak for 24 hours. The next day the farmer covers the moist soil with more chaff and rolls it with a heavy roller until the soil is fairly compact. Then he covers the yard with chaff and allows it to dry slowly to avoid severe cracking. The solar energy reaching the earth in India varies from 400 to 600 Btu/hr/ sq.ft. The use of solar collectors is coming into use for drying of agricultural products. Changing methods in crop harvesting are leading to the new design of crop drying installations. The first drying installation was built in 1850 in England for drying oats. 'This kiln was circular (Bailey, 1958) in shape and had a conical roof but later this was changed to a square one. The heating of the kiln was with charcoal and wood; later coal stoves used with simple or complex heat exchanger systems. A concrete hay dryer was built at Pennsylvania 15 State University by Fulmer in 1927. This dryer was unique in its plan and method of operation. The plant depends on artificial heat for operation and is supplied by burning cheap grade hard coal. Short cut hay was placed on a con- tinuous chain conveyor which slowly carried over the inlet vents of the flue to the opposite end of the building, thus giving the alfalfa sufficient time to dry out on its journey from one end of the building to the other. This alfalfa was used as hay meal and was crushed into powder and sold to dairy and poultry farmers. The important feature of this dryer was low cost of construction and use of local materials available. The Institute of Agricultural Engineers at Oxford developed the first crop dryer and little modifications were made at Purdue University. Aikenhead (1927) used gases of combustion mixing with air blown into the stack of alfalfa and soybeans, and reported that the larger stacks were greatly overdried and dried somewhat in patches. He also reported that the drying was faster in this case as com- pared with unheated air and gave assurance against losses suffered in the harvest season of 1926. Lehman (1926) built a portable dryer in 1926 to dry beans and indicated that for quick drying and for a minimum loss of grain, forced heated air is more effective. He estimated the drying cost was $5.00 per 100 lb. of water from 37 per cent moisture to 21 per cent moisture content. 16 After the second World War new mechanical harvesting equipments were devised and as a result, above 90 per cent of wheat, beans, and corn are now machine picked. It is estimated that more than 99 per cent of the 1957 crop was machine picked. Mechanized harvesting operation gives the greatest independence from seasonal labor. A continuous dryer directly coupled to the harvesting machine was devel- oped in Washington State in the year 1951 and a five-pass counter flow conveyor was installed in England in 1955. More conveyors cd‘a.single-pass.design were installed in Britain in 1957. At present, there are a large number of portable dryers on the farm. Most of them use fuel oil or gas for heating air. The current practice favors direct firing by furnaces burning fuel oil. Hall (1957) has re- ported that the thermal efficiency of heated air dryers is greatest for direct-type heaters, low air flow, high initial moisture content, high atmospheric temperature and thick columns of grain. He reported that the efficiency of an oil-fired direct heater runs about 34.6 per cent at 7.7 cfm per bu; for coal, about 17.2 per cent at 4.6 cfm per bu, and that the cost of fuel and power was $.05 per bu. Between 1918 and 1932 fans came into general use and experiments on crop drying began to show the optimum drying air temperature and the use of higher air velocities than had been possible with natural draft. Thus, it enabled the more efficient use of drying installations and accelerated 17 the development of the present day type. Hall (1957) has developed a method for rapidly and accurately determining air flow values in grain drying structures of non-rectangular cross section. Fans are used for drying grain with unheated forced air. At present, fans are mostly used in aeration of grain. Rabe (1952) has shown the primary objects of aeration, the rate of cooling grains and factors deciding the cost of equipment and installations. Hukill (1947) re- ported on mechanical ventilation of corn with air rate varying 0.5 to 1.2 cfm per bu.and derived an equation for the cooling time. The cooling time is inversely proportional to the resistance offered by grain. The power requirement for the fan depends on fan characteristics and pressure loss through the grain. Hukill, Ives, and Hall (1945) have given an analysis of the procedure required to calculate the air pressure required for radial flow. For shallow bed tests Simmonds (l953)found that most of the grain drying takes place in the falling rate period and none in the constant rate period. Simmonds developed the equations for thin layer drying of wheat on the basis of the total moisture content, the initial moisture content, the equilibrium moisture content of air, and drying time. He showed that the drying rate constant depends on physical properties of grain and the drying conditions. His approach is based on the average moisture content of the whole bin and vapor pressure difference between the vapor pressure of 18 water at the mean grain temperature and vapor pressure of water vapor in drying air. 9:2“. = KgAm (Pg—Pa) C18 Simmons (1953) indicated that the air velocity is not as critical in thin layer drying as it is in deep layer drying. The rate of drying depends solely on the properties of grain at any air temperature. He also found that the rate of drying increases with rising air temperature and that the equilibrium moisture content correspondingly falls. Increasing relative humidity decreases the rate of drying, but the effect is much smaller than the effect of tempera— ture changes. He did not make any effort to compare drying rates. The rate of drying of wheat is inversely proportional to the mean grain diameter over a given range. Newton's equation of heating or cooling approach is based on the assumption that the surrounding air is at constant temperature and that the temperature difference between the drying air and grain is small. This equation is written as follows: £3.32 = -k(t—te) do where k is heating or cooling constant, t is temper- ature in deg.F, in hours at time Q and te is external temperatur in deg.F. Hall (1957) has shown that the equa- tion expresses a relationship between a function and its derivative. By substitution moisture contents (dry“basis), 19 “for the temperature in the above equation, the equation is changed to moisture content ratio Hall (1957). M-Me = 8 -k9 Mo'Me Bailey (1958) has derived an equation for thin layer drying of hops in kilns and shown that drying time is inversely proportional to the difference between vapor pressure of water at the temperature of drying air inlet and vapor pressure of water already present in the atmosphere. This drying time is directly proportional to the loss of water per square foot area per minute and explained by the same equation in terms of air speed in feet per minute leaving the hops. He analyzed the vapor pressure driving force in terms of pressure difference related to water at that inlet air temperature. His work is based on the adiabatic drying and higher air velocities. Simmonds (1953b) propbsed a method for predicting the rate of drying of wheat grain in beds 2 inch to 12 inch deep for air velocities l2 - 130 feet per minute and an average temperature of 70 - 170 deg. F. with accuracies of i 10 per cent. In this method, drying took place entirely in the decreasing rate period. The behavior of decreasing drying rate period of wheat was described in terms of its average moisture content and he believed this relationships would be more valuable if the drying rate constant could be simply correlated with air conditions. 20 He proposed that the mean temperature to be used for predicting the performance of adiabatic dryers in the logar- ithmic mean temperature between the air temperature and its adiabatic saturation temperature. He showed from a moisture balance equation that the point of maximum rate of drying is proportional to the bed depth, and the rate of drying de- pends on mass velocity of air. Simmonds (1953) believed that a correlation of the rate constant with temperature would be sufficient for most practical purposes and considered that at any given temperature a certain fraction of molecules present in a system are capable of undergoing chemical re— actions, diffusion, viscous flow, et cetera. He developed an equation for the variation of the rate constant with air temperature and worked out a method for predicting drying performance which is based on the drying constant and logarithmic mean temperature of drying air and wet bulb temperature. He suggested that the drying zone could be expressed in terms of drying percentage. Hukill's approach for analysis of deep layer drying: the computed relation- ship between drying time, grain moisture, and grain depth units have been generalized to make them applicable to the drying problem. In the equation of drying rate he makes use of the drying time unit which is half response time, moisture content ratio, and depth factor. Henderson (1955) suggested a method for calculating moisture content of the deep bed at any given time. The 21 solution is based on stepwise integration from one layer to the other. ,He divided the depth into several thin layers and made an assumption of uniform drying of each layer to carry out the procedure. He illustrated a table of calcula— tions which gives the moisture content at any depth with various intervals of time. This method requires more time to calculate the results and is rather laborious. Ives (1957) showed an analysis for traverse time and drying time relationships in parallel and non-linear flow. His analysis is based on the mass balance of water removed per pound of dry matter, and air flow per pound of dry matter times the amount of water per pound of air. THE INVESTIGATION Part I Procedure This part of the research work consists of studying the effects of filling the bin in six layers at an interval of four days, and study the effectiveness of drying due to sucking drying air through the grain. The good drying weather of three weeks in October, 1956 was made use to dry the shelled corn and following two weeks heated air was used. The heated as well as unheated air was first directed to the wet grain and then through the remainder of the bin. This was done to avoid the over drying of the grain which is observed in the forced heated air drying systems. By making the use of good drying weather in October and with supplemental heat for drying grains it was believed that the drying would be economical and uniform as compared to the present methods of drying grains. Shelled corn with average moisture content of 25-28 per cent, wet basis, was placed in the quonset-l6 building. The total quantity of grain was approximately 2200 bushels. The corn harvested with picker—sheller and was hauled in tractor driven wagon and was transferred to an elevator and dropped inside the bin through the two hatch openings. 23 The first layer of shelled corn at 28 per cent mois- ture content covered the duct to acknfifllof one foot. After filling the first batch the suction or exhaust fan was started and was kept running throughout the entire experi- ment. Second and third layers of shelled corn were placed at 26.6 moisture content on October 15 and 19, respectively. The fourth layer was placed on October 25, 1956, at 25 per cent moisture content. The fifth layer was placed on October 31 and layer sixth was placed on November 10, 1956 to bring the total height of the bin six feet above the duct. 0n the first of November 1956 the heater was started and heated air was sucked through the depth of six feet shelled corn. The temperature of the heated air was main- tained at 115 deg. F. until the last three days of the test at which time the temperature was set at 140 deg. F. Samples were taken by means of auger sampler and moisture content of the samples was determined by Tag-Heppenstall electrical resistance moisture meter. The static pressure drop was measured with a tap at the end of the duct opposite the fan. Apparatus The quonset—16, 28 feet long with a 4 foot additional workroom a plywood bulkhead forms one end of the bin, was equipped with aduct whichwas 54 inches wide and 30 inches high. The duct was semicircular in shape and was covered 24 with 16 mesh screen to avoid the falling the grain inside the duct and making the duct perforated to facilitate the air movement through the grain. The floor of the bin was made of concrete and walls were made of double corrugated sheet metal of galvanized iron. The bin had a sliding door in front as shown in Figure 2. An Aerovent fan, No. 58882, propeller type, with a three horse power motor was used for exhausting the air from the bin. The fan was placed at the rear side of the bin. A Campbell crop dryer, model 11019 with an air flow of 14,000 cfm at 1.5 static pressure was used for heating air using No. 1 fuel oil. Discussion and Results With good drying weather of three weeks in October, shelled corn was dried from 28 per cent to 12 to 14 per cent moisture content within four days after drying began when the height of the corn was one foot above the duct. After putting the third layer of shelled corn in, the moisture content of the first or bottom layer was increased 22 per cent. This was due to the fact that the air with high relative came in contact with the bottom layer from the top wet shelled corn. This resulted in the absorption of moisture by the dry grain from the humid air. The moisture gained by the bottom layer was only on the outside surface of the grains and was removed much faster than the moisture content at the center of the kernels. . .- f“. . 4 . ‘i’;13: _{'—., ... x!) .A.(. ‘4 _ Fig. la. Filling the bin with shelled corn through hatch openings Fig. 1b. Supplemental heater used for drying shelled corn 26 Emmi 2.4mm hwy—Lb; o._. omhomma «=4 ouhdm: .zmoo own—qmzm mo oz_>m0 SEOEZD macs. 02.2.4kmo «Om kzmimozn‘mmd N .07.. 25 kmmzozo .385 96 ca... 30530 .uaogxm .3550 cc... I t T :3 5 £2. .._< \ I H o no use»... 5 0303 £93 .25 a e I / / / / f 5.4 92.00: 27 As the height of the corn was increased, the drying of the bottom layer was delayed. The moisture content of the bottom layer was as high as 26.6 after adding five to six feet of corn and pulling unheated air through the grain of a high relative humidity during periods of inter— mittent showers. The moisture content of the bottom layer was increased as much as 6 per cent over a period of 24 hours after the addition of wet corn on the top of the previous layers. During the period of high humidity, the moisture content of the layers was increased with the greatest increase being on the top layer when using unheated air. When heated air was used, there was considerably more uniformity in moisture content of the bin. A variation in moisture content from the top layer to the bottom layer was approximately 3 - 4 per cent when the top layer was dried down to 12 per cent or below. If heated air had been used from the bottom, the variation in moisture content would have been considerably greater. During the sixteen days of heater operation 700 gallons of No. 1 fuel oil were used. During the period of the experiment, the exhausé fan was operated 960 hours, using approximately 2000 kwh of elec- tricity. The estimated cost of drying for fuel and electri— city was about six cents per bushel for drying from about 28 per cent moisture content to from 8 - 12 per cent mois- ture content for 2200 bushels based upon 14 per cent mois; ture content. 28 The moisture content in the corner of the bin was approximately 4 per cent higher than that of moisture con- tent above the duct. With heated air, the variation across the bin was only 1 per cent above the grain over the duct. Conclusions 1. Moisture content of the grain at the bottom layer next to the duct increased as much as 10 per cent when high moisture layer was placed over it and the grains were dried with unheated air. 2. The moisture content of the bottom layer was increased only about 1 per cent when heated air was used for drying the wet layer placed over it. The dry layer just under the wet layer only gained about 2 per cent mois- ture content when heated air was used for drying by this methos. 3. While operating the fan during rainy weather, the moisture content of all layers increased from 3-5 per cent. 4. The cost of drying was 6.1 cents per bushel for electricity and fuel oil for removing moisture from 25-28 to 10-12 per cent moisture content. 5. By using a heated air unit into the top of the bin down to the grain heating the wet grain first and ex- hausting the air from the bin provides an excellent means of drying high moisture corn in the fall when the weather conditions are generally unfavorable for forced air drying without over drying part of the grain. 29 Part II Apparatus The experimental apparatus was constructed for the purpose of measuring the velocity of the drying layer in deep bin of grain. The drying bin was, therefore, con- structed so that the samples could be taken without dis- turbing the bed. The general layout is shown in Figure 3. A refrigerated box of 40 cubic feet capacity was a source of incoming air. The box maintained a reasonably constant temperature and a constant relative humidity. A backward curved centrifugal fan was used to force air from the refrigerated box to the heater box where the air was heated by means of an electrical resistance heater. An 8 inch wooden square pipe was used to connect the fan to the heater box to minimize the frictional loss. A sliding door was used at this entrance of the heater box to control the air flow. The air was heated 14 deg. F. and its relative humidity reduced from 12 - 20 per cent depending upon the incoming temperature,relative humidity of air. 0n the exit side of this box, another sliding door was provided to check the air flow nearest. The temperature of the air was regu- lated by means of a bimetallic thermostat located in the 22% do 02.29 52.. do“. wiéqddq no: 20.5.4 12.268 w xom 32m: magmas. mo“. zm>o 755m: _ 3.0.53: ‘III a memmmma 0:45 PQLMOEINIF ’_ _ Zdu 1 «3.12% , .5528 oi El cub INEOEZ . .ozamoomm 3O o RH 25 r me... 84880355 8:: rmpmzoz; xom omh> mo mmO... .90.“. mKDOI Om Ox. 0% . On 0? On ON 0. .1! n n P n r - .\\ . ' o . IN I O O 4 1.1V 0 N I O O u o . . .e :9 EB w o 4 a O O. e. um .. .. o ._ 0\omwimm :Im fiO. ARA: 2.“: :JO SONOOd HBIVM .0... 25 do 5 .4 Educ 8243. 2.32.. magma: pzmomud n. no >tood> we: 2. and 2.8 m. a“. a. m 1.. .1. .N O I O I . 54 a we? a no I D .. u ¢NDI O. O O r. . demo n. -o.~ .. DN 30 OH U 3:! SBHONI r%._._,—m._.zou map—.905. mDOE<> h< ¢u>13— " [jiwua-(ZEINSEéEJ 21:24:“:- (2%)]: + [Elm -(.2t)(XWIIlc + Lita -Li_tl£_2;|.c+ [in (21121) 3.. ._-, Elie -czu(zn:lc + [21> - _z_%2_ 4+ [EDT @2912; : ZDe-<21>)<29)] 4. [in-WE +[ZMi-‘erflfic i :Z‘i‘“ M39]? —~ _ -FC£ £56 HERZ .__121J3 __ fgile i)( l] q - 5 - bt - cm - fd - gq e=a.+bt+cm+fD +gq+<~c Four equations and four unknowns solved simultaneously: 2392(b) - 25.7(c) + o(f) - 8.67(g) = -3640 -25.7(b) + -489(C) + 0(r) - .855(s) = -22.36 - o (b) + o (c) + 2.027(f) + o(g) = 471 .867(b) - .855(C) + 0(f) + 8.311(8) 175.33 b = ‘1-39) f = 35-02: g = "13°C: C = 8'0, a = 173.8 fir-cap” -. rue-cam] «is 411"] — 3th h"5 =:t2r3 +1.39 (+3640) - q (~22.36) + 35 (1166) + 13 (175.33) % Azmoo .mv2_m Ten 2. mm><4 mmahmaz hzmommm n. no >2004w> m6; «2 n.3, an «ma Emu 2.. "V 'N IN. 83d SEHONI 800M . M.r.oi.ll. HI .l.) in, \H TABLE Pelatio ship of observed and calculated values for dry ng time. 108. Pounds Of Air Time in H:urs Temp. M - Me Depth 99? 5?. ft- def.F ._______ Factor per minute Observed Calculated MQ- Me t —m d’ a 01 02 60 1.2757 0.614 3.0 63 71.8 60 1.2757 ' 1.27 3.0 80 84. 60 1.0000 1.12 2.17 83 104. 60 1,0000 1.96 2.17 120 133.40 :0 0.9136 1.22 1.30 116 108.5 60 0.9136 1.93 1.30 144 133.5 60 60 74 1.0506 0.3 5 2.93 34 41.92 74 1.0506 0.69 2.93 53 53.80 74 1 0223 0.282 2.14 5 62.70 74 1.0223 0.638 2.14 73 74.95 74 0.8774 0.186 1.27 74. 64.92 74 0.0877 1.000 1.27 116 83 14 74 74 88 0.7212 0.50 2.84 22 27.18 88 0.7212 0.735 2.84 36 35.25 88 0 7399 0 282 2.10 28 26.18 88 0 7399 0.66 2.10 41 39.31 8 0 8099 0.624 1.22 61 50.83 88 O 8399 1. 5 1.22 90 69.24 ........... ...t. .‘iilll. mmw»<4 ...zummmufi z. o_._.- . z '. ’v MJ ‘. b— X z ‘ \ ‘. O “ \\ \ u ‘ ‘ \\ #201 \ . D \ \ \ p. :0 s i .1 _ ‘\~ \ ’\ r f Y fi 50 60 To 80 FIGD LAYER DRYING OF SiELLED CORN YEW 86-88”? AIR FLOW 6 c fm/bu PERCENT mm: WTEM FIG I2 LAVER WWW CF SHELLED CO"! TEMP 72°F NR FLW l0 chum VCIS Y UK CMJENT FENCE-NY ' " ‘ 1 V r 1 1 :0 20 30 40 50 60 70 w HOUR mo 14 LAYER DRYING OF SNELLED CORN TE. .0- If? All FLO. DOOM N O A a; 5i PERCENT “was comm: 6 l J V V 1' IO 20 ” 03 0'0 6'0 10 so ms FIG H L“. "V“ “m CM" IE”? 72’ F AIR FL“ I4 “Nil LE6 1'0 307 g ~m as 15 1 Fmsuvumoormuzom main-r AIR FL“ 0,“ L O I! in.“ To 5 i Ii «an woman-acumen: o ‘ raw 12°F TEMP 25 {m - ' M FLWZdW 35- AIH ‘Jw 14 amino :0 29 ' ° . . 0 aa- ' ° I54 . —-0———-——- m I Y W q '7 t I T “1 ' ' ' "—"‘ 2° .0 é $8 do lab do IO 20 30 4G 50 cc it so MURS FIG I7 Lm DRYING OF SELLED COVN TEMP 53-60: am now .0 an. 'bu - ramp sews 3 . - _ me now 6 c'm/Iu E30 ”30* g E $54 9234 §20 £2 .. °1 B '5 * ° I54 2: g... . V V I T f Y j T _1 ' . _. : to 20 30 40 50 60 70 lo I 26 JO 0‘ 30 ndc 12(‘ 14c :60 Moms HOUR: FIG no LAYER DRYING 0F GILLEDCORN HG '9 LAYER DRYING 0‘ SHE...E'J ..m-u 'I \. nw-sa-cdr - m . TEM!‘ 73-74 F . AIR FLOW z dun/bu AIR FLow I4 urn/... 'i . i '5‘ U U o o 3 . . ' E 9 U o g . I 1: '° ' ST % V v V j 1‘ V I t n 40 ‘0 no ‘0 050 I40 ‘0 ‘ J J ' v W 1 1 IO 20 30 40 50 '~(‘ HOURS F020 LAYER mo G'HEUJD COIN HOURS FIG 2| LAYER MYING OF “EA 5E A‘u‘; “- g pennrynasruag c Y‘ K: 1 HOURS FIG 22 LAYER DRYM G" PEA BEANS gar 9 ? mem * 495 ab .3 ' 13 9'0 ' a... '°° m FICZQImlmwmm ‘ , >5: TWO-00‘s ,. .\ . mecm I." ' g m . I41 r . ”“75 3‘0 ' .3 7'0 To FENCE!" mam COUNT I PERCENT WISTURE CWTENT ms FIG 23LAYER DRYING Cf PEA BEANS TEMP 38’08" ’ _ ARFLOW I4 cfm/In I /< 3 J I — N J. IO 20 30 40 so CO 70 8) noun FIG-25 LAYER DRYING N PEA KANS TEMP 86 '88’F 22- me new 8 Jm E I gm I- 0) i 2... z 2 E I4< _ FIG 27 LAYER DRYNG U? Pia “:n'a; TEMP “iI'F AIR FLOW? cfm/bu 20 o E I §.« 0 u A ' mi . 5. - U, 9", p. o 5 S I2< o \ ‘ \\ \ \\. 3K \, _ . W V 7 fi' 1 v\> v V 1 IO 20 30 ‘0 50 GO TO 80 "”5 FIG 2. LAYER ”WW 0' PEA BEANS TEMF‘50'0F 20 All FLW Dena/ho .- z :2!" 2 8 U I“ E a 3 w .- 8 D to no Q 50 u 70 .0 M F. ”LAYER WI“ 0' RA IAN. YEMP 58'60‘F AR FLOW 2 cfm I'bu 4 a 25 03 6 ‘0 (E 150 030 so mm m 32 LAYER mm or m anus PERCE‘IVLGE W'JS'JRE CC’JTE‘IT Cl: N8 M.,?! 1' Fa; TJG. VONTE'VIT PERCENT MOISTURE CUITENT Q 1 3 l b A 5 A 15.3! ~ ‘1’ ~ 9 IFM“ '38".‘ °F L‘F—J I .. H 4 "I in J 1' I V Y I Y T l IO 2 0 3C7 40 C-C c.( T( 81 ‘ H( “*3 F36 (:9 HER DHVWG r = ‘vEA SEL’IS TEWSB'UO’C AIR CLLW t ,Im RH Lh'l'r gr 4'5 FIG 3. .Aven ammo ot PEA BEN-s. ,\ . :tf' _ ~~\ TEMP 72°F / m. \\ ..an 1, . AIR now suntan <\ \ \ . \ ' \\ \_\ a . ‘\ . .15 \. ‘\ O O ‘ \ - \ \ \ ‘ _ \ Pf“- .\. . , I5 30 45 60 75 90 '05 2' H<3HRS FIG I5 LAYER DRYING 0F SHELIID cow. $106511 USE Gé‘ILY 93 03071 063 31 A“ R” mm L" H T” " u H "I T”! "I H S" NI A“ ml! HI