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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

Approved 5%” M @4- {IL/£3

 

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.

The air flows used were 2, 6, lO, and 14 cfm per bu.
and drying temperatures were 58 - 60, 72 - 7M, 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)

9 = time, hours
t = air temperature, deg. F.
m zlog U9.

Mo - Me

d = depth factor, feet

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. Farrall 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 mem-
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.

11

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, 1949-1952
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

Page

12
13
22
22

22

TABLE

\H

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

COPI’I

Relationship of observed and calculated values
for drying time

Page
41

42
50

55

59

FIGURE

la.

lb.

4a.
4b.

LIST OF FIGURES

Filling the quonset bin with shelled corn
through hatch openings. . . . .

Supplemental heater used for drying shelled
COPn. . . . . . . . . . . . .

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
30
35
35

44
45

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(1957j.0ften 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 formation<i‘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 20 million dollars from
spontaneous combustion in the United States in 1950. Con-
siderable damage occurs to the stored oat crop because

excess moisture results in loss of vitality.

b,

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-dryingof 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 100 lb.
bags of pea beans which was 96.1 per cent of all pea beans
produced in the United States and 93.3 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
forced 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

 

Brief 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 3.51
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 oom-
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 of 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 011. 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,
hand 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 (1953)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.

83 = KgAm (Pg-Pa)
de

Simmons (1953) indicated that the air velocity is not
was 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:

.QE = -k(t-te)
do

where k is heating or cooling constant, t is temper-
ature in deg.F, in hours at time 0 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 (drwrbasis),

19
for the temperature in the above equation, the equation is

changed to moisture content ratio Hall (1957).

M"Me -k0

=8
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) proposed a method for predicting the
rate of drying of wheat grain in beds 2 inch to 12 inch deep
for air velocities 12 - 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 matte; 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 acknflfilof 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.

On 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-l6, 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.

 

Fig. la. Filling the bin with shelled corn through hatch
openings

 

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Fig. lb. Supplemental heater used for drying shelled corn

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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 exhaust 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
oapproximately 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. On 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

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31
heater box. From the heater box, air was forced through a
3 inch insulated steel pipe to the equalizing box to assure
uniform air flow through the grain. From this box air
traveled through the grain and returned to the cooler.

‘ A round bin was used for this test which was con-
structed of steel with 4 inch outside diameter, .0625 inch
thick and 42 inch height. One inch diameter holes were
provided along the height of the bin, 6 inches apart for
sampling. The bin was insulated with asbestos for adiabatic
drying. A false floor was made with screen wire having
10.5 x 10.5 inch mesh, and 16 gage wire was used to support
the grain and established a plenum chamber 12 inch x 12 inch
x 12 inch under the perforated floor. The bin was filled
to a depth of 42 inches with a full capacity of 0.24 bushel.
Air flow was measured by means of an orifice plate with a
differential manometer. This orifice plate was located on
the exit side of the grain, and the outlet air was moved
through the orifice plate back to the cooler where it was
cooled and moisture was condensed on the cooling coil.

The orifice plate was calibrated from the formula of

Q = 4000 CAATP which was taken from the Buffalo Fan Engine-
ering Book. Dry bulb and wet bulb temperatures were
measured and recorded with the thermocouples and recording
potentiometer. The pipe joints were sealed with masking
tape to insure against air leakage throughout the system.

An .025 inch diameter tube sampler was used to obtain

32
uniform samples from the cross section of the test bin.
The power required to move air through the grain was taken
from a one horse power, 220 volt, 3 phase electrical motor.
The static pressure drop was measured with tap and water

manometer.

Procedure

 

Because of the difficulty in obtaining and handling
the large quantities of grain necessary to fill a grain bin
up to 6-7 feet, a laboratory size test bin was constructed.
With this bin, variables such as temperature, air flows,
and relative humidity were more accurately and readily
controlled than in a regular storage bin. Wet pea beans
having moisture content of about 21 per cent on wet basis,
which were harvested in theikflj.of 1956, were stored in 100
pound bags in a 40 deg. F. box. Pea bean bags were obtained
from the Michigan Bean Company, Saginaw, Michigan.

Due to wet harvesting conditions in the Fall of 1957,
shelled corn was harvested at 35 per cent moisture content,
wet basis. The total amount d?corn required was 8 bushels.
This moisture content was too high to store in a 40 deg. F.
box; therefore, it was necessary to store the corn in a
zero deg. F. box. Before starting the drying test it was
necessary to defrost the frozen grain. The corn was
allowed to defrost in 40 deg. F. box for three days in a
polyethylene bag to avoid the loss of moisture from the

top surface. The corn was well stirred 3-4 times during

33
the defrosting period. The test bin was filled to 42 inches
in height and was insulated with 0.5 inch asbestos insula-
tion. The bin was filled by a method called pack filling.
This method consisted of pouring the grain into the bin
6-12 inches deep with the use of a funnel and then tapping
the bin wall to settle the grain. This was done to measure
the loss in volume of the bin during the drying operation.
The bin was weighted empty and with grain to an accuracy
of 0.125 pound. The bin was then fastened on the equal-
izing box with four bolts. The pipe was covered with in-
sulation, thermocouples were inserted at proper locations
and the bin was capped with 3 inch pipe which carried air
to the cooler. All joints were made air tight with masking
tape. After making sure everything was properly adjusted,
the fan was started. The fan was operated continuously
until the drying was completed. The drying was completed
when the top layer of the bin was below 12 per cent moisture
content, wet basis. Total air flow through the grain was
measured by a sharp edged half-inch orifice in a thin plate
mounted in a 3 inch pipe. A well—type inclined tube water
manometer was used to measure the pressure drop across the
orifice plate. Air flows of 2, 6, 10, and 14 cfm per
bushel were used for drying the grain, and drying tempera-
tures were 86-88 deg. F., 72-74 deg. F., and 58460 deg. F.
Grain samples were taken at various time intervals depending
upon the rate of drying, but at the end of 2, 6, and 10

hours for the first day of drying.

34
A methdd was developed by which a sample could be

removed without disturbing the rest of the bed or altering
its drying characteristics. The type of grain sampler used
in this work is shown in Figure 4a. The sampling unit
consists of a 1 inch diameter pipe, of which one end was
tapered, and a 4 inch long and 0.25 inch wide slit was made
to catch the grain sample. When a sample was to be taken,
the insulation was removed from the test bin, the masking
tape was taken off from the sampling hole, and the sampling
probe was inserted in the grain with the slit up side down.
After making sure that the sampler was touching the other
side of the bin, it was turned up to get the sample from the
entire width. When samples were to be taken, the fan was
stopped, the temperatures were recorded with the recording
potentiometer, and it was made sure that the desired air
flow was coming. In using this technique the moisture dis—
tribution in the bin up to 42 inch depth was determined.
Moisture determination was made in an air oven heated by
electricity at 212 deg. F. for 72 hours. The average weight
of the sample was 4—6 gm and approximately 7—8 samples per
test were taken. Thus, a series of tests were carried out
on a bed 42 inches deep with different air velocities and

different air temperatures for pea beans and shelled corn.

 

 

Fig..4b.

- A
i ' -
-< \ . I.
- - 5
\
‘1 . ~
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The mold growth on shelled corn

35

n)“~‘

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36

Discussion and Results

 

.Pea beans. In these experiments three different

 

temperatures and four different air flows were used. Tem-
peraturs were 58 - 60, 72 - 74, and 86 - 88 deg. F.

Drying first occurs where the air enters the grain and
proceeds through the grain. If the bed of grain is deep
enough the air flowing through the bed will become saturated
before it leaves, and saturation continues until the zone

of vaporization reaches the top of the bin. At this stage
the rate of drying decreases and this phenomena is indepen—
dent of the actual mechanism of drying since it depends only
on the moisture carrying capacity of the air. As air moves
through the grain it picks up moisture and heat of respir-
ation. Thus, the relative humidity and temperature of
drying air increases and when this warm and humid air comes
in contact with cold grain condensation takes place, usually
on or near the top of the bin.

For the above tests, wet pea beans harvested in Fall
of 1956 were stored in 40 deg. F. box to prevent the
formation of mold. The condensation was more at low tem-
peratures and low air flow such as 2 cfm per bushel than
higher air flows. The condensation took place in upper
6-12 inch layers, and was noticed in less than 40 hours at
2 cfm per bushel air flow. At 6 cfm per bushel air flow
condensation took place 12 inches from top and was observed

in less than 10 hours. This condensation is a familiar

37
phenomena which is observed during grain drying, with

unheated and heated air. During the night air the temper-
ature of the air drops and as a result the air reaches the
dew point temperature.

In these tests for drying of pea beans at constant
temperatunaand constant relative humidity, decrease in
drying rate towards the end of the process has been observed.
This is shown in Figures 21-31. At higher air flows, such
as 14 cfm per bu. and 74 deg. F. air temperature, all
layers were dried below 12 per cent moisture Content and
the top layer was only 1.6 per cent higher’in moisture
conetnt than the bottom layer. This variation was 1.7 per
cent moisture at 58-60 deg. F. and 3.2 per cent moisture
at 86-88 deg. F. for the same air flow. This indiCates
that as the temperature of the drying air was increased the
difference between the moisture content of the top and
bottom layer was increased. It is also evident that for
given conditions the effective drying time was shorter
with slight increase in air temperature, but this was not
evident with air flows between 2 to 6 cfm per bu. At 10
cfm per bu. air flow and at 72 deg. F. air temperature the
time required to dry the grain below 12 per cent was 76
hours and the difference between the top and bottom layer
was 2.75 per cent moisture content. The time was 85 hours
at 58-60 deg. F. and 46 hours at 88 deg. F. with 2.3 per

cent difference in moisture content of the top and bottom

38
layers. At 6 cfm per bu the difference was 3.6 at 58-60
deg. F., 4.2 at 72—74 deg. F., and 5.3 per cent moisture
content at 86-88 deg. F. air temperatures.

As the temperature of the drying air was increased
the uniformity of drying bin was decreased. Using
air temperature and high air flow rate, the uniformity
of drying was obtained. At 6 cfm per bu. the condensation
near the top was observed in less than 10 hours. The drying
rate was much faster for the bottom layer in contact with
the entering air and the rate was less with the successive
layers in the bin. The air flow of 2 cfm is not enough for
drying grains in deep layers. For beans mold did not occur
at 86 to 88 deg. F. and 2 cfm per bu. air flow because the
beans were at a lower moisture content.

At a low air flow of 2 cfm per bu, due to the low
drying potential, the drying rate was slow and the total
time required to dry the whole bin was longer than the
other air flows. In this the condensation was much more
predominant and occurred in the top two layers thus the
top two layers had the same drying rate. At 2 cfm air flow
and 72-74 deg. F. air temperature, it took 32 hours for
the bottom layer to dry_from 20 per cent moisture content
to 12 per cent moisture content, and 200 hours for the top
layer.

The lowest air flow for drying pea beans is 6 cfm

per bu. at 72-74 deg. F. and 66 per cent relative humidity,

39
as shown in Figure 26. The 2 cfm per bu. is too lOW’an
air flow and it results in considerable amount of conden-
sation. For drying 42-inch depth required 8-9 days. It
is often obvious that recommended time for drying a bin of
42 inches deep under East Lansing conditions will not
always meet the requirements of the other conditions. This
point is pertinent because the drying time is selected on
the basis of air temperature and at a nearly fixed relative
humidity.

For a bin of 6 feet depth the time required to dry
will be 16-18 days. The time for drying may be longer if
the temperature of the drying air is lower with higher
relative humidity. Time element is an important factor in
layer drying and, hence, should be determined with reasonable
accuracy. If good drying is wanted then the minimum air .
flow rate for different localities and for different grains
should be established. At 6 cfm air flow it took 3.5 days
to dry the same bin at 72-74 deg. F., 3 days at 86-88 deg.
F. and 6 days at 58-60 deg. F. from 20 per cent moisture
content to 12 per cent.

From the above discussion a relation has been estab-
lished for 15 per cent moisture layer and different air
flows. With increased temperature and air flows the
velocity of 15 per cent layer increases, as shown in Figure
6, and expressed in the following equation

Q2. -.54

V1=V2(“§1"‘"’)

40

Where

V1, V2 = velocity of 15 per cent moisture layer
inches per hour

Q1, Q2 = air velocities cfm per bu.

One of the major objectives of the work is to define
the drying layer or drying zone. For the purpose of the
discussion the drying layer is defined on the basis of
initial and equilibrium moisture Content of‘grain.The drying
layer extends between initial moisture content minus 2 per
cent and equilibrium moisture content plus 2 per cent, and
also initial moisture content minus 4 per cent to equilibrium
moisture content plus 4 per cent moisture content (Table2).
The relationship between air flows and moisture variation
within the bin, and the time required to dry the bin is
shown in Table 1. This thickness was increased as the air
flow was increased for a given condition of air flow. At
higher air flows the drying layer has has more depth than
at low air flows (Table 2). Also at the higher temperature,
the depth of drying layer is more than at lower temperatures
(Table 2). This difference was significant even though
there was only 14 deg. F. temperature difference in the
incoming air used for drying. The movement of the drying
layer can be noted from Figures 6 and 7. The lines on
Figure 7 indicate the moisture content at various locations
in the bin. The distance between moisture contours can be
used to visualize the drying layer. It is evident from

these figures that the lines become farther apart as the

41

TABLE 1. Drying pea beans with different air flows.

m

Air Difference between moisture Time required for the
Flow content of top layer and top layer to come to
cfm bottom layer, when all layers 12 per cent moisture
per were less than 12 per cent content or below,

bu. moisture content. hour.

 

At 72 to 74 deg. F. and 58 to 66 per cent relative humidity

 

fl i

14 1.6 less than 70
10 ' 2.75 . 76

6 3.0 80

2 4.2 more than 140

 

v a

At 85 to 88 deg. F. and 32 to 44 per cent relative humidity

 

14 3.2 42

10 4.0‘ 46
6 5.3 70
2 6.49 120

 

At 58 to 60 deg. F. and 58 to 70 per cent relative humidity

 

v—y

14 1.7 ' 7o
10 2.3 85
6 3.6 115

2 3.8 170

 

 

42

TABLE 2. Depth of drying layer, inches, at various air
flows and three different temperatures.*

 

 

 

Temp. Drying Layer 14 10 6 2
85 to 88 Me + 2% more than 36" 9"
to 42"
MO -
85 to 88 Me + 4% 36" 2o" 5" 8"
to ' condensation
MO - 4% effect
72 to 74 Me + 2% 33" 29" 18 to 15"
to condensation
MO _ 2% 30"
72 to 74 Me + 4% l2" 9" 4" 3.6"
to
M0 - 4%
58 to 60 Me + 2% 26" 2o" 20" 20"
to
M0 -
58 to 60 Me + 4% 9" 8" 6" 4"
to
M0 - 4% .

 

 

*Initial moisture content 21 to 22 per cent, w. b.

43

time increases which means an increase in drying depth.
Figure 6 shows the velocity of 15 per cent moisture content
layer in the bin. As the air flow was increased the velocity
of this layer was increased. The change of velocity of the
drying layer is moved from 2 to 6 cfm per bu. air flow

after which it decreases.

If we compare the rates of 88 deg. F. and 74 deg. F
in Figure 6, it appears that the variation between these
two velocities is small as compared to the variation between
74 deg. F.and 60 deg. F. for the same degree of temperature
difference of the drying air. After 6 cfm per bu. air flow
these lines begin to level off which indicate that the
velocity of drying layer becomes a constant.

Figure 5 indicates the amount of water removed per
bushel of pea beans at various time intervals. The dis-
tance between 2-6, 6-10, or 10-14 cfm per bu. air flow
lines decreases with the increased air flows. This also
shows that the drying rate does not double with the appli-
cation of twice the air flow, at the same air temperature
and relative humidity. It also gives an indication of
average moisture content of the whole bin at a given time
and for a given air flow.

Figure 6 gives the velocity of 15 per cent moisture
layer at various temperatures. In this analysis 15 per
cent moisture layer is used because the safe storage mois-

ture content for pea beans is 15 per cent. At 4 cfm per bu.

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47
the velocity of this layer is 0.4 inches per hour at 60 deg.
F., 0.65 inches per hour at 74 deg. F., and 0.8 inches per
hour at 88 deg. F. The following relationship between

temperature and velocity of drying layer is presented:

t2
2 ( t1 )
t1, t2 = temperature in deg. F.

V1 __.\'T

velocity of 15 per cent moisture layer,
inches per hour

V1, V2
Thus, with the increase of 14 deg. F. of incoming tempera-
ture the change in velocity of this layer was 62.5 per cent
from 60 - 74 deg. F., and this increased 22 per cent when
the temperature of air was increased from 74 - 88 deg. F.
The change in velocity increases up to 6 cfm per bu. at all
temperatures and above this air flow the change in velocity
decreases gradually. Figure 6 shows the necessary temper-
ature and air flow requirement for drying a given depth

of bin within a given time for pea beans.

 

 

V = V ( t2 )"‘2) Fig. 6
1 2 t
l
D = D ( t1 )1'12 Table 1
l 2 t2
- 4
v1 = V2 ( Q2 ) ~5. Fig. 6
Q1
V1 Q1 ‘ o4

48

V
<—l _ <—-——Ql r ‘ ,<_D——Dl ) (Ta ) “ . V1 y
V .4. " _‘ “'7 rc
(i) - {—93-} = / D2 = ’12
l
*1 1'7
D _
Vl = V2 (DI )

This shows us the relationship between the velocity
of 15 per cent layer with respect to the depth of grain.)
From this the velocity of 15 per cent layer in a deep bin
can be determined and the total time requirement to dry a

given bin can be calculated.

V1, V2 = velocity of 15 per cent moisture layer,inches

per hour
D1, D2 = depth of dried grain below 15 per cent,inches
Q1, Q2 = air flow,cfm per bu.

Shelled corn. Shelled corn used for this work was

 

harvested with an Oliver experimental picker-sheller in the
Fall of 1957. The corn was at 35 - 37 per cent moisture.
content and was stored at zero deg. F. The same procedure,
apparatus, air flows, and air temperatures were used for
corn as for pea beans.

In general, for drying shelled corn takes less time
than pea beans. To dry shelled corn from 30.8 per cent

moisture content to 12 per cent wet basis required 41 hours,

49
whereas, to dry pea beans from 22 per cent to 12 per cent
required 40 hours. In both cases the air flow was 14 cfm
per bu. and temperature drying air was 86-88 deg. F. Table
3 gives the drying time required to dry the top layer below
15 per cent moisture content. The time required to dry
the top layer was 18.4 per cent greater for 10 cfm per bu.
than 14 cfm per cfm per bu., and was 144 per cent greater
at 6 cfm per bu. than for 10 cfm per bu. at 86 ’- 88 deg.

F; air temperature. At 6 cfm per bu. and 86 '- 88 deg. F.
condensation took place in the upper top 18 inches which
makes it longer to dry than expected. with 72 - 74 deg. F.
air. The drying time to bring the top layer up to 15 per
cent was 7.9 per cent more at the 10 cfm per bu. than at
14 cfm per bu. and the drying time was 52.2 per cent more
at 6 cfm per bu. than at 10 cfm per bu with 58 - 60 deg. F.
air. The drying time to bring the top layer below 15 per
cent was 26.4 per cent more for locfm per bu. than 14 cfm
per bu. and was 55 per cent higher for 6 cfm per bu. than
for 10 cfm per bu.

Condensation did not occur at 14 and lchm per bu. air
flows at all temperatures which were used in this work.
Maximum condensation occurred with 6 cfm per bu. air flow
and maximum amount of condensation was 4.2 per cent increase
in moisture content at 58 - 60 deg. F. air temperature and
occurred after 20 hours. At 2 cfm the drying rate was low

and the extent of condensation was 3.3 per cent increase in

50

i

TABLE 3. Drying shelled corn with different air flows.

 

 

Air Difference between moisture Time required for the
Flow content of top layer and bot- top layer to come to

cfm tom layer, when all layers 15 per cent moisture

per were less than 15 per cent content or below,

bu. moisture content. hours.

 

At 86 to 88 deg. F. and 40 to 47 per cent relative humidity

 

14 3.1 38

10 2.0 ' 45
6 3.5 110
2 ' mold growth

 

At 72 to 74 deg. F. and 50 to 57 per cent relative humidity

 

14 3.0 70
10 2.5 ' 92
6 I 4.7 122

 

At 58 to 60 deg. F. and 58 to 64 per cent relative humidity

 

14 .34 76
10 4.0 120
6 3.7 172

2 . 3.0 250

._V— I“

 

 

 

51
moisture content and was noticed less than 10 hours at
58 - 60 deg. F. At 72 -— 74 deg. F. condensation increased
the moisture content of the top layer by 1.6 per cent.

In drying shelled corn the extent of over drying was
noticed. The difference between the moisture content of
the top and bottom layer was as high as 4.7 per cent and
was noticed at 6 cfm per bu. and 72 - 74 deg. F. ‘This
difference was minimum (2 per cent) at 86 - 88 deg. F. and
10 cfm per bu. air flow. At 14 cfm per bu. air flow this
difference was constant with various temperatures (Table 3).

At the end of the drying test shrinkage in volume of
the bin was noticed. This shrinkage was due to the removal
of grain samples and drying of corn. The maximum shrinkage
in volume was 27.3 per cent, out of which decrease in
volume due to sampling was 2.72 per cent, which occurred
at 14 cfm per bu. air flow and 86 - 88 deg. F. While
drying the corn offered more resistance to the air flow.
The increase in static pressure was 0.18 inch of water for
3.5 foot depth. .

At a low air flow of 2 cfm per bu., due to low drying
potential, the drying rate was slow and the total time re-
quired to dry a bin of 3.5 feet below 15 per cent moisture
content was 250 hours.

The initial moisture content of shelled corn was 35
per cent, wet basis, and at 2 cfm per bu. and 86 - 88 deg..

F. mold occurred in all the layers except the bottom. The

52

grains had a musty flavor and grain clods were formed. To
dry a bin of 3.5 feet below 15 per cent required 250 hours
at 2 cfm perlml.and 58 - 60 deg. F. air temperature (Table
3). The time will be more if the air temperature was low
or if the relative humidity of drying air was high. For
drying a bin of 6 feet deep it will require 496 hours which
is 20.30 days. The time is longer than that is recommended
(2-3 weeks) for drying shelled corn in Michigan.

The relationships of time of drying, temperature of
air, and depth which can be dried to 15 per cent moisture

are presented below:

 

 

t1 '65
V1 = V2 (__ ) From Fig. 8
t2
Q .
D = D2 L——£—) 93 From Table 3
1 Q
2
D1 = D2 (EL__)O'63 From Table 3
t
2
Q1
D2 .1. X.63
1
I
D .63
= V 2 —_
2 ( ).93
D1
_ D2 .678
V1 ‘ V2 (‘57—)
l
V1,V2 = velocity of 15 per cent moisture, w.b.,
layer, inches per hour
D1,D§ = depth of grain dried below 15 per cent,

inches

53

t1, t2 = temperature of drying air, deg. F.
_ 72 0.678
V1 — .10 (—erj

.145 in. per hr.

Total time required to dry 6 foot bin of shelled corn
with 2 cfm air flow will be as follows:

Vl = .145 in. per hr., at 2 cfm bu.
bl = 72 in.
72
0 = -—-— = 4 6 hours at 58-60 deg. F. air

.145 12::

This drying time is 3 weeks, and under conditions such

as higher initial moisture content of the shelled corn or
lower temperature or higher relative humidity the time
requirement for the bin will be more than 3 weeks. Thus,
to be on the safe side the air flow for drying shelled corn
should be 3.5 cfm per bu. The air flow of 3.5 cfm per bu.
will dry the bin of 6 feet deep in 13.7 days at 58to 60

deg. F. air temperature.

.678 ’
Vl = (.170) (%g) for 3.5 cfm per bu.

.218 inch per hour

9 = "“ = 330 run > = 13.7 days

. 54

Table 4 shows the depth of drying layer at different
air flows and air temperatures. The depth of drying layer
is expressed in terms of initial moisture content of the
grain (MO) and equilibrium moisture content of drying air
(Me) for

1. (MO - 2) per cent moisture content to (Me + 2)

per cent moisture content, and
2. (MO - 4) per cent moisture content to (Me + 4)
per cent moisture content.

The depth of drying layer was 42 inches or more at
all temperatures at 14 cfm per bu. air flow on the basis
of (MO - 2) per cent to (Me + 2) per cent. The depth of
drying layer was 33.2 per cent higher at 88 deg. F. than
72 deg. F. at 6 cfm per bu. air flow and 8 per cent higher
at 74 deg. F. than 60 deg. F. air temperature. '

Using the depth of drying layer as (MO - 4) per cent
to (Me+4) per cent, at 14 cfm bu., 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 60 deg. F.
air temperature. At 6 cfm bu. air flow the depth of drying
layer was 23.1 per cent higher at 88 deg. F. and 30 per
cent higher at 74 deg. F. than at 60 deg. F. air temperature.

The depth of the drying layer expressed in terms of
(MO - 4) per cent to (Me + 4) per cent gives the following

relationship:

Q1 1.06

55

TABLE 4. Depth of drying layer, inches, at four air flows
and three different temperatures for shelled corn.

 

 

 

 

-—::~—- i 11 w _:=
cfm per bu.
Temp. of Drying Layer 14 10 6 2 VI
86-88 Me + 2% 42 42 36 —
to
M0 -
72-74 Me + 2% 42‘ 36 27 22
to .
MO -
58-60 Me + 2% 42 32 25 20
to
M0 -
86-88 Me + 4% 42 22 16 —
to
M0 - 4%
72-74 Me + 4% 32 18 13 10
to
M0 — 4%
58-60 Me + 4% 24 14 10 8
to
M0 - 4%

 

*Values for an initial moisture content of 35 per
cent, w. b.

56
Q1, Q2 = air flow, cfm per bu.

depth of drying layer, inches

d1, d2

From the above equation, for a given depth of drying
layer at a particular air flow, the depth of drying layer
at any other air flow between 2 to 14 cfm per hour air

flows can be calculated.

Statistical Analysis

Sample calculation

 

 

Moisture content ratio = M . Me
”0‘ Me
M = loge M ' Me
Mo' Me
Depth factor = 'g = d 0 = 13.6 lb. total grain
g _ x 60 x .24 x t x 0
.01 x M x H
g
37 x 60 x .24 x 15 x 24
= .01 x 20 x 1170 = 8~“ lb.of grain
8.4

d = I376_ = .614

General formula to find the time requirement:
9 = 173.8 - 1.39 (t) + 8 (.m) + 35 (d) - 13(Q)
= 173.8 - 1.39 (60) - 8 (1.3757) + 35 (.614) -13(3)
= 71.8 hr.

0 = time to dry shelled corn below 15 per cent
moisture content, hours

t = temperature of drying air, deg. F.
d = depth factor, feet
air flow,pounds per minute per square foot

_ 57
The following standard statistical analysis, as sug-
gested by Dr. W. Baten, Agricultural Experiment Station

Statistician, was used:

1. [ztm 'Q-K—Z—W MIFMLQUC +[ZnD-Qelgm f +
[55"I”'<Z:21£;33 j ==(:Ir~e-(ZEEH§E§E]
2, [214. @7935 + :Ltm -tzt)(2mlic + L511 211L222}...
211 {my 3 .. [its 43.00.95]
3. [21313122191293 t +[Zmo «gleégggjc + F21?- (zn +11%
[Di-w? :- i-ZDe 1211x219]
4. [iti‘EUQ-ilbl [2W1 irng-lgc 1' C-Z‘lm -(zm (21)]2

 

 

 

 

 

“[21 12L. 3 ___ L216 411M: 9)]
a 5 - bt - cm - fd - Sq
e = a. + bt +' cm + fD + gq + it“ 6

Four equations and four unknowns solved simultaneously:

2392(b) - 25.7(6) + o(f) - 8.67(s) = ~364o
—25.7(b) + -489(C) + o(f) - .855(2) = ~22.36
- O (b) + o (c) + 2.027(f) + o(g) = 471

.867(b) - .855(c) + o(f) + 8.311(2) 175.33
b = —1.39, f = 35.02, g = -l3.0, c = 8.0, a = 173 8

 

Te = fill-@331 -b Ito—Qt)(29.)J-CLG] "FEEJ'jL-FJ

h"5

 

=:12r3
+1.39 (-364o) - q (~22.36) + 35 (1166) + 13 (175.33)

8

rRzmoo .mvza Mm z. cub: mmakmaz hzmomma n. “.0 >._.~ooi_m> 0.0:.

 

an mum Emu
e._ ~._ 6.. m w w w
VIN.
D
v V.
«:4. mean
I m.
m NF
'0.
O
u on T.

 

83d SSHONI

BOOH

\ )1
\0

TABLE 5. Relationship of observed and calculated values
for drying time.

 

 

 

 

los. Pouncs Of Air Time in Hours
Temp. M _ Me Depth per sq. ft.
def.F .__~__~_ Factor De1n minute Observed Calculated
MO— Me
t -m (i, q @1 92
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
60 0.9136 1.22 1.30 116 108.5
60 0.9136 1.93 1.30 144 133.5
60
60
74 1.050 0.325 2.93 34 41.92
74 1.0506 0.69 2.93 53 5 .80
74 1.0223 0.282 2.14 54 62.70
74 1.0223 0.638 2.14 73 74.95
74 0.8774 0.486 1.27 74.2 64.92
74 0.08774 1.000 1.27 116 83.14
i
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 3 .31
88 0.8099 0.624 1.22 61 50.83
88 0.8099 1.15 1.22 90 69.24

 

 

0.0.

meow umn aim...
3561.00 304mm?

mmmkj ._.memn_n=o z. 0_._.<m ._.zm._.zoo 9.50.902 m 0E
$50:
03 o.~_ Om: 0.0 00

N
, /

  
 

. 00

Z .3

/ 0..

//
//

 

oxomn u 02

SUMMARY

The effect of air flow rate and temperature for drying
pea beans and shelled corn in deep bins was investigated on
a laboratory scale.

A refrigerated box of 40 cubic feet was a source of
incoming air. The box was maintained at a constant tem-
perature and 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 electrical
resistance heater, 14 deg. F. higher. From heater box air
was forced through the grain and back to the refrigerator.

The test bin was constructed of steel with a 4 inch
outside diameter and 42 inch height. The bin was insulated
with 1.0 inch asbestos insulation to provide adiabatic
drying.

Pea beans were dried satisfactory at 6 cfm per bu. air
flow at 58-60 deg. F. air temperature. Cracking of pea beans
did not occur at all temperatures, 58-88 deg. F., and air
flows, 2-14 cfm per bu., applied in this study. The rate
of drying of pea bean is slower than that of shelled corn.
The velocity of 15 per cent moisture is a good indication
of movement of drying zone. By knowing the velocity of the
<irying layer the total time required to dry a bin can be

estimated. At higher air flow, the temperature has much

62

less effect on drying layer depth than at low air flows.
Equal moisture content lines show how the depth of drying
layer increases with increase in time units for a given
air condition.

From the general formula presented, the total time
required to dry a bin of shelled corn can be calculated.
Also after certain time of drying, the depth of grain below
15 per cent moisture content can be predicted. At the
higher temperatures with 2 cfm per bu. air flow, mold
growth occurred on shelled corn. For drying shelled corn
3.5 cfm per bu. is the lowest air flow that can be used.
The velocity of 15 per cent moisture layer is expressed in
terms of inches per hour movement. This velocity remains
fairly constant at all temperatures considered at 14 cfm
per bu air flow. The drying of shelled corn was more

uniform at lower temperatures.

Pea Beans

 

1.

CONCLUSIONS

For drying of pea beans with unheated air
minimum air flow is 6 cfm per bu. within the
temperature range of 60 - 88 deg. F.;2 cfm per
bu. air flow is low which takes longer time to
dry for a given bin of 6 feet depth.

The velocity of 15 per cent moisture layer for
pea bean is expressed in terms of temperature
of drying air for air flows 2 - l4 cfm per bu.

and relative humidity 36-70 per cent.

t
2 -l. 27
V1"‘V2 (t1)

The depth of drying layer for pea bean increases
with increased temperature, for a given air flow.

This can be expressed as follows:

t1 ‘O.91

 

The velocity of 15 per cent moisture layer for
pea beans is related in terms of air flow, within

the range of air temperature studied

-.54

64

Shelled Corn

 

5.

The time required to dry a given depth of bin

can be calculated by the following formula:

D .658
_ 2
v1 .. v2 (_.__._._._Dl )
0 =_D_.’e‘_
V2

V1, V2 are the velocities inches per hour of
15 per cent moisture layer at depths D1 and D2
in inches. This formula works all temperatures
between 60 to 88 deg. F. and at 6 cfm to 14 cfm
per bu. air flow.

The lowest acceptable air flow for drying shelled
corn without mold damage under Michigan conditions
is 3.5 cfm per bu. over the temperature range
considered.

The depth of drying layer is expressed in terms

of air flow as follows:

 

dl =d2

This formula applies from 2-14 cfm per bu. air
flows and 50-60 deg. F. air temperatures.

The velocity of the 15 per cent moisture layer
can be expressed in terms of drying air temper-

ature deg. F.

 

65

V = velocity of 15 per cent moisture layer, inches
per hour. This equation applies within the range
of 60-88 deg. F. air and 2-14 cfm per bu. air
flow. This equation can be used to determine the
time to dry a given depth of grain.

The time, 0, hours, is related to the moisture
content ratio, m, temperature, t, deg. F., air
flow, q, pound of dry air per square foot per
minute and the depth factor, d, of grain. These
variables are related by the following general

formula:

0 = 173.8 - 1.39(t) + 8.63(m) 7+ 35.02(d)-13(q)

From this equation the time required to dry a

given bin of shelled corn can be calculated.

,
74-!W’

SUGGESTIONS FOR FUTURE STUDY

From the experience gained, further studies should
be undertaken to further develop the relationship
between drying time, moisture content ratio, air
flow, and temperature of drying air and relative
humidity with gains above 40 per cent moisture
content, wet basis.

With picker-sheller grains are harvested at higher
moisture content and work should be done on corn
above 40 per cent moisture content.

a. Study the resistance to the air flow

b. Shrinkage problems

c. Pressure drop

Additional studies of drying grains in fluidized
bed by agitation should be carried on for getting
sufficient basic data.

Consideration should be given to develop the
theory involved beyond the given limitations.
Further efforts should be directed toward the
development of equipment and procedure for measure-
ment of moisture contents and temperature at
various locations in a single kernel.

Determine the effect of drying on size and shape

of grains at different moisture content.

10.

11.

REFERENCES

Agricultural Statistics. (1956) Data on grain pro-
izction and storage on the farm, pp. 27-30,3l, 33,
2.

Bailyq P. H. (1958) Hop Drying Investigations, Journal
of Agricultural Engineering Research, Vol. 3-1, pp.
315-46.

Deshmukh, A. P. (1957) Unpublished Research Data,
Department of Agricultural Engineering, Michigan
State University, East Lansing, Michigan.

Hall, 0. w. (1957) Drying Farm Crops, Edwards Brothers,
Inc., Ann Arbor, Michigan.

Hall, C. W., J. H. Rodriguez-Avias.(l958) Equilibrium
Moisture Content of Shelled Corn Agricultural
Engineering, Vol. 39-8, pp. 466-470.

Henderson, S. M., R. L. Perry. (1955) Agricultural
Process Engineering, John Wiley and Sons, Inc.,
New York.

Hukill, W. V. (1947) Basic Principles in Drying Corn
and Grain Drying, Agricultural Engineering, Vol.
28-8, pp. 338-440.

Hurlbut, L. W., G. M. Petersen. (1952) Harvesting and
Conditioning, Grain Storage, Drying, and Shrinking

Problems, Agricultural Engineering, Vol. 32-7, pp.
421-424.

Lehman, E. W. (1926) Grain Storage, Drying, and
Shginkage Problems, Agricultural Engineering, Vol.
7-. .

Perry, J. S. (1957) Aeration of Bulk-stored Pea Beans
in Michigan, quarterly Bulletin of Mich. Agri. Expri.
Station, Michigan State University, East Lansing,
Michigan, Vol. 40-2, pp. 331-17, November.

Shedd, C. K. (1953) Resistance of Grains and Seed to
Air Flow, Agricultural Engineering, Vol. 33-9, Pp.
616-17.

68

12. Simmonds, W. H. C., G. T. Ward, and E. McEwen. (1953)
The Drying of Wheat Grain, Part I, The Mecanisms of
Drying, Trans. Instn., Chem. Engr., Vol. 31, pp.
267-78.

13. Simmonds, W. H. C., G. W. Ward, and E. McEwen.(l953)
The Drying of Wheat Grain, Part II, Through-Drying
of Deep Beds, Trans. Instn. Chem. Engr., Vol. 32.

14. Wenner, H. L. Die voraussetzungen far die Lagerung und
Beluftung von feficht geerntetem Getreide, Aus den
Arbeiten des lnstituts fur Landtechnik, Bonn (1955).

APPENDIX

TEW S-BS'F
M FLOW Helm/m

'1. WISTURE CON VENT

  

 

40 so so 70 no
ms

FIGIO LAYER DRYING OF SIELLED CORN

YEW BG-M'F
AIR FLW 6 elm/bu

    
 
  
 

 

so
2
u so
“a
U 2
5
.-
§ZO
..
z
...
U
x I
X”.
‘ «6 2'0 at 4'0 5'0 ab 73 to
runs
no 12 men name or swim cam
TED 72’F
m now 10ch
E
530
3
U
£25-
5
t
i d D
120“ "1
E. \
g
g l5 D\

; .11 i,

no 20 30 00
HG 14 LAYER DRYING 0F SWELL!!! CORN

1) r
'5

TE. 00- II’F
AIR FLOW Del-II-
.47

  
  

FEKBIT WSW CONTENI

 

5
3
3.1.
S
8

. fl

‘0 70 N
ms

F16“ LMRWMG 07m CW

TE” 72'F
AM FLW Helm

 

N
9

'1'

”CENT “SHINE ooumn'
1‘

 

 

' nun.
PI. LIVE. “NOW MC“

1/17 M. Jada-I

   
 
  

TEMP n": ’51.”: ge-grvr
AIR FLW 2 chm ‘ 35. am FL’W .4 am It...

 

 

 

 

 

! I-
S g ~
0
g 254*- was-1
" 5
§ 11
.— zo-ii \ ‘m— 8204
z \ *\ F
2
k In
E 4 .4— - .1... .
a! I’
4 l é I I
' ' ‘ V I Y — Y ’ " ' 7-1
20 w ”'58 w '26 'h a '0 2° 30 40 50 £0 7C. an
FIB I6 LAYER m N m COM nouns

FiG I7 LNER DRYiNG OF SELLED COMO

'EMP 56-60" ,
Aifl FLOW :0 din 'bu

   

TEMP WP

 

 

 

 

 

33 35 - - AIR ‘.CW 6 Urn/h;
‘ I
530‘ 530‘
y E
8
1.925" O J
a
a g“
r- l-
§20" g2 d
.—
5 E O
gran Er r
—o
.6 2'0 3'0 :6 Jo at} as ' . . 15-8
HOURS 6 40 Gr "80%“ 100 IZC 14C 160
s
“6 I3 LAYER 0‘1““ 0" S‘ELLED CORN HG I9 LAYER DRYING CF SHE_.ED VCR“!

  

TIIP‘SO'CU F

 

 

 

 

 

T . . 0
3° ma now 2 elm/bu E” 73 7‘ F
AIR FLOW 14 cfm/m
S .-
ia‘ '
.. a . g
0
I!
a 10‘ .
y.
9.. . g
Eh. J - '
S . a;
1w . 2 t
(l ‘
a 7:} ‘7.
l ' ' ' U U f 1 a 4"
go 40 00 to DO IZO I40 50
HOURS 0 ‘ .
FIG-20 LAYER mo N SHELLEO COIN “CURB

FIG 2| LAYER MYING Of “(4 Hi .1‘.

nut-3'

 

 

1020506506on

MOMS
FIG 22 LAYER mm W PEA BEANS

10» W70!

  
  
  

505mg current

:3

PERCENT

 

 

is ab 4'5 0'0 13 9'0 son an
ms
neuwumoormm

 

m
..me0' PIA“

 
 

  
  

   

N '0 a U
M
FIG 23mm 0 rule”.

mmm m7

   

D 10 IO 4 D I) 70 U

was:
H04. LAYER mu 0 NA“.

 

  

1'" am
AIR FLOW 6 din

70366-5!

TEN? .G'OI'F
AIR FLOW 2 cfm/bu

N
O
J

O O
l 1

PERCENT MOISTURE CLN'LENT
I

I2-

 

 

 

:o 20 so 40 so 80 7'0 so
nouns
FIG 20 LAYER Dawns or 95.: scans

     
 

TEMP 50 'GO’F
AR FLOd DCFM/bu

NT
f ‘3

PERCENT MOISTURE CDN TE
3

B
A

 

 

I0 20 30 Q 50 00 7'0 00
nouns
FIG- 30 LAYER DRYING G PEA CANS

TEMP 58"60‘F
AIR FLOW 2 dm ’bu

 
 
 
 
 
    

a
1

7?

PERCENT Maswat coursm
¥

 

 

2'0 4'0 ab 30 160 I50 :40 60

FIG 32 LAYER onvma OF PEA BEANS

PERCENTAGE 'A’IS' IRE CONTENT 0" W8

YEW 53'60‘F
AIR FLOW I4 L'm’m

 

 

 

no 50 3'0 4'0 50 so 70 so
nouns
FIG 2, -JVEQ DRV'NG OF DEA BEANS

TEA? 58-bO'F
AIR FLOW 6 .fm
RH 50-70

 
 
  
 
 
   

_ — - '9
b m G 0
l L

r?)
1

WPCENT MET“ LIONTENT

 

4%.

T I
b 30 Q5

 

rK)
FIG 3: LAYER DRYING OF PEA BEANS

 

 

 

TEMP 72°F
3:? AIR FLOW 6 cIr 1»
\\
2 ‘
11‘ so 5‘
é
§25«
g \ \
120-4
p.
Z “\I
§
I54 W 4 .
g " z. .\.
\ x A \" fl. 1‘
‘J ‘—T* _— r” Y ' I \ "
'5 30 45 60 75 90 :05 .2-
HI URS

FIG I5 LAYER DRYING CF SHELLI a L'un

70366-5