Design Grain Dryer

7/27/2019 Design Grain Dryer

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Design &Study of Grain Dryer

CHAPTER - I

INTRODUCTION

I) HISTORY & IMPORTANCE OF DRYING

India produces about 150 million tonnes of food grains per year. The major

components of production are 47 million tonnes of wheat, 4 million tonnes of rice, and 1!

million tonnes of pulses "#non. 1$%7&. 'ue to technological ad(ances in agriculture and the

introduction of high)yielding (arieties, this may increase. *rom this production, an a(erage

10+ is lost during posthar(est operations between the field and consume. This means that

about 15 million tonnes of food grain, (alued at about #-40 million "Indian upees 10,%00

million& goes to waste. The major share of the loss occurs during storage of surplus stoc/.

#mong the (arious causes of losses, the most important one is improper drying before

storage.

The preser(ation of agricultural produce by drying is a long)established

techniue. un drying in the open, on mud)plastered or concrete floors, is the con(entional

method of drying grain and also cash crops li/e chillies, and plantation and horticultural

crops. The drying time reuired in the open sun for these crops ranges from 5 to 45 daysdepending upon the crop to be dried. 2nfa(ourable weather conditions are li/ely to occur

during the drying period and degradation in uality of the final produce therefore becomes

una(oidable.

It is well)/nown that deterioration in uality caused by improper drying cannot

be eliminated until impro(ed drying systems based on mechanical dryers ha(e been adopted.

3owe(er, for many reasons, these systems ha(e not been adopted. The main reason that is

encountered is a lac/ of organiational or go(ernment incenti(e to the farmer to deli(er a

uality product that might command a premium price. This results in not only a negati(e

attitude, but also leads to the o(erall uality of the product gathered at mar/et points being

alarmingly poor.

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# second important reason for not using dryers is their high initial costs. ost

of the commercially a(ailable dryers are designed to suit the needs of the processing industry

and their output capacity is therefore far abo(e the needs of indi(iduals, or e(en of farmer

groups. #n awareness of a(ailability of dryers and of their use and ad(antages in drying food

grain for better storage and mar/eting is lac/ing among crop growers. The main reason for

this is inadeuate e6tension programs. o far, e6tension agencies ha(e concentrated on

increasing production. The time has now come to see that grain sa(ed is eui(alent to grain

produced. 3igh technology has led to production targets being achie(ed, but much less

attention has been gi(en to minimising losses, which ha(e remained constant since the

beginning of the 8reen e(olution. #nnual postproduction losses by crop in India, e6pressed

as a percentage of total production, are estimated to be as follows9 wheat, %+: paddy, 11+:

pulses, $.5+: and all food grains, $.!+.

Commercial use o !r"ers

'ryers are used e6tensi(ely in grain processing industries such as rice milling,

pulse milling, and oil e6traction. 3ere the need for dryers has been realised not only for

proper storage of stoc/ but also for timeliness of subseuent operations where wetting ofgrain and redrying are in(ol(ed.

In the case of the rice milling industry, parboiling of rice is a common practice.

The population of the coastal belt of the country consumes parboiled rice and about 70+ of

production is processed in this manner. The paddy is soa/ed in water for (ariable lengths of

time depending on the process used and is then steaming.

3igh moisture content "m.c.& paddy is dried to 1-)14+ m.c. for milling. There

are about 100 000 rice mills with a total installed capacity of about 40 000 tonnes of paddy

per hour. #bout !0000 dryers of 1)- t;h drying capacity are in use in the industry. The most

commonly used dryer is the


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tempered for !0 minutes after e(ery hour of drying so to euilibrate the moisture and a(oid

stress crac/ing in further milling operations.

'ryers are also used in the pulse milling industry. 3ere both


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charges, loans paid, and interest on ad(ances. uch a system would no doubt benefit farmers.

They would not be reuired to ma/e forced sales of their produce and, as a result, storage

losses would be minimised.

*or such comple6es, selection of a dryer of the correct design is (ery

important. The large capacity dryers used in grain)processing industries are not economical or

feasible for most farmer groups. In India, the a(erage (illage has a population of about 1000

and the small amount of surplus grain a(ailable for drying at this le(el suits dryers of -)4

t;day capacity operating for 0 days per year. In India, many research organiations ha(e

de(eloped, or are currently de(eloping dryers for (illage groups, but so far with little success.

The main considerations for selection of a grain dryer suited to this le(el are9

The dryer should be of a sie that matches the amount of grain a(ailable in a (illage or

a cluster of (illages:

The dryers cost should be within the reach of users:

It must be simple in construction and operation and easily understandable to users:

The dryer should be simple in design so that it is easy for local artisans to repair, and

The dryer should be suitable for drying a range of crops.

S%eciic Prolems

'(" #(ere is a #reme!ous ee! o !r"ers *

To Farmers :

In year -00- near about %0+ loss of crops li/e blac/ gram, green gram etc. due to

hea(y rain at the time of har(esting. If there is a facility of dryers in e(ery (illage may be at

8rampanchayat le(el, this hea(y loss may be eliminated.

orghum crop 9) #fter total maturity period of sorghum crop. is not har(ested for near about

one month due to presence of moisture. ?ormally the problem faced by farmer is that rain

comes during this period and sorghum is affected, which results in bad uality as it turns

blac/. 'ue to this reason, the cost in mar/et is reduced. This loss can be reco(ered if the

dryers are used at this stage.

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#fter drying farmers can store the grains for a long period and it will send in

mar/et at the highest rate.

To Dal Mill:

In the 'al mill the pulses are dried at different stages. The drying is done on the

platform by using solar energy, which is time consuming and large manpower reuired. o to

a(oid this the dryers are used in the 'al mills.

To Food Corporation of India (FCI)

In foreign countries the grains are stored in ilos where there is on line drying of

grains but in India grains are stored in bags which is unhealthy. o, by applying dryers, the

problems of storage should be o(ercome.

To Industries

'ifferent types of dryers are used in following industries

1& Te6tile industries, paper mills.

-& >lastic and polymer industry.

!& @hemical industries.

4& *ood storage plants.

II) CHEMICA+ COMPOSITION OF GRAIN,-

8rain is a li(ing biological product, which germinates and respires also. The

grain is composed of both organic and inorganic substances, such as carbohydrates, proteins,

(itamins, fats, water, mineral salts and enymes.

III) EFFECT OF TEMPERATURE ON UA+ITY OF GRAIN.

Pro#eis, - #t temperature abo(e 500@ denaturation and e(en coagulation of proteins ta/es

place. #s a result, the water absorbing capacity of proteins and their capacity for swelling

decreases.

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S#arc(, -#t temperature abo(e 700@ and especially in presence of high moisture in the grain,

gelatinisation and partial caramelisation of sugars with the formation of caramel may ta/e

place which causes deterioration in colour of the product.

Fa#s, -#t temperature abo(e 700@, fats may also undergo a partial decomposition resulting in

an increase of acid numbers.

/i#amis, - The heat sensiti(e A ) (itamins present in the germ and aleurone layer are

destroyed at high temperature.

I/) PHYSICA+ PROPERTIES, -

The /nowledge of physical properties such as shape, sie, (olume, surface

area, density, porosity, colour etc. of different grain is necessary for design of (arious storing

and drying systems.

Porosi#", - It is the percentage of (olume of inter grain space to the total (olume of grain

bul/.

S%(erici#"9 ) phericity is the ratio of surface area of sphere ha(ing same (olume as thatof

particle to the surface area of particle.Coeicie# o ric#io, -The coefficient of friction between granular materials is eual to the

tangent of the angle of internal friction and depends upon grain shape, surface characteristics.

A0le o re%ose, -#ngle of repose is the angle between base and slope of cone formed on a

free (ertical fall of the grain mass to a horiontal plane.

/) THERMA+ PROPERTIES, -

The raw foods are subjected to (arious types of thermal treatment namely,

heating, cooling, drying etc. for processing. The change of temperature depends on the

thermal properties of the product. Therefore, /nowledge of thermal properties namely,

specific heat, thermal conducti(ity, thermal diffusi(ity is essential.

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Resis#ace o 0rai e! #o air lo1,

In the design of blowers for grain dryers, it is necessary to /now resistance

e6erted by grain bed to the air current blown through it. The resistance is dependent upon i&

bed thic/ness ii& air (elocity iii& orientation of the grains and i(& type of grain.

/I) CHANGES IN STORED PRODUCTS -

There are many changes, which occurs to a product during transportation,

handling, storage and preser(ing.

C(emical C(a0es -The effect of canning upon the minerals, proteins and (itamins of

(arious food products is a large scientific field in itself. In stored hay and grains, changes

occur in fat acidity, enymes, color and (itamins. These changes are influenced greatly by

moisture content and temperature, which are often used as a means of indicating the uality of

stored products.

Res%ira#io a! Hea#i0, - In hay, grains, fruit and (egetable products respiration or

breathing continues after storage. 3eat is produced by respiration process. The uantity of

heat produced is greatly influenced by moisture content and temperature of product.


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Tale 2.2 , Es#ima#e! loss o %ro!uc#io !uri0 (ar$es# a! s#ora0e.

>roduct 3ar(esting + torage +

Cheat, oat, rice, barley 5+ 4.5+

@orn 4+ +

@otton -.5+ 0.-5+

>otato 7+ %+

oyabean 5+ )

Pre$e#io, 3

a6imum loss occurs because of an accumulation of moisture in grain, e(en

though dry when placed in the storage. Two terms are used for preser(ation of grain through

moisture control, drying and aeration.

'rying is the procedure used to remo(e e6cess moisture from the grain to

reduce the moisture to a le(el acceptable for safe storage or for commercial sale. 'rying may

be accomplished by using either heated or unheated air.

#eration refers to mo(ing a small amount of air through the grain to cool and

(entilate the grain at freuent inter(als. The re(erse operation, turning refers to mo(ing the

grain through the air by transferring the grain from one bin to another.

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CHAPTER - II

THEORY OF GRAIN DRYING

8enerally the term refers to the remo(al of relati(ely small amount of moisture

from a solid or nearly solid material by e(aporation. Therefore, drying in(ol(es both heat and

mass transfer operations simultaneously. In con(ecti(e drying the heat reuired for

e(aporating moisture from the drying product is supplied by the e6ternal drying medium,

usually air. Aecause of the basic difference in the characteristics of grains in thin layer and

deep bed, the whole grain drying process is di(ided in to thin layer drying and deep bed

drying.

I) MOISTURE CONTENT, -

2sually the moisture content of a substance is e6pressed in percentage by

weight on wet basis. Aut the moisture content on dry basis is more simple to use in

calculation, as the uantity of moisture at any time is directly proportional to the moisture

content on dry basis.

The moisture content, m per, wet basis )

100CdCm

Cmm

+=

The moisture content, , dry basis percent

1006m100

m100

Cd

Cm

==

Chere Cm E weight of moisture.

Cd E weight of bone dry material.

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TA4+E 5.2 A%%ro6ima#e mois#ure co#e# or sae s#ora0e 7 81..)

CROPFOR SAFE STORAGE

FOR ONE YEAR FOR T'O YEAR @orn 1! 11

Cheat 1!)14 11)1-Aarley 1! 11

orghum 1! 10)11>ea beans 17 )

ice 1! )oyabeans 1! 10

II) EMC, - ost of agricultural products, specially the food grains absorb moisture from

en(ironment or loose moisture. #t a particular condition the moisture content of grain

depends upon the temperature and relati(e humidity of en(ironment. If the (apour pressure of

water present in grains is more than the (apour pressure of water (apours in the air, the water

present in grain (aporises and diffuses in the atmosphere. #lternati(ely, if the (apour pressure

of water present in grain is less than the atmospheric (apour pressure, grain will absorb

moisture from atmosphere. This property of gaining or loosing of moisture as per the

atmosphere condition is /nown as hygroscopicity.

The moisture content attained by a grain with respect to a set of atmosphereic

temperature and relati(e humidity is called the F@. In such condition, the grain moisture is

in euilibrium with surrounding air.

ethods for determination of F@. There are two methods for determination

of F@ )

i) S#a#ic Me#(o!, -

In the static method, the grain is allowed to come to euilibrium with the

surrounding still air without any agitation. This method is time consuming: at high relati(e

humidities mould growth in the grain may ta/e place before euilibrium is reached.

ii) D"amic Me#(o!, -

In the dynamic method, the air is generally mechanically mo(ed. The dynamic

method is faster and is thus preferred. The F@ is to be determined under constant relati(e

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humidity and temperature conditions of air. 8enerally, a thermostat is used to control the

temperature and aueous acid or salt solution of different concentrations are used to control

the relati(e humidity of air.

TA4+E 5.5 , Grai e9uilirium mois#ure co#e#: 7: 'e# asis: Rela#i$e (umi!i#": 7

8#I?3umidity

Temp0@10 -0 !0 40 50 0 70 %0 $0 100

>addy -! 4.$ 7.! %.7 $.%1

0.$1-.4 1!.5 15.$ 1$ )

>addy !0 ) 7.1 %.5 101

0.$11.$ 1!.1 14.7 17.1 )

>addy 44 ) ) ) ) ) 10.! 1-.! 14.! 1.5 )

Cheat white -5 5.- 7.5 %. $.41

0.511.% 1!.7 1 1$.7 -.!

Cheat !- ) 5.! 7 %.1

0.!11.5 1-.$ 14.! ) )

Cheat 4$ ) ) .- 7.4 $. 10.4 11.$ 1!. ) )helled corn

"C'&-5 5.1 7.- %.5 $.% 11.- 1-.! 1!.$ 15.5 1%.$ -4.

helled corn

"G'&!- ) ) 5.! . %.! 10.- 1-.1 1!.$ ) )

helled corn"G'&

4$ ) ) ) 5.! .5 7.% $.! 10.7 ) )

helled corn

"G'&70 !.$ .- 7. $.1

1

0.411.$ 1!.$ 15.- 17.$ )

orghum -5 4.4 7.! %. $.% 11 1- 1!.% 15.% 1%.% -1.$

orghum !- ) 7 %.71

0.-11.% 1-.- 1!.1 14.% ) )

orghum 70 ) . % $.41

0.711. 1-.7 14.! ) )

=ats -5 4.1 . %.1 $.1 10.!

11.% 1! 14.$ 1%.5 -4.1

Aarley -5 4.4 7 %.5 $.71

0.%1-.1 1!.5 15.% 1$.5 -.%

ye -5 5.- 7. %.7 $.$1

0.$1-.- 1!.5 15.7 -0. )

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III) DETERMINATION OF DRYING CONSTANT, -

There are two methods of determination of drying constant )

i) Gra%(ical Me#(o!, -The drying constant, H can be wor/ed out easily by finding out the slope of the

straight line.1

.1

y .01

x

.001 -0 40 0 %0 100 1-0 140 10 1%0 -00 -10 --0

'rying Time, inGra%( #o calcula#e !r"i0 cos#a#

ii) Hal lie %erio! me#(o!, -

If the time of one ) half response in a drying process be defined as the ?umber

of hours necessary to obtain a moisture content ratio of one)half, then drying euation.

eo

e

E F6p ) H

J can be written as )

H

-InorJHe6p

-

1-;1-;1 ==

andH

4InorJHe6p

4

14;14;1 ==

Therefore, by /nowing the (alues of 1;-or 1;4, H can be found out.

1-

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I/) DRYING EUATION,-

Aased on ?ewtonKs euation for heating or cooling of solids, a simple drying

euation is deri(ed as follows)

The ?ewtonKs euation is) &tt"Hd

dte=

If the temperature term t is replaced by the moisture term , then

&"Hd

de=

......................... "1&

where E oisture content "d.b&, +

E time, hr,

eE F@, "d.b&, +

H E drying constant , 1;hr

earranging the euation "1&

=

Hd

d

e

Integrating the abo(e euation within proper limits, we get

JHe6p

e0

e

=

ore

eo

In

H

1

=

e

eo

is /nown as the moisture ratio, ..

/) THIN +AYER DRYING, -

Thin layer drying refers to the grain drying process in which all grains are fully

e6posed to the drying air under constant drying conditions. i.e. at const air temperature and

humidity. 8enerally, up to -0 cm thic/ness of grain bed "with a recommended grain ratio& is

ta/en as thin layer. #ll commercial flow dryers are designed on thin layer drying principles.

i) Cos#a# ra#e %erio!, -

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ome crops including cereal grains at high moisture content are dried under

constant rate period at the initial period of drying. *alling rate period follows subseuently.

#s for e6ample, wheat is dried under constant rate period when its moisture content e6ceeds

7-+.

In the constant rate period the rate of e(aporation under any gi(en set of air

condition is independent of the solid and is gi(en set of air condition is essentially the same as

the rate of e(aporation from a free liuid surface under the same condition. The rate of drying

during this period is dependent upon.

'ifference between the temperature of air and temperature of the wetted surface at

constant air (elocity and relati(e humidity.

'ifference in humidity between air stream and wet surface at constant air (elocity and

temperature.

#ir (elocity at construction air temperature and humidity.

2nder adiabatic and controlled drying air conditions, the temperature of wetted

surface attains the wet bulb temperature. In the constant rate period drying ta/es place by

surface e(aporation and moisture mo(es by (apour pressure difference. The moisture contentat which the drying rate ceases to be constant is /nown as the critical moisture content of the

solid. The a(erage critical moisture content Lc for a gi(en type of material depends upon the

surface moisture concentration, bed thic/ness, rate of drying and characteristics of solids such

as shape, sie and the drying conditions.

ii) Falli0 - ra#e %erio!, -

@ereal grains are usually dried entirely under falling ) rate period. The falling )

rate period enters after the constant drying rate period and corresponds to the drying cycle

where all surface is no longer wetted and the wetted surface continually decreases until at the

end of this period the surface is dry.

The falling rate period is characterised by increasing temperature both at the

surface and within the solid. *urther more, changes in air (elocity ha(e a much smaller effect

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than during the constant rate period. The falling rate period of drying is controlled largely by

the product and is dependent upon the mo(ement of moisture within the material from the

center to the surface by liuid diffusion and the remo(al of moisture from the surface of the

product.

The falling rate period of drying can be di(ided into two stages )

"a& 2nsaturated surface drying.

"b& 'rying where the rate of water diffusion within the product is slow and is the controlling

factor.

>ractically all cereal grains are dried under falling rate period if their moisture

content is not (ery high.

iii) Remar;s o #(i la"er Dr"i0, -

?one of the theoretical euations represents the drying characteristics of grains

accurately o(er a wide range of moisture and temperature, on account of the following

limitations )

The theoretical drying euations are based on the concept that all grains in thin layer

are fully e6posed to the drying air under constant drying conditions and drieduniformly. Therefore, there is no gradient in thin layer of grain, which is not true for

finite mass depth.

The grain drying euation de(eloped from diffusion euations are based on the in

correct assumptions that '( and H are independent of moisture and temperature.

It is not possible to choose accurate boundry conditions and shape factors for drying of

biological materials.

'rying euation de(eloped from ?ewton euation for heating or cooling does not ta/e

into account of the shape of the material.

Therefore, the uses of theoretical drying euations are limited. 3owe(er, if

accurate results are not desired and the (alues of '( and H are /nown then the theoretical

drying euation can be used and gi(e fairly good results within a limited range of moisture.

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any empirical drying euation for different cereal grains are found to be

useful and freuently used as they gi(e more accurate results in predicting drying

characteristics of a particular grain for a certain range of moisture, temperature, air flow rate

and relati(e humidity. # few empirical drying euation are presented below9 )

Aec/er "1$5$& proposed the following euation for wheat9 )

E 1 ) %.7% "'( &1;-M 1!.-- "'( &

*or "'( &1;-N 0.0104

E 0.50$ 6 e6p ) 5%.4 '( J

*or "'( &1;-0.0104

where, '( E 7.1!5 e)1$$44;T

'( E m-;hr, E hr and T E 0H

Aased on drying euation for planar symmetry >abis and 3enderson "1$1&

de(eloped the following e6pression for diffusi(ity for thin layer drying of corn

' ( corn E 5.%5! 6 10)10e6p )1-50-;TJ on the basis of drying euation for

sphere, the following e6pression for drying constant H corn has been de(eloped )

H corn E 5.4 6 10

)1

e6p ) $041;TJChere / E 1;sec, T E 0H

/I) DEEP 4ED DRYING, -

In deep bed drying all the grains in the dryer are not fully e6posed to the same

condition of drying air. The condition of drying air at any point in the grain mass changes

with time and at any times it also changes with the depth of the grain bed. o(er and abo(e the

rate of o(erflow per unit mass of grain is small compared to the thin layer drying of grain. #ll

on farm static bed batch dryers are designed on deep bed drying principle. The condition of

drying in deep bed is shown in figure.

1

*ig.-.1

5o

isturecontentofpaddy"+&

'rying time in hr.

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The drying of grain in deep bin can be ta/en as the sum of se(eral thin layers.

The humidity and temperature of air entering and lea(ing each layer (ary with time depending

upon the stage of drying, moisture remo(ed from the dry layer until the euilibrium moisture

content is reached.


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8 E ass flow rate of dry air, Hg;hr m-

3s E 3umidity of the saturated air lea(ing the dryer Hg.;/g.

31E 3umidity of the air entering in to the dryer, Hg;Hg.

wd E Ceight of dry grain in the bin, Hg.

ii) Decreasi0 ra#e %erio!, -

#s soon as the drying front reaches the top of the bin, the rate of drying. tarts

decreasing and is termed as decreasing rate period. The time of drying for this decreasing rate

period can be e6pressed by )

=e

e6In

H

1-

where, -E Time of drying during decreasing rate period, hr.

e E Fuilibrium moisture content of grain "db&

H E 'rying constant, 1;hr.

E #(erage moisture content "db& at the end of decreasing rate period.

6 E #(erage initial moisture content "db& at the beginning of decreasing period.

The total drying time for grains in the bin is )

Total drying time , E 1M -

iii) Remar; o !ee% e! !r"i0, -

"1& If drying air at high relati(e humidity and relati(e low temperature is used, then the total

drying time will be (ery long due to slow rate of drying which may cause spoilage of grains.

"-& The correct choice of air flow rate is (ery imp.

"!& 'rying air at high temperature cannot be used due to the de(elopment of moisture

gradients within the grain bed. It leads to non ) uniform drying of grain. In general an air

temperature of 400@ " 150@ rise& is recommended for deep bed drying.

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/II) EFFECTS OF DIFFERENT FACTORS ON THE DRYING PROCESS, -

The drying rate is depend upon many factors, namely air temperature, air flow

rate, relati(e humidity, e6posure time, types, (ariety and sie of grain, initial moisture content,

grain depth, etc. of them, first four factors are imp. They are )

i) Eec# o air #em%era#ure, -

The rate of drying increases with the rise of air temperature. Aut the

euilibrium moisture content falls as air temperature increases.

ii) Eec# o air $eloci#", -

3enderson and pabis found that air rate has no obser(able effect on thin layer

drying of wheat when air flow was turbulent. #;c to them, air flow rate (arying from

10cm!;sec;cm-to % cm!;sec;cm-had no significant effect on the drying rate of wheat. Aut in

case of paddy and corn it has been found that air rate has some effect on rate of drying.

iii) Eec# o air (umi!i#", -

Chen the humidity of air increases the rate of drying decreases. The effect is

much smaller in comparison to the effect of temperature changes.i$) Eec# o air e6%osure Time, -

In the case of intermediate drying, drying rate of grain depends on its e6posure

time to the drying air in each pass. Total drying time, which is the sum of all e6posure times,

is dependent upon e6posure time. Total drying time reduces as e6posure time decreases.

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CHAPTER - III

METHODS OF GRAIN DRYING

o far, drying systems ha(e not been classified systematically. 3owe(er,

drying methods can be broadly classified on the basis of heat transfer to the wet solid.

#ccording to mode of heat transfer, drying methods can be di(ided in to 9

"a& @onduction drying "b& @on(ection drying and "c& radiation drying. There are other

methods of drying also, namely dielectric drying, chemical or sorption drying, (accum drying,

freee drying.

=f them, con(ection drying is commonly used for drying of all types of grain.

Co!uc#io Dr"i0, - Chen the heat for drying is transferred to the wet solid mainly by

conduction through a solid surface "metallic& the phenomenon is /nown as conduction or

contact drying. In this method, conduction is the principal mode of heat transfer and the

(aporised moisture is remo(ed independently of heating media. @onduction drying is

characterised by )

a& 3eat transfer to the wet solid ta/es place by conduction through a solid surface, usually

metallic. The source of heat may be hot water, steam, flue gases, hot oil, etc:b& urface temperature may (ary widely:

c& 'ust and dusty materials can be remo(ed (ery effecti(ely. @onduction drying can be

carried out either continuously or batch wise.

Co$ec#io Dr"i0 ,- In this drying, the drying agent " hot gases & in contact with wet solid

is used to supply heat and carry away the (aporised moisture and the heat is transferred to the

wet solid mainly by con(ection. The characteristics of con(ection drying are )

a& 'rying is dependent upon the heat transfer from drying agent to wet material.

b& team heated air, direct flue gases of agricultural waste, etc. can be used as drying agent :

c& *uel consumption per /g of moisture e(aporated is always higher than that of conduction

drying.

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@on(ection drying is most popular in grain drying. It can be carried out either

continuously or batch wise.

Convection drying further classified as -

Na#ural air !r"i0, -The unheated air as supplied by nature is utilised.

Su%%leme#al (ea# !r"i0, -drying with supplimental heat just sufficient amount of heat

"temperature rise 50to 100@& only is supplied to drying air.

Hea#e! air !r"i0,-

In heated air drying air is heated to a considerable e6tent. The natural air

drying and drying with supplemental heat method which may reuire one to four wee/s or

e(en more, heated air drying is most useful when large uantity of grain is to be dried within a

short time.

Ra!ia#io !r"i0 ,-

adiation drying is based on the absorption of radiant energy of the sun and its

transformation in to heat energy by the grain, sun drying is an e6ample of radiation drying.

The effecti(eness of sun drying depends upon temperature and relati(e humidity of the

atmospheric air, speed of the wind, type and condition of the grain, etc.Su !r"i0, -

un drying is the most popular traditional method of drying. # major uantity

of grain is still dried by the sun in most of the de(eloping countries.

Ira - Re! Dr"i0, -

Infra)red rays can penetrate into the irradiated body to a certain depth and

transformed into heat energy, special infra red lamps used as generators in infra red radiation.

adiation dryers ha(e been used in many countries for drying the painted surfaces of

machinery, te6tile industry and food industries.

Dielec#ric !r"i0 ,-

In dielectric drying, heat is generated within the solid by placing it in a fi6ed

high freuency current. In this method, substance is heated at the e6pense of dielectric loss

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factor. The molecules of the substance, placed in a field of high freuency current are

polaried and begin to oscillate in accordance with the freuency. The oscillations are

accompanied by friction and thus a part of the electric energy is transformed into heat. The

main ad(antage of this method is that the substance is heated with e6traordinary rapidity.

C(emical !r"i0 ,-

Barious chemicals such as sodium chloride, calcium propanate, copper

sulphate, ferrous sulphate, urea etc ha(e been tried for the preser(ation of wet paddy of these,

common salt has been pro(ed to be effecti(e and con(enient. The common salt absorbs

moisture from paddy but it cannot penetrate in to endosperm through hus/ layer. This is

uniue property of paddy.

Sac; !r"i0, -

This method is particularly suitable for drying of small uantity of seed. The

grain bags are laid flat o(er holes cut on the floor of a tunnel system so that heated air can be

forced up through the grain from an air chamber underneath.

DDD

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CHAPTER - I/

GRAIN DRYERS

8rain dryers can be di(ided in to two broad categories, unheated air dryers and

heated air dryers. 'ifferent types of grain dryers of both groups ha(e been discussed in this

chapter.

I) UNHEATED AIR DRYERS, -

2nheated or natural air)drying is usually performed in the grain storage bin.

?atural air)drying is commonly used for on farm drying for a relati(ely small

(olume of grains. Fither full bin or layer drying system is employed in natural air drying.

The period of drying for either system may be as long as se(eral wee/s depending on the

weather. In layer drying, the bin is filled with a layer of grain at a time and drying, is begun.

#fter the layer is partially dried, other layers of grain are added periodically, perhaps daily

with the continuation of drying until the bin is full and whole grain mass is dried. In full bin

drying a full bin of grain is dried as a single batch. Then the drying bin is used for storage

purposes. The air flow rate pro(ided is relati(ely low. Though natural air is supposed to be

used, an air heating system should be /ept so that supplemental heat may be supplied tonatural air during rainy seasons. 8rain containing moisture more than -0 + should not be

dried with natural air. #s in natural air drying the grain is aerated and stored in the same unit,

the complete installation simply consists of a storage unit euipped with ducts for air

distribution and de(ices for air e6haustion and a blower.

II) HEATED AIR DRYERS ,-

3eated air dryers of different types are as follows.

i) Dee% e! !r"ers ,- These batch in bin dryers are of large capacities to se(eral hundred

tonnes. The most common shapes are round or rectangular. To operate deep bed dryers

efficiently following rules may be followed 9)

-!

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#n air flow rate of -.$4 ) !.$- m!;minute per tonne is

recommended. ates abo(e !.$- m!;minute per tonne may

result in une(en drying and is e6pensi(e in operation.

If the moisture content of grains is up to 1%+ the layer

depth of grain should be limited to ! m and for abo(e 1%+

moisture depth recommended is -.5m.

The net perforated are of the floor should be 15+ of total

floor area. #ir (elocity of !00 m;minute through opening

is preferable.

ii) Fla# e! !r"er ,-

In the flat bed batch type dryer

surface area of dryer is more and depth of drying

layer is less. These dryers are of usually 1 ) - tonne

capacity. 8rains are spread 0. to 1.- m deep o(er

the perforated floor and dried. The main

ad(antages are The whole batch is dried uic/ly.

There is less li/ehood of o(er drying.


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In mi6ing dryers, baffles are pro(ided to cause the grains to mi6 during their

downward flow. These dryers use low air flow rates of

50)$5m!;min tonne and high drying temperature of

50@ Oig)Oag columns enclosed by screens on both

sides are used primarily to achie(e mi6ing action during

drying process.

5) No-Mi6i0 !r"ers ,-Aaffles are not pro(ided in

the column and drying ta/es place between two parellel

screens, 15)-5 cm apart. In these dryers high air flow

rates of 1-5)-50 m!;min ) tonne can be used. 'rying

air temperature of 540@ used in non mi6ing dryers.

i$) Recircula#i0 !r"ers ,-

In this type, a multipass

procedure is used to a(oid e6cessi(e drying stress.

'uring each pass, the grain are e6posed to the

heated air for short time " 15)!0 minutes & andabout 1 ) ! + of moisture is remo(ed. 'rying

temperature is 0 ) %00@ is used. 'rying is faster

and effecti(e because of continuous mo(ement of

grains during short drying times.

$) +. S. U. !r"er ,-The design of this continuous dryer was de(eloped at the


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C.O.E.&T.,Akola

Fi0. +SU !r"er

# 1.garner -. duct !. dry material outlet 4. hopper 5.continuous flow .door 7.roofA 1. @ross section of drying chamber 1. air e6haust -. air inta/e


$i) Flui!i


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Fi0. Tra" !r"er1. e6it air -.blower !.heater 4. inter spacebetween trays 5.trays . plenum chamber

Fi0. Direc# !r"er 8a#ural co$e#io)

1.e6it air-.chimney!.transferablepanel4.bamboo5.air inta/e .clear plastic sheet


inclined flights, then dropped, ensuring good air;grain contact. In small scale rotary dryers,

the walls are heated by direct contact with flue gases.

$iii) Tra" !r"er ,-

In a tray dryer, many shallow trays are

/ept one abo(e the other with a gap between in the

drying chamber. Try dryer is generally used for drying

(egetables. If the heated air is coming from the sides of

drying chamber, the trays may not ha(e perforated

bottom. >roducts are /ept in thin layers in the trays.

i6) Tuel !r"er ,-

It is similar to tray dryer. Chen

the group of trays is mo(ing in a tunnel, the

system becomes a tunnel dryer. The flow of

heated air in a tunnel dryer may be concurrent

or counter current.

6) Grai !r"i0 i a0s ,- This method is useful to dry grains in

small uantities. ethod reuires large number of uns/illed labours and more space is

needed. The heated air is forced through the rac/s and

bags. 'uring drying, the bags are in(erted at least once to

accomplish drying on both sides of the bags.

6i) Solar !r"ers ,-olar drying of agricultural products

can be ad(antageous to sun drying for the farmers of

de(eloping nations. Two basic principles are inherent in the

operation of solar dryers, firstly solar heating of air

and secondly the remo(al of moisture from the wet

material by the heated air.

-7

Fi0. Tuel !r"er

1.blower -. heater !.trays 4.e6it air chimney

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CHAPTER - /

SE+ECTION OF GRAIN DRYERS

any factors are to be considered before the final selection of the most

suitable type of dryer for a gi(en application. The selection is little but made difficult by a

whole range of dryers in to days mar/et.

The commercial dryers are not enough fle6ible enough to compensate design

factors and the problems associated with handling of different types of food materials, which

are not ta/en into consideration pre(iously. *or this reason, it is particularly important that all

pertinent points be considered and drying tests be conducted before the final selection for

particular operation.

I) PRE+IMINARY DRYER SE+ECTION ,

The important factors to be considered in the preliminary selection of a crop

dryer are as follows 9)

i) P("sico c(emical %ro%er#ies o #(e cro% ei0 (a!le!.

ii) Dr"i0 c(arac#ers o cro%.

"1& Type of moisture."-& Initial, final and euilibrium moisture content.

"!& >ermissible drying temperature.

"4& 'rying cur(es and drying times for different crops with different dryers.

iii) Flo1 o cro% #o a! rom #(e !r"er.

Puantity to be handled per hour.

@ontinuous or batch generations.

>rocess during drying and subseuent to drying.

i$) Pro!uc# uali#ies

"a& @olour

"b& *la(our

"c& hrin/age

-%

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"d& @ontamination

"e& 2niformity of drying

"f& 'ecomposition or @on(ersion of product constituents.

"g& =(erdrying

"h& tate of subdi(ision.

"i& >roduct Temperature

"j& Aul/ density.

"/& @ase hardening and

"l& @rac/ing and other desirable ualities of the end products.

$) Dus# reco$er" %rolems.

$i) Facili#ies a$ailale a# #(e si#e o %ro%ose! is#alla#io.

a& pace

b& Temperature, humidity, cleanliness of air.

c& #(ailability of fuels.

d& #(ailable electric power.

e& >ermissible ?orse, (ibration dust or heat losses.f& ource of wed feed

g& F6haust gas outlets.

II) COMPARISON OF DRYERS ,-

The dryers selected are to be e(aluated on the basis of drying performance and

the cast data.

Barious drying tests for (arious crops ha(e to be carried out with the dryers

under consideration to determine product characteristics. #n appro6imate cost analysis is also

useful for e(aluation of dryers.

-$

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III) FINA+ SE+ECTION OF DRYERS.

*rom the results of the drying tests and analysis the final selection of the must

suitable dryer can be made.

*or successful introduction of any grain dryer at farm le(el, a few additional

parts are to be borne is mind in the section and design of grain drying system. They are as

follows 9)

The dryer should be of proper sie matching with the demand of a farmer :

The price of the dryer should be reasonable.

The design of layer should be simple and made of different cheap and locally a(ailable

materials so that it can be manufactured locality.

It should be easy to operate.

It should be possible to ma/e the dryer portable if necessary.

The operating cast should be minimum solar or furnance "i.e. fired with agricultural

waste li/e hustic shells etc.& air heating system should be introduced in grain drying to

minimise the cast of grain drying.

The repair and maintenance reuirement should be minimum.

It should be possible to use the dryer for different grains and to be used as a storage bin

later for its ma6imum utiliation.

D D D

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CHAPTER - /I

DESIGN PROCEDURE OF GRAIN DRYERS

The heated air grain dryers can be di(ided into three major groups.

1& tatic deep bed batch dryers.

-& @ontinuous ) flow ) batch dryers. "either mi6ing or non ) mi6ing type& and

!& @ontinuous dryer.

8rain dryers mainly consist of

"a& 'rying chamber.

"b& #ir distribution system.

"c& 'irect or indirect air heating system.

"d& Alower.

"e& @ontrol system "if any& and

"f& 8rain con(eying system "for flow dryers&

The following important factors are ta/en into consideration in the design of

heated air grain dryers )

DRYER FACTORS, -"a& ie, shape and type of dryer :

"b& 8rain feeding rate :

"c& Total drying time :

"d& #ir flow pattern and air distribution system:

"e& 'epth of grain bed in the dryer: and

"f& ystem of cooling grain "if any&.

AIR FACTORS ,-

"a& Belocity and air flow rate per unit mass of the grain.

"b& Temperature and relati(e humiditys of the heated air and e6haust air.

"c& tatic pressure of the air at which it is blown and

"d& #(erage ambient conditions.

!1

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GRAIN FACTORS ,-

"a& Type, (ariety and condition of grain.

"b& Initial and final moisture contents of grain.

"c& The usage of dried grain and

"d&


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85) Calcula#io o air a! (ea# or (ea#e! air !r"ers i.e. Mass a! Hea# 4alace i 0rai

!r"i0,-

The air flow rate reuired for heated air drying systems can be calculated as follows 9

The rate of air flow reuired for drying may be calculated by ma/ing heat

balance. The heated air drying system is represented by 9

where

8 E air flow rate, m!;min.

31, 3- E humidities of ambient and heated air, /g;/g.

3! E humidity of e6haust air, /g;/g.

31,3-Q 3! E relati(e humidities of ambient, heated and e6haust air,

respecti(ely, per cent.

t1, t-Q t! E dry bulb temperatures of ambient, heated

and e6haust air respecti(ely, 0@.

Cd E total weight of bone dry grain in the dryer, /g.

L1, L- E initial and final moisture contents of grain, /g;/g.

-1 88 t,t E initial and final grain temperatures, 0@.

(1 E initial humid (olume, m!;/g.

3eat supplied by drying air, a, /cals 9

aE "0.-4M0.45 31& 8 "t-) t!&

!!

#A. #I

@1B1t131,31

3F#TF #I

t-31,3-

FL3#2T #I

t!,3!,3!

3F#TF

L1.t.c1

'GF

Cd

L-,t8-

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Chere 8 E rate of air supply, /g;min.

E total drying time, min.

#mount of heat reuired 9

3eat reuired for e(aporation of moisture from the grain, 1, /cals 9

1E C d" L1) L-&

where,

E a(erage (alue of latent heat of (aporisation of moisture from the grain

/cals;/g.

ensible heat reuired to raise the temperature of the grain and its moisture, , /cals 9

188wd88gd L&tt"@C&tt"@C 111- +=

where

@g, @wE specific heats of grain and water respecti(ely,

H cal;/g 0@

Therefore

1a +=

or 8

E "0.-4M0.45 31& "t-) t!& E JL&tt"@&tt"@&LL"C 188w88a-1d 1--- ++

or+

++=

&t"t&345.0-4.0"

JL&tt"@&tt"@&LL"C8

!-1

188w88a-1d 1-1-

8 E 8 6 (1

where (1E humid (olume.

8=) Calcula#io o uel re9uireme#,-

*uel consumption 9

The rate of fuel consumption can be calculated as follows 9

ne6b

a

@...

f

=

!4

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--

%

d?

p10!5.- =

where E pressure coefficient

d E diameter of the impeller, inch

5. *ind out the typical (alue of flow coefficient from table and then calculate the width.

-?d

P175C

=

Chere, E flow coefficient

CE width of the impeller, inch

!

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Tale ?.2 /alues o s%eciic s%ee!s: #"%ical %ressure co-eicie#: #"%ical lo1 co-

eicie# a! !imesios o ce#riu0al lo1ers

'imension pecific peed

Typicalpressurecoeff.

Typicalflowcoeff.

# A @ ?s 1!,000 1 0.15

1.7"'& 1.5"'& 1.-5CM0.1' -0,000 -.0 0.540,000 1.0 0.75

4,000 1.4 0.00-

1.4"'& 1.!5"'& CM0.1' %,000 1.0 0.01-0,000 0.% 0.10

15,000 1.0 0.0%-.0"'& 1."'& CM0.1' !0,000 0.75 0.!

45,000 0.5 0.5

!7

Fi0.?.2 S%eciic s%ee! $s. s#a#ic

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# re(iew of manufacturers literature is done to see that whether blower wheel

of calculated dimensions is a(ailable. If it is not a(ailable, then slightly smaller or larger

wheel is selected and the performance reuirement is re(ised.

4lo1er (ousi0,-

The configuration of the housing considerably affects the performance of a

centrifugal blower and thus is as important as the blower wheel. The sie of the housing must

be considered /eeping in (iew the space a(ailable. The standard housing dimensions

recommended by the blower manufacturers may be followed to ma6imise performance of a

particular blower wheel. These dimensions are generally gi(en as proportions of wheel

diameter and width and so can be determined after the selected procedure is completed.

The purpose of

centrifugal blower housing as shown in

*ig. .-, is to control the air flow from

inta/e to discharge, and in the process,

to con(ert the (elocity head into the

static pressure head. >ressure con(ersionis accomplished as the cross)section of

the air stream increases in the increasing

annular space on the periphery of the

blower wheel from cutoff to discharge.

ince the amount of pressure con(ersion is determined by the scroll configuration, the shape

of the housing considerably affects air performance. The cutoff eliminates almost all free

circulation of air within the housing.

Diuser a0le,-

The increase in annular cross)section in the scroll around a blower wheel is

proportional to the de(eloped length of the wheel periphery "*ig .!&. The angle between the

!%

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de(eloped scroll surface and blower wheel periphery is called the diffuser angle. Cheel

diameter and diffuser angle determines the shape and dimensions of the scroll.

The diffuser angle can be determined graphically and e6pressed in terms of

impeller diameter and either the ma6imum height or ma6imum width of the housing. 'iffuser

angle may be gi(en as,

= 1d

31- h .................................. "1&

=1

d

C1- w .................................. "-&

#s shown by abo(e euations, the diffuser angle decreases if either dimensions

#F or @8 decreases. 3owe(er it is less sensiti(e to change in #F.

#s the diffuser angle increases, the flow rate increases significantly at any

particular static pressure. 'iffuser angle also affects performance of the blower in a particular

system.

The diffuser angle generally used as the basis for blower performance data is

10R. #lthough large diffuser angle impro(e performance, the relati(e amount of impro(ement

gradually diminishes and the sie of the housing with respect to the diameter of the blower

wheel becomes too large.

!$

Fi0. ?.= Scroll !e$elo%me# o a ce#riu0al lo1er

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The housing width may be determined by the following euation

E1.-5 C M 0.1 d .................................. "!&

where, E housing width

C E impeller width

d E impeller diameter

The optimum diameter is based on a blower wheel mounted close to the inlet

ring and minimal clearance between the wheel bac/ plate and side of the housing.

If the width of the housing recommended for the standard blower wheel is too

large, a narrower housing should be selected. If either dimension #F or @8 of the

recommended housing is too large for the space a(ailable, a housing with a smaller diffuser

angle should be selected. The resulting reduction in air flow rate should then be determined

and compared to the original reuirement.

Calcula#i0 !iuser a0le,-

The diffuser angle, h, euation "1& may be calculated with dimensions #F

eual to the ma6imum dimension G of the space a(ailable "*ig. .!&.

The diffuser angle, w, euation "-& may be calculated with dimension @8eual to the ma6imum dimension L of the space a(ailable.

The smaller of two diffuser angles corresponds to the housing that will fit into

the space a(ailable for blower. If the calculated diffuser angle is 4R or less, the housing is too

tight. If possible, a smaller blower wheel that produces the reuired air performance at a

higher operational speed should be selected.

8@) Dr"i0 air #em%era#ure ,-

@orrect choice of drying air temperature for a gi(en type of grain is (ery imp.

as it has effects on the uality of dried product. The highest allowable air temperature for

drying of grain depends on the type and condition of grain and the usage of dried grain.

The upper limit of drying air temperature for different grain to be used for food, feed and seed

purpose are different and are gi(en in following table.

40

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8?) Grai %arame#ers ,-

The grain factors which affect the rate of drying are as follows 9)

Type, (ariety and condition of grain.

Initial har(est moisture content, final moisture and euilibrium moisture content of

the grain.

tructure and chemical composition of the /ernel, seed, coat, hus/ etc. and

*oreign materials present in the grain.

The abo(e stated, factors are therefore to be considered in the design of grain

dryers.

Tale ?.5 , 4ul; !esi#ies o 0rai a# !iere# mois#ure co#e#s

8rain oisture content + "w.b.& 'ensity Hg;m!

>addy 14.0

1%.0

5%7.$

15.-Cheat 11.0

14.1

7%$.%

75.1@orn "helled & 1!.0

1.-

7!.$

7-0.$Aarley 1.%

10.%

5$-.7

57.7orghum 1-.0

14.!

75-.$

75-.$

Tale ?.= , +a#e# Hea# o $a%ori


42/101

C.O.E.&T.,Akola


+"w.b.& Hcal;/g

Cheat 1! !% -$.41! 5 11.17 !% 5%$.$

17 5 57!.%@orn 1! !% $%.%

1! 5 7$.417 !% 44.417 5 -.1

orghum 1! !% -4.41! 5 0.-17 !% 5$!.!17 5 57.

Cater ) !% 57.1) 5 50.0

Tale ?.> , S%eciic 0ra$i#" o cereal 0rais

8rain oisture content + "w.b.& pecific gra(ity of /ernel

ice %. 1.!

Cheat %.5 1.41

@orn .7 1.-$

Aarley 7.5 1.4-

illets $.4 1.11

=ats 10.!! 0.$$

Tale ?.@ , T(ermal %ro%er#ies o cereal 0rais.

8rain oisturecontent+"w.b&

Temperaturerange 0@

pecific heat/cal;/g 0@

Thermalconducti(ity/cal;m hr 0@

Thermaldiffusi(ity

m-;hr

>addy 1- ) 0.!$!4 ) )15 ) 0.4-55 ) )17 ) 0.44$ ) )

Cheat $.- ) 0.!70 0.11$% 0.00041411.7 -.50 to !1.0 ) 0.1-% )

Cheat, hard 1- ) 0.!7 ) )

4-

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white

15 ) 0.!$1 ) )Cheat, soft

white

14.4 $.0 to -!.0 0.5 0.11 0.000-$5

@orn, yellow

dent

$.%

1!.-

%.! ) -!.-

-.)!1.1

0.4!%

)

0.1!0%

0.10-

0.000!!%

)=ats 1- ) 0.!%0 ) )

15 ) 0.415 ) )17 ) 0.4!$ ) )

8) Air lo1 %a##er a! air !is#riu#io ,-

#ny one of the three systems of airflow namely crosses flow: counter flow and

co)current flow can be adopted in flow type grain dryers. 8enerally cross flow of air is

preferred. 'ouble screen and baffle type of columnar dryers ha(e a plannum chamber and


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(a) Perforated flow

The circular storage bin can be fitted with the perforated false floor through

which unheated air is blown. Though the system is suitable for small and medium sied round

bins and for small depths of grain, it is used for large rectangular bins and for higher grain

depths as well.

(b) Central horizontal duct

This system is used in the uonset type units. This type of duct with openings

in the wall can distribute air more uniformly through the grain bul/.

(c) Main duct and laterals

The system )of main duct and laterals is most commonly used and is adopted

in ground, suare and rectangular bins. The laterals are open at the bottom and raised off the

floor of .the bin so that the air can flow through the mass. The literals are in(erted B or 2 or

rectangular in shape and are made of wood or steel or concrete or ferro)cement. The laterals

are spaced in accordance with the sie of the storage unit, uantity of grain to be aerated or

dried and depth of the grain "*igs. .4 to .&. In round bins the ducts can also be placed in the

form of a ring on the bin floor.

44

*ig .4

*ig .5

*ig. . *our common floor layouts for themain duct and lateral in bins

*ig. .7

*ig. .%

*ig .$

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*uel 'ensity 3eating Balue

/g;m! lb;ft! Hcal;/g /S;/g Atu;lb

#gricultural @rop residues

Aagasse, dry 444! 1%,00 %,000

@orn stal/s, dry !$5 1,00 7,150

@otton batting !$5! 1,550 7,114

@ottonseed hulls 477% -0,000 %,00

?ewspaper 4!7% 1%,!!0 7,%%0

>ecan shells 4$40 -0,%0 %,%$0

traw !!!- 1!,$50 ,000

Cheat "traw& 45 417 17,445 7,500

#lcohol gas

Fthyl "@-35=3& 1.$5 0.1-- -5 -7,750 11,$!0

ethyl "@3!=3& 1.!! 0.0%5 504! -1,115 $,0%0

#lcohol ) liuid "pure&

Fthyl "@-35=3& %15.! 50.$ -% -,-40 11,-%0

ethyl "@3!=3& 7$.1 4$.7 477 1$,5%0 %,4-0

@oal

#nthracite 711- -$,77- 1-,%00

Aituminous pecific 8ra(ityE1.1-)

1.!5

7500 !1.401 1!,500

emi)bituminous %11- !!,$0 14,00

anufactured briuets 7-51 !0,!55 1!,050

*uel oil lb;gal

?o.1 %1!. .7$ 10!%4 4!,47! 1%,$0

?o.- %!.$ 7.-1 1017! 4-,5$0 1%,!10

4

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?o.4 $!-.- 77% $%5 41,-! 17,740

?o.5 $!%.- 7.%! $%00 41,0!0 17,40

?o. $4.- %.05 $545 !$,$0 17,1%0

8asoline 7!.$ .15 10500 4!,$0 1%,$10

Herosene %17.- .%- 10!7 4!,40! 1%,00

8as " @n3-nM-& lb;ft!

?atural, methane "@34& 0.%0 0.04-4 11$5 50,055 -1,5-0

Fthane "@-3& 1.-%7 0.0%0! 11!4! 47,4%% -0,41

anufactured 0.7$ 0.04% 5%7% -4,10 10,5%0

>ropane "@!3%& 1.$-4 0.1-0 110%1 4,!$0 1$,$44

Autane "@4310& -.5!- 0.15% 10$!4 45,775 1$,%0

Cood dry 5000 -0,$!4 $,000

2) Sae#" ea#ures

afet! Features of "urner

*armers, insurance companies, euipment manufacturers, and euipmentdealers are interested in the safe operation of burners used for heated air drying systems.

Important considerations of an installation designed for safe operation include the following9

"1& a flame control to shut off the fuel supply in the case of ignition failure, "-& a high

temperature limit switch which will stop the burner but allow the fan to continue to operate,

"!& a temperature control on the bonnet of the burner to pre(ent o(erheating of heater, "4&

proper electrical wiring connecting the fan and burner to the electric circuit "*ig. 7.!&. #ll

units should be designed to Ufail safe.U

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There is a tendency to o(eremphasie the danger of starting a fire from

particles of trash getting into the open flame of a heated air dryer operated outside. The

(elocity of the air passing the flame is so great that straw, chaff, and e(en cotton lint carriedinto the airstream do not remain in contact with the flame long enough to ignite, although

such a circumstance is not recommended.

afet! Features of Installation

# properly designed heater can be used in an unsafe manner. afety features of

an installation should include the following9 "1& fuel pump and piping located a safe distance

from the flame of the burner, "-& the fuel feed line from the tan/ to the fuel pump protected

from mechanical injury, "!& the fuel tan/ located at least 5 m "1 ft& from the bin and other

buildings, "4& oil drums refilled a safe distance from the drying unit or the drying unit shut

down when the drums are refilled, "5& separate drying and storage installations pro(ided for

safe and efficient grain drying by heated air, "& if the crop is dried in batches, on wagons, or

in a batch bin, drying euipment separated from the main building by ! m "10 ft&, "7& the

4%

Fi0. ?.2 Au#oma#ic co#rol s"s#em or a %or#ale !r"er (ea#er

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drying unit connected to the bin by a duct of flameproofed can(as or other noncombustible

material. Insurance companies may reuire that a special permit be obtained to install and use

a heated air crop dryer. The insurance company representati(es will determine if the

installation is reasonably safe, and if appro(ed, a permit may be purchased.

CHAPTER - /II

DRYER PERFORMANCE & TESTING

'ryer performance can be e6pressed in terms of (arious efficiency factors

which are gi(en below 9)

8a) T(ermal eiciec" ,-

Thermal efficiency can be defined as the ratio of the latent heat of e(aporation

credited to the heat energy of the fuel charged.

Thermal efficiency can be e6pressed mathematically as follows 9)

dCd

d

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where

&hh"(

B#0 01=

Hghr;Hg,ratedryingd

d=

Cd E weight of dry material, Hg.

E latent heat of e(aporation, H cal;Hg

E rate of heat flow, H cal ;hr

B E air rate, m!;min m-

# E area, m-

( E humid (olume of air " at the point of rate measurement & m!;Hg.

h1and h0E enthalpy of drying and ambient air H cal;Hg.

8) Hea# u#ili of a grain dryer is e6press mathematically as follows 9)

01

0-

tt

tt@=>

=

where 9) t-E dry bulb temperature of e6haust air,0@

t0E dry bulb temperature of ambient air, 0@

t1E dry bulb temperature of drying air,0@

8!) Rela#io 4e#1ee HUF a! COP ,-

32* E 1 ) @=>

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$. #(erage e6haust air d.b. temp. " 0@ &'rying capacity 1. Total drying time "hr&

-. @ooling time "if any& "hr&!. Total moisture e(aporation "/g&

4. ate of moisture e(aporation "/g;hr&5. ate of dried grain productions "tonnes;hr&

3eater and *uel 1. #ir heating method "oil fired burner;hus/ fired furnace;steam heat

e6changer&-. Type of air heating "direct;indirect&!. Chen oil fired burner;hus/ fired furnance is used"a& type of fuel and cal. (alue"b& total fuel consumption "/g&"c& rate of fuel consumption "/g;hr&

4. Chen steam heat e6changer is used

"a& incoming steam pressure "/g;cm-

&"b& rate of condensate outflow "/g;hr&"c& Temperature of condensate " 0@&

>ower 1. >ower consumption for blowing air to burner "HC&-. >ower consumption for pumping oil to burner "HC&!. >ower consumption for blowing heated air "HC&4. >ower consumption for loading and unloading grain "HC&5. >ower consumption for running feed rolls "HC&

Puality of driedgrain

1. 8ermination of grain before drying "per cent&

-. 8ermination after drying "per cent&

!. 3ead yield before drying "per cent)for paddy&4. Total yield before drying "per cent&5. 3ead yield after drying "per cent&. Total yield after drying "per cent&7. =ther uality factors

T(e sim%le #es# %roce!ure or co#iuous lo1 !r"er

Aesides the test items tabulated in the abo(e. Table, the following items are to

be ta/en into consideration for continuous flow dryers 9

"1& oisture content after each pass " per cent &

"-& esidence time in the dryer for each circulation "hr& :

"!& ?umber of passes :

"4& Tempering time "hr& :

5-

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"5& #(erage rate of moisture reduction or rate of moisture e(aporation in each circulation

"/g;hr& :

"& ate of grain recirculation "tonnes;hr& :

"7& 'rying air temperature at each pass " 0@& :

"%& Ceight of remaining grain in the dryer, ele(ator, etc."/g&.

b) #i$orous method

igorous test procedures for some batch and continuous flow dryers are gi(en

as follows. The whole test procedure can be grouped into the following major heads 9

"1& @hec/ing of construction :

"-& 'rying performance test :

"!& *an;blower performance test :

"4& @ontrol system performance test :

"5& 3andling euipments performance test : and

"& @hec/ing of different dryer)parts after disassembling "after the drying tests&.

82) C(ec;i0 o Cos#ruc#io

The purpose of this test is to ascertain the major dimensions, material ofconstruction and other necessary specifications of the dryer and its accessories.

Investigation items pecifications of 9 "a& dryer as a whole, "b& drying chamber with air

distribution system, "c& blower, "d& heating system and "e& con(eying units such as buc/et

ele(ator, grain distributor, screw con(eyor, belt con(eyor, etc. The specifications of the abo(e

items ha(e already been discussed earlier.

85) Dr"i0 Perormace Tes#

The objecti(es of this test are to determine the drying performance of a dryer

on the basis of rate of drying, rate of consumption of fuel and electricity, heat utilisation,

uality of the dried grain and other operating conditions.

The in(estigation items ha(e already been tabulated.

8=) 4lo1er Perormace Tes#

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The objecti(e of this test is to determine the performance of the fan;blower

attached with the dryer.

Investigation items >ower input, /w, "b& air flow rate, m!;min., "c& static and total pressure,

mm water, "d& static pressure efficiency and "e& (ibration, noise and other wor/ing conditions

of the blower.

CHAPTER /III

SUGGESTED MODE+S

DESIGN OF SUGGESTED MODE+S FOR DA+ MI++S,

Case,- Pulses

'esign a rectangular bin batch dryer ha(ing hole capacity of -.5 tonnes of pulses with 1-+

w.b.

Solu#io ,-#ssume the following data.

#mbient air temperature E !00@

elati(e humidity of ambient air E 70 +

Initial moisture content of pulses E 17+ w.b.*inal moisture content of pulses E 1-+ w.b.

8rain inlet temperature E !00@ E t81

8rain =utlet temperature E 700@ E t8-

3eated air temperature E %50E t-

F6haust air temperature E 400@ E t1


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#ssumption specific heat of grain E 0.!$!4 Hcal;Hg0@ "from grain

parameters table .5&

3eight of the dryer

3 E height of bin M height of plenum chamber M !

3 E -.5 M 0.75 M ! E .-5 ft

Bolume of plenum chamber

B E % 6 7 6 0.75 E 4- ft!

Bolume of drying chamber

!$

!

10-4.!

-47.!

770

-500

mm

m!

=

==

#ir reuirement 9)

) Aone dry paddy E -500 " 1 0.1- &

E --00 Hg

) Initial moisture content E 17+ w.b E "dm

m.100

100

E "d.4%-.-010017100

17

=

*inal moisture content E 1-+ C.b.E "dm

m.100

100

E "d.4.1!1001-100

1-=

Ceight of moisture e(aporated

E Ceight of bone dry paddy 6 " 61 6-&

E --00 " 0.-04%- 0.1!4 &

E 150.04 Hg

*rom psychrometric chart " #ppendi6 1& 9)

#bsolute humidity of ambient air E 0.01$ Hg;Hg

) 3umid heat of ambient air

55

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E 0.-4 M 0.45 3

E 0.-4 M 0.45 6 0.01$

E 0.-4%55 Hcal;Hg0@

C" t8- t81&

E --00 6 0.-04%- 6 1.0 6 " 7.0 !0 &

E 1%0-4.1 H cal

iii& #s latent heat of water (apour

E Cater e(aporated 6 latent heat of water

E 150.04 6 00 E $0,!-.4 Hcal

) Total heat utilied E sum of abo(e heats

E !4,1$.- M 1%,0-4.1 M $0,!-.4

E 14!005.7 H cal

uppose heat loss E 10+

?et heat reuired E 14!005.7;0.$ E 1,5%,%$ Hcal.

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3ence,

71.0%58 E 1,5%%$

8 E -!.774 Hg;min

) *rom psychrometric chart humid (olume of the ambient air E 0.%% m!;Hg

o air reuired E -!.774 6 0.%%4

E -0$.!0% m!;min

E -0$.!0% 6 !5.!4

E 7!$.$4

E 7!$7 cfm

tatic pressure drop

) urface area of plenum chamber E % 6 7 E 5ft-

) ince ma6imum 50+ area is perforated area through which air passes E -% ft-

#ir reuirement per ft-ft;cfm1%.-4

-%

7!$7=

from sheddKs cur(e " #ppendi6 -&

0 cfm E 0.7 inch of water per 1 ft grain depth

for -4.1% cfm;ft-E !.0%-1 per 1ft grain depth

'epth of grain E 1.5 ft

o pressure drop E waterofinch-!15.41%1-

0%-1.!=

>ac/ing of grain in bin may cause 50+ higher resistance air flow than the (alues shown

Total pressure drop E .$!47-5 in of water

#dd the static pressure drop from the duct and floor, usually about V in water if the air

(elocity is /ept at 1,000 fpm or less

Total pressure drop E .$!5 M 0.-5 E 7.1%47-5 in

E 7.1%5 6 -.54 E 1%.-5 cm

) 'ensity of air E 1.1! Hg;m!

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>ressure drop in terms of air column E1.1!

1000

100

-5.1%

E 11.5 m

3.>. reuired

hp10hp$4$.%4500

774.-!5.11

4500

min&;/g"rateflowair&m"columnairof3eight

=

=

=

3eating ystem 9)

#uel consum$tion -

'iesel

hr;Hg171-.1

1%5.4;41-!11

15%%$

@,

*

ne6b

a

==

=

ame as abo(e

>etrol E 15.1! 1 Hg;hr Aagase dry E !5.7 ! Hg;hr

Herosene E 15.!- 1 Hg;hr @otton batting E 40.1$ 41 Hg;hr

.8. E 14.!! 15 Hg;hr Cheat straw E !%.1! !$ Hg;hr

Cood E !1.77 !- Hg;hr

election;'esign of a @entrifugal blower 9)

1& pecific speed "?s&

rpm>s

P??s

75.0= Chere P E cfm : >s E inch

5%

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rpm-%--1%5.-%--0

1%5.7

7!$7144075.0

=

=

E -%--1 rpm

-& *igure .1 indicates that two types of air units are uite efficient at ?s E -%,--1 rpm a

forward cur(ed. @entrifugal blower and a bac/ward cur(ed "wide& centrifugal blower. Chile

the forward cur(ed centrifugal blower seems to ha(e a substantially higher static efficiency

Table shows that both the pressure and flow coefficient of forward cur(ed centrifugal blower

are high. Therefore, a forward cur(ed unit is selected.

!& from Table .1 E 1.5

4& ince--

%

d?

>s10!5.- =

5.1&1440"

1%5.710!5.-d

-

%- =

d E -!.-$ -4W E 0$. 10 mm

5& from table .1 E 0.-

-?d

P175C =

-&-$.-!"1440-.0

7!$7175

=%

C E -.7W E 7.%$ % mm

Alower housing

Cidth of housing E

E 1.-5 C M 0.1 d

E 1.-5 6 % M 0.1 6 10

E 14 mm

'iffuser angle

5$

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@101-.$w

110

141-w

0=

=

Tale B.2 ,- Air: a: (ea#: uel: 4lo1er a! H.P. re9uireme#s or Dr"i0 %ulses 1i#(

(ea#e! air rom !iere# %erce#a0e o m. c. & !iere# 0rai !e%#(s

Pulses Ca%aci#" 5.@ #oes(r

8rain mois)ture cont)ent+ w.b

>ractical graindepth, ft

taticpressuredrop waterinch;mmof water

ecomm)endedminimum airflow rate,cfm orm!;min

3eatreuiredHcal;hr

*uelconsumption, Hg;hr

Alowerreuirement

3.>.euired

Ini *inal

17 1- 1.5 7.1$;1%! 7!$7;-10 15%%$ 'iesel)17

Herosene)18)15

?sE-%--1rpm

dE10mmCE%mm

10

15 1- 1 4.07$;104 5!-%;151 1144$7 'iesel)11Herosene)108)$

?sE!-0rpmdE44mmCE%-mm

!)5

Su00es#e! Dra1i0

0

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Tec(ical S%eciica#io

odel 1 odel -

3eat output Hcal;hr 1,0,000 1,15,000'rying capacity /g;hr -,500 -,500oisture remo(ingcapacity "from initialmoisture content of17&

+;hr 5 !

*uel consumption1& 'iesel Hg;hr 17 17-& Herosene Hg;hr 1 10!& .8. Hg;hr 15 $

>ower upply 415 B 50 3 ! phase 4 wire

Flectric loadingAlower motor 3> 10 !.5*uel pump motor 3> 0.5 0.5

Cos# Es#ima#io

>articulars @ost s. eference

Aurner " 'iesel fired& 40,000 Puotation "attached &3eat F6changer 10,000


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CATA+OGUE

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DESIGN OF SUGGESTED MODE+ FOR DRYER FOR FARMERS

Case I , SORGHUM

'esign a rectangular bin batch dryer ha(ing holding. @apacity of -.5 tonnes of

paddy with 10+ moisture content w.b.

Solu#io, -#ssume the following data.


elati(e humidity of ambient air E 70+

Initial moisture content of paddy E 15+ w.b.

*inal moisture content of paddy E 10 + w.b.


8rain outlet temperature E 700@ E t8-

3eated air temperature E %50@ E t-

F6haust air temperature E 400@ E t1


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/olume o %leum c(amer, -

B E % 6 7 6 0.75 E 4- ft!

/olume o !r"i0 c(amer, -

!$

!

!

10!-.!

!!-04$4

!-04$40$.!$.75-

-500

mmx

cm

m!

=

=

==

Air re9uireme#, -

Aone dry paddy E -500 " 1 0.10 & E --50 /g

Initial moisture content E 15+, w.b. E 100100

xm

m

E "d.5.1715100

15=

*inal moisture content E 10+w.b. E 11.111db

'ei0(# o mois#ure e$a%ora#e!, -

E wt. of bone dry paddy 6 "61)6-&

E --50 "17.5 + ) 11.11+&

E --50 "0.175 0.1111&

E 147.0 Hg

From %s"c(rome#ric c(ar#, - 8 A%%e!i6 2)

#bsolute humidity of ambient air E 0.01$ Hg;Hg

3umid heat of ambient air

E 0.-4 M 0.45 3

E 0.-4 M 0.45 6 0.01$

E 0.-4%55 Hcal;Hg0@


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E 8.. " t-) t1& @o

E 8 "0.-4%55& "%5)40& 6 0

E 71.0%5 8

Hea# U#ilise!, -

i& #s sensible heat of grain

E .'. grain 6 p. 3eat of grain 6 temperature rise

E Cd 6 @>$6 "t8-)t81&

E --50 6 0.!$!4 "70)!0&

E !540 Hcal

ii& # E sensible heat of water

E total Ct of water 6 sp.heat of water 6 temperature rise

E Cd "L1& 6 @>w"t8- t81&

E --50 6 0.175 6 1.0 6 "70)!0&

E 15%%5 H cal

iii& #s latent heat of water (apour

E Cater e(aporated 6 latent heat of waterE 147.0 6 00

E %%-! H cal

Total heat utilied E sum of abo(e heats

E !540 M 15%%5 M %%-!

E 1,!$,5-7 H cal

uppose heat loss E 10+

?et heat reuired E$.0

1!$5-7 E 1,55,0!0 Hcal

If heat loss E -0+

?et heat reuired E%.0

1!$5-7E 1,74,0%.75 H cal.

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3ence, 71.0%58 E 1550!0

8 E -!1.01!$55 /g;min

*rom psychrometric chart humid (olume of the ambient air

E 0.%% m!;Hg

o air reuired E -!1.01!$55 6 0.%%4

E -04.-- m!;min

E -05 m!;min E -05 6 !5.!4 E 7-44.7 cfm.

S#a#ic %ressure !ro%,-

urface area of plenum chamber

E % 6 7 E 5 ft-

ince ma6imum 50+ area is perforated, area through which air passes E -% ft -

#ir reuirement per ft-E-%

7.7-44E -5%.74 cfm;ft-

*rom sheddKs cur(e " #ppendi6 - & static pressure drop

*or -0 cfm;ft-E ! inch of water per 1 ft grain depth.

'epth of grain E 1.5 ft.

o pressure drop E 5.41%1-

! =x inch of water

) >ac/ing of the grain in bin may cause 50+ higher resistance to airflow than the (alues

shown

Total pressure drop E .75 inch of water

) #dd the static pressure drop from the duct and floor, usually about V in water if the air

(elocity is /ept at 1,000 fpm or less.

Total pressure drop E .75 M 0.-5 E 7 inch of water E 17.7% cm

'ensity of air E 1.1! Hg;m!

>ressure drop in terms of air column E1!.1

1000

100

7%.17

E 157.!45 m

$

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H. P. re9uire!, -

E4500

min&;Hg"rateflowair&m"columnairof3eight

4500

01!$55.-!1!45.157 =

E %.077

$ hp E 10 hp

Hea#i0 S"s#em, -

#uel Consum$tion - ne6b

a

@.

* =

f E1%5.4;41-!11

0!0,55,1

xx

f E 15.7-$ 1 Hg;hr

2sing ?et heating (alue

* E1%5.4;407%511

1550!0

xx

* E 15.$1 1 Hg;hr

@alculated same as abo(e ))))

>etrol E 15 Hg;hr Aagass "dry& E !5Hg;hr

Herosene E 15 Hg;hr @otton batting E 40Hg;hr

.8. E 14Hg;hr Cheat E !% Hg;hr

Cood E !- Hg;hr

Selec#ioDesi0 o a Ce#riu0al lo1er, -

1& pecific peed "?s&

r$ms

'((s

75.0=

Chere ? speed of motor rpm E 1440

70

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) #ir flow rate m!;min or cfm

>s E static press m wa/e gauge or inch.

?s E75..077-451440

?s E -%4%1.1$

-& *ig .1 indicates that two types of air units are uite efficient at ?s E -%451.1$ a forward

cur(ed centrifugal blower. Chile the forward cur(ed centrifugal blower seems to ha(e a

substantially higher static efficiency Table .1 shows that both the pressure and flow

coefficient of forward cur(ed centrifugal blower are high. Therefore, a forward cur(ed unit is

selected.

!& from Table .1 E 1.5

4& ince--

%

d?

>s10!5.- =

=

-

!-

?

>s10!5.-d

5.1&1440"

710!5.--

!- =d

d E --.$$ -!W

d E 5%4.- 5%5 mm

5& *rom Table .5 E 0.-

C E -?d

P175

C E -&$$.--"1440-.0

7-45175

C E -.%7W

C E %.-4 7 mm

71

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.com


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C.O.E.&T.,Akola


) # re(iew of manufacturerKs literature is done to see that whether blower wheel of

calculated dimensions is a(ailable. If it is not a(ailable, then slightly smaller or larger

wheel is selected and the performance reuirement is re(ised.

4lo1er (ousi0, -

) Cidth of housing E

E 1.-5 C M 0.1 d Chere E housing width

E 1.-5 6 7 M 0.1 6 5%5 C E impeller width

E 14-.-5 14! mm d E impeller diameter

Diuser a0le

= 1

5%5

14!1-w

01007.$w =

TA4+E , Air: Fa: Hea#: Fuel: lo1er a! H.P. Re9uireme# or !r"i0 sor0(um 0rais

1i#( (ea#e! air rom !iere# %erce#a0e o M.C. a! !iere# 0rais !e%#(s.

orghum @apacity

8rain mois)ture cont)ent+ w.b

>racticalgrain depth,ft

taticpressuredrop waterinch;mmof water

ecomm)endedminimum airflow rate, cfmor m!;min

3eatreuiredHcal;hr

*uelconsumption,Hg;hr

Alowerreuirement 3.>.euired

Ini *inal

17 10 - %.-5;- -0 $!-!;-4 -0040- 'iesel )-1.8. )-0Cood ) 40

?s)-7-d)40 mmC)$ mm

1!

15 10 1.5 7;17% 7-45;-05 1550!0 'iesel )-1Cood ) 40cottonAatting )40

?s )-%4%-rpmd)5%5 mmC)7 mm

10

17 10 1 7;17% 5-01;14% 111771 'iesel )1->etrol )11@ottonAatting )-$

?s )-41!-rpmd)5%5 mmC)4$ mm

5)7.5

Case II , U!i! or Mu0 or so"aea

7-

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.com


73/101

C.O.E.&T.,Akola


'esign a rectangular bin batch dryer ha(ing holding capacity of -.5 tonnes of

2did or ug or soyabean with 1!+ w.b.

Solu#io, -#ssume the following data.


elati(e humidity of ambient air E 70+

Initial moisture content of paddy E -0+ w.b.

*inal moisture content of paddy E 1!+ w.b.


8rain outlet temperature E 700@ E t8-

3eated

Date post:	13-Apr-2018
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