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ABE 2 Second Exam > Module 5: Drying > Flashcards

Module 5: Drying Flashcards

1
Q

preservation of an agricultural crop that involves the removal of moisture to a level considered safe for storage

A

drying

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2
Q

process of removing moisture from a material until the desired level is reached and equilibrium with the storage environment is achieved

A

drying

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3
Q

drying is most concerned with what property of the air?

A

vapor pressure

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4
Q

in drying, grain is exposed to ambient air with low relative humidity or to heated air, this will evaporate the moisture from the grain

true or false

A

true

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5
Q

in drying, the _______ remove the moisture from the grain bulk

A

drying air

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6
Q

rice is a hydroscopic material

true or false

A

false; hygroscopic yon haha

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7
Q

if dry rice is exposed to air with high RH, what will happen to the grains?

A

it will absorb water from the air (re-wetting)

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8
Q

when wet rice is exposed to air with _____(low/high) RH, the rice grains will release water to the air

A

low RH; this is drying

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9
Q

drying permits the farmer to secure a greater economic return for the ff reasons

A
  • production operations are facilitated for products like cotton and corn.
  • higher economic value products, such as tobacco and dried fruits and vegetables, are produced.
  • waste products can be converted into useful products, like livestock feed from fruit pulp and almond hulls.
  • early harvest at high moisture content minimizes field damage, shatter loss, and facilitates tillage operations.
  • long-term storage without product deterioration is possible.
  • seed viability is maintained over long periods.
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10
Q

during drying, these two processes are occurring at the same time

A
  1. heat transfer
  2. mass transfer
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11
Q

during drying, heat from the heated air transfers to the solid, providing energy for __________ ____________

A

moisture evaporation

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12
Q

in drying, moisture (liquid or vapor form) moves from within the grain to ___ _______ and then evaporates into the _________ ___.

A

its surface; drying air

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13
Q

in paddy grain, moisture is present at two places:

A
  1. at the surface of the grain
  2. inside the kernel
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14
Q

moisture in paddy grain that readily evaporate when grain is exposed to heated air

A

surface moisture

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15
Q

internal moisture has to move first from the kernel to the outside surface for it to evaporate

true or false

A

true

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16
Q

evaporation of surface moisture is slower than internal moisture

true or false

A

false; it is faster

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17
Q

since surface moisture and internal moisture evaporate at a different rate, the difference in results leads to different ‘________ ____’ for different period of drying

A

drying rates

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18
Q

four main stages of drying

A
  1. initial induction period
  2. constant rate period
  3. 1st falling rate period
  4. 2nd falling rate period
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19
Q

in the first stage of drying, drying rate is slowly increasing and there is a very slight change in MC

true or false

A

true

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20
Q

after the grain’s contact with the drying medium, its temp temperature increases to a ______ state while the air temperature remains ________.

A

steady; constant

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21
Q

after adjustment, the drying rate and grain _______________ (temperature/moisture content) remain constant, while the ______________ (temperature/moisture content) continuously decreases over time.

A

temperature; moisture content

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22
Q

at constant rate period, heat is transferred from the drying air to the grain, providing the energy needed for moisture evaporation

true or false

A

true

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23
Q

at constant rate period, mass transfer occurs how?

A

moisture moves from the grain surface to the surrounding air

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24
Q

how is surface water removed in constant rate period?

A

the entire surface of the grain is saturated with water during this phase –> the continuous heat transfer and mass transfer facilitate the removal of that surface moisture

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25
Q

this refers to the difficulty in converting liquid moisture at the surface of the solid into vapor

A

resistance to evaporation

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26
Q

refers to the difficulty of moisture moving from the interior of the solid to its surface

A

internal resistance to diffusion

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27
Q

if the resistance to evaporation is much greater than the internal resistance to diffusion, what does it mean?

A

it means that the primary bottleneck for drying is the evaporation process at the surface rather than the movement of moisture from within the solid to the surface

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28
Q

factors affecting drying

A
  • surface area
  • drying air temp
  • drying air RH
  • air velocity
  • rate of removal of water vapor from the surface
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29
Q

in convective drying by hot air, heat is transferred from the hot air to the _______ ____ _________ through a boundary layer

the wet material ________ this heat, inducing evaporation

the resulting water _______ is then transferred from the surface to the air by convection

A

cooler wet surface; absorbs; vapor

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30
Q

stage

in the ____________________ of grain drying, moisture moves from within the material to the surface and is then removed from the surface

A

first falling rate period

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31
Q

in first falling rate period, when the MC reaches CMC, the grain surface temperature _______ (decreases/increases), and the drying rate _________ (decreases/increases) rapidly

A

increases; decreases

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32
Q

constant rate period takes shorter than first falling rate

true or false

A

true

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33
Q

in first falling rate period, the internal resistance to moisture movement is significantly higher than external resistance to evaporation

true or false

A

true

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34
Q

in the first falling rate period, it is important to note that the structure of agricultural materials complicates moisture movement due to

A
  • their internal and external cavities
  • capillaries
  • cell walls
  • spaces
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35
Q

mechanisms of moisture mo

A
  • diffusion (liquid water and/or vapor)
  • capillary action
  • shrinkage
  • vapor pressure gradients
  • gravity
  • vaporization
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36
Q

in the second falling rate, drying rate rate further decreases until it becomes zero and MC reachers?

A

CMC

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37
Q

in the ____________________, all evaporation occurs from the interior of the solid (transfer of internal moisture to the surface)

A

second falling rate period

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38
Q

in the last stage of drying, grain temp increases until it reaches the temperature of _________ ___

A

drying air

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39
Q

rate at which grain moisture content declines during the drying process

A

drying rate

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40
Q

_________ ____ is normally expressed in percent moisture removed per hour

A

drying rate

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41
Q

typical drying rate of rice dryers are in the 0.5-1%/hr range

true or false

A

true

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42
Q

stirring, turning, and circulating grains in various drying methods improve drying consistency and maintain grain quality by preventing re-wetting

this process is referred as

A

uniform drying

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43
Q

process of stopping intermittently

A

tempering

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44
Q

resuming the drying process after tempering results in a higher drying rate compared to continuous drying

true or false

A

true

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45
Q

when drying is paused, the moisture inside the grain redistributes evenly due to __________

A

diffusion

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46
Q

in modern re-circulating grain dryers, grains undergo cycles of drying followed by tempering, this cycling have benefits which are

A
  • improves drying rates
  • enhances grain quality
  • reduces energy costs
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47
Q

factors in selecting a dryer

A
  1. farm size and output
  2. crop
  3. future development
  4. local atmospheric conditions
  5. marketing
  6. labor
  7. capital
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48
Q

factors affecting the selection of dryer type

A
  1. raw material characteristics
  2. operation costs
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49
Q

types of dryer

A
  1. cabinet dryer
  2. tunnel dryer
  3. continuous conveyor dryer
  4. spray dryer
  5. drum dryer
  6. fluidized bed dryer
  7. freeze dryer
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50
Q

types of dryer

uses air-convection tray drying intended for relatively small-scale operations

A

cabinet dryer

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51
Q

types of dryer

applications of cabinet dryer

A
  • air dried foods in piece form
  • preservation of variety of fruits and veggies
52
Q

types of dryer

a continuous type of dryer where wet mats are loaded in a thin, uniform layer on the drying trays at one end of the dryer

A

tunnel dryer

53
Q

types of dryer

in a tunnel dryer, dried products are removed at the other end

true or false

A

true

54
Q

types of dryer

food mats are dried in warm circulating air

A

continuous conveyor dryer

55
Q

types of dryer

in a continuous conveyor dryer, wet mats supplied to the __________ _____ at the left is loaded evenly on the surface of a slowly moving conveyor belt

A

spreader device

56
Q

types of dryer

in a continuous conveyor dryer, hot air flows through the _______ or ____________ in the conveyor

A

meshes or perforations

57
Q

types of dryer

mats are dried and dispersed into a stream of heated air

A

spray dryer

58
Q

types of dryer

in a spray dryer, moisture evaporates into the?

A

air stream

59
Q

in a sprayer dryer, the dryer particles are separated from the air and collected

true or false

A

true

60
Q

the mat to be dried in a spray dryer must have at least ____% soluble solids

A

20%

61
Q

types of dryer

comprises of a roll or drum with heating medium circulating through the drums

A

drum dryer

62
Q

in a drum dryer, viscous material is fed from the top to the _______ surface

A

hot drum

63
Q

in a drum dryer, product dries on the drums and is scraped off by the ________ ____ fixed along the surface of the drum

A

stationary blades

64
Q

milk and juices powder are produced using drum dryer

true or false

A

false; using spray dryer

65
Q

3 types of drum dryer

A
  1. dip-feed drum dryer
  2. twin-cylinder drum dryer
  3. single-cylinder drum dryer
66
Q

types of dryer

product is fed in at one bed to lie on a porous plate

A

fluidized bed dryer

67
Q

in a fluidized bed dryer, product is agitated and moved along towards the exit at the other end by ___ ___ which is blown up through the product

A

hot air

68
Q

soup mixes are produced by fluidized bed dryer

true or false

A

true

69
Q

type of dryer

it is also known as a dehydrator

A

freeze dryer

70
Q

in freeze drying, water is removed by ________ __________ from the frozen state to the vapor state, without water passing through an intermediate liquid state

A

direct sublimation

71
Q

freeze drying temp for most products is at -21.7 degree Celsius

true or false

A

true

72
Q

freeze drying temp for fruit juices is?

A

-32 to -34 degree Celsius

73
Q

driver of heat transfer

A

difference in temp

74
Q

driver and agent of vapor transport

A

difference in vapor pressure

75
Q

process of removing moisture from a material until the desired level is reached and equilibrium with the storage environment is achieved

A

drying

76
Q

accomplished by vaporizing the water that is contained in the food

A

drying

77
Q

a process of simultaneous heat and moisture transfer

A

grain drying

78
Q

categories of drying process

A
  1. air and contact drying
  2. vacuum drying
  3. freeze drying
79
Q

categories of drying process

a drying process where heat is transferred through the foodstuff either from heated air or from heated surfaces

A

air and contact drying

80
Q

categories of drying process

evaporation of water occurs more readily at lower pressures than at higher ones

A

vacuum drying

81
Q

categories of drying process

the water vapor is sublimed off frozen food

A

freeze drying

82
Q

heated air used in drying has two functions

A
  1. supply heat for moisture evaporation
  2. carry away the evaporated moisture
83
Q

a drying system must have the following:

A
  • method of heating the drying air
  • blower to force the heated air through the grain mass
  • device to hold the grain being dried
  • system for loading, moving, and unloading the grain on the holding device
  • central system for programming the drying process for prevention of damage to the quality of the
    grain
  • safety control network
84
Q

predominant method of drying in the Philippines because of economic considerations

A

sundrying

85
Q

drying methods

A
  1. sundrying
  2. mechanical drying
  3. solar drying
86
Q

drying methods

a blower forces the heated air through the mass of grains

A

mechanical drying

87
Q

purposes of the plenum in a mechanical dryer

A

it equalizes the air pressure in the drying bin, which holds the grains

88
Q

types of mechanical dryer

A

a. burners/furnace
- direct-fired burner
- indirect-fired burner
b. blowers
- propeller type
- centrifugal type
c. drying bins
- shallow-bed batch type bin
- deep-bed batch type bin
- continuous-flow non-mixing type bin
- continuous-flow mixing type bin

89
Q

drying methods

burned fuel is forced through the mass of grains

A

direct-fired burner

90
Q

drying methods

makes efficient use of heat, which makes operation less expensive

A

direct-fired burner

91
Q

disadvantage of using a direct-fired burner

A

possibility of damage or undesirable odor, color, and taste imparted on the grains because of smoke and unburned fuel comes in contact with the grains being dried

92
Q

drying methods

burned fuel is directed to a heat exchanger and discharged through a smokestack

A

indirect-fired burner

93
Q

drying methods

_______-_____ _____ is safer but less efficient in heat utilization and more expensive to acquire and operate

A

indirect-fired burner

94
Q

drying methods

used for large air volume at low static pressure, air moves parallel to the fan axis and at a right angle to the field of rotation of the blades

A

propeller type blower

95
Q

drying methods

used for high static pressure at low air volume, air enters the housing parallel to the axis and is discharged perpendicular to the direction in which it enters the fan

A

centrifugal type blower

96
Q

drying methods

drying bins can be classified into two

A
  1. batch-type
  2. continuous
97
Q

drying methods

type is widely used by small farmers because of their relatively low cost and ease of operation

A

shallow-bed batch type bin

98
Q

drying methods

a deep-bed batch type bin has perforated floor with a flat or sometimes inclined bed to facilitate unloading

true or false

A

false; it’s shallow-bed batch type bin

99
Q

drying methods

type is usually used for in-storage drying using slightly heated air to prevent overdrying at the bottom and low air flow rate

A

deep-bed batch type bin

100
Q

drying methods

shallow-bed batch type bin

optimum drying parameters are __ inches depth, ___ °F air temperature and 30 – 35 cfm of grain air flow

A

12 inches; 110 degree Fahrenheit

101
Q

drying method

consist of two parallel screen columns up to 18 inches apart

A

continuous-flow non-mixing type bin

102
Q

drying method

mixing of grains occurs as the grains flow down the system, consist of a bin with layers of air channels shaped like inverted “V”s

A

continuous-flow mixing type bin

103
Q

drying methods

solar radiation would be allowed to pass through a transparent sheet where heat absorbent

A

solar drying

104
Q

solar drying systems are categorized as passive or active

A
  1. passive system
  2. active system
105
Q

solar drying

depends on natural convention, conduction, or radiation to transfer thermal energy from the point of collection to the storage component and to the point of use

A

passive system

106
Q

solar drying

has a mechanical mean such as pump or fan to drive a heat-transfer fluid from one part of the system to another

A

active system

107
Q

solar drying

active system has many agri applications such as greenhouses, field drying of crops use passive solar systems

true or false

A

false; active system

108
Q

efficient utilization of solar energy for drying grains and crops depends on

A
  1. geographical location
  2. crop type
  3. size of operation
  4. government policy
109
Q

factors to consider in selecting a dryer

A
  1. farm size and output
  2. type of crop
  3. future and development
  4. local atmospheric conditions
  5. labor
  6. capital
110
Q

type of dryer

A
  1. cabinet dryer
  2. tunnel dryer
  3. continuous conveyor dryer
  4. spray dryer
  5. drum dryer
  6. fluidized bed dryer
  7. freeze dryer
111
Q

factors to consider in selecting a type of dryer

A
  1. raw material specification
  2. operating costs
112
Q

drying techniques

A
  1. continuous-flow intermittent drying
  2. flash drying
113
Q

drying techniques

grain heating time is __ minutes per exposure

A

15 minutes

114
Q

drying techniques

heated air temp at 140-170 degree Fahrenheit

A

continuous-flow intermittent drying

115
Q

continuous-flow intermittent drying

after heating, it is followed by a tempering time of __-__ hours

A

3-4 hours

116
Q

continuous-flow intermittent drying

blower remains running during the ________ period

A

tempering

117
Q

drying technique

the grain moisture is reduced to an intermediate level of 18% MCwb which is a safe level to store grains up to three weeks while waiting for sundrying

A

flash drying

118
Q

in flash drying, grains are subjected to high air temp of ___ degree Fahrenheit for a ___ min and then discharged

A

170 degree Fahrenheit; 15 mins

119
Q

drying efficiencies

each time unit is the time of one-half response of rain fully exposed to the air entering the drying systems

A

drying time

120
Q

drying efficiencies

moisture is expressed as moisture content ratio

A

grain moisture

121
Q

drying efficiencies

a depth factor is describe as “containing enough grain that if all the theoretical available heat could be used it would all dry to equilibrium” in a period of time equal to the time of one half response

A

grain depth

122
Q

drying efficiencies

drying air fulfills two functions in a mechanical grain drying system: (1) to carry the necessary energy to the grain to evaporate the moisture, and (2) to carry the evaporated water out of the grain

A

air movement

123
Q

efficiency of the drying operation is an important factor in the assessment and selection of the optimum dryer for a particular task

A

drying efficiency

124
Q

three groups of factors affecting drying efficiency

A
  • related to the environment, in particular, ambient air conditions;
  • those specific to the crop; and
  • those specific to the design and operation of the dryer
125
Q

REVIEW QUESTIONS (no answer in the flashcard)

  1. Define each type of dryer.
A

EXPLAIN

ABE 2 Second Exam (6 decks)

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