Topic 1- Drying

Question 1

it is the process of removing water from a material

Answer 1

drying

Question 2

this can also mean removal of other solvents (e.g. benzene) from solids

Answer 2

drying

Question 3

this is the removal of relatively small amounts of water from a material

Answer 3

drying

Question 4

Many ___________ that cause chemical changes in food require the presence of water.

Answer 4

enzymes

Question 5

these can be stored for extended periods of time

Answer 5

dried foods

Question 6

removing water from a material mainly
through filter medium/pressure gradient

Answer 6

filtration

Question 7

removing water from a material mainly through centrifugal forces

Answer 7

centrifugation

Question 8

removing water from a material mainly through application of heat

Answer 8

evaporation

Question 9

this unit operation stops once pores clog or capillary forces dominate; cannot remove bound moisture

Answer 9

filtration

Question 10

this unit operation is limited by capillary forces and adhesion; residual moisture always remains

Answer 10

centrifugation

Question 11

this unit operation requires bulk
boiling/evaporation; not designed for porous solids or internal moisture

Answer 11

evaporation

Question 12

it is the removal of water to obtain solid products

Answer 12

drying

Question 13

this is the removal of water to obtain concentrated liquid solutions

Answer 13

evaporation

Question 14

this involves relatively large amounts of water removed from a material

Answer 14

evaporation

Question 14

this involves relatively small amount of water removed from a material

Answer 14

drying

Question 15

this is the removal of water at a temperature below boiling point

Answer 15

drying

Question 16

this is the removal of water by boiling the liquid solution

Answer 16

evaporation

Question 17

in this unit operation, water is removed from the solution as pure water

Answer 17

evaporation

Question 17

in this unit operation, water is carried away from the material as water vapor using air as medium

Answer 17

drying

Question 17

how does drying work based on physical conditions?

Answer 17

1. simple drying
2. vacuum drying
3. freeze drying

Question 18

how does drying work based on mode of operation?

Answer 18

1. batch method
2. continuous method

Question 19

this type of drying is where material to be dried is held in contact with heated air. the water vapor formed is removed by the moving air

Answer 19

simple drying

Question 20

this type of drying is due to lower pressure, water evaporates from the material quickly

Answer 20

vacuum drying

Question 21

this type of drying is where heat is usually added indirectly by contact with a metal wall or through radiation

Answer 21

vacuum drying

Question 22

this type of drying is where water is sublimed (solid to gas) from the frozen material

Answer 22

freeze drying

Question 23

this drying equipment is also called shelf, cabinet, or compartment dryer

Answer 23

tray dryer

Question 24

this type of drying method is where material to be dried is introduced to the dryer for a given period; the material is then removed after drying

Answer 24

batch method

Question 25

this type of drying method is where there is a steady flow of material to be dried entering the dryer and consequently, there is a steady flow of material continuously removed from the dryer

Answer 25

continuous method

Question 26

what are the 6 type of drying equipment

Answer 26

1. tray dryer 2. continuous tunnel dryer 3. rotary dryer 4. drum dryer 5. spray dryer 6. freeze dryer

Question 27

in this type of drying equipment, the solid to be dried is spread uniformly across a metal tray

Answer 27

tray dryer

Question 28

in this type of drying equipment, the solids are placed on a tray or trucks (small moving batch of trays) which move continuously through a tunnel with hot gases passing over the surface of each tray

Answer 28

continuous tunnel dryer

Question 28

in tray dryers, some designers use no fresh air while others use ____________ fresh air

Answer 28

10-20%

Question 29

in this type of drying equipment, gases can be cocurrent, countercurrent, or combination

Answer 29

continuous tunnel dryer

Question 30

in continuous tunnel dryer, gases can be ____________, ________________, or _____________

Answer 30

cocurrent, countercurrent, combination

Question 31

in this type of drying equipment, heating is provided by direct contact with hot gases

Answer 31

rotary dryer

Question 31

this type of drying equipment consists of a hollow cylinder which is rotated and usually inclined toward the outlet

Answer 31

rotary dryer

Question 32

this type of drying equipment consists of an internally heated cylindrical metal roll (usually steam), outside of which the material to be dried, usually slurry, is spread

Answer 32

drum dryer

Question 33

what are the 3 variations of drum dryer

Answer 33

1. double drum dryer 2. dryer with dip feed 3. dryer with applicator feed

Question 33

powdered milk is an example of product by this drying equipment

Answer 33

spray dryer

Question 34

in this type of drying equipment, the liquid or slurry is sprayed into a hot gas stream in the form of mist of fine droplets

Answer 34

spray dryer

Question 35

this type of drying equipment is also called Lyophilization

Answer 35

freeze dryer

Question 36

what is the other term for freeze dryer

Answer 36

Lyophilization

Question 37

it is a process where material to be dried is first frozen and then placed under vacuum so that the ice sublimes (from solid to gas)

Answer 37

Lyophilization or freeze drying

Question 38

this type of drying equipment is normally used in the food industry to extend shelf-life of food products

Answer 38

freeze dryer

Question 39

in freeze dryer, the heating source provides the ____________________________ once the frozen product is already at high vacuum conditions

Answer 39

freeze dryer

Question 40

At the start of contact, the moisture from the solid material will migrate to the air if the air has __________________________

Answer 40

lower humidity

Question 41

If the air has ____________________, moisture will migrate from the air to the solid material.

Answer 41

higher humidity

Question 42

it is a measure of the amount of water vapor present in air

Answer 42

humidity

Question 43

this refers to mass of water vapor contained in unit mass of dry air

Answer 43

humidity or absolute humidity (H)

Question 44

what law does the formula for humidity are derived from?

Answer 44

dalton's law

Question 45

it is the pressure exerted by a gas in a mixture of gases

Answer 45

partial pressure

Question 46

this refers to the ratio of mass of maximum water vapor that can be contained in unit mass of dry air at specified condition

Answer 46

saturation humidity (Hs)

Question 47

vapor pressure of pure water vapor at given temperature can be solved using?

Answer 47

antoine's equation or steam tables

Question 48

at _______________, the partial pressure of water vapor in the air-water vapor mixture is equal to the vapor pressure of pure water vapor in the given temperature

Answer 48

saturation

Question 49

it refers to the ratio of the current humidity of air to the humidity of air if it were saturated

Answer 49

percent humidity (Hp)

Question 50

it refers to the ratio of H and Hs

Answer 50

percent humidity (Hp)

Question 51

this refers to the ratio of the present partial pressure of water vapor to the vapor pressure of pure water at same temperature

Answer 51

relative humidity (RH)

Question 52

this is usually expressed as %HR

Answer 52

relative humidity

Question 53

it is the temperature where given air and water vapor mixture will become saturated

Answer 53

dew point temperature

Question 54

this occurs at 100% RH (saturated)

Answer 54

dew point temperature

Question 55

this can be determined from the antoine's equation or tables

Answer 55

dew point temperature

Question 56

5 ways to describe the properties of air-water vapor mixture

Answer 56

1. dew point temperature (Tdp) 2. humid head (Cs) 3. adiabatic saturation temperature 4. dry bulb temperature (Tdb) 5. wet bulb temperature (Twb)

Question 57

this refers to the amount of heat (J or kJ) required to raise the temperature of 1 kg of dry air plus the water vapor present by 1 K or 1 deg C

Answer 57

humid head (Cs)

Question 58

heat capacity of air

Answer 58

1.005 kJ/kg dry air - K

Question 59

heat capacity of water vapor

Answer 59

1.88 kJ/kg water vapor - K

Question 60

this refers to the temperature at which water will saturate air by evaporation adiabatically into it

Answer 60

adiabatic saturation temperature

Question 60

this is a classic chemical engineering device used to study humidification and psychrometrics—basically how air and water vapor interact when no heat is added or removed from the surroundings

Answer 60

adiabatic saturator

Question 61

this is a cooling process where air is cooled by direct contact with water, without any external heat transfer

Answer 61

direct adiabatic cooling

Question 62

other term for direct adiabatic cooling

Answer 62

evaporative cooling

Question 63

it is a cooling method that uses evaporation to cool air—without adding moisture to the supply air

Answer 63

indirect adiabatic cooling

Question 64

what is the system of saturation temperature

Answer 64

pure substance

Question 65

what is the system of dew point temperature

Answer 65

moist air (air-water vapor)

Question 66

what is the system of adiabatic saturation temperature

Answer 66

moist air + liquid water

Question 67

this refers to the temperature of the ambient air as measured by a thermometer directly exposed to air

Answer 67

dry bulb temperature (Tdb)

Question 68

this refers to the temperature of air indicated by an ordinary thermometer

Answer 68

dry bulb temperature (Tdb)

Question 69

this refers to the temperature of the ambient air as measured by a thermometer covered by a wet wick

Answer 69

wet bulb temperature ( Twb)

Question 70

this ____________________ temperature is always lower than ______________________ temperature

Answer 70

wet bulb, dry bulb

Question 71

if given an air-water vapor mixture, how many thermodynamic properties should be defined or known first to get any property of this mixture?

Answer 71

2

Question 72

If you are given an air-water vapor mixture, the properties of this mixture can be quickly determined using the?

Answer 72

psychrometric chart

Question 73

The current moisture level in the material is said to have achieved equilibrium with the relative humidity and temperature of the surroundings. This level of moisture is called the?

Answer 73

equilibrium moisture content (EMC)

Question 73

equilibrium moisture content (EMC) is usually expressed on a?

Answer 73

dry basis or bone-dry solid

Question 74

these materials tend to have low EMC value

Answer 74

nonporous materials (glass wool and kaolin)

Question 75

these display large value of EMC

Answer 75

spongy, cellular materials of organic or biological in origin (leather and wood)

Question 76

examples of spongy, cellular materials

Answer 76

leather and wood