HEAT AND MASS TRANSFER Flashcards
To remove all the moisture from a wet solid requires exposure to
a. perfectly dry air c. highly humid air
b. air at high temperature d. none of these
a. perfectly dry air
The portion of water in the wet solid that cannot be removed by the air in its contact is called
a. free moisture
b. final moisture content
c. equilibrium moisture content
d. critical moisture content
c. equilibrium moisture content
Moisture contained by a substance in excess of the equilibrium moisture is called
a. unbound moisture b. critical moisture
c. free moisture d. bound moisture
c. free moisture
When drying banana chips under the sun, the rate of drying is faster on a
a. slightly breezy day
b. cloudy day
c. calm day
d. hot and windy day
d. hot and windy day
The critical moisture content in case of drying indicates
a. beginning of falling rate period
b. beginning of constant rate period
c. end of falling rate period
d. none of these
a. beginning of falling rate period
In drying at the falling rate period, the rate at which moisture is removed from the solid material
a. increases with time
b. remains constant
c. decreases with time
d. no more drying takes place
c. decreases with time
Heat sensitive materials like certain pharmaceuticals and food stuff can be dried
a. in indirect tray dryer c. in spray dryer b. by freeze drying d. festoon dryer
b. by freeze drying
Other term for freeze drying
Lyophilization
Detergent solution is dried to a powder in a
a. spray dryer c. spouted bed dryer
b. tunnel dryer d. pan open to atmosphere
a. spray dryer
Calcium ammonium nitrate (a fertilizer) is dried in a a. rotary dryer c. vacuum dryer
b. tunnel dryer d. none of these
a. rotary dryer
Rotary dryer cannot handle
a. free flowing materials c. dry materials
b. sticky materials d. granular materials
b. sticky materials
Involves the transfer of material between a pure liquid phase and a fixed gas that is nearly insoluble in the liquid
HUMIDIFICATION
The mass of vapor carried by a unit mass of vapor-free gas
HUMIDITY
A gas in which the vapor is in equilibrium with the liquid at the gas temperature
SATURATED GAS
Defined as the ratio of the partial pressure of the vapor to the vapor pressure of the liquid at the gas temperature
RELATIVE HUMIDITY,
Ratio of the actual humidity, H, to the saturation humidity, HS, at the gas temperature
PERCENT HUMIDITY
Heat energy necessary to increase the temperature of 1 g or 1 lb of gas plus whatever vapor
it may contain by 1°C or 1°F
HUMID HEAT,
Total volume of a unit mass of vapor-free gas plus whatever vapor it may contain at 1 atm
and the gas temperature
HUMID VOLUME
Temperature to which a gas-vapor mixture must be cooled (at constant humidity) to become saturated
DEW POINT
Temperature of the gas that would be attained if the gas were saturated in an adiabatic process
ADIABATIC SATURATION TEMPERATURE
Actual gas temperature
DRY BULB TEMPERATURE
Temperature obtained when the heat required to vaporize a small amount of liquid (water for air-water system) into a large volume of gas (air for air-water system) exactly equals the sensible heat transferred from the gas to the liquid.
WET BULB TEMPERATURE
A convenient diagram showing the properties of mixtures of a permanent gas and a condensable vapor
HUMIDITY CHART
During this process, the moisture content of air remains constant but its temperature decreases as it flows over a cooling coil.
SENSIBLE COOLING
During this process, the moisture content of air remains constant and its temperature increases as it flows over a heating coil.
SENSIBLE HEATING
Which of the following processes may always be regarded as a constant-humidity process?
a. cooling of air
b. air conditioning
c. water-cooling in a cooling tower
d. heating of air
d. heating of air
Steady state temperature reached by a small amount of liquid evaporating into a large amount of unsaturated vapor-gas mixture is
a. dry-bulb temperature
b. wet bulb temperature
c. dew point
d. adiabatic saturation temperature
b. wet bulb temperature
Which of the following remains constant during sensible cooling process?
a. specific humidity
b. partial pressure of vapor
c.both a and b
d. neither a nor b
c.both a and b
During sensible cooling process
a. relative humidity decreases
b. relative humidity increases
c. wet bulb temperature increases
d.bothbandc
b. relative humidity increases
Wet bulb and dry bulb temperatures become identical at
a. 100% saturation curve
b. 78% saturation curve
c. 50% saturation curve
d. none of these
a. 100% saturation curve
The degrees of freedom associated with a humidification process is
a.1 c.2
b.3 d.4
c.2
Refers to a solid-liquid separation process in which solid particles are formed within a homogenous phase. It can occur as:
CRYSTALLIZATION
_____ is a measure of the quantity of solids actually present in solution as compared to the quantity that is in equilibrium with the solution
Supersaturation
[True or False] Crystallization cannot occur without supersaturation
True
In industrial crystallization from a solution, the two phase mixture of mother liquor and crystals of all sizes, which occupies the crystallizer and is withdrawn as product is called
a. product crystals c. mother liquor
b. magma d. invariant crystals
b. magma
States that if all crystals in magma grow in a supersaturation field and at the same temperature and if all crystal grow from birth at a rate governed by the supersaturation, then all crystals are not only invariant but also have the same growth rate that is independent of size
Law of Crystals
In practice, slow cooling maintaining a low level of supersaturation produces ___ crystals and fast cooling produces ___ crystals.
a. small, large b. fine, coarse
c. large, small d. coarse, fine
c. large, small
It is the process by which crystalline bodies are created within a supersaturated fluid.
a. polymorphism b. crystal growth
c. nucleation d. seeding
c. nucleation
Evaporation is also sometimes called as
a. thermal compression c. water distillation
b. liquid compression d. vapor compression
The concentration of glycerin from a water solution by the application of heat is
a. distillation
b. evaporation
c. crystallization
d. reverse osmosis
The total amount of evaporation an evaporator is capable of producing per unit of time.
a. economy
b. capacity
c. steam consumption
d. fouling factors
When the pressure of the chamber is decreased, the boiling point of the solution inside the chamber will
a. increase
b. remain the same
c. decrease
d. increase or decrease
A heat transfer device that is normally used to liquefy vapors is
a. evaporator c. reboiler
b. condenser d. humidifier
The temperature driving force in an evaporator is determined as the difference between the condensing steam temperature and
A) condenser temperature
B) boiling point of the solution
C) boiling point of the solvent
D) BPR of the solution
In a country where capital is appropriate to install?
a. multiple effect evaporator b. single effect evaporator
The fresh feed enters at the coldest effect.
a. feed-forward
b. parallel-feed
c. feed-backward
d. none of these
