IndiaBIX Chemical Engineering: Mass Transfer Section 9 Flashcards
Which of the following parameters remains constant during chemical dehumidifica-tion?
Dry bulb temperature
Partial pressure of vapour
Wet bulb temperature
None of these
Dry bulb temperature
Drying of a solid involves __________ transfer.
only heat
only mass
both heat and mass
none of these
both heat and mass
Mechanism of moisture removal in case of freeze drying of food stuff is by
evaporation
sublimation
dehydration
adsorption
sublimation
The dew point of an unsaturated gas-vapor mixture does not depend upon the __________ of the mixture.
composition
temperature
total pressure
all (a),
(b) and (c)
temperature
Which is not concerned directly with mass transfer ?
Schmidt number
Sherwood number
Lewis relationship
Froude number
Froude number
Removal of __________ exemplifies an adsorption unit operation.
uranium from its ore
water from petrol
ammonia from coke oven gas
mustard oil from mustard seed
water from petrol
Can the efficiency of a plate in the distillation tower be greater than 100% ?
Yes
Normally not; but is possible if infinite number of plates are put.
Never
Yes ; if the reflux ratio is maximum.
Never
With increase in the mass velocity of the gas,
the rate of drying during the constant rate period __________ ,
if the conduction and radiation through the solid are negligible.
increases
decreases
remains same
increases linearly
increases
For gas absorption,
low viscosity solvents are preferred,
because of their
better flow characteristics.
low pumping pressure drop.
rapid absorption rates.
all (a),
(b) and (c).
all (a),
(b) and (c).
To remove all the moisture from a wet solid it requires exposure to __________ air.
perfectly dry
highly humid
high temperature
none of these
perfectly dry
The operating cost of a distillation column at minimum reflux ratio is
minimum
maximum
infinite
zero
minimum
The reflux to a distillation column is 100 moles/hr,
when the overhead product rate is 50 moles/hr. The reflux ratio is
2
0.5
50
150
2
Molecular diffusivity of a liquid
increases with temperature.
decreases with temperature.
may increase or decrease with temperature.
is independent of temperature.
increases with temperature.
The wet and ‘dry bulb temperature for a vapour-gas mixture are 25°C and 30°C respectively. If the mixture is heated to 45°C at constant pressure,
the wet bulb temperature will be __________ °C.
25
> 25
< 25
- 25
> 25
Henry’s law states that the
partial pressure of a component over a solution is proportional to its mole fraction in the liquid.
partial pressure of a component over a solution is proportional to the mole fraction in the vapour.
vapour pressure is equal to the product of the mole fraction and total pressure.
partial pressure is equal to the product of the mole fraction and total pressure.
partial pressure of a component over a solution is proportional to its mole fraction in the liquid.
Ammonia present in the coke oven gas is removed by washing with
caustic solution
dilute ammoniacal liquor
dilute HCl
ethanolamine
dilute ammoniacal liquor
With increase in temperature,
the leaching rate increases due to
decreased liquid viscosity
increased diffusivity
both (a) and (b)
neither (a) nor (b)
both (a) and (b)
Which of the following processes is not an example of adsorption applied to gaseous separations ?
Recovery of valuable solvent vapors from dilute mixture with air and other gases.
Dehumidification of air and gas.
Removal of objectionable odour and impurities from industrial gases.
Decolouration of yellow glycerene.
Decolouration of yellow glycerene.
The critical moisture content in case of drying indicates the __________ rate period.
beginning of falling
beginning of constant
end of falling
none of these
beginning of falling
Pick out the wrong statement
A horizontal line on the humidity chart indicates the temperature changes at constant molal humidity.
When water is cooled from 80 to 70°C by exposure to the air with a wet bulb temperature of 60°C,
then both the approach & the range would be 10°C.
For unsaturated air-water vapor mixture at atmospheric conditions,
the wet bulb temperature & adiabatic cooling lines are the same.
Relative saturation of unsaturated mixture of water vapor & air can not be increased by either reducing the mixture temperature or by increasing the total pressure.
Relative saturation of unsaturated mixture of water vapor & air can not be increased by either reducing the mixture temperature or by increasing the total pressure.