Multiple Choice Questions (MCQ) and Answers on Mass Transfer
Question 1 : In distillation columns, the number of bubble caps per tray primarily depends upon the
- allowable liquid velocity.
- allowable gas velocity.
- allowable gas and liquid velocities.
- feed composition.
Answer : 3
Question 2 : In distillation, overhead product contains
- only one component
- two components
- any number of components
- only saturated liquid
Answer : 3
Question 3 : With increase in pressure, the relative volatility for a binary system
- increases.
- decreases.
- remains same.
- either (1) or (2), depends on the system.
Answer : 3
Question 4 : Low viscosity absorbent is preferred for reasons of
- rapid absorption rates and good heat transfer characteristics.
- improved flooding characteristics.
- low pressure drop on pumping.
- all (a), (b) and (c).
Answer : 4
Question 5 : Mass transfer co-efficient (K) and diffusivity (D) are related according to film theory as
- K ∝ D
- K ∝
- K ∝ D1.5
- K ∝ D2
Answer : 1
Question 6 : Which of the following liquid-vapor contacting devices provides maximum contact surface area for a particular duty ?
- Sieve plate column
- Bubble cap column
- Randomly packed column
- Wetted wall column
Answer : 4
Question 7 : The equipment frequently used for adiabatic humidification-cooling operation with recirculating liquid is
- natural draft cooling tower
- induced draft cooling tower
- spray chamber
- none of these
Answer : 3
Question 8 : Chemisorption (chemical adsorption) is
- same as “Van der Waals” adsorption.
- characterised by adsorption of heat.
- an irreversible phenomenon.
- a reversible phenomenon.
Answer : 3
Question 9 : The rate of solid-liquid extraction is limited by the
- phase change of the solute as it dissolves in the solvent.
- diffusion of the solute through the solvent in the pores to the outside of the particle.
- diffusion of the solute from the solution in contact with the particle to the main bulk of the solution.
- all ‘1’, ‘2’ & ‘3’.
Answer : 4
Question 10 : Raoult’s law applies to the
- all liquid solutions
- non-ideal solution only.
- non-volatile solute.
- solvents.
Answer : 4
Question 11 : Make up water is required in a cooling tower to replace the water lost by
- evaporation
- drift
- blowdown and leakage
- all (a), (b) and (c)
Answer : 4
Question 12 : Which of the following quantities need not be fixed before starting the design of a co-current absorber ?
- Heat gain or loss
- Flow rate of entering liquid
- Flow rate of gas
- None of these
Answer : 2
Question 13 : Mass transfer co-efficient of liquid is
- affected more by temperature than that for gases.
- affected much less by temperature than that for gases.
- not affected by the temperature.
- none of these.
Answer : 1
Question 14 : Absorption accompanied with chemical reaction is exemplified by the absorption of
- ammonia in water.
- benzol present in coke oven gas by wash oil.
- SO2 in alkaline solution.
- all (a), (b) and (c).
Answer : 3
Question 15 : Which of the following unit operations makes use of Thiele-Geddes equation ?
- Liquid-liquid extraction
- Solid-liquid extraction
- Multicomponent absorption with chemical reaction
- Multicomponent distillation.
Answer : 4
Question 16 : As the reflux ratio in a distillation coloumn is increased from the minimum, the
- slope of the operating line in stripping section decreases.
- number of plates decreases very slowly first and then more and more rapidly.
- total cost first decreases and then increases.
- liquid flow increases while the vapor flow decreases for a system.
Answer : 3
Question 17 : Absorption factor is defined as (where, S1 = slope of the operating line S2 = slope of the equilibrium curve)
- S2/S1
- S1/S2
- S1 – S2
- S1 x S2
Answer : 2
Question 18 : A plait point is the point on the solubility curve, where the tie line reduces to a point. What is the number of plait point for a ternery system containing twopairs of partially miscible liquids ?
- 0
- 1
- 2
- 3
Answer : 1
Question 19 : Which of the following remains constant during sensible cooling process ?
- Specific humidity
- Partial pressure of vapour
- Both (1) and (2)
- Neither (1) nor (2)
Answer : 3
Question 20 : Physical absorption is
- an irreversible phenomenon.
- a reversible phenomenon.
- accompanied by evolution of heat.
- both (2) and (3)
Answer : 4
Question 21 : The mass diffusivity, the thermal diffusivity and the eddy momentum diffusivity are same for, NPr = NSc = __________
- 1
- 0.5
- 10
- 0
Answer : 1
Question 22 :Dew point of a gas-vapour mixture
- increases with temperature rise.
- decreases with temperature rise.
- decreases with decrease in pressure.
- increases with increase in pressure.
Answer : 3
Question 23 : In a packed absorption tower, if the equilibrium and operating lines are both straight lines, then the ratio, HETP/HTUOG __________ the absorption factor.
- increases with increase in
- is one at unity value of
- both (1) and (2)
- neither (1) nor (2)
Answer : 3
Question 24 : Which of the following plays an important role in problems of simultaneous heat and mass transfer ?
- Lewis number
- Schmidt number
- Prandtl number
- Sherwood number
Answer : 1
Question 25 : In case of an absorber, the operating
- line always lies above the equilibrium curve.
- line always lies below the equilibrium curve.
- line can be either above or below the equilibrium curve.
- velocity is more than the loading velocity.
Answer : 1
Question 26 : Relative humidity is the ratio of the
- partial pressure of the vapour to the vapour pressure of the liquid at room temperature.
- partial pressure of the vapour to the vapour pressure of the liquid at gas temperature.
- actual humidity to saturation humidity.
- none of these
Answer : 2
Question 27 : In batch distillation with constant reflux, overhead product composition __________ with time.
- increases
- decreases
- does not vary
- may increase on decrease, depends on the system.
Answer : 2
Question 28 : Psychrometry deals with the properties of gas-vapor mixture. Humidity can be determined by the measurement of the __________ of a fibre.
- electrical resistance
- thermal conductivity
- strength
- none of these.
Answer : 1
Question 29 : Heat in BTU necessary to increase the temperature of 1 lb of gas and its accompanying vapour by 1°F is called the
- latent heat
- humid heat
- specific heat
- sensible heat
Answer : 3
Question 30 : To increase the absorption factor, (where, G = gas flow rate, S = solvent flow rate)
- increase both ‘G‘ and ‘S‘.
- decrease both ‘G‘ and ‘S‘.
- increase ‘S‘ and decrease ‘G‘.
- increase ‘G‘ and decrease ‘S‘
Answer : 3
Question 31 : Drying operation under vacuum is carried out to
- dry those materials which have very high unbound mositure content.
- reduce drying temperature.
- increase drying temperature.
- dry materials having high bound moisture content.
Answer : 2
Question 32 : Air initially at 101. 3 kPa and 40°C and with a relative humidity of 50%, is cooled at constant pressure to 30°C. The cooled air has a
- higher dew point
- higher absolute (specific) humidity.
- higher relative humidity
- higher wet bulb temperature.
Answer : 3
Question 33 : Separation of two or more components of a liquid solution can not be achieved by
- fractional crystallisation
- liquid extraction
- absorption
- evaporation
Answer : 3
Question 34 : Stefan’s law describes the mass transfer by
- diffusion
- bulk flow
- both ‘a’ & ‘b’
- neither ‘a’ nor ‘b’
Answer : 3
Question 35 : At minimum reflux ratio for a given separation
- number of plates is zero.
- number of plates is infinity.
- minimum number of the theoretical plates is required.
- separation is most efficient.
Answer : 2
Question 36 : Pick out the correct statement.
- In case of liquid-liquid extraction, no separation is possible, if the selectivity of the solvent used is unity.
- With increase in temperature, the selectivity of the solvent used in solvent extraction decreases.
- The selectivity of solvent used in solvent extraction is unity at the plait point.
- all (1), (2) and (3).
Answer : 4
Question 37 : __________ columns are used for liquid dispersion in a continuous gas phase.
- Packed
- Pulse
- Bubble cap
- Sieve plate
Answer : 1
Question 38 : Overall efficiency of the distillation column is
- the ratio of number of ideal plates to actual plates.
- the ratio of number of actual plates to ideal plates.
- same as the Murphree efficiency.
- always more than the point efficiency.
Answer : 1
Question 39 : On addition of solute in the solvent, the __________ of the solution decreases.
- boiling point
- freezing point
- vapour pressure
- both (2) and (3)
Answer : 4
Question 40 : Which is the controlling factor for a drum drier?
- Diffusion
- Heat transfer
- Both (1) and (2)
- Neither (1) nor (2)
Answer : 2
Question 41 : Total reflux in a distillation operation requires minimum
- reboiler load
- number of plates
- condenser load
- all (1), (2) and (3)
Answer : 2
Question 42 : The amount of steam required per unit quantity of distillate in case of steam distillation will be reduced by
- raising the temperature.
- lowering the total pressure.
- both (1) and (2)
- neither (1) nor (2).
Answer : 3
Question 43 : The difference of wet bulb temperature and adiabatic saturation temperature of unsaturated mixture of any system is
- +ve
- -ve
- zero
- none of these
Answer : 1
Question 44 : Fenske’s equation for determining the minimum number of theoretical stages in distillation column holds good, when the
- relative volatility is reasonably constant.
- mixture (to be separated) shows negative deviation from ideality.
- mixture (to be separated) shows positive deviation from ideality.
- multicomponent distillation is involved.
Answer : 1
Question 45 : When the temperature and humidity of air is low, we usually use __________ draft cooling tower.
- natural
- forced
- induced
- none of these
Answer : 1
Question 46 : Mass transfer rate between two fluid phases does not necessarily depend on the __________ of the two phases.
- chemical properties
- physical properties
- degree of turbulence
- interfacial area
Answer : 1
Question 47 : In a solution containing 0.30 Kg mole of solute and 600 kg of solvent, the molality is
- 0.50
- 0.60
- 2
- 1
Answer : 1
Question 48 : Fenske equation determines the
- maximum number of ideal plates.
- height of the distillation column.
- minimum number of theoretical plates.
- optimum reflux ratio.
Answer : 3
Question 49 : The term “cooling range” in a cooling tower refers to the difference in the temperature of
- cold water leaving the tower and the wet bulb temperature of the surrounding air.
- hot water entering the tower and the wet bulb temperature of the surrounding air.
- hot water entering the tower and the cooled water leaving the tower.
- none of these
Answer : 3
Question 50 : Which of the following is the most suitable for extraction in a system having very low density difference ?
- Mixer-settler extractor
- Centrifugal extractor
- Pulsed extractor
- Packed extraction tower
Answer : 2