The mass transfer co-efficient for a solid sphere of radius 'a' dissolving in a large volume of quiescent liquid, in which D is the diffusivity of solute, is

Dependent on the Reynolds number

In a liquid-liquid extraction, 10 kg of a solution containing 2 kg of solute C and 8 kg of solvent A is brought into contact with 10 kg of solvent B. Solvent A and B are completely immiscible in each other whereas solute C is soluble in both the solvents. The extraction process attains equilibrium. The equilibrium relationship between the two phases is Y* = 0.9X, where Y* is the kg of C/kg of B and X is kg of C/kg of A. Choose the correct answer.

The entire amount of C is transferred to solvent B

Less than 2 kg but more than 1 kg of C is transferred to solvent B

Less than 1 kg of C is transferred to B

At the same gas flow rate, the pressure drop in a packed tower being irrigated with liquid __________ that in dry packed tower.

Cannot be predicted as data are insufficient

Fenske equation for determining the minimum number of theoretical stages in distillation column holds good, when the

Mixture (to be separated) shows negative deviation from ideality

Relative volatility is reasonably constant

Mixture (to be separated) shows negative deviation from ideality

Mixture (to be separated) shows positive deviation from ideality

Multi-component distillation is involved

For the same feed, feed quality and separation (in a distillation column), with the increase of total pressure, the number of ideal plates will

Data insufficient, can't be predicted

For the flow of gases through a capillary, with increase in temperature, the permeability __________ as per Knudsen law.

Either (A) or (B); depends on the gas

Sides of equilateral-triangular co-ordinates (on which ternary liquid system is plotted) represent

Partially miscible ternary system

With decrease in the throughput (compared with the design capacity) for a bubble cap distillation column, its efficiency

May increase or decrease; depends on individual design

35 + Mcqs in Mass Transfer in Mechanical Engineering Page 1 McqOptions

1.	The mass transfer co-efficient for a solid sphere of radius 'a' dissolving in a large volume of quiescent liquid, in which D is the diffusivity of solute, is
A.	D/a
B.	D/2a
C.	Proportional to D
D.	Dependent on the Reynolds number
Answer» E.

Discussion

2.	Cox chart, which is useful in the design of distillation column particularly for petroleum hydrocarbons, is a plot of (where, P = vapor pressure, T = temperature).
A.	log P vs. T
B.	log P vs. log T
C.	T vs. P
D.	P vs. log T
Answer» B. log P vs. log T

Discussion

3.	Wet bulb and dry bulb temperatures becomes identical at __________ percent saturation curve.
A.	100
B.	50
C.	78
D.	None of these
Answer» B. 50

Discussion

4.	In a liquid-liquid extraction, 10 kg of a solution containing 2 kg of solute C and 8 kg of solvent A is brought into contact with 10 kg of solvent B. Solvent A and B are completely immiscible in each other whereas solute C is soluble in both the solvents. The extraction process attains equilibrium. The equilibrium relationship between the two phases is Y* = 0.9X, where Y* is the kg of C/kg of B and X is kg of C/kg of A. Choose the correct answer.
A.	The entire amount of C is transferred to solvent B
B.	Less than 2 kg but more than 1 kg of C is transferred to solvent B
C.	Less than 1 kg of C is transferred to B
D.	No amount of C is tr
Answer» E.

Discussion

5.	The relative saturation of a partially saturated mixture of vapour and gas can be increased by __________ of the mixture.
A.	Reducing the total pressure
B.	Increasing the total pressure
C.	Reducing the temperature
D.	Both (B) and (C)
Answer» E.

Discussion

6.	When the __________ the relative humidity of air decreases, despite an increase in the absolute humidity.
A.	Temperature rises
B.	Pressure rises
C.	Temperature falls
D.	Pressure falls
Answer» B. Pressure rises

Discussion

7.	In case of __________ distillation, a solvent is added to alter the relative volatility of the mixture to be separated.
A.	Molecular
B.	Azeotropic
C.	Extractive
D.	Flash
Answer» D. Flash

Discussion

8.	Psychrometry deals with the properties of gas-vapor mixture. Humidity can be determined by the measurement of the __________ of a fibre.
A.	Electrical resistance
B.	Thermal conductivity
C.	Strength
D.	None of these
Answer» B. Thermal conductivity

Discussion

9.	A natural draft cooling tower is filled with wooden grids, which covers about __________ percent of the tower height.
A.	10-15
B.	30-40
C.	70-80
D.	90-100
Answer» B. 30-40

Discussion

10.	The partial pressure distribution of an ideal gas diffusing through another stagnant ideal gas at steady state follows a/an __________ law.
A.	Exponential
B.	Parabolic
C.	Linear
D.	Cubic
Answer» B. Parabolic

Discussion

11.	For turbulent mass transfer in pipes, the Sherwood number depends on the Reynolds number as
A.	Re0.33
B.	Re0.53
C.	Re0.83
D.	Re
Answer» D. Re

Discussion

12.	At the same gas flow rate, the pressure drop in a packed tower being irrigated with liquid __________ that in dry packed tower.
A.	Is greater than
B.	Is lower than
C.	Is same as
D.	Cannot be predicted as data are insufficient
Answer» B. Is lower than

Discussion

13.	Which of the following gas-liquid contacting devices incurs the least pressure drop for a particular duty?
A.	Grid tray tower
B.	Perforated tray tower
C.	Wetted wall tower
D.	Bubble cap tower
Answer» E.

Discussion

14.	With increase in the liquid flow rate at a fixed gas velocity in a randomly packed counter current gas-liquid absorption column, the gas pressure drop
A.	Decreases
B.	Remains unchanged
C.	Increases
D.	Decreases exponentially
Answer» D. Decreases exponentially

Discussion

15.	Mass transfer co-efficient varies as DAB 0.5, according to the __________ theory.
A.	Film
B.	Surface renewal
C.	Penetration
D.	None of these
Answer» C. Penetration

Discussion

16.	At __________ reflux, theoretical number of plates in a distillation coloumn is calculated using Fenske-Underwood equation.
A.	Operating
B.	Total
C.	Minimum
D.	Maximum permissible
Answer» C. Minimum

Discussion

17.	Fenske-Underwood equation used for calculating the minimum number of theoretical plates in distillation column is valid for
A.	Constant molal overflow
B.	Total reflux
C.	Constant relative volatility
D.	All (A), (B) and (C)
Answer» E.

Discussion

18.	Fenske equation for determining the minimum number of theoretical stages in distillation column holds good, when the
A.	Relative volatility is reasonably constant
B.	Mixture (to be separated) shows negative deviation from ideality
C.	Mixture (to be separated) shows positive deviation from ideality
D.	Multi-component distillation is involved
Answer» B. Mixture (to be separated) shows negative deviation from ideality

Discussion

19.	For the same feed, feed quality and separation (in a distillation column), with the increase of total pressure, the number of ideal plates will
A.	Increase
B.	Decrease
C.	Remain same
D.	Data insufficient, can't be predicted
Answer» B. Decrease

Discussion

20.	The amount of steam required per unit quantity of distillate in case of steam distillation will be reduced by
A.	Raising the temperature
B.	Lowering the total pressure
C.	Both (A) and (B)
D.	Neither (A) nor (B)
Answer» D. Neither (A) nor (B)

Discussion

21.	For __________ drying, the effects of velocity, temperature and humidity of the gas and the thickness of the solid are the same.
A.	Unsaturated surface
B.	Constant rate
C.	Both (A) and (B)
D.	Neither (A) nor (B)
Answer» D. Neither (A) nor (B)

Discussion

22.	Which of the following is the most suitable for extraction in a system having very low density difference?
A.	Mixer-settler extractor
B.	Centrifugal extractor
C.	Pulsed extractor
D.	Packed extraction tower
Answer» C. Pulsed extractor

Discussion

23.	The velocity, concentration and temperature boundary, for the boundary layer development on a flat plate during connective mass transfer will be same, if
A.	NSc = 1
B.	NSc = NPr = NLe
C.	NPr = NLe
D.	NSc = NLe
Answer» C. NPr = NLe

Discussion

24.	The diffusivity, DAB (for component A diffusing in B) is equal to the diffusivity DBA (for component B diffusing in A) for a binary mixture of
A.	Newtonian liquids
B.	Non-Newtonian liquids
C.	Ideal gases
D.	Real gases
Answer» D. Real gases

Discussion

25.	Liquid diffusivity is of the order of __________ cm2 /second.
A.	0.01
B.	0.1
C.	10-5 to 10-6
D.	> 1
Answer» D. > 1

Discussion

26.	For the flow of gases through a capillary, with increase in temperature, the permeability __________ as per Knudsen law.
A.	Increases
B.	Decreases
C.	Remain same
D.	Either (A) or (B); depends on the gas
Answer» B. Decreases

Discussion

27.	Sides of equilateral-triangular co-ordinates (on which ternary liquid system is plotted) represent
A.	A pure component
B.	A binary mixture
C.	A ternary mixture
D.	Partially miscible ternary system
Answer» C. A ternary mixture

Discussion

28.	For continuous drying of granular or crystalline material, the dryer used is the __________ dryer.
A.	Tunnel
B.	Tray
C.	Rotary
D.	None of these
Answer» D. None of these

Discussion

29.	__________ number indicates the ratio of the rates of the heat and mass transfer incase of a cooling tower.
A.	Sherwood
B.	Stanton
C.	Lewis
D.	Peclet
Answer» D. Peclet

Discussion

30.	Corresponding to Nusselt number in heat transfer, the dimensionless group in mass transfer is the __________ number.
A.	Sherwood
B.	Schmidt
C.	Peclet
D.	Stanton
Answer» B. Schmidt

Discussion

31.	With decrease in the throughput (compared with the design capacity) for a bubble cap distillation column, its efficiency
A.	Increases
B.	Decreases
C.	Remain same
D.	May increase or decrease; depends on individual design
Answer» B. Decreases

Discussion

32.	In the absorption of ammonia in water, the main resistance to absorption is by the __________ phase.
A.	Liquid
B.	Gas
C.	Both (A) & (B)
D.	Neither (A) nor (B)
Answer» C. Both (A) & (B)

Discussion

33.	For experimental determination of mass transfer co-efficient by wetted wall tower, the mass transfer area is
A.	Calculated
B.	Unknown
C.	Known
D.	Not required
Answer» D. Not required

Discussion

34.	The diffusion co-efficient in m2 /s. of acetic acid in benzene (liquid in liquid) is
A.	2.09 10-4
B.	2.09 10-5
C.	2.09 10-9
D.	2.09 10-12
Answer» B. 2.09 10-5

Discussion

35.	For the case of flow of air past a wet bulb thermometer (air water vapour system), the approximate value of h2/ky .Cz is around
A.	0.60
B.	0.24
C.	1
D.	0.72
Answer» D. 0.72

Discussion

Explore topic-wise MCQs in Mechanical Engineering.

The mass transfer co-efficient for a solid sphere of radius 'a' dissolving in a large volume of quiescent liquid, in which D is the diffusivity of solute, is

Cox chart, which is useful in the design of distillation column particularly for petroleum hydrocarbons, is a plot of (where, P = vapor pressure, T = temperature).

Wet bulb and dry bulb temperatures becomes identical at __________ percent saturation curve.

The relative saturation of a partially saturated mixture of vapour and gas can be increased by __________ of the mixture.

When the __________ the relative humidity of air decreases, despite an increase in the absolute humidity.

In case of __________ distillation, a solvent is added to alter the relative volatility of the mixture to be separated.

Psychrometry deals with the properties of gas-vapor mixture. Humidity can be determined by the measurement of the __________ of a fibre.

A natural draft cooling tower is filled with wooden grids, which covers about __________ percent of the tower height.

The partial pressure distribution of an ideal gas diffusing through another stagnant ideal gas at steady state follows a/an __________ law.

For turbulent mass transfer in pipes, the Sherwood number depends on the Reynolds number as

At the same gas flow rate, the pressure drop in a packed tower being irrigated with liquid __________ that in dry packed tower.

Which of the following gas-liquid contacting devices incurs the least pressure drop for a particular duty?

With increase in the liquid flow rate at a fixed gas velocity in a randomly packed counter current gas-liquid absorption column, the gas pressure drop

Mass transfer co-efficient varies as DAB 0.5, according to the __________ theory.

At __________ reflux, theoretical number of plates in a distillation coloumn is calculated using Fenske-Underwood equation.

Fenske-Underwood equation used for calculating the minimum number of theoretical plates in distillation column is valid for

Fenske equation for determining the minimum number of theoretical stages in distillation column holds good, when the

For the same feed, feed quality and separation (in a distillation column), with the increase of total pressure, the number of ideal plates will

The amount of steam required per unit quantity of distillate in case of steam distillation will be reduced by

For __________ drying, the effects of velocity, temperature and humidity of the gas and the thickness of the solid are the same.

Which of the following is the most suitable for extraction in a system having very low density difference?

The velocity, concentration and temperature boundary, for the boundary layer development on a flat plate during connective mass transfer will be same, if

The diffusivity, DAB (for component A diffusing in B) is equal to the diffusivity DBA (for component B diffusing in A) for a binary mixture of

Liquid diffusivity is of the order of __________ cm2 /second.

For the flow of gases through a capillary, with increase in temperature, the permeability __________ as per Knudsen law.

Sides of equilateral-triangular co-ordinates (on which ternary liquid system is plotted) represent

For continuous drying of granular or crystalline material, the dryer used is the __________ dryer.

__________ number indicates the ratio of the rates of the heat and mass transfer incase of a cooling tower.

Corresponding to Nusselt number in heat transfer, the dimensionless group in mass transfer is the __________ number.

With decrease in the throughput (compared with the design capacity) for a bubble cap distillation column, its efficiency

In the absorption of ammonia in water, the main resistance to absorption is by the __________ phase.

For experimental determination of mass transfer co-efficient by wetted wall tower, the mass transfer area is

The diffusion co-efficient in m2 /s. of acetic acid in benzene (liquid in liquid) is

For the case of flow of air past a wet bulb thermometer (air water vapour system), the approximate value of h2/ky .Cz is around