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Mass Transfer

Total questions: 30

Worksheet time: 40mins

Name
Class
Date
1.

Convective mass transfer involves

a)

Only molecular diffusion

b)

Only bulk fluid motion

c)

Both molecular diffusion and bulk fluid motion

d)

Only chemical reaction

2.

The driving force for convective mass transfer is generally

a)

Pressure difference

b)

Temperature difference

c)

Velocity difference

d)

Concentration difference

3.

The unit of mass transfer coefficient kc is

a)

m/s

b)

kg/m³

c)

mol/s

d)

m²/s

4.

Which of the following best represents the mass flux equation?

a)

NA​ = kc ​(CA,b​−CA,i​)

b)

NA​ = kc

c)

NA​ = DAB​/Z

d)

NA​ = ρv

5.

In convective mass transfer, resistance to mass transfer mainly exists in the

a)

Bulk fluid

b)

Solid surface

c)

Thin fluid film near the interface

d)

Entire fluid equally

6.

Which of the following is an example of convective mass transfer?

a)

Diffusion of perfume in a closed room

b)

Dissolution of sugar in stagnant water

c)

Dissolution of sugar in stirred water

d)

Dissolution of sugar in hot water

7.

The symbol kL generally represents

a)

Diffusivity

b)

Gas-phase mass transfer coefficient

c)

Liquid-phase mass transfer coefficient

d)

Overall mass transfer coefficient

8.

Local mass transfer coefficient refers to the value of coefficient

a)

At a particular point on the surface

b)

Averaged over entire surface

c)

For bulk fluid only

d)

At infinite distance

9.

Increasing fluid velocity generally causes the mass transfer coefficient to

a)

Decrease

b)

Remain constant

c)

Increase

d)

Become zero

10.

The concentration at the interface during mass transfer is denoted by

a)

CA,b​

b)

CA,f​

c)

CA,o​

d)

CA,i​

11.

The average mass transfer coefficient is obtained by

a)

Using molecular diffusivity only

b)

Taking value at midpoint only

c)

Integrating local coefficient over the surface

d)

Using only bulk concentration

12.

The overall mass transfer coefficient accounts for

a)

Only gas-phase resistance

b)

Only liquid-phase resistance

c)

Combined resistance of both phases

d)

Chemical reaction rate

13.

Which situation increases convective mass transfer rate?

a)

Lower concentration gradient

b)

Lower fluid velocity

c)

Higher viscosity

d)

Higher turbulence

14.

The physical meaning of mass transfer coefficient is

a)

Total mass transferred

b)

Resistance to mass transfer

c)

Diffusion flux only

d)

Rate of mass transfer per unit area per unit driving force

15.

If interfacial area doubles while all coefficients remain constant, mass transfer rate will

a)

Halve

b)

Remain same

c)

Increase four times

d)

Double

16.

A mixture contains non-volatile solute dissolved in a volatile solvent. Which process is most suitable to separate solvent based on mass transfer and phase equilibrium?

a)

Adsorption

b)

Distillation

c)

Membrane gas separation

d)

Screening

17.

In a steady-state diffusion process through a stagnant gas film, if the concentration at one boundary increases while the other remains constant, the system will respond by

a)

Decreasing diffusivity

b)

Reducing film thickness automatically

c)

Increasing the molar flux of the diffusing species

d)

Stopping molecular motion

18.

Two gases A and B diffuse in opposite directions at equal molar rates. This situation indicates

a)

Non-steady state diffusion

b)

Equimolar counter diffusion

c)

No concentration gradient

d)

Eddy diffusion only

19.

During diffusion through a solid wall, the rate is very slow compared to gases because

a)

Molecules are closely packed restricting movement

b)

Concentration gradient is always zero

c)

Temperature is low

d)

Pressure is high

20.

Which statement correctly explains the difference between molecular diffusion and eddy diffusion?

a)

Molecular diffusion occurs only in solids, while eddy diffusion occurs only in gases.

b)

Molecular diffusion requires bulk motion of fluid, while eddy diffusion does not.

c)

Both processes occur only at high pressure.

d)

Molecular diffusion is due to random molecular motion, whereas eddy diffusion is due to turbulent mixing.

21.

The SI unit of molar flux is

a)

kmol/m²·s

b)

kmol/m3

c)

kmol/s

d)

m²/s

22.

The proportionality constant in Fick’s First Law is called the

a)

Diffusion coefficient

b)

Mass transfer coefficient

c)

Heat transfer coefficient

d)

Viscosity

23.

Which of the following is an example of a mass transfer operation?

a)

Heat conduction

b)

Distillation

c)

Fluid flow in a pipe

d)

Mechanical crushing

24.

An increase in fluid velocity in convective mass transfer

a)

Increases the local mass transfer coefficient

b)

Decreases the local mass transfer coefficient

c)

Has no effect on mass transfer

d)

Reduces concentration gradient

25.

Local mass transfer coefficient is measured

a)

At one point on the surface

b)

Over the whole surface

c)

In the bulk fluid

d)

Only at high temperature

26.

Increasing temperature generally

a)

Decreases diffusivity

b)

Increases diffusivity

c)

Reduces mass transfer rate

d)

Has no effect

27.

Diffusivity differs from mass transfer coefficient because diffusivity

a)

Depends on flow conditions

b)

Is a fluid property independent of hydrodynamics

c)

Has units of mol/m²·s

d)

Exists only in turbulent flow

28.

Sherwood number is the ratio of

a)

Convective to diffusive mass transfer

b)

Inertial to viscous forces

c)

Thermal to mass diffusivity

d)

Pressure to velocity

29.

Reynolds number in mass transfer indicates

a)

Diffusion strength

b)

Flow regime (laminar/turbulent)

c)

Concentration gradient

d)

Surface roughness

30.

Higher Schmidt number implies

a)

Turbulent flow

b)

No diffusion

c)

Faster mass diffusion than momentum diffusion

d)

Slower mass diffusion compared to momentum diffusion

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