Mass Transfer – Multiple Choice Questions (MCQs)

1. 49. What is the 'Sherwood number' (Sh)?

   • A. A dimensionless number representing the ratio of convective mass transfer to diffusive mass transfer
   • B. A dimensionless number for heat transfer
   • C. A dimensionless number for fluid flow
   • D. A dimensionless number for reaction rates

2. 50. What is the 'Lewis number' (Le)?

   • A. Ratio of thermal diffusivity to mass diffusivity
   • B. Ratio of momentum diffusivity to mass diffusivity
   • C. Ratio of heat transfer to mass transfer
   • D. Ratio of heat capacity to thermal conductivity

3. 51. What is the primary factor affecting the diffusion coefficient in gases?

   • A. Temperature and pressure
   • B. Concentration
   • C. Viscosity
   • D. Density

4. 52. What is the primary factor affecting the diffusion coefficient in liquids?

   • A. Temperature and viscosity
   • B. Concentration
   • C. Pressure
   • D. Density

5. 53. What is the concept of 'wetting' in packed columns?

   • A. The ability of the liquid to spread over the packing material
   • B. The ability of the gas to flow through the packing
   • C. The amount of packing material used
   • D. The pressure drop across the packing

6. 54. What is 'flooding' in a packed column?

   • A. A condition where the liquid accumulates in the column due to high gas flow rate
   • B. The column operating at maximum efficiency
   • C. The column operating at minimum flow rates
   • D. A condition where the packing material breaks down

7. 55. What is 'loading' in a packed column?

   • A. The point at which the liquid holdup begins to increase significantly with increasing gas flow rate
   • B. The maximum gas flow rate
   • C. The minimum liquid flow rate
   • D. The point where flooding occurs

8. 56. What is the major advantage of packed columns over plate columns for absorption/stripping?

   • A. Lower pressure drop
   • B. Higher efficiency per unit height
   • C. Better handling of foaming liquids
   • D. Easier to scale up

9. 57. What is the major advantage of plate columns over packed columns for absorption/stripping?

   • A. Lower pressure drop
   • B. Higher flexibility in operation
   • C. Better handling of foaming liquids
   • D. Easier to scale up

10. 58. What is 'channeling' in a packed column?

    • A. Uneven distribution of liquid and gas flow
    • B. Uniform distribution of liquid and gas
    • C. Optimal operation of the column
    • D. Breakdown of packing

11. 59. What is the purpose of 'weirs' on distillation trays?

    • A. To maintain a liquid level on the tray
    • B. To prevent liquid from flowing down
    • C. To increase gas velocity
    • D. To support the packing

12. 60. What is 'downcomer' in a plate column?

    • A. A pipe that carries liquid from one tray to the tray below
    • B. A pipe that carries vapor up the column
    • C. A device for distributing liquid
    • D. A device for collecting product