Mass Transfer - Engineering

Q1:

Which of the following liquid-vapor contacting devices provides maximum contact surface area for a particular duty ?

A Sieve plate column

B Bubble cap column

C Randomly packed column

D Wetted wall column

ANS:D - Wetted wall column

Among the options provided, the randomly packed column typically provides the maximum contact surface area for a particular duty in liquid-vapor contacting. Explanation:

  1. Randomly Packed Column:
    • In a randomly packed column, the column is filled with randomly arranged packing material, such as Raschig rings, Berl saddles, or Pall rings.
    • The packing material creates a large interfacial area between the liquid and vapor phases as they pass through the column.
    • Due to the random arrangement of the packing material, the surface area available for mass transfer is maximized, allowing for efficient contact between the liquid and vapor streams.
  2. Advantages:
    • Randomly packed columns offer several advantages, including high mass transfer rates, low pressure drop, and versatility in handling various liquid-vapor systems.
    • The large surface area provided by the packing material enhances the efficiency of mass transfer operations such as distillation, absorption, and stripping.
  3. Comparison with Other Devices:
    • Sieve plate columns and bubble cap columns also facilitate liquid-vapor contact, but their contact surface area may be limited compared to randomly packed columns.
    • Sieve plate columns feature perforated plates with holes or slots through which vapor bubbles rise and come into contact with the liquid on the plate surface.
    • Bubble cap columns utilize bubble caps mounted on the tray surface to create turbulence and enhance contact between the phases.
    • While these tray columns are effective in certain applications, they may not provide as much contact surface area as randomly packed columns for a given duty.
  4. Wetted Wall Column:
    • Wetted wall columns consist of a vertical tube with a thin film of liquid flowing down the inner wall, while vapor flows upward on the outside of the tube.
    • While wetted wall columns can achieve good contact between the liquid film and vapor phase, their surface area may be limited compared to randomly packed columns, especially for larger-scale operations.
In summary, among the options provided, the randomly packed column is generally preferred when maximum contact surface area is required for a particular duty in liquid-vapor contacting applications. It offers high efficiency and versatility in various mass transfer operations.