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

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.