ANS:A - half

Operating velocity in a packed tower is usually less than the flooding velocity. Here's why:

• Flooding Velocity: Flooding velocity is the maximum velocity at which the gas can rise through the packed bed without causing flooding. Flooding occurs when the liquid phase is unable to flow downward through the packed bed, leading to channeling and reduced efficiency of mass transfer.
• Operating Velocity: Operating velocity is the velocity at which the gas flows through the packed tower during normal operation. It is typically maintained below the flooding velocity to ensure proper wetting and distribution of the liquid phase over the packing material.
• Reason for Operating Velocity being Less than Flooding Velocity: If the operating velocity were equal to or greater than the flooding velocity, it could lead to flooding, causing liquid to accumulate and flow unevenly through the packed bed. This uneven distribution of liquid would result in decreased contact between the gas and liquid phases and reduced efficiency of mass transfer.