Adiabatic humidification with liquid recirculation — Which equipment is frequently used to perform adiabatic humidification–cooling with a recirculating liquid stream?

Introduction:
Adiabatic humidification–cooling is the process where a gas (often air) is contacted with a liquid (often water) so that the gas approaches an adiabatic saturation state while the liquid recirculates and warms slightly. The question asks which piece of equipment is frequently used for such operations with explicit liquid recirculation.

Given Data / Assumptions:

• Gas–liquid contact with recirculating water.
• Negligible external heat addition (adiabatic).
• Objective: cool and humidify the gas while slightly heating the liquid.

Concept / Approach:
A spray chamber provides direct-contact mass and heat transfer by spraying liquid into a flowing gas stream; the sprayed liquid is collected at the bottom and recirculated to maintain adequate wetting and approach the adiabatic saturation temperature. Cooling towers are also adiabatic contactors, but the “textbook” example highlighting adiabatic humidification with controlled recirculation and adiabatic saturation charts is the spray chamber apparatus.

Step-by-Step Solution:
Identify adiabatic gas–liquid contacting with free-surface sprays.Recognize that recirculation is a standard feature of spray chambers for steady approach to saturation conditions.Select “Spray chamber.”

Verification / Alternative check:
Psychrometric analyses of spray chambers show gas outlet states approaching the adiabatic saturation line; recirculation maintains steady liquid conditions.

Why Other Options Are Wrong:

• Cooling towers indeed perform similar duties but are generally categorized as tower contactors; the canonical adiabatic humidifier with controlled recirculation in design problems is the spray chamber.
• “None of these” and bubble columns do not match standard adiabatic humidifier descriptions for air–water service.

Common Pitfalls:
Equating all air–water contactors; while cooling towers are practical, the spray chamber is the classic teaching device for adiabatic humidification with recirculation.

Final Answer:
Spray chamber