How does a flooded evaporator operate?

• A. The evaporator is filled with liquid refrigerant; heat is absorbed as the refrigerant boils, and vapor rises from the liquid.
• B. The evaporator has no liquid refrigerant.
• C. It relies on direct expansion of refrigerant within the coils.
• D. It uses air cooling to remove heat.

Answer: (A)

Flooded evaporators rely on keeping a pool or film of liquid refrigerant inside the evaporator. As heat is absorbed from the space being cooled, this liquid boils at the evaporation temperature, turning into vapor. The energy transfer is dominated by the latent heat of vaporization, so a large amount of heat can be removed with only a small temperature change. The vapor rises out of the liquid and moves to the compressor suction, while excess liquid is circulated back to maintain the flooded condition. This approach contrasts with direct expansion, which uses only refrigerant that evaporates inside the coils without a liquid pool, and with ideas like air cooling, which refers to the heat-transfer medium on the air side rather than how the evaporator itself is filled.