Where does the final stage of cooling occur in an air-cycle air-conditioning system?

In an air-cycle air-conditioning system, the final stage of cooling occurs in the expansion turbine. During the cooling process, air is compressed in the compressor, causing its temperature to rise significantly. This hot, high-pressure air then passes through the condenser, where it is cooled and partially liquefied. Following this, it enters the expansion turbine, where it undergoes a pressure drop.

As the air expands in the turbine, its temperature decreases significantly due to the Joule-Thomson effect. This drop in temperature is what constitutes the final stage of cooling in the air-cycle system, providing the cool air that is circulated into the cabin. The efficiency of this cooling process is critical, as it directly impacts the comfort level within the aircraft.

In this context, the evaporator is responsible for absorbing heat from the cabin air but is not the site of final cooling. The compressor's role is to compress and raise the temperature of the air, and the condenser's task is to condense and remove heat but happens before the final cooling step of expansion. Thus, the expansion turbine is clearly where the ultimate cooling takes place.