What distinguishes a vapor-cycle cooling system from an air-cycle system?

The distinguishing aspect of a vapor-cycle cooling system is that it relies on a refrigerant liquid to absorb and release heat in a process involving evaporation and condensation. In this system, the refrigerant circulates through various components, such as an evaporator, compressor, condenser, and expansion valve. When the refrigerant evaporates in the evaporator, it absorbs heat from the surrounding environment, providing cooling. Upon reaching the condenser, the refrigerant releases the absorbed heat as it changes back to liquid form, completing the cycle.

This characteristic of using a refrigerant liquid for the phase-change process is what sets vapor-cycle systems apart from air-cycle systems, which typically use air as the working fluid and do not rely on a phase-change refrigerant for their cooling effect. Understanding this fundamental difference can help in identifying and utilizing each system effectively in aviation applications.