Aerospace applications impose unique requirements on vapor cycle compressor designs and capabilities, far removed from commercial applications. They must operate in hot, ground static conditions which usually require high capacity and high pressure differential, throughout cruise segments which typically imply low loads and low ambient temperature operation, and in dynamic maneuvers that subject the machine to high structural loads and possible liquid ingestion, among other effects.
Vapor cycle systems find application in aerospace whenever high efficiency cooling is needed. Examples include externally or internally mounted pods containing electronic equipment, supplemental systems to augment the aircraft's ECS, and cooling on unpressurized platforms such as helicopters and UAV. They also fit “more-electric” and “all-electric architectures quite well. This range of applications creates a need for multiple cooling system configurations and architectures.
To support these diverse types of systems, modifications have been developed to expand the range and applicability of a twin-screw positive displacement compressor to satisfy the range of applications with a single machine. Screw compressors are well-suited for aerospace because of their compactness, insensitivity to attitude and adverse-g environments, ability to handle liquid slugging, and high efficiency over a wide speed range. This paper describes the modifications made to the basic machine design to expand its' operating range, increase its' efficiency, allow for cooling of multiple loads at different temperatures, and accommodate newly emerging refrigerants with lower environmental impact.