Air Cycle Machine cooling and principals

Air Cycle Machines, high-pressure bleed air from the engines is first passed through a compressor, further squeezing the already hot gas. It is then routed through a heat exchanger or two to remove heat. The now cooler but still highly compressed air then passes through an expansion chamber into a larger chamber. The combined effects of driving the turbine and expanding into a larger chamber dramatically cools the air (usually down close freezing; water traps are critical in the system to prevent freeze-up).

The expansion turbine is connected by shaft to the ACM’s compressor, so expanding air works to compress the upstream bleed air similar to the way a turbine engine or a piston engine turbocharger works. This cycle may be repeated several times, with the end result that system air temperature is cooled far below ambient temperature.

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