Powered turbo-expander combining centrifugal compressor and an axial flow turbine

An environmental control system (ECS) of an aircraft, comprising:

• a heat exchanger;
• a compressor that receives a first airflow from a first air source, compresses the first airflow, and directs the first airflow to the heat exchanger;
• an axial flow turbine that receives a second airflow from a second air source, extracts energy from the second airflow, and directs the second airflow to the heat exchanger,
• wherein the heat exchanger directs the first airflow to a cabin of the aircraft and directs the second airflow overboard;
• and
• a shaft connected between the turbine and the compressor,
• wherein one of the first and second air sources is RAM air and the other of the first and second air sources is RAM air, recirculated cabin air, or engine bleed air or a mixture of RAM air and engine bleed air;
• wherein the system includes a turbine bypass branch, which includes a first valve, wherein the turbine bypass branch fluidly couples the second air source to the heat exchanger, bypassing the turbine,
• wherein the system includes a compressor bypass branch, which includes a second valve, wherein the compressor bypass branch fluidly couples the first air source to the cabin, bypassing the compressor and the heat exchanger,
• wherein the compressor is a centrifugal compressor and the turbine is an axial flow turbine.