Abstract: The present invention provides a unitary sliding-vane type compressor-expander comprising a housing with a compressor inlet and outlet, and an expander inlet and outlet. A single rotor is disposed therein defining in cooperation with the housing a compression chamber on one side and an expansion chamber on the opposite side. The rotor includes a plurality of regularly spaced vanes slidingly disposed in slots about the periphery of the rotor. The bottoms of the vane slots may be vented through a passage in the housing to the inlet air, or alternatively through a groove between the vane and vane slot to the compression or exhaust chambers. Permanent magnets are used in the vanes and housing to increase or decrease the contact force between the vane tip and housing. An integral condenser-humidifier is provided in the path of the expanded gas exhausting from the turbine outlet for condensing water out of the expanded gas and returning the condensed water to the compressor-expander.