Design considerations for a second-generation CO2-expander.

If one replaces the throttle valve in a transcritical CO2 refrigeration cycle by a work extracting expander, the COP of the cycle can theoretically be improved by about 60%. In the past few years, in the authors' laboratory, a first-generation expander for this purpose was tested and a COP improvement of about 30% was achieved. Apparently there is room for further improvement. In the first-generation machine, the expander could be operated only in the so-called full-pressure mode. The authors present design considerations for a second-generation expander-compressor, which should overcome this drawback.