The paper describes the investigations of the R718 refrigerating cycle with single stage centrifugal compressor and two-phase ejector as a second stage compression device. The limitations of the R718 centrifugal compressor stage pressure ratio are discussed, and possibilities for introduction of two-phase ejectors in the R718 refrigerating systems with direct evaporation and condensation are analyzed. The complex thermal and flow phenomena connected with additional compression, desuperheating and condensation inside the two-phase ejector flow field are investigated and performance characteristics are estimated. The implementation of the two-phase ejector in the R718 centrifugal compressor refrigerating systems causes simplification of the R718 unit, and reduction of their size and cost. The energy efficiency of these refrigerating systems may also be increased.
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