Experimental characteristics of R744 ejectors for expansion work recovery in heat pumping installations

R744 ejector geometries were investigated experimentally at the multifunctional test facility designed specifically for ejector mapping. Based on the recorded primary and secondary mass flow rates, individual operation curves were determined for a typical range of operating conditions in refrigeration units for supermarkets. It was concluded that the two independent variables influencing the motive nozzle mass flow rate are inlet pressure and inlet temperature, i.e., the nozzle mass capacity was independent of the backpressure. Significant influence of pressure lift on the ejector efficiency was registered for each specified combination of inlet conditions. The maximum recorded efficiency values, equal to 0.368 for vapour compression, outperformed significantly the results reported so far in the literature. The approximation functions for both the primary mass flow rate and entrainment ratio were provided.