Abstract
An experimental study of R134a refrigerant expansion in a two-phase ejector with no induced flux has been performed under a number of conditions commonly encountered in refrigerators and heat pumps. The intent is to develop a better understanding of the parameters and conditions influencing the critical flow, necessary for efficient and stable operation, generally desirable for improved performance of ejector enhanced mechanical compression cycles. Tests have been conducted for two nozzle lengths in the pressure range of 7.7-16.8 bars with subcooling up to 55 degrees C. Ejector critical flow is strongly influenced by the nozzle geometry and the operating conditions. The degree of inlet subcooling appears to play a more important role than the pressure in this process. Compared with an isenthalpic expansion valve, a two-phase ejector has been shown to be a pseudo-isentropic device which produces slightly less refrigerant flashing, thereby offering a potential for performance improvement in the conventional refrigeration cycle. Experimental critical flow rate have been compared with the theoretical predictions of models currently being developed in this project. Homogeneous Equilibrium Model (HEM), a slip model and a thermal non-equilibrium version based on Henry-Fauske approach have been successively used. Results have shown that depending on the degree of inlet subcooling and geometry, each model could correctly predict only part of the subcooling range. HEM predicted fairly well the range of subcooling above 30 degrees C, irrespective of the geometry used. Below 30 degrees C to saturation, the slip model predictions were very good for the short nozzle version while its thermal non-equilibrium alternative better predicted the experiments for the longer nozzle. (C) Her Majesty the Queen in Right of Canada, as represented by the Minister of Natural Resources, 2016. Crown Copyright 2016 Published by Elsevier Inc. All rights reserved.