Entropy analysis of a solar-driven variable geometry ejector using computational fluid dynamics

•Entropy generation is proposed as a criterion to evaluate ejector geometry and performance.•Correlation between the entropy generation and entrainment ratio was investigated.•The contribution of each flow phenomena in entropy generation was showed.•Effect of primary nozzle position on the overall entropy generation was investigated in the variable geometry ejector. In the present paper, a study of flow pattern in a variable geometry ejector used in solar refrigeration system was conducted in an effort to achieve the optimum geometry and improve the understanding of the important flow behaviors that lead to ejector performance drop. Since the entropy generation is equivalent to performance losses, this parameter was investigated in numerical simulations. The results showed that the mixing phenomenon act as a main role in the entropy generation when the temperature of the condenser is higher than critical temperature, meanwhile the shock event operates the major parameter when the condenser temperature is lower than critical. In addition, a remarkable correlation between the entropy generation and the ejector performance was revealed, and so 37% performance improvement obtained.