Zeotropic mixture ejector: Modeling approach, validation, and assessment based on composition ratio

Abstract

The ejector refrigeration system (ERS) using zeotropic mixtures obtains better performance and lower refrigeration temperature than that of the ERS using pure refrigerants, and the characteristics of the zeotropic mixture ejector are a theoretical basis for its optimal design. However, there are few literatures on the performance mechanism of the zeotropic mixture ejector. From the perspective of the binary zeotropic mixture, the R32/R245fa ejector model is developed in this paper based on computational fluid dynamics (CFD) theory, and an experimental setup is also built to validate the CFD model of the ejector. Firstly, the mixing process characteristics of two streams with different composition ratios entering the ejector are investigated, and the key parameters affecting the mixing process are evaluated. Secondly, the impact of zeotropic mixture composition ratio on the ejector's performance is analyzed in terms of entrainment ratio, velocity distribution, and pressure distribution. Finally, aiming at the entrainment ratio, a performance comparison between the R32/R245fa ejector and the pure refrigerant R245fa ejector is conducted under various primary stream conditions, yielding the optimal composition ratio range for the mixture when the R32/R245fa ejector outperforms the R245fa ejector. The findings demonstrate that the R32 mass fraction in both the primary and secondary streams significantly influences the performance of the R32/R245fa ejector. The composition distribution inside the ejector is primarily influenced by the shock chain. The optimal entrainment ratio is achieved by selecting an appropriate R32 mass fraction in the primary stream, and increasing the R32 mass fraction in the secondary stream leads to a linear enhancement in the entrainment ratio. Moreover, when the R32 mass fraction in the primary stream falls within the range of 0–0.08, the entrainment ratio of the R32/R245fa ejector surpasses that of the R245fa ejector operating in the critical mode. Furthermore, this advantage becomes more pronounced as the R245fa ejector gradually deviates from the critical mode.