Evaluation of Design Approaches for the Primary Nozzle Throat in Two-Phase Ejectors

Two-phase ejectors are a promising alternative for improving the performance of direct expansion vapor compression refrigeration systems, especially in transcritical applica-tions. Extensive literature has been produced on modeling, simulations and experiments related to two-phase ejectors. In particular, 0D models have proven to offer a trade-off be-tween simplicity and precision. In these models, there remains significant uncertainty re-garding the estimation of the two-phase speed of sound and the choking conditions at the primary nozzle throat. These choking conditions have a considerable impact on the throat geometry. This study proposes a novel approach that relies solely on conservation equa-tions (mass and energy) to determine the thermodynamic conditions at the throat for de-sign purposes. The results of the proposed approach and 13 other approaches reported in the literature were compared with published experiments data regarding the throat diam-eter and pressure. The proposed approach showed robust when validated against three experimental cases, predicting the throat diameter and pressure of a primary convergent–divergent nozzle with deviations of -8 % and +15 %, while the other approaches exhibited larger deviations of -12 % to +574% and -73 % to +21 %, respectively. Moreover, the pro-posed approach reliably generates a convergent-divergent nozzle configuration across a wide range of operating conditions, including variations in primary and secondary pres-sures as well as variations in primary nozzle efficiency using R1234yf and CO2 as work-ing fluids.