Comparative Assessment of Primary Nozzle Throat Design Methods for Two-phase Ejectors

Two-phase ejectors are a promising technology for improving the performance of direct expansion vapor compression refrigeration systems, particularly in transcritical applications. Extensive studies have been conducted on modeling, simulation, and experimental investigation of two-phase ejectors.  Among the available approaches, zero-dimensional (۰-D) models provide a valuable compromise between simplicity and predictive capability. They remain essential for preliminary ejector design, even when more advanced approaches such as one-dimensional (۱-D) models or computational fluid dynamics (CFD), are used. However, significant uncertainty remains in the estimation of the two-phase speed of sound and the choking conditions at the primary nozzle throat, which strongly influences the predicted throat geometry. This study presents a comparative assessment of primary nozzle throat design methods used in two-phase ejector models. Thirteen approaches reported in the literature and a newly proposed method based solely on mass and energy conservation equations were evaluated against published experimental data in terms of throat diameter and throat pressure. The results reveal significant discrepancies among the different approaches, with deviations ranging from -۱۲% to +۵۷۴% for the throat diameter and from -۷۳% to +۲۱% for the throat pressure. In contrast, the proposed approach showed comparable stability under the tested conditions, predicting the throat diameter with deviations ranging from -۸% to +۱۵%, and the throat pressure with a deviation of +۷%, respectively. Furthermore, the method consistently generates a convergent-divergent nozzle configuration over a wide range of operating conditions, including variations in primary and secondary pressures and primary nozzle efficiency using R۱۲۳۴yf and CO۲ as working fluids.

کلیدواژه ها:

Two-phase ejectors ، Convergent-divergent nozzle ، Choked flow ، Speed of sound