Investigation on formation, evolution, and performance impact of mixing layer in the zeotropic mixture ejector

Abstract

This study investigates the fluid mixing mechanisms in zeotropic mixture ejectors, which are critical for enhancing the performance of ejector-based refrigeration cycles. A fluid dynamic model of an R245fa/R32 ejector is developed from the perspective of mixing layer evolution and validated against experimental data. The initiation and development of the mixing layer are analyzed under both subcritical and critical operating conditions, focusing on key characteristics such as the growth of the mixing boundary layer, mixing layer thickness, and non-mixing length. Results reveal that the mixing layer originates at the initial interface between the primary and secondary streams and gradually thickens along the flow direction. Its evolution is significantly affected by the operating mode: subcritical conditions lead to pronounced fluctuations in mixing layer thickness, whereas critical conditions maintain greater stability. Furthermore, the R245fa mass fraction influences the development of the mixing layer, which shows two distinct growth stages. Lower R245fa mass fraction slows the growth rate, while a more stable mixing boundary layer and an extended initial growth phase contribute to enhanced entrainment performance. This work establishes a systematic relationship between mixing layer evolution and ejector efficiency, offering a theoretical foundation for the design and optimization of zeotropic mixture ejectors.