Abstract
Two-phase ejectors play a major role as refrigerant expansion devices in vapor compression systems and can find potential applications in many other industrial processes. As a result, they have become a focus of attention for the last few decades from the scientific community, not only for the expansion work recovery in a wide range of refrigeration and heat pump cycles but also in industrial processes as entrainment and mixing enhancement agents. This review provides relevant findings and trends, characterizing the design, operation and performance of the two-phase ejector as a component. Effects of geometry, operating conditions and the main developments in terms of theoretical and experimental approaches, rating methods and applications are discussed in detail. Ejector expansion refrigeration cycles (EERC) as well as the related theoretical and experimental research are reported. New and other relevant cycle combinations proposed in the recent literature are organized under theoretical and experimental headings by refrigerant types and/or by chronology whenever appropriate and systematically commented. This review brings out the fact that theoretical ejector and cycle studies outnumber experimental investigations and data generation. More emerging numerical studies of two-phase ejectors are a positive step, which has to be further supported by more validation work.
Highlights
Ejectors have been extensively studied for decades mainly for use in ejector cooling and refrigeration systems, as a potential alternative to conventional compression systems or more generally to assist conventional systems and improve their overall performance
Zhu and Jiang [87], in a study of transcritical CO2 ejector expansion refrigeration cycle proposed an analytical model taking into account non-equilibrium effects by means of a correlation based on experimental data of several case studies and capable of predicting primary and secondary mass flow rates
In a conventional expansion refrigeration cycles (EERC) (Figure 8a), instead of an isenthalpic expansion, which results in substantial throttling losses, a two-phase ejector is used to expand the condensate in a quasi-isentropic manner, recovering part of the work that would otherwise be lost in the expansion valve
Summary
Ejectors have been extensively studied for decades mainly for use in ejector cooling and refrigeration systems, as a potential alternative to conventional compression systems or more generally to assist conventional systems and improve their overall performance. Two-phase ejectors where a primary liquid drives a secondary vapor are finding an increased use as expansion devices They reduce throttling losses and recover expansion work (replacement of expansion valves) in heat pumps, air-conditioning and refrigeration systems. The recent work of Elbel and Lawrence [10] provided more information on emerging CFD efforts, new control measures, alternate cycle configurations and progress towards the development of applications based on ejectors for expansion recovery in cooling-refrigeration setups. This work presents updates of representative and recent progress in two-phase ejector modeling, integration in air-conditioning, refrigeration and heat pump cycles as well as in diverse potential applications
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