Recent developments in HVAC&R systems utilizing two-phase ejector for expansion work recovery

This paper gives an overview of the technical challenges encountered with two-phase ejector refrigeration systems. Of particular interest are attainable improvement potentials for different working fluids, including CO₂ and as well as lower pressure refrigerants such as R410A or R1234yf. Numerous ways of how to best integrate the ejector have been studied. Besides the standard two-phase ejector cycle it is also possible to utilize the recovered expansion energy to drive evaporator overfeed or to provide cooling at different temperature levels. Ejector design plays an important role in achieving high work recovery efficiencies, but the design of other system components, such as the evaporator or the vapor/liquid separator that many of the cycle architectures require are equally influential and offer large improvement potentials. Finally, the paper will give an overview of various ejector control options which are important, especially when capacity modulation requirements need to be met.