Two-phase ejectors have received increased attention in recent years because of their ability to improve the performance of automotive air-conditioning cycles by means of expansion work recovery. Much attention in recent years has been given to how high-pressure fluids, such as carbon dioxide, perform with ejector cycles; high-pressure fluids tend to have higher throttling loss, making them more attractive for expansion work recovery cycles, such as the two-phase ejector cycle. However, low-pressure fluids, such as those commonly used in automotive air-conditioning applications, tend to offer significantly lower work recovery potential. Nonetheless, the limited previous work on low-pressure refrigerants in ejector systems has shown that there is some improvement potential when using these fluids with ejector cycles.
This paper presents the results of experimental and analytical investigations in which the performance of the low-pressure fluids R134a and R1234yf is compared between a conventional cycle without an ejector and several two-phase ejector cycles. An analytical comparison of the theoretical COP's and other practical advantages of several different twophase ejector refrigeration cycles is presented. An ejector cycle was constructed in which the pressure lift provided by the ejector was utilized in order to provide multiple evaporation temperatures. Multiple evaporators provide the potential for reduced exergetic losses between refrigerant and a single air stream as well as the possibility of cooling multiple air streams, which can be beneficial in some applications. Experimental results comparing the performance of the two fluids on the cycles are presented.