Performance comparison of ejectors in ejector-based refrigeration cycles with R1234yf, R1234ze(E) and R134a.

To look for new refrigerants replacing R134a, environmentally friendly refrigerants R1234yf and R1234ze(E) were chosen as the alternatives in an ejector refrigeration system. The tested system contained a single-phase ejector, and numerical analysis regarding the performance of the ejector was done by CFD. The entrainment ratio, static pressure and Mach number were chosen as indicators revealing the ejector performance. Changes of the indicators of ejector utilizing a given refrigerant under varying operating temperature conditions were analysed. With the increasing condenser temperature, the shocking position moved upstream until it combined with the first series of oblique shocks. With the increasing generator temperature, the entrainment ratio increased firstly and decreased subsequently. With the increasing evaporator temperature, the primary-fluid jet expansion weakened. Comparisons of the indicators of ejector utilizing three working fluids (R134a, R1234yf and R1234ze(E)) under a given operating temperature condition were also made. The results showed that R1234yf had a greater entrainment ratio than R134a and R1234ze(E). But the shocking position of R1234yf was also closer to the upstream than the other two refrigerants, which caused the smaller critical mode region. Compared with the entrainment ratio close to 1.4 times, the critical temperature difference of only 3 °C could not weaken the advantages of R1234yf. Besides, heat transfer inside the ejector was considered and not much different trends with the three working fluids were found. Therefore, R1234yf could be the better candidate for R134a in the ejector refrigeration system.