Energetic and exergetic performance comparison of an ejector refrigeration system using modern low GWP refrigerants

In this study, a novel model is used to precisely predict the performance of an ejector refrigeration system utilizing modern environmentally benign working fluids in both the critical and subcritical modes of operation. Energetic and exergetic performance of low global warming potential and non-ozone depleting HCFO and HFO refrigerants: R1233zd(E), R1224yd(Z), R1225ye(Z), hydrocarbon refrigerants: Isobutane and Isopentane and RE245cb2 is compared with that of conventional refrigerants: R141b and R245fa. The model takes the ejector area ratios, generator pressure, and evaporator pressure into account in the determination of the ejector loss coefficients. A program written in Engineering Equation Solver (EES) was used to obtain solutions of the developed mathematical model. In the analysis, ejector area ratios between 6.44 and 12.76, evaporator temperatures between 4 and 16°C, condenser temperatures between 25 and 50°C as well as generator temperatures between 70 and 110°C were used. Results show that Isobutane and R1225ye(Z) have the greatest performance, giving an over 150% increase in the coefficient of performance (COP) compared to R245fa. The increase in the COP with isopentane, RE245cb2, R1224yd(Z) and R1233zd(E) were as high as 22%, 32%, 16% and 14%, respectively at the lowest area ratio. Results further show that the ejector contributes the highest exergy losses (up to 55%, depending on the evaporator, condensing and generator temperatures) compared to the other components. The contribution of the condenser to the total exergy loss is up to 28%, for the generator it is up to 34% and up to 12% for the evaporator. The pump and the throttle valve give values lower than 0.5 and 9%, respectively for all the refrigerants.