Thermodynamic analysis of two-stage and dual-temperature ejector refrigeration cycles driven by the waste heat of exhaust gas

This paper presents two-stage and dual-temperature ejector refrigeration cycles (TDERCs) driven by the waste heat of exhaust gas. One-dimensional modelling of the ejector is performed, and thermodynamic analysis for the TDERCs is carried out. Based on simulation results, R1234yf/R1234ze with a mass fraction of 56.2% R1234yf is selected as the working fluid, showing an improvement of 5.64% in COP over R134a under the basic operating condition. Comparing with the TDERC1, the TDERC2 shows improvements of 1.07% and 0.69% on the COP and exergy efficiency with a superheater outlet temperature of 300 °C, while the cooling capacity is reduced by 0.107 kW. Moreover, the multi-objective optimization results indicate that the TDERC2 has improvements of 1.20% in COP and 0.666 kW in cooling capacity compared to the TDERC1 under the optimum operating condition. Overall, the TDERC1 can provide a larger cooling capacity with sufficient waste heat of exhaust gas, while the TDERC2 is more suitable for limited waste heat or low exhaust gas temperature due to its higher COP. The simulation results reveal the advantages and disadvantages between the TDERC1 and TDERC2 under different operating conditions and provide guidance for refrigerated and frozen applications in light refrigerated trucks.