Analysis of modified CO2 based combined power and ejector-expansion refrigeration cycle with dual evaporators activated by engine exhaust

In this research, a combined system consisting of a supercritical CO2 Brayton cycle and an ejector-expansion refrigeration cycle with dual evaporators is presented with the aim to harness the engine exhaust heat effectively. Cascade ejectors are adopted to further reduce the destruction caused by the isenthalpic expansion process, which also can be considered as pressure recovery process. Comparative analysis in terms of thermodynamic and economic is performed between the previously reported system and the modified system under the combined power, refrigeration, and freezing mode (mode 1) and combined refrigeration and freezing mode (mode 2). It is found that improvements of 0.57% and 10.22% in exergy efficiency under mode 1 and mode 2 were achieved by the modified system, respectively, and the sum unit cost of product is reduced by 7.72% compared to the basic system. In the optimized condition, cooling capacities of 18.79 kW and 33.80 kW can be provided for refrigerated zone and freezing zone, respectively. And the exergy efficiency and sum unit cost of product of the system are 16.95% and 108.64 $/GJ, respectively, with a dynamic payback period of 4.994 years.