Design and evaluation of a novel bi-evaporator combined power and refrigeration cycle working with various zeotropic mixtures

In the present research, a novel bi-evaporator combined cooling and power cycle based on the integration of a double-stage organic Rankine cycle and an ejector refrigeration cycle is devised to recycle heat from the exhaust gas of a marine diesel engine. Instead of using conventional pure organic fluids, various appropriate zeotropic mixtures are screened for the proposed system and the results are discussed in terms of the first and second laws of thermodynamics. The results indicated that by recycling 434kW energy from the exhaust gases and using R142/Pentane with 51/49 percent a maximum thermal efficiency of 43.28% and an overall cooling load of 166.36 kW can be achieved. In this case, the net produced electricity and exergy efficiency are obtained as 21.83 kW and 20.22% which can be increased by selecting other appropriate mixtures. Additionally, using R142/Pentane with 51/49 percent as the working mixture, it is figured out that the auxiliary vapor generator contributes to the highest exergy destruction by 62.3 kW out of overall exergy destruction of 122.15 kW. Also, the energy and exergy efficiencies of the system can be increased simultaneously by increasing the evaporator bubble point temperature.