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Analysis of thermodynamic parameters' effects on the S-CO2 recompression Brayton cycle for recovering the main engine exhaust gas waste heat of an ocean-going 9000 TEU container ship are carried out first in this paper. NSGA-II algorithm-based multi-objective optimizations are conducted to maximise net power output and exergetic efficiency as well as to minimise the levelized cost of energy (LCOE). The final optimal result from Pareto front solutions is decided by decision-making processes. The results show that the LCOE increases along with the enhancement of net power output and exergetic efficiency, and the maximal objectives always appear near the upper boundary of exhaust gas temperature. The final optimal result decided by TOPSIS decision-making has higher rationality and accuracy than that obtained by the LINMAP method. Regarding the final optimal results of triple-objective and dual-objective optimizations obtained by the TOPSIS method, the former achieved more reasonable results, since its optimal net power output and exergetic efficiency are 1.29% and 5.11% higher than the latter, while its LCOE increased by 2. 28% as a result of the increase of the net power output. The recompression Brayton cycle is better for recovering the exhaust gas waste heat in ships compared with the simple recuperative cycle without recompression. [ABSTRACT FROM AUTHOR]

The S-CO2 power cycle has the advantages of compact structure and high energy density, which can be used to recover the waste heat of ship exhaust, thus improving the energy efficiency of ships and reducing emissions. The hybrid heat exchangers with etched plates and fins can be used as the heat transfer device of S-CO2 and exhaust, its heat transfer and pressure drop characteristics have a great influence on S- CO2 power cycle performance. In this study, a CFD model of the hybrid heat exchangers was established. The effects of different exhaust inlet temperatures, inlet mass flow rates and inlet pressures on the heat transfer and the pressure drop characteristics were analyzed by Fluent. The results show that the inlet temperatures and inlet mass flow rates of exhaust have a great influence on the heat transfer characteristics of the hybrid heat exchanger. The inlet mass flow rates and inlet pressures of exhaust have a great influence on the pressure drop characteristics of the hybrid heat exchangers. In the design of the hybrid heat exchangers, the status of the exhaust need to be considered to ensure efficient operation of the heat exchangers. The study can provide guidance for the design of the hybrid heat exchangers.