Evaluation and optimization of supercritical cycles using CO2 based mixtures as working fluids: A thermodynamic study

This study focuses on the thermodynamic performance analysis and optimization of CO2-based binary fluid mixtures in supercritical thermodynamic power cycles exploiting high-temperature waste heat. Response surface method is used to establish relationships between cycle performances and significant cycle parameters. Multi-objective optimization is carried out to obtain optimal solutions with higher cycle specific work and higher cycle efficiency. The analysis reveals that increasing additive molar fraction of the considered mixtures improves cycle thermodynamic performance. Among considered mixtures, the CO2-R152a mixture exhibits a higher cycle specific work and a larger cycle efficiency. For instance, in the recompression cycle configuration, the CO2-R152a mixture achieves cycle specific work of 83.9 kJ/kg and corresponding cycle efficiency of 37.2% at the optimal conditions. Comparative analysis demonstrates improved cycle-specific work for CO2-based mixtures compared to supercritical pure CO2 power cycles. In the recompression cycle configuration, the CO2-R152a mixture shows an average increase of 12 kJ/kg in cycle specific work compared to the supercritical CO2 power cycle. The simple recuperated cycle configuration exhibits an average increase of 13 kJ/kg. The utilization of these mixtures results in a substantial gain in cycle specific work, thereby contributing to enhanced energy efficiency and sustainability in high-temperature waste heat recovery applications.