Working fluid design and performance optimization for the heat pump-organic Rankine cycle Carnot battery system based on the group contribution method

Abstract

Among various energy storage technologies, the heat pump-organic Rankine cycle (HP-ORC) Carnot battery technology exists comparably long-life cycles, geographical independence, high energy density and efficient storage energy at low temperatures, which shows the potential of application in large-scale energy storage. As the core of the heat pump and organic Rankine cycles, the employed working fluid significantly influences component design, system performance, its stability and safety. Thus, this paper proposes a novel method for evaluating the HP-ORC Carnot battery performance using different working fluids based on the group contribution method. It is beneficial for improving the designed efficiency of working fluids and the performance optimization of this presented system at the molecular scale. In this study, the basic thermophysical properties of 70 working fluids were first estimated based on the group contribution method and then the power-to-power-efficiency of the proposed system was calculated under the given boundary conditions. Finally, the working fluids with power-to-power-efficiency in the top 20% were evaluated by the entropy weighting method, taking into account thermodynamic, environmental and safety properties, and the optimal working fluids of the proposed system were obtained. The results show that the proposed system was accurately predicted according to the group contribution method, where the average absolute deviation of generation efficiency is 0.61%. Besides, the proposed system with R272fa had the highest power-to-power-efficiency of 57.5%. Finally, R272ea, R272fa, R1261zf and R1243zc were recommended as optimal candidates. Their corresponding total evaluation scores are 0.528, 0.592, 0.667 and 0.526, respectively.