A thermally integrated Carnot battery incorporating a novel dual-pressure evaporation cycle for deep utilization of waste heat: Parameter analysis and working-fluid optimization

The majority of contemporary thermally integrated Carnot batteries have inadequate waste heat use during the discharging process. Leveraging the integrated heat exchange capability of the multi-stream heat exchanger, this study proposes a thermally integrated Carnot battery incorporating a new dual-pressure evaporation cycle (DPE-CB). In order to achieve deep coupling and effective recovery of waste heat energy, this system uses a dual-pressure cascade heat addition mode during the discharging process, where the low-pressure stage absorbs heat first, followed by preheating in the high-pressure stage. Parameter analysis and working-fluid optimization are conducted after the simulation of the proposed system. The results revealed that the levelized cost of storage is reduced by 5.84%, and the round-trip efficiency, exergy efficiency, and energy storage density are improved by 15.85%, 3.58%, and 16.19% for this system, respectively, when compared to the traditional system based on a single-pressure evaporation cycle. According to working fluid optimization using the working fluid selection coefficient method, the DPE-CB system's performance is greatly enhanced when applying a blended working fluid. Useful design guidance for the effective systemic structure design and choice of working fluid for Carnot battery systems is provided by this study.