Performance analysis of a two-phase direct cooling system for electric vehicle batteries using CO2 heat pump

Driven by regulations restricting high Global Warming Potential (GWP) refrigerants, CO2 direct cooling has attracted increasing attention in battery thermal management (BTM). However, conventional single plate designs suffer from limited heat transfer area and non-uniform temperature distribution, which degrade system performance and underscore the importance of optimizing cooling plate configurations. In this study, a novel model combining a second-order equivalent circuit with a thermal resistance network was developed and rigorously validated within the AMESim platform. To address these limitations, co-flow and counter-flow dual direct cooling plate configurations were proposed and systematically compared. The results indicated that at a mass flow rate of 0.03 kg/s, the dual cooling plate configuration achieved a maximum battery temperature of 28.6 °C with a temperature difference of 3.2 °C, corresponding to reductions of 25.4% and 36.3%, respectively, compared with the single plate design. Furthermore, the counter-flow configuration exhibited a wider operational range, maintaining efficient performance at a lower mass flow rate of 0.014 kg/s, whereas the co-flow configuration required 0.022 kg/s. The effects of ambient temperature and compressor speed on system performance were further analyzed. Based on these findings, recommended compressor speeds were provided to balance system efficiency and battery safety. Overall, this study provides a systematic framework for optimizing cooling plate configurations in BTM systems.