Refrigeration Performance and Energy Efficiency Assessment of a Battery direct-cooling system

Efficient battery thermal management is essential for preventing thermal runaway and enhancing electric vehicle performance. Although refrigerant direct cooling technology offers superior heat transfer capabilities, its transient cooling characteristics and system energy efficiency under multi-gear regulation have not been fully characterized. This study combines experiments on a constructed hot water bath platform with numerical simulations to comprehensively investigate a refrigerant direct cooling system. A multi-point validated three-dimensional computational fluid dynamics (CFD) model incorporating the Mixture multiphase phase-change mechanism was established for both direct cooling and liquid cooling systems to evaluate thermal response and flow behavior. Comparison between direct cooling experiments and simulations shows close agreement in temperature curves, with nearly identical final temperatures, confirming the reliability of the simulation model. The results demonstrate that the direct cooling system achieves final temperatures 6.07–8.18 °C lower than those of the liquid cooling system, with the advantage becoming more pronounced at higher gear levels. Crucially, parametric energy efficiency analysis reveals that the system coefficient of performance (COP) varies between 3.24 and 4.35 across different compressor gears, highlighting a distinct trade-off between peak cooling rate and cumulative power consumption. These findings provide a useful quantitative basis and a theoretical reference for improving real-time control strategies in electric vehicle thermal management.