Comparative Numerical Investigation of Single- and Multi-Pass PCM-to-Air and Liquid Heat Exchangers

This study presents a comparative numerical investigation of a novel cross-flow heat exchanger with slab fins for dual-fluid operation integrated with Phase Change Material (PCM) in single-pass (SP) and multi-pass (MP) configurations, aimed at improving thermal comfort in electric vehicle cabins during engine idle periods, such as traffic light stops, by introducing a novel SP geometry. While most previous work has focused on MP heat exchangers, the research gap lies in developing a simple, easily manufacturable single-pass heat exchanger without curved bends that can promote more uniform heating, melt a larger fraction of PCM, and enhance passive heating performance. To address this gap, this study introduces and evaluates an SP PCM-to-air and liquid heat exchanger using three-dimensional transient computational fluid dynamics simulation. The analysis compares PCM melting behavior during charging and its effect on thermal output during discharging. Results show that for PCMs with high melting point, the SP design achieves a more uniform distribution of heat transfer fluid with higher temperature and improved melting efficiency, whereas the MP configuration performs better for low melting point PCMs. These differences significantly influence discharge performance: the SP design maintains air outlet temperatures above 25 °C for around 60 s longer and increases total heat absorption by the air by up to 30 kJ. Using N-Octadecane, the SP system delivered the highest cumulative heat release of about 290 kJ. The findings highlight the importance of PCM selection and the effect of geometry on maximizing latent heat utilization and enhancing vehicle heating energy efficiency.