Geometry-driven and nano-enhanced fin-assisted multilayer PCM systems for passive thermal management of EV batteries

Thermal control of lithium-ion batteries remains a key challenge for electric vehicles, especially during fast charging and sustained heat generation. This study presents a numerical investigation of fin-assisted phase change material (PCM) based passive cooling systems using Rubitherm RT-42, RT-50, and their 5% Al₂O₃ nano-enhanced versions. Two triplex tube designs are analyzed: Model 1 with a single PCM layer and combined cylindrical and radial fins, and Model 2 with a double-layer PCM arrangement and dual cylindrical fins. The melting process is simulated using the enthalpy–porosity method under a constant heat flux of 1000 W/m 2 , considering transient conduction and natural convection. Results show that the integrated geometric configuration has the strongest influence on melting behavior and thermal performance. Model 2 reduces complete melting time by 14 to 19.5% compared to Model-1 and lowers the melting completion temperature by about 4 K. It also improves temperature uniformity and reduces thermal stratification inside the PCM domain. PCM type mainly influences activation timing and buffering duration. RT-42 melts earlier and maintains temperatures 4 to 6 K lower during phase change, but shortens buffering time by up to 10.2 min relative to RT-50. RT-50 provides 9 to 14% longer latent heat protection under continuous heating conditions. Nano-enhancement has limited impact on melting time but reduces peak temperature at 60 min by up to 7.3 K in Model 1 and 5.8 K in Model 2 by enhancing internal heat diffusion. Overall, geometry, melting temperature, and nano loading must be selected together to balance rapid temperature control and extended passive cooling performance.