Influence of pack orientation and fin design on hybrid PCM–liquid cooled Li-ion battery systems

Effective thermal management is critical for lithium-ion battery safety and longevity in electric vehicles, particularly under high-discharge conditions. This study investigates a novel hybrid battery thermal management system (BTMS) integrating phase change material (PCM) RT35, liquid cooling, and aluminum fins, assessing the enhancement effects of adding cell-to-cell and cell-to-channel fins alongside pack orientation (θ = 0°, 30°, 60°, 90°). Using computational fluid dynamics (CFD), this study models a cylindrical cell array (18650-type, 3 C/5 C discharge) embedded in PCM, flanked by water-cooling channels. The model varies inclination angles and coolant velocities (0–0.5 m/s) to evaluate buoyancy-driven convection effects on maximum temperature (Tmax) and liquid fraction. Results show that, in the no-fin case, θ = 30° reduces Tmax by ∼6.7 K at 5 C compared to horizontal/vertical setups, driven by enhanced PCM recirculation. Moderate coolant velocities (0.05–0.2 m/s) optimize latent heat utilization, while higher velocities increase parasitic pumping power (∼100 ×) without thermal gains. Cell-to-channel fins reduce Tmax by 9.4 K at θ= 30°, outperforming cell-to-cell fins (as with the maximum 0.4 K reduction at θ=90°), enhancing conduction and convection in a hybrid PCM-liquid BTMS. Unlike prior studies isolating PCM or fixing orientation, this work couples fin enhancements, inclination, and flow, providing design maps for energy-efficient BTMS, guiding next-generation EV battery designs.