Numerical Characterization and Optimization of Hybrid Battery Thermal Management System Integrating with Nano-PCM and Passive and Active Cooling Synergies under Variable Discharge Rates

Abstract Efficient thermal management of lithium-ion battery packs is vital to ensuring performance reliability, safety, and extended cycle life, particularly under high discharge conditions. This study presents a comprehensive numerical investigation of a hybrid Battery Thermal Management System (BTMS) integrating Phase Change Material, Heat Pipe, Fins, and air Ducts, evaluated under various discharge rates (2C, 3C, 4C) and convective heat transfer coefficients (15, 30, and 60 W/m2·K). Three system configurations were analysed: PCM+HP+Duct, PCM+HP+Fin+Duct, and PCM+HP+Duct with horizontally oriented cells. Transient simulations were carried out using ANSYS Fluent, incorporating an enthalpy-porosity formulation to capture PCM melting dynamics and heat transfer behaviour. Results demonstrate that the PCM+HP+Fin+Duct configuration delivers the best thermal performance, reducing the maximum cell temperature by up to 15 K and minimizing temperature differences (ΔT < 1.5 K) even at 4C discharge rate. The addition of fins significantly enhances radial heat spreading and thermal uniformity, complementing the axial conduction provided by heat pipes and convective cooling from the air duct. The horizontally arranged battery setup showed greater PCM melting (liquid fraction up to 0.63), but at the expense of elevated core temperatures and poor uniformity. Moreover, increasing HTC was found to decrease both Tmax and PCM usage, indicating a trade-off between active cooling effectiveness and latent heat utilization.