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 (2 C, 3 C, 4 C) and convective heat transfer coefficients (15, 30, and 60 W/m2 K). Three system configurations were analyzed: 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 behavior. Results demonstrate that the PCM + HP + Fin + Duct configuration delivers the best thermal performance, reducing the maximum cell temperature by up to 15 K. It also minimizes temperature differences (ΔT < 1.5 K) even at a 4 C 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. Although a liquid fraction of up to 0.63 was observed, indicating greater PCM melting, this resulted from localized heat accumulation rather than efficient heat distribution. Consequently, peak cell temperatures increased and temperature uniformity degraded, highlighting that higher melting alone does not guarantee improved thermal performance. Moreover, increasing HTC was found to decrease both Tmax and PCM usage, indicating a trade-off between active cooling effectiveness and latent heat utilization. Overall, the study highlights the synergistic role of passive (PCM, HP, fins) and active (air duct) elements, where optimal design integration can maintain battery temperatures well within safe limits. The findings provide critical insights for the design of compact, efficient BTMS architectures for electric vehicle and high-power applications.