Design and optimization of a passive cooling system for electric vehicle battery packs using phase change materials and heat pipes

Project Abstract

The escalating demand for electric vehicles (EVs) intensifies the need for reliable thermal management of high-energy-density battery packs to ensure performance, safety, and longevity. This research presents a comprehensive design and optimization of a passive cooling system that integrates phase change materials (PCMs) with heat pipes to regulate battery temperatures under diverse operating conditions. The study begins with a thermodynamic and heat transfer assessment of typical lithium-ion battery modules used in EVs, identifying critical temperature thresholds and transient heat generation profiles during rapid charging, high-load driving, and ambient temperature extremes. A multi-objective framework is developed to balance thermal stability, system mass, cost, and charging efficiency, with constraints derived from battery chemistries, enclosure geometries, and safety standards. The proposed passive cooling architecture employs encapsulated PCMs with high latent heat capacity to absorb peak heat fluxes during transient events, while strategically placed heat pipes provide rapid lateral and vertical heat spreading from hotspots to the PCM banks, mitigating localized thermal gradients. Numerical simulations across a parametric space explore PCM materials (e.g., eutectic mixtures with paraffin or salt hydrates), phase transition temperatures aligned to battery operating windows, porosity and finite-element modeling of the heat transfer in composite envelopes, and the capillary-driven return of condensed vapor to the evaporation zone. An optimization algorithm, integrating genetic algorithms with finite element analysis, identifies optimal PCM type, melting temperature, PCM mass fraction, heat pipe diameter and configuration, and fin geometry to minimize peak temperatures, temperature variance, and response time while keeping mass and cost within practical limits. Experimental validation is conducted on a modular test rig featuring a battery simulator, PCM-embedded enclosure, and a looped heat pipe network. Thermal performance is evaluated under controlled slow, moderate, and aggressive duty cycles, as well as environmental temperatures ranging from ?10 to 50 °C. Results demonstrate a significant reduction in maximum battery temperature (up to 25–35% compared to passive air cooling), smoother temperature trajectories with diminished peak-to-average differentials, and extended pack life projected via acceleration factor analyses. The integration approach shows robust performance against PCM phase segregation and thermal fatigue, with effective sealing and encapsulation strategies mitigating leakage risks. Sensitivity analyses reveal critical dependencies on PCM quality, heat pipe thermal conductance, and enclosure insulation, guiding design choices for manufacturability and reliability. The research also outlines a scalable deployment pathway for modular battery packs, addressing manufacturability, retrofit potential, and maintenance considerations in automotive supply chains. The study advances passive thermal management by synergizing latent heat storage with highly efficient heat spreading, offering a safer, lighter, and more energy-efficient alternative to active cooling systems. Practical guidelines for material selection, geometry optimization, and validation procedures are provided to facilitate adoption in EV cooling strategies and inform future standards in battery thermal management technology.

Project Overview

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