Computational Fluid Dynamics (CFD) modeling has become a critical tool for analyzing thermal runaway propagation in battery packs, enabling engineers to simulate complex heat transfer mechanisms, gas venting dynamics, and flame spread behavior. By coupling electrochemical-thermal models with CFD, researchers can achieve high-fidelity predictions of failure scenarios and optimize pack designs to mitigate risks. This article explores the key aspects of CFD modeling for thermal runaway, focusing on heat transfer, gas venting, flame spread, and design improvements.

Thermal runaway in lithium-ion battery packs is driven by exothermic reactions within cells, leading to rapid temperature increases, gas generation, and potential ignition. CFD simulations capture these phenomena by solving conservation equations for mass, momentum, and energy while incorporating chemical reaction kinetics. The primary heat transfer mechanisms include conduction through cell components, convection from ejected gases, and radiation from flames. Accurate modeling requires resolving temperature gradients within cells and between adjacent cells, as well as the thermal properties of materials such as electrodes, separators, and casing.

Gas venting is a critical aspect of thermal runaway, as internal pressure buildup leads to cell rupture and the release of flammable electrolytes and decomposition products. CFD models simulate venting by tracking gas flow paths, pressure waves, and species transport. The composition of vented gases, including hydrogen, carbon monoxide, and hydrocarbons, influences combustion behavior. Simulations must account for turbulent flow, buoyancy effects, and interactions with pack enclosures to predict gas accumulation and potential ignition points. High-fidelity models incorporate real gas equations of state and reaction mechanisms to capture combustion dynamics.

Flame spread simulations extend the analysis to post-venting scenarios, where ejected gases ignite and propagate flames within the pack. CFD models use combustion chemistry to predict flame speed, temperature distribution, and heat feedback to neighboring cells. The presence of barriers, vents, or cooling channels alters flame paths, and simulations help evaluate their effectiveness. Radiative heat transfer from flames can accelerate thermal runaway in adjacent cells, making it essential to model surface emissivity and view factors accurately.

Coupling electrochemical-thermal models with CFD enhances prediction accuracy by integrating cell-level reaction kinetics with pack-level fluid dynamics. Reduced-order electrochemical models simulate heat generation from short circuits, SEI decomposition, and electrode reactions, providing boundary conditions for CFD. This approach captures feedback loops where heat from one cell triggers reactions in others, enabling analysis of propagation delays. Case studies demonstrate that coupled models can predict temperature rise within 5% of experimental data when validated parameters are used.

Pack design improvements focus on delaying thermal runaway propagation by interrupting heat and gas flow paths. CFD simulations have identified several effective strategies. One approach involves incorporating thermal barriers between cells, such as ceramic or phase-change materials, which reduce heat transfer rates. Simulations show that barriers with low thermal conductivity can delay propagation by up to 60 seconds, providing critical time for safety systems to activate. Another strategy uses optimized venting channels to direct gases away from adjacent cells, reducing the risk of ignition. CFD analysis reveals that staggered vent layouts minimize gas recirculation and flame impingement.

Case studies highlight the impact of pack geometry on propagation dynamics. In a prismatic cell configuration, simulations showed that increasing the gap between cells from 2 mm to 5 mm reduced peak temperatures in neighboring cells by 15%. For cylindrical cells, adding heat-resistant spacers between rows delayed propagation by disrupting convective heat transfer. CFD models also evaluate the role of cooling systems, demonstrating that liquid-cooled plates can extract heat faster than air cooling, but their effectiveness depends on flow rate and contact resistance.

Material selection plays a key role in mitigating thermal runaway. CFD studies compare aluminum and steel enclosures, showing that steel’s higher melting point delays structural failure but may retain more heat. Insulating coatings on busbars and connectors reduce heat conduction to adjacent modules. Simulations of polymer-based enclosures reveal trade-offs between weight savings and flame resistance, guiding material choices for specific applications.

Validation of CFD models relies on comparisons with standardized tests, such as nail penetration or oven heating, but focuses on replicating temperature and pressure trends rather than full-scale fire scenarios. Sensitivity analyses identify critical parameters, including heat release rates, gas composition, and thermal contact resistance, which must be tuned for accurate predictions. Uncertainty quantification methods assess the impact of input variability on propagation timelines.

Future advancements in CFD modeling include high-performance computing to resolve larger packs with finer meshes, machine learning to accelerate solver convergence, and integration with battery management systems for real-time risk assessment. Multiphysics approaches combining structural deformation with thermal-fluid simulations will further improve accuracy. These developments will enable safer battery designs and more reliable predictions of thermal runaway behavior.

In summary, CFD modeling provides a powerful framework for analyzing thermal runaway propagation in battery packs. By simulating heat transfer, gas venting, and flame spread, engineers can identify design improvements that delay propagation and enhance safety. Coupled electrochemical-thermal models offer high-fidelity insights, while case studies demonstrate the effectiveness of thermal barriers, optimized venting, and cooling strategies. As computational methods advance, CFD will play an increasingly vital role in battery pack development and risk mitigation.