Thermal and flow characteristics of an array of cylinders in a converging and confined channel: The case of battery cooling

Abstract

As lithium-ion batteries become essential in electric vehicles and energy storage, managing their heat generation is critical. Without effective thermal control, excessive temperatures can degrade performance, trigger thermal runaway, and cause structural failures. Optimizing battery thermal management systems (BTMS) is vital to ensuring safety, efficiency, and long-term reliability. This study presents a numerical investigation into the influence of longitudinal and transverse pitch, channel convergence angle, and confinement ratio on the thermal and fluid flow behavior of an air-cooled BTMS. A finite volume-based two-dimensional model was developed to simulate heat transfer and flow characteristics within a confined, converging channel containing 16 cylindrical batteries arranged in a staggered configuration. Increasing the longitudinal pitch (P_L) expands wake regions and elevates upstream fluid temperatures, reducing convective heat transfer. Conversely, optimizing the transverse pitch (P_T) enhances coolant circulation, improving heat dissipation and thermal uniformity in battery packs. A higher convergence angle (β) enhances shear-driven convective cooling beyond β = π/18, whereas an increased confinement ratio ($\psi$) thickens the thermal boundary layer, reducing heat dissipation. Furthermore, two empirical correlations for Nusselt number and friction factor were developed using computational fluid dynamics (CFD) simulations yielding high predictive accuracy (R² = 0.9886 for Nusselt number and R² = 0.8686 for friction factor). These correlations serve as robust predictive tools for optimizing air-cooled BTMS, striking a balance between heat transfer efficiency and flow resistance minimization. The findings offer valuable design insights applicable to LIB thermal management and other convective heat transfer systems, including tube bundle heat exchangers and finned surfaces.