Coupled effects of inclination and vertical vibration on immersion cooling performance of lithium-ion batteries

Immersion cooling is an effective thermal management strategy for lithium-ion batteries under high-rate discharge. In electric vehicles, mechanical vibration and battery pack inclination are unavoidable and can alter coolant flow distribution and convective heat transfer around battery surfaces, yet their coupled influence on cooling performance remains unclear. This numerical study investigates the synergistic effects of vertical vibration at frequencies from 6 to 14 Hz and amplitudes from 1 to 5 mm, combined with inclination angles from 0° to 180°, on the immersion cooling of a cylindrical battery module. Vibration substantially enhances heat dissipation, but the degree of enhancement is strongly inclination-dependent. The horizontal configuration at 0° yields the largest temperature reduction: the maximum battery temperature decreases by 21.0% and the thermal equilibration time shortens by 52.6% from 390 s to 185 s relative to static conditions. However, vibration does not universally improve temperature uniformity. At moderate inclinations between 30° and 60°, it paradoxically aggravates intra-pack temperature differences. A mechanistic framework is established based on the vibration Richardson number, oscillatory wall shear stress, and the coefficient of variation of the Nusselt number. When the vibration Richardson number falls below 0.2, corresponding to an amplitude of 5 mm or higher, the influence of inclination angle becomes negligible. Vibration amplitude is identified as the dominant control parameter governing heat transfer enhancement and thermal fluctuation intensity. These findings provide a quantitative basis for understanding the coupled inclination-vibration effects on immersion cooling and offer design guidance for battery thermal management systems under dynamic vehicle conditions.