Experimental and numerical investigation of an inclined U-shaped micro heat pipe array–liquid cooling system for large-capacity energy-storage lithium-ion batteries

Effective thermal management is crucial for the safety and durability of large-capacity energy-storage lithium-ion batteries. However, micro heat pipe array (MHPA)–liquid cooling systems have mainly been studied for smaller power batteries, and their applicability to large-capacity energy-storage batteries remains insufficiently investigated. To address this gap, an inclined U-shaped MHPA–liquid cooling system was developed for 314 Ah energy-storage batteries with upward-facing electrode tabs. The inclined MHPA provides an additional heat-transfer path from the cell surface to the liquid-cooling region and promotes gravity-assisted condensate return, improving heat dissipation and temperature uniformity without changing the vertical cell arrangement. Experiments and numerical simulations were conducted to evaluate the proposed system and compare it with conventional bottom liquid cooling under different coolant temperatures, flow rates, and ambient temperatures. The numerical results were compared with the experimental data to verify the accuracy of the numerical model. At 25 °C ambient temperature, 15 °C coolant temperature, 1 L/min, and 0.5P constant-power operation, the proposed system limited the maximum module temperature to 27.52 °C, compared with 33.01 °C for bottom liquid cooling, while reducing the maximum temperature differences of the single cell and whole module by 57% and 36%, respectively. Increasing coolant temperature weakened cooling but improved temperature uniformity, whereas increasing flow rate reduced the maximum temperature with limited effect on module-level uniformity. The heat-transfer advantage of the proposed system became more pronounced as the ambient temperature increased. Equivalent-area numerical comparisons with U-shaped aluminum and copper structures showed that the superior performance of the MHPA mainly resulted from rapid heat spreading and phase-change heat transfer rather than increased heat-transfer area. The proposed system therefore provides an efficient and compact thermal management solution for large-capacity energy-storage battery packs.