Numerical and experimental investigation of different methods for effective cooling of lithium-ion vehicle batteries and ensuring homogeneous temperature distribution

Today, electric vehicles are rapidly becoming widespread in line with environmental sustainability goals, and batteries are critical to system performance. Lithium-ion batteries, preferred for their long cycle life and high energy density, can experience performance loss and safety issues due to thermal loads generated during charge-discharge cycles. Therefore, battery thermal management systems must be designed to ensure battery packs operate within an optimal temperature range and with minimal temperature differences between cells. In this study, battery packs consisting of 28 cylindrical 18650 cells were designed in four different configurations: triangular, concave, convex, and angular. Three different thermal management systems—air-cooled, heat pipe-cooled, and liquid-cooled—were experimentally and numerically investigated. In the air cooling studies, natural convection was insufficient at currents above 10 A, so forced convection was applied. In the study, where the inlet fan speeds varied between (4–12) m/s and the outlet fan speeds between (0–7) m/s, the maximum temperature was approximately 31.5 °C with a single outlet structure at 10 A discharge, while it dropped to 29.8 °C with a dual outlet structure. At a current of 15 A, the temperature was reduced from 52.8 °C to 35 °C, and the effect of the air direction strategy was clearly observed. Furthermore, the package temperature, which reached 65 °C with natural convection, was reduced to 31.15 °C using a 9.6 m/s inlet and fan-assisted outlet, achieving an improvement of approximately 52%. The use of multiple outlet fans in symmetric inlet-outlet configurations provided the highest thermal homogeneity and cooling performance in air cooling systems. In heat pipe cooling studies, different numbers (1-2-3) of copper heat pipes placed between the cells and air flow were evaluated together. In tests conducted at air speeds of 5–20 m/s, the concave arrangement showed the best performance for all numbers of pipes, and the temperature difference fell below 1 °C for the three-pipe structure at an air speed of 20 m/s. The temperature difference of (9–10) °C at 5 m/s in the angular arrangement was reduced to approximately 3 °C in the three-pipe structure at a flow velocity of 20 m/s. Increasing the number of pipes provided a significant improvement in all arrangements. In liquid cooling systems, water and antifreeze were used as coolants with different numbers of pipes, and flow rates ranging from (0.25–0.93) L/min were tested. Temperatures decreased as the flow rate increased, and antifreeze provided more homogeneous temperature distribution, yielding more successful results compared to water. It was determined that liquid cooling provides a lower temperature difference and more stable thermal behavior compared to air and heat pipe systems under high heat loads. The results obtained demonstrate that the arrangement geometry and flow rate control play a critical role in the thermal performance of battery modules under different cooling strategies, such as air, heat pipe, and liquid cooling. Multiple outlet and symmetrical flow patterns have emerged as the most effective designs for both reducing maximum temperature and increasing temperature homogeneity. Air cooling has yielded successful results, particularly with optimized fan placement, while heat pipe and liquid cooling systems have demonstrated superiority under high heat loads by offering lower temperature differences and more stable operation.