Investigation of immersion type thermal management system for lithium ion batteries

Lithium ion batteries are widely used energy storage systems in electric vehicles due to their advantages such as high energy density and long life. However, their high heat generation potential can lead to problems such as capacity loss and thermal runaway, requiring an effective thermal management system. In this study, a three-dimensional numerical model of a 28-cell pouch type lithium ion battery module consisting of 14 series and 2 parallel connections and an immersion type battery thermal management system based on direct liquid contact has been created in ANSYS-Fluent program. Within the scope of the model, it is aimed to limit the maximum temperature of the battery module and to keep the temperature distribution between the cells homogeneous. Accordingly, parametric analyses were carried out by considering the distance between cells, different mass flow rates and the locations of fluid inlet and outlet ports. In the analyses performed by placing thermal interface material between the battery cells, it was revealed that despite the increase in flow rate, the maximum temperature limit of 313.15 K was exceeded and homogeneity was not achieved. In order to avoid this problem, the thermal interface material was removed and a new structure was developed in which the surfaces of the battery cells are in direct contact with the dielectric fluid. As a result of the analysis performed in this second model, although the temperature value was reduced below 313.15 K, the maximum and minimum temperature difference remained around 13 K on average. For this reason, five different input-output port designs were developed both to ensure temperature uniformity and to reduce the maximum and minimum temperature difference. Among the designs developed, Design 3 with U-type flow was found to provide the most effective temperature homogeneity. In this design, the temperature difference was reduced to about 9 K and the difference was reduced to less than 5 K by increasing the flow rate to 0.21 kg/s. The findings show that immersion type liquid cooled systems are an effective method for both temperature control and thermal homogeneity in high power battery modules. In this context, the study provides data on the basic geometrical and flow parameters that should be considered in the design of battery thermal management systems.