Effects of control volume outlet variation on axial air cooling of lithium-ion batteries

This paper addresses cylindrical lithium-ion cells' heating and non-uniform cooling by simulating a simple battery pack design with 24 cells and axial airflow. Cooling a battery pack using forced air convection in a rectangular container causes non-homogeneous temperature distribution. The middle cells and the second half of the battery pack (near the exit) get less cooling compared to the cells near the inlet. To solve this issue of non-uniform cooling, in this paper, we propose an optimized Battery Thermal Management System (BTMS) which allows higher amounts of turbulent kinetic energy to be generated near the cells closer to the exit and farther away from the inlet. We attempted to create a narrow region in the middle of the pack which leads to an increase in mixing and turbulence in the airflow. This directs the flow precisely, hence getting rid of dead air flow zones behind the cells. The convergence functions like a nozzle, propelling the air flow into the second half of the battery pack. Using COMSOL Multiphysics, the mixing and turbulence of the airflow, as well as the temperature increase and homogeneity inside the battery pack, are investigated. Three separate investigations are conducted in order to determine the optimal shape for the BTMS control volume as well as to determine the effect of system's inlet pressure and outlet velocity on the cooling performance. Results indicated that the system's temperature decreased significantly by lowering the outlet dimensions and introducing convergence to the BTMS's central area. Increasing outlet velocity increased cooling in a case with a single fan significantly, whereas increasing pressure in a case with two fans increased cooling slightly.