Numerical Modelling of Coolant Filling and De-aeration in a Battery Electric Vehicle Cooling System

Trapped air bubbles inside coolant systems have adverse effect on the cooling performance. Hence, it is imperative to ensure an effective filling and de-aeration of the coolant system in order to have less air left before the operation of the coolant system. In the present work, a coolant/air multiphase VOF method was utilized using the commercial CFD software SimericsMP+® to study the coolant filling and subsequent de-aeration process in a Battery Electric Vehicle (BEV) cooling system. First, validations of the numerical simulations against experiments were performed for a simplified coolant recirculation system. This system uses a tequila bottle for de-aeration and the validations were performed for different coolant flow rates to examine the de-aeration efficiency. A similar trend of de-aeration was captured between simulation and experimental measurement. Next, the same numerical techniques were further applied to a BEV cooling system to evaluate the efficiency of de-aeration processes. The first step of the process involved a vacuum filling simulation. After the filling process, the air remained in the system is about 10% of total system volume. Different combinations of a multi-position valve and pump on/off cycles strategies were explored to decrease trapped air in the system. It is found that the opening/closing strategy of the multi-position valve plays a crucial role for an effective de-aeration. The devised methodology is observed to be numerically robust and accurate, while having good computational efficiency for modelling the coolant filling and de-aeration process that takes large physical time.