Numerical investigation on nucleate bubble departure by electrowetting-on-dielectric in battery cooling plates

Abstract

A thermal management system is necessary to control battery operating temperature in electric vehicles (EV). Typically, the most common way to dissipate heat from the battery pack is to use the cooling plate. The cooling medium in the cooling plate removes the excess heat from the battery pack through boiling heat transfer. This paper proposes an electrowetting-on-dielectric (EWOD) method to enhance the bubble departure in nucleate boiling heat transfer in a cooling plate. In order to investigate the bubble splitting due to the EWOD effect, theoretical models are developed to solve for the electrophoretic force, dielectrophoretic force, and electrostrictive force. The theoretical model coupled a phase field method with an electric conservation model, where the body force acts as an external force due to the electric field. Our preliminary simulation results demonstrated that the EWOD effect can change the apparent contact angle when applied to a certain electric field. The free charge density displays at the dielectric layer interface with water and at the bubble’s interface near the triple contact point. Then two types of simulation case were investigated to apply the voltage in the battery cooling plates. In the first case, a pair of parallel discs are used as the electrodes at the bottom and top of the region. In the second case, the voltage is applied at the top of the nucleate bubble in a rod electrode. The various behavior of bubble dynamics were compared and discussed to indicate the optimized case for enhancing the nucleate bubble departure in the EV battery cooling plates.