Design And Optimization Of Heat Dissipation Structure Of Lithium-ion Battery Packs For Electric Vehicles

The number of cars is rising rapidly,and electric vehicles are very effective solutions in the face of increasing greenhouse effect and depletion of natural energy.Lithium-ion batteries,with the advantages of high energy density and long cycle life,are often used as power batteries for electric vehicles.However,the temperature has a great influence on the performance of the battery.It will not only reduce the battery life,capacity and power,but even cause safety problems.Therefore,in order to make the battery perform better,the function of the battery heat dissipation structure is essential.The basic theories of battery heat production,battery heat dissipation and convection heat transfer were summarized,and the control theory of CFD simulation was expounded,laying the foundation for battery temperature simulation and fluid analysis.The thermal properties of battery were determined and the temperature rise of battery at high rate discharge was simulated.The cooling performance of phase change material was studied,and the phase change material cannot control the rise of battery temperature for a long time when the heat generation rate of the battery was relatively high.Then,a battery heat dissipation structure combining phase change material and constant-diameter channel was designed.The influences of constant-diameter channel quantity,inlet size,flow direction and mass flow on the performance of heat dissipation were studied.The results showed that,although the constant-diameter channel could help the phase change material recover latent heat quickly and control the maximum temperature of the battery effectively,the temperature uniformity of the battery was seriously destroyed.Therefore,the battery heat dissipation structure combining phase change material and constant-diameter channel cannot meet the requirements.In order to improve the temperature uniformity of the battery,a battery heat dissipation structure combining phase change material and the channel with gradually expanding diameter was proposed,and a thermal model was established in the CFD software to study and prove the advantages of the channel with gradually expanding diameter.The results demonstrated that,the channel with gradually expanding diameter could effectively protect the battery temperature uniformity created by the phase change material under the premise of timely recovery of the latent heat of phase change material.In the same situation,the combination of the channel with gradually expanding diameter and phase change material could achieve better temperature uniformity and significantly reduce the mass flow rate and the number of channels at the same time.Finally,under the conditions of normal temperature,high temperature pre-cooling and low temperature pre-heating,it was verified that the combination of the channel with gradually expanding diameter and phase change material could more effectively control the maximum temperature and maximum temperature difference of the battery.