Numerical Simulation Study On Cooling Of Power Battery Pack Based On Phase Change Structure

Power battery system is the core component of new energy vehicle,and the performance of the whole vehicle is closely related to the working state of the battery.Lithium battery is the most widely used type of power battery for new energy vehicles because of its unique advantages such as high specific energy and high power density.The power battery pack has a compact structure,and the heat generated during operation is not easy to be eliminated.The performance of lithium battery is restricted by the temperature of the working environment.Too high temperature or uneven distribution will seriously affect the working performance of the battery.Therefore,an effective thermal environment control system for battery pack is essential.In this paper,a phase change structure is designed to solve the heat dissipation problem of power lithium-ion battery pack,and the maximum temperature of the battery pack is controlled by phase change coupled with air cooling,which improves the uniformity of the internal temperature of the power battery pack and the controllability of the thermal environment of the battery pack.According to the theory of phase change heat transfer,a battery cooling module based on phase change structure is designed.Phase change structures with different structures and parameters are embedded in the lithium battery array,and the lithium battery pack and phase change structure are simulated and analyzed in three dimensions.Taking the maximum temperature in the battery pack and the maximum temperature difference in the battery pack as evaluation indexes,the effects of different environmental temperatures,structural parameters of phase change structures and thermophysical properties of phase change materials on the thermal environment of the battery during a charging and discharging cycle were studied.The results show that when the ambient temperature is 308.15 K,the phase change structure with the size of 5.5mm×41mm×505mm can ensure the battery to work in a safe temperature range;When the ambient temperature is313.15 K,the filling amount of phase change material is increased between the battery and the battery box.When the phase change temperatures are 42-44℃ and46-50℃,the maximum temperature difference in the battery pack is 3.82 K and3.98 K,which effectively improves the temperature uniformity in the battery system.In order to further improve the cooling capacity of phase change structure,an air channel was designed,and a phase change coupled air-cooled hybrid cooling system for lithium battery pack was established.The influences of channel structure,phase change material filling amount and ventilation rate on the thermal environment of lithium battery pack were simulated and analyzed.When the wind speed is 3m/s,the maximum temperature drops by 6.69 K when the channel width increases from 5.5mm to 19.5mm,and by 2.84 K when it increases from 19.5mm to 29.5mm.Under the same wind speed and channel width,the optimal ratio of air channels and phase change structures is five phase change structures and five air channels.Compared with four and six phase change structures,five phase change structures can better improve the temperature uniformity and reduce the maximum temperature of the battery pack.