Structure Design And Optimization Of Heat Pipe Cooling System For Lithium-ion Battery Pack Of Pure Electric Vehicle

Faced with the severe situation of increasingly serious environmental pollution and increasingly depleted fossil fuels,traditional vehicles must be transformed and upgraded to new energy vehicles represented by pure electric vehicles.Lithium-ion battery,now as the mainstream of power batteries,is the only energy source for pure electric vehicles,and its performance is closely related to temperature.A large amount of heat will be generated when the lithium-ion battery is discharged at high temperature and large rate.If it is not released in time,the performance of the battery will be seriously affected and then the performance of the vehicle will be affected,and even lead to thermal runaway of the battery.Therefore,in order to make the lithium-ion battery work in a proper temperature range,give play to the best working performance of the battery,and ensure the performance of pure electric vehicles,it is necessary to design an effective cooling system for the battery pack.This paper first summarized the research progress of battery thermal management system at home and abroad and the advantages and disadvantages of different cooling methods.The internal structure,working principle,heat generation and heat transfer characteristics of lithium-ion battery was analyzed in depth,and the basic method and process of simulation analysis by using computational fluid dynamics was expounded.On this basis,a heat generation model of lithium-ion battery was established,and the temperature rise of the battery under the condition of natural convection cooling under different discharge rate was simulated.Combined with the experimental data,the accuracy of the model was verified,and the temperature field distribution of the battery under different conditions was simulated and analyzed.Then,a battery module composed of 6 batteries was taken as the research object,a heat pipe-aluminum plate chimeric cooling structure was designed for the module to increase the contact area between the heat pipe and the battery,enhance the heat flow.The temperature field distribution of the battery module under different discharge rate and ambient temperature was simulated.The effect of the addition of aluminum plate and its thickness on the temperature of the module were studied.The results show that adding aluminum plate can significantly improve the cooling effect than using the heat pipe alone.The maximum temperature and maximum temperature difference can be reduced by increasing the thickness of aluminum plate,and the temperature drop gradually decreases with the increase of thickness.Through the simulation process,the heat transfer of the heat pipe was analyzed theoretically and a simplified heat pipe model was adopted to reduce the amount of calculation.The influence degree of the main factors of the cooling system on the module temperature was studied by orthogonal experiment analysis.The results show that,for the maximum temperature and maximum temperature difference of the module,the order of the influence of each factor is:the convective heat transfer coefficient of condensation section of heat pipes>the length ratio of condensation section and evaporation section of heat pipes>the thickness of aluminum plates>the spacing between heat pipes.Combined with the analytic hierarchy process,the specific influence weight of each factor was determined,and the optimal parameters combination was determined as follows:the convective heat transfer coefficient of condensation section of heat pipes was 25W·m-2·K-1,the length ratio of condensation section and evaporation section of heat pipes was 0.8,the thickness of aluminum plates was 2mm,the spacing between heat pipes was 20mm.The maximum temperature of the module at the end of 2C discharge was 41.60℃,and the maximum temperature difference was 1.35℃.Finally,a certain pure electric vehicle was taken as the research object,according to its technical parameters and performance indicators’ requests,the matching design of the battery and motor was carried out.The vehicle model was established in ADVISOR,and the distribution characteristics of output current of battery pack under different driving cycles were obtained.Combined with the parameter optimization results,the cooling structure of the battery pack was designed,and one of the modules was taken as the research object,the temperature field distribution of the module under different driving cycles was simulated.The results show that the maximum temperature and temperature difference of the module can be maintained in a proper range,which verifies the effectiveness of the cooling system.