Analysis And Optimization Of Temperature Field Of Air Cooled Power Battery Pack

With the development of the times,energy crisis and environmental pollution are becoming more and more serious.The research of new energy electric vehicles will play a positive role in reducing pollution and improving energy efficiency.Battery pack,as the key component of new energy electric vehicle power plant,is required to have large specific energy and power,high safety and long service life.For this purpose,new energy electric vehicle chooses Li-ion battery as power battery.However,Li-ion batteries are often in high rate discharge state in new energy vehicles,Its service performance,safety performance and life expectancy are reduced due to temperature rise and temperature difference caused by heat generated during work,and the serious even fire,explosion and cause safety accidents.Whether the heat management system of electric vehicles can distribute the generated heat quickly and effectively to the outside world to reduce the temperature and temperature difference of the battery is getting more and more attention.In this paper,the development of new energy electric vehicles at home and abroad was summarized,and the research on the battery heat management system at home and abroad was studied and analyzed.On this basis,the numerical simulation method of finite element simulation was used to study the temperature field distribution of the battery under constant current discharge and a heat dissipation system for Li-ion power battery based on heat pipe technology was also designed.The change of temperature field under different parameters was analyzed and was used to optimize the system and improve the temperature management performance of the thermal management system.The main contents of this paper are as follows:(1)The internal structure,working principle,heat generation mechanism and heat transfer mechanism of Li-ion battery were analyzed.The Bernadi model of the heat generation rate of Li-ion battery was used to analyze the conditon of heat generation.heat calorific analysis.It was clear that the internal resistance and the temperature entropy coefficient are related to the heating rate.So it is necessary to measure the parameters of the battery through Peak Power and HPPC tests,and obtain the relationship curve between the SOC state and the parameters of internal resistance and the temperature entropy coefficient of the battery.(2)The thermal model of lithium battery was built and the finite element simulation model was established.The physical parameters of lithium battery were calculated by the weighted average method.According to the model of heat generation rate and the data obtained from the experiment,the UDF of the heat generation rate of a single cell was written.Fluent software was used to simulate the temperature field of the 1C discharge under the natural convection condition whlie the heat generation rate of the battery changes with the SOC and temperature.The experiment results showed that the temperature of the cell exceeds the optimum operating temperature range,and the temperature difference of each part of the cell was large.Therefore,it is necessary to design a thermal management system to ensure the performance of batteries when they are grouped or packaged.(3)The battery thermal management mechanism of heat pipe was designed,The heat transfer performance of the heat pipe under different parameters(working quality,filling rate,heating power and length of condensing section)was simulated by using the computational fluid dynamics(CFD)method.The influence of heat pipe parameters on the temperature rise and temperature difference of the battery pack was studied,and the two parameters are optimized to obtain the optimal combination.(4)According to the heat pipe thermal management system under the optimal parameters,the temperature distribution of the battery pack is analyzed by CFD simulation of the 1C discharge of the battery pack under natural convection.The heat pipe battery management system designed in this paper solved the problems of excessive temperature rise and high temperature difference between the cells,and provided a design idea for the application of heat pipe technology in the power battery thermal management system.