Optimization Design Of Battery Pack Structure Based On CFD Thermal Simulation Analysis

With the increasingly serious problems of energy safety and environmental pollution in China,the traditional automobile industry has come to a revolutionary opportunity.In order to achieve the goal of sustainable development,electric vehicles have become the mainstream development direction.At present,the research and development of electric vehicles are facing fierce competition all over the world.As the core component of electric vehicle,power battery pack has a great influence on the range and safety performance of electric vehicle.Because lithium ion batteries in the battery pack generate a lot of heat during the charging and discharging process,the temperature of the batteries keeps rising.Failure to effectively heat them will seriously affect the working state and cycle life of the lithium ion batteries,and even lead to thermal runaway phenomenon during long-term use.To ensure the safety of the battery pack,a battery thermal management system needs to be designed.In addition,the electric vehicle will encounter some extreme operating conditions during driving.The battery package as a battery carrier plays a key role in the stable and safe operation of the power battery.Therefore,it is very important to study the box structure of the power battery package.Based on computer simulation technology and taking power battery package as research object,this paper researches on the following aspects of battery liquid cooling heat dissipation system and battery package structure:(1)The structure,working principle,heat generating mechanism and heat transfer mode of lithium ion battery were studied in depth,and the thermal effect model of battery monomer was established.Then,based on the theory of computational fluid dynamics,the temperature field distribution of cell monomer in 1C,2C,3C and 4C rate discharge was simulated and analyzed in Fluent software.The results show that the temperature of lithium ion batteries decreases from the center to all sides,and the peak temperature and maximum temperature difference inside the batteries increase with the increase of discharge rate,which exceeds the normal operating temperature range for the batteries and requires thermal management of the batteries.(2)The three-dimensional model of the battery module was established and the thermal simulation analysis was carried out.The results show that when the ambient temperature is 25℃ and the battery is discharged at 2C multiple,the maximum temperature of the battery in the module is 60.61℃ and the maximum temperature difference is 8.5℃,which far exceeds the optimum operating temperature of the battery.Therefore,the structure of the battery module is optimized and the liquid cooling and heat dissipation system of the battery is designed.The influence of number and position of cooling plates on module heat dissipation is analyzed.The simulation results show that the maximum temperature and maximum temperature difference of the optimized battery module are only 27.44℃ and 4.85℃.Compared with the module structure of natural convection heat dissipation,the maximum temperature and maximum temperature difference of the optimized battery module are reduced by 54.7% and 42.9%,which fully satisfy the design requirements that the maximum temperature of lithium ion in the module does not exceed 40℃ and the maximum temperature difference does not exceed 5℃.(3)Based on the design requirements of lightweight power battery package and mechanical safety performance,the upper cover and lower box of power battery package are designed in structure,and the liquid-cooled heat dissipation system of power battery package is established according to the optimized battery module structure.Then,static analysis and dynamic analysis of power battery pack under limit condition are carried out in ANSYS software by using finite element analysis method.The simulation results show that the firstorder natural frequency of the power battery pack is 69.71 Hz,and its maximum stress and strain under extreme conditions are 126.73 MPa and 1.063 mm,which meet the design requirements of the strength and stiffness of the battery pack.