Multi-scale Multi-field Coupling Simulation Of Power Battery Thermal Management System

As the power source of electric vehicle,power battery is one of the three core technologies of electric vehicle.For the current mainstream power battery,temperature has an important impact on the performance and service life of the battery.When the power battery is used in electric vehicle,it needs to be packaged into a battery pack,which makes the heat of the battery difficult to dissipate,and the working temperature of the power battery needs to be controlled.Therefore,designing an effective battery thermal management system has a crucial impact on the development of electric vehicle.This topic comes from the key project(industry prospect and key technology)of Jiangsu Province.For the electric light truck provided by the project partner,in this paper,the research on the electrochemical thermal coupling problem and thermal characteristics of the battery cell,the design of the battery pack,the design of the battery thermal management scheme and the multifield coupling calculation are carried out.The main work and conclusions are as follows:(1)Correlating the micro-parameters and macro-parameters in the actual microstructure of the electrode,based on the equations of charge conservation,mass conservation and energy conservation,a multi-scale electrochemical thermal coupling model of lithium iron phosphate battery cells was established,and the boundary conditions were determined.(2)In order to understand the temperature characteristics of the soft coated lithium iron phosphate battery used in the project,this paper built a test platform for studying the thermal characteristics of the battery cell,and carried out the constant current discharge test of the battery under different environmental temperature and different discharge rate.The following conclusions are obtained: when the ambient temperature is 25? and the discharge rate is 1C,the maximum temperature of the battery at the end of the discharge process appears at the center of the battery,which is 30.1?;The lower the ambient temperature,the greater the temperature rise of the battery,and the maximum temperature rise of the battery reaches 9.1? when the ambient temperature is 5 ?;The greater the discharge rate,the greater the temperature rise of the battery,and the worse the average temperature,when the discharge rate is 2C,the temperature rise of the battery reaches 15.1?.And the established multi-scale electrochemical thermal coupling model was used to simulate and calculate the test condition,the change law of the heat generation rate under different discharge rates of the battery was obtained.And the cross scale electrochemical thermal coupling model was used to simulate the test condition,and the change rule of heat generation rate under different discharge rates was obtained.(3)The design of battery pack for electric light truck was carried out,the number of batteries,series and parallel form were determined,and the size of battery box and battery module were selected according to the requirements of national standard.(4)According to the preliminary size of the battery module,a typical liquid cooling scheme using liquid cooling plate for heat dissipation was designed,which determined the flow rate of the cooling liquid,the structure and size of the liquid cooling plate.And a new heat pipe cooling scheme was proposed,which determined the working medium and size of the heat pipe and the number of cold plates and fins.(5)Finally,the multi-field coupling simulation analysis of liquid cooling and heat pipe cooling are conducted separately.For the liquid cooling scheme,the liquid cooling plate structure was improved according to the calculation results,the maximum temperature of the power battery module was controlled at 34.77 ?,the temperature difference was 4.71 ?.The influence of the flow and temperature of the coolant on the improved liquid cooling system of the power battery is analyzed.In the heat pipe cooling scheme,when considering the influence of the fin space,it was found that the battery system had good temperature uniformity when the fin space was 4 mm,and the temperature difference could be controlled at 4.09?.And the influence of air volume and inlet air temperature on the heat pipe cooling system of power battery was also considered.Compared with the typical liquid cooling scheme,the results showed that the heat pipe cooling scheme had better temperature uniformity.In this paper,a multi-scale electrochemical thermal coupling model of battery cell was proposed.On this basis,a battery pack was designed,a new thermal management scheme based on heat pipe cooling was designed and a multi-field coupling analysis was carried out,which plays a certain reference role on the research of battery thermal management system applied to electric vehicle.