Study On Heat Dissipation Characteristics Of Li-ion Battery Pack Based On Jacketed Liquid Cooling Structure

Man-made carbon emissions are considered to be one of the main cause of environmental pollution.China has set a target of becoming carbon neutral by 2060.Energy system reform is the fundamental measure to achieve the above goals,and the electrification of vehicle power system is one of the core means to achieve carbon neutrality in the transportation sector.At present,the number of electric vehicles is increasing rapidly,and the power battery is the core component of the power system of electric vehicles.Lithium-ion batteries,which are light in weight and large in capacity,have become the main form of power batteries for electric vehicles.Car batteries made of lithium-ion batteries,however,are significantly affected by temperature.High temperature and uneven temperature may be caused by the accumulation of heat generated by the battery during charging and discharging.This will not only shorten battery life and affect battery power,but may even induce thermal runaway and thermal runaway propagation.Therefore,the battery thermal management system(BTMS)is needed to effectively cool the battery pack and ensure the stability and safety of electric vehicles.Liquid cooling has been widely used in middle and high-end models for its advantages such as high heat dissipation efficiency,fast cooling rate and good temperature uniformity.Jacket cooling is a kind of indirect heat transfer,and the jacket is installed on the outer wall of the battery.The cooling medium flows away the heat in the flow passage surrounded by the jacket.This cooling method has the advantages of simple structure,convenient installation,low cost and easy modular production.In order to improve the heat transfer coefficient and temperature uniformity of the jacketed cooling mode,this study enhanced the cooling effect by adding internal cooling fins and designing flow directions in groups on the basis of in-depth analysis of the flow field and thermal field of the traditional jacketed cooling mode.Taking a lithium ion battery pack used by an electric vehicle as the research and optimization object,the parameters required for calculating the heating model of a single battery were measured experimentally,and the electric field-thermal field-flow field coupling simulation was carried out using COMSOL Multiphysics software.Analyzed the coupling of electric field,thermal field and flow field in the jacketed liquid cooling structure,optimized the structure and arrangement of heat fin,reduced the maximum temperature of the battery pack,improved the temperature uniformity in the battery pack,and improved the cooling system of the jacketed liquid cooling structure,further optimized the cooling effect of the thermal management system of the liquid cooling battery.It provides a reference for the development of battery thermal management system.The main research contents of this thesis are as follows:(1)Firstly,the heating characteristics of lithium ion batteries were studied,and the required battery performance parameters were measured by experiments.The heating model was established by using the electrochemical thermal cell module and non-isothermal flow module.The heat flow model of the jacketed liquid cooling during the battery cooling process was coupled by COMSOL Multiphysics multi-field coupling software.The three dimensional prediction model of battery pack temperature was established and its parameters were analyzed.(2)Based on the original battery structure,the influence of the jacketed liquid cooling BTMS on the heat dissipation performance of the battery pack was analyzed by comparing the parameters.In order to improve the cooling performance of the jacketed liquid cooling structure,the pressure drop loss of the system was reduced by adding fins and changing the fin structure,and the heat dissipation performance of the battery pack was improved.Finally,through the analysis of the simulation results,the inner fin of the jacketed liquid cooling structure was upgraded and optimized.(3)A variety of coolants were compared and analyzed in a jacketed liquid cooling BTMS with fin structure.Different coolants can have different cooling effects on the temperature of the jacketed liquid cooling structure.The temperature uniformity of the system can be improved by changing the type and concentration of coolants,and the reasons for the influence of different coolants on the temperature of the battery are discussed.(4)Finally,the influence of changing the flow direction of the coolant on the system heat dissipation is analyzed.The results show that the positive and negative flow structure of changing the flow direction of the coolant can effectively improve the heat exchange efficiency of the liquid cooling system,improve the cooling effect and enhance the heat transfer.Finally,the cooling effects of three different coolants were compared.This chapter can provide ideas for the practical application of coolant in liquid cooled BTMS.