| The popularization of automobile has not only promoted the rapid development of human society and economy and modern civilization,but also brought severe energy and environmental problems.Traditional fuel vehicles not only have high costs,but also cause particularly serious pollution to the environment.As an alternative to traditional fuel vehicles,electric vehicles are attracting more and more attention.The domestic pure electric vehicle industry has developed rapidly in recent years,and battery performance is one of the most important technical bottlenecks restricting the development of pure electric vehicles.Temperature has a huge impact on the electrochemical performance of the battery.Too low temperature will increase the internal resistance of the battery and significantly reduce the battery capacity.Too high temperature of the battery will cause spontaneous combustion or even explosion of the battery pack.Therefore,an effective battery thermal management system must be designed for the battery pack to ensure the power performance and safety of pure electric vehicles.In this paper,theoretical analysis,numerical simulation and experimental test are combined to study the thermal characteristics of lithium iron phosphate batteries and battery groups.The main research contents are as follows:Through reading and studying the domestic and foreign literatures,the advantages and disadvantages of various thermal management methods were analyzed,and the solution of liquid cooling was determined.Through the study of related literatures,the heat generation mechanism,thermo-physical parameters and heat generation characteristics of the lithium iron phosphate battery used in this paper are analyzed.Then the simulation model was established through corresponding theoretical analysis,and the temperature field of lithium ion battery under natural convection,0.5c,1C and 1.5c was simulated in Fluent software.Finally,the surface temperature rise test of the li-ion battery is carried out.The experimental results are compared with the simulation results to verify the reliability of the simulation model.According to the temperature field distribution of the battery,the liquid cooling thermal management system is designed,and the optimal scheme is selected by comparing the number of different cooling pipelines and the flow rate of different cooling fluids.Aiming at the problem of large temperature difference of li-ion battery,this paper introduced phase change material to control the temperature difference of battery,and selected the optimal cooling scheme by comparing the phase change temperature of different phase change materials and the thermal conductivity of different phase change materials.Based on the above research and related characteristics of the battery pack,the cooling system is improved accordingly.The temperature field of the battery pack in different ambient temperatures and discharge rates was simulated by Fluent software.Meet heat dissipation requirements of battery pack.In this paper,the heating system of the battery pack in the cold environment is designed and simulated.According to the simulation results,the heating requirements of the battery pack in the low temperature environment are met.Through the above research,the thermal balance system designed in this paper meets the design goal of battery thermal management. |
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