Simulation Analysis On Heat Dissipation Performance Of Lithium-ion Battery Thermal Management System In EV

With the rapid development of economic and society,energy crisis and pollution becomes more serious.The Chinese government began to actively promote the development of new energy vehicles,especially electric vehicles.Battery is a key part providing power for electric vehicles,which affects vehicle performance.Battery performance is sensitive to temperature and usually controlled by battery thermal management system.Battery cooling methods mainly contain the liquid cooling,air cooling,phase change cooling,etc.This paper studies battery temperature change characteristics when using air cooling,and discusses the cooling effect of battery pack with fin.Taking the highest temperature and the maximum temperature difference as evaluation index to control the uniformity of battery temperature by thermal management system,we applied Pro/E to establish three-dimensional model of single battery and battery packs.Using ANSYS Fluent to simulate battery temperature distribution with 2C discharge rate,the reliability of the simulation analysis was verified by experiment.The constant internal resistance and experimental fitting internal resistance polynomial were used respectively to calculate battery heat generation.The influence of battery thermal conductivity on battery pack temperature was studied and found that battery pack temperature remains steady when battery thermal conductivity in thickness varies between 0.48 ~ 1.2 K Wm–1K-1.On this basis,firstly,this paper discusses the battery pack temperature field with different forms of air inlet and outlet.The highest temperature of battery pack with 4°inclination in air inlet and outlet is lower than no inclination or inlet inclination.Orifices in the chamber body(top or side of high temperature battery)can effectively improve the uniformity of battery pack temperature field.Secondly,we studied the improving effect of battery thermal management system heat dissipation performance with fins in different structure or size.After inserting fins in battery packs,the highest temperature and maximum temperature difference decreased obviously.In order to choose the right size of fin,we changed fin’s length and thickness in battery gap.When aluminum fin’s extended length increases from 1.5cm to 6cm,the highest temperature reduce.But the battery temperature remains unchanged when we continue to increase fin length.Battery temperature uniformity of fin thickness equals to 0.5 mm is worse than 1,2,3 mm,and later models’ highest temperature difference is small.Again,the fin ventilation length and slotted size have impact on battery cooling effect.Forced air cooling length equals to 3cm in the end of fins has a good heat dissipation performance.Slotted fin reduces thermal management system quality and could save cost.At the same time,slits have the effect of disturbing flow field.Keeping the slits and remaining portion 1/1,when fin slit width decreases,the highest temperature of battery pack reduce.When fin width is equal to 10 mm,the highest temperature decreased with the increasing of slit number.Finally,using experiment results of battery pack temperature,we verify the reliability of simulation analysis.Battery heat generation rate was fitted by a curve and was inputted into UDF in simulation process.Simulated temperature curve versus time is consistent with the experiment results and the maximum deviation is far less than 5% which confirmed the correctness of simulation results.