Thermal Behavior Analysis And Heat Dissipation Performance Optimization Of Liquid Cooling Lithium-ion Battery Pack

The energy crisis and environmental pollution have promoted the transformation and upgrading of traditional fuel vehicles to new energy vehicles.The introduction of policies banning the sale of fuel vehicles at home and abroad has promoted the vigorous development of key technologies in the new energy vehicle industry.However,as one of the core components of new energy vehicles,the working state of the power battery will determine the strength of the vehicle performance.The battery pack is accompanied by a large amount of heat generation in the process of high rate discharge.The continuous accumulation of temperature not only affects the output of the single battery and the remaining effective life,but also leads to explosion phenomena such as uncontrolled heat.Therefore,in order to improve the heat dissipation performance of the thermal management system of large-scale high discharge rate battery and improve the temperature uniformity,this topic takes commercial 10Ah lithium iron phosphate battery as the research object,explores the voltage and temperature characteristics of the single battery,and effectively heats the battery pack by constructing a new mini-channel liquid cooling system,so as to control the temperature index within a reasonable range.Firstly,a one-dimensional and three-dimensional coupled electrochemical thermal coupled cell model was constructed to more accurately simulate the temperature characteristics of the battery.The voltage and temperature characteristics of a single battery at different discharge rates（1C,2C,3C,and 5C）were investigated.The voltage curve and temperature data of simulation analysis were compared with the experimental data,which effectively verified the reliability of the simulation model.The results show that the greater the discharge rate,the more obvious the voltage drop at the beginning and end of discharge.The temperature rise of the battery is positively correlated with the discharge rate.The maximum temperature of the battery reaches 317.95K after the discharge at 5C,which is 6.67K,10.65K and 15.6K higher than that at 3C,2C and 1C respectively.Secondly,for the battery pack containing 24 single cells at high discharge rate（3C）,build two mini-channel cold plates arranged on the top and bottom of the battery pack with opposite inlet direction of the cold plate,and explore the three-dimensional thermal field distribution,maximum temperature and maximum temperature difference of the battery pack under different mini-channel section aspect ratio,cold plate width and mass flow.Increasing the length-width ratio of the mini-channel section helps to reduce the maximum temperature of the battery pack,but the coolant inlet mass flow rate is constant,and increasing the length-width ratio of the mini-channel section leads to the decrease of the coolant flow rate in the mini-channel,and the ability to take away the heat of the battery pack is relatively weakened;The narrower the width of the cold plate is,the more serious the temperature accumulation is.The temperature uniformity of the battery pack with the width of 80mm,90mm and 100mm of the cold plate is 2.4%,6.0%and 8.4%better than that of the battery pack with the width of 70mm of the cold plate;The increase in mass flow rate significantly reduces the maximum temperature and temperature difference of the battery pack.But excessive increase will increase the pressure drop of the liquid cooling system and the power consumption.Finally,the battery thermal management system was optimized by orthogonal test and comprehensive balance method.The L16（4⁵）orthogonal table was established by orthogonal test,and the maximum temperature and maximum temperature difference of the battery pack were used as evaluation indicators to explore the influence ranking of different factors.Finally,the optimal parameter combination of the heat dissipation performance of the battery thermal management system was obtained by comprehensive balance analysis.Factors have the same order of influence on temperature indicators.:Mass flow rate>Length to width ratio of mini-channel section>Width of cold plate.The best parameter combination of heat dissipation performance of battery thermal management system is obtained by comprehensive balance analysis method.Combined with the structural strength of cold plate B₃W₄V₄,the best combination of temperature indicators is B₄W₄V₄,that is,the mass flow rate is 40g/s,the length-to-width ratio of different mini-channels is 4:1,and the width of cold plate is 100mm.The optimization research scheme combining single factor and orthogonal test proposed in this paper can effectively improve the temperature uniformity of the battery pack,and control the temperature index within a reasonable range,providing a constructive reference for the optimization research of large-scale high discharge rate battery thermal management system.