Structural Design And Optimization Of Liquid Cooling System Based On Minichannel For Li-ion Battery Pack

Electric vehicles are widely recognized for their advantages such as zero pollution and low energy consumption.As the main power source of electric vehicles,lithium-ion batteries have become the key factors for the performance of electric vehicles.With the increasing power density of lithium-ion batteries,heat generation during charging and operation can easily cause thermal safety problems such as overheating and uneven temperature distribution,which affects the charging and discharging efficiency and service life of lithium-ion batteries,and the recharge mileages of electric vehicles.It can also cause explosion and combustion.Therefore,the study of the temperature distribution of lithium-ion batteries under different conditions is very significant to design a reasonable cooling system to solve the problem of battery thermal safety.Based on the temperature rise of the battery cell,a lithium-ion battery heat generation rate model is established.At the same time,a reasonable cooling system is designed,and the typical operating conditions of the vehicle are considered.The purpose is to ensure that the maximum temperature of the battery pack is within 40? when the battery pack discharges at a high rate continuously,and the temperature difference between the cells in the battery pack is controlled within 8?.This article mainly carried out in-depth research from the following points:Firstly,the HPPC hybrid power pulse test was used to test the internal resistance of lithium-ion battery at different ambient temperatures.The experimental results showed that the internal resistance of lithium-ion battery in the first 80% of the discharge capacity changed little,but in the latter 20% discharge capacity,the internal resistance rises sharply,and the lower the ambient temperature,the greater the internal resistance of the battery.Using the numerical simulation method,the temperature distribution of the battery cell is obtained and verified by experiments.The results show that when the lithium-ion battery discharges at2 C rate,the maximum temperature reaches 52.58?,which is beyond the reasonable operatingtemperature range of the lithium-ion battery.Secondly,the dynamic simulation model of the electric vehicle was established by the MATLAB/ADVISOR simulation platform.The results show that the limiting current of pure electric vehicles under three typical dynamic conditions is less than 40 A,which provides a theoretical basis for determining the discharge rate of the battery in the heat dissipation system.Thirdly,a liquid cooling model for the combination of a battery pack and the minichannel cold plates was built.Numerical simulations show that the system can reduce the maximum temperature of the battery pack to below 40? under normal temperature conditions.And the model was optimized.Then considering the energy consumption of the integrated system,the maximum temperature of the battery pack,and the maximum temperature difference,a cold plate with 7 flow channels and the length-to-width ratio of 3:1was selected.The inlet speed of the coolant was 0.08 m/s and the initial temperature was 25?,and the inlet and outlet direction of the coolant are opposite,The battery pack is discharged to the cut-off voltage at 2C rate.Finally,the maximum temperature of the entire battery pack is reduced to 36.68?.Within the high rate discharge capacity of 85%,the maximum temperature difference of the battery pack is lower than 5?,during the discharge process,the maximum temperature difference is 7.88 ?.Finally,in order to solve the problem of starting the lithium ion battery at extremely low temperatures,consider the changes of the average temperature and the maximum temperature difference of the battery pack over time under the conditions of proper external power supply and battery self-heating.The results show that when the initial temperature of the heating liquid is 20? and the inlet flow rate is 0.01m/s,the temperature increase rate of using the external power supply and the self-heating of the battery is respectively 0.458?/min and0.912?/min.