| With the increasingly serious energy crisis and environmental pollution in the world,automobile manufacturers around the world have made great efforts to develop new energy vehicles represented by electric vehicles to achieve further energy conservation and emission reduction in recent years.As the core component of pure electric vehicle,power battery is the key to the market application and popularization of electric vehicle.However,when the power battery is working in a high temperature environment or under the condition of charging and discharging at a high rate,the temperature is often too high,and thermal runaway accidents such as fire and explosion may even occur.In addition,if the power battery in the cell temperature uniformity is poor,it will also greatly affect its performance and life.The efficient and optimized heat dissipation structure can significantly improve the temperature state of the power battery pack,thus improving the performance of the vehicle.In this paper,the module of lithium ion battery of electric vehicle and its structure of liquid cooling heat dissipation are studied.On the basis of establishing the thermal effect model of the battery and analyzing the performance of the original heat dissipation structure under different working conditions,the one-dimensional and three-dimensional numerical models for simulating the battery module and its heat dissipation structure are established.Then,the heat dissipation structure is optimized based on the one-dimensional model,and the heat dissipation performance of the new structure is verified based on the three-dimensional model.The main contents are as follows:1.The heat dissipation and temperature uniformity of the battery modules under different discharge rates and different coolant flows are analyzed.The results show while the battery discharges at the rate of 2C,4C,8C respectively,the highest temperature of the battery are 26.1?,28.69? and 36.64?,the maximum difference of the average temperature are 0.25?,0.63? and 1.74? respectively,and temperature of mean square error are 0.0749?,0.1962? and 0.5540?.It can be seen that with the increase of discharge ratio,the highest temperature of the battery will be significantly improved,the temperature uniformity between monomer battery also becomes poor,of which 8C discharge the value of the temperature of mean square error value under the condition is greater than 0.5?.Beyond the design specification of the battery thermal management system.While inlet cooling fluid flow are 0.04 kg/s,0.06 kg/s,0.08 kg/s,the highest temperature batteries are 38.51?,36.64? and 35.64?,the maximum difference of the average temperature are 2.11?,1.74? and 1.59? respectively,and the temperature of mean square error are 0.6825?,0.5540? and 0.5048?.It can be seen that with the increase of coolant flow rate,the highest temperature of the battery will be reduced,the battery temperature uniformity between monomer will be improved,but it's still relatively bad.Different coolant flow also causes different flow distribution in each cooling channel,which makes the position of the high-temperature area in the battery module somewhat offset.As the discharge rate of the battery increases,the maximum temperature of the battery will increase significantly,and the temperature uniformity between the cells will decrease.With the increase of coolant flow,the maximum temperature of the battery will be reduced,and the temperature uniformity between the cells will be improved.However,different coolant flows also cause different flow distribution in each cooling channel,which makes the location of the high-temperature area in the battery module somewhat offset.2.To solve the problem of poor homogeneity of single body temperature of each battery in the original structure,the heat dissipation structure is optimized under the basic condition of "ambient temperature 25?,battery discharging at 8C and coolant flow at 0.06kg/s".The optimization design is carried out in two steps by using onedimensional-three-dimensional coupling.Firstly,Flowmaster software is used to conduct one-dimensional modeling of the battery cooling structure,and based on the greedy algorithm,the battery temperature mean square deviation is taken as the optimization target,and the optimization solution is achieved through the joint simulation of Flowmaster and Excel/VBA.Then 3D simulation is used to verify the optimization results.This two-step optimization method introduces a one-dimensional modeling link on the basis of the traditional CFD method,which can not only greatly accelerate the optimization speed and improve the optimization efficiency,but also more conveniently adopt the optimization algorithm to assist the structural optimization design.The results show that in the optimized new heat dissipation structure,the maximum temperature of the battery at the termination of discharge is reduced from 36.64? to 35.62?,the maximum difference of the average temperature of the battery is reduced from 1.74? to 0.28?,the temperature of mean square error is reduced from 0.5540? to 0.0812?,which is successfully reduced to less than 0.5?,which meet the control goal of the battery thermal management system.The heat dissipation effect and battery temperature uniformity were greatly improved,and the optimization effect was obvious.It also shows that the heat dissipation structure optimization process and method presented in this paper are effective.3.The optimized heat dissipation structure of the battery module was applied to other working conditions except the basic working conditions to further verify and analyze the heat dissipation performance of the new structure.Results show that under the other conditions unchanged,the discharge rate is 2C,4C and 8C,respectively.The maximum temperature of the battery at the termination of discharge is reduced from 26.1?,28.69? and 36.64? to 25.93?,28.28? and 35.62?,the maximum difference of the average temperature of the battery is reduced from 0.25?,0.63? and 1.74? to 0.13?,0.12? and 0.28?,the temperature of mean square error is reduced from 0.0749?,0.1962? and 0.5540? to 0.0374?,0.037? and 0.0812?.Under other conditions unchanged,the coolant flow rate is 0.04kg/s,0.06kg/s and 0.08kg/s respectively.The maximum temperature of the battery at the termination of discharge is reduced from 38.51?,36.64 ? and 35.64? to 37.85?,35.62? and 34.95?,and the maximum difference of the average temperature of the battery is reduced from 2.11?,1.74? and 1.59? to 0.97?,0.28? and 0.43?,respectively.The temperature of mean square error is reduced from 0.6825?,0.5540? and 0.5048? to 0.3566?,0.0812? and 0.1473?.The new structure improves the heat dissipation and temperature uniformity of the battery modules under different discharge rate and different coolant flow rate.After adopting the new structure,the original temperature of mean square error exceeded the control target of the battery thermal management system.The original poor mean square error of battery temperature was improved effectively.The optimization process and method of radiator structure presented in this paper are highly adaptable.From what has been discussed above,after the optimization of the original heat dissipation structure,the new heat dissipation structure has obviously improved the temperature homogeneity of electric vehicle power batteries,thus effectively guaranteeing the good performance of the battery,improving the service life of the battery and ensuring the safety and reliability of the electric vehicle.At the same time,the heat dissipation structure optimization process and method have good effectiveness and wide adaptability. |
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