| With the serious pollution of the ecological environment and the rapid development of new energy vehicles,the development of new energy vehicles has become an inevitable trend.As the vehicle’s power source,the 18650 lithium-ion battery is the primary choice for replacing fossil energy with its own advantages.However,lithium-ion batteries are often operated in high-rate discharges in new energy vehicles,and their performance,safety performance,and lifetime are reduced due to the effects of temperature rise and temperature differences caused by heat generated during operation.At the same time,the frequent occurrence of thermal safety issues has seriously hampered the development of electric vehicles.Therefore,the numerical simulation method is used to study the temperature distribution of the battery under specific operating conditions,design a suitable lithium-ion battery pack thermal management system,and analyze and optimize the thermal management system to improve its thermal performance,for the development of lithium-ion batteries and new energy sources.The application of the car has a landmark significance.The main research content of this article can be summarized as follows:(1)Analyze the working structure,working principle and heat production of lithiumion batteries.Based on the battery heat rate model established by Bernardi et al.’s theory,the heat power of lithium-ion batteries relate with the ohmic internal resistance and temperature entropy coefficient.Through the Peak Power test and the HPPC test of the lithium ion battery,the SOC curve of the ohmic internal resistance and the temperature entropy coefficient as a function of the residual power of the battery is obtained.(2)The basic heat transfer theory of lithium-ion battery was studied and a threedimensional thermal model of lithium-ion battery was established.Lithium-ion batteryrelated thermal properties parameters were calculated,and according to the heatgenerating rate model,a battery-cell heat source UDF was programmed in Fluent to achieve dynamic changes in the battery’s simulated heat rate.Computational fluid dynamics(CFD)method was used to simulate the heat generation of lithium ion battery cells discharged at different rates under natural convection.The results show that the battery peak temperature exceeds the battery’s best performance temperature range under different rate discharge conditions,and the temperature of the battery itself varies greatly.When batteries are used in groups,a thermal management system should be designed.(3)A liquid cooling method was designed for thermal management of the battery pack.The cooling medium was ethylene glycol.Fluent software was used to simulate the temperature field of the lithium-ion battery pack at different flow rates under three different discharge rates.The effect of the cooling liquid flow rate on the temperature field of the battery was studied under the conditions of three different discharge rates.However,it is found that the heat dissipation effect under relatively high rate discharge conditions is relatively unsatisfactory,affecting the heat management system’s ability to dissipate heat.Therefore,it is necessary to optimize the battery-related indicators under high discharge rate.(4)In order to optimize the heat dissipation performance of the liquid cooling system,an optimization method combining computational fluid dynamics and orthogonal tests is used to determine the ratio of ethylene glycol,cooling medium,convection heat transfer coefficient,and cooling medium flow rate.The optimization of these factors reveals the influence of the four factors on the three test indicators,and the optimal combination is obtained after comprehensive consideration. |
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