| With the rapid development of the automobile industry,the exhaust gas emitted by automobiles has become the main cause of air pollution,and as a new type of industry,new energy vehicles have great advantages in energy conservation and tail gas emissions.As the most important electrochemical energy storage component,lithium ion battery has been widely used in the field of new energy vehicles.However,lithium-ion batteries will generate severe heat during operation,which causes problems such as capacity reduction,life reduction,fire and explosion caused by thermal runaway.Therefore,a good thermal management system is needed to ensure that the battery operates within a safe temperature range.The purposes of this study are as follows:(1)We analyzed the lithium ion battery’s operating principle and characteristics,the heat generation and heat transfer mechanism,and tested the internal resistance of the battery at 40 °C through experiments.The experimental results showed that the internal resistance would increase as the depth of discharge increases.Finally,relying on the measured data,we calculated the density,specific heat capacity,thermal conductivity and heat generation rate of the battery,and compiled the UDF heat source program under different rate discharge through empirical formula,which provided a reliable basis for the next chapter simulation calculation.(2)The heat generation simulation of the natural convection single lithium ion battery was carried out under different discharge conditions.The simulation results demonstrated that the peak temperature of the battery exceeded the optimal performance temperature range of the battery,and there was a large temperature difference between different positions of the battery cells.When battery was applied in groups,the temperature difference was further aggravated,and a thermal management system of graphite and foam aluminum composite was designed for this situation.FLUENT simulation was used to analyze the temperature distribution of the battery pack under different charge and discharge rates when the ambient temperature was 40 °C.The results showed that the peak temperature of the battery was within the optimal temperature range of the battery,but the temperature difference between single cells was relatively large.(3)The thermal management system was designed through phase change materials and liquid-cooled composite cooling methods.Taking into account the porosity of the phase change material,the thickness of the liquid cooling plate,the flow rate of the coolant,the type of coolant and the effect of the discharge rate on the temperature field of the battery pack,we designed a 5-factor 3-level orthogonal experiment to simulate the temperature field of the thermal management system,which can optimize the heat dissipation performance of the battery management thermal management system.Then we obtained the optimal combination of parameters.The simulation analysis of the further cooling effect of the optimization scheme showed that the heat dissipation effect of the battery pack cooling system was significantly improved.(4)The optimized battery pack structure is applied to the battery pack model,and the obtained optimal parameter combination is applied to the heat dissipation analysis of the battery pack,we simulated and analyzed the heat dissipation of the battery pack under the condition of 2C rate discharge.The results showed that the phase change material and liquid-cooled composite heat dissipation method can control the battery temperature within the safe working range,but the battery temperature distribution is not uniform enough.This situation was further improved by changing the order of coolant inlet and outlet of the liquid-cooled plate.The effects of three different coolant inlet and outlet sequences on the battery pack cooling system were investigated under the condition of 2C rate discharge.Then we obtained the best way to arrange the entrance and exit.Finally,considering the uneven temperature distribution and the double-layer structure of the battery pack,we studied the heat dissipation of the battery pack under the condition of 2C rate discharge with changing the pipe arrangement and adding a layer of cooling plate in the middle,the results showed that the system can control the battery temperature in a safe range,and temperature distribution was uniform. |
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