Research On The Optimization Design Of Coupled Heat Dissipation Of Vehicle Lithium Battery

Recently,the economy and technology have developed rapidly,especially automobile industry.However,it also caused a crisis of energy and environment.The exhaust emission of automobile leads to the high PM2.5 index.Under the strong support of the country's policies,the new energy electric vehicles will take the development of the car market,which reduce the emission of pollutants,and enhance the energy efficiency.In the high-power operation,the lithium-ion battery will generate a lot of heat as the core power component of new energy electric vehicles.If the battery cannot effectively dissipate heat,the undesired heat can result in battery performance degradation and lifetime shortage.In short,the large average temperature and temperature difference of the battery pack may cause safety accidents.Therefore,to ensure the safety and sustainable operation of new energy vehicles,it is crucial to design a thermal management system of lithium battery with excellent comprehensive performance.In this study,a thermal management system combining the air cooling and the phase change material cooling is selected,and a lithium iron phosphate battery is chosen to be the research object.First,we introduce the internal structure and operating principle of the battery.Moreover,the principle of heat generation,the thermal transmission process of battery and phase change material are introduced and measured.The electrochemical-thermal coupling model of lithium iron phosphate battery and the thermal model of phase change materials are established and verified.We have studied the parameters of the battery pack under the pure air-cooling system,which mainly includes the arrangement spacing,the rotation angle,the discharge rate and the inlet wind speed of battery pack.It can be observed that optimizing the arrangement spacing and rotation angle of battery pack can improve the cooling efficiency of air-cooling system by a third than of the traditional arrangement,in which the thermal performance shows maximum potential when the rotation of battery pack is 45°.Furthermore,we analyze and optimize the discharge rate and the inlet wind speed of battery pack,which amplifies the heat exchange defects at the rear of the battery pack and fully utilizes the capacity of the air-cooling.In order to improve the temperature consistency of the battery pack,we add fins to the tail of the battery.It is found that the temperature consistency of the battery pack which is in-line and cross-flow with the fins is obviously improved due to the difference in the flow path between the two new arrangements.The temperature difference within the battery pack decrease from 24.5K to 19.19K,and the streamline density of the cooling fluid increases when it passes through the last row.However,there is no significant improvement on the battery pack which is cross-line and cross-flow.Finally,the geometric parameters of the fin in the feasible scheme are optimized.When the layout density is 150 and the thickness is 1.5mm,the thermal performance of the battery pack is optimal.We add the phase change material cooling method.In this case,we choose the mixture of paraffin,expanded graphite and low-density polyethylene as the composite phase change material.After adding composite phase change materials,the average temperature decreased from 304.20K to 302.36K and the temperature difference within the battery decreased from 24.5K to 11.69K under the in-line and cross-flow battery pack.Meanwhile,the average temperature decreased from 303.78K to 302.02K and the temperature difference decreased from 18.97K to 10.59K under the cross-line and cross-flow battery pack.In addition,we compare and analyze the layout way of phase change material and the composite cooling system.It can be obtained that the thermal properties of the battery pack show the best performance when we choose the circular columnar layout way of PCM within the air-cooling system.In summary,the method of combining cooling method combines air cooling and phase change material cooling has excellent heat dissipation effect,which has certain positive significance for new energy electric vehicles under high-power operation.