| Currently the trend of the development of electric vehicles is excellent with the significant promotion given by the government who considers the pressure of environmental prevention and sustainable development.The developmental and evolutionary technology in power batteries is a key factor that makes electric vehicles a breakthrough in progress.The thermal management is the bottleneck technology that blocks the extensive application of power batteries,since overheat and heterogeneous dissipation in cells easily make the performance deteriorate,the capacity decrease and so on.Thus,it is necessary to study the thermal characteristics of lithium-ion batteries and to design a cooling system of the battery pack,ensuring the temperature in the battery pack varied with a reasonable range.The operating principle and heat generation mechanism of the cell are analyzed firstly in the process of thermal properties research and modeling.The heat generation rate of the cell is obtained in the test of charge and discharge and hybrid pulse.Main factors those determine temperature distribution in the cell are studied.A thermal model is built by the COMSOL software based on heat transfer theories.By simulation of the temperature variation in the cell with different discharge rates,the result shows that the temperature increases with increment of discharging rates.The maximum temperature with 1.5C discharge is about 4.9? higher than the maximum temperature with 1C discharge.The experimental data is obtained to verify the accuracy of the battery thermal model.The error between experimental data and simulation data is less than 1%.The comparison of the experiment and simulation shows that the model enables exactly estimate the temperature inside the cell.Three kinds of cooling systems—the air cooling system,liquid cooling system and phase change material cooling system,are proposed to decrease the temperature differences inside the cell pack based on the theory of computational fluid dynamics.The characteristics of the temperature field and flow field are analyzed in the natural convection condition and the air cooling condition.Compared to the air cooling system,the maximum temperature decreases 6? significantly with a liquid cooling system.However,for the liquid cooling system,the temperature distribution is not uniform,and the maximum temperature difference is nearly 20?.The structure is very complex and the cost is high.A phase change material cooling system for the temperature control is also studied.The result demonstrates that no apparent improvement of heat dissipation capability in the pack is observed.Considering the advantages and disadvantages of these three kinds of cooling system,we conclude that the air cooling system is the best choice for the cell pack.Finally,we propose the methods to improve the optimization of the flow field and temperature field distribution of the pack.An analytical multi-physics approach incorporating a three-dimensional CFD model has been developed to effectively estimate the thermal behaviors of virtual battery packs.A comprehensive optimization for air-cooling system of lithium-ion battery packs is proposed,which follows the single variable principle in this study.Based on the theory of heat transfer and computational fluid dynamics,the thermal characteristics of the battery and the cooling design of the battery pack are studied.The accuracy of the battery thermal model is verified by the experimental data.On this basis,some strategy schemes for the optimization of the heat dissipation of lithium-ion battery pack are proposed.The heat dissipation capability in the pack is obviously promoted.The results of this study can be used as a reference of the further design of battery thermal management system. |
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