| Electric vehicle(EV)are considered to be the mainstream of the future transport vehicle under the situation of oil shortage and global warming.Because of their high energy,high power density,long cycle life,long work hours and negligible memory effects,lithium-ion batteries are the primary choice of dynamic lithium-ion battery for EV.Despite their obvious advantage and widespread use,lithium-ion has still significant technical challenges.Generally,battery pack that is made up of many single cells will generate a large amount of heat for long distance travel.A single cell overheats and failure can degrade the performance of the entire battery pack,thereby affecting the performance of the vehicle.So,in order to guarantee the safety and reliability of the battery pack,the paper need to study the temperature field distribution characteristics of the lithium-ion battery under different conditions and the thermal stability of heat dissipation structure of battery pack in air cooling mode,which has very important significance to make the working temperature of battery pack maintain within optimum ambient temperature range.In the paper,the method of the numerical simulation will be applied to study the characteristics of heat generation and heat dissipation of the lithium-ion battery.(1)Based on the analysis of the structure,working principle,heat generation and heat dissipation mechanism of the lithium-ion battery,the relationship between temperature and capacity,resistance of the lithium-ion battery were studied.(2)Based on the reasonable simplification and assumption,the paper built lithium-ion battery's heat conduction differential equation.the paper simulated the influence of the discharge rate,the coefficient of convection heat and the environmental temperature for the temperature field distribution of the lithium-ion battery,by using the physical model of 18650 cylindrical lithium-ion battery with the simulation analysis software FLUENT.The simulation result shows that with the increasing of discharge current or the decreasing of battery environmental temperature,the battery temperature rise increased and the battery temperature difference increased.With the increasing of the convection heat transfer coefficient,the battery temperature rise reduced and the battery temperature difference increased.(3)The paper set four different structure schemes about position and number of inlet and outlet of battery pack under the precondition that the other parameters were unchanged.In the mode of forced air cooling,analyzed the temperature field distribution and velocity field distribution of battery pack through steady mode.On this basis,byimproving the layout of inlet and outlet of the lithium-ion battery,the paper designed cooling structure scheme of two into two out and four into two out to improve the temperature distribution of battery pack.The air inlet was arranged on the longitudinal direction of battery pack and the air outlet was arranged on the transverse direction of battery pack.The simulation result shows that the improved structure scheme can effectively reduce the highest temperature of battery pack and the temperature difference of battery pack of the improved four into two out scheme was less than6?.which met the design requirements of battery pack cooling. |
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