Simulation Study On Liquid Cooling Characteristics Of Lithium-Ion Battery For Electric Vehicles

With the global energy shortage and environmental pollution problems becoming more and more serious,and the strong support of governments,new energy vehicles have developed rapidly.Electric vehicles are considered to be the best alternative to traditional fuel vehicles because of their simple overall structure,zero pollution emissions,quietness,high efficiency and no use of energy.Lithium-ion batteries are widely used in electric vehicles due to their high cycle life,high specific power,high specific energy and fast charging and so on.The performance of the power lithium battery is very sensitive to temperature.If the heat generated during operation is not released in time,it will not only affect the efficient operation of the lithium battery,but also cause thermal loss of the lithium battery.Therefore,it is especially important to develop a reasonable thermal management system to ensure efficient and safe operation of lithium batteries.This paper first calculates the thermal property parameters of lithium battery by theoretical formula.Then based on the ideal Bernardi heat generation theory,the relation between the heat generation rate of lithium battery and time is obtained.A single lithium battery model is established.Under the condition of natural convection,Ansys-Fluent software is used to simulate the temperature field of single lithium battery under different discharge rates.The results show that the maximum temperature of the single lithium battery increases with the increase of discharge rate,and the highest temperature of the battery begins to appear in the positive electrode,and then distributes in the center of the battery,but the positive electrode temperature is always higher than the negative electrode.Then,the liquid-cooled plate was applied to the battery pack thermal management system,and the thermal characteristics of the lithium batteries liquid cooling module under the 3C discharge rate are analyzed by Ansys-Fluent software.Firstly,the heat dissipation of the liquid cooling modules with side by side “U” shaped channel and “1” shaped channel is compared and analyzed.Then,under the premise of single inlet and outlet,the heat dissipation of the liquid cooling module of four different shape flow channels is compared and analyzed.Finally,taking the “Z” shaped channel liquid cooling module as an example,the effects of the number of channels,the mass flow rate of coolant,the ambient temperature,the width of channel and the spatial layout of the channel on the heat dissipation performance are studied,and the optimized structure is proposed.The results show that the heat dissipation of the side-by-side "U"-shaped flow channel liquid cooling module is better than that of the side-by-side "1"-shaped liquid cooling module.Compared the four-shaped flow channel liquid-cooled plate,the "Z"-shaped flow channel liquid cooling module has the best dissipation,The pressure drop difference at the inlet and outlet of "I" shape liquid cold module is the smallest.Increasing the number of flow channels,the mass flow of coolant and the width of the flow channels can reduce the maximum temperature rise of the batteries and improve the temperature uniformity between the batteries.However,the increase of coolant mass flow will increase energy consumption,and the increase of the number and width of the flow channel will reduce energy consumption.The ambient temperature will affect the maximum temperature of the battery pack,but has no effect on the maximum temperature difference of the battery pack.The dense arrangement of the channel near the inlet end and the sparse arrangement of the outlet will help to improve the heat dissipation performance of liquid cooling module.Compared with the original model,the maximum temperature of the optimal model after structural and spatial layout optimization is reduced by 0.76 ?,and the maximum temperature difference is reduced by 1.06 ?.Finally,the side-by-side "U"-shaped channel liquid-cooled plate and battery pack are combined to form a reasonable battery-packed liquid cooling module,and the optimal model combination is selected by orthogonal optimization method.The results show that the combination of the flow channel width of 12 mm,the cooling medium flow rate of 0.07 m / s,and the number of flow channels of 4 is a better combination,which can meet the safe use of the battery pack at 1C rate discharge.The highest temperature of the optimal model is 7.81 ? lower than the maximum temperature in the 16 model.