对流换热系数考虑温度影响时对锂电池热扩散影响的数值分析

Numerical analysis of the convective heat transfer coefficient effect on lithium batteriy thermal diffusion when considering temperature effect

基于电化学-热耦合模型,以4节18650锂离子电池为研究对象,分析考虑温度效应时的对流换热系数对锂电池热扩散的影响及其程度。首先基于传热理论中的流体横掠顺排管束平均表面换热系数计算方法,计算得到不同温度和流速下锂离子电池表面对流换热系数,通过曲线拟合得到空气流速分别为0.05、0.1、0.2和0.3 m/s时对流换热系数与温度的函数关系,得出对流换热系数与温度不完全呈线性变化;其次基于以上函数关系,通过数值模拟分析了考虑温度效应时的对流换热系数对锂电池热扩散的影响。结论表明,考虑温度效应时的对流换热系数对锂电池温度场影响的程度不同。当空气流速分别为0.05、0.2、0.3 m/s时,锂电池的温度函数使锂电池放电过程中的温差变化均小于1%;但是当空气流速为0.1 m/s、锂电池放电至729 s时,考虑温度因素的对流换热系数的温度场比常数时的温度场下降了21.71%。该影响规律与不同流速下对流换热系数随温度变化相一致,也表明对流换热系数与流速、温度均有关,而且对流换热系数越大,锂电池越容易与外界空气发生热交换,锂电池放电过程中温差越小。

Based on the electrochemical-thermal coupling model,four 18650 Li-ion batteries were used as research objects to analyze the effect of convective heat transfer coefficient on the thermal diffusion of Li-ion batteries and its degree when considering the temperature effect.Firstly,the convective heat transfer coefficients on the surface of lithium-ion batteries at different temperatures and flow rates were calculated using the calculation method.Convective heat transfer coefficients as a function of temperature were obtained by curve fitting for air flow rates of 0.05,0.1,0.2 and 0.3 m/s,respectively,and it was concluded that the convective heat transfer coefficient did not vary completely linearly with temperature.Secondly,based on the above functional relationship,the effect of convective heat transfer coefficient on the heat diffusion of lithium battery when considering temperature was analyzed by numerical simulation.The conclusion showed that the convective heat transfer coefficient when considering temperature had a different degree of influence on the temperature field of the battery.When the air-cooling flow rate was 0.05,0.2 and 0.3 m/s,respectively the temperature functions of the battery changed less than 1%during the discharging process.However,when the air flow rate was 0.1 m/s and the lithium battery was discharged to 729 s the temperature field of the convective heat transfer coefficent considering the temperature factor decreased by 21.71%compared to the temperature field at the constant.This effect law was consistent with the variation of convective heat transfer coefficients with temperature at different flow rates.It also showed that the convective heat transfer coefficient was related to both flow rate and temperature.Moreover,the larger the convective heat transfer coefficient,the easier the lithium battery exchanged heat with outside air,and the smaller the temperature difference during the discharging of the battery.