方形动力锂电池CPCM/翅片液冷式散热系统性能优化

Optimization on heat dissipation performance of prismatic power lithium battery based on cooling system of CPCM/liquid-cooled with fin

为了降低方形锂电池在高温、高倍率放电下的最高温度和温差,提出了一种复合相变材料(CPCM)/翅片液冷式复合冷却结构。对提出的电池热管理系统进行了3 C放电工况下的数值模拟,分析了CPCM中膨胀石墨(EG)质量分数、冷却液流速及入口温度对系统散热性能的影响规律。结果表明:12%EG质量分数的CPCM表现出良好的散热性能,继续增大质量分数对最高温度及温差几乎没影响。增大冷却液流速降低了电池最高温度,但是也增加了电池温度的不均匀性。考虑到流速对CPCM液相率影响,流速为0.022 m/s已满足散热需求。当入口温度为40℃时,CPCM与液冷的协同效率更好,最大温差达到最小值,仅为2.78℃。

Lithium-ion battery has become the most potential power battery with its good comprehensive performance, but poor heat dissipation would cause heat serious safety problem, especially under high temperature and a high charge or discharge rate. Therefore, it is essential to establish a reasonable and efficient battery thermal management system. In order to ensure the safety of a prismatic lithium battery with a rated capacity of 25 Ah at a high ambient temperature and high discharge ratio, a composite heat dissipation structure is proposed, which combines phase change material(CPCM) and liquid cooling using some channels with fins. Based on the structural design and computational fluid dynamics, a three-dimensional geometric model of the battery module is established and the heat transfer model of the lithium battery, mathematical model for PCM and coolant are analyzed. Under the conditions of the ambient temperature of 40 ℃ and the natural convection coefficient of 5 W/(m^(2)·K), the mesh independence of proposed heat dissipation model is verified. And then, under 3 C discharge rate, the effects of the different expansion graphite(EG) mass fraction(0%, 6%, 9%, 12%, 20%, 30%), coolant flow rate(0.014~0.026 m/s) and coolant inlet temperature(32, 34, 36, 38, 40 ℃) on heat dissipation performance are investigated. The results show that the increase mass fraction of EG significantly reduces the maximum temperature of the battery. When the mass fraction of EG is less than 12%, the highest temperature and temperature difference change significantly;when more than 12%, the temperature improvement is not obvious. The flow rate of coolant has a great influence on the maximum temperature of the battery. With the increase of the flow rate of coolant, the maximum temperature of the battery gradually decreases. When the flow rate is 0.022 m/s, the heat dissipation structure meets the heat dissipation requirements, and the highest battery temperature is 46.85 ℃. The coolant inlet temperature is also an important factor affecting the heat dissipation performance. Its value is directly proportional to the change of the maximum temperature of the battery and inversely proportional to the change of the temperature difference of the battery. the coolant inlet temperature of 40 ℃ is the best. Finally, in order to explore effects of the mass fraction of EG, the coolant flow rate and the cooling liquid inlet temperature on the heat dissipation of the battery, and antest indicators, the Range of each factor is compared. It is found that the effect rules of the factors on the two test indicators are consistent. The range corresponding to the coolant inlet temperature is the largest, and the range corresponding to the coolant flow rate is the smallest the result indicates, that the coolant inlet temperature has the greatest influence on the maximum temperature and temperature difference of the battery, and the coolant flow rate has minimal influence on the heat dissipation.