梯度孔隙率泡沫金属复合相变材料蓄热过程研究
发布时间：2018-08-17 10:50
【摘要】：在能源危机的背景下,新能源汽车得到了世界各国政府的大力支持并得到迅猛的发展。大容量锂离子电池作为电动汽车的动力核心,其性能的优劣在很大程度上决定了电动汽车的性能,因此对锂离子电池工作性能的研究尤为重要。温度是影响锂离子电池工作的重要因素之一。合理的温度范围能够提高电池的输出性能,延长电池的使用寿命,因而需要对电池进行有效的热管理。相变蓄热具有蓄热密度大、结构简单、无耗能、体积小和温度变化小等优点,因此具有良好的发展前景。本文根据电动汽车电池系统的发热情况,搭建泡沫铝-石蜡复合相变材料蓄热可视化实验台,对泡沫铝-石蜡复合相变材料蓄热系统进行相变界面的移动、温度变化、温差变化的研究。实验结果表明:自然对流会对相变界面的移动产生较大影响,并恶化复合相变材料底部的换热,使得沿热流密度方向上的温差较大,在热流密度垂直的方向上温差较小。根据获得的实验现象和实验数据,对泡沫铝的结构进行调整,优化复合相变材料的蓄热过程。鉴于实验手段有限,本文将重点采用数值模拟方法对复合相变材料的蓄热过程进行研究。根据泡沫铝的实际结构进行简化,建立与实际结构相近的十四面体多孔介质模型,并与实验结果进行对比验证。验证结果表明:模拟结果与实验结果高度一致,这表明简化的多孔介质模型能够很好的反映泡沫铝的真实结构,数值模拟获取结果的可靠性较好。通过多孔介质模型对复合相变材料的相变界面的移动、温度均匀性及蓄热性能进行了研究,针对泡沫金属的孔隙率变化对复合相变材料蓄热过程的影响,并分析了不同均匀孔隙率泡沫铝复合相变材料与孔隙率梯度变化的复合相变材料的蓄热过程。研究结果表明:相变界面的移动受孔隙率的影响较大。孔隙率越大,相变界面的移动与加热面的夹角越明显。孔隙率越大,复合相变材料的温度均匀性越差。孔隙率梯度变化(从底部到顶部,孔隙率呈0.86-0.90-0.94三段式和0.86-0.94线性增大)能有效改善底部传热较差,改善复合相变材料的内部传热,加速相变材料的融化。孔隙率三段式梯度变化和孔隙率线性变化的复合相变材料的内部温差较均匀孔隙率为0.9的复合相变材料的内部温差降低了10.8℃。孔隙率梯度变化的蓄热速率较均匀等效的孔隙率复合材料的蓄热速率提高了142%。另外,研究表明:复合相变材料的热传递主要通过泡沫金属的导热进行传递。
[Abstract]:Under the background of energy crisis, new energy vehicles have been supported by governments all over the world and developed rapidly. As the power core of electric vehicle, the performance of large capacity lithium ion battery determines the performance of electric vehicle to a great extent, so it is very important to study the performance of lithium ion battery. Temperature is one of the important factors that affect the operation of lithium ion battery. The reasonable temperature range can improve the output performance of the battery and prolong its service life, so it is necessary to effectively heat manage the battery. Phase change heat storage has the advantages of high heat storage density, simple structure, no energy consumption, small volume and small temperature change, so it has a good development prospect. According to the heating condition of electric vehicle battery system, a visualized experimental platform for thermal storage of foam aluminum-paraffin composite phase change material is built, and the phase change interface and temperature change are carried out for the thermal storage system of aluminum foam and paraffin composite phase change material. The study of the variation of temperature. The experimental results show that natural convection will have a great effect on the movement of phase transition interface, and worsen the heat transfer at the bottom of the composite phase change material, which makes the temperature difference along the direction of heat flux larger and the temperature difference smaller in the vertical direction of heat flux. According to the experimental phenomena and experimental data, the structure of aluminum foam was adjusted to optimize the heat storage process of composite phase change materials. In view of the limited experimental means, the numerical simulation method will be used to study the heat storage process of the composite phase change materials. According to the actual structure of aluminum foam, a decahedron porous media model is established, which is similar to the actual structure, and the results are compared with the experimental results. The results show that the simulation results are in good agreement with the experimental results, which indicates that the simplified porous media model can well reflect the true structure of aluminum foam, and the reliability of the numerical simulation results is good. The movement, temperature uniformity and heat storage performance of phase change interface of composite phase change materials were studied by porous media model. The effect of porosity change on the heat storage process of composite phase change materials was studied. The heat storage process of aluminum foam composite phase change material with different uniform porosity and composite phase change material with different porosity gradient was analyzed. The results show that the movement of phase change interface is greatly affected by porosity. The larger the porosity, the more obvious the angle between the movement of phase change interface and the heating surface. The larger the porosity, the worse the temperature uniformity of the composite phase change material. The change of porosity gradient (0.86-0.90-0.94 three-stage porosity and 0.86-0.94 linear increase from bottom to top) can effectively improve the poor heat transfer at the bottom, improve the internal heat transfer of the composite phase change material, and accelerate the melting of the phase change material. The internal temperature difference of the composite phase change material with three-segment gradient of porosity and linear variation of porosity is 10.8 鈩，
本文编号：2187371
[Abstract]:Under the background of energy crisis, new energy vehicles have been supported by governments all over the world and developed rapidly. As the power core of electric vehicle, the performance of large capacity lithium ion battery determines the performance of electric vehicle to a great extent, so it is very important to study the performance of lithium ion battery. Temperature is one of the important factors that affect the operation of lithium ion battery. The reasonable temperature range can improve the output performance of the battery and prolong its service life, so it is necessary to effectively heat manage the battery. Phase change heat storage has the advantages of high heat storage density, simple structure, no energy consumption, small volume and small temperature change, so it has a good development prospect. According to the heating condition of electric vehicle battery system, a visualized experimental platform for thermal storage of foam aluminum-paraffin composite phase change material is built, and the phase change interface and temperature change are carried out for the thermal storage system of aluminum foam and paraffin composite phase change material. The study of the variation of temperature. The experimental results show that natural convection will have a great effect on the movement of phase transition interface, and worsen the heat transfer at the bottom of the composite phase change material, which makes the temperature difference along the direction of heat flux larger and the temperature difference smaller in the vertical direction of heat flux. According to the experimental phenomena and experimental data, the structure of aluminum foam was adjusted to optimize the heat storage process of composite phase change materials. In view of the limited experimental means, the numerical simulation method will be used to study the heat storage process of the composite phase change materials. According to the actual structure of aluminum foam, a decahedron porous media model is established, which is similar to the actual structure, and the results are compared with the experimental results. The results show that the simulation results are in good agreement with the experimental results, which indicates that the simplified porous media model can well reflect the true structure of aluminum foam, and the reliability of the numerical simulation results is good. The movement, temperature uniformity and heat storage performance of phase change interface of composite phase change materials were studied by porous media model. The effect of porosity change on the heat storage process of composite phase change materials was studied. The heat storage process of aluminum foam composite phase change material with different uniform porosity and composite phase change material with different porosity gradient was analyzed. The results show that the movement of phase change interface is greatly affected by porosity. The larger the porosity, the more obvious the angle between the movement of phase change interface and the heating surface. The larger the porosity, the worse the temperature uniformity of the composite phase change material. The change of porosity gradient (0.86-0.90-0.94 three-stage porosity and 0.86-0.94 linear increase from bottom to top) can effectively improve the poor heat transfer at the bottom, improve the internal heat transfer of the composite phase change material, and accelerate the melting of the phase change material. The internal temperature difference of the composite phase change material with three-segment gradient of porosity and linear variation of porosity is 10.8 鈩，
本文编号：2187371
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