自然对流对套管式相变蓄热器蓄热性能的影响

针对蓄热器内相变材料融化、相变区域自然对流换热过程中蓄热效率不确定问题，以套管式相变蓄热器为基本结构，以添加质量分数为10%膨胀石墨的石蜡作为相变蓄热材料，采用数值模拟的方法研究由重力引起的自然对流对相变蓄热器蓄热性能的影响。结果表明，固液相密度差引起的自然对流对相变蓄热过程有明显的促进作用，数值模拟过程中，考虑与不考虑自然对流时，蓄热器的蓄热时间相差近2倍；不同区域相变材料受自然对流的影响不同，在相变材料融化前期，套管上方由于液相自然对流的影响，融化速率更快。根据蓄热器融化速率和融化状态的特点，通过传热过程理论分析，将融化过程进行分段，可以更加深入地了解蓄热器蓄热过程的机理和规律，为优化蓄热器结构提供理论依据。

Effect of natural convection on heat storage performance of tubular phase change heat accumulator

Aiming at the uncertaity of heat storage efficiency during the melting process of phase-change materials in the heat accumulator and the natural convection heat transfer process in the phase-change region, the influence of natural convection caused by gravity on the heat storage performance of the phase change heat storage was studied by numerical simulation with the tube-type solar phase change accumulator as the basic structure and the paraffin with 10% expanded graphite as the heat storage material. The results show that the natural convection caused by solid-liquid density difference has an obvious promoting effect on the phase change heat storage process. The heat storage time of the heat accumulator considering natural convection is nearly twice that of the heat accumulator without considering natural convection. The influence of natural convection on phase change materials in every region is different. In the early stage of melting of phase change materials, the melting rate above the innertube is faster due to the influence of natural convection of liquid phase. Based on the theoretical analysis and according to the characteristics of the melting rate and melting state of the heat accumulator, the melting process is segmented, which can further understand the heat storage process of the heat accumulator and provide certain theoretical guidance for optimizing the structure of the heat accumulator.