相变微胶囊功能流体相变区间的影响因素和变化趋势分析

相变微胶囊功能流体所具有的相变区间是影响其强化传热效应和工程应用价值的主要因素。采用双流体数学模型通过数值模拟发现:在层流条件下,双流体模型能够很好地模拟颗粒相体积分数、管径和R e对相变区间的影响。功能流体的相变段长度和总吸热量都随着这三个因素的增大而显著增大。同时相变段长度还取决于入口温度和边界条件等因素。以直链烷烃为相变材料的功能流体在相变段的蓄热能力相近。但在同R e下,功能流体的相变段长度和总吸热量都随着囊芯材料相变温度的升高而减小。入口温度是影响相变材料熔化速度的重要因素。相变段的长度、总温升和总吸热量与流体入口过冷度都呈线性关系。在第一类边界条件下,相变段长度与壁面过热度呈指数为负的幂指数关系,而相变段总温升和总吸热量都随壁面过热度的增大而增大。

Analysis of influential factors on heat transfer in phase-change region for MCPCM slurry

The phase-change process for the microencapsulated phase-change material(MCPCM) slurry is the key factor affecting the heat transfer enhancement and the engineering application.In this paper,the Euler-Euler model was used to numerically analyze the influences of the particle volume fraction,the diameter of tube and the Reynolds number on the phase-change region.It is found that the length and the total heat absorption of the phase-change region increased significantly with the increasing of these three factors.The length of the phase-change region is also affected by the inlet temperature and the boundary conditions.The heat storage capacity of MCPCM slurry is almost the same,but the length and the total heat absorption in the phase-change region of the slurry will decrease with the increase of the phase-change temperature of the core metrical in the same Re Number.The inlet temperature is one of the most important factors to dominate the melting rate.The length as will as the temperature raise and total heat absorption of the phase-change region increase linearity with the entrance super-cooling of the slurry.In the constant temperature boundary conditions,the length of the phase-change region can meet the super-heat temperature of the wall in power curve,and the temperature raise and total heat absorption of the phase-change region will increase with increasing of the super-heat temperature of the wall.