Abstract: Microencapsulated phase change materials (MPCM) have the advantages of high energy storage density and small volume expansion rate. A novel heat transfer working medium, microencapsulated phase change materials suspension, can be obtained by mixing MPCM with single-phase heat transfer working medium and adding nanoparticles. It has the advantages of faster heat transfer rate, higher thermal conductivity and lower pumping power, and has broad application prospects in the field of heat energy storage and transport. In this work, the solid-liquid two-phase flow and heat transfer of microencapsulated phase change materials suspension in a long straight tube are numerically simulated based on OpenFOAM-DEM model. The effects of particle mass fraction, wall heat flux and Re number on the flow and heat transfer characteristics are discussed. The result show that, due to the boundary layer effect, the particle concentration is dense near the wall and sparse in the main stream area, and the uneven distribution of particles in the main stream area gradually increases with the increase of particle mass fraction. When the particle mass fraction is 10wt%, the uneven particle distribution is the most obvious. Because of melting heat absorption and particle perturbation, the particle mass fraction has a significant effect on the temperature distribution and heat transfer enhancement of the suspension. With the increase of the wall heat flux, the change trend of the low temperature region of the suspension in the tube is opposite to that of the particle mass fraction, and the low temperature region is gradually shrinking. In other words, the heat flux has a great influence on the melting rate of the phase change materials. The increase of local Nux number in pipe is not synchronized with the increase of Re number, so the synergistic effect of heat flux, flow rate and particle mass fraction should be considered comprehensively in practical engineering applications.

Key words: phase change microcapsule suspension, OpenFOAM, flow and heat transfer characteristics

摘要： 基于OpenFOAM平台的DEM模型对长直圆管内相变微胶囊悬浮液固-液两相流动与传热进行了数值模拟，对颗粒质量分数、壁面热流密度以及雷诺数等参数在流动与传热特性方面所产生的影响展开了讨论。由于边界层效应，颗粒浓度呈现靠近壁面处大、主流区域小的分布特征，且主流区内颗粒分布不均匀性随颗粒质量分数增大而逐渐增强，当颗粒质量分数为10wt%时，颗粒分布不均匀性最为明显；由于融化吸热和颗粒扰动，颗粒质量分数对悬浮液的温度分布和传热强化具有显著影响；随着热流密度增大，融化区域逐渐向管道轴心延伸；管道内悬浮液局部Nux增大幅度与雷诺数增加幅度不同步，在实际中需要综合考虑热流密度、流速与颗粒质量分数三者的协同效应。

关键词: 相变微胶囊悬浮液, OpenFOAM, 流动传热特性