关键词: 相变材料, 纳米材料, 等效介质理论(EMT)模型, 流体体积(VOF)模型, 焓-多孔介质模型

Abstract: The latent heat thermal energy storage can be applied widely in aerospace domain and many other industrial fields. However, phase change materials suffer from low thermal conductivity that constrains their engineering application. Nano materials with high thermal conductivity can effectively improve the thermal conductivity of phase change materials. For simulating the melting process in more detail, the physical properties of paraffin composited with three representative kinds of nano materials were founded based on the Maxwell-Garnett type effective medium theory (EMT). The volume of fluid (VOF) model and the enthalpy-porosity model were coupled to simulate the melting process of the pure paraffin and the paraffin composited with nano diamond (ND), single-walled carbon nanotube (SWCNT) and grapheme nano platelets (GnP) under a constant wall temperature. Meanwhile the volume expansion was taken into account. Numerical calculations show that the natural convection is mainly distributed at the region closed to the solid-liquid interface, the region closed to the heating surface and the region adjacent to air-liquid interface. Among these three kinds of nano materials, GnP is the most promising additive that can enhance thermal conductivity of phase change material. For a fixed GnP loading of volume fraction of 3%, the solid phase heat conductivity coefficient of nanoparticle-enhanced phase change materials increases by 486% compared to that of pure paraffin, and the melting time of phase change materials decreases by 69%. Meanwhile, the melting process of the nano-composite phase change materials can be significantly shortened by raising the temperature of the heating surface.

Key words: phase change materials, nano materials, effective medium theory (EMT) model, volume of fluid (VOF) model, enthalpy-porosity model