关键词: 相变蓄热, 无机水合盐, 泡沫石墨, 自然对流

Abstract:

Adding porous media is an effective way to improve the thermal conductivity of PCM and reduce its melting time. By establishing a physical model of inorganic hydrated salt composite phase change material (CPCM) with irregularly distributed porous skeleton, the influences of porosity, pore size, and skeleton shape on thermal storage characteristics were studied numerically. The results demonstrated that the melting rate of CPCM increased with smaller porosity. Under gravity driving force caused by the density difference between solid and liquid CPCM, the natural convection phenomenon was found to promote the melting process. At a porosity of 0.80, the porous skeleton with smaller pore size had a larger surface area, which results in absorption of more heat flux and reduced melting time. CPCM possessing tetrahedral skeletons with a maximum specific surface of 30.02 mm^-1 completed melting in 41 s, which is 13.5 s faster than an icosahedron with a specific surface of 19.93 mm^-1. Although the smaller porosity was beneficial to melting, the heat storage capacity was reduced. According to the numerical results, the determined equilibrium porosity was 0.80, which may help balance the acceleration of the melting rate and heat storage capacity, as well as make the effective thermal conductivity reach 8.07 W/(m·K). Thus, this paper provides a theoretical basis and reference for low-temperature heat storage materials.

Key words: phase change heat storage, inorganic hydrated salt, foam graphite, natural convection