关键词: 过冷度, 多孔介质, 统计方法, 热导率

Abstract:

In order to study the effects of bead-packed porous structure, balls of different materials such as aluminum, stainless steel and glass with different diameters of 5, 8 and 11 mm are added into distilled water forming porous media. Since the supercooling degree of water is not a certain value, the experiments are repeated many times at the same cooling condition and analyzed with statistical methods. The results show that the distribution of the supercooling degree of distilled water in porous media is more concentrated than that of pure distilled water and the supercooling degree of water in porous media is smaller. The average supercooling degree of distilled water decreases with decreasing diameter of the same material balls on the whole. The larger the thermal conductivity of solid substrate is, the more concentrated the distribution of supercooling degree of distilled water in porous media and the smaller the average supercooling degree. In addition, the heterogeneous nucleation is more likely to occur when the thermal conductivity of the solid substrate is small. An annulus solid ice begins to grow slowly from the inside wall to the center region and the phase change time is longer than homogeneous nucleation. Once the crystal nucleus is formed, it will grow up instantly, forming the loose ice of homogeneous nucleation. Therefore, the heterogeneous nucleation should be avoided in engineering application.

Key words: supercooling degree, porous media, statistical methods, thermal conductivity