Heat and Mass Transfer of Freezing of Melting Process of Soil Containing Sea Water

土壤作为热泵系统的热源和冷能带是一种有用的材料。对于包括潜热在内的热能储存在含有海水的土壤中的情况，研究饱和了氯化钠水溶液的多孔介质的冻结或融化过程是很重要的。在本文中，考虑地下水流动或涨落，从解析和实验两方面研究了自然对流和强迫对流对饱和3wt%氯化钠水溶液多孔介质中水平圆柱体周围冻结的影响。在实验中，使用玻璃微珠填充床作为多孔介质。为了弄清自然对流和强迫对流的相互作用，通过不同流量的多孔介质，使溶液沿圆柱体向上或向下流动。通过将钢瓶冷却到共晶温度以下，开始了钢瓶周围的冻结。为了可视化冻结层周围的相互作用流动，进行了Hele-Shaw流动中圆柱体周围的冻结实验。数值分析中同时考虑了液体和糊状区的热、质扩散和流动。分析得到的温度分布与实验结果吻合较好。阐明了自然对流和强迫对流对凝固过程的影响-温度分布、流函数等值线、冻结区形状、糊状区液体体积分数和固相区共晶体积分数。阐明了Peclet数和流动方向对Nusselt数和固相无因次体积的影响。

Soil is one of useful materials as a heat source for a heat pump system and as a cold energy strage. For a case that thermal energy including the laten heat is stored in soil containing sea water, it is important to study a freezing or melting process of a porous medium saturated with a NaCl - aqueous solution. In the present report, considering ground water flow or the ebb and flow, effects of natural and forced convection on the freezing around a horizontal cylinder in a porous medium saturated with 3 wt% NaCl aqueous solution was investigated analytically and experimentally. In the experiments a packed bed of glass beads was used as the porous medium. In order to clarify an interaction of natural convection and forced convection, the solution was let to flow upwardor downwared across the cylinder through the porous medium with various flow rates. By cooling the cylinder below the eutectic temperature the freezing around the cylinder was initiated. In order to visualize the interactive flow around the frozen layr, and experiment of freeaing around a cylinder in Hele-Shaw flow was carried out. A numerical analysis, in which heat and mass diffusions and flow in both liquid and mushy regions were taken into account, was carried out. The temperature distributions obtained from the analysis agreed well with the experimental results. Effects of the natural and forced convection on the freezing process --- the temperature distribution, the stream function contour, the shape of frozen region, the volume fraction of liquid phase in the mushy region, and the volume fraction of eutectic solid in the solid region --- were clarified. Effects of Peclet number and the flow direction on Nusselt number and a dimensionless volume of the solid phase were clarified.