Fundamental research on storage process of ice/water mixtures for effective ice thermal energy storage

研究了多孔冰/水混合物在融点条件下储存过程中渗透率的变化规律，以及渗透率随冰颗粒类型和压缩力的变化规律。实验中使用由切片冰、半球冰和碎冰构成的多孔介质进行，并测量了样品在0℃下储存在罐中的混合物之前和之后的渗透性。通过储存24小时，切片冰和压缩碎冰增加了渗透性。然而，半球形的冰块却没有任何变化。研究了冰粒的形态。测量储存前后的比表面。在0℃水槽中放置24 h后，冰粒的形态发生了变化。表面形貌由粗糙变为圆整、光滑，比表面积减小。采用Kozeny Charman方程计算Kozeny常数。结果发现，该常数减小，并达到一个值的光滑球，无关的孔隙率和冰粒的大小。因此，可以得出结论，颗粒上的尖锐边缘和粗糙表面转化为更光滑的表面导致比表面积和Kozeny常数的降低，并且其导致渗透性增加。此外，还对压缩进行了研究。每次实验都测量了冰包装高度的时间变化。结果表明，压缩粘度与孔隙度之间存在一定的相关性，且与时间无关。利用该关联式，估算了大型冰/水储热箱的孔隙率和渗透率分布，并阐明了总有效渗透率随时间变化，与平均孔隙率估算值不同。

The purpose of the research was to study how porous ice/water mixture changes its permeability during storage under the condition of melting point, and how those change vary with types of ice particles and compressive force. Experiments were performed using porous media constructed with sliced ice, semispherical ice and frazil ice, and the permeability of the samples were measured before and after storing the mixture in a tank where the samples were kept at 0℃. The sliced ice and compressed frazil ice increased the permeability by storing for 24 hours. However, the semispherical ice had no change. Morphology of the ice particle was investigated. Specific surface before and after the storage was measured. It was found that the morphology of ice particle changed by storing for 24 hours in 0℃ of water tank. The shape seems to be changed from rough surface into round and smooth, and the specific surface decreased. Kozeny constant was calculated using Kozeny Charman equation. It was found that the constant decreased and reached to a value for smooth sphere, independent on the porosity and the size of ice particles. Hence, it was concluded that transformation of sharp edges and rough surfaces on the particles into smoother surfaces causes the decrease in specific surface and Kozeny constant, and it leads to increase the permeability. Furthermore, study on compression was carried out. Time variation of height of ice packing was measured for each experiment. It was found that there is a correlation between viscosity of compression and porosity, and it is independent on time. Using the correlation, distribution of porosity and permeability in a large ice/water heat storage tank was estimated, and it was clarified that the total effective permeability changes with time and it differs from the value estimated using the average porosity.