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

本研究的目的是研究多孔冰/水混合物在熔点条件下储存过程中渗透性的变化，以及这种变化随冰粒类型和压缩压力的变化。实验使用了由切片冰、半球形冰和脆性冰组成的多孔介质，并在0℃的储罐中测量了样品储存前后的渗透率。切片冰和压缩脆冰通过储存24小时增加了渗透性。然而，半球形的冰层并没有变化。对冰粒的形态进行了研究。测定了贮存前后的比表面积。结果表明，在0℃水箱中放置24小时，冰粒的形态发生了变化。形状由粗糙表面变为圆滑，比表面积减小。用Kozeny-Charman方程计算了Kozeny常数。结果表明，随着冰粒大小和孔隙率的增大，该常数逐渐减小，并达到一个光滑球的值。因此，颗粒表面的锐边和粗糙表面转变为较光滑的表面会导致比表面积和Kozeny常数的减小，从而导致磁导率的增加。此外，还对其压缩性能进行了研究。每次实验都测量了冰芯高度随时间的变化。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。利用该关联式对大型冰水蓄热罐的孔隙率和渗透率分布进行了估算，发现总有效渗透率随时间变化，与用平均孔隙率估算的值不同。

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.