Elucidation of the Shark Skin Phenomena Appeared in the Melting of an Ice Plate with a Temperature and Concentration Combined Effect

对方形空腔内水平冰板从上方溶入氯化钙水溶液的过程进行了实验和数值研究。将温度为-5℃的a20wt %氯化钙混合物倒入底部水平放置-5℃冰板的空腔中。在融化锋附近出现浓度梯度的驱动下，冰板块融化。熔化表面很快出现了一层浓度扩散层。由于吸收了熔化潜热，熔化表面温度降低。随着熔化锋温度的降低，扩散层厚度在熔化过程中逐渐增大。当扩散厚度达到小于1mm的临界值后，由于低密度熔体水的浮力作用，扩散层中出现了许多小的低密度液体羽流。羽流之间的距离约为1毫米。上升羽流的出现导致了高浓度的向下液体流动。因此，向下流动导致冰的融化增强。另一方面，由于液体浓度较低，在向上流动（即羽流）的位置，冰融化得较慢。这些融化速度的局部差异造成了粗糙的表面，就像一个“山和谷”（即鲨鱼皮）。在融化过程中，鲨鱼皮的“山谷”结构在融化前沿的位置基本没有变化。然而，一个较小的山谷很快就被周围较大的山谷侵蚀而消失了。

Experimental and numerical investigation were carried out of the melting of a horizontal ice plate from above into a calcium chloride aqueous solution inside the square cavity. A20 wt % calcium chloride mixture at the temperature of -5℃ poured into the cavity in which an ice plate in the temperature of -5℃ was located horizontally at the bottom. The ice plate melted with a driving force of the concentration gradient appeared near the melting front. A diffusion layer of the concentration soon appeared on the melting surface. The temperature of the melting surface decreased due to the absorption of the latent heat for melting. The thickness of the diffusion layer increased during the melting process along with the temperature depression of the melting front. After the diffusion thickness reached a critical value less than 1mm, many small plumes of low density liquid appeared from the diffusion layer due to the buoyancy of the low density melt water. The distance among the plumes was about 1mm. The appearance of the upward plumes caused the downward liquid flow of high concentration. Therefore, the downward flow caused the enhancement of the melting of ice. On the other hand, the ice melted more slowly at the locations of the upward flow (i.e., plumes) due to the low concentration of the liquid. These local differences of the melting rates caused the rough surface like a "mountain and valley" (i.e., a shark skin). The locations of the "mountain and valley" structure of a shark skin at the melting front basically did not vary during the melting process. However, a smaller valley soon disappeared eroded by the around larger valleys.