圆柱腔体内水凝固过程热对流实验研究

本文通过匹配折射率和标定技术,应用PIV测量了圆柱腔体内水在底部冷却过程中热对流的变化规律．实验发现了主流场的涡结构;另外在底部拐角处出现新的涡,并且不断向上推移;冷却后期整个液相区出现流动反转现象,靠近壁面处水向上流动,中心区域水向下流动。因为存在着复杂的热交换和密度变化,水在凝固过程中存在流动结构失稳,使得液相区内发生强烈的热对流．最后流动强度减弱,重新形成稳定结构。结合泰勒不稳定性分析,本文对这一过程给出了合理解释．

EXPERIMENTAL STUDY OF THERMAL CONVECTION DURING THE WATER SOLIDIFICATION PROCESS IN CYLINDER CAVITY

The thermal convection in cylindrical cavity during the solidification of water was studied by PIV with the techniques of refractive index matching and calibration under the condition that water was cooled at bottom. There was a vortex structure in the main liquid region. During the solidification process, a new small vortex flow occurred on the corner of cavity bottom and moved upward gradually. The original direction of vortex was reversed in liquid region at the final stage of cooling. The water which was close to the sidewalls flowed upward, and in the center region the water flowed downward. Instability of flow due to complex heat exchange and density variation leads to strong thermal convection in liquid region during the water solidification process. At the end of solidification process, intensity of flow decayed and the stable structure was rebuilt. This phenomenon was explained by Taylor instability analysis.