Abstract: Visual experimental studies were conducted on the condensation process of a gravity-assisted heat pipe with electrical capacitance tomography (ECT) technology. The heat pipe was made of silica glass, and alcohol was used as working fluid. The heating temperature of its evaporation segment was controlled by a heater with different power outputs. The alcohol vapor in the condensation segment was cooled to condense through heat convection with cooling water. The condensation process of alcohol vapor was monitored by an ECT measurement system to observe the distribution characteristics of liquid and its vapor, and the formation and development of liquid film on the wall of the heat pipe. Considering the access limitations of the structure of the condensation segment, the traditional structure of the ECT transducer was changed. The shielding case was abandoned, and the measuring electrodes were sealed with insulating hydrophobic layer. This method made it possible to permit the transducer to be used in a liquid environment, and effectively expand the application fields of ECT technology. Alcohol vapor condensed in strips and unevenly on the wall surface when heating temperature of the evaporation segment was low. With increasing heating temperature, the condensing liquid would change to annular flow around the whole circumference. When heating temperature exceeded a specified limit, a kind of cyclical phenomenon happened. The liquid film gradually became thicker and even occupied the whole cross section of the heat pipe, and then fell off. This phenomenon occurred repeatedly, and its frequency increased with increasing heating temperature. When the gravity heat pipe was inclined 30° from the vertical direction, the same phenomenon appeared when heating temperature was 110℃.

Key words: evaporation, condensation, tomography, gravity-assisted heat pipe, condensation segment, visualization

摘要： 应用电容层析成像技术（ECT）对重力热管冷凝段的流动换热进行了可视化实验研究。重力热管以乙醇为工作介质，通过加热器控制重力热管蒸发段加热温度，冷凝段采用冷却水与乙醇蒸气进行逆向对流换热。通过ECT测量系统对冷凝段乙醇蒸气的冷凝过程进行监测，观察不同工况条件下重力热管冷凝段的气、液分布特性和液膜的形成及发展过程。摒弃了传统电容传感器的屏蔽罩结构，通过将测量电极用绝水层密封实现了传感器在液下环境工作，有效地拓展了ECT技术的应用领域。实验结果显示：当蒸发段加热温度较低时，乙醇蒸气在冷凝段壁面凝结形成条索状流动；随加热温度升高，冷凝液流动过渡至环状流；加热温度超过一定限值后，冷凝段出现液膜增厚甚至闭合脱落的周期性现象，并且频率随温度升高而升高。重力热管与垂直方向夹角为30°倾斜放置时，在高加热温度条件下同样存在液膜增厚甚至闭合脱落的周期性现象。

关键词: 蒸发, 凝结, 成像, 重力热管, 冷凝段, 可视化