关键词: 蒸发, 凝结, 成像, 重力热管, 冷凝段, 可视化

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