Visualization and evaporator resistance measurement for a groove-wicked flat-plate heat pipe

This work experimentally studied the evaporation characteristics in a groove-wicked flat-plate heat pipe charged with water. The parallel, U-shaped grooves had a width of 0.25 mm and a depth of 0.16 mm. Uniform heating was applied to the copper base plate near one end, and a cooling water jacket was connected at the other end. The evaporator resistance was calculated based on the difference of the plate temperature and the vapor temperature respectively under and above the center of the heated zone. With stepwise increase of heat load, the behavior of the working fluid in the grooves was visualized and the evaporator resistances were measured. Above a certain heat load, longitudinal liquid recession with a steep-sloped liquid front could be visualized. Behind the short liquid front is the accommodation region where the meniscus appeared to anchor on the top corners of the groove walls. Under a thermally stable situation, independent longitudinal oscillations of the liquid front existed in different grooves, forming a constantly varying zigzag front line. With increasing heat load, the liquid fronts gradually left the heated zone, accompanied by increasing plate temperatures. The evaporator resistance first remained at a low value before local dryout appearing beyond a certain heat load and then increased in a growing pace in response to the expanding dryout zone. No boiling was observed in all present tests.