VISUAL STUDY OF FLUID DYNAMICS IN WICKLESS TRANSPARENT HEAT PIPES

Though heat pipes are recognized as viable heat transfer devices for many different applications, the thermal mechanisms driving the heat transfer are still not fully understood. By fabricating and testing a fully transparent, sapphire heat pipe, with water as the working fluid, the dominant mechanisms of boiling and condensation were visualized. The results of this investigation suggest that for low operating pressures there is a complex geyser boiling regime occurring in the evaporator section at lower powers (~20 W). Through all power levels slugs of water and plugs of vapor were observed, similar to a pulsating heat pipe. The regime shifted towards more explosive boiling at higher powers (~70 W). These phenomena were observed using high speed imaging and the corresponding local temperature data.