Flat plate pulsating heat pipe with self-rewetting fluids in parabolic flight condition

This article reports the results of experiments carried out on board a 'zero-g' plane during the 65th Parabolic Flight Campaign of the European Space Agency. A Flat Plate Pulsating Heat Pipe filled with ordinary liquid (water) and self-rewetting mixture (dilutes aqueous solutions of long-chain alcohols with unusual surface tension behaviour) is investigated under variable gravity conditions. The experimental setup includes a transparent plate enabling the visualization of the oscillating flow pattern during the experiments. The thermal performances in terms of temperatures, start-up levels and flow regimes have been characterized for the two working fluids and for a power input ranging from 0 to 200W. The most important results show that, even for low power input, the heat pipe filled with pure water is not able to work under low-g conditions, because the evaporator immediately exhibits dry-out conditions. During the low-g period, the evaporator became completely dry and the oscillations stopped, preventing heat transfer between the hot and cold side and resulting in increased temperatures. On the other hand, the heat pipe filled with self-rewetting fluid still operated during the microgravity phase. Under some conditions, the liquid rewets several times the evaporator zone triggering the oscillatory cycle. The results are discussed and the phenomenon is explained on the basis of the different surface properties at the slug-vapour interfaces.