Experimental Investigation of Capillary-Driven Two-Phase Flow in Water/Butanol under Reduced Gravity Conditions

The capillary flow of water/butanol mixture is investigated in a single groove heat pipe model on board the Airbus A310 ‘Zero-G’ of the European Space Agency. As working fluid for evaporation-based heat transfer devices like conventional or pulsating heat pipes, these kinds of mixtures give more stable behaviour and higher dry-out limit with respect to pure water because of an anomalous behaviour of the surface tension with temperature. The groove is embedded in a semi-transparent test cell that allows for the qualitative visualization of the liquid distribution along the channel and is heated and cooled at two opposite sides with an electrical resistance and a water circulation system. The evaporation/condensation process is regulated changing the power input in a range between 5 and 30 W and the liquid distribution is detected from a top window using a CCD camera and a LED illumination device. The results show that the liquid distribution is affected by the gravity level and this effect is normally masked on ground.