Microgravity experiments on phase change of self-rewetting fluids.

A series of microgravity experiments on self-rewetting fluids has been conducted at the 10-second drop shaft of the Japan Microgravity Center (JAMIC). In all the experiments, 1.5 wt% of 1-butanol aqueous solution were employed as a self-rewetting fluid. The objective of the first experiment was to observe the boiling behavior of two-dimensional adjacent dual vapor bubbles with the aid of a two-wavelength interferometer and tracer particles. A significant difference was observed between a self-rewetting fluid and a normal fluid (CFC-113 in this experiment) in bubble interaction and flow developed along vapor/bubble interface. The second experiment focused on the flow at the bubble/heater contact area and around the three-phase interline, visualized with tracer particles. Differing behavior among three fluids, 1-butanol aqueous solution, CFC-113, and ethanol aqueous solution, was observed. The last microgravity experiment was a demonstration of wickless heat pipes containing three different fluids as a working fluid, 1-butanol aqueous solution, water, and ethanol aqueous solution. The temperature variation of working fluid in the heat pipe was monitored, and the liquid flow returning from the condensation region to the evaporation region was visualized by tracer particles. In addition to microgravity experiments, the performance of conventional heat pipes with 1-butanol aqueous solution was evaluated on the ground, and compared with water heat pipes. Our preliminary results are presented.