Rewetting velocity in quenching at reduced gravity

The results of quenching tests in tubes at microgravity and normal gravity conditions are presented. The aim of the experimental campaign was to gather both quantitative data and direct observations regarding phenomena involved in the rewetting of tubes. The rewetting velocity at different refrigerant flow-rate and subcooling conditions is obtained from experimental data. Test sections are made of Pyrex tubes with three different inner diameters: 2.0 mm, 4.0 mm and 6.0 mm. They are coated with Indium-Tin-Oxide (ITO), which is transparent but allowing the direct heating of the Pyrex tube. Tests are performed with vertical test section and downward liquid flow. The working fluid is FC-72, a fluorinert liquid. Measurements included wall temperatures along the flow channel, inlet and outlet temperatures, pressures and mass flow-rate. The 6.0 and 2.0 mm tubes show a significant decrease in the quenching velocity at reduced gravity and a dependence on the coolant mass flow-rate, especially for ground experiments. The results of the 4.0 mm tube show a contradictory behaviour in micro/normal gravity comparison.