Microgravity experiments and analysis of oscillatory thermocapillary flows in cylindrical containers

Results are reported of thermocapillary flow experiments performed aboard the Spacelab. Oscillatory thermocapillary flows were investigated in open cylindrical containers filled with 2 cS kinematic viscosity (Prandtl number = 27 at 25 degrees C) silicone oil. The fluid was heated by a cylindrical cartridge heater placed at the symmetry axis of the container while the container sidewall was maintained at a lower temperature. Test containers with three different diameters of 1.2, 2.0 and 3.0 cm were used. The ratio of heater to test container diameter was fixed at 0.1. The liquid free-surface shape was either flat or concave. The now and temperature fields were investigated for steady and oscillatory flows. Free-surface deformation was observed during oscillations. The conditions for the onset of oscillatory flow were determined. It is shown that the Marangoni number alone does not correlate the onset conditions. A new parameter, which represents free surface deformation, is derived for Rat free surfaces and is shown to correlate the onset conditions well. Infrared images of free surface and oscillation frequencies are also presented.