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 °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 flow 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 flat free surfaces and is
shown to correlate the onset conditions well. Infrared images of free surface and
oscillation frequencies are also presented.