Marangoni and buoyant convection in an open cavity under reduced and under normal gravity

We give the first full analysis of the microgravity experiment MKB ( arangoni onvektion im offenen oot) conducted on board of the space shuttle during the D1-mission in 1985, together with that of some ground based experiments on thermocapillary flow in a rectangular liquid volume with free upper surface. Streamlines and velocity profiles under μ-g and l-g are presented and discussed. Strong thermocapillary flow was observed under μ-g after the rupture of a dirt-film suppressing surface tension forces. The Nusselt-number under microgravity due to thermocapillary flow for Ma = 4.6 · 10⁵ is at least Nu = 6 ± 1. Under l-g a separation of the surface tension driven convection roll of hot fluid circulating on top of colder fluid was found for large Ma. The coupling and decoupling of buoyant and thermocapillary forces has been further studied in an experiment varying the temperature gradient along the free surface independently from that in the bulk fluid.