Investigation of thermocapillary convection in a three-liquid-layer system

This paper presents the first experimental results on Marangoni-Bi nard ins tability in a symmetrical three-layer system. A pure thermocapillary phenom enon has been observed by performing the experiment in a microgravity envir onment where buoyancy forces can be neglected. This configuration enables t he hydrodynamic stability of two identical liquid-liquid interfaces subject ed to a normal gradient of temperature to be studied. The flow is driven by one interface only and obeys the criterion based on the heat diffusivity r atio proposed by Scriven & Sternling (1959) and Smith (1966). The measured critical temperature difference for the onset of convection is compared to the value obtained from two-dimensional numerical simulations. The results of the simulations are in reasonable agreement with the velocimetry and the thermal experimental data for moderate supercriticality. Numerically and e xperimentally, the convective pattern exhibits a transition between differe nt convective regimes for similar temperature gradients. Their common detai led features are discussed.