The Bénard-Marangoni-Instability in small circular containers under microgravity: Experimental results

Abstract

During the 12-minute microgravity-phase of the sounding rocket MAXUS 2 a 3.0-mm-thick layer of 10 cSt silicone oil was heated from below to generate the Bénard-Marangoni-Instability (BMI) due to surface tension forces in the free oil surface. The layer was partly covered with a solid lid from Polycarbonate (LEXAN) with circular openings with diameter D for a flat free oil surface with aspect ratio A= D/d= 1.0, 1.5, 2.0, 3.0, 4.0, 8.0, 10.0. The flow structure in these 7 “containers” with liquid lateral walls was visualized by aluminum flakes which orient parallel to the flow direction. The BMI was clearly observed under microgravity, and the onset of convection as function of A was measured and compared to theory and ground-based experiments, of which the latter suffer under the additional action of buoyancy. Beautiful and sharp convection patterns have been observed in the containers A = 4, 8, and 10. At the end of the microgravity time an instability of the boundary between two convection cells in the container with A= 4 was observed (switching between modes (2,1) and (1,1)).