Pure thermocapillary convection in a multilayer system: First results from the IML-2 mission

Abstract

The first experimental results on pure thermocapillary convection in a multiplayer system are presented. The Marangoni-Bénard instability in a symmetrical three layer system has been investigated during a six hours experiment which flew on the IML-2 mission June 1994. The system studied consisted of a silicone layer sandwiched between two identical Fluorinert layers. The thermal gradient applied perpendicular to the two free interfaces was up to five times the critical value for the onset of the Marangoni-Bénard instability in this configuration. The preliminary analysis of the experimental data, video recording and thermistor values, indicates that most of the scientific objectives have been met. The mechanical stability of a three layer system in microgravity has been achieved taking advantage of the differential wetting properties of the liquids. Valuable informations on the management of liquid/liquid interfaces in space have been gained. The critical temperature difference for the onset of convection has been estimated and is compatible with the results of a linear stability analysis. Digital image processing of some video sequences confirms the prediction of the numerical simulations showing that in this case the hot interface is driving the convective flow. The absolute amplitude of the velocity of the free interface is in good agreement with values obtained numerically.