INSTABILITY OF THERMOCAPILLARY CONVECTION IN LIQUID BRIDGES

It is well known that thermocapillary convection arises in liquid brid ges when the support discs are heated differentially and uniformly. Up on increasing the temperature difference, the convective flow shows a transition from an axisymmetric to an oscillatory regime. This phenome non has been investigated both experimentally and theoretically, but p rior experimental results exhibit some discrepancies with respect to t he predictions of stability analyses. The present paper discusses expe rimental results obtained under microgravity conditions, comparing the m with previous experimental observations made on ground and in space and with recent theoretical models of the instability. The results agr ee with the description of oscillations in terms of superposition of h ydrothermal waves. Finally, a possible mechanism for a ''pulsating'' i nstability is proposed, together with a new scaling law for the oscill ation frequencies at onset; this law, which correlates the critical fr equency to the fluid properties, the geometrical parameters and the cr itical temperature difference, agrees with all the available experimen tal data. (C) 1998 American Institute of Physics.