THERMOCAPILLARY INTERACTION BETWEEN A SOLID PARTICLE AND A LIQUID-GASINTERFACE

When a hot solid particle is submerged into an ambient fluid near a fr ee liquid-gas interface, a non-uniform temperature field around the pa rticle produces surface tension gradients at the interface and generat es thermocapillary how in the surrounding fluid. This flow sets the pa rticle itself in motion towards or away from the interface. In the fir st part of the paper, the interaction between a hot spherical solid pa rticle and a plane undeformable liquid-gas interface is studied. The v elocity of the thermocapillary induced motion of the solid particle is proportional to the surface tension gradient at the liquid-gas interf ace, and is calculated in the approximation of the Stokes how and a ze ro Peclet number as a function of the separation distance between the particle and the interface. The asymptotic cases of both small and lar ge separation distances are studied. In the second part of the paper, the interaction between a hot solid sphere and a gas bubble submerged into an ambient fluid is studied in the limiting case when the separat ion distance between them tends to zero. The velocity of a pairwise mi gration of a particle and a bubble in contact is calculated as a funct ion of their radius ratio. The asymptotic values of the individual vel ocities of a solid particle and a gas bubble in near contact are also computed. The relative velocity of their motion towards each Ether is found to be proportional to the separation distance between them. In t he third part of the paper, we investigate the effect of gravity on th e thermocapillary driven motion of a solid particle for the two cases. It is shown that due to the thermocapillary interaction, a particle c an move against the buoyancy forces. (C) 1997 American Institute of Ph ysics.