Experimental Observation of the Thermocapillary Driven Motion of Bubbles in a Molten Glass Under Low Gravity Conditions

Abstract

ABSTRACTTheory and ground based studies of bubble behavior in a fluid in the presence of a temperature gradient strongly indicate the action of a thermocapillary force which causes the bubbles to move. This'phenomenon been considered in the traditional treatments of glass fining. To demonstrate that the observed motion conformed to theoretical prediction it was necessary to perform the experiment under low gravity conditions. NASA's SPAR program provided an excellent opportunity to do this.A sodium borate melt containing a specific bubble array was subjected to a well defined temperature gradient for more than 4 minutes. The sample was contained in a platinum/ fused-silica cell which permitted photographic coverage of the experiment. Photographs were taken at one second intervals during the course of the experiment. They clearly show that the bubbles move toward the hot spot on the platinum heater strip. The observed motion is consistent with the theoretical predictions for the temperature gradients parallel and perpendicular to the heater strip.