Experimental Observation of the Thermocapillary Driven Motion of Bubbles in a Molten Glass Under Low Gravity Conditions
- PDF / 1,365,202 Bytes
- 10 Pages / 414.72 x 648 pts Page_size
- 111 Downloads / 156 Views
Inc.
MATERIALS PROCESSING IN THE REDUCED GRAVITY ENVIRONMENT OF SPACE Guy E. Rindone, editor
EXPERIMENTAL OBSERVATION OF THE THERMOCAPILLARY
279
DRIVEN MOTION OF BUBBLES IN A
MOLTEN GLASS UNDER LOW GRAVITY CONDITIONS H. D. SMITH AND D. M. MATTOX Westinghouse R&D Center, Pittsburgh, PA 15235 W. R. WILCOX, R. S. SUBRAMANIAN, M. MEYYAPPAN Clarkson College of Technology, Potsdam, NY 13676 ABSTRACT Theory 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 This'phenomenon which causes the bubbles to move. 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 NASA's SPAR experiment under low gravity conditions. 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 The sample was contained in a platinum/ more than 4 minutes. fused-silica cell which permitted photographic coverage of the experiment. Photographs were taken at one second interThey clearly show vals during the course of the experiment. 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.
One of the main benefits of space processing of glass melts is that they can be melted without the use of a container. Accoustic levitation techniques can be employed to position the molten mass in a suitable heating chamber and the entire melting process carried out without the melt ever contacting a solid It surface. Melting without contacting a surface has important consequences. would allow ultrapure melts to be made and hence the attainment of optimal physical and optical properties. Certain glasses which are difficult to form and which tend to nucleate in contact with container walls could readily be Production formed as glasses using the containerless melting techniques [1-3]. of these difficult-to-melt-glasses is expected to open up a whole new class of materials which will find applications as lasers, fibers, and windows, etc. Low gravity melting is not wirhout its problems, however. Processing glass melts in a zero gravity environment will require new methods to remove imperfections such as bubbles from the melt since there will be no buoyancy Bubble formation is a common characteristic of glass manufacture. Gases fill the intergranular voids between the batch grains, while additional gases are liberated from the surfaces of the grains and by reactions during These melting. As melting proceeds, the voids are closed off, forming bubbles. bubbles must be removed to produce a useful, homogeneous glass material. On earth, bubbles are removed from glass melts by a general process called "fining. " Buoyant fining, wherein bubbles are allowed to float out of a melt, is the simplest
Data Loading...
