An Experimental Study of Heat Induced Surface-Tension Driven Flow
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AN EXPERIMENTAL STUDY OF HEAT INDUCED SURFACE-TENSION DRIVEN FLOW
Y. KAMOTANI, S. OSTRACH AND S. LOWRY Case Western Reserve University, University Circle,
Cleveland,
Ohio
44106
ABSTRACT Velocity and temperature measurements are taken of heat induced surface-tension driven flows in both silicone oil and Fluorinert FC-43. Each fluid is contained in an open rectangular box and heated from above by a single strand of electrically heated nichrome wire suspended slightly above the fluid's surface. Velocity measurements are obtained for both liquids with a laser anemometer system. For silicone oil the general flow pattern is recorded using time-lapse photography. The surface temperature measurements are taken by a radiation thermometer and the bulk temperature distributions are measured by thermocouples. The velocity and temperature measurements are compared with numerical solutions obtained for the present configuration.
INTRODUCTION It is now recognized that under reduced gravity conditions surface-tension gradients become significant driving forces for fluid motions in configurations with free surfaces or fluid interfaces [1]. The subject, thus, has started to receive increased attention not only for its intrinsic scientific interest but also because of its importance to the containerless processing of materials [2,3]. Although surface-tension gradient flows cannot be truly simulated on earth because the interface shape and damping will
be significantly
different,
it
is
the object of the present work to investigate predominantly surface-tension gradient driven flows on earth in order to gain some insights into such flows in space. In addition, the purposes of the present work include the selection of suitable test fluids and the development of experimental techniques for future space experiments. In the past, several investigators theoretically studied the fluid motion induced by surface-tension gradient (e.g. [4,5,6]). Pimputkar and Ostrach [3] analyzed the fluid motion in a thin film including the free surface shape variation. Ostrach [1,2] derived the important dimensionless parameters in the problem. The past experimental investigations were mainly confined to small scale models and to mainly qualitative studies (e.g. [7,8]). Prior to the present work, Ostrach and Pradhan [9] investigated the surface-tension driven convection in large containers with water under a reduced-gravity condition in a drop tower. Although some fluid motions were observed, it was not clear whether they were induced by temperature gradients or concentration gradients caused by the spreading of methylene blue particles sprinkled on the surface. In the present work silicone oil and Fluorinert FC-43 were tested and found to be much less sensitive to contamination than water. The bulk flow structures in large containers were studied in detail by non-incursive methods. Most of the results presented in this paper are taken from the work by Lowry
[10].
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