Properties of a Constricted-Tube Air-Flow Levitator
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PROPERTIES OF A CONSTRICTED-TUBE AIR-FLOW LEVITATOR AND E. C. ETHRIDGE** J. E. RUSH,* W. K. STEPHENS, *Department of Physics, University of Alabama in Huntsville, Alabama, USA **Space Sciences Lab, Marshall
Space Flight Center,
Huntsville,
Alabama, USA
ABSTRACT A constricted-tube gas flow levitator first developed by Berge, Oran, and Theiss shows promise both as a spacepositioning device and as a levitator for ground-based work. We present results of laboratory studies which were designed to predict the behavior of the device in a low-g environment.
INTRODUCTION There is much interest in levitation techniques which can be used in ground based research to study a number of phenomena. The effective levitation of liquid nonconductors remains an elusive goal in materials science. A constricted-tube gas flow levitator has been developed at the Marshall Space Flight Center by Berge, Oran, and Theiss [1]. Its advantages are that it is a simple levitator which is essentially orientation and gravity independent, will operate over a broad temperature range, and can be used to process both conducting and nonconducting materials. Solid spherical samples of a number 0 of different densities at 1200 C have been successfully levitated. We have continued to study the properties of such levitators as a possible solution to this goal and as a possible levitator for low g and report here on our work to date (Sept., 1981). The levitator
consists of a constricted
(quartz)
tube fed at
one end by a
source of heated air or gas. A spherical sample is positioned by the air stream on the downstream side of the constriction, where it can be melted and resolidified without touching the tube. The primary source of heat for the sample is the air itself, although secondary sources are also being investigated. The air is heated by being passed through a furnace, by being blown past a torch, or both. (See Appendix.) The behavior of spheres in flowing fluid in a lg environment has been studied by many investigators. The earliest work was on spheres in free flow [2], where the drag coefficient vs. Reynolds number Re was determined. Also investigated was the pressure distribution around the sphere and the behavior of the fluid as a function of Re. A more complex situation is flow past spheres in vertical, slightly tapered tubes forming the basis of flowmeter technology. Quite a bit of work has also been done on spheres in straight tubes and pipes, both experimentally [3] and theoretically [4]. However, the only published work on spheres in duffusers which we have found is by Schmidt and Springer [5]. In a straight, vertical tube one can maintain an unstable equilibrium in the vertical direction by balancing the gravitational force with a drag force. A relatively stable equilibrium exists laterally because of a Bernoulli effect due to the radial variation in fluid velocity, coupled with a weaker Magnus force due to rotation of the sphere [6]. With a slightly tapered tube, as in a flowmeter, one can easily produce stable equilibrium, but
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