In addition to its basic scientific value, this interaction has important relevance to many practical problems such as the adverse impact droplet deposition may have on the integrity and functionality of hygroscopic materials and water-sensitive instruments that are contained inside enclosures which are rapidly evacuated (such as inside launchers and spacecraft payload bays). It is also of fundamental relevance to some problems in combustion and material processing. This interaction was responsible for a costly accident to a recent Shuttle payload.

In moderate to enhanced-g environments, the free convection boundary layer (FCBL) around the body governs the interaction and sets the mist standoff distance, d from the body. In the case of a turbulent FCBL (large Grashof numbers), water droplets may be entrained by eddys and deposited onto the surface. In m-g environments, other competing mechanisms (e.g.\ thermophoresis, conduction and other buoyancy-independent convection mechanisms) may dominate and govern the magnitude of d. The results of 1-g studies of this effect cannot be extrapolated to cases of enhanced and, especially, reduced gravity.

We propose an experiment in enhanced and reduced gravity in which we would generate a mist of water by pumping down a vessel containing humid air, and study the parametric dependencies governing the mist formation, its interaction with the thermal boundary layer near a warm surface, the magnitude of d and the deposition of water droplets on the surface. A vertical flat plate and a sphere will be used, alternatively, as the test body. Various temperature, pressure, humidity and deposition diagnostics will be used along with a simple but powerful visualization technique based on laser light scattering. Our main goal is to clarify the nature and dependencies of this interaction as well as define useful semi-empirical scaling parameters and laws that govern it.

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Last Modified: Tue May 19 1998
CSR/TSGC Team Web