Condensation Stefan-flow mechanism

Elace. Hence, if particle buildup is to De sought, the scrubber should e preceded by an appropriate gas-conditioning section. On the other hand, particle collection by Stefan flow can be induced simply by scrubbing the hot, humid gas with sufficient cold water to bring tne gas below its initial dew point. Any practical method of inducing condensation on the dust particles will incidentally afford opportunities for the operation of the Stefan-flow mechanism. The hot gas stream must, of course, have a high initial moisture content, since the magnitude of the effects obtained is related to the quantity of water vapor condensed. 

The other mechanism appears in scrubbers. When water vapor diffuses from a gas stream to a cold surface and condenses, there is a net hydrodynamic flow of the noncondensable gas directed toward the surface. This flow, termed the Stefan flow, carries aerosol particles to the condensing surface (Goldsmith and May, in Davies, Aero.sol Science, Academic, New York, 1966) and can substantially improve the performance of a scrubber. However, there is a corresponding Stefan flow directed away from a surface at which water is evaporating, and this will tend to repel aerosol particles from the surface. 

Condensation Scrubbing The collection efficiency of scrubbing can be increased by the simultaneous condensation of water vapor from the gas stream. Water-vapor condensation assists in particle removal by two entirely different mechanisms. One is the deposition of particles on cold-water droplets or other surfaces as the result of Stefan flow. The other is the condensation of water vapor on particles as nuclei, which enlarges the particles and makes them more readily collected by inertial deposition on droplets. Both mechanisms can operate simultaneously. However, for the buildup of particles by condensation to be effective, there must be adequate time for the particles to grow substantially before the principal gas-liquid-contacting operation takes... 

There are several possible mechanisms to explain the enhancement of absorption during surface renewal. The Marangoni Effect results from the fact that dilute solutions of water C10 %) exhibit abnormalities in regard to surface tension. Jones and Ray [8] have observed that absorption of ions at the surface continues until a specific number of sites are occupied. The concentration of these sites is about 5 per 10 surface molecules. If liquid vapor is continually condensed on the drop surface, new surface for sites is being formed at a rate fixed by condensation. A second mechanism for enhancement, Stefan flow, is a trapping of the gas molecules into the liquid phase by the condensing vapor flux. The Stefan flow flux can be expressed as [9] ... 

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