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Title:The study of gas absorption at a wavy air-water interface
Author(s):Wolff, Leslie Marie
Doctoral Committee Chair(s):Hanratty, Thomas J.
Department / Program:Chemical and Biomolecular Engineering
Discipline:Chemical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Engineering, Chemical
Abstract:Two techniques were developed to relate gas absorption to waves formed at the interface of an air-water flow. The first measured the instantaneous concentration profile of oxygen in water very close to the interface. The second measured the instantaneous wave slope.
The concentration measurement is new; it is the first to determine the concentration gradient within the mass transfer boundary layer of this system. The technique uses a tracer whose fluorescent intensity is inversely proportional to oxygen concentration. The fluorescence of the tracer was recorded using a CCD camera so that spatial resolution is preserved.
Measurements were obtained in a horizontal channel with air and water flowing concurrently. Concentration profiles were measured at a smooth interface, gas velocity = 1.5 m/s, and at a wavy interface, gas velocity = 2 m/s. The mass transfer boundary layer at the smooth interface had a thickness of 700 microns which is a dimensionless thickness of y$\sp+$ = 6. It was found that at a smooth interface the gas absorption rate is constant with time.
Measurements with waves showed a much larger mass transfer rate which varied with time. The mass transfer boundary layer varied from less than 100 microns (y$\sp+$ = 0.9) to 600 microns (y$\sp+$ = 5.4). The lower limit that could be detected was 100 microns. There was some evidence that the very large mass transfer rates (boundary layers less than 100 microns) are associated with large wave slopes.
Wave slopes were obtained by measuring the optical displacement of a laser beam which vertically pierces the water surface and bends due to the curvature at the surface. Measurements were obtained at various gas and liquid Reynolds numbers.
The data suggest that wave slope rather than wave height is the appropriate parameter to relate mass transfer to wavy motion. A consequence of this is that mass transfer is related to higher frequency velocity fluctuations than would be suggested from wave height spectra.
Issue Date:1991
Rights Information:Copyright 1991 Wolff, Leslie Marie
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9211038
OCLC Identifier:(UMI)AAI9211038

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