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Title: Mechanism of mass transfer of gases for the case of flowing liquid films
Author: El-Sawy, Mohamed
ISNI:       0000 0001 3443 4921
Awarding Body: University of Surrey
Current Institution: University of Surrey
Date of Award: 1977
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Studies of absorption and desorption for the carbon dioxide/water system on inclined planes have been made both experimentally and theoretically. A general review of wetted-wall columns, the hydrodynamics of flowing liquid films, eddies or convective disturbances, and surface resistance are considered. Theoretical models are presented with emphasis on simple penetration and film models. Particular attention is paid to a 'diffusion film model' for flowing liquid films. Difficult practical hydrodynamic problems are described, the solutions to which are essential to successful experimentation. The methods employed for their solutions are detailed; for example, the deter- mination of 'end-effects', and the significance of meniscus effects'. During the work, measurements of film thicknesses were made at each new operating condition. A modified Michelson type interferometer was constructed and attached to the inclined plane. This ensured that the optical system was not affected by adjustment. For desorption there is a deflection effect near the interface which obscures the fringe to an extent dependent on the path length of the light and the concentration gradient in the liquid film. Its significance is discussed in relation to the interfacial concentration. This problem does not occur in absorption. Smooth surface laminar flow was obtained at the lower angles of inclination (1°, 2° and 3°), and at low flow rates. As the flow rate or angle of inclination increases above 3°, surface waves appear and become vigorous at the highest flow rate and angle of inclination of the plane. Mass transfer rate is increased by the presence of waves. In the case of absorption, the presence of convective disturbance, which is primarily buoyancy driven, enhances the mass transfer rate even in the absence of surface waves. This has been shown from optical and titration results. Both in absorption and desorption it has been shown that there exists a surface resistance, but the magnitude of this resistance differs in each case. Using titration and optics as separate means of investigation it is clearly demonstrated that the mechanism of desorption is not a mirror image of absorption. It has been quite usual to assume or even state that the two processes are identical. This is not so, and the present work discusses this in depth. Supplementary studies were carried out, some of which were essential to the major study. It was necessary to establish the relationship between the concentration of carbon dioxide in water and its refractive index. A separate optical apparatus was constructed using a Twyman-Green interferometer and special cells. This is detailed and an equation is presented for the relationship. Preliminary experiments were carried out: (1) with the inclined cell suitably thermally insulated to determine absorption and desorption rates at elevated temperatures; (2) with an inclined cell where the floor of the cell was covered with special beads of 1. 5-2. 0 mm diameter.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available