The measurement of wetting layers in two-phase flows in capillaries and the effect of surfactant on the wetting layer thickness.
Item
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Title
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The measurement of wetting layers in two-phase flows in capillaries and the effect of surfactant on the wetting layer thickness.
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Identifier
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AAI9720098
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identifier
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9720098
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Creator
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Huang, Wei.
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Contributor
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Adviser: Charles Maldarelli
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Date
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1997
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Language
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English
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Publisher
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City University of New York.
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Subject
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Engineering, Chemical
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Abstract
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When a capillary tube is filled with a fluid which strongly wets the tube wall, and a slug of a second nonwetting immiscible fluid is forced to move through the tube, the slug moves over a thin annular layer of the wetting fluid. This flow finds applications in foam displacement of oil or contaminants in rock pores, where surfactant is added to stabilize the foam. The effect of surfactant adsorption on the wetting layer thickness is a crucial but not well understood effect and is the focus of this thesis. A model for this flow is studied consisting of a 1 mm circular quartz capillary tube, with aqueous solutions of a polyethoxylated surfactant as the continuous phase and air or decane as the slug phase arranged in a periodic train flow.;The thesis consists of two parts. In the first, a new optical adsorbance technique is developed to measure the thickness. In the absence of surfactants, measurements agree with the asymptotic low capillary number theory. In the second part the thickness of wetting layers as a function of surfactant concentrations and velocities are measured. At high velocities and low bulk concentrations, surfactant is swept into a stagnant zone at a back ring of the slug, and the measured thickness is the value for the clean interface. As the velocity decreases or the concentration increases, the surfactant monolayer extends over the entire surface, and the increase in deformability and rigidification increases the film thickness. For a further reduction in the velocity or increase in concentration, an additional increase in the film thickness is measured. The increased importance of bulk diffusion relative to surface convection increases the interfacial mobility, and depletes the surfactant concentration in the film. This creates a Marangoni force as the tension in the film is larger than at the slug ends, which draws fluid into the film accounting for the thickness increase. Finally, at fixed velocity, as the bulk concentration increases beyond the critical micelle concentration, increased rates of bulk eliminates depletion and the measured thickness is of a clean interface with a tension equal to the equilibrium surfactant tension.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
