Date of Award

12-2009

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Mechanical Engineering

Advisor

Saylor, John R

Committee Member

Beasley , Donald E

Committee Member

Tong , Chenning

Abstract

A set of laboratory experiments are presented that reveal the effect of a surfactant monolayer on the transport of oxygen across an air-water interface during mixed convection conditions. The experiments were conducted in a wind/water tunnel with water tanks of differing depth. Forced convection was imposed via the air flow, while natural convection was imposed by heating the water bulk above the air temperature. For the range of wind speeds being considered, mixed convection conditions resulted. Experiments were also conducted with only forced convection present. The data acquired during these experiments were used to develop a parameterization between the Sherwood number for oxygen transport (Sh) and the Reynolds (Re), Rayleigh (Ra), and Schmidt (Sc)
numbers. This parameterization was obtained for the case of a clean water surface and for a water surface covered with one of two surfactant monolayers, controlled (oleyl alcohol) and uncontrolled (indigenous). The data reveal that, at a given Ra, the presence of a surfactant monolayer reduces the value of Sh by approximately one order of magnitude. This reduction is caused by the reduction of subsurface turbulence caused by the presence of the surfactant monolayer. The data also show that Sh was relatively insensitive to Re and Sc when a surfactant monolayer was present, which is verified by the forced convection only results. However, Sh was dependent on Ra, Re, and Sc for the clean water surface condition. For the two surfactant conditions, no change in behavior of the gas exchange was noticed. The elasticity of the air-water interface which results from the presence of a surfactant is used to explain the difference between clean surface and surfactant-covered results.
The elasticity imparted by a surfactant monolayer is also used to explain the similarity of the results
for the two surfactants. For both the clean and surfactant cases, Sh increases with Ra.

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