Mixed Convection Gas Transfer across Surfactant-Contaminated Air/Water Interfaces

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National Science FoundationABSTRACTProposal Number: CTS-0500155Principal Investigator: John SaylorAffiliation: Clemson University Proposal Title: Mixed Convection Gas Transfer Across Surfactant-Contaminated Air/Water InterfacesThis proposal was received as an unsolicited submission to the Chemical and Transport Systems Division and was funded by the Thermal Transport and Thermal Processing Program. The transfer of dissolved gases across the air/water interface of freshwater lakes is critical to numerous ecosystems. Protection of these ecosystems requires an understanding of this interfacial gas exchange problem. While there is a large body of research on gas exchange across air/water interfaces at the high wind speed conditions typical of oceans, little has been done to study the low wind speed conditions that are common on lakes. The proposed research seeks to address this critical need, focusing on the transport of dissolved gases such as oxygen and carbon dioxide, under low wind speed conditions where both forced convection and natural convection play a role; a transport regime referred to as mixed convection. This research will also focus on how gas transfer is affected by the single molecule thick organic films called 'surfactant monolayers', which are ubiquitous on lakes. The research will consist of a set of laboratory experiments utilizing a wind/water tunnel where the transfer of dissolved gases such as oxygen and carbon dioxide will be measured as a function of wind speed and air-water temperature difference. The effect of surfactant contamination on transport will be quantified by introducing these surfactants on the water surface in a controlled fashion. The fluid flow structures responsible for the observed gas exchange phenomena will be investigated using flow visualization techniques, including infrared imaging of the water surface and laser induced fluorescence imaging of the subsurface flow. The proposed research will result in improved models of the effect of human activity on lakes, more accurate global climate change models, and improvements in the efficiencies of numerous industrial processes.