<?xml version="1.0" encoding="UTF-8"?><xml><records><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>13</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">A. Falkenroth</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Visualisation of Oxygen Concentration Profiles in the Aqueous Boundary Layer</style></title></titles><dates><year><style  face="normal" font="default" size="100%">2007</style></year></dates><urls><web-urls><url><style face="normal" font="default" size="100%">http://www.ub.uni-heidelberg.de/archiv/7672</style></url></web-urls></urls><publisher><style face="normal" font="default" size="100%">Fakultät für Chemie und Geowissenschaften, Univ.\ Heidelberg</style></publisher><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">In environment studies as well as for technical application, the study of air-water gas exchange is crucial. For process studies, a novel visualisation technique of oxygen concentrations in water was realised with high spatial resolution. To resolve turbulent processes in water, also the temporal resolution was pushed to the limit of a imaging frame rate of 185 Hz. For this purpose, the well-established method of laser-induced fluorescence (LIF) was extended introducing in this type of studies a new phosphorescent ruthenium dye that is more than 15 times more sensitive to oxygen than the previously used indicator dye. The chemical synthesis of this metal-ligand complex MLC was adapted to a preparation without intermediate steps. The challenge of this imaging technique for small-scale interactions was to resolve a very thin boundary layer extending less than a millimetre below the water surface. An image processing algorithm was developed that allow the automatic detection of the exact location of the air-water phase boundary within the resolution of 25 um/pixel. Only by this step, an accurate direct determination of an important parameter for gas-exchange studies, the boundary-layer thickness, is feasible. The developed methods were applied to systematic gas-transfer measurements mostly with surfactants, conducted in a range of wind speeds between 0.8-7 m/s in a circular wind-wave facility. The measured gas-transfer velocities compared extremely well to exchange rates derived from mass-balance methods. The novel visualisation technique drastically increased the poor signal quality inherent to standard LIF techniques. This enabled accurate measurements of gas-transfer velocities from aqueous concentration profiles for the first time.</style></abstract></record></records></xml>