Development of a method for quantitative imaging of air-water gas exchange

Using a fluorescent pH indicator (pyranine), a new measurement method to investigate the exchange of a soluble alkaline gas (ammonia) from air to water was developed. Key feature of the method is that a linear relationship between the concentrations of the dissolved gas and the alkaline form of the indicator, that is selectively excited to fluorescence in the water-side mass boundary layer, is established by using a high total concentration of the indicator (1e-4 mol/l) and a pH value of 6. This relationship was verified with experiments at the Heidelberg linear wind-wave tunnel at a fixed wind speed. For different, constant gas fluxes into the water, the intensity of the fluorescence induced by LED illumination on a two-dimensional patch of the wind-driven, wavy water surface was imaged at 400 Hz by three cameras from below and one camera from above with a spatial resolution of 140 µm/px and 167 µm/px, respectively. With the verified relationship, the fluorescence signal could be used to obtain horizontally resolved, quantitative information on local changes in the concentration of a dissolved gas in the water-side mass boundary layer for the first time. During the experiments, also a fluorescence profile created by a focused laser beam was imaged at 800 Hz by a camera with a spatial resolution of 5.8 µm/px to observe vertical transport processes.

Level thesis:degree_level

master

Grantor dc:publisher

Universität Heidelberg

Year

2019

Author dc:creator

• Papst, Maximilian

Contributors dc:contributor

• Jähne, Bernd

Repository record source_url

http://www.ub.uni-heidelberg.de/archiv/27271

OAI identifier oai:identifier

oai:archiv.ub.uni-heidelberg.de:27271