Zum mechanismus des stofftransports lami-narwelligen rieselfilm

660 30 Fluorescence Imaging of Air-Water Gas Exchange

30.4 Critical discussion and outlook

Jähne et al. [19] propose a variation of the method, which is in devel-opment right now. The camera visualizes the water surface from above. The laser light sheet is perpendicular to the water surface so the cam-era sees a line that consists of the fluorescence light originating from all different depths. A spectrometer analyzes this light. A second dye in the water strongly absorbs in the range of emission of fluorescein. Because of the second dye the shape of the observed fluorescence spec-tra is dependent on the length of the path the light traveled through the water. With adequate calculations it seems to be possible to ob-tain depth resolved profiles of the boundary layer. With this new setup simultaneous measurements with the controlled flux technique (CFT, [18]) are feasible.

30.5 References 661

[4] Hiby, J., (1968). Eine Fluoreszenzmethode zur Untersuchung des Trans-portmechanismus bei der Gasabsorption im Rieselfilm. Wärme und Stoff-übertragung, 1:105–116.

[5] Braun, D., (1969). Die effektive Diffusion im welligen Rieselfilm. Disserta- tion, Technische Hochschule, Aachen.

[10] Asher, W. and Pankow, J., (1988). Direct observation of concentration fluctuations close to a gas-liquid interface. Chemical Engineering Science, 44:1451–1455.

[11] Wolff, L. M., Liu, Z. C., and Hanratty, T. J., (1990). A fluorescence technique to measure concentration gradients near an interface. In Air-Water Gas Transfer, Selected Papers from the Second International Symposium on Gas Transfer at Water Surfaces, S. Wilhelms and J. Gulliver, eds., pp. 210–218. Minneapolis, Minnesota: ASCE.