Advances in Water Treatment and Enviromental Management

MEASUREMENTS OF MASS TRANSFER IN A BUBBLE COLUMN 153A plotting of the specific mass transfer coefficient k L • a/U S L considers the influenceof spatial mean velocity of the liquid phase U SL and also the residence time of thebubbles. Figure 10 shows that the largest values can be reached with a low waterflow rate Q w =0.01 m3/s. The influence of the turbulent single water flow conditionsis also seen in this figure.4. CONCLUSIONSOverall volumetric mass-transfer coefficients k=k L • a and maximum efficiency ofoxygen transfer η for air bubbles rising in water with different hydrodynamicconditions have been measured in order to quantify oxygen mass-transfer. Theresults of the experimental measurements suggest the following conclusions: Masstransferdepends on• the air flow rate Q a influencing bubble diameter as well as bubbledeformation and residence time,• the water flow rate Q w mainly affecting the residence time of the bubbles• the turbulent conditions of the water flow.To clarify these effects and to assess the importance of each of them further work isnecessary. Currently, experiments are prepaired with a variety of turbulence grids,producing different turbulence conditions in the water flow. At present the influenceof the differnet hydrodynamic conditions on the bubble diameter distribution,produced by the air-input system with variable nozzels is investigated. For thisphotographic and opto-electronical methods are used.ACKNOWLEDGEMENTSThis work was supported by the Bundesministerium fur Forschung und Technologie(BMFT), Project number: 02-WA 8680/4BIBLIOGRAPHY[1] ASCE (1984): A Standard for the Measurement of Oxygen Transfer in CleanWater. ASCE, Vol.6.[2] Haines, W.D.; Peterson, E.G. (1951): An Investigation of Flow ThroughScreens. ASME, Vol.7, 467–480.[3] Brauer, H. (1971): Mass Transfer. Sauerlander, Frankfurt.[4] Danckwerts, P.V. (1970): Gas-Liquid-Reactions. McGraw Hill, New York.[5] Davies, J.T. (1972): Turbulence Phenomena, Academic Press, New York.[6] Deckwer, W.-D. (1985): Technical Reactions in Bubble Columns. Salle +Sauerlander, Frankfurt.[7] Dobbins, W.E. (1956): The Nature of the Oxygen Transfer Coefficient inAeration Systems. Treatment of Sewage and Industrial Wastes, McCabe.[8] Dobbins, W.E. (1962): Mechanism of Gas Absorption by Turbulent Liquids.Water Pollution Research, Pergamon Press, Vol. II.