Reduction of Mixing in Jet-Fed Water Storage Tanks
Publication: Journal of Hydraulic Engineering
Volume 130, Issue 1
Abstract
Contrary to usual mains-water practice, mixing in water storage tanks used in rainwater harvesting systems is undesirable because pathogen die-off can occur in the unmixed water prior to its extraction for use. The principal cause of mixing in these tanks is the momentum of the inflow during a rainfall event. We investigate the effect of inflow-jet configuration on the proportion of stored water in a tank which mixes with the slightly cooler inflow of rooftop water. Scale experiments are conducted which show that the nondimensional height of the mixing front above the jet inlet is proportional to the inflow-jet densimetric Froude number for both single and multijet arrangements of various geometries. For each arrangement a coefficient of mixing is found. The results are then used to assess the level of mixing in full-scale rooftop rainwater harvesting storage tanks and determine whether residence time in such tanks is a viable strategy for pathogen reduction. For such applications, a radial manifold of jets outwardly directed from the tank center is found to be the most promising.
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References
Barr, D. I. H., and Sharp, J. J. (1968). “Discussion of ‘Three dimensional density current,’ by T. R. Fietz and I. R. Wood.” J. Hydraul. Div., Am. Soc. Civ. Eng., 94(6).
Davidson, J. H., and Adams, D. A.(1994). “Fabric stratification manifolds for solar water heating.” ASME J. Sol. Energy Eng., 116, 130–136.
Droste, R. L. (1997). Theory and practice of waste-water treatment, Wiley, New York.
Fischer, H. B., List, E. J., Kohl, R. C., Imberger, J., and Brookes, N. H. (1979). Mixing in inland and coastal waters, Academic, New York.
Geldreich, E. E.(1970). “Applying bacteriological parameters to recreational water quality.” J. Am. Water Works Assoc., 62, 113–120.
Geldreich, E. E., Best, L. C., Kenner, B. A., and Von Donsel, D. J.(1968). “The bacteriological aspects of stormwater pollution.” J. Water Pollut. Control Fed., 40, 1861–1872.
Geldreich, E. E., and Kenner, B. A.(1969). “Concepts of faecal streptococci in stream pollution.” J. Water Pollut. Control Fed., 41, R336–R352.
Gould, J., and Nissen-Petersen, E. (1999). Rainwater catchment systems for domestic supply, Intermediate Technology, London.
Linden, P. F.(1999). “The fluid mechanics of natural ventilation.” Annu. Rev. Fluid Mech., 21, 201–238.
Rossman, L. A., and Grayman, W. M.(1999). “Scale-model studies of mixing in drinking water storage tanks.” J. Environ. Eng., 125(8), 755–761.
Information & Authors
Information
Published In
Journal of Hydraulic Engineering
Volume 130 • Issue 1 • January 2004
Pages: 75 - 81
Copyright
Copyright © 2004 American Society of Civil Engineers.
History
Received: May 31, 2001
Accepted: Mar 12, 2003
Published online: Dec 15, 2003
Published in print: Jan 2004
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