Axial Dispersion Coefficients in Laminar Flows of Water-Distribution Systems
Publication: Journal of Hydraulic Engineering
Volume 137, Issue 11
Abstract
Because longitudinal dispersion is becoming increasingly germane to the problem of accurately determining water quality, water-resource managers and engineers seeking to represent solute transport in drinking-water systems must be able to compute relevant dispersion coefficients. Accordingly, the present study was undertaken to develop and experimentally verify a modified advection-dispersion-reaction transport equation as well as the formulas used to calculate the axial dispersion coefficient. The analysis assumes laminar flows, constant mean velocities, and short travel times (dimensionless time, ). With regard to the modified transport equation, the dispersion term was assumed to be direction-dependent. Thus, two distinct dispersion rates (forward and backward) were recognized and quantified as opposed to the single value used in conventional dispersion models. With the dimensionless travel time taken to be the independent variable, the developed dispersion coefficients increased at about one-fourth of the growth rate exhibited by the conventional dispersion formula. The proposed scheme demonstrated a large improvement over the conventional formula when its performance was judged against experimental runs using various combinations of pipe lengths, tracer injections, mean flow velocities, and solute properties. This study’s findings should lead to accurate water-quality predictions and corresponding quantitative risk assessments, especially in pressure zones where low-speed flows prevail.
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Acknowledgments
This work is supported by the EPA/Department of Homeland Security (under grant no. USEPA613383D). We would like to acknowledge collaborators Dr. Steve G. Buchberger and Dr. Zhiwei Li at the University of Cincinnati as well as Mirjam Blokker at KWR in the Netherlands. The following students contributed their valuable time during the experimental phase of this work: Ryan G. Austin, Mario Mondaca, Malorie Teich, Fernando Rojano, and Alex Andrade.
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Information
Published In
Journal of Hydraulic Engineering
Volume 137 • Issue 11 • November 2011
Pages: 1500 - 1508
Copyright
© 2011 American Society of Civil Engineers.
History
Received: May 5, 2010
Accepted: Mar 29, 2011
Published online: Mar 31, 2011
Published in print: Nov 1, 2011
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