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DISPERSION IN STEADY PIPE FLOW WITH REYNOLDS NUMBER UNDER 10,000

by CUTTER, MATTHEW R.

Abstract (Summary)
The longitudinal dispersion coefficient of a conservative tracer (CaCl2) was calculated from continuous flow tests in a dead-end pipe system. The system consisted of 6-inch diameter PVC pipe with a test length of approximately 44 meters. Flow conditions ranged from laminar to turbulent regimes, with a Reynolds number range of 1000 to 10000. Two static mixers in series were used to homogenize the tracer concentration across the cross-section of pipe. The conductivity of the tracer was measured at two locations downstream of the injection and mixers using a conductivity probe at a point in the cross-section. Dispersion coefficients calculated by the method of moments are plotted versus Reynolds number. Test results show increasing time-averaged dispersion rate in the laminar flow regime and a portion of the transitional flow regime with increasing Reynolds number. At a flow rate corresponding to a Reynolds number (Re) of approximately Re=2400, the dispersion rate reaches a maximum value and then decreases until approximately Re=4000. As the tests enter the turbulent flow regime, the dispersion rate is minimized due to the plug-flow behavior inherent to turbulent flow. Results indicate that dispersion plays a more important role in mass transport in laminar and transitional flow than advective mass transport. Incorporating dispersion estimates into network water quality models will improve quality predictions for the dead-end portions of the network.
Bibliographical Information:

Advisor:

School:University of Cincinnati

School Location:USA - Ohio

Source Type:Master's Thesis

Keywords:key words longitudinal dispersion coefficient tracer laminar water distribution network dead end simulator

ISBN:

Date of Publication:01/01/2004

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