Characterization of Mixing in Upflow Solids-Contacting Clarifier
Publication: Journal of Environmental Engineering
Volume 125, Issue 8
Abstract
It has been recognized that flocculation performance can be related to the mixing process. This process has traditionally been described by vessel average parameters such as the root-mean square velocity gradient , which may not represent local mixing conditions within a vessel, particularly in the impeller vicinity. The analysis of turbulence in the flocculator allows a more refined specification of flow, energy, and dissipation, which have long been known to be important to the flocculation process. Presented is a study to characterize hydrodynamic conditions in the impeller zone of an upflow solids-contacting clarifier using a laser Doppler anemometer. Results were analyzed based on an analogy of the impeller-generated flow to a swirling radial jet. It was found that mean and fluctuating velocities scaled on the tip speed of the impeller. Use of the swirling radial jet analogy also allowed the scaling of local dissipation rates. Results compared favorably to other impeller studies and true radial jets, indicating the applicability of concepts for the assessment of other flocculation impellers. It was found that local dissipation rates near the impeller were significantly higher than the vessel average values. These high values highlight the need for further study of the impact of local mixing conditions on flocculation performance.
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Information & Authors
Information
Published In
Journal of Environmental Engineering
Volume 125 • Issue 8 • August 1999
Pages: 762 - 773
History
Received: Mar 15, 1995
Published online: Aug 1, 1999
Published in print: Aug 1999
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