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0409_Velocity and Solids distribution in circular secondary clarifiers: Full scale measurement...

 
 
ESEL Paper Review_20130409
By Hong Guo
Mail: hongguo@gist.ac.kr
Phone: (+82) (0)10 82276568
1, Title and Author
Title: Velocity and Solids distribution in circular secondary clarifiers: Full scale measurement and numerical modeling
Journal: Water Research
Authors:
A. Deininger1, E.Holthausen2 and P.A. Wilderer3*
1 Vermincon, Engineering and Microbiology,, Nymphenburger Strabe 81, 80636 Munich, Germany
2 TOR Engineering GmbH, Siebenmorgen 43, 51427 Bergisch Gladbach, Germany
3 Insitute of Water Quality and Waste Water Management, Technische Universitat Munchen, Am Coulonbwall, 85748 garching, Germany
2. Summary of Paper
In this paper, the results of full scale measurements of the solids and velocity distribution in a circular secondary clarifier are presented.
3. Results
? In this plan view, the continuity condition is not fulfilled. Since the currents in the clarifier must be treated as three dimensional in character, the continuity condition can only be fulfilled in the three dimensional field.
? Small eddies exist in the tank due to a turbulent flow. Therefore within a relatively short measuring time (22s), the mean velocity values might be slightly higher than over an increased measuring time
? The change of the flow direction during measuring time is due to those small eddies or to an unstable flow.
? From both profiles it can be seen that a circular current in radial direction exists
? The circular current shows the following characteristics:
? Forward flow velocities in the zone close to the tank bottom
? Backward flow velocities in the upper zone of the tank
? Higher forward flow velocities in the inlet region than in the rim region.
? Higher backward flow velocities in the inlet region than in the outlet region.
? Vertical currents downwards to the tank bottom in th inlet region
? Vertical currents upwards to the water level in the outlet region
? Obviously, density current exists due to a higher density of the incoming sludge suspension.
? The density current sinks toward the sludge blanket right after leaving the inlet structure and flows toward s the tank rim, Thus backward
velocities are induced in the upper water zone of the tank for the continuity equation.
? When a constant value of the turbulent viscosity was used for turbulence modeling instead of the k-epsilon turbulence model, the zone of forward velocities became smaller
? The vertical velocity of the solid phase represents the relative settling velocity between sludge and water: it depend on the solids concentration.
? The vertical velocity of the liquid phase is higher than the solid phase due to density and hydrodynamic effects
? Frictional forces affect transports of the solid particles.
? Using a constant turbulent viscosity value for turbulence modeling instead of the k-epsilon model, similar maximum downward velocity values were obtained
4. Contribution:
This paper was published 1998, which the computer power is not strong as today. The author elaborate the applied governing equation; the numerical method for predicting the solid distribution and velocity profile. It is useful skills, which could be applied for future CFD modeling study in our lab.
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