ESEL Paper Review_201200818

 

By Hong Guo

 

1,Title and Author

 

Title: The effect of influent temperature variations in a sedimentation tank for potable water treatment- A computational fluid dynamics study

 

Journal: Chemical Engineering Journal

 

Authors:

 

Athanasia M. Goula, Margaritis Kostoglou, Thodoris D. Karapantsios ^*, Anastasios I. Zouboulis

 

Division of Chemical Technology, School of Chemistry, Aristotle University, University Box 116,541 24 Thessalonik, Greece

 

2.  Summary of Paper

 

In this paper, the authors apply the computational fluid dynamics model to assess the effect on influent temperature variation on solids settling in a sedimentation tank for potable water treatment. And they found that a temperature difference of only 1 Celsius degree between influent and tank content is enough to induce a density current. When the influent temperature rises, the tank exhibits a rising buoyant plume that changes the direction of the main circular current. As the warmer water keep s coming in, the temperature differential decreases, the current stars going back to its original position, and, thus, the suspended solids concentration decreases.

 

 

3.  Results

1. Flow pattern

 

The direction of the circular current is changed by the influent temperature rising. Here, the buoyant plume is the changing factor

As results, we could find that the effect of the temperature to the influent water is depending on the inflow solids concentration. The lower concentration leads to the temperature becomes more important in determining the location of the interface and the water temperature difference defines the nature of the current.

 

2. Solid distribution

 

The settling effectiveness is inversely related to the extent of the temperature differential in the tank. (When the influent temperature rises, the efficiency of the sedimentation would change from 99% to 76%. However, It would be increased by decreasing of the temperature difference.)

Moreover, the effluent turbidity generally presents higher values during the winter conditions. This observation could be attributed to the traditional discrete settling model proposed by the Stokes’ law, which suggests that the settling velocity of discrete particles depends indirectly on the temperature of the fluid since the settling velocity is inversely proportional to the kinematic viscosity of the liquid.

 

4.  Contribution:

 

This paper discuss about temperature effect on the flow pattern and solid setting distribution on the sedimentation tank. By apply the CFD, we could find that behavior of the steam line and solid setting. Moreover, this paper probably gives a direction for a reason for the settling effect of the sedimentation process. On my work , I could find why the removal efficiencies of phosphorus are different for summer, autumn, and winter with same operational condition (especially pH ).

 

5. Authors’ mail: athgou@chem.auth.gr