You are viewing an old version of this page. View the current version.

Compare with Current View Page History

« Previous Version 12 Next »

Flocculation Tank with Three Baffles Turning

The simplification of a single baffle turn eliminates important behavior within the flocculator. Multiple baffles enable separation regions to interact with each other. The velocity magnitude plot below in Figure 1 displays how the flow before separation at the second turn is not uniform and moves fastest at the edge of the baffle. The faster moving fluid can't turn fast enough and impinges on the edge of the third baffle. The contours of turbulence dissipation rate are illustrated in Figure 2.


Figure 1: Velocity Magnitude for three turns case

 

Figure 2: Turbulence Dissipate Rate for three turns

Flocculation Tank with Five Baffles Turning

The five baffle turns enables high dissipation regions to interact.

case results below shown in Figure 3 reveals a similar velocity profile after each turn. In this case, there is not a high velocity region followed by a high dissipation region, and the flow seems more uniform.
 
The flow obviously relates to the geometry of the problem. Altering the geometry of the problem will result in different flows with a different distribution of energy dissipation.

Automation of Mesh Creation Process

In order to save time, a script was written to automate the mesh generation process in Gambit. The script file can be accessed here.


Using the script, the user just have to change the parameter of baffle spacings, clearance height and flocculation tank height. Upon changing those parameter, the user can execute Gambit and run the journal files for mesh generation. The script can be accessed here.

Similarly, a script in FLUENT can process a completed mesh, and automatically set up the solver, initial conditions, fluid properties, convergence criteria, and save the convergence solution data file to be analyzed later. The incomplete script can be accessed here.

Nondimensional Analysis

Dimensional analysis relates ε to K,V, π and baffle width, as follows:

    ε = KV^3 /(2*π-cell*b)

Thus, 2ε*b/KV^3 represents a dimensionless quantity where K is the minor loss coefficient (the drop in the pressure coefficient per baffle), b is the baffle spacing, and V is the average velocity flowing through the channel when the space is b.

For the optimized geometry below, the baffle spacing is fixed at .1, and baffle height enables a fully developed dissipation region:
 
The nondimensionalized epsilon plot is shown below:

 
The plot is equivalent to 50*ε (since (2*.1)/(.1^3*4.2)=48). Similarly for the 1-turn baffle case the nondimensional parameters can be plotted:

 
The nondimensional values are one order of magnitude lower corresponding to how multiple baffles induce a much higher level of mixing and turbulent energy dissipation independent of the geometry and velocity.

  • No labels