Uniform Energy Dissipation Rate Approach in Determining Optimal Geometry

One way to determine the optimal geometry is by evaluating the uniformity of energy dissipation rate. Since energy dissipation rate is the core parameter that influence the particle collision, it is reasonable to assume that uniform energy dissipation rate will give a better performing flocculation tank.

Different geometric space was explored to determine flocculation tank with uniform energy dissipation rate. The optimization method utilized started with an initial geometry. From the initial geometry, we then changed the geometry parameters such as clearance height, baffle spacing and flocculation tank height. If changes in geometry resulted in a more uniform energy dissipation rate than the initial geometry, the new geometry is called incumbent.  

Following this process, geometries were investigated in all possible geometric space. At the end of the investigation, the final incumbent will be chosen as the optimal solution.

Figure 1. Turbulent Dissipation Rate (fh = 2b bs = 0.1 ch = 1b) 

Getting Started with an Initial Geometry
From first semester, we concluded that clearance height should be no smaller than the baffle spacing. We would also like to start our investigation of the geometric space by having the most overlapping energy dissipation region. Employing the two constraints, we come up with the initial flocculation tank height of 2b. Figure 1 shows the contour of turbulent dissipation rate with such geometry. We see that the energy dissipation rate is fairly uniform. Since this is our starting geometry, there is no other geometry to compare with. So this will be the new incumbent.

Baffle Spacing Investigation

From initial geometry in figure 1, we see that there is large blue region in the inner turn. By reducing the baffle spacing we hope to reduce the non-active region. 

Figure 2. Turbulent Dissipation Rate (fh = 0.2 bs = 0.07 ch = 0.1) 

Reducing the baffle spacing don't give the desired effect. We do not have a new incumbent. The non uniformity increase. Therefore, this is not the right parameter to change.  

Clearance Height Investigation

Another geometric space that we can investigate is the clearance height. Though it was recommended from previous semester that clearance height of one baffle spacing is optimal for the design for one baffle turn, it would be interesting if we observe different results for multiple baffles turning.

Figure 3. Turbulent Dissipation Rate (fh = 2b bs = 0.1 ch = 0.7b) 

Changing clearance height parameter also did not give desirable result. Decrease in clearance height create a constriction of the flow and we have very high energy dissipation rate in that region. The result observed is the same as of last semester's result of one baffle turning. Changing clearance height geometric space will not give us a better result.

Flocculation Tank Height Investigation

Having investigated two of the three parameters, we are left with final parameter, which is the flocculation tank height. Flocculation tank height of 2b might be providing too much overlapping region. Reducing overlapping of the tail of the energy dissipation region might give a more uniform distribution. 

Figure 4. Turbulent Dissipation Rate (fh = 3b bs = 0.1 ch = 1b) 

Figure 4 shows the longer flocculation tank height of 3b. This geometry give us a more uniform energy dissipation rate than the previous incumbent (Figure 1). This geometry configuration will be the new incumbent. Since changing this geometric space give desirable result, further investigation into this parameter is needed.  

Figure 5. Turbulent Dissipation Rate (fh = 0.4 bs = 0.1 ch = 0.1) 

Comparing figure 4 and 5, we see that flocculation tank height of 4b does not give a more uniform energy dissipation rate. Therefore, flocculation tank height of 3b is still the incumbent.

Adding of Slots Investigation

Notice that there is a region of low energy dissipation rate right before the turning.  Another interesting geometric space that might be worth investigating is to add a small slot at the baffle so that water can flow directly through the baffles. The hope is that this method will reduce the stagnant region.  

Figure 6. Turbulent Dissipation Rate (fh = 0.4 bs = 0.1 ch = 0.1 slot = 0.1b) 

From figure 6, we see that adding small slots at the bottom of baffles does not give us the desired result. The small slot causes the water to flow directly through them and the constriction effect of the flow causes undesirably high energy dissipation rate region. 

After considering all possible geometric space, we concluded that the optimal geometry for flocculation tank is fh = 3b, b = 0.1, ch = 1b as seen in figure 4.