Uniform Energy Dissipation Rate Approach in Determining Optimal Geometry
One of the ways to determine the best geometry is by evaluating the uniformity of energy dissipation rate. Since energy dissipation rate is the core parameter that influence the particle collision, flocculation tank with uniform energy dissipation rate will perform better. We investigated different geometric space to come out with a flocculation tank with uniform energy dissipation rate. The optimization method started with an initial condition. We then changed the geometry parameters such as clearance height, baffle spacing and flocculation tank height. If change in geometry resulted in a more uniform energy dissipation rate than the initial geometry, the new geometry is called incumbent. Following this process, investigate the geometry in all possible geometric space and the final incumbent will be chosen as the optimal solution.
Figure 1: Turbulent Dissipation Rate (fh = 2b bs = 0.1 ch = 1b) From first semester, we concluded that clearance height should go 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. Using 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. This will be the new incumbent. 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. We can now explore the clearance height geometric space.
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. Since changing this parameter wont work, we are left with final parameter, which is the flocculation tank height. Flocculation tank height of 2b might be providing too much overlapping region. We can try to reduce the overlapping region by extending the flocculation tank height.
Figure 4: Turbulent Dissipation Rate (fh = 3b bs = 0.1 ch = 1b) Flocculation tank height of 3b give us a more uniform than the original incumbent we have. This geometry 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 5 and 6, 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. 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 them. 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 undesirable 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.