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Demo Plant Spring 2008 Sedimentation Tank Design
Design Goal
Our goal this semester was to redesign the sedimentation tank to be open to the atmosphere on the top, eliminating the need for a weir to control the plant water levels. Also, this would make it easier to fill and clean for demonstrations. We also explored various methods for creating equal flow rates in neighboring lamellas in the sedimentation tank.
Theoretical Design
Principle Formulae
MathCAD Files
Algorithm
Design Results
Unknown macro: {toggle-cloak} OpenTopDesign">Unknown macro: {toggle-cloak} Open Top Design
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This design will be very similar to the Summer 2007 design, with the exception that the top of the sedimentation tank will be open to the atmosphere. Due to this adjustment, the weir will no longer be necessary for plant water level control. Also, the sedimentation tank will now need to be almost as tall as the flocculator, to prevent overflowing. The water levels in the flocculator and sedimentation tank will be approximately the same.
According to the MathCAD Files, this design will need 13 lamella to maintain the proper upflow velocity.
Unknown macro: {toggle-cloak} PerpendicularOpenTopDesign">Unknown macro: {toggle-cloak} Perpendicular Open Top Design
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This sedimentation tank design will address the problem of uneven flow lengths, rates, and shears through each lamella of the sedimentation tank in the Spring 2007 Demo Plant. This problem is further described in the [Demo Plant Problems Encountered] page.
The proposed sedimentation tank will be oriented perpendicular to the axis of the flocculator. Additionally, to accommodate the new design, water will exit the flocculator from the top, instead of the bottom. In order to eliminate differences in lengths of flow paths through the sedimentation tank, water exiting the flocculator will be split into several tubes of equal diameters and lengths, which will enter the bottom of the sedimentation tank. The tubes entering the sedimentation tank will be evenly spaced.
The sedimentation tank itself will be redesigned so that lamella still form the optimal 60 degree angle. However, the lamella will now guide the water in a path parallel to the axis of the flocculator, so that the whole tank will have an incline, and will need to be either very bottom-heavy, or have a support for the upper ends of the lamella. This design, along with the new entry method, will normalize the head loss through individual channels in the sedimentation tank.
The proposed sedimentation tank will also incorporate an open-top design, similar to the flocculator of the Fall 2007 Demo Plant.
This design also allows us to consider the incorporation of a drain for built up sediments in the sedimentation tank, adding the functionality to clean the sedimentation tank while the plant is still running.
The [*MathCAD design*|^Demo Plant Sedimentation Tank.xmcd] and [*AutoCAD drawing*|^Demo Plant Sedimentation Tank.pdf] of the proposed sedimentation tank have been uploaded.
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Unknown macro: {toggle-cloak} OpenTopParallelLamellaDesign">Unknown macro: {toggle-cloak} Open Top Parallel Lamella Design
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This design is very similar to the first Open Top Design, but it will take into account the varied flow rates observed throughout the lamellas of the sedimentation tank. Instead of one row of lamellas, we will have two parallel sets of lamellas. Each set will have 7 lamellas, resulting in a total of 14 lamellas on the entire sedimentation tank.
Construction
This semester, we constructed two sedimentation tanks based on the Open Top Design and the Open Top Parallel Lamella Design.
Materials
In building the sedimentation tanks, we used materials similar to those used in previous plants. For the section of the tank containing lamellas, we used corrugated plastic that was left over from previous teams. The water entry section on the bottom of the sedimentation tank was made out of a cylinder of transparent acrylic. The Open Top Design also required a water collection section on the top, which was also made out of transparent acrylic. The Parallel Lamella Design required a double tap for the top of the tank, which was made out of acrylic as well. The plug at the end of the tank furthest from the flocculator was made of a dark gray PVC material.
Description of Construction Process
Pictures of Finished Product
Post-Construction Modifications
Open Top Design
In the Open Top Design sedimentation tank, we found that flow was unequal through each of the lamella. Water tended to flow through the first 3 lamella at a very fast rate, through the next 3 lamella at a slow rate, and through the last ones at a very slow rate, or not at all. This was determined by adding red dye to the last column of the flocculator, and observing the movement of the dye through the sedimentation tank.
To rectify this, we designed the Parallel Lamella Design sedimentation tank, and had it constructed at the Machine Shop in Hollister Hall of Cornell University.
Parallel Lamella Design
In the Parallel Lamella Design, we found that flow through the sedimentation tank was highly dependent on the angle at which the lamellas were oriented. Due to imperfections in the construction process, the flow through each set of lamella was uneven when the tank was exactly perpendicular to the table surface (parallel to plane of flocculator).
To rectify this problem, we varied the angle of the sedimentation tank while observing its effects on the flow rate in each set of lamellas. We found that a slight angle (with respect to the plane of the flocculator) was necessary to achieve equal flow in both sets of parallel lamellas. We hypothesized that this was due to very slight differences in the height of the orifice through which water exited each set of lamellas, which had a significant affect on the amount of head loss experienced by water flowing through each side of the sedimentation tank. By changing the angle of the whole tank, we solved this problem.