Abstract
As the flow rate through an AguaClara plant is increased, the plants design will need to be altered. More specifically, to achieve the required amount of energy dissipation for adequate alum mixing, we would need to redesign the entire entrance tank. Since the flow is so much greater than that of previous plants, the orifice exiting the entrance tank will need to be much larger. This presents a problem as the alum orifice will not be as large, and thus we would require a greater amount of mixing. This problem will be achieved by using two hydraulic drops.
Gracias Entrance Tank Design
Design Schematic
Rapid Mix Chamber
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Rapid Mix Chamber design (Dimensions are in cm.)
The AutoCAD file for this preliminary design is attached to this page.
The rapid mix chamber is made of concrete and is attached to one side of the entrance tank. The water within the entrance tank initially enters the horizontal channel through a rectangular orifice. This rectangular orifice will help provide the necessary energy dissipation to create the large eddies that are necessary for global mixing. The water that enters this rectangular orifice will experience free fall into the horizontal channel. Then, another waterfall occurs when the water flows from the horizontal channel into the vertical channel. The water that flows into the vertical channel will be in free fall. The water will experience will experience a contraction at the rectangular orifice that leads into the flocculation tank. This will allow for the necessary energy dissipation to achieve the molecular diffusion of the alum.
Design Assumptions and Specifications
The majority of the assumptions made for this design were the same as in past designs.
The design of the orifice that leads into the flocculator must provide the necessary energy dissipation to achieve the required molecular diffusion of the alum in the water. Energy dissipation rate from minor head loss has to be greater than diffusion requirements: ε = 0.5-1.0W/kg. The following equation is used to determine the minimum energy dissipation required to overcome the diffusion requirements.
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$$
_{\varepsilon _
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= {{\pi {D
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}4 \nu _{
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}^3 } \over {D_m^2 \tau _
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^2 }}}
$$
The minimum energy dissipation is calculated to be approximately to be 0.733 W/kg. We assume a minimum energy dissipation of 0.8 W/kg is required at the flocculation entrance orifice to be safe during our design process.
$$
V = \left( {{
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\over {K_
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}}} \right)^2 \over 7
$$