h1. Launder Design Program
This program is used to design the manifold that will be used for transporting water out of the sedimentation tank to the exit channel. The launder will be located between the top of the lamella and the surface of the water in the sedimentation tank. The orifices will be at the center of the launders for water intake. The Launder program uses equations found in the [fluids functions|Fluids Functions Design Program] and [sedimentation|Sedimentation Tank Dimensions Design Program] programs.
!Launder.JPG!
h2. Launder Design Program Algorithm
[Launder AutoCAD Drawing Program| AutoCAD Manifold Pipe Program]
h3. Algorithm
Given the maximum flow rate through the treatment plant, and the number of sedimentation tanks in the plant, the flow rate for each sedimentation tank is equally divided between the number of sedimentation tanks. The length of the manifold section of the launder is the same as the length of the tank, minus the width of the entrance tank and the wall thickness.
{include:L.SedLaunderEst}
To determine the number of orifices in the launder, the length of the established manifold is divided by the specified orifice spacing (center to center), found in the [Design Assumptions|Design Assumptions Design Program]. Note that there are two rows of orifices on a single manifold. This number is rounded down to the nearest whole number.
{include:N.SedLaunderOrifices}
There will be 2 sedimentation launder pipes within each sedimentation tank (N.SedLaunders), as defined in the the Design Assumptions program. From that number the flow rate through each orifice is calculated.
{include:Q.SedLaunderOrifices}
Using an iterative program found in the [Fluids Functions|Fluids Functions Design Program] (ND.Manifold) and the available pipe sizes, the nominal diameter of the manifold is determined and defined as ND.SedLaunderEst. This equation is a function of different parameters established in the [Design Assumptions|Design Assumptions Design Program].
The total head loss in the launder is then calculated using the HL.Manifold equation found in the Fluids Functions. This equation is defined below with the given inputs and a minor head loss of 0.
{include:HL.SedLaunderEst}
Next, the head loss through the orifice is the given head loss, HL.SedLaunderBod, minus the calculated head loss through the whole launder. This is defined as HL.SedLaunderOrificeEst.
Finally, the diameter of the orifice holes is calculated using the D.Circle equation from the fluids functions. This number is rounded to the nearest available drill size. Written out, the equation is as follows:
{include:D.SedLaunderOrificeEst}
h4. Flow through the Launder
The launder fits into a coupling that extends through the wall separating the sedimentation tank and the exit channel. Control pieces that fit into this coupling have been designed to stop the flow between the sedimentation tank and the exit channel when it is necessary to drain the tank.
To stop the flow, a PVC cap is fitted onto the end of the coupling extending into the exit channel. The dimensions for this cap are derived from the PipeSizes matrix in the Pipe Database that defines the dimensions for a cap based on Nominal Pipe Size.
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To re-fill the sedimentation tank with clean water from the exit channel, a uniquely designed control piece is fitted into the launder coupling. The launder is removed from its place when the tank is drained. Then, a control piece consisting of a short pipe covered by a cap with a single orifice is fitted in its place. The size of this orifice is calculated so that the flow rate of water into the empty sedimentation tank is not higher than the flow rate of water out of the other sedimentation tanks.
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{latex}
\large
$$
A_{Orifice} = {Q_{Sed} \over (Pi_{VenaContractaOrifice})\sqrt{2g(H_{LaunderCap})}}
$$
{latex}\\
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The height used in the equation is the difference in height between the water flowing in the exit channel and the height of the orifice, calculated as:
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{latex}
\large
$$
H_{LaunderCap} = {H_{Sed} - H_{ExitChannel} + HW_{ExitChannel}}
$$
{latex}
\\ !laundercapside.PNG|width=443,height=318!\\
\\ !laundercaptop.PNG|width=442,height=431!
Once the tank is refilled, the control piece is removed and the launder replaced. | 