Sludge Drain Design Program

This program designs the channel that will be used for the sedimentation tank sludge drainage. The sludge drain runs along the bottom of the each sedimentation tank and collects the flocs as they fall from the lamella and slopes.

Sludge Drain Design Algorithm

Sludge Drain Inputs
Sludge Drain Outputs
Sludge Drain AutoCAD Drawing Program

Algorithm

The number of sludge drains is determined by the number of sloped pairs in the sedimentation tanks. This is defined as N.SedSludge, and uses the number of slope pairs calculated in the Sedimentation Inlet Slopes program.

The orifice spacing of the sludge drain is set so that there are two orifices per slope plate. So orifice spacing is calculated as W.SedSlopePlate/2. The width of the sed slope plates is a basic user input.

Next, the number of orifices in the pipe can be calculated given the orifice spacing and the length of the sedimentation tank from the [Sedimentation] program.

The dimensions of the sludge drain channel and the sludge valve are determined based on the maximum acceptable head loss through the drain. Here it is assumed that we are willing to use 80% of the available head to get the flow through the valve. So HL.Valve = 0.8 HW.Sed.

Calculation of the diameter of the valve requires that we now the drain rate through the drain. This value is determined by the dimensions of the sed tank and the time needed to drain the tank, a user defined value.

This initial drain rate is then used to calculate the diameter of the valve needed via the D.pipeschedule funcion of the Fluids Functions program.

The diameter of the sludge drain pipe is estimated through an iterative process, using the ND.Manifold equation found in the Fluids Functions program.

Because the sludge drain is no longer a pipe but now a rectangular channel, this diameter is then used to calculate the required cross-sectional area of the drain. Based on manifold theory, the total area of the sludge orifices is equal to the cross sectional area of the manifold.

Given the required area for uniform flow, and the depth of the drain, H.SedSludge (set to be 5 cm in Design Assumptions), the width of the drain is calculated.

Once the total area of the orifices and the number of orifices have been calculated the diameter of each orifice is found by rounding the required diameter up to the next available drill diameter.
The initial flow rate through the sludge drain is calculated using the Q.Orifice equation found in Fluids Functions:

The initial flow rate is then used to calculate the total time needed to empty the sludge drain: