Lamella Design Program

Lamella Design Program Inputs and Outputs

Lamella Program Inputs
Lamella Program Outputs

Lamella Design Program Algorithm

The Lamella Design Program uses the triple constraints of the a critical velocity of 10 m/day, an upward velocity at the bottom of the tank of 70 m/day to calculate the space needed between the lamella and the length of the tank set by the Sedimentation Program. The critical velocity is the rate at which a particle must fall to ensure that it settles out in the plate settlers. If the critical velocity is too large, flocs will not settle out. However a small critical velocity comes at the expense of area (so it is not practical to have an unnecessarily small velocity). The upward velocity at the bottom of the tank is important for sludge blanket formation. If the velocity is too low the blanket will either settle out or the shear value in the blanket will be so high that floc will get broken up in the blanket and thus the sludge blanket could be detrimental to the sedimentation process.
The program starts by determining the height available for the lamella. After the height available is determined the length of the lamella can be found given an assumed angle of 60deg. Inorder to find the vertical height avaiable for the lamella, first the height of the water needed above the lamella is found.

The distance below the lamella, H.SedBelowSlope, was found in the sedimentation program and based off of the tank fraction given by the user. The vertical height available for the lamella is simply the remainder of the water depth in the sedimentation tank after the slopes and the space needed above the lamella has been accounted for.

The lenght of the lamella:

The next step is to determine the space between the lamella needed to satisfy the critical velocity given the tank length found previously. In order to determine the space between the lamella the inactive length of the tank and the upward velocity under the lamella must be found first. The inactive length of the tank consists of the space occupided by the inlet and exit channels.

The upward velocity under just the active lamella area is flow through the sed tank divided by the cross sectional area of the active portion of the sedimentation tank.
Upward Velocity under the Active Area below the Lamella:

The perpendicular distance between the lamella is found from the equation below. typicalyl the lamella spacing should be around 5cm apart. Closer distances are thought to possibly lead to floc not settling properly and possible clogging.
Distance from Center to Center between Lamella:

Horizontal Distance Center to Center between Lamella:

The open space between the lamella is the area for water to flow up through the lamella. This spacing is the center to center spacing between the lamella minus the thickness of the lamella material.
Open Space between Lamella:

The number of lamella placed in the tank is determined by the maximum number that can fit in the tank. This number is calculated using the following equation.
The Number of Lamella:

Without knowing the exact number of lamella that will be placed in the tank it is not possible to calculate the exact parameters of the tank. Now that the exact number of lamella has been calculated the exact active tank length, upward velocity, and critical velocity up through the lamella. The exact parameters are found using the equations below.

Active Length of the Tank:

The Actual Upward Velocity at the Bottom of the Tank:

The Critical Velocity Up through the Lamella: