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The number and spacing of floc spaces and floc baffles is calculated, as well as the CP, for the specific tank being drawn. Both the minimum and maximum number of floc spaces use the equation:

{latex}
\large
$$
N_{Spaces} = {{L + T} \over {S + T}}
$$
{latex}

The ceiling, floor, and round functions are used to force this number to be even (so that the water flows from port to port in all channels except the last). When trying to find the minimum number of spaces that can fit in a channel, the value is rounded up. When trying to find the maximum number of spaces that can fit into a channel, the value is rounded down. Otherwise, the value is just rounded.

When calculating both the min and the max, L represents the length of the sed tank L.Sed and T represents the thickness of a baffle T.FlocBaffle. To get the maximum number of floc baffles, S is taken as the minimum floc baffle spacing S.FlocBaffleMin. However, to get the minimum number of floc baffles, S is taken as

{latex}
\large
$$
{{J } \over {Pi_{JSMin} }}
$$
{latex}

where Pi.JSMin is a parameter describing the minimum ratio of water depth to baffle spacing.

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The center-to-center distance between baffles includes the spacing between baffles and the thickness of the baffles, for each channel. This is an array with an element for each channel, as each channel may have different baffle spacing.

{latex}
\large
$$
B_{FlocBaffle} = S_{FlocBaffle} + T_{FlocBaffle}
$$
{latex}

The residence time in the flocculator is determined as follows:

{latex}
\large
$$
Ti_{Floc} = {{J_{FlocChannel} \cdot L_{FlocTank} \cdot P_{FlocChannel}} \over {Q_{Plant}}}
$$
{latex}

The height of water at the beginning of the flocculator is based on the height of water at the end of the flocculator plus the headloss through the flocculator. The head loss is determined per baffle (and per channel, and in the whole flocculator) using the HL function in the fluids functions program. An additional freeboard space was added to the water level (HW) found at the beginning of the flocculator to determine the height of the flocculator walls.

The head loss per baffle in each channel:

{latex}
\large
$$
HL_{FlocBaffle} = {{{Kp \cdot ({{J_{FlocChannel}} \over {S_{FlocBaffle}}}) \cdot Q_{Plant}^2 } \over {2 \cdot g \cdot (S_{FlocBaffle} \cdot P_{FlocChannel})^2 }}}
$$
{latex}

Water flows between channels in the flocculator through ports cut in the concrete. The area of these ports is determined to ensure flocs will not be broken up.
The energy dissipation rate through the ports is set to be same as around the baffles; the dimensions of the port are calculated to be the same as that of the baffles.

{latex}
\large
$$
W_{FlocPortEst} = S_{FlocBaffle}
$$
{latex}

The width of these ports is set to include the thickness of the concrete lip needed to hold the baffle in place.

{latex}
\large
$$
W_{FlocPort} = W_{FlocPortEst} - S_{FlocChannel}
$$
{latex}

Position Calculations for Each Baffle

The length of the lower floc baffles is determined based on the height of water at the end of the floc tank and the water as it goes around each turn. The baffles are oriented to go up-down-up-down so that the flow of water is smooth through the tank. This order, however, is reversed in the last channel, since there is an even number of baffles and the water must flow under the last baffle and up to the exit port that leads to the sed tank.

Length of Lower Baffle:

{latex}
\large
$$
L_{FlocBaffleLower} = J_{FlocChannel} - S_{FlocBaffle} \cdot Pi_{FlocBaffle}
$$
{latex}

The upper baffles are set to line up with the top of the tank rather than the water level.

Length of Upper Baffles:

{latex}
\large
$$
L_{FlocBaffleUpper} = H_{Floc} - S_{FlocBaffle} \cdot Pi_{FlocBaffle}
$$
{latex}

The last channel in the flocculator must be treated differently than the other channels since there are more constraints. The inlet channel to the sed tank connects to the outlet of the floc tank by an exit port. This already has a size and location by the time the floc tank is drawn and designed. Additionally, as described above, there are an even number of baffles in this last channel, and there obviously cannot be any baffles drawn in the way of the exit port.
Therefore the program that places the baffles for the last channel first considers the baffle spacing. If the spacing for the baffles is smaller than the width of the exit port, there will either be one or two baffles that fall within the exit port space.

{float:left|border=2px solid black}
[!baffle in exit port.PNG|width=450px!|AutoCAD Channel Program]
Baffle in the Way of the Exit Port
{float}

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As long as the port area is no larger than the valve area, the port area limits the flocculator drain time.  For this reason, the port area is set to be equal to the area of the valve used to drain the flocculator. The area of the ports, and therefore the diameter of the valve, is calculated based on a drain time set in the expert inputs. The time required to drain a tank is:

{latex}
\large

$$
t = {{\sqrt {h_0 } - \sqrt h } \over {{{A_{or} } \over {2A_{res} }}\sqrt {{{2g} \over {K_{minor} }}} }}
$$

{latex}

where h_o is the initial water height in the tank, h is the water height at time t, A_or is the area of the orifice through which the water drains (in this case the port or valve area), A_res is the plan area of the reservoir or tank (i.e. the space between two lower baffles), and K_minor is the minor loss coefficient associated with the flow.

The flocculator can be separated into two parts. The first part is the horizontal portion above the top lower baffles where the water drains as a single tank; the highest lower baffle was used for this calculation, resulting in a slight overestimate of the total drain time. The second part is the portion below the top of the lower baffles where these baffles form small "tanks" within the flocculator. For the upper portion, the area of the orifice is the area of the valve,

{latex}
\large

$$
({{\pi D_{valve}^2 } \over 4})
$$

{latex}

and the minor loss coefficient is that associated with the chosen valve.
The flow through the tank is calculated as follows:

{latex}
\large

$$
Q = {{\pi D^2 } \over 4}\sqrt {{{2g(h_1  - h_2 )} \over {K_{minor} }}}
$$

{latex}

where h₁ (the height inside the tank) is greater than h₂ (the height outside the tank). If the water height outside the tank is higher than that inside the tank, the flow is assigned a value of zero. This equation is easily applied to the upper portion of the tank, but must be applied individually to the spaces between the lower baffles.

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