Page History

...

• Length (L) = 23.125"
• Width (W) = 23.125"
• Height (H) = 36"
• Water Level (WL) = 33.25"
• Flow Rate (Q) = 30L24 L/min

Below is an AutoCAD drawing of the proposed sedimentation tank design.

...

Upward Velocity Calculation:
To determine the The upward velocity parameter determines what size of floc particles are removed from the sedimentation tank the flow rate through the tank was divided by the cross sectional area of the tank. In order to make our model comparable to the sedimentation tanks that are built on a full scale the upward velocity . Thus in order for our design to be comparable to exist sedimentation tank design Vup needs to be the same. The upward velocity in Ojojona was found Vup was set to be 100m/day. Thus this was the parameter we used for this model as well. We allowed our design velocity to exceed 100 m/day with the idea that we will probably have to modify the flow after construction to allow a stable sludge blanket to form.

Insert Upward Velocity Equation.

From this we calculated the flow rate through the tank was necessary to achieve this Vup.
Given there are no lamella the equation is fairly straight forward.

From this equation the flow rate was determined to be 24 L/min.

Inlet Pipe Calculations:
To determine the diameter of the inlet pipe we used the constraint that the maximum shear due to minor losses had to be less than Gav in the last section of the flocculator (Gav = 24/s). The predominant minor losses from the inlet pipe will occur at the exit point and the elbow. The minor loss coefficient for the elbow is 0.9 and the exit is 1.0 so K was set to be 1.0 for this design. The equation to calculate shear due to a pipe elbow is shown below. This equation is solved for D, the diameter of the pipe that would provide shear equal to Gav. The equation used is very similar to the equation used to find the baffle spacing for the flocculator. //

Variables:
K = 1.0 (minor loss for an exit)

• This equation was derived from a series of substitutions that can be seen above

...

• .

Insert epsilon equation here.

Insert head loss equation here.

• The head loss

...

• term that is found in the above derivation is assumed to

...

• include only minor losses. The minor head loss for this pipe is assumed to be the dominating factor because the pipe is designed to be relatively short in length and the bends and exit are our major sources of shear, the primary locations where floc break up would occur.
• The velocity

...

• equals Q/A for the pipe.
• The residence time term is found to be the volume over the flow rate through that volume.
• The volume used was assumed to be the cross sectional area of the pipe times 2 diameters of the pipe.

Initially when this equation was solved, we used Note: Initially during preliminary design with a large tank, we were using 55 L/min as the plant flow rate, and MathCAD returned that the pipe diameter would be 5.11 inches to achieve the desired Gav value. Due to the cost of 6 inch bulkhead fittings (nearly $300), we had to find an alternative design. We decided to lower the flow until a pipe with inlet diameter equal to 4 inches was achieved. We found that the maximum flow for these conditions is 24 .5 L/min, so we changed the flow rate of the plantsedimentation tank. The option of having two 4" multiple inlets was considered but this was discarded because then 2 - 4 bulk head fittings would be needed. Thus, the overall flow of the tank was lowered and a smaller tank was chosen. This change in flow rate necessitated a change in tank size (to a smaller cross sectional area).

Launder Calculations:

Pipe Diameter
The effluent launder will span the length of the tank about 4in off of center of the tank. The launder is placed 2 in beneath the water level. This value was assumed to be constant to allow for uniform flow through all of the launder orifacesorifices.  The The diameter of the effluent launderer launder was calculated by iterating through pipe diameters to find the existing diameter of pipe that matched up with gave the desired flow rate and orifice holes. The diameter was selected based on the following equation:

• Qratio is assumed to be 0.90, this indicates that flow through the first orifice will be 90% of the flow through the last orifice.
  The best pipe diameter is 1.5 inches. The number of orifice holes was

...

• tweaked until the orifice hole diameter would match up with a drill bit size

...

• and still

...

• gave the proper

...

• amount of head. (equations for this can be seen in the following section) This head loss was defined to be about 5 cm, or the head available above the launder. If the head loss through the launder orifices exceeded the available head, we would have encountered issues because the water in the outlet system would have had less energy than the surrounding system, which would have effected the flow rate and caused air to collect in the outlet pipe. The total number of orifices was

...

• determined to be 15.

Orifice Diameter
The diameter of the orifices was calculated by finding orifice equation was used to determine the necessary area of the orifice based on the head at the launder, the minor loss of the orifice, and the flow rate through the orifice (that gives the correct amount of head and matches with an existing drill bit size. The flow rate used in this equation was the total plant flow rate divided by the number of orifices). The equation to find the area is found below. With the area, the diameter of the orifice can easily be calculated by solving the area of a circle for the diameter. The minor loss coefficient of for an orifice is assumed to be 0.63, and the head, h, is equal to the height of the sed tank minus head loss through the launder minus the velocity head through the orifice. The head loss term in the equation is total head available less the head loss in the manifold pipe less the velocity component of head loss through the pipe.
This area, was then converted into a diameter. This value was a rounded to the next smallest drill bit size. The diameter of each orifice was figured out to be 19/64". This value was rounded to the next smallest drill bit size.

Orifice Head Loss
The head loss due to the orifice ends up being is an important parameter because it effects how evenly the water will flow through the orifices. This quality is quantified in the parameter Q ratio, which is the ratio of flow through the first orifice divided by the ratio of flow through the last orifice. We have set the value of Q ratio to be 0.90.Orifice Head Loss
Thus we back calculated the actual head loss achieved given the diameter adjustment that was made to achieve an existing drill bit size.
The head loss through the orifice was calculated by using the following equation:

...

D is the diameter of the orifice (21.6 cm19/64 in), the minor loss coefficient of the orifice is 0.63, and the flow is the flow through one of the orifices. The minor loss for an orifice was calculated to be 4.55 54 cm. The head loss through an orifice is parallel to other orifices, so you do not add the head loss in each orifice. This parameter is the level that the water in the plant leveling tank needs to be below the water level in the sed tank in order for our plant to be operated at the designed water levels.

...