Automated Design Final Algorithm Report Spring 2008

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Spring 2008 Team Members: Raul Santiago, Cherish Scott, Becky Katz, Tamar Sharabi, Sarah Long, Leslie Campbell, Rachael Moxley

The Automated Design Team is responsible for determining the best algorithms, or the basis of design, for each component of the small-scale water treatment plant. The ensemble constitutes the automated design program that will be used by the AguaClara team to quickly develop plans for new water treatment plants to be built in Honduras. Thus far this semester the team has worked hard to get the working skeleton of the code in place. Over the past couple of weeks we have made progress constructing and documenting our basis of design.

The Master; Program is the driver of the automated design program. It is the central file where values are entered, functions are called, and parameters are returned and displayed. Originally the hope was to be able to run the file through a MathCAD supported server, thus allowing anyone with an internet connection to type in the specifics for their community and receive the plant designs. This proved to be cumbersome because of its many limitations including the inability to enter non integer numbers and a large question about how to get the script functions for the AutoCAD drawings to the user. The most recent thoughts about the user interface include LabView, but the process is still in the idea phase. For now the master program is the main page for the design team to test and develop the automated design program. This report aims to explain both the large scale basis of design and the small scale components of the program in so far as they have been determined thus far.

The AguaClara Automated Design Master Program is rooted in many different assumptions. All detailed programs outlined in this report use the following

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The Pipe Database contains arrays of nominal pipe sizes, their actual outer diameters and the minimum wall thicknesses based on Pipe Schedules 10, 30, 40, 80, 120,160 and Pipe Standard Dimension Ratios 17, 21, 26,32.5, and 41. From this information an array of available pipe sizes can be constructed given the Pipe Specification, which is the Pipe Schedule or SDR selected in the Master Program. The Pipe Database will be updated to include tee and cross dimensions for use in drawing the plant in autoCAD.

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A pipe design function was created so that all pipes could be designed quickly and corrected.In order to find the proper diameter the program iteratively solves for the flow that can fit through a pipe of a given diameter with the given headloss until a large enough diameter is found in the pipe database.

The inputs of this function are the maximum flow of the plant (Q _plant ), the pipe specification of available dimensions (PipeSpecification), the maximum headloss ( h _lmax), the sum of all the individual headloss coefficients of elbows, tees, valves, expansions and contractions (K _sum) and the length of the pipe (L _pipe).

The Q _plant , and L _pipe are assumed design values.

The PipeSpecification calls the Pipe Database, please refer to the Pipe Database section.

K _sum values equal to the number of elbows, tees, valves, expansions and contractions multipled by their corresponding K ~ values~. All corresponding K _values are given in the Basis of Design tab.

h _lmax values calculated using the following set of equations.

Re = Reynolds Number, to determine if flow is turbulent or laminar
Q = Flow Rate
D = Pipe Diameter
¿ = Kinematic viscosity of water

f = Friction factor, equation for either turbulent or laminar flow
epsilon = Roughness factor of PVC

h = Major head loss

The outputs of this function are actual pipe diameter referenced from the pipe database.

Inputs- Q _plant, PipeSpecification
Outputs- SedPipe _length , D _orifice, orifice _dist, manifold _depth

This program is used to design the manifold that will be used for transporting water from the sedimentation tank to the plant leveling tank. 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 given. The length of the launder is the same as the length of the tank. Water level on the sedimentation tank, measured from the bottom, is 2m. The water height above the launder is equal to the water level in the sedimentation tank minus the height of the top of the lamella, measured from the bottom, minus half the difference between the water level in the sedimentation tank. The orifices will go parallel at each side of the launder, and they will be spaced every two lamella.
The diameter of the pipe is estimated through an iterative process, given the pipe database, the flow rate ratio, Q_ratio, and the following equation:

Later the head loss in the manifold is determined, and with it, the diameter of the orifices. Lastly, the head loss through the orifices is calculated.
To design the pipe component that transports water to the leveling tank the pipe design program is used. After setting an acceptable head loss, the diameter of the outlet pipe is determined. In case the diameter for the outlet pipe is different from the diameter determined in the launder program, then the largest one should be chosen.

Inputs- Q _plant, PipeSpecification
Outputs- waste _inr, D _orifice, orifice _dist

This program is used to design the manifold that will be used for the sedimentation tank drainage. 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 given. Using the critical velocity, the plate settler's length and diagonal spacing, the upward velocity can be determined, which in turn can be used to determine the active area of the sedimentation tank. With the active area, the length of the sedimentation tank is determined, and with a constant orifice spacing of 10 cm, the exact number of orifices in the pipe can be calculated.
With the drainage time set at 30 min, the constant water level of 2m, the width and length of the sedimentation tank, the initial drain flow rate is estimated.
The diameter of the pipe is estimated through an iterative process, given the pipe database, the flow rate ratio, Q_ratio, and the following equation:

Later the head loss in the manifold is determined, and with it, the diameter of the orifices. Lastly, the head loss through the orifices is calculated.

The purpose of this function is to determine the dimensions of the channel. The channel will run along the ends of the sedimentation tanks, such that its length will be equal to the widths of the three sedimenation tanks. The dimensions of the width and depth of the channel depend on the water level in the sedtank, which should be about the same as in the channel and the flocculator, and the length of the flocculator, since water runs from the end of the flocculator through the channel.

The primary constraint for designing the channel connecting flocculation and sedimentation tanks is the depth of the channel. The channel must be designed to make sure that the transition between the two tanks does not break up the flocs formed in the flocculation tank. Therefore the average velocity gradient, (G.cell) was a key parameter in the design. G.cell is the average velocity gradient in the cell where the energy dissipation is assumed to be occurring. A G.cell of 15/s was used because it is the desired velocity gradient for the end of the flocculation tank. Anything higher could result in the breakup of flocs.

K.cell the loss coefficient for the channel transition and ¿.cell, energy dissipated were additional parameters. The factor b takes into account the flow rate of the plant, the average velocity gradient and energy dissipation.

The width and height is multiplied by 1.5 by convention. Opening of channel height determines the height for the entire channel. The width of the channel may also be based on construction constraints, such as the maximum space available between the flocculation and sedimentation tanks.

The length of the channel is a function of the number of sedimentation tanks, which is three in this design, and the thickness of the walls between the sedimentation tanks.

The purpose of this program is to design the dimensions of the grit chamber, the number of risers in the chamber through which rapid mix takes place, and the number of holes in each riser.

The first step taken to design the number of risers in the grit chamber is to create an array of available pipe sizes based on the pipe schedule or SDR specified by the engineer and call on the AvailPipeSizes1(Pipe Specification) function in the PipeDatabase.

A maximum head loss through the riser pipe is assumed to be 20 cm, and the maximum head loss though a single orifice is assumed to be 20 cm as well. A function was created (K.sum) to sum the head loss coefficients throughout the system. This function was then referenced with appropriate amount of components specified. The diameter of the riser pipe was then calculated using the fluids function that determine the diameter of the pipe based on a specified flow rate and head loss through the pipe (D.pipe). The orifice head loss coefficient was specified then used along with the flow rate through the plant and the maximum head loss through an orifice to determine the area of the orifices. The (A.orifice) fluids function was used in the calculation.

The diameter of each orifice is set to 1.5 in (3.75 cm), which was found rather arbitrarily only constrained by what sizes could be drilled. A ratio of the maximum inlet orifice area to the pipe area is set to 0.3, so that the riser pipe will not lose too much strength by having too many holes around its perimeter. It also assumes that the total pipe length between the orifices and the flocculator (rapid mix pipe) is 2 m.

The diameter of the riser is found from a specified headloss allowable through the rapid mix pipes and the flow rate into the plant. For each diameter available the program will iterate until the flow calculated through the pipe is greater than or equal to the flow through the plant.

The orifice equation:

The total area of the risers was used to design the dimension of the grit chamber. This area was found using the diameter of each riser pipe, and the (n.risers). In the final design of the plant the grit chamber should be a no smaller than the area of the chemical feed drum. This is simply a practicality constraint. If the riser.areaTotal is smaller than drum.area then the grit chamber will designed using drum.area instead. From the riser.areaTotal the grit.width and grit.length is found. The grit depth is 2 m by convention.
The outputs of the function are the grit chamber dimensions (grit.dim), the number of risers (n.risers), and n.orifice, which is an array of orifices for a specified vertical height.

The purpose of this program is to design the leveling tank that will keep a constant water level throughout the plant, which in turn will optimize the operation of the plant, as well as facilitating the monitoring of the plant. This component must maintain some dimensional consistency with the other components of the plant. It consists of having inlet pipes that connect to each sedimentation tank, and a circular weir in the center that will transport the water to the storage tank. It is in the weir where water will be chlorinated.
As specified in the assumptions, the height of the leveling tank's wall will be the same as the height, measured from the platform of the plant, as the wall for the channel and the sedimentation tank. Setting the base of the leveling tank at the same level as the center of the plate settlers, the height of the wall will be equal to the 2 m of the water level minus the height of the center of the plate settlers, measured from the bottom of the sedimentation tank, plus the freeboard of the sedimentation tank, which is 10 cm.
The height of the weir is equal to the water level of the sedimentation tank minus the height of the center of the plate settlers minus the head loss going through the launders. To determine the diameter of the weir, the weir equation is used:

q = 2/3 c_d ¿D (2 g)^1/2 h^3/2 (1)

where

q = flow rate (m³/s)

h = head on the weir (m)

D = diameter of weir (m)

g = 9.81 (m/s²) - gravity

c_d= discharge constant for the weir -0.62

The Plant Leveling Tank function determines all of the water level elevations throughout the plant first relative to the bottom of the sedimentation tank.
Any variables with HW indicate the depth of water. Any value Z indicates a height.
The program first assigns values from the inputs that are arrays to individual values so that it is easier to determine what they are based on the variable name.

The headloss through the launder is found in the launder function and the height of the water in the channel is set as a design assumption. From these the actual height of the water in the PLT is calculated from the height of the water in the channel minus three times the headloss through the launder since there are three launders.

The number of orifices in the grit chamber are calculated by multiplying the sum of number of orifices at each height per riser by the number of risers in the grit chamber.

L.sedexits is the length of the exit pipes from the sedimentation tanks to the plant leveling tank, but for now it is set as a constant until we determine how to calculate it.

The headloss through the weir, will determine the height of water in the level tank: The headloss through the weir in the plant leveling tank is calculated with the headloss equation for a weir in the fluids functions file. Headloss is also calculated through the total number of launder orifices and the headloss through the launder manifolds.

The height of the sed tank is found by the height of the water in the sed tank plus the height of the freeboard, which is a design assumption.

The height of the top of the plate settlers (lamella) in the sed tank is found by adding the height of the bottom of the plate settlers to the vertical projected height of the lamella at angle alpha.

The height of the launders centered in the water above the plate settlers is found by subtracting the height of the top of the plate settlers from water in the sed tank, dividing by two, and adding the height of the height of the top of the plate settlers back again. This may be different from how the depth of the water above the launder is calculated in the sedimentation tank function. This should be checked.

The head loss through the pipes that take the water to the level tank needs to take into account that the flow won't divide quite equally between the pipes because of different total loss coefficients. We use conservation of mass and the fact that the head loss through each of the paths is the same to determine the actual head loss. First we calculate the minor loss coefficients for the exit pipes. This is based on the number of ninety degree turns in the pipe, which is a design assumption since it depends on the plant layout, times the Kel90 added to the Kexit for each pipe. Then the function HLsedexits is called on to calculate the headlosses.

ZTsed is, I think the height of the wall in the tank, calculated from the height of the water in the sed tank plus the freeboard. this is probably the same as the height dimension calculated from the sed tank program.

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The purpose of this function will be to return any necessary parameters relating to aluminum sulfate or chlorine dosage.

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