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Pilot Plant Construction and Research
Author: AguaClara Pilot Plant Sub-Team ses88@cornell.edu
Sections on initial Design and Tank Construction were written by:
- Mandy Chu
- Earl James "EJ" Foster
- Kavita Mahulikar
- Carol Serna
- Tamar Sharabi
- Jordan Warner
Sections on the Testing of the Uniform Baffle Configuration were written by:
- Carol Serna
Unknown macro: {toggle-cloak} Abstract">Unknown macro: {toggle-cloak} Abstract
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The Vertical Flocculator Pilot Plant division of the Research and Development team has constructed and is working on testing a turbulent-flow hydraulic flocculator and rapid mix unit at the Cornell University Water Treatment Plant (CUWTP). A flow control module and sedimentation tank are also being added at adjacent parts that will work in conjunction with the main flocculator. Prior to the construction of the present tank, flocculation research was done on a small scale, laminar flow tube flocculator. In order to test flocculation under turbulent flow conditions the pilot plant hydraulic flocculator was built. It is a rectangular tank that is divided into three sections that are filled with vertical baffles similar to the baffles used in Ojojona, Honduras.
The vertical baffles were spaced using equations written in a MathCAD program created to test for different velocity gradients, G and amount of mixing, Gtheta. An alternative baffles set-up was also created that has varying baffle spacings, where the baffles get farther and farther apart through the tank. The previous setup has a baffle spacing of 6.45 cm with 27 baffles per section. The new set- up is split into four sections with four separate baffle spacings. After preliminary testing, it was determined that the tapered spacing is more efficient and just as affective in a shorter residence time. Settling tubes were designed to measure flocculation performance at different locations in the tank. Through manipulation of the flocculator flow rate, it will be possible to manipulate G. The effects of changing the parameter Gtheta can be easily measured by varying the location of the sedimentation tubes. This setup will allow a systematic method to identify an optimal combination of the two parameters and verify their roles in efficient flocculation. Our goal for efficient turbidity removal is defined as NTU < 1. A sedimentation tank is also being constructed to work in conjunction with the flocculator and thus allow for testing of the entire aguaclara process. A flow control and measuring unit is also being added to the flocculator. The digital flow meter is currently in place will be used to test the accuracy of the flow control device that is in place in Honduras.
Keywords: turbulent-flow, hydraulic flocculator, rapid mix, vertical flocculator, Cornell Water Treatment Plant, velocity gradient, Gtheata, efficient flocculation, efficient turbidty removal, tapered flocculation flow control device, sedimentation tank.
Unknown macro: {toggle-cloak} Introduction">Unknown macro: {toggle-cloak} Introduction
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Since 2004, Cornell University's AguaClara team has worked in conjunction with Engineers for a Sustainable World (ESW), and Agua Para El Pueblo (APP)to design and build four water treatment plants in Honduras. In addition to providing clean water to the La 34 and Ojojona, a plant in Marcala is under construction and a design for a plant in Tamara is also being completed. The plant at Ojojona also functions as a pilot operation, demonstrating successes and potential problems for future plants.
The R&D team focuses on optimizing flocculation technologies to make them more efficient and effective. Multiple sub-teams work on this task, each using a unique approach. The lab sub-team runs bench-scale experiments in the AguaClara lab, using a tube flocculator that operates in the laminar flow regime. In spring 2007, the Vertical Flow Pilot Plant sub-team worked with various Cornell University staff to design and build a larger-scale vertical flow flocculator at the Cornell University Water Treatment Plant (CUWTP), to facilitate to facilitate testing under turbulent flow conditions. The new flocculator more closely models Ojojona's existing configuration, hopefully allowing for more practical testing. This experiment will also allow verification and possible reduction of the large G¿ range (20,000 to 150,000) recommended for community-based flocculation. Flocculation effectiveness is influenced by a number of factors, including coagulant dosage, mixing value, influent turbidity and velocity gradient. The team hypothesizes that velocity gradient is the central variable for optimizing flocculation.
After construction of the plant was completed at the end of the Spring 2007 semester, during the summer testing was done on the uniformly spaced baffles. Then in the Fall 2007 semester the uniform baffle spacing set-up was exchanged for a tapered baffle configuration. The Spring 2008 semester is going to be spent doing more extensive testing on the tapered set-up.
Initially the main goal for this semester was to do research on this set-up to learn more about where flocs were breaking up in the flocculator. Research over the summer was focused on several areas of the interest with this test flocculator. First, we wanted to determine a floc formation and floc break-up profile through the flocculator. This would help us determine different aspects of the tank that were either helping or hindering flocculation. Secondly, there was a focus on determining the optimum alum dose based on raw water turbidity for ideal floc formation. This test was designed to help in the design of a better alum dosing algorithm. After the summer ended, the overall goals of the flocculator changed, attention shifted to the set-up and design of the flocculator itself.
Experiments were leading to the conclusion that good floc formation would require an average velocity gradient that changed throughout the flocculator. Thus this semester's focus switched to the design and construction of a tapered baffle set-up. It was planned that this new set-up would be tested in the flocculator and performance compared to the previous baffle arrangement. The overriding goal is to determine which set-up is more effective at creating large flocs and doing so in the most efficient manner, and shortest residence time. Initial tests were designed to compare both baffle set-ups and determine which is more efficient.
Research done on other sub-teams determined that the highest values of G were in the 180 degree bend and that the majority of flocculation was happening in these turns. The channels themselves seemed to be doing little to further flocculation. Thus the average velocity gradient that we were using for our calculations was not actually an accurate representation of the actual gradients that are occurring in the tank. Thus floc break could be occurring in the turn arounds because of a low estimate of the gradient. Our next step was to increase the G values in the channels to levels that were closer to those found in the turn arounds, essentially decreasing the variation in the gradient throughout the flocculator, and thus making the average gradient a more accurate representation of what was happening in the tank. A preliminary idea was to add some sort of obstacle structure to the channels to increase G. An initial design of interconnected PVC pipes that would be suspended in the channels between baffles creating higher shear levels and thus a higher velocity gradient.
Unknown macro: {toggle-cloak} Methods">Unknown macro: {toggle-cloak} Methods
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PilotPlantConstructionandBaffleDesign(UniformSpacing)">There have been three major phases dealing with the pilot plant. The first phase was the initial design and construction of the tank and the uniformly spaced baffles. The second stage was the testing of the uniformly spaced baffles that resulted in some tank modification. Third stage was the construction of the tapered baffles configuration. The current stage is testing the tapered baffles set-up and making additional tank changes based upon results.
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Pilot Plant Construction and Baffle Design (Uniform Spacing)
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Plastic Tank that was the starting design constraint for the vertical flow hydraulic flocculator.
The construction of the tank was started during the Spring 2007 semester. The floc tank was designed to be contained in a polyethylene tank of dimensions 182.9 cm × 91.4 cm × 121.9 cm (length × width × height) with a wall thickness of about 0.8 cm.[#tank] The design goal was to divide the tank into 3 separate sections, basically condensing a long, narrow flocculation tank into a more compact space by snaking the flow back and forth. The initial design divided the total minimum mixing value (20,000) evenly among the three sections, with each section having an even velocity gradient (G) of 45 s-1.
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Plastic dividers that create three sections for a serpentine flow path through the tank.
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The serpentine flow path can be clearly seen in the top view of the flocculator.
The tank needed to be divided into three sections. At first the team planned to purchase two plastic sheets as dividers, potentially welding them vertically into the tank This option was soon rejected due to two major concerns: difficulties of welding inside the cramped spaces of the tank, and lack of strength in the welds. After much contemplation, the maintenance shop proposed a plan to build a structure that would provide support and flexibility. The sketch shows that the dividers were welded onto a base slab and the completed module was placed into the tank. A port (hole through which water flows between sections) was cut in each divider prior to welding. The dimensions of the dividers are approximately 182.9 cm x 121.9 cm with a 0.6 cm thickness . The choice of material for the dividers as well as the base slab is high-density polyethylene and was specifically chosen for its non-reactive property in water treatment process, and most importantly its ability to be welded.
Originally the dividers did not create a tight fit with the tank because of the curvature of the tank wall.Water-safe caulk was considered for sealing the spaces between the divider unit and the tank walls. However, we opted to add extra plastic material, the same kind as the dividers to cover the gaps.
This initial design will then be compared and contrasted with alternative designs with different G distributions. In these alternative configurations, the velocity gradient (G) will be gradually decreased along the flow path by either widening the baffle spacing or introducing small obstacles between baffles. Initially a high G is used to maximize floc formation. Then G is gradually decreased in later sections to minimize breakup of large flocs. It is hypothesized that larger and better quality flocs will be formed in the latter tapered configurations. Below is a list of fixed parameters (or "givens") and the values of G to be used in the initial setup.
Givens:
- Tank dimensions: 182.9 cm × 91.4 cm × 121.9 cm
- Tank wall thickness: 0.8 cm
- Tank divided into 3 sections (serpentine flow path)
- Total minimum mixing value (Gtheta) = 20,000
- Initially 1st, 2nd, and 3rd sections of tank to have velocity gradient (G) of 45 s-1
Variables:
With initial design constraints defined, a MathCAD program was used as a design/calculation tool to determine variables.
- Flow rate (Q)
- Number of baffles per section
- Baffle spacing (b)
- Baffle dimensions:
- Width x height
- Different heights for top and bottom baffles)
- Baffle dimensions:
- Dimensions of openings in dividers
- Width x area of flow path - Total head loss (ht)
- Water level (L)
Calculations:
The purpose of adding baffles was to increase mixing (G) by acting as an obstacle and forcing water through a restricted flow-path. G is a variable that controls the upper limit of shear. There is a maximum G (and thus a maximum shear) that a floc can experience before being broken up. The value of G directly controls the baffle spacing needed for efficient floc formation and preservation. A flow rate of 120 L/min and an effluent depth of 76.2 cm were chosen for baffle configuration design. Presented below are the equations and values used for design calculations.
- Baffle Design
Total minimum mixing value (Gtheta = 20,000) is a function of path dimension and residence time. The equations used to calculate baffle spacing are presented below:
Insert Equation and Variable Key here
Since both V and f are functions of baffle spacing (b), the above equation cannot be solved explicitly, and thus multiple iterations were employed in MathCAD to solve for b within a 1% error tolerance. The resulting b value for the first configuration with identical G (45 s-1) is 6.45 cm with a total headloss of 11 cm. Given these b values and the corresponding flow velocity (V), the below equations were then used to calculate the number of baffles in the each section:
Insert equation here:
The number of baffles that was calculated for each section was found to be 27.
After the spacing and number of baffles was designed next was the height of the baffles. The baffles needed to be large enough to control the flow of the water and produce mixing. However, if they were too large the turning radius of the water would be small and create unwanted shear, which could break up flocs. To control this, the flow expansion around the turn of the baffles needs to be large enough to minimize unwanted shear. In order to do this, a flow space of 1.5b × w is required. Here w is the width of one section of the flocculator. The equations below were used to determine the dimensions of both types of baffles. The two types of baffles are top and bottom baffles.
The figure shown below shows what is considered a top and bottom baffle.
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Side view of the baffles. Top and Bottom baffles and flow path can be clearly seen.
The resulting fabrication height of top baffle is 88.9 cm while that of bottom baffle is 71.1 cm.
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Corrugated Baffles spaced and connected with the cpvc caps and pipes. Pressure connection holds baffles together.
The baffles are cut from plastic corrugated roofing material which can be purchased at most local hardware stores such as Lowe's and Home Depot. It is cheap, accessible and very similar to the material used in Honduras.
Since baffle design and dimensions depended on the divider design, baffles were not cut until the dividers [#dividers] were installed. Baffle [#baffles] dimensions were determined to be approximately 88.9 cm × 30.5 cm for the top baffles and 71.1 cm × 30.5 cm for the bottom baffles. Baffles were cut slightly wider than the section width (30.5 cm) . This was done to tighten the fit of the baffles, provide support for the dividers, and to prevent leakage of water between the baffle and the tank walls.
Baffles were attached as a contiguous unit for each of the three sections and then slid into the proper section. To assemble these units, plastic caps were screwed into four locations on each baffle. Short lengths of PVC pipe were fitted into the caps. The arrangement is shown below in Figure 10. This design has various advantages. First, it allows for relatively easy assembly. It also allows for easy disassembly, which means that it is easy to take apart the units to change baffle spacing by adding shorter or longer pipe sections. The design also decreases the amount of material used. To achieve the baffle spacing of 6.4 cm we cut connecting pipes to about 5.3 cm, accounting for the thickness of the caps. A band saw was used to cut the pipes at this dimension. A lathe and a mill were both used to bore ¼" holes into the caps.
Four different ¼" (0.6 cm) screw holes had to be drilled into each individual baffle at the location of the connectors. To position the holes we placed one top baffle on a bottom baffle and marked the desired location at the center of the nearest concave to improve accuracy and get a clean cut. The average position is about 2.5 cm from the top and 2.5 cm from the side for those holes at the bottom of the bottom baffles.
To move from one section to the next, water must travel through a port in the divider. The dimensions of these ports were determined with the following equations:
Insert port hole equations here:
To avoid short-circuiting of flow, the ports were cut in rectangular shape of lesser width than the corresponding baffle spacing for that section. Dimensions of hole between 1st and 2nd sections = 21.8 cm × 4.1 cm, while that between 2nd and 3rd = 20.1 cm ×6.1 cm.
Excess pipe material (standard schedule 40 pipe) from the rapid mix unit was used to build the outlet pipe. The turns were composed of two elbows joined at the ends by a small cut of piping. Each length of pipe for the rapid mix was about a meter in length to provide the 2 m flow length. A sanitary tee-fitting serves as the inlet of the unit.
The operational effluent flow depth was set to 96.5 cm to ensure the flow over the bottom baffles would not cause floc break-up because of high shear levels. A MathCAD program (N:\Research and Development\Vertical Flocculator PPT\AutoCAD\Flowrate trouble-shoot (identical G).mad) was made to understand how the manipulation of G and Gtheta can be achieved by altering Q. As both G and Gtheta are functions of head loss (hl) and hydraulic residence time (theta), two sets of equations (for computing hl and theta) are used to assess their values. Total head loss can be separated into major and minor loss. Minor loss is a function of the friction factor (f), which can be obtained from the Moody's diagram for a known Reynolds number. For this particular baffle configuration, major loss only makes up for less than 1 cm of the total head loss (11 cm); majority of total head loss comes from corner-turning which is accounted for by minor loss.
Insert equations section here:
The following set of equations listed below is used to compute theta, and thus G and Gtheta along with the previously calculated head loss of the configuration.
Insert Equations here:
All the equations described above were input into the MathCAD program for generation of the graph in the graph which dictates the exact relationship between Q and G and Gtheta. [#Q,G,Gtheta graph]
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Graph of the relationship between flow rate, velocity gradient and mixing factor (Gtheta) for the uniform baffle spacing.
Our initial experimental condition was to test flocculation at G of 45 s-1. According to graph above a flow rate of 138 L/min is required to attain a G value of 45 s-1. With this flow rate applied, however, Gtheta will greatly exceed the original estimate of 20,000 at the tank outlet, instead reaching a value of 34,170 for Q = 138 L/min. A different function was programmed in the same MathCAD file mentioned in the previous paragraph to re-estimate the new location of where Gtheta = 20,000 is reached in the tank. Knowing the values for the target Gtheta (20,000) and average G (45 s-1), adjusted reactive volume can be computed with the equation below. To assess this volume change in terms of tank length, see the appropriate equation below. thetaLocation value indicates the new sampling port location measured from the influent end of tank. For this particular design, the sampling tube would have to be placed 320 cm (thetaLocation = 320 cm) in the flow-path away from the influent end of the tank to measure a turbidity value for Gtheta = 20,000. In other words, since one section of the tank is 182.9 cm long, this sampling port would reside at 137.1 cm from the flow-entry end of the 2nd section in order to measure turbidity for a Gtheta of 20,000.
Insert equations here:
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Schematic of the Rapid Mix Set-up. This configuration was designed and constructed in Spring 2007. It should be noted that in the Spring 2008 semester the main tube was lengthened to accommodate an entrance tank.
A total Gtheta of 1000 was estimated to be the required mixing in the rapid-mix unit in order to completely blend the alum with the inflow water before entering the tank. This is done to ensure that the clay and alum are well mixed and the two types of particles are in close proximity to allow efficient collision and adhesion to occur along the flow path in the tank. The initial design was based on only having a 3-inch inner diameter (I.D. = 7.6 cm) PVC pipe. The following equations were used to determine the number of 90degree turns and required path length to achieve the desired G¿theta.
Insert Rapid Mix Equations here:
These calculations yielded a flow path (L) of 2 m with 4 90 degree-turns. [#rapid mix unit] shows the configuration of the rapid-mix unit.
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After the completion and installation of the flocculation tank in the water treatment plant, tube settlers are used to test effluent turbidity at different locations. The tube settlers were designed to mimic the sedimentation tank that would traditionally follow the flocculator. Tube settlers were chosen because they provide an inexpensive way to sample and create a minimal disturbance within in the tank. Using this method, different locations of the tank can be sampled. Data gathered can be used to assess how each stage of the tank is affecting the final effluent turbidity. The tube settlers were designed using the following equipment.
Equipment:
- Glass tube settlers (3)
- Length: 60 cm
- Diameter: 2.5 cm
- Peristaltic pump
- Turbidimeters (3)
Once the equipment was gathered, the next step was to design the flow rate for the peristaltic pump. The following assumptions were used in the calculation for the flow rate:
Assumptions:
- The optimum angle for tube settler is 60°
- The critical velocity is 10 m/day
Sixty degrees is used because it is the angle at which the distance required for floc settling is minimized and still allows the solids that settled on the side of the tube to slide down. The critical velocity is taken from a range of accepted values and has been found to be the critical velocity in previous plants in Honduras. The flow rate was calculated using the following equations.
Dimensions and Variables chosen:
- b = diameter = 2.5 cm
- L = length of the tube settler = 60 cm
- alpha = optimum angle = 60°
Equations:
The following equations were adopted from Shultz and Okun for determining critical velocity for up flow through a tube. The flow rate calculated for our initial configuration was 44 mL/min. There is a linear relationship between pump speed and the flow rate through the settling tube. The flow rate though the settling tube also has a linear relationship to the critical velocity of the sedimentation process in the tube. It is important to note that the critical velocity of the settling tubes is the same as the critical velocity that can be found in the sedimentation tanks at Ojojona.
The setup of the tube settlers in the tank was the next design step. Originally the tube settlers were to be hung from the edge of the tanks at designated locations. On further inspection however, when laid between the baffles on top of the connectors they are at the correct angle and so can easily be relocated and do not require any attachment to the tank.
The final design consists of the tube settlers nestled between the baffles, and then connected to the peristaltic pump. The peristaltic pump pulls water from the peristaltic pump at the correct velocity and the water is routed through a turbidimeter in order to measure the turbidity. Also installed is a turbidimeter that measures the influent turbidity of the water before it reaches the tank. This turbidimeter is gravity fed.
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TheoryofTaperedBaffleConfiguration">The tapered baffles set-up that was the result of new research about velocity gradients in the tank was done during the Fall 2007 semester. The baffle set-up was made using the same materials and with the basic construction design as the previous set-up. Caps and piping were used as the connection holding the baffles a set distance apart. These caps and the pipe were made of CPVC material. The caps were attached to the baffles by #6-32 stainless steel ½ inch screws and nuts. These screws placed through a ¼ inch hole that was drilled in one cap and then through a hole in the baffle and then through another cap. The hole in the baffle what about ¾" wide but this was an error in construction the hole should be the same size as the holes drilled in the caps, ¼". The nut was screwed on to the other end of the screw to keep the structure and ensure that the caps stayed firmly attached to either side of the baffles.
The baffles were made out of blue transparent corrugated plastic roofing material. The size of the baffles was determined based on the water level and necessary baffle spacing at the end of the tank. The distance between the water level and the top of the bottom baffle or the height between the bottom of the tank and the top baffle was kept the same through out the tank. This distance was taken as the spacing in the last section times 1.5, resulting in a turnaround of 15.1 cm.
The 20 upper baffles were cut to be 31cm wide by 88 cm long. The 19 lower baffles were cut to be 31cm wide by 62cm long. The values for the baffle spacing and number of baffles per section can be seen in the table below.
Section |
N (number of Baffles) |
B (baffles spacing) |
Pipe Cut Length |
1 |
2 |
3.339 cm |
2.239 cm |
2 |
4 |
3.952 cm |
2.852 cm |
3 |
5 |
5.794 cm |
4.694 cm |
4 |
28 |
10.071 cm |
8.971 c |
Table 1: The above table contains the exact values for the baffle spacings, number of baffles and length of the pipes connecting the baffles for each individual section.
The main difference between the previous set-up and the current set-up is that instead of having the spacing be uniform across the entire flocculator, a tapered spacing that was found above was used. The baffles were also cut ½ cm wider than for the previous set-up. This was done to help create a better seal so that less short circuiting will occur through out the flocculator. The wider baffles also help stabilize the slightly flexible section dividers. Although the wider baffle did help these issues upon observation the section support structure that was put in place over this past summer was still necessary to provided added support.
The design described above produced a flocculator that was two thirds the size of the previous flocculator, taking up two sections of the divided flocculator. The flocculator was set-up so that the baffle structure was placed in the first two sections of the flocculator and data was only collected from these sections. The final section was left with the old set-up in it just to fill the space and help keep the dividers from bowing. This section was not tested, and was just used to fill the tank until the water reaches the exit pipe at the end of the third section. In future set-ups it is hoped that this third section can remain empty and then can be used as sort of sedimentation tank to perform further research on this project.
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Theory of Tapered Baffle Configuration
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The first step in designing the tapered baffle configuration to determine a theoretical relationship of how G¿ and Gmax are related. Our baffle set-up was developed so that our values of Gmax and G¿ remained below the theoretical curve. The theoretical curve that was used can be seen below.
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This curve shows the theoretical relationship that is believed to exist between G, the maximum velocity gradient and Gtheta the mixing parameter.
The region from 0 to the maximum G¿ was divided into a specified number of equal sections that would be present in the flocculator. For this set-up it was decided to create four sections. The corresponding Gmax values were then read off of the graph. The values for Gmax are larger than the curve because for our original model the assumed the energy dissipation length in the channel was assumed to be b, the distance between two baffles. This parameter was altered in a later model and thus our values appear to be larger than the theoretical curve. These values were also the result of working backwards. G¿ values were found by rearranging the equation that was used to find the number of baffles in each section. The number of baffles was multiplied by the residence time for one baffle and then multiplied by the value of Gaverage for that section. These values can be seen in the table below. These numbers are a bit odd because G¿ should be increasing through the sections. I believe that these numbers are off because of the changes that were made to the model and the attempt at back calculating. Values of Gtheta from a new model were given below.
Typically when using the model properly the G¿ values would be found arbitrarily by dividing the range of the G¿ values from the curve by the number of sections chosen for the design. Gtheta values found with this method using the new model are also listed in the table for comparison.
Below are listed the know values for the flocculator:
- Q=100L/min - plant flow rate
- w= 1ft - width of the flocculator
- K=0.3 - minor loss coefficient for 180 degree turn arounds
- ¿ = 1x10-6 m2/s - kinematic viscosity of water
- h=76.4cm - the approximate height of the water in the tank.
- ¿ = 0.12mm roughness coefficient
- Values for Gmax can be seen in the matrix below and they are split up by section. Gmax represents the maximum velocity gradient that is seen in each section.
Note: The version of the model that we built was altered after we had created the baffle set-up, but before the report was written so some values from the model were lost. If these values were needed they were back calculated from the values we had and using the model's equations. The only values where this was done were for The Gmax and G¿ values for individual sections.Parameter
Section 1
Section 2
Section 3
Section 4
GMax (1/s)
444.185
317.075
147.516
48.826
Gtheta
5.186x10^4
3.981x10^4
2.197x10^4
9.407x10^3
Gtheta New Model
3.245x10^3
7.044x10^3
1.047x10^4
2.022x10^4
Theta (s)
3.888
4.601
6.746
11.726
GBar (1/s)
133.583
102.535
56.587
24.23
Baffle Spacings
The baffle spacing needed to attain these levels of Gmax was then determined using the following equation.
Insert Baffle Spacing Equation.
After the baffle spacing for each section was determined. The number of baffles for each section was then found using the theoretical graph again. First, the residence time for one baffle section was determined using the flow rate of the plant and the volume of one baffle spacing. This calculation was computed for each of the four specified sections. The residence times for one baffle in the individual sections are listed in the table of above. The equation calculating the residence time for one baffle is listed below.
Insert residence time Equation here.
The next design step was to find the number of baffles that were found in each section. Basically this was done by using the theoretical value of G¿ for each section and then diving by the G¿ value calculated for one baffle in that section. This number was then truncated to make it an integer. Truncation was used over rounding to ensure than that all values of G¿ used would fall below the theoretical curve.
Enter Equation for the number of baffles here.
Gaverage is the average velocity gradient found in each section.The lowest Reynolds number found for this flocculator was found in the fourth section and was 53,000 this is well into the turbulent range. So turbulent flow is confirmed and the appropriate equation for friction factor was used. The friction factor for all sections was found to be 0.047. The subsequent series of equations represents the chain of substitutions that results in the final equation used for G average. Values for G average can be found in the table above.
Enter the Average velocity gradient question here.
Enter Head loss, Reynolds number, hydraulic radius, friction,and the final equation for Gbar equations here.
The MathCAD program written performed the calculations described above and out putted the following values, baffles spacing, number of baffles, tank length, total head loss and G¿ and Gmax for all sections specified. These outputs were then used in the final construction of the tapered baffle set-up that was added to the pilot plant.
Inline Obstacles
MathCAD was used for this portion of the design as well. The basic idea for this was that the obstacles are added to help even out the velocity gradients throughout the flocculator. The flocculator is design around what the gradients are for the 180 degree turn-arounds at the top and bottom of each baffle, but the gradients in the channels between the baffles are typically much lower and thus flocculation is not occurring as efficiently as it could. With the addition of these inline obstacles we hope to increase the velocity gradients in the channels between the baffles and thus encourage flocculation similar to what occurs in the bends.
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Schematic for the construction of the inline obstacles. These obstacles are designed to increase velocity gradient levels in the channels.
Cylinders placed perpendicular to flow were thought to be the most effective. See the figure below for details on the design and placement of the obstacles in the flocculator, which are to be built and implemented this upcoming semester.
The obstacles will be constructed of PVC. The long pipe seen in the Top View will run along the length of the tank. It will lay on top of the baffles, perpendicular to them. The longer pipe seen on the Side View will be hanging down vertically from the pipe lying perpendicularly across the baffles. The horizontal bars seen on the Side View will be connected by tees to the longer pipe in the Side View. The horizontal bars will be perpendicular to the flow path of the water through the baffles.
The number of obstacles in each baffle spacing in each tapered unit still needs to be determined, but we hope that this design will prove effective when it comes time to construct the flow obstacles.
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Current Testing and Tank Modifications
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Currently testing of the tapered flocculation baffle arrangement is underway. The first few weeks of the Spring 2008 semester were spent making a few additional tank modifications. When the tapered configuration was put in the baffles around the port holes were set farther apart and thus the port holes had to be enlarged to ensure flocs were not being broken up. Sludge that had settled to the bottom of the tank was removed and tank was cleaned before it was started for the semester. Additional sand was re-added to the bottom of the tank before the baffles were placed in. It was determined that a significant amount of flow is by-passing the system and flowing under the bottom panel, which is supporting the section dividers. It was noticed when the tank was filled that that the first and third sections were filling at all most the same rate. Before caulking was done additional sand was added to the bottom of the tank in the third section to try and see if significant enough head loss could be created in the tank to cause most of inflow to follow the correct flow path. The tank was drained, cleaned and dried of sand again so that caulk could be added to seal the gap.
Unknown macro: {toggle-cloak} TestingSet-upModifications">Unknown macro: {toggle-cloak} Testing Set-up Modifications
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Schematic of the proposed Suspension System to hold tube settlers under water but still allowing it to collect at an angle of 60 degrees.
When the temperatures dropped this winter the sampling set-up started to have problems reporting viable results. One hypothesis was that the half submerged tube settlers, acting as sedimentation tanks, were not settling as well because of extreme temperature change between the submerged portion and the portion at room temperature. It is believed that the water was flowing faster at the edges of the tubes than in the center, and because of this the residence time in the tube was made shorter. This issue was corrected by submerging the entire settling tube. A suspension system ([#Submerged Settling Tube]) was created to submerge the tubes and still keep it hanging at the correct angle. The schematic designed for this can be seen below.
The temperature difference between the air temperature at the plant and the water temperature (close to freezing) is causing air to bubble out of solution in the turbiditimeters and it is believed that this might be causing false readings.The air doesn't stay in solution because the water is less soluble. To correct this problem the plan is to raise the pressure on this system ([#new schematic]) to a point that will keep the air in solution. The configuration of how water is drawn from the settling tubes to the turbiditimeters and then discarded was rearranged. Water flows from the tubes, through the pump then into the meters. From the meters the water travels up and drops into an exit tube about a meter above the tank.
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Unknown macro: {toggle-cloak} Results">Unknown macro: {toggle-cloak} Results
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It is important to understand the high flexibility of the facility for characterizing the optimal values of G and Gtheta. As mentioned earlier, the highlight of this design is to provide the ability to model Honduran treatment plants and to improve flocculation performance. Through manipulation of G and Gtheta, this set-up allows a systematic method to identify an optimal combination of the two parameters and verify their roles in efficient turbidity removal.
Initially, the plant would be operating at a constant G of 45 s-1 (controlled by Q). Easy relocation of sampling ports makes turbidity measurements possible at any point in the tank; and because of this arrangement, more refined turbidity vs. Gtheta trends can be dictated along the flow path for any particular G value applied. Performance is measured by effluent turbidity; and the current goal is set at 1 NTU.
Overall data was collected from two flocculator set-ups. We tested the original set-up where there where 79 baffles spaced equally throughout the flocculator at 6.4 cm apart. And then we switched the flocculator set-up and collected more data for a tapered flocculation set-up that consisted of 39 baffles. The purpose of these experiments was to test whether or not our assumption that better and more efficient flocculation could be achieved with a tapered baffle configuration was accurate.
A head loss analysis was done on the tapered set-up to determine if the theoretical parameters being used were accurately describing the system. The collected head loss data was found by comparing water height in a free surface tube to the water height in the tank. A hole was drilled between the third and fourth baffles a tube was inserted into a quik-connect fitting attached there. This tube was open to the atmosphere at the other end and the water height in this tube is a direct measure of head loss through the plant when compared to water levels at other points. The graph seen below compared the theoretical head loss for the tapered set-up with data that was collected from the first section of the tapered set-up. Data was not collected from the section because method used for collecting the data in the first section could not be repeated in the second section. The graph of our measured headloss versus the theoretical head loss can be seen below.
Based off of looking at the graph it seems that at least for the first three sections we are over calculating the amount of head loss that the system is creating.
Further analysis will include changing the theoretical parameters such as K to try and get the theory curve to match the data curve. This analysis should give us a better representation of what K is for the AguaClara plants.
Unknown macro: {toggle-cloak} Conclusions">Unknown macro: {toggle-cloak} Conclusions
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Enter your Conclusions here.
Unknown macro: {toggle-cloak} ExampleTable">Unknown macro: {toggle-cloak} ExampleTable
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Wiring standard used for combining power supplies and analog data acquisition in a Category 5 Ethernet cable.
T-568B standard |
T-568A standard |
voltage |
|---|---|---|
white/orange |
white/green |
S- |
orange |
green |
S+ |
white/green |
white/orange |
ground |
blue |
blue |
-5 V |
white/blue |
white/blue |
+5 V |
green |
orange |
+10V |
white/brown |
white/brown |
-15 V |
brown |
brown |
+15 V |
Here is an example table. I refer to the table by creating an internal link (an anchor) that will take the viewer to the top of the table. For example here I am talking about the [#analog wiring standard] that we use in the AguaClara laboratory. Note that I position the floating table above the paragraph where it is first referenced so that it appears along the side of that paragraph. I haven't figured out an automatic way to set the width of the table. Currently I am doing it by trial and error. If someone figures out a better way, please edit this!
Unknown macro: {toggle-cloak} Figuresandcaptions">Unknown macro: {toggle-cloak} Figures and captions
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[!Process Controller^stampbox.jpg|width=200px!|Process Controller^stampbox.jpg]
Basic Stamp® microprocessor control box with ports for 6 on/off devices and 6 variable speed peristaltic pumps.
An [#output control box] designed and fabricated around the Basic Stamp® Microprocessors (Parallax 16 port BS2sx and 40 port BS2p BASIC Stamp® modules) is used for on/off control of up to six devices and for variable control of up to six peristaltic pumps.
The float macro
keeps the graphic and the caption together and floats the figure on the page with text wrapping around it automatically. Because the top of the figure will align with the text that the float is above, I recommend insert the figure wrapped in the float macro immediately above the paragraph where the first reference to the figure occurs. This will place the figure along side the paragraph with the reference. Use anchors to refer to the figure just like you would use "Figure 11" refernces in a conventional manuscript. There is no way to implement auto numbering of the Figures so for now don't even bother to use numbers in the Figure. Instead, in the body of the report where you first reference the [#output control box] add an anchor link that connects to the Figure. Use heading 5 for table and figure captions. This makes it possible to generate a list of tables and figures. Note that there is no numbered Figure reference in the caption. Also note that the image is a hyperlink to the full size original image. If the image is from a different source file the hyperlink should be to the original source file such as a MathCAD or Excel sheet.
In this example I set the size of the float and the size of the image to 200px. The viewer can see the full image by clicking on it.
You can also use the [chart macro] to create a chart dynamically within the wiki.