Automated Flow Control Scientific Paper Rough Draft
I will finish the paper by tuesday I just have to study for an exam. Hopefully that is acceptable. I thought it would go faster but it's hard to get the formatting right.The actual formated word version of the paper is available here, it is formatted after the papers in Water Research
Title: Linearize the Correlation between Head and Flow Rate for Use in Water Purification Plants
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Adaptation of water purification technology for use in developing countries is a concern of growing urgency. The lack of clean drinking water provides avenues for infection by waterborne pathogens which are currently one of the major causes of mortality for children under five years old. The Agua Clara team is working to bring clean water to communities throughout Honduras with a flocculation-sedimentation water treatment design. The design requires the addition of aluminum hydroxide as a coagulation agent. Plant operators manually adjust the alum dose based on the daily flow rate of the treatment facility. A useful innovation is necessary in the regulation of aluminum hydroxide into the system as flow changes without the use of electrical devices. Currently options for the control of chemical additions to water treatment plants are either an electric pump or manual adjustment of chemical flows. The design proposed uses an entrance tank as a way to transfer information about the flow rate to the aluminum hydroxide flow control module through a float system. The system accurately delivers consistent aluminum hydroxide dosing into the incoming water based on the height of the water in the entrance tank. Without intervention the flow rate through the entrance tank is proportional to the square root of the pressure head, height of the water in the entrance tank, as shown in equation 1.
Equation 1: The Orifice Equation.
The relationship between water height and flow rate create a problem when transferring of data to other mechanisms. A predictable linear relationship between the height of the water in the entrance tank and the flow rate through the plant allows for a system of floats to meter the aluminum hydroxide flow rate. The sutro weir developed by Victor Sutro in 1915 can be used to create a linear correlation between head and flow rate. The configuration is shown below in figure 1.
Figure 1: The Sutro Weir Image.
The bottom width of the sutro weir is relatively large and the width gradually decreases as the height increases. As the height of the water in the tank increases the pressure created by the weight of the fluid causes the flow rate through the bottom of the weir to increase. By minimizing the weir width as height increases the change in the total flow through the weir as height increases is kept in a linear relationship. Implementation of sutro weirs in currently operating water treatment facilities is infeasible due to restrictions of shape and space. Grit chambers receive the inflow first and transmit the water to the rest of the plant through pipes. If a sutro weir shaped hole were cut into a pipe the pipe would become unstable and require skilled labor for construction. Therefore we are approximating the sutro weir with a riser pipe added onto the pipes that connect the initial grit chamber (entrance tank) and the flocculation tank. The pipe would be easily introduced into previously constructed plants and new plants at low cost. Holes would be drilled into the riser pipe that would mimic the sutro wier basics of design. The drilling of holes as specified heights doesn't require skilled labor. The water is forced to flow through the riser pipe in order to leave the entrance tank and enter the flocculation tank. Experimental tests were conducted to evaluate the accuracy of the simulated sutro weir in a pilot plant application.
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The distribution of entrance tank water height was correlated directly with the flow rate through the pilot plant. The data from the three trails was plotted
on figure 2.
Figure 2: Experimental data on the three trials showing the correlation between the Flow rate and the water theight in the entrance tank. The trend line for trial one is y = 18.116x - 4.3486 with an R2 = 0.994, trial two is y = 17.527x - 2.7457 with an R2 = 0.993, trial three is y = 17.55x + 2.5598 with an R2 = 0.9974, Predicted is y = 15.814x + 0.3126 with an R2 = 0.9999.
The predicted data set from the Matlab program was also plotted on the graph to provide a comparison for the collected data. All of the collected data have trend lines with slopes of approximately 0.05 which shows high precision among the three trials. There is a deviance between the predicted values and the observed values as the flow rate increase above 90 L/min. The difference between the predicted and actual values is displayed in figure 3.
Figure 3: Plotted difference between experimental data and predicted values.
Further analysis on the percent deviation of the data shows a more significant difference at low flow rates. The percent difference levels out under ten percent as displayed in figure 4.
Figure 4: Plotted percent difference between experimental data and predicted values.
The difference between the observed and predicted values is within 10 percent for the majority of the flow rate range. The high percentage ratings in the low flow range are due to the impact of small errors on small values. The data supports the accuracy of the sutro weir approximation.
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