Page History

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Overview

A linear dosing meter is being utilized in current AguaClara plants to control the flow of alum, based on varying plant flow rates. In this system, major losses through the tubes control the head loss. In this system, there is one orifice that often gets clogged, impairing the dosing. The 0.23 cm orifice is located in the constant head tank float valve. Because the new design has multiple orfices ( in the constant head tank and the one controlling dosing), we designed an experiment to test clogging in orifices. In our experiment, we chose to use a 0.1 cm diameter orifice, the smallest size orifice in our newdesign, to test the weak point in our design with regard to clogging. If we can remove the issue of clogging with this small orifice size, it would be more likely that we would also resolve the issue in the constant head tank float valve orifices, which are larger. The clogging in the constant head tank float valve orifice due to the accumulation of chemical precipitate is probably a combination of calcium carbonate, aluminum hydroxide, or some other unknown substance. The frequency of the cleaning probably varies a lot, but we should recognize the importance of keeping the orifices clear of buildup (either from precipitate or foreign material) due to its detrimental effect on dosing accuracy and thus subsequent flocculation and sedimentation processes.

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A control experiment, using deionized water, was performed to depict normal pressure readings without the possibility of a clog at the orifice. These pressure readings serve as a basis for comparison to the data obtained when alum is run through the system. The results from pressure sensor 1 can be seen in the figure below.

Next, alum was used in order to determine the time it would take for a clog to form in our 0.1 cm orifice. The experiment was run for four days but the most conclusive data was seen within the first hours. The pressure readings, from pressure sensor 1, are shown in Figure 3 below.

As can be seen from the graph there is a large spike in the pressure readings about 4 hours after beginning the test. The pressure sensor reads a gradually increasing pressure, due to the clogging orifice, until the pressure it built up enough to "blow out" the clog.

As stated earlier, the build up of water pressure at pressure sensor 1 (data sensor), the pressure at sensor 2 (safety sensor) should decrease. However, since the supposed "clog" was short-lived there was no corresponding data from the safety sensor to confirm the clog.

Another trial with alum was done over 24 hours. As seen in Figure 4, there are spikes in the pressure readings. We are unsure whether or not these represent clogs because the maximum difference in height of the water is at most 0.2cm. This could be in the range of the pressure sensor error.

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