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To determine the effects of inner-diameter, flow rate, and floc blanket height on settling efficiency, we completed an experiment to vary these three parameters. Based on the two-inch lamella spacing currently used in AguaClara plants, we chose a range of diameters less than two-inches to push the lower-limit of lamella spacing. Similarly, the range of flow rates that we tested was based on the current capture velocity used in the plants. The final variable in this experiment, the floc blanket height, was set to both fully submerge the inlet of the tube settlers and to leave the inlets resting above the top of the floc blanket. Table 1, in the results section below, illustrates the parameters for the experiment.
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To begin, we observed a "rolling" movement of the floc as it travels up the tube. This movement can begin to be described by a quantitative drag analysis which is in the process of being completed. We predict that the flocs based on the varying velocity gradidents within the settling tubes. Flocs in the smaller diameter tubes experience enough are more likely do experience a greater drag force to which can overpower the settling force due to gravity.
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