Methods
In this experiment, we seek to determine what direct impact the diameter of the tube settler has on sedimentation efficiency. From the experiment detailed on the previous page, we were able to identify a range of capture velocities that produce low turbidity effluent regardless of tube diameter. For this experiment, we chose three capture velocities within this range and adjusted the length of the tube settlers to satisfy this velocity. Upflow velocity through the tubes was held constant. Recall that
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\large[V_c = \frac{{dV_
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}}{{L_
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\sin (\alpha )\cos (\alpha ) + d}}]
is the capture velocity equation.
As the capture velocity equation above indicates, holding the capture velocity constant and varying the length to satisfy this velocity, allows isolation of the diameter of the tube as the parameter that should most directly impact settling efficiency.
Results
To this point, we have tested four different diameter tube settlers with a capture velocity of 8 m/day. Unfortunately, the data for the 9.5 mm inner diameter tube settlers are not convincing. These data do not follow the trend of the other tubes and the effluent turbidity is quite low. We will rerun the 9.5 mm tubes and be sure that water is flowing at all times. However, the other data to this point are quite interesting.
The graph below shows the average effluent turbidity over a six hour period for the four tube settler diameters.