Experiment 2: March 2, 2010
Procedure
Our manifold setup was the same as in Experiment 1, but the way we took our data changed. Our experiment consisted of a very simple setup.
The manifold we designed is a 10' long, 6" PVC pipe with 1" diameter holes drilled every 5cm. The manifold had water pumped through it at a rate of 3.8 L/sec (roughly 1 gallon/min) and the water flows through a whole 10' section of 6" PVC pipe before it gets to the manifold to ensure that the effects of the pump have dissipated in the pipe. The manifold is suspended 14" above the bed of the flume by U-clamps and the manifold is spaced 7" from the flume wall to make sure that it runs straight in the flume. The ports of the manifold are positioned so that the jets exiting from them run parallel to the bottom of the tank.
The ADV used to take velocity readings was mounted to a beam running across the width of the flume. The ADV was positioned so that it was aimed head on into the ports (so it also lies parallel to the bed of the flume) at a fixed distance of 17 cm from the port openings.
The measurements were taken every 5-6 ports, which gave us 10 different data points along the manifold. For each port, we maneuvered the ADV to the edge of the port hole. We then took measurements as we moved the ADV across the port in steps of 0.5cm. We recorded data for approximately 1 minute and then moved the ADV 0.5cm further and measured again until we were sure we had captured the entire jet profile.
Unknown macro: {float}
Example graph of a velocity profile across one of the ports
In the analysis of our data, we took the mean of the velocities at each port. Then we plotted the velocity profile for each port, assuming a Gaussian profile, and estimated the maximum flow rate at each port. These calculations were than plotted along the length of the manifold to give a velocity profile for the uniform manifold setup.
Results & Discussion
The results of our second experiment seem to reaffirm the results that we found in the first experiment. The flow starts low then peaks in the first quarter of our manifold and then gradually decreases after that.
The good news with these results is that we feel like the flow is sufficiently uniform, only varying +-0.05m/s, for it to work in the AguaClara plants. It also achieves the goal of not dropping below the scour velocity of 0.15m/s, so we can be confident that flocs will not settle out in the manifold. We still do not understand the fluid mechanics of what is happening in the manifold and need to investigate that further.