Experiment 4: May 6, 2010
Setup
This experiment consisted of one 10' Manifold with 1 in. holes drilled every 5 cm on BOTH sides of the pipe. This resulted in an Am/Avc = 0.5. This ratio was already tested with the 20' Manifold setup, but we were interested to see if the length of the manifold played a role in the flow distribution or if the results for this experiment would be proportional to that of the 20' Manifold setup.
Procedure
The procedure for this test was the same as the procedure for experiment 2. A sample size was chosen (1 in every 5 ports). The Acoustic Doppler Velocimeter (ADV) was then positioned approximately 17 cm from the port being measured. We had attempted to position the ADV closer to the manifold to get a more accurate reading, but we were getting poor readings and thought this might be due to interference of the sonar waves by the PVC pipe. The ADV would be positioned on the edge of this port. Thirty seconds to a minute of data would be recorded, and then it would be shifted to the other side of the port by a centimeter. This process would be repeated until it was ascertained that the ADV had moved out of the range of the port jet (signified by a velocity of, or close to 0 m/s).
This was repeated on each port that was decided to be part of the sample size.
Results
The graph below shows the results from the experiment. The red line indicates the theoretical velocity profile if the effects of pressure recovery were included. The green line indicates the theoretical velocity profile if the effects of pressure recovery were not included. The blue x's indicated the data that we collected for the experiment.
Conclusion
It is evident from looking at the graph that the results are far off from what theory predicts. In past experiments, although we did not obtain the results we that theory predicts, the measured velocities were still in the same range of of the predicted values. Another red flag comes up when we estimate the flow rate inside the manifold. This is done by calculating the average port flow rate by summing up the flow out of all of the ports, multiplying by the area of the vena contracta, then dividing by the number ports measurements were taken at. This average port flow is then multiplied by the total number of ports. This value should typically be roughly the same as the total manifold flow rate, which in the case of the vacuum pump setup is approximately 6.7 L/s (calculated in Experiment 3). However the estimated flow rate using the data collected is 0.436 L/s (This estimation was calculated using the same methods in Experiments 2&3). This is a major discrepancy and reveals that something went wrong during data collection.
The ADV had been giving us a lot of trouble for the week preceding this experiment and may be the source of the problem. The ADV should be tested in a known velocity in order to make sure it is functioning properly.