FlowMeasLab_and_Worksheet.pdf

# 7 a calculate the scale readings for the 12 vertical

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7 a. Calculate the scale readings for the 12 vertical positions indicated in Figure 4 . Remember that the P-S tube has a diameter of 1/8", so your initial velocity measurement will be 1/16" away from the wall. Double-check your positions. You must take readings at appropriate positions, or data analysis will be difficult. b. Turn the fan on and sample the P-S tube DP cell output at each of the 12 positions across the diameter of the duct. Be sure to sample long enough. Record the mean value and standard deviation at each position. 8. Repeat steps 5 and 6 at a location just downstream of the orifice plate . If you are in the developing flow region, you may get a reading that is negative. If so, rotate the P-S tube to face downstream and note in your notebook that the velocity calculated at that point will be negative (toward the fan) rather than positive when integrating to find volumetric flow. 9. In order to evaluate potential error in the measurement caused by aligning the pitot tube off-axis, the range of angles must be determined for the P-S tube. Using the protractor, measure the alignment of the P-S tube to determine the maximum off- angle at which measurements were taken. When performing the data analysis,

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ME 4600:483 Lab Notes Revised 11/16/2015 Flow Measurement Page 9 of 18 use Figure 6 to determine the uncertainty in the pressure measurement due to this alignment error. Recoverable and Non-Recoverable Pressure Drop Measurement 1. a. Use a simple static probe to measure the sum of the recoverable and unrecoverable static pressure drop along the tube. First, measure the positions of each pressure port along the length of the duct relative to the fan outlet. b. Next, connect the high-pressure hose of the 5-inch DP cell to the static pressure port of the Pitot-static probe. Leave the low-pressure port of the gauge open to the atmosphere. Zero the DAQ system again by adjusting the bias (if necessary). c. Turn the fan ON. Starting at the farthest upstream location (closest to the fan), insert the static probe to the centerline of the duct, and align it with the flow. The position is not critical but the alignment is. Sample the static pressure at this location and record the mean value and standard deviation. d. Move the static probe to the next downstream port and repeat the measurement. Continue until you have readings for the entire length of the duct. Note: the indicated pressure can become negative downstream of the orifice plate. The DP cell isn't designed to read negative pressure, so switch the hoses. Remember that a positive measurement now means a negative pressure, so be sure you record it that way. Don't forget to switch the hoses back. 2 a. Measure the total duct non-recoverable pressure drop as a function of flow rate by taking the difference between the static pressure readings of a far upstream (near the fan) and a far downstream static probe. Position two Pitot-static probes in the center of the pipe; one far upstream and one far downstream of the orifice plate. Choose locations that are in regions of fully developed flow, away from any obstructions.
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