We can account for this by finding the mass ratio of

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We can account for this by finding the mass ratio, , of water vapor mass to dry air mass in the air and then correcting for the difference in the gas constant R, which is 0.4615 kJ / kg K for water vapor compared to 0.2870 kJ / kg K for dry air as given by ] 1.608 + 1 + 1 [ = ] ) R R ( + 1 + 1 [ = air dry air vapor air dry air humid One can determine the mass ratio, , from the psychrometric chart (Figure 3) as a function of the temperature of the air and the relative humidity, , which is the ratio of the vapor pressure of the partially saturated humid air to the vapor pressure of fully saturated air at the given temperature. IV. Procedure The experiment will be conducted in two parts. In the first part, flow rate measurements will be made using both the orifice and Pitot-static probe traverses and the results will be compared. Here we will see the development of the flow downstream of the orifice. In the second part, the static pressure port of the Pitot-static probe will be used to study the recoverable and unrecoverable components of static pressure drop across the orifice plate and along the duct. Differential pressure readings are to be taken across the orifice taps and the pitot-static tube ports with the DP cells. Using these pressure readings and the dimensions of the duct and orifice, calculation of flow through the duct will be possible. The room temperature, barometric pressure and relative humidity will be measured so that accurate estimates of the density of the air in the duct may be made for the velocity calculations. Velocity Traverse and Differential Pressure Measurement 1. Build a VI to measure two channels of data. a. Set up the DAQ Assist to read two voltage channels, AI0 and AI1. Set voltage range to -10 10 V and continuously collect 1000 samples at 1000 Hz. b. Split the signal into the two channels using the “Split Signals” com mand. Express Sig Manip Split Signals. Drag down on the icon to show both outputs. c. Add a statistics command to both channels. Mathematics Prob & Stat S.D. & Variance. d. Add numeric indicators to show the mean and standard deviation of the signals.
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ME 4600:483 Lab Notes Revised 11/16/2015 Flow Measurement Page 7 of 18 2. a. Make sure that the fan and the duct sections are assembled together without gaps or leaks. The orifice plate should be installed with the sharp edge facing UPSTREAM and the chamfered edge facing DOWNSTREAM. Record the orifice parameters from the tag on the plate. The flow straightener should be installed at the fan end of the duct. Be sure that all access ports other than the one to be used at the moment are sealed. Make sure that the duct is fully opened by removing the plate at the end of the duct. b. Measure the inside diameter of the duct -average several angles. c. Connect the high-pressure hose of a 5" DP cell to the flange tap at the UPSTREAM side of the orifice and the low-pressure hose to the flange tap on the DOWNSTREAM side of the orifice. Verify that the DP cell is also connected to the data acquisition board. Zero the DP cell readout with the TARE control.
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