AME 20213 LEX-4: Velocity Measurements TA: Patrick Bowles Email: [email protected] Phone: 631-2317 Office: B028 Hessert Team Report Due: April 17, 2008 Revised: March 17, 2008

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Objective

Pitot-static (P-S) tubes, connected to pressure transducers, are frequently used in a variety of different applications to measure flow speed. This laboratory exercise involves the use of a P-S tube to measure the velocity of airflow. During the first week’s exercises, Part 1, the portable pressure transducer will be calibrated against an already calibrated pressure transducer by measuring the flow speed in a wind tunnel. Also, uncertainties due to non-exact alignment with free-stream flow will be explored. During the second part of this lab, Part 2, the volumetric and mass flow rates of a hand dryer will be measured using a P-S tube, your calibration results from Part 1, and a thermocouple.

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Part 1:Wind Tunnel Lab Procedure

2.1

Calibration: Data acquisition

1. Record the lab’s ambient temperature (◦ F) and pressure (in. Hg), using the thermometer and barometer located on the north side of the wind tunnel. 2. Check out a toolbox from the learning center with the Setra pressure transducer (from now on this will be referred to as “Setra PT”) and EL-USB-3 data logger (from now on will be referred to as “data logger”). The Setra PT converts pressure into an electrical signal, voltage, which is recorded or save by the data logger. This box will have the equipment for the second week’s lab as well, so some equipment in your box will not be used for this part of the lab. 3. There are two pressure take-offs on the P-S probe. The static pressure tap is perpendicular to the probe shaft and the total pressure tap is at the end of the probe shaft. See Figure 1.

Figure 1: Pitot-Static tube There should be tubing already connected to each of these take-offs and going to a “T”. One side of each of the “T’s” should be attached to pressure transducer number 1 which is already

at the wind-tunnel. Using the tubing provided, attach the port marked “low” on the Setra PT to the static pressure take-off “T”. The other port on the Setra PT should then be connected to the total pressure take-off “T” (marked with blue tape). 4. Ensure that the P-S tube is oriented in the direction of the flow (the flow goes from left to right as you are facing the tunnel from the computer). 5. Open the cover on the left side of the Setra PT and set the Range (top switch) to 0.25 kPa. Flip the small switch below it to the left (unidirectional setting). Finally, move the Output switch (bottom switch) all the way to the right (10 V setting). 6. Turn on the Setra PT by flipping the switch on the power supply. 7. If the output on the Setra PT screen is not zero, press and hold the “zero” button next to the switches on the Setra PT. Once the reading is zero, you can let go of the button. 8. Log onto the computer at the wind tunnel station. Use a user-name of “ame20213” and a password of “ame20213”. 9. Data from the calibrated pressure transducer will be stored using the Labview package “AME 20213” located on the computer desktop. First create a folder in the desktop folder “ame20213” to save your data files during the procedure. Next, open “AME20213”. 10. In the software, verify that the “Pitot/Cylinder” switch is thrown to the “Pitot” setting and that data is sampled 1000 times at 500 Hz. 11. In Labview, label Channel 1 “Pitot” and click the grey area, checking to make sure a green light switches on. 12. Click the “Start Experiment” tab in Labview. Create a file in your folder with a .txt extension. 13. After designating a file and saving the first data point, Labview will ask if you would like to move the traverse and record another data sample. Before moving on to the next point, use the data logger to collect data from the Setra PT (steps 14-21). 14. Connect the USB data logger to the Setra PT. 15. Remove the USB data logger from it’s cap and insert it into one of the computer’s USB ports. 16. Open the EasyLog USB software and click on the “setup and start data logger” button. 17. Change the Logger name to something of your choosing and change the sample rate to 1s (9 hrs) using the drop down menu. The Logger will now take data at the rate of one sample per second. Then click Next. 18. Click next again and then click Finish. Unplug it from the computer and plug it back into the cap. 19. After about 30 s of collecting data, unplug the data logger from the cap and plug it into the USB port on the computer. 20. Go to the EasyLog USB program and click on the “Stop the USB data logger and download data” button. The press Next then OK. 21. Save the data to that folder created earlier. This data, along with the data from the calibrated pressure transducer, will be used to calibrate the Setra PT. 22. Once you have saved the data from the data logger, set up the data logger to collect data at the next speed similar to before. 23. Flip the switch to supply power to the tunnel motor. Use the meter on the right side of the tunnel to set the power to 10.

24. Unplug the data logger from the computer and plug it into the cap. 25. Next, click record sample in the Labview program. 26. Once the Labview program asks if you would like to record another data point, unplug the data logger and save the data similar to the way you did before (make sure you name the file something that will remind you at which power setting this was run). 27. Repeat the previous steps for power settings from 20 to 100 in increments of ten and then take data at a power setting of 80 to verify your free-stream velocity value in your data analysis. 28. When finished recording data, click “No, I’m done.” in the Labview program. Make sure to save the final data point from the data logger as well.

2.2

Effect of Non-Alignment with Free-Stream

1. Set the tunnel power to 100. 2. Set up the USB data logger to collect data similar to the way you did in the previous section. 3. Begin collecting data with P-S tube still oriented in the direction of the flow. 4. Download the data from the data logger similar to the way you did it in the previous section. Save the data to the same folder as the rest of the data. 5. Using the available protractor, rotate the Pitot-static tube 10 degrees off center. 6. Set up the data logger to collect data again and take data for this yaw angle. 7. Repeat these steps for angles from 0 degrees to 80 degrees in increments of 10 degrees (notice that 0 degrees corresponds to 90 degrees on the protractor). Label your files so you know the yaw angle they were taken. Once you are done, save your data to a thumb drive (or email it to yourself) and erase your folder on the computer. Also, make sure to return the equipment you checked out back to the learning center.

2.3

Calibration: Data analysis

In order to calibrate the Setra PT, you will need to convert the voltage data from the calibrated pressure transducer to a pressure for each of the flow speeds using Equation 1, ∆P = 0.997Ept1 − 0.0017,

(1)

where ∆P is the pressure difference in in. H2 O and Ept1 is the voltage from the calibrated pressure transducer. Using this equation, you can relate the voltage from the Setra PT to the pressure from the calibrated pressure transducer in order to obtain a calibration curve. This curve should be linear. You will use the Setra PT and your calibration curve when measuring the mass/volumetric flow-rate of a hand dryer for the second part of the lab.

3 3.1

Measuring the Volumetric/Mass Flow Rate of a Hand Dryer Background

For this part of the lab you will use the knowledge gained from the first part of the lab to measure the volumetric/mass flow rate of a hand dryer. You will need to check out a toolbox from the learning center for this part of the lab. This toolbox will contain a Setra pressure transducer, a P-S tube, a thermocouple (and the

circuitry needed for it), and two USB data loggers along with all of the cables/tubing needed. You will also need to check out a Level and the EasyLog USB software. Please check the toolbox to make sure you have everything. You will only be able to check out this equipment for three hours at a time and so it is important to have a plan for collecting data before checking it out. That is, develop your own procedure for data acquisition before checking out the equipment. You will be using this equipment in order to measure the volumetric and mass flow rates of a typical hand dryer (found in most bathrooms on campus). To do this, you will need to measure the velocity distribution of the jet and integrate this distribution with respect to the two spacial dimensions to get the volumetric flow rate. The mass flow rate can be found by integrating the product of density and velocity over the two spacial dimensions. Remember, it’s up to you to determine the procedure for this section of the lab. Some things to think about are: • How many points do I need to take in order to accurately characterize the blow dryer’s velocity field? • What assumptions are reasonable to make about the flow and temperature distribution? For instance, is the flow steady, incompressible, or one-dimensional? • What computer am I going to use and, if it is not able to be taken into the bathroom with you, what is the best way to use the data logger to collect data? • Which hand dryer do I want to use? Does it have an electrical outlet near the hand dryer for the pressure transducer? • How long should each sample be? The data logger records data at 1 sample/sec. In order to have good statistical data, you should record many points (at least 60!). • How far away from the jet exit should the probe be? Recall how the Setra PT behaved at low-velocity in Part 1. • What kinds of uncertainties are involved in this measurement - how can they be minimized? Creativity is encouraged, but be sure that your methodology is scientifically sound. You must be able to justify all assumptions. This may include sample calculations, sample data, etc. In order to calculate the velocity from the voltage data you will be collecting, you will need to use the calibration curve you found in the previous section. Also, keep in mind the lessons learned from the previous section (for instance the effects of non-alignment with flow, how to hook up the equipment, etc.). Lastly, be sure to check your data from the Logger frequently. Do not take data for several hours, return to your computer, and then discover that you did not record any data because the battery was dead. Think like an engineer!

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Deliverables

For this lab, each group will turn in a technical report that will be due in class on April 17, 2008. The report will be graded based on proper formatting, grammar, and the other standard categories found on the Technical Memo/Report Grading Sheet (which is posted on the course website) along with the following technical deliverables: 1. A calibration curve including calibration equation. 2. A plot of measured velocity with respect to yaw angle. 3. A description of the data collection procedure used to collect velocity and temperature data for the hand dryer.

4. A description (manufacturer, model, and location on campus) and pictures of the hand dryer you used for Part 2. 5. A plot of the velocity distribution of the hand dryer’s exhaust. 6. Calculated values for volumetric and mass flow rates. 7. Calculated values for uncertainties for volumetric and mass flow rates and the largest source of uncertainty in the measurement along with any ideas of ways to reduce the uncertainty in the measurement.