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ME 322: Instrumentation Lecture 16

ME 322: Instrumentation Lecture 16. February 26, 2014 Professor Miles Greiner. Announcements/Reminders. HW 6 due Friday No lab this week Career Fair, Tomorrow , February 27, 2014 Internships Prepare for permanent employment next year www.unr.edu/engineering/careerfair

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ME 322: Instrumentation Lecture 16

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  1. ME 322: InstrumentationLecture 16 February 26, 2014 Professor Miles Greiner

  2. Announcements/Reminders • HW 6 due Friday • No lab this week • Career Fair, Tomorrow, February 27, 2014 • Internships • Prepare for permanent employment next year • www.unr.edu/engineering/careerfair • Differential Fees pay for this

  3. Lab 6 Air Volume Flow Rate and Centerline Speed in a Wind Tunnel • Plexiglas Tube and Schedule-40 Pipe have different diameters • Control flow rate using a variable speed blower • Cover blower exit for very low speeds • For a range of flow rates, measure • Volume flow Q rate using a Presso Venturi Tube (in pipe) • Centerline speed VC using a Pitot-Static Tube (in Plexiglas tube) • For both measure pressures difference using calibrated transmitters/digital multimeters • Both VC and Q increase with blower flow rate • Is VS < VC < VP?

  4. Instrument Schematic Variable Speed Blower Plexiglas Tube Pitot-Static Probe VC Barometer PATM TATM Venturi Tube Q Pipe • Measure atmospheric conditions PATM and TATM • Using hand-held digital-barometer • = 0.5 kPa, = 1°C (95%?) • Need PStat to find pressure • Is PStat< = or > than PATM? • Use 40-in-WC transmitter to find Gage Pressure PG = PATM – PS • PS = PATM - PG • To measure Pitot-Static tube pressure difference PP • Use 3-in-WC transmitter • To measure Venturi tube pressure difference PV • Use 40-in-WC transmitter DTube DPipe PV - Static + 40 in WC Total PP PG Atm IV - - + + 3 in WC 40 in WC IG IP

  5. Summary • Before Experiment • Measure tube diameter • Calculate transmitter uncertainties • Use hand held barometer to measure • PATM • TATM • °C

  6. During Experiment • For each blower setting measure currents and find the values & uncertainties • Pressure Measurements • P = rgh = rg(FS)(I – 4mA)/16 mA • WP = 0.0025rg(FS) • Static Pressure, PStat = WOB (Work on Board) • WOB • WOB • Air density WOB • WOB • Volume flow rate WOB • WOB • Centerline speed WOB • WOB • Check Pipe Reynolds numbers, = • (300 K) • Venturi calibration (KPresso) is within 2% for 54,000 < < 137,000

  7. Consistency Check • For a given volume flow rate Q • VS = Q/A • VP = 2VS • What area should we use? • APipe or ATube

  8. Measured Results • Determine speed and flow rate uncertainty for a range of blower speeds

  9. Demonstrate Excel Calculations • Lab 6 Sample Data • http://wolfweb.unr.edu/homepage/greiner/teaching/MECH322Instrumentation/Labs/Lab%2006%20Fluid%20Flow/Lab%20Index.htm • Values and uncertainties • Pressure Units • Error Bars

  10. Pressure Transmitter Uncertainty • Pressure • = 998.7 kg/m3, g = 9.81 m/s2 • FS = (3 or 40 inch) • Manufacturer stated uncertainty: 0.25% Full Scale • (95%?) • For FS = 3 inch WC • PFS = rWghFS= (998.7 kg/m3)(9.81 m/s2) (3 inch) = 746.6 Pa • wP = 0.0025 PFS = 1.9 Pa • For FS = 40 inch WC • PFS = rWghFS= (998.7 kg/m3)(9.81 m/s2) (40 inch) = 9954 Pa • wP = 0.0025 PFS = 25 Pa

  11. Static Pressure • PStat = PATM – PG • Use for , RAir = 0.2870 kPa-m3/kg-K • So want PStat in [kPa] • Inputs • PATM • Measure using barometer • = 500 Pa = 0.5 kPa (95%) • PGAGE • Measure using 40 inch WC gage • = 25 Pa = 0.025 kPa (95%)

  12. Static Pressure Uncertainty • PStat = PATM – PG(Linear Sum?)

  13. Transmitter Pressures 3” or 40” WC

  14. Gas Pressure and Density

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