ME 322: Instrumentation Lecture 16 February 24, 2016 Professor Miles Greiner Lab 6 calculations (Excel demo)

Regional Science Olympiad Will be held 8 am to 4 pm Saturday, March 5th 2016 On campus: SEM, PE and DMS ME 322 students who participate in observing and judging the events for at least two hours (as reported) will earn 1% extra credit. To sign up, contact Rebecca Fisher, rnfisher@unr.edu, (775) 682-7741 Today is the last day to sign up Details You cannot get extra-credit in two courses for the same work. If you sign-up but don’t show-up you will loose 1%!

Announcements/Reminders HW 6 due Friday NEW: Upload L6PP to WebCampus Joe Young will hold office hours today after class (PE 2) Marissa will hold a Lab 6 tutorial on Friday Time and place by email? General Advising Session for Upper Division Students Friday, March 11 from 1:30pm to 2pm in WRB 2030 Conducted by Dr. Padilla For juniors and seniors, or students who are taking 300- and 400-level classes in mechanical engineering

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 (and outlet cover) 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 Need air density to calculate both Both VC and Q increase with blower flow rate Is VS < VC < VP?

Instrument Schematic Variable Speed Blower Plexiglas Tube Pitot-Static Probe VC Venturi Tube Q Barometer PATM TATM Pipe DPipe DTube PV - + Static 40 in WC Total PP PG IV - Atm + - + 3 in WC IP IG 40 in WC Measure atmospheric conditions PATM and TATM Using hand-held digital-barometer 𝑤 𝑃 𝐴𝑇𝑀 = 0.5 kPa, 𝑤 𝑇 = 1°C (95%?) Need 𝜌 𝐴𝑖𝑟 = 𝑃 𝑆𝑡𝑎𝑡 𝑅 𝐴𝑖𝑟 𝑇 , so need 𝑃 𝑆𝑡𝑎𝑡 Use 40-in-WC transmitter to find Gage Pressure 𝑃 𝐺 = 𝑃 𝐴𝑇𝑀 − 𝑃 𝑆𝑡𝑎𝑡 𝐼 𝐺 𝑃 𝑆𝑡𝑎𝑡 = 𝑃 𝐴𝑇𝑀 − 𝑃 𝐺 To measure Pitot-Static tube pressure difference PP 𝐼 𝑃 Use 3-in-WC transmitter To measure Venturi tube pressure difference PV 𝐼 𝑉 Use 40-in-WC transmitter

Summary Before Experiment Measure tube diameter Calculate transmitter uncertainties Use hand held barometer to measure 𝑃 𝐴𝑇𝑀 , 𝑊 𝑃 𝐴𝑇𝑀 =0.5 𝑘𝑃𝑎 𝑇 𝐴𝑇𝑀 , 𝑊 𝑇 𝐴𝑇𝑀 =1°C

During Experiment For each blower speed measure transmitter currents, and find values & uncertainties Transmitter Pressure: P = 𝜌 𝑊 gh = rg(FS)(I – 4mA)/16 mA, 𝜌 𝑊 = 998.7 kg/m3 𝑤 𝑃 𝑝 =1.9 𝑃𝑎; 𝑤 𝑃 𝑣 = 𝑤 𝑃 𝐺 =25 𝑃𝑎 𝑎𝑠𝑠𝑢𝑚𝑒 95% Static Pressure, 𝑃 𝑆𝑡𝑎𝑡 = 𝑃 𝐴𝑇𝑀 − 𝑃 𝐺 (Linear Sum) 𝑊 𝑃 𝑆𝑡𝑎𝑡 2 = Work on Board 𝑊 𝑃 𝑆𝑡𝑎𝑡 = ____ (units!) Air density 𝜌 𝐴𝑖𝑟 = 𝑃 𝑆𝑡𝑎𝑡 𝑅 𝐴𝑖𝑟 𝑇 ; RAir = 0.2870 kPa-m3/kg-K 𝑊 𝜌 𝐴𝑖𝑟 𝜌 𝐴𝑖𝑟 2 = WOB Volume flow rate 𝑄= 𝐴 𝑝𝑖𝑝𝑒 𝐾 𝑝𝑟𝑒𝑠𝑠𝑜 2 𝑃 𝑣 𝜌 𝐴𝑖𝑟 𝑊 𝑄 𝑄 2 = WOB Centerline speed 𝑉 𝑐 =𝐶 2 𝑃 𝑝 𝜌 Air 𝑊 𝑉 𝑐 𝑉 𝑐 2 = WOB Check Pipe Reynolds numbers, 𝑅𝑒 𝑃𝑖𝑝𝑒 = 𝑉 𝑃𝑖𝑝𝑒 𝐷 𝑃𝑖𝑝𝑒 𝜌 𝐴𝑖𝑟 𝜇 𝐴𝑖𝑟 = 4𝑄 𝜌 𝐴𝑖𝑟 𝜋𝐷 𝑃𝑖𝑝𝑒 𝜇 𝐴𝑖𝑟 𝜇 𝐴𝑖𝑟 =1.846𝑥 10 −5 𝑁𝑠 𝑚 2 (300 K) Venturi calibration, KPresso = 0.3810 is within 2% for 54,000 < 𝑅𝑒 < 137,000

Consistency Check For eac volume flow rate 𝑄 (show calculations next time) 𝑉 𝑆𝑙𝑢𝑔 =𝑄/𝐴 (APipe or ATube) 𝑉 𝑃 =2 𝑉 𝑆𝑙𝑢𝑔 What area should we use APipe or ATube ?

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

Pressure Transmitter Uncertainty 𝑃= 𝜌 𝑊 𝑔ℎ= 𝜌 𝑊 𝑔(𝐹𝑆) 𝐼−4 𝑚𝐴 16 𝑚𝐴 𝜌 𝑊 = 998.7 kg/m3, g = 9.81 m/s2 FS = (3 or 40 inch) 2.54 𝑐𝑚 1 𝑖𝑛𝑐ℎ 1 𝑚 100 𝑐𝑚 =0.0762 𝑜𝑟 1.016 𝑚 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) 2.54 𝑐𝑚 1 𝑖𝑛𝑐ℎ 1 𝑚 100 𝑐𝑚 = 746.6 Pa wP = 0.0025 PFS = 1.9 Pa For FS = 40 inch WC (998.7 kg/m3)(9.81 m/s2) (40 inch) 2.54 𝑐𝑚 1 𝑖𝑛𝑐ℎ 1 𝑚 100 𝑐𝑚 = 9954 Pa wP = 0.0025 PFS = 25 Pa

Static Pressure PStat = PATM – PG Inputs Use for 𝜌 𝐴𝑖𝑟 = 𝑃 𝑆𝑡𝑎𝑡 𝑅 𝐴𝑖𝑟 𝑇 , RAir = 0.2870 kPa-m3/kg-K So want PStat in [kPa] Inputs PATM Measure using barometer 𝑤 𝑃 𝐴𝑇𝑀 = 500 Pa = 0.5 kPa (95%) PGAGE Measure using 40 inch WC gage 𝑤 𝑃 𝐺𝐴𝐺𝐸 = 25 Pa = 0.025 kPa (95%)

Static Pressure Uncertainty PStat = PATM – PG (Linear Sum?) 𝑤 𝑃 𝑆𝑡𝑎𝑡 2 = 𝑖=1 2 𝛿 𝑃 𝑆𝑡𝑎𝑡 𝛿 𝑥 𝑖 𝑤 𝑖 2 = 1 𝑤 𝑃 𝐴𝑇𝑀 2 + −1 𝑤 𝑃 𝐺 2 = 1 0.5kPa 2 + −1 0.025kPa 2 𝑊 𝑃 𝑆𝑡𝑎𝑡 =0.5006 𝑘𝑃𝑎

Gas Pressure and Density