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

2. 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, (775)
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%!

3. 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 ?
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

4. 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?

5. 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

6. 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

7. 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 = 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 = Work on Board
𝑊 𝑃 𝑆𝑡𝑎𝑡 = ____ (units!)
Air density 𝜌 𝐴𝑖𝑟 = 𝑃 𝑆𝑡𝑎𝑡 𝑅 𝐴𝑖𝑟 𝑇 ; RAir = 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 (300 K)
Venturi calibration, KPresso = is within 2% for 54,000 < 𝑅𝑒 < 137,000

8. 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 ?

9. Demonstrate Excel Calculations
Lab 6 Sample Data
Values and uncertainties
Pressure Units
Error Bars

11. Pressure Transmitter Uncertainty
𝑃= 𝜌 𝑊 𝑔ℎ= 𝜌 𝑊 𝑔(𝐹𝑆) 𝐼−4 𝑚𝐴 16 𝑚𝐴
𝜌 𝑊 = kg/m3, g = 9.81 m/s2
FS = (3 or 40 inch) 2.54 𝑐𝑚 1 𝑖𝑛𝑐ℎ 1 𝑚 100 𝑐𝑚 = 𝑜𝑟 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 = Pa
wP = 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 = PFS = 25 Pa

12. Static Pressure PStat = PATM – PG Inputs
Use for 𝜌 𝐴𝑖𝑟 = 𝑃 𝑆𝑡𝑎𝑡 𝑅 𝐴𝑖𝑟 𝑇 , RAir = 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 = kPa (95%)

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

14. Gas Pressure and Density