Slide 1

ME 322: Instrumentation Lecture 15 February 23, 2015 Professor Miles Greiner Relating speed and flowrate, Lab 6 equipment, Presso flow coefficient, linear sum uncertainty Slide 2 Announcements/Reminders HW 6 due Friday Lab today (Lab 5) but not the rest of this week Career Fair, Thursday, February 26, 2015 Internships Prepare for permanent employment next year www.unr.edu/engineering/careerfair www.unr.edu/engineering/careerfair Slide 3 Pipe Speed and Volume Flow Rate Centerline speed increases in the entrance region In fully-developed flow, speed profile V(r) is Parabolic in laminar flow (Re10 4 ), and develops rapidly Slide 4 Speed and Flow Rate Consistency Does the centerline speed increase with flow rate? Is there a unique centerline speed for every volume flow rate and every location? What does this relationship dependent on? For a given volume flow rate, what is the range of centerline speeds in which we expect V C to be? Slide 5 Possible Centerline Speeds Slide 6 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 V C using a Pitot-Static Tube (in Plexiglas tube) For both measure pressures difference using calibrated transmitters/digital multimeters Both V C and Q increase with blower flow rate Check to see if V S < V C < V P Slide 7 Venturi Tube Slide 8 In Lab 6 use a Presso Venturi Tube Slide 9 How to find V C and Q (and uncertainties)? Slide 10 Instrument Schematic To measure P ATM and T ATM Use hand-held digital-barometer Is P Stat than P ATM ? Use 40-in-WC transmitter to find Gage Pressure P G = P ATM P S P S = P ATM - P G To measure P P Use 3-in-WC transmitter To measure P V Use 40-in-WC transmitter D Tube D Pipe P PGPG PVPV Static Total + + - - IVIV IPIP IGIG + - Variable Speed Blower Pipe Plexiglas Tube Pitot-Static Probe V C Venturi Tube Q Atm 40 in WC 3 in WC 40 in WC Barometer P ATM T ATM Slide 11 Inlet Pressure and Temperature Slide 12 Pressure Transmitter Uncertainty Slide 13 Static Pressure Slide 14 Static Pressure Uncertainty Slide 15 General Expression Likely Error of Linear Sums Slide 16 Summary Slide 17 During Experiment Slide 18 Consistency Check For a given volume flow rate Q V S = Q/A V P = 2V S What area should we use A Pipe or A Tube ? Slide 19 Measured Results Determine speed and flow rate uncertainty for a range of blower speeds Slide 20 Slide 21 Wind Tunnel Schematic D Tube D Pipe P PGPG PVPV Static Total + + - - IVIV IPIP IGIG + - Variable Speed Blower Pipe Plexiglas Tube Pitot-Static Probe, V C Venturi Tube, Q Atm 40 in WC 3 in WC 40 in WC Slide 22 During Experiment