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Volume Flow Measurements

Volume Flow Measurements. Obstruction Meters. Orifice Meters Venturi Meters Flow Nozzles. Flow through a Nozzle. Basic Equations: a.) Continuity: mass in = mass out b.) Bernoulli’s Eqn. Total pressure is constant throughout. Flow through a Nozzle. Flow through a Nozzle.

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Volume Flow Measurements

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  1. Volume Flow Measurements

  2. Obstruction Meters • Orifice Meters • Venturi Meters • Flow Nozzles

  3. Flow through a Nozzle Basic Equations: a.) Continuity: mass in = mass out b.) Bernoulli’s Eqn. Total pressure is constant throughout

  4. Flow through a Nozzle

  5. Flow through a Nozzle

  6. Flow through a Nozzle DP

  7. Flow through a Nozzle Y = Compressibility Factor =1 for incompressible flow or when DP<< Pabs C= Discharge Coefficient =f(Re) and nature of specific flow meter DP P

  8. Flow through a Venturi Meter In a venturi, 0.95 < C < 0.98 Advantage: Pressure recovery Uses little power

  9. Flow through a Venturi Meter 0.98 C 2 x 105 Re Based upon the conditions in the pipe approaching the meter

  10. Back to the Nozzle P1 P2 P1 P P2

  11. The Nozzle Flowmeter Shorter and cheaper than venturi But larger pressure drop. Thus, more power lost in operating. 0.98 C 0.86 105 103 Re

  12. Flow Through an Orifice Meter

  13. Flow Through an Orifice Meter P1 P2 d D P1 P

  14. Flow Through an Orifice Meter • Cheapest and Simplest • But biggest pressure drop and power lost (C~0.6 - 0.7) • Side Note: • Pressure drop caused by friction and turbulence of shear layer downstream of vena contracta 10k Re 0.85 5000 100k 0.6 b=d/D 0.1 0.8

  15. Elbow Flowmeter

  16. Laminar Flowmeter

  17. Pitot-Static Tubes

  18. Rotameter, variable-area-flowmeter • Force balance • Drag Force • Gravity • Buoyancy • (usually negligible) Derived on next slide

  19. Rotameter Equations For a fixed x-position, A is fixed. Then

  20. Turbine Flow Meters

  21. Vortex meters operate on the principle that when a non-streamlined object is placed in the middle of a flow stream, vortices are shed alternately downstream of the object. The frequency of the vortex shedding is directly proportional to the velocity of the liquid flowing in the pipeline.

  22. Magnetic flowmeter

  23. Magnetic flowmeter Based upon Faraday’s Law The fluid is the conductor, must be electrically conductive. E=BDVx10-8 E=voltage, volts B=magnetic flux density, gauss D= length of the conductor, cm V=velocity of the conductor, cm/sec

  24. Magnetic Flow Meter

  25. Coriolis Mass Flow Meter

  26. Coriolis Mass Flow Meter Flow Flow Force Flow Flow Force Fluid Force is Reacting to Vibration of Flow Tube Vibrating Flow Tube Twist Angle Twist Angle End View of Flow Tube Showing Twist

  27. Coriolis Mass Flow Meter

  28. Positive Displacement Meters

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