Overview

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Chapter 9 Flow Measurement

• Overview
• Flow Rate Concepts
• Pressure Differential Meters
• Insertion Flow Meters

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Flow Rate Concepts

• Mass flow rate
• Mass/unit time kg/s, kg/min, etc.
• Measure flow of small particles of solids
• The mass flow rate through any area A
• Where ?fluid density average mass
  flux through the control surface
• Volume flow rate
• Volume/ unit time m3/min, cm3/s
• Measure flow of all materials (gaseous, liquid,
  semi-liquid slurry form, etc.)
• The volume flow rate where
  average velocity over the control surface

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Differential Pressure Meters

• Insert a restriction into a pipe
  velocity?pressure? ? Q(p1p2)
• Incompressible volume flow rate
• From energy equation between two control
  surfaces
• From conservation of mass
• We have
• hL1-2 head losses by friction between surfaces
  1 and 2
• Orifice meter
• Venturi meter
• Flow nozzle

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Differential Pressure Meters
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Orifice meter
Venturi meter
Flow nozzle
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Insertion Volume Flow Meter

• Electromagnetic flow meters
• for electrical conductive fluids
• inaccuracy ?1.5 f.s
• expensive
• 15 market share
• stainless steel tube, field coils placed either
  side of tube, two electrodes inserted into
  opposite sides of the tube? V flow rate

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Insertion Volume Flow Meter

• Vortex-shedding flow meters (ultrasonic)
• Based on the natural phenomenon of vortex
  shedding
• Shedding frequency fluid velocity
• Types Thermal, magnetic, ultrasonic, capacitive
  vortex-detection
• low power input, wide flow range, little
  maintenance
• measure both liquid and gas flows
• inaccuracy ?1 f.s

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The Vortex-shedding Flow Meter (Ultrasonic Flow
Meter)
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Insertion Volume Flow Meter

• Turbine flow meters
• Multi-bladed wheel mounted in a cylinder along
  an axis // fluid flow
• Rotating rate flow rate of fluid
• Low friction, small inaccuracy
• ?0.1 f.s
• less rugged, less reliable than flow-restriction
  type instruments, bearing wear, permanent
  pressure loss
• cost and market share positive displacement
  meters
• application low-viscosity, high-flow, oil
  industry

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Examples

• Example 1 What is the volume rate of flow of
  water through a pipe of cross sectional area of
  10cm2 if the average velocity of the flow is 2
  m/s
• Solution Q 10 . 10-4. 2 0.002 m3/s
• Example 2 The mass of water passing through a
  flow meter in 400s was measured as being 36.08kg.
  If the density of water is 1000kg/m3 at the
  temperature at which the measurement was made,
  what is the average rate of flow?
• Solution
• Volume mass/density 36.08/1000 36.08 10-3
• Q (36.0810-3)/400 9.0210-5m3/s