PEC

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Industrial Instrumentation
Dr. Ing. Naveed Ramzan
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Flow Sensors
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Reasons for Flow Metering

• Plant control, for product quality and safety
  reasons.
• Custody transfer, both interplant and selling to
  outside customers.
• Filling of containers, stock tanks and
  transporters.
• Energy, mass balancing for costing purpose and
  health monitoring of heat exchangers.
• Health monitoring of pipelines and on-line
  analysis equipment, Government and company
  legislation may dictate the use here of such
  equipment.

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Types of Flow Meters

• Differential Pressure Meters.
• Rotary Meters.
• Displacement
• Inferential
• New Flow Meters.
• Electromagnetic
• Vortex Shedding
• Ultrasonic
• Cross Correlation
• Tracer
• Swirl
• Fluidic
• Point Velocity Meters.
• Mass Flow Maters.

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Differential Pressure Meters

• Orifice Plate
• Dall Tube
• Venturi Tube
• Pitot Tube
• Rota meter
• Target mater
• Averaging Pitot
• Nozzle
• Spring Loaded
• Intake Meter
• Elbow Meter
• Bypass Meter

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Parts of differential flow meters

• Primary element
• (Part of meter used to restrict the fluid flow in
  pipe line to produce differential pressure)
• They include
• Orifice plate
• Venturi tubes
• Flow nozzles
• Pitot tube etc.

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Parts of differential flow meters

• Secondary element
• (measure the differential pressure produced by
  primary elements and convert them to usable
  forces or signals )
• Secondary elements
• Manometers
• Bellow meters
• Force balance meters etc.

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Obstruction Meters

• Orifice Meters
• Venturi Meters
• Flow Nozzles

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

• Cheapest and Simplest
• But biggest pressure drop and power lost (C0.6 -
  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
bd/D
0.1
0.8
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Obstruction Meters

• Orifice Meters
• Venturi Meters
• Flow Nozzles

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Flow through a Venturi Meter
In a venturi, 0.95 lt C lt 0.98 Advantage
Pressure recovery Uses little power
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Back to the Nozzle
P1
P2
P1
P
P2
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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
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Obstruction Meters

• Orifice Meters
• Venturi Meters
• Flow Nozzles

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Flow through a Nozzle
Basic Equations a.) Continuity mass in mass
out b.) Bernoullis Eqn. Total pressure is
constant throughout
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Flow through a Nozzle
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Flow through a Nozzle
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Flow through a Nozzle
DP
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Flow through a Nozzle
Y Compressibility Factor 1 for
incompressible flow or when DPltlt Pabs
C Discharge Coefficient f(Re) and nature of
specific flow meter
DP
P
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Differential Pressure Meters ( Contd)
Elbow Flow meter
Rota meter
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Rotameter, variable-area-flowmeter

• Force balance
• Drag Force
• Gravity
• Buoyancy
• (usually negligible)

Derived on next slide
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Rotameter Equations
For a fixed x-position, A is fixed. Then
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Pitot Tube
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Rotary Meters ( Displacement Meters)

• Displacement Meters
• Gear
• Oval wheel
• Vane Meter
• Gear (Roots)
• Diaphragm Meter
• Liquid Sealed Meter
• Inferential Meters

• Turbine Meter
• Hoverflo Meter

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What are Rotary Meters ( Displacement Meters)

• Devices which are used to measure mass or
  volumetric flow rate of gas or liquid by using a
  rotating element.

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Types of Rotary Meters
Types of Rotary Meters ( Displacement Meters)

• Positive Displacement Rotary Meters
• Inferential Rotary Meters

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PD Rotary Meters ( Displacement Meters)

• Positive displacement flow meters, also know
  as PD meters, measure volumes of fluid flowing
  through by counting repeatedly the filling and
  discharging of known fixed volumes.

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Principle of Operation
PD Rotary Meters ( Displacement Meters)

• POSITION 1. As the bottom impeller rotates in a
  counterclockwise direction towards a horizontal
  position, fluid enters the space between the
  impeller and cylinder.
• POSITION 2. At the horizontal position, a
  definite volume of fluid is contained in the
  bottom compartment.

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Principle of Operation
PD Rotary Meters ( Displacement Meters)

• POSITION 3. As the impeller continues to turn,
  the volume of fluid is discharged out the other
  side.
• POSITION 4. The top impeller, rotating in
  opposite direction, has closed to its horizontal
  position confining another known and equal volume
  of fluid.

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PD Rotary Meters ( Displacement Meters)

• Oval Gear
• Nutating Disk
• Oscillating Piston
• Multi Piston
• Rotating Impellers
• Rotating Valve
• Birotor
• Roots Meter
• Helix Meters

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Nutating Disk
PD Rotary Meters ( Displacement Meters)

• A nutating disc meter has a round disc mounted on
  a spindle in a cylindrical chamber.
• By tracking the movements of the spindle, the
  flowmeter determines the number of times the
  chamber traps and empties fluid.

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Oval Gear
PD Rotary Meters ( Displacement Meters)

• Two identical oval rotors mesh together by means
  of slots around the gear perimeter.
• The oval shaped gears are used to sweep out an
  exact volume of the liquid passing through the
  measurement chamber during each rotation.

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Oval Gear
PD Rotary Meters ( Displacement Meters)

• The flow rate can be calculated by measuring the
  rotation speed.

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Roots Meter
PD Rotary Meters ( Displacement Meters)

• The roots meter is similar in many respects to
  the oval gear meter.
• Two-lobed impellers rotate in opposite
  directions to each other within the body housing.

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Roots Meter
PD Rotary Meters ( Displacement Meters)

• These peanut-shaped gears sweep out an exact
  volume of liquid passing through the measurement
  chamber during each rotation.
• The flow rate can be calculated by measuring the
  rotation speed.

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Rotating Impeller
PD Rotary Meters ( Displacement Meters)
Birotor
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Advantages
PD Rotary Meters ( Displacement Meters)

• High accuracy over a wide range of viscosities
  and flow rates up to 2000 cP with proper
  clearances.
• Extremely good repeatability on high viscosity
  fluids, very low slippage, long life if little or
  no abrasive material in the fluid
• Low pressure drop
• Functions without external power

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Rotary Meters ( Displacement Meters)
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Advantages
PD Rotary Meters ( Displacement Meters)

• Special construction available for high
  viscosities and temperatures
• Can register near zero flow rate
• Measures directly, not an inferential device, for
  more consistent results
• Easy to repair and economical.

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Disadvantages
PD Rotary Meters ( Displacement Meters)

• Increased maintenance compared to other meters,
  more moving parts
• May become damaged by flow surges and gas slugs
• Chance of corrosion and erosion from abrasive
  materials
• Derated flow rate capacity for high viscosities
  and temperatures
• Relatively high cost for large sizes

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Inferential Meters

• The inferential type meters are so-called because
  rather than measuring the actual volume of fluid
  passing through them, they infer the volume by
  measuring some other aspect of the fluid flow and
  calculating the volume based on the measurements

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Inferential Meters

• The inferential type meters are so-called because
  rather than measuring the actual volume of fluid
  passing through them, they infer the volume by
  measuring some other aspect of the fluid flow and
  calculating the volume based on the measurements

• Turbine Meters
• Paddle Wheel
• Insertion Type

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Turbine Flow Meters
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Turbine Flow Meters

• It consists of a multi-bladed rotor mounted at
  right angles to the flow and suspended in the
  fluid stream on a free-running bearing.
• The diameter of the rotor is very slightly less
  than the inside diameter of the metering chamber,
  and its speed of rotation is proportional to the
  volumetric flow rate.

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Turbine Flow Meters

• The rotational speed is a direct function of flow
  rate and can be sensed by magnetic pick-up,
  photoelectric cell, or gears. Electrical pulses
  can be counted and totalized.

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Paddle Wheel
Paddle Wheel Meters
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Advantages
Inferential Meters

• Very good repeatability
• Reduced susceptibility to fouling and deposits
• Less sensitive to viscosity changes
• Available in large sizes, good value for high
  flow rates
• Low maintenance
• Registers near zero flow rate

Disadvantages

• High pressure drop that increases drastically
  with viscosity
• Relatively high cost
• Indirect measurement

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New Flow Meters

• Electromagnetic
• EM Meter
• Vortex Shedding Meter
• Vortex Generation Meter
• Ultrasonic Flow Meters

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New Flow Meters (Contd)
Magnetic Flowmeter
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New Flow Meters (Contd)
Swirl Meter
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Coriolis Mass Flowmeter
In the Coriolis meter the fluid is passed through
a tube. The tubes are available in different
design like tubes of U-shape or horseshoe-shaped.
The tubes can either be curved or straight. When
two tubes are used the flow is divided when
entering the meter and then recombined. The flow
when enters the tube encounters oscillating
excitation force that causes the tubes to vibrate
at a fixed frequency. The vibration is induced
in the direction that is perpendicular to flow of
fluid. This creates the rotation frame of
reference. Consider the tube during oscillation
moving up and downward, when the tube is moving
upward the fluid flowing in it tends to resist
this and forces it downward. When the tube moves
in the opposite direction, so does the fluid and
a twist in introduced in the tube. All this might
not be visible by directly observing. The twist
at inlet of fluid and outlet of fluid results in
phase difference or time lag and that is
dependent on the fluid mass passing through the
tube.
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• Discussion Questions?

Dr. Shahid Naveed 30. Mai
2014 / Dr. Ing Naveed Ramzan
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