TYPES OF FLOWMETERS AND THEIR APPLICATIONS: Part 3 of 3 - What is Piping

TYPES OF FLOWMETERS AND THEIR APPLICATIONS: Part 3 of 3

Continued from part 2.. Click here to go to part 1.Click here to go to part 2…

POSITIVE DISPLACEMENT FLOWMETERS (Fig. 6):

  • This meter repeatedly entraps the fluid into a known quantity and than passes it out.
  • The quantity of the fluid that has passed is based on the number of entrapments.
  • The volume flow rate can be calculated from the revolution rate of the mechanical device.

FEATURES OF POSITIVE DISPLACEMENT (PD) FLOWMETERS:

  • Design Pressure: 1500 PSIG (liquids)/ : 100 psig (gases)
  • Design Temperature : 293 Deg. C (liquids)/ : -34 to 60 Deg. C (gases)
  • Sizes: 6 mm to 400 mm
  • Fluids : Clean Liquids/ gases
  • Flow range: 0 – 20000 GPM (liquids)/ : 0 – 3000 cub.m/hr (gases)
  • MOC: mostly in aluminum, stainless steel, plastics, hastelloy
  • Accuracy is + 0.5% to + 1% of flowrate
  • Range ability is 15 : 1
Positive Displacement Flowmeters and Thermal mass flowmeters
Fig. 6: Positive Displacement Flowmeters and Thermal mass flowmeters

ADVANTAGES OF PD FLOWMETERS:

  • Good accuracy and high range ability
  • Can be used in viscous liquid flow
  • Low to medium initial set up cost
  • Require no power supply and available in wide variety of read out devices

DISADVANTAGES OF PD FLOWMETERS:

  • Maintenance required at frequent intervals because of the `moving parts.
  • High pressure drop due to obstruction
  • Not suitable for low flow rate
  • Not suitable for fluids with suspended solids
  • Gas (bubbles) in liquid could significantly decrease the accuracy

THERMAL MASS FLOWMETER (Fig. 6):

  • Operates by monitoring the cooling effect of a gas stream as it passes over a heated transducer.
  • Gas flow passes over two PT100 RTD transducers.
  • The temperature transducer monitors the actual gas process temperature, whilst the self-heated transducer is maintained at a constant differential temperature by varying the current through it.
  • The greater the mass flow passing over the heated transducer, the greater current required to keep a constant differential temperature.
  • The measured heater current is therefore a measure of the gas mass flowrate.

FEATURES OF THERMAL MASS FLOWMETERS:

  • Design Pressure: 1200 PSIG
  • Design Temperature: 176 Deg. C
  • Sizes: 15 mm to 1000 mm
  • Fluids : Clean gases
  • Flow range: 0 – 2500 SCFM
  • MOC: mostly in stainless steel/ glass, teflon, monel
  • Accuracy is +1% to + 2% of flowrate
  • Range ability is 10 : 1 to 100:1
  • Upstream length/ Downstream straight length is 5/ 3

ADVANTAGES OF THERMAL MASS FLOWMETER:

  • No temperature or pressure compensation required
  • Linear output (as temperature differential is proportional to mass flow)
  • Can be used on corrosive process streams if proper materials are specified
  • DC voltage or 4 to 20 mA dc outputs available

DISADVANTAGES OF THERMAL MASS FLOWMETER:

  • Practical for gas flows only
  • Subject to blockage by foreign particles or precipitated deposits due to small openings in flowmeter
  • Power requirements excessive in larger pipe sizes
  • Has to taken out of process line for servicing
  • Accurate field calibration is difficult

CORIOLIS MASS FLOWMETER (Fig. 7):

  • When a moving mass is subjected to an oscillation perpendicular to its direction of movement, Coriolis forces occur depending on the mass flow.
  • When the tube is moving upward during the first half of a cycle, the fluid flowing into the meter resists being forced up by pushing down on the tube.
  • On the opposite side, the liquid flowing out of the meter resists having its vertical motion decreased by pushing up on the tube. This action causes the tube to twist.
  • This twisting movement is sensed by a pick up and is directly related to mass flow rate

FEATURES OF CORIOLIS MASS FLOWMETERS

  • Design Pressure: 345 bar
  • Design Temperature: 200 to 426 Deg. C
  • Sizes: 1.5 mm to 150 mm
  • Fluids/ Applications : Liquids (clean/ dirty/viscous/ slurries) clean /liquified gases
  • Flow range: 0 – 25000 lb/m
  • MOC: mostly in stainless steel, hastelloy/titanium
  • Accuracy is + 0.15% to + 0.5% of flowrate
  • Range ability is 20 : 1
  • Bidirectional flow measurement
Coriolis Mass Flowmeter
Fig. 7: Coriolis Mass Flowmeter

ADVANTAGES OF CORIOLIS MASS FLOWMETERS:

  • Capable of measuring difficult handling fluids
  • Independent of density changes, flow profile and flow turbulence. Hence straight lengths are not required.
  • No routine maintenance required since no moving parts
  • High accuracy

DISADVANTAGES OF CORIOLIS MASS FLOWMETERS:

  • Not available for large pipes (upto 150 mm only)
  • High flow velocities required for detection resulting in high pressure drop
  • Expensive compared to other flowmeters
  • Difficulty in measuring low pressure gases.

APPLICATIONS OF FLOWMETERS:

CLEAN LIQUIDS/ GASES:

  • Orifices
  • Venturi
  • Annubar
  • Variable Area
  • Magnetic (only liquids)
  • Ultrasonic
  • Vortex
  • Coriolis Mass Flowmeters
  • Thermal mass flowmeter (only gases)
  • PD meters

DIRTY LIQUIDS:

  • Most suited: Magnetic/Coriolis Mass Flowmeters
  • Limited applications: Venturi meters

DIRTY GASES:

  • Most suited: Vortex meters
  • Limited applications: Venturi meters/Thermal mass flowmeter/Variable area flowmeter

CORROSIVE LIQUIDS: Magneticflowmeters/Ultrasonic flowmeters

NON-NEWTONIAN LIQUIDS: Coriolis Mass Flowmeters

VISCUOUS LIQUIDS: Coriolis/Magnetic/Positive Displacement Meters

ABRASIVE SLURRIES: Magnetic flowmeters/Coriolis Mass Flowmeters

FIBROUS SLURRIES: Magnetic flowmeters/Coriolis Mass Flowmeters (limited applications)

SATURATED STEAM:

  • Most suited: Orifice DP meters/ Vortex flowmeters
  • Limited applications: Venturi meters/Variable area meters

SUPERHEATED STEAM:

  • Most suited: Orifice DP meters
  • Limited applications: Venturi meters

CRYOGENIC: Venturi meters/Orifice plates

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6 thoughts on “TYPES OF FLOWMETERS AND THEIR APPLICATIONS: Part 3 of 3”

  1. Coriolis flowmeter do not operate on the coriolis effect or coriolis forces. Their operation is based on the principle of inertia of fluid flowing through the tubes. Coriolis mass flowmeter has nothing to do with the coriolis effect.

  2. thermal mass flow meter upstream & downstream straight length requirement is not 5 d to 3d but actual vendor requirement is 15 d to 5d.

  3. If you want to describe how it Works, why not to use product descriptions from manufacturers?
    e.g.:
    Measures principles: As a practical application of the Coriolis effect, the Coriolis mass flow meter operation principle ivolves inducing a vibration of the flow tube through which the fluid passes. The vibration, though is not completely circular, provides the rotating reference freame which gives rise to the Coriolis effect. While specific methods vary according to the design of the flow meter, sensors monitor and analyze changes in frequency, phase shift, and amplitude of the vibrating flow tubes. The changes obseerves represents the mass flow rate and density of the fluid.

    “up to 150 mm” – that is not true!!! – see e.g. Emerson ELITE series – up to DN350mm according their product data sheet (jan. 2019)

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