Mass Flow Meters

Mass Flowmeter

THERMAL MASS FLOWMETER

CORIOLIS MASS FLOWMETER

THERMAL MASS FLOWMETER

  1. Operates by monitoring the cooling effect of a gas stream as it passes over a heated transducer.
  2. Gas flow passes over two PT100 RTD transducers.
  3.  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.
  4. The greater the mass flow passing over the heated transducer, the greater current required to keep a constant differential temperature.
  5. The measured heater current is therefore a measure of the gas mass flowrate.
Thermal Mass Flowmeter

Thermal Mass Flowmeter

Features of Thermal Mass Flowmeter

  • 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 be taken out of process line for servicing
  • Accurate field calibration is difficult

CORIOLIS MASS FLOWMETER

  1. When a moving mass is subjected to an oscillation perpendicular to its direction of movement, Coriolis forces occur depending on the mass flow.
  2.  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.
  3.   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.
  4.   This twisting movement is sensed by a pick up and is directly related to mass flow rate
Coriolis Mass Flowmeter

Coriolis Mass Flowmeter

Features of Coriolis Mass Flowmeter

  • 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

Advantages of Coriolis Flowmeter

  • 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 Flowmeter

  • 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.
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