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Advantages & Disadvantages of Different Flow Meters

Advantages and Disadvantages of Flow Measurement Techniques

Electromagnetic Flowmeters

Advantages:

– Unobstructed flow passage without projecting parts
– No moving parts
– No additional pressure drop
– Essentially flow profile insensitive, only short inlet and outlet sections required
– Unaffected by changes in temperature, density, viscosity, concentration and electrical conductivity
– Favorable choice of materials for chemically aggressive or abrasive measuring media
– Unaffected by contamination and deposits
– Especially suitable for hydraulic solids transport
– Linear relationship between flow rate and measured variable
– Operates in both flow directions (forward and reverse)
– Measuring range setting can be optimized
– Low maintenance, but still easy to maintain

Limitations:

– For liquids only
– Lower conductivity limit 0.05 μS/cm
– Gas inclusions cause errors

Ultrasonic Flowmeters

Advantages:

– Unobstructed flow passage
– No moving parts
– No additional pressure drop
– Favorable choice of materials for chemically aggressive liquids
– Linear relationship between flow rate and measured variable
– Low maintenance
– Operates in both flow directions (forward and reverse)
– Transit time meters unaffected by temperature, density and concentration
– Later installation in existing pipe possible with individual elements, but onsite calibration required

Limitations:

– Still problematic for liquid and gas measurements
– Sound beam must traverse a representative cross section, therefore flow profile dependent. Long inlet and outlet sections required
– Errors due to deposits
– Transit time meters require clean liquids
– Doppler meters only for slight contamination or few gas bubbles
– Doppler meters affected by sound velocity changes due to temperature, density and concentration
– Unsuitable for heavily contaminated liquids
– Gas bubbles cause errors

Coriolis Mass Flowmeters

Advantages:

– True mass flow measurement
– Additional temperature and density measurements
– Very high accuracy for mass flow measurements
– Highly accurate density measurement
– Unaffected by pressure, temperature and viscosity
– No inlet and outlet sections required
– Operates in both flow directions (forward and reverse)
– Measuring range settings can be optimized for flow rate and density
– Self-draining

Limitations:

– Affected by gas inclusions
– Vibration sensitive when improperly installed
– Limited choice of materials
– Nominal diameter limited at the top

Thermal Mass Flowmeters

Advantages:

– Direct gas mass flow measurement
– No pressure and temperature compensation required
– Very low pressure drop
– High measuring accuracy
– Large span
– No moving parts
– Rugged construction
– Short response time
– Easily sterilized

Limitations:

– For gases only
– Inlet and outlet sections required

Differential Pressure Flowmeters

Advantages:

– Universally suitable for liquids, gases and steam
– Also usable in extreme situations, e.g. viscosity, due to variety of versions
– Calculations possible for unusual situations
– Suitable for extreme temperatures and pressures
– Range changes possible
– Low pressure drop for nozzles

Limitations:

– Square root relationship between flow rate and differential pressure, therefore smaller span
– Affected by pressure and density changes
– Pressure drop for orifice plates
– Edge sharpness for orifice plates must be assured, therefore no solids or contamination
– Very long inlet and outlet sections
– Expensive installation requiring differential pressure lines, fittings and sensors
– Installation and maintenance experience advantageous
– High maintenance requirements

Turbine Flow Meters

Advantages:

– No external power supply for Rotating vane and Woltman meters
– Turbine flowmeters suitable for cryogenic liquids
– Turbine flowmeters usable at extreme temperatures and pressures

Limitations:

– Limited choice of materials
– Only for low viscosities
– Moving parts, wear
– Sensitive to contamination
– Axial flow totalizers are flow profile sensitive
– Inlet and outlet sections required (not for rotating vane meters)
– Affected by overloading and quick changes at high differential pressure, danger of over speeding
– Vibration sensitive

Variable Area Flowmeters

Advantages:

– Inexpensive
– No external power supply required for local indication
– Suitable for liquids, gases and steam
– No inlet and outlet sections required
– Simple meter design, therefore easy to install and maintain
– Indication also with opaque liquids
– Metal cone meter with transmitter
– Metal cone meter can be sterilized, CIP tested

Limitations:

– Vertical mounting position
– Constant pressure drop
– Affected by density, temperature and viscosity changes
– Solids damage metering edge, otherwise slight contamination allowed
– Affected by pulsation and vibration
– Expensive when exotic materials are required

Vortex Flowmeters

Advantages:

– No moving parts
– Rugged construction
– Suitable for liquids, gases and steam
– Easily sterilized
– Unaffected by pressure, temperature and density changes
– Linear relationship between flow rate and measured value

Limitations:

– Inlet and outlet sections required
– Minimum Reynolds number required

Swirl Flowmeters

Advantages:

– No moving parts
– Short inlet and outlet sections → 3 x D/1 x D
– Suitable for liquids, gases and steam
– Excellent repeatability
– Unaffected by pressure, temperature and density changes

Limitations:

– Pressure drop
– Minimum Reynolds number required

Weirs

Advantages:

– Simple design
– Minimum space requirements at the measuring point
– Low construction costs

Limitations:

– Damming, therefore higher space requirements upstream of the measuring point
– Risk of deposit build up upstream of the weir, not suitable for waste water
– Stream separation through ventilation must be assured
– Affected by large floating items

Venturi Flumes

Advantages:

– No potential energy differences compared to the weir
– Low pressure drop
– Suitable for unclean waste water
– Easy to maintain

Limitations:

– Nonlinear flow characteristic
– Channel constriction resulting in damming of the headwater and risk of deposit build up in the event of velocity decrease
– Risk of plugging through larger floating items
– Measurement impossible when backflow exists in tail water up to Venturi flume
– Quality and reliability of the measurement depending on connected sensor
– Installation costs

Oval Gear Flow Meters and Oscillating Piston Flow Meters

Advantages:

– High measuring accuracy
– Suitable for measuring media with high viscosity
– Operates in both flow directions (forward and reverse)
– No flow profile effects, thus no inlet and outlet sections required
– No external power supply

Limitations:

– Volume totalizer
– For liquids only
– High pressure drop
– Moving parts, wear
– Accuracy decrease for lower viscosities due to gap losses
– Sensitive to contamination, filter required
– Flow blockage at zero flow through solid impurities
– Sensitive to overloading
– Monitoring and maintenance

Lobed Impeller Flow Meters

Advantages:

– Excellent measuring accuracy for gas measurements
– No inlet and outlet sections required
– No external power supply

Limitations:

– Volume totalizer
– For gases only
– Moving parts, wear
– Flow blockage at zero flow through solid impurities
– Sluggish toward quick changes
– Also affected by quick changes at high differential pressure, danger of over speeding
– Monitoring

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3 comments

AYON BHOWMIK June 9, 2016 at 6:36 pm

Sir why straight run are required for installation of orifice ?

Reply
cullen langford December 29, 2016 at 9:59 pm

The orifice pressure difference is affected by flow swirl and a flow profile which is different from the research flow data. The only way to get accurate data is to replicate, as best as possible, the same flow patterns as were to develop the data. It is far easier to reproduce straight runs than the various possible not-straight. Note that the equations for flow through an orifice plate show a correction factor from the theoretical of about 0.60. The difference is in the chaotic flow pattern as the fluid is gathered to the center to go through the orifice and then as it expands downstream. Much of the differential is recovered as the fluid slows and some of the kinetic energy is converted back to pressure.

Reply
S Bharadwaj Reddy December 30, 2016 at 4:08 am

Thank You Cullen Langford for sharing valuable knowledge with all of us.

Reply

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