Flowmeters

FlowmetersFlowmeters

Andre PenningtonAndre PenningtonKat WitherspoonKat Witherspoon

Pam BuzzettaPam Buzzetta

http://www.emersonprocess.com/rosemount/products/flow/m8800cr.html

IntroductionIntroduction

Flowmeters are process instruments that Flowmeters are process instruments that measure a fluid’s linear or non-linear flow at measure a fluid’s linear or non-linear flow at volumetric or mass flow ratesvolumetric or mass flow rates

A fluid can either be a liquid or a gasA fluid can either be a liquid or a gas

IntroductionIntroduction Key features to consider in flow meter Key features to consider in flow meter

selection:selection: Fluid properties:Fluid properties:

Liquid or gasLiquid or gas Temperature and pressureTemperature and pressure DensityDensity ViscosityViscosity Chemical propertiesChemical properties Presence of other phasesPresence of other phases


selection:selection: Installation considerations:Installation considerations:

OrientationOrientation Flow directionFlow direction Upstream/downstream pipe workUpstream/downstream pipe work Location for servicingLocation for servicing Location of valvesLocation of valves Effects of local vibrationEffects of local vibration Electrical connectionsElectrical connections Effects of unsteady flowEffects of unsteady flow


selection:selection: Performance considerations:Performance considerations:

AccuracyAccuracy RepeatabilityRepeatability LinearityLinearity Rangeability (turndown)Rangeability (turndown) Pressure dropPressure drop Output signal characteristicsOutput signal characteristics Response timeResponse time


selection:selection: Economic considerations:Economic considerations:

Cost of ownership (i.e. purchase, installation, operation, Cost of ownership (i.e. purchase, installation, operation, maintenance, calibration, meter life, spares)maintenance, calibration, meter life, spares)

Pressure lossPressure loss Environmental considerations:Environmental considerations:

Ambient temperature effectsAmbient temperature effects Humidity effectsHumidity effects Safety factorsSafety factors Electrical interferenceElectrical interference

Positive Displacement FlowmetersPositive Displacement Flowmeters

Fluid goes through a chamber with a unit Fluid goes through a chamber with a unit that repeatedly fills and discharges a fixed that repeatedly fills and discharges a fixed volumevolume

The total volumetric flow rate can then be The total volumetric flow rate can then be calculated from the rate of filling and calculated from the rate of filling and discharging the discrete volumesdischarging the discrete volumes

Positive Displacement FlowmeterPositive Displacement Flowmeter

Accuracy: 0.25 to 1%Accuracy: 0.25 to 1% Line sizes: ¼ to 3”Line sizes: ¼ to 3” Rangeability: 2:1 to 10:1Rangeability: 2:1 to 10:1

Common Applications:Common Applications: Fluids generally need a degree of lubricityFluids generally need a degree of lubricity Clean, non-abrasive, medium to high viscosity liquidsClean, non-abrasive, medium to high viscosity liquids Good for batch operation, low-tech plantsGood for batch operation, low-tech plants Often used in oil and gas refining, chemical, pulp and Often used in oil and gas refining, chemical, pulp and

paperpaper


Nutating DiscNutating Disc Rotating ValveRotating Valve


Oscillating PistonOscillating Piston Oval GearOval Gear


Advantages:Advantages: Moderately inexpensiveModerately inexpensive No Reynolds number constraintsNo Reynolds number constraints No upstream/downstream requirementsNo upstream/downstream requirements High accuracy – 0.25 to 1% of rateHigh accuracy – 0.25 to 1% of rate Can measure very low and very viscous flowsCan measure very low and very viscous flows


Disadvantages:Disadvantages: Moving partsMoving parts Can create large pressure dropsCan create large pressure drops Maintenance is necessary; must disassemble Maintenance is necessary; must disassemble

to unplug if using a dirty fluid and subject to to unplug if using a dirty fluid and subject to deteriorationdeterioration

Measures discrete fluid flows instead of actual Measures discrete fluid flows instead of actual flow rateflow rate

May take up a lot of spaceMay take up a lot of space

Differential Pressure FlowmeterDifferential Pressure Flowmeter

Flow goes through a section with different Flow goes through a section with different cross section areas that cause pressure cross section areas that cause pressure and velocity variationsand velocity variations

Employ Bernoulli equation by observing Employ Bernoulli equation by observing relationship between pressure drop and relationship between pressure drop and velocity to get volumetric flowvelocity to get volumetric flow

Differential Pressure FlowmeterDifferential Pressure Flowmeter Most common method to measure flowMost common method to measure flow Smart transmitters simplify useSmart transmitters simplify use Accuracy: ±2% of full scaleAccuracy: ±2% of full scale Line size: greater than ½”Line size: greater than ½” Rangeability: 4:1Rangeability: 4:1

Common Applications:Common Applications: Most gases and low viscosity fluidsMost gases and low viscosity fluids Used for chemical, oil and gas refining, power, and Used for chemical, oil and gas refining, power, and

transfer of natural gastransfer of natural gas


Orifice PlatesOrifice Plates

Calculate mass flow: mCalculate mass flow: mactualactual = KA = KAtt*(2*(2ρ(pρ(p11-p-p22))))0.50.5


Venturi TubeVenturi Tube Flow NozzleFlow Nozzle


Advantages:Advantages: Well known system of measurementWell known system of measurement VersatileVersatile Line size flexibilityLine size flexibility Inexpensive initiallyInexpensive initially Highly repeatableHighly repeatable East to maintainEast to maintain Economical to correct sizing mistakeEconomical to correct sizing mistake


Disadvantages:Disadvantages: High installation costsHigh installation costs Moderate system accuracyModerate system accuracy An abrasive or sticky process will erode An abrasive or sticky process will erode

accuracy and increase maintenance costaccuracy and increase maintenance cost Moderate rangeabilityModerate rangeability High relative pressure lossHigh relative pressure loss

Turbine Flow MetersTurbine Flow MetersOverviewOverview

Uses flow to turn a turbine Uses flow to turn a turbine rotorrotor

Magnetic sensor transmits Magnetic sensor transmits a voltage pulse to a a voltage pulse to a processorprocessor

Axial-vane rotor is free Axial-vane rotor is free turningturning

Rotor continuously moving Rotor continuously moving under pressure of the liquidunder pressure of the liquid

Accuracy in the range of +/- Accuracy in the range of +/- 0.25% with 10:1 turndowns.0.25% with 10:1 turndowns.

Turbine Flow Meters Turbine Flow Meters Common ApplicationsCommon Applications

Turbine flow meters are widely used for Turbine flow meters are widely used for both liquid and gas applicationsboth liquid and gas applications

Typical applications include:Typical applications include: Oil and gas, refining, chemical, semiconductor, Oil and gas, refining, chemical, semiconductor,

agricultural, pharmaceutical, food beverage agricultural, pharmaceutical, food beverage dispensing, photo development, process dispensing, photo development, process control, and morecontrol, and more

Turbine Flow MetersTurbine Flow MetersBenefits/AdvantagesBenefits/Advantages

High degree of accuracy at low cost, especially High degree of accuracy at low cost, especially when combined with a flow computerwhen combined with a flow computer

Flexibility in connecting to associated electronic Flexibility in connecting to associated electronic readout devices for flow control and computer readout devices for flow control and computer interfaceinterface

Wide flow rangeability Wide flow rangeability Construction materials that permit use with many Construction materials that permit use with many

process fluidsprocess fluids Simple, durable, field-repairable constructionSimple, durable, field-repairable construction Operation over a wide range of temperatures and Operation over a wide range of temperatures and

pressurespressures

Turbine Flow MetersTurbine Flow MetersLimitations/DisadvantagesLimitations/Disadvantages

Poor interchangeability from unit to unitPoor interchangeability from unit to unit Bearings depend on lubricity and cleanliness of Bearings depend on lubricity and cleanliness of

process fluidprocess fluid Turbine blades are susceptible to wear and Turbine blades are susceptible to wear and

must be frequently calibratedmust be frequently calibrated Liquid applications may be suspect to problems Liquid applications may be suspect to problems

involving cavitation, specific gravity, and involving cavitation, specific gravity, and viscosityviscosity

Intended for clean fluid applicationsIntended for clean fluid applications

Magnetic Flow MetersMagnetic Flow MetersOverviewOverview

Nonmagnetic tube Nonmagnetic tube surrounded by coilssurrounded by coils

Must pump conductive liquidsMust pump conductive liquids Flow rate inferred by sensing Flow rate inferred by sensing

linear velocitylinear velocity Principle of operation based Principle of operation based

on Faraday’s Law, E=kBDVon Faraday’s Law, E=kBDV 30:1 rangeability30:1 rangeability Accuracy 0.5% of volumetric Accuracy 0.5% of volumetric

raterate Line size of 0.15” to 60”Line size of 0.15” to 60”

Magnetic Flow MetersMagnetic Flow MetersCommon ApplicationsCommon Applications

Turbine flow meters are widely used for Turbine flow meters are widely used for corrosive, dirty, or slurry-like liquidscorrosive, dirty, or slurry-like liquids

Typical applications include:Typical applications include: Wastewater applications or any dirty liquid which is Wastewater applications or any dirty liquid which is

conductive or water based (large water flows) conductive or water based (large water flows) Pulp & paper industry, acid flows or other highly Pulp & paper industry, acid flows or other highly

corrosive liquids, abrasive fluids such as mining ore corrosive liquids, abrasive fluids such as mining ore slurries and pulp stockslurries and pulp stock

Also ideal for applications where low pressure drop Also ideal for applications where low pressure drop and low maintenance are requiredand low maintenance are required

Magnetic Flow MetersMagnetic Flow MetersBenefits/AdvantagesBenefits/Advantages

Relatively unaffected by changes in liquid density Relatively unaffected by changes in liquid density or viscosity (compatible with wide range of process or viscosity (compatible with wide range of process fluids)fluids)

Liquid turbulence has a very limited affectLiquid turbulence has a very limited affect Suitable for high viscosity and slurriesSuitable for high viscosity and slurries Low maintenance, high accuracy and rangeabilityLow maintenance, high accuracy and rangeability No pressure lossNo pressure loss Obstructionless flowObstructionless flow Flow profile has minimum effect on measurement Flow profile has minimum effect on measurement

accuracy (Re# constraints and little flow accuracy (Re# constraints and little flow conditioning needed)conditioning needed)

Magnetic Flow MetersMagnetic Flow MetersLimitations/DisadvantagesLimitations/Disadvantages

Measures conductive liquids onlyMeasures conductive liquids only High initial costHigh initial cost 4-wire device (requires external power source)4-wire device (requires external power source) Must be lined with non-conductive material Must be lined with non-conductive material

(lower temperature and pressure limits)(lower temperature and pressure limits) Grounding problemsGrounding problems Unstable zero with empty meterUnstable zero with empty meter

Ultrasonic Flow MeterUltrasonic Flow MeterOverviewOverview

Use transmitted sound waves Use transmitted sound waves to determine flow rate to determine flow rate

Measures liquids and gases Measures liquids and gases with different designswith different designs

Accuracy 1-5% for Accuracy 1-5% for microprocessor-based unitsmicroprocessor-based units

Rangeability 20 to 50:1Rangeability 20 to 50:1 Can be divided into 2 typesCan be divided into 2 types

Transit Time (pulsed type)Transit Time (pulsed type) Doppler (frequency shift type)Doppler (frequency shift type)

Ultrasonic Flow MeterUltrasonic Flow MeterTransit Time (Pulsed Type)Transit Time (Pulsed Type)

Sonic transducers are Sonic transducers are mounted diagonally on mounted diagonally on opposite sides of a pipeopposite sides of a pipe

Requires clean liquid and Requires clean liquid and uniform flow profileuniform flow profile

Rangeability: 10:1Rangeability: 10:1 Accuracies:+/- 1% of rateAccuracies:+/- 1% of rate Advantages: Advantages:

Bi-directional and non-Bi-directional and non-intrusiveintrusive

Ultrasonic Flow MeterUltrasonic Flow MeterDoppler (Frequency Shift Type)Doppler (Frequency Shift Type)

Established 1843 by Christian Established 1843 by Christian DopplerDoppler

Measures the shift in Measures the shift in frequency due to motion of frequency due to motion of particles or bubbles in the particles or bubbles in the process pipeprocess pipe

Turndowns: 10:1Turndowns: 10:1 Accuracy: +/- 1% of rateAccuracy: +/- 1% of rate Not suitable for clean liquidsNot suitable for clean liquids Requires straight pipe runs for Requires straight pipe runs for

installationinstallation Pipe must have good Pipe must have good

acoustical propertiesacoustical properties

Open Channel (Weirs and Flumes)Open Channel (Weirs and Flumes)

Oldest method to measure Oldest method to measure flow, used by Romans to flow, used by Romans to measure flow in their measure flow in their aqueductsaqueducts

Any time the fluid flows with a Any time the fluid flows with a free surfacefree surface

Examples: aqueducts, log Examples: aqueducts, log flumes, channels, etc.flumes, channels, etc.

Flow measured by inserting a Flow measured by inserting a calibrated restriction to the calibrated restriction to the channelchannel

Two types of restrictionsTwo types of restrictions Weirs Weirs FlumesFlumes

Ultrasonic Flow MetersUltrasonic Flow MetersCommon ApplicationsCommon Applications

Liquids and some gas applicationsLiquids and some gas applications Doppler flowmeters require entrained gas or particles Doppler flowmeters require entrained gas or particles

to reflect ultrasonic energyto reflect ultrasonic energy Where non-wetted sensors are applicableWhere non-wetted sensors are applicable Existing installations where pipe modifications are Existing installations where pipe modifications are

difficult or uneconomicaldifficult or uneconomical Where exotic materials make other flowmeter Where exotic materials make other flowmeter

uneconomicaluneconomical Large pipes where in-line meters are uneconomicalLarge pipes where in-line meters are uneconomical Temporary installationsTemporary installations Typical applications include:Typical applications include:

Water and wastewater, chemical, refining, oil and gas Water and wastewater, chemical, refining, oil and gas

Ultrasonic Flow MetersUltrasonic Flow MetersBenefits/AdvantagesBenefits/Advantages

Some designs allow measurement to be Some designs allow measurement to be made external to the pipe (utilize no wetted made external to the pipe (utilize no wetted parts)parts)

Low maintenance Low maintenance

Ultrasonic Flow MetersUltrasonic Flow MetersLimitations/DisadvantagesLimitations/Disadvantages

Fluid changes (% solids, bubbles, etc) affect Fluid changes (% solids, bubbles, etc) affect measurementmeasurement

Proper installation is criticalProper installation is critical Longer upstream/downstream straight piping Longer upstream/downstream straight piping

requirementsrequirements Minimum Reynolds number constraintMinimum Reynolds number constraint 4-wire operation (external power source)4-wire operation (external power source) Low user confidenceLow user confidence Only mixed success in industrial flow Only mixed success in industrial flow

applicationsapplications

Oscillatory FlowmetersOscillatory Flowmeters

Two types:Two types: Vortex SheddingVortex Shedding FluidicFluidic

Vortex Shedding Flowmeter

Fluidic Flowmeter

http://www.fluidicflowmeters.com/images/140MX.jpg

Vortex SheddingVortex Shedding Vortex shedding is caused by fluid flowing around an Vortex shedding is caused by fluid flowing around an

objectobject Blunt object placed in the flowing streamBlunt object placed in the flowing stream The frequency of the vortices is measuredThe frequency of the vortices is measured The relationship between flow and frequency is: V = k*d*fThe relationship between flow and frequency is: V = k*d*f The frequency is directly proportional to the flow rate.The frequency is directly proportional to the flow rate.

Measuring the VorticesMeasuring the Vortices

Different objects manufactured to produce Different objects manufactured to produce stable vorticesstable vortices

Vortices are measured by:Vortices are measured by: High frequency pressure transducersHigh frequency pressure transducers Measuring variations in heat transfer from a Measuring variations in heat transfer from a

heated resistorheated resistor UltrasonicsUltrasonics

Pros & ConsPros & Cons

ProsPros Good accuracy (+/- 0.5%) Good accuracy (+/- 0.5%)

and rangeability (40:1)and rangeability (40:1) No moving parts, less to No moving parts, less to

breakbreak Moderate costsModerate costs Can handle liquid, gas, Can handle liquid, gas,

and steamand steam Low pressure dropLow pressure drop Not affected by fluid Not affected by fluid

density changesdensity changes

ConsCons Intrusive, obstruct flowIntrusive, obstruct flow If using ultrasonics to If using ultrasonics to

measure the vortices, measure the vortices, straight runs of pipe are straight runs of pipe are neededneeded

Re < 20,000 (high) for Re < 20,000 (high) for linear performancelinear performance

Sensitive to increasing Sensitive to increasing Viscosity Viscosity

Expensive in larger sizesExpensive in larger sizes

Common ApplicationsCommon Applications

Low viscosity fluids Low viscosity fluids Pressurized gasesPressurized gases Steam and other utility fluidsSteam and other utility fluids Pressurized gases with high densitiesPressurized gases with high densities Single-phase fluids (no particulate matter)Single-phase fluids (no particulate matter)

FluidicFluidic

As fluid enters device, flows along one interior wallAs fluid enters device, flows along one interior wall Some fluid diverted back to inlet (feedback flow) causing the fluid to Some fluid diverted back to inlet (feedback flow) causing the fluid to

be pushed against other wallbe pushed against other wall The flow shifts from side to side creating oscillationsThe flow shifts from side to side creating oscillations Oscillations sensed by an electronically heated thermistor on one Oscillations sensed by an electronically heated thermistor on one

sideside Alternating flow causes the thermistor to be cooled, this signal is Alternating flow causes the thermistor to be cooled, this signal is

directly proportional to velocitydirectly proportional to velocity


ProsPros Accuracy between Accuracy between

0.5% and 1.0% of 0.5% and 1.0% of raterate

Minimum Minimum maintenancemaintenance

InexpensiveInexpensive

ConsCons Can only be used on Can only be used on

clean low-viscosity clean low-viscosity fluids fluids

Re Re ≥ 3,000 (requires ≥ 3,000 (requires turbulent flow)turbulent flow)

Only used in pipes 4” Only used in pipes 4” or less diameteror less diameter

Target FlowmetersTarget Flowmeters

Target FlowmeterTarget Flowmeter

Use an object that is placed in the fluid flowUse an object that is placed in the fluid flow Object mounted at right angleObject mounted at right angle Force exerted on the target is measured by Force exerted on the target is measured by

strain gaugesstrain gauges Gauges produce electronic output that is Gauges produce electronic output that is

proportional to the square of flow rateproportional to the square of flow rate Optimum size of target depends on liquid being Optimum size of target depends on liquid being

studiedstudied

DrawbacksDrawbacks

While accuracy is good at low scale, at full While accuracy is good at low scale, at full scale the accuracy can vary as much as scale the accuracy can vary as much as 5+%5+%

Straight pipe length requirementsStraight pipe length requirements 20 x diameter upstream20 x diameter upstream 10 x diameter downstream10 x diameter downstream

Mass FlowmetersMass Flowmeters

Thermal Thermal Angular MomentumAngular Momentum CoriolisCoriolis

Two general categoriesTwo general categories Inferred mass (uses density to convert Inferred mass (uses density to convert

volumetric to mass flow)volumetric to mass flow) Direct Mass (actually measure mass)Direct Mass (actually measure mass)

Thermal MassThermal Mass

Measures heat loss from a heat sourceMeasures heat loss from a heat source Measures temperature rise as flow passes Measures temperature rise as flow passes

a hot tubea hot tube Mass flow is Mass flow is inferredinferred from known physical from known physical

properties of fluidproperties of fluid Usually used for gas applicationsUsually used for gas applications

Coriolis Coriolis

Operates on gyroscopic Operates on gyroscopic principleprinciple

Based on coriolis forces Based on coriolis forces (angular velocity of earth (angular velocity of earth imparts force on a moving imparts force on a moving object)object)

Fluid flows through U- or Fluid flows through U- or S-shaped tube which S-shaped tube which vibrates at its natural vibrates at its natural frequencyfrequency

CoriolisCoriolis

Motion of fluid in the Motion of fluid in the tubes resist this tubes resist this vibration (the tubes vibration (the tubes twist)twist)

Velocity of the tube Velocity of the tube deflection is deflection is proportional to mass proportional to mass flowflow


ProsPros Extremely accurate Extremely accurate

(0.15%)(0.15%) Directly measures massDirectly measures mass No Re constraintsNo Re constraints Low maintenanceLow maintenance Can measure density, Can measure density,

temperature, mass and temperature, mass and volumetric flowvolumetric flow

ConsCons High initial capital High initial capital

costscosts Small pipe diameters Small pipe diameters

needed cause large needed cause large pressure droppressure drop

Not recommended for Not recommended for measurements measurements involving gasesinvolving gases

Angular Momentum Angular Momentum Measures the force required to Measures the force required to

resist the angular momentum resist the angular momentum of flowing fluidof flowing fluid

This force proportional to massThis force proportional to mass Device consists of:Device consists of:

MotorMotor Impeller (imparts the Impeller (imparts the

momentum)momentum) Turbine to resist the Turbine to resist the

angular momentum torque angular momentum torque is appliedis applied

The torque needed to resist The torque needed to resist rotation of the turbine is rotation of the turbine is transmitted to a displaytransmitted to a display

DrawbacksDrawbacks

Only clean liquids can be usedOnly clean liquids can be used Lots of moving parts that often require Lots of moving parts that often require

maintenancemaintenance ExpensiveExpensive

SourcesSources http://www.manufacturing.net/ctl/article/CA185726http://www.manufacturing.net/ctl/article/CA185726 http://www.efunda.com/designstandards/sensors/flowmeters/flowmeter_pd.cfmhttp://www.efunda.com/designstandards/sensors/flowmeters/flowmeter_pd.cfm http://www.efunda.com/designstandards/sensors/flowmeters/flowmeter_dp.cfmhttp://www.efunda.com/designstandards/sensors/flowmeters/flowmeter_dp.cfm www.manufacturing.net/ctl/article/CA325984www.manufacturing.net/ctl/article/CA325984 http://www.jlcinternational.com/gas_liquid_turbine_flowmeters.htmhttp://www.jlcinternational.com/gas_liquid_turbine_flowmeters.htm http://www.ddc-online.org/inout/inout_chapt02_ana_06flow.aspxhttp://www.ddc-online.org/inout/inout_chapt02_ana_06flow.aspx http://www.omega.com/prodinfo/magmeter.htmlhttp://www.omega.com/prodinfo/magmeter.html http://www.envitech.co.uk/Product_Images/FlowMeter4210.jpghttp://www.envitech.co.uk/Product_Images/FlowMeter4210.jpg http://www.seilenterprise.co.kr/English/Technology/flowmetertypes.htm http://www.seilenterprise.co.kr/English/Technology/flowmetertypes.htm http://www.efunda.com/designstandards/sensors/flowmeters/flowmeter_tar.cfm http://www.efunda.com/designstandards/sensors/flowmeters/flowmeter_tar.cfm http://www.omega.com/literature/transactions/volume4/images/10_Fig_01_l.GIFhttp://www.omega.com/literature/transactions/volume4/images/10_Fig_01_l.GIF

http://www.manufacturing.net/ctl/article/CA325984

http://www.jlcinternational.com/gas_liquid_turbine_flowmeters.htm

http://www.omega.com/prodinfo/magmeter.html

http://www.envitech.co.uk/Product_Images/FlowMeter4210.jpg

Flowmeters

Engineering

flow meter selection

nonlinear flow

mass flow ratesa fluid

actual flow ratemay

installation considerations

meter life

performance considerations

economic considerations