Flow measuring devices - It contents all type of Flow Measuring devices like Orificemeter, Venturimeter, Rotameter etc.

There are several types of flowmeter that rely on Bernoulli's principle. The pressure is measured either by using laminar plates, an orifice, a nozzle, or a Venturi tube to create an artificial constriction and then measure the pressure loss of fluids as they pass that constriction or by measuring static and stagnation pressures to derive the dynamic pressure.

1. FLOWMEASUREMENT
Prof. S D Yadav
[email protected],
MGM’s JNEC.

2. Prof. S D YADAV
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3. Classification of Flow-meters
Prof. S D YADAV
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4. VARIABLE HEAD OR DIFFERENTIALMETER
❖OrificePlates
❖VenturiTubes
❖FlowNozzle
❖PitotTube
❖Rotameter
❖Weir
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5. VARIABLE HEAD OR DIFFERENTIALMETER
❖Differential pressure meterswork on the principle of partially obstructing the flow in a pipe.
This creates a difference in the static pressure between the upstream and downstream side of the
device. This difference in the static pressure (referred to as the differential pressure) is measured
and used to determine the flow rate.
❖Headflowmetersoperateontheprincipleofplacingarestrictioninthelinetocausea
differentialpressurehead.Thedifferentialpressure,whichiscausedbythehead,is
measuredandconvertedtoaflowmeasurement.
❖Thedevicesingeneral,canthereforebetermedas“obstructiontype”flowmeters.
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6. VARIABLE HEAD OR DIFFERENTIALMETER
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7. MERITS AND DEMERITS –DIFFERENTIAL FLOWMETER
❖Merits
1.They are simple to make, containing no moving parts
2.Their performance is well understood
3.They are cheap –especially in larger pipes when compared with other meters
4.They can be used in any orientation
5.They can be used for most gases and liquids
6.Some types do not require calibration for certain applications
❖The Demerits
1.Rangeability (turndown) is less than for most other types of flow meter
2.Significant pressure losses may occur
3.The output signal is non-linear with flow
4.The discharge coefficient and accuracy may be affected by pipe layout or nature of flow
5.They may suffer from ageing effects, e.g. the build-up of deposits or erosion of sharp edgesProf. S D YADAV
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8. ORIFICEMETER
❖AnOrificeMeterisaconduitandarestrictiontocreateapressuredrop.Anhourglass
isaformoforifice.
❖Inordertouseanyofthesedevicesformeasurementitisnecessarytoempirically
calibratethem.Thatis,passaknownvolumethroughthemeterandnotethereadingin
ordertoprovideastandardformeasuringotherquantities.
❖Anorificeinapipelineisshowninfigurewithamanometerformeasuringthedropin
pressure(differential)asthefluidpassesthroughtheorifice.Theminimumcross
sectionalareaofthejetisknownasthe“vena-contracta.”
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9. ORIFICEWORKING
❖Asthefluidapproachestheorificethepressureincreasesslightlyandthendropssuddenlyasthe
orificeispassed.Itcontinuestodropuntilthe“venacontracta”isreachedandthengradually
increasesuntilatapproximately5to8diametersdownstreamamaximumpressurepointis
reachedthatwillbelowerthanthepressureupstreamoftheorifice.
❖Thedecreaseinpressureasthefluidpassesthrutheorificeisaresultoftheincreasedvelocityof
thegaspassingthruthereducedareaoftheorifice.
❖Whenthevelocitydecreasesasthefluidleavestheorificethepressureincreasesandtendsto
returntoitsoriginallevel.
❖Thepressuredropacrosstheorificeincreaseswhentherateofflowincreases.Whenthereisno
flowthereisnodifferential.Thedifferentialpressureisproportionaltothesquareofthevelocity.
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10. ORIFICE PLATE
1.Concentric –commonly used for general applications (gas, liquid &vapour).
2. Eccentric –recommended for fluids with extraneous matter to a degree that wouldclog
up concentrictype.
3. Segmental –recommended for fluids combine with vapour or vapour withfluids.
a) Square Edge –applicable for higher pipe Reynolds Number; typical Re 500 to10,000
b) Quadrant –for lower pipe Reynolds Number; typically ranges from Re 250 to3300.
c) Conical –for Reynolds Number typically range from Re 25 to75.
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11. ADVANTAGES AND DISADVANTAGES OF ORIFICE
Advantages
❖Simpleconstruction.
❖Inexpensive.
❖Easily fitted betweenflanges.
❖No movingparts.
❖Large range of sizes and openingratios.
❖Suitable for most gases andliquids.
❖Well understood andproven.
❖Price does not increase dramatically with
size.
Disadvantages
❖Inaccuracy, typically1%.
❖Low rangeability, typically4:1.
❖Accuracy is affected by density, pressure
and viscosityfluctuations.
❖Erosion and physical damage to the
restriction affects measurementaccuracy.
❖Cause some unrecoverable pressureloss.
❖Viscosity limits measuringrange.
❖Require straight pipe runs to ensure
accuracy ismaintained.
❖Pipeline must be full (typically forliquids).
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12. VENTURIMETER
❖Aventurimeter,orventuriflowmeter,isadeviceusedtomeasurethevelocity,orflowrate,offluid
flowingthroughapipeline.TheventurimeterconstrictstheflowusingaHerschelventuritube.
❖Astheliquidflowsthroughthepipeline,thedevicemeasuresthepressureoftheliquidbeforeitentersthe
venturitubeandasitexitstheconstrictedarea.Thesemeasurementsarethencomparedtofigurethe
volumetricflowrateofthefluid.Theflowmeteriscommonlyusedinplumbingapplicationstodetermine
theflowoffluidssuchaswater,liquidpropane,andoil.
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13. COMPARISON ORIFICE AND VENTURIMETERS
1.Orificereducingelementissharpedgedwhileventuriistaperedtube.
2.Permanentpressurelossoforificeis65%ofmeasuredd/pwhileventuriisonly10%.
3.VenturitubeislesssensitivetoReynoldsNumberandgivesmore
accuratemeasurementwhentheprocessflowvariesoverawiderange.
4.Venturitubeislessaffectedbydirtyfluidwhichbuildupdepositsatorificeplatesand
pressuretapconnections.
5.Venturitubemeterismorecostlycomparedtoorificeplatecostlycomparedtoorifice
plateandrequiresgreaterlengthofpipeline.
6.Orificeplateisrelativelyeasytochangefornewrange.
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14. PITOTTUBE
❖A pitot tube, also known as pitot probe, is a flow measurement device used to measure fluid flow
velocity.
❖The pitot tube was invented by the French engineer Henri Pitot in the early 18th century and was
modified to its modern form in the mid-19th century by French scientist Henry Darcy.
❖It is widely used to determine the airspeed of an aircraft, water speed of a boat, and to measure
liquid, air and gas flow velocities in certain industrial applications
Working:
❖Pitotor Pitotstatic tubeis an open ended tubewhere moving fluid flows in order to measure the
stagnation pressure . It is usually mounted under the wings of an aircraft . The Pitottubeis then
connected to a Diaphragm which expands and contracts depending on the speed of the air
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15. PITOT TUBE
Advantages of Pitottube
❖Lowcost.
❖Low permanent pressureloss.
❖Ease of installation into existingsystems.
Disadvantages of Pitottube
❖Lowaccuracy.
❖LowRangeability.
❖Requires clean liquid, gas or vapouras
holes are easilyclogged.
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16. VARIABLE AREA -ROTAMETER
❖Arotameterisadevicethatmeasuresthevolumetricflowrateoffluidinaclosedtube.
❖Itbelongstoaclassofmeterscalledvariableflowmeter,whichmeasureflowratebyallowingthecross-sectionalareathefluid
travelsthroughtovary,causingameasurableeffect
❖ThefirstvariableareameterwithrotatingfloatwasinventedbyKarlKueppersinAachenin1908
❖Arotameterconsistsofataperedtube,typicallymadeofglasswitha'float',insidethatispushedupbythedragforceofthe
flowandpulleddownbygravity.
❖Ahighervolumetricflowratethroughagivenareaincreasesflowspeedanddragforce,sothefloatwillbepushedupwards.
However,astheinsideoftherotameterisconeshaped(widens),theareaaroundthefloatthroughwhichthemediumflows
increases.
❖Floatsaremadeinmanydifferentshapes,withspheresandellipsoidsbeingthemostcommon.Thefloatmaybediagonally
groovedandpartiallycoloredsothatitrotatesaxiallyasthefluidpasses.
❖Thisshowsifthefloatisstucksinceitwillonlyrotateifitisfree.Readingsareusuallytakenatthetopofthewidestpartofthe
float;thecenterforanellipsoid,orthetopforacylinder.Somemanufacturersuseadifferentstandard.
❖The"float"mustnotfloatinthefluid:ithastohaveahigherdensitythanthefluid,otherwiseitwillfloattothetopevenifthere
isnoflow.
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17. VARIABLE AREA -ROTAMETER
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18. VARIABLE AREA -ROTAMETER
Advantages
❖Arotameterrequiresnoexternalpowerorfuel,itusesonlytheinherentpropertiesofthefluid,along
withgravity,tomeasureflowrate.
❖Arotameterisalsoarelativelysimpledevicethatcanbemassmanufacturedoutofcheapmaterials,
allowingforitswidespreaduse.
❖Sincetheareaoftheflowpassageincreasesasthefloatmovesupthetube,thescaleisapproximately
linear.
❖Clearglassisusedwhichishighlyresistanttothermalshockandchemicalaction.
Dis-Advantages
❖arotametermustbeorientedvertically.Significanterrorcanresultiftheorientationdeviates
significantlyfromthevertical.
❖Duetothedirectflowindicationtheresolutionisrelativelypoorcomparedtoothermeasurement
principles.Readoutuncertaintygetsworsenearthebottomofthescale.
❖Sincethefloatmustbereadthroughtheflowingmedium,somefluidsmayobscurethereading.
❖Rotametersarenoteasilyadaptedforreadingbymachine.
❖Rotametersarenotgenerallymanufacturedinsizesgreaterthan6inches/150mm,butbypassdesigns
aresometimesusedonverylargepipes.
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19. FLOWNOZZLE
❖Flownozzleisarestrictionconsistingofanellipticalcontouredinletandacylindricalthroat
section.Pressuretapsusedtomeasurethedifferenceinstaticpressurecreatedbyflownozzleare
commonlylocatedonepipediameter(1D)upstreamand½pipediameter(1/2D)downstreamfrom
theinletfaceofthenozzle.
❖TheFlowNozzleissimilartotheventuributareintheshapeofanellipse.Theyhaveahigherflow
capacitythanorificeplates.
❖Anothermaindifferencebetweentheflownozzleandtheventuriisthatalthoughtheyhavesimilar
inletnozzles,theflownozzlehasnoexitsection.
❖Thesedevicesaremorecosteffective,butassuchtheyprovidelessaccuracythanventuris,andhave
ahigherunrecoverablepressureloss.
❖FlowNozzlescanhandlelargersolidsandbeusedforhighervelocities,greaterturbulence
andhightemperatureapplications.
❖Theyareoftenusedwithfluidorsteamapplicationscontainingsomesuspendedsolids,andin
applicationswheretheproductisbeingdischargedfromservice.
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20. FLOWNOZZLE
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21. FLOWNOZZLE
Advantages of Flownozzle
❖High velocityapplications.
❖Operate in higherturbulence.
❖Used with fluids containing suspendedsolids.
❖More cost effective thanventuris.
❖Physically smaller than theventuri.
Disadvantages of Flownozzle
❖More expensive than orificeplates.
❖Higher unrecoverable pressureloss.
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22. OPEN CHANNEL FLOW -METER -WEIR
❖The"openchannel"referstoanyconduitinwhichliquidflowswithafreesurface.
❖Includedaretunnels,non-pressurizedsewers,partiallyfilledpipes,canals,streams,and
rivers.
❖Ofthemanytechniquesavailableformonitoringopen-channelflows,depth-related
methodsarethemostcommon.
❖Thesetechniquespresumethattheinstantaneousflowratemaybedeterminedfroma
measurementofthewaterdepth,orhead.
❖Weirsandflumesaretheoldestandmostwidelyusedprimarydevicesformeasuring
open-channelflows.
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23. OPEN CHANNEL FLOW -METER -WEIR
❖Theflowrateoveraweirisafunctionoftheweirgeometryandoftheweirhead(the
weirheadisdefinedastheverticaldistancebetweentheweircrestandtheliquid
surfaceintheundisturbedregionoftheupstreamflow).
❖Weirsarevariablehead,variableareaflowmetersemployedformeasuringlarge
volumesofliquidsinopenchannels.
❖Thedeviceoperatesontheprinciplethatifarestrictionofspecifiedshapeandformis
introducedinflowpath,ariseintheupstreamliquidoccurswhichisafunctionofthe
flowratethroughtherestriction.
❖Weirsoperateontheprinciplethatanobstructioninachannelwillcausewatertoback
up,creatingahighlevel(head)behindthebarrier.
❖Theheadisafunctionofflowvelocity,and,therefore,theflowratethroughthedevice.
Weirsconsistofverticalplateswithsharpcrests.
❖Thetopoftheplatecanbestraightornotched.Weirsareclassifiedinaccordancewith
theshapeofthenotch.ThebasictypesareV-notch,rectangular,andtrapezoidal.
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