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Transcript of Centrifugal Compressor - Wikipedia, The Free Encyclopedia

  • 9/6/2015 CentrifugalcompressorWikipedia,thefreeencyclopedia

    https://en.wikipedia.org/wiki/Centrifugal_compressor 1/22

    Centrifugalimpellerwithahighlypolishedsurfacelikelytoimproveperformance

    Jetenginecutawayshowingthecentrifugalcompressorandotherparts

    CentrifugalcompressorFromWikipedia,thefreeencyclopedia

    Centrifugalcompressors,sometimestermedradialcompressors,areasubclassofdynamicaxisymmetricworkabsorbingturbomachinery.[1]

    Theidealizedcompressivedynamicturbomachineachievesapressurerisebyaddingkineticenergy/velocitytoacontinuousflowoffluidthroughtherotororimpeller.Thiskineticenergyisthenconvertedtoanincreaseinpotentialenergy/staticpressurebyslowingtheflowthroughadiffuser.Thepressureriseinimpellerisinmostcasesalmostequaltotheriseinthediffusersection.

    Contents

    1Theoryofoperation2Historicalcontributions,thepioneers

    2.1Partialtimeline3Turbomachinerysimilarities

    3.1Turbomachineryusingcentrifugalcompressors4Componentsofasimplecentrifugalcompressor

    4.1Inlet4.2Centrifugalimpeller4.3Diffuser4.4Collector

    5Applications6Performance

    6.1Performancemaps6.2Surge6.3Maximumflowlineversuschoke6.4Otheroperatinglimits

    7Dimensionalanalysis7.1theorem7.2Classicturbomachinerysimilitude7.3Otherdimensionlesscombinations7.4Affinitylaws

    8Aerothermodynamicfundamentals8.1Conservationofmass8.2Conservationofmomentum8.3Conservationofenergy8.4Equationofstate

    9Prosandcons10Aerodynamicdesignmethodology11Structuralmechanics,manufactureanddesigncompromise12Seealso13References

  • 9/6/2015 CentrifugalcompressorWikipedia,thefreeencyclopedia

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    Inletvelocitytrianglesforcentrifugalcompressorimpeller

    Exitvelocitytrianglesforcentrifugalcompressorimpeller

    13References14Externallinks

    Theoryofoperation

    Inthecaseofwhereflowsimplypassesthroughastraightpipetoenteracentrifugalcompressortheflowisstraight,uniformandhasnovorticity.Asillustratedbelow1=0deg.Astheflowcontinuestopassintoandthroughthecentrifugalimpeller,theimpellerforcestheflowtospinfasterandfaster.AccordingtoaformofEuler'sfluiddynamicsequation,knownas"pumpandturbineequation,"theenergyinputtothefluidisproportionaltotheflow'slocalspinningvelocitymultipliedbythelocalimpellertangentialvelocity.

    Inmanycasestheflowleavingcentrifugalimpellerisnearthespeedofsound(340metres/second).Theflowthentypicallyflowsthroughastationarycompressorcausingittodecelerate.Thesestationarycompressorsareactuallystaticguidevaneswhereenergytransformationtakesplace.AsdescribedinBernoulli'sprinciple,thisreductioninvelocitycausesthepressuretoriseleadingtoacompressedfluid.[1]

    Historicalcontributions,thepioneers

    Overthepast100years,appliedscientistsincludingStodola(1903,19271945),[2]Pfleiderer(1952),[3]Hawthorne(1964),[4]Shepard(1956),[1]Lakshminarayana(1996),[5]andJapikse(manytextsincludingcitations),[6][7][8][9]haveeducatedyoungengineersinthefundamentalsofturbomachinery.Theseunderstandingsapplytoalldynamic,continuousflow,axisymmetricpumps,fans,blowers,andcompressorsinaxial,mixedflowandradial/centrifugalconfigurations.

    Thisrelationshipisthereasonadvancesinturbinesandaxialcompressorsoftenfindtheirwayintootherturbomachineryincludingcentrifugalcompressors.Figures1.1and1.2[10][11]illustratethedomainofturbomachinerywithlabelsshowingcentrifugalcompressors.Improvementsincentrifugalcompressorshavenotbeenachievedthroughlargediscoveries.Rather,improvementshavebeenachievedthroughunderstandingandapplyingincrementalpiecesofknowledgediscoveredbymanyindividuals.

    Figure1.1representstheaerothermodomainofturbomachinery.ThehorizontalaxisrepresentstheenergyequationderivablefromTheFirstLawofThermodynamics.[1][11]Theverticalaxis,whichcanbecharacterizedbyMachNumber,representstherangeoffluidcompressibility(orelasticity).[1][11]TheZaxis,whichcanbecharacterizedbyReynoldsNumber,representstherangeoffluidviscosities(or

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    Figure1.1Aerothermodomainofturbomachinery

    Figure1.2Physicaldomainofturbomachinery

    stickiness).[1][11]MathematiciansandPhysicistswhoestablishedthefoundationsofthisaerothermodomaininclude:[12][13]SirIsaacNewton,DanielBernoulli,LeonhardEuler,ClaudeLouisNavier,SirGeorgeGabrielStokes,ErnstMach,NikolayYegorovichZhukovsky,MartinWilhelmKutta,LudwigPrandtl,TheodorevonKrmn,PaulRichardHeinrichBlasius,andHenriCoand.

    Figure1.2representsthephysicalormechanicaldomainofturbomachinery.Again,thehorizontalaxisrepresentstheenergyequationwithturbinesgeneratingpowertotheleftandcompressorsabsorbingpowertotheright.[1][11]Withinthephysicaldomaintheverticalaxisdifferentiatesbetweenhighspeedsandlowspeedsdependingupontheturbomachineryapplication.[1][11]TheZaxisdifferentiatesbetweenaxialflowgeometryandradialflowgeometrywithinthephysicaldomainofturbomachinery.[1][11]Itisimpliedthatmixedflowturbomachineryliebetweenaxialandradial.[1][11]Keycontributorsoftechnicalachievementsthatpushedthepracticalapplicationofturbomachineryforwardinclude:[12][13]DenisPapin,[14]KernelienLeDemour,DanielGabrielFahrenheit,JohnSmeaton,Dr.A.C.E.Rateau,[15]JohnBarber,AlexanderSablukov,SirCharlesAlgernonParsons,gidiusElling,SanfordAlexanderMoss,WillisCarrier,AdolfBusemann,HermannSchlichting,FrankWhittleandHansvonOhain.

    Partialtimeline

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    Cutawayshowinganaxicentrifugalcompressorgasturbine

    Centrifugalcompressorsaresimilarinmanywaystootherturbomachineryandarecomparedandcontrastedasfollows:

    Similaritiestoaxialcompressor

    Centrifugalcompressorsaresimilartoaxialcompressorsinthattheyarerotatingairfoilbasedcompressorsasshownintheadjacentfigure.[5][7]Itshouldnotbesurprisingthatthefirstpartofthecentrifugalimpellerlooksverysimilartoanaxialcompressor.Thisfirstpartofthecentrifugalimpellerisalsotermedaninducer.Centrifugalcompressorsdifferfromaxialsastheyuseagreaterchangeinradiusfrominlettoexitoftherotor/impeller.

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    Alowspeed,lowpressurecentrifugalcompressororcentrifugalfan,withupwarddischargingconeusedtodiffusetheairvelocity

    Asquirrelcagefan,withoutadischargediffuser

    Similaritiestocentrifugalfan

    Centrifugalcompressorsarealsosimilartocentrifugalfansofthestyleshowninneighboringfigureastheybothincreasetheflowsenergythroughincreasingradius.[1]Incontrasttocentrifugalfans,compressorsoperateathigherspeedstogenerategreaterpressurerises.Inmanycasestheengineeringmethodsusedtodesignacentrifugalfanarethesameasthosetodesignacentrifugalcompressor.Asaresult,theycanattimeslookverysimilar.

    Thisrelationshipislesstrueincomparisontoasquirrelcagefanasshowninfigurefarthestright.

    Forpurposesofgeneralizationanddefinition,itcanbesaidthatcentrifugalcompressorsoftenhavedensityincreasesgreaterthan5percent.Also,theyoftenexperiencerelativefluidvelocitiesaboveMachnumber0.3[5][16]whentheworkingfluidisairornitrogen.Incontrast,fansorblowersareoftenconsideredtohavedensityincreasesoflessthanfivepercentandpeakrelativefluidvelocitiesbelowMach0.3.

  • 9/6/2015 CentrifugalcompressorWikipedia,thefreeencyclopedia

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    A3Dsolidsmodelofatypeofcentrifugalpump

    Cutawayofacentrifugalpump

    CutawayshowingaradialinflowturbinethatlookssimilartotheturbineshowninFigure3.1

    Similaritiestocentrifugalpump

    Centrifugalcompressorsarealsosimilartocentrifugalpumps[1]ofthestyleshownintheadjacentfigures.Thekeydifferencebetweensuchcompressorsandpumpsisthatthecompressorworkingfluidisagas(compressible)andthepumpworkingfluidisliquid(incompressible).Again,theengineeringmethodsusedtodesignacentrifugalpumparethesameasthosetodesignacentrifugalcompressor.Yet,thereisoneimportantdifference:theneedtodealwithcavitationinpumps.

    Similaritiestoradialturbine

    CentrifugalcompressorsalsolookverysimilartotheirturbomachinerycounterparttheRadial_turbineasshowninthefigure.Whileacompressortransfersenergyintoaflowtoraiseitspressure,aturbineoperatesinreverse,byextractingenergyfromaflow,thusreducingitspressure.[7]Inotherwords,powerisinputtocompressorsandoutputfromturbines.

    Turbomachineryusingcentrifugalcompressors

    Apartiallistofturbomachinerythatmayuseoneormorecentrifugalcompressorswithinthemachinearelistedhere.

  • 9/6/2015 CentrifugalcompressorWikipedia,thefreeencyclopedia

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    Figure3.1Cutawayviewofaturbochargershowingthecentrifugalcompressor(blue)ontherightendoftherotor

    AuxiliarypowerunitCentrifugaltypesuperchargerGasturbineTurbochargerTurbopropTurboshaft

    Componentsofasimplecentrifugalcompressor

    Asimplecentrifugalcompressorhasfourcomponents:inlet,impeller/rotor,diffuser,andcollector.[1]Figure3.1showseachofthecomponentsoftheflowpath,withtheflow(workinggas)enteringthecentrifugalimpelleraxiallyfromrighttoleft.Asaresultoftheimpellerrotatingclockwisewhenlookingdownstreamintothecompressor,theflowwillpassthroughthevolute'sdischargeconemovingawayfromthefigure'sviewer.

    Inlet

    Theinlettoacentrifugalcompressoristypicallyasimplepipe.Itmayincludefeaturessuchasavalve,stationaryvanes/airfoils(usedtohelpswirltheflow)andbothpressureandtemperatureinstrumentation.Alloftheseadditionaldeviceshaveimportantusesinthecontrolofthecentrifugalcompressor.

    Centrifugalimpeller

    Thekeycomponentthatmakesacompressorcentrifugalisthecentrifugalimpeller,Figure0.1,whichcontainsarotatingsetofvanes(orblades)thatgraduallyraisestheenergyoftheworkinggas.Thisisidenticaltoanaxialcompressorwiththeexceptionthatthegasescanreachhighervelocitiesandenergylevelsthroughtheimpeller'sincreasingradius.