Centrifugalchiller1,advantagecomparison

Withtherapiddevelopmentofairconditioningsystemandpetrochemicalindustry,thereisanurgentneedforlargeandlowtemperaturecoldstoragerefrigerationcompressors,andcentrifugalrefrigerationcompressorsmeetthisdemandwellwiththeirownadvantages.Itsmainadvantagesare:

(1)Therefrigerationcapacityislarge,andtheefficiencyoflargecentrifugalcompressorsisclosetothatofmodernlargeverticalpistoncompressors.

(2)Compactstructure,lightweight,80~88%lighterthanthepistoncompressorwiththesamerefrigerationcapacity,andthefloorareacanbereducedbyabouthalf.

(3)Nowearparts,smoothoperation,lowvibration,lownoise.

(4)Canbeeconomicallysteplessadjustment.Whentheairinletguidevanevalveisused,theloadoftheunitcanbeadjustedefficientlyintherangeof30~****.Basedontheaboveadvantages,centrifugalcompressorshavebeenwidelyusedanddevelopedinashorttime.However,ifyoudonotsolvetheproblemsthatoccurintheoperationofthecentrifugalcompressor,notonlytheefficiencyofthemachineisgreatlyreduced,butalsothemachinemaybeseriouslydamaged.

2.Surgephenomenon

Therateshouldbereduced,andthefurtherthedeviation,themoretheefficiencywillbereduced.PointEisthepointofmaximumdisplacement.Whentheexhaustvolumeincreasestothispoint,theinletvelocityofthecompressorimpellerreachesthespeedofsounda.Thevolumeofexhaustcannotbeincreasedanyfurther.Pointsisthesurgepoint.Whentheflowrateofthecompressorisreducedtobelowpoints,duetothelargeincreaseintheenergylossoftherefrigerantthroughtheimpellerflowpath,theeffectiveenergyheadofthecentrifugalcompressorwillcontinuetodecline,atthistime,thegasoutsidethecompressoroutletwillflowbacktotheimpeller.Forexample,iftheevaporationpressureisunchangedandthecondensingpressurerisesforsomereason,theenergyheadrequiredtocompressthegaswillincrease.Theexhaustcapacityofthecompressorshouldbereduced.Whenthecondensingpressureincreasesandtheexhaustvolumedecreasestopoints,theeffectiveenergyheadgeneratedbythecentrifugalcompressorreachesthehighest.Ifthecondensingpressureincreasesagain,theenergyheadgeneratedbythecompressorisinsufficient,andthegasmustflowbackfromthecondensertothecompressor.Afterthegasbackflow,thecondensingpressureisreduced,andthecompressorcanpressthegasoutandsendittothecondenser,andthecondensingpressurewillcontinuetorise,andthebackflowwilloccuragain.Thegasbackflowimpactphenomenonthatoccurswhenthecentrifugalcompressorisrunningiscalledsurgephenomenon.Afterthesurgephenomenon,itnotonlycausesperiodicincreaseofnoiseandvibration,butalsocausesthetemperatureoftheshellandbearingtoriseduetothehightemperaturegasbackflowfillingcompressor.Ifmeasuresarenottakenintime,itwilldamagethecompressorandevendamagetheentirerefrigerationdevice.Therefore,theoccurrenceofsurgeshouldbeavoidedduringoperation.

Themainreasonforthesurgephenomenonofcentrifugalrefrigerationcompressorsisthatthecondensingpressureistoohighorthesuctionpressureistoolow,sokeepingthecondensingpressureandevaporationpressurestableduringoperationcanpreventtheoccurrenceofsurge.However,whenthecompressorrefrigerationcapacityisadjusted,itsloadistoosmall,themachinewillalsoproducesurge,whichrequiresprotectiveanti-surgeregulation.Bypassregulationisameasuretocountersurge.Whentherefrigerationcapacityofthecompressorisrequiredtobereducedbelowthesurgepoint,apartofthegaseousrefrigerantisdrawnfromthecompressoroutletanddirectlyflowstothecompressorsuctiontubewithoutcondensation,sothattherefrigerantflowthroughtheevaporatorcanbereducedtoreducetherefrigerationcapacityoftherefrigerationsystem,andthecompressorexhaustvolumeisnottoosmall,soastopreventthesurgefromtakingplace.

3,thefactorsaffectingthecoolingcapacityofcentrifugalcompressor

Whenthecentrifugalcompressorisrunningintheworkingrange(betweenSandE),thesmallertheexhaustvolume,thehighertheeffectiveenergyhead.Becausethedifferencebetweenthecondensingtemperatureandtheevaporationtemperatureislarger,theenergyheadrequiredwhenthegaseousrefrigerantiscompressedislarger,sothecentrifugalrefrigerationcompressorandthepistonrefrigerationcompressorarethesame,withtheincreaseofthecondensationtemperatureandthedecreaseoftheevaporationtemperature,theactualexhaustvolumewillbereduced,therebyreducingtherefrigerationcapacityofthecompressor.

However,theextenttowhichchangesinevaporationtemperatureandcondensationtemperatureaffectthecoolingcapacityisdifferentbetweenthetwocompressors.

3.1Influenceofevaporationtemperature

Whenthenumberofrevolutionsoftherefrigerationcompressorandthecondensingtemperaturearefixed,therefrigerationcapacityofthecentrifugalrefrigerationcompressorismoreaffectedbythechangeofevaporationtemperaturethanthatofthepistonrefrigerationcompressor,andthelowertheevaporationtemperature,themoredrasticthecoolingcapacitydrops.

3.2Influenceofcondensingtemperature

Whentherotationnumberandevaporationtemperatureoftherefrigerationcompressorareconstant,andthecondensationtemperatureislowerthanthedesignvalue,thecoldstoragetemperaturehaslittleeffectontherefrigerationcapacityofthecentrifugalrefrigerationcompressor.However,whenthecondensationtemperatureishigherthanthedesignvalue,withtheincreaseofthecondensationtemperature,therefrigerationcapacityofthecentrifugalrefrigerationcompressorwilldropsharply,whichmustbegivenenoughattention.

3.3Influenceofrevolution

Forthepistonrefrigerationcompressor,whentheevaporationtemperatureandcondensationtemperaturearecertain,therefrigerationcapacityofthecompressorisproportionaltothenumberofrevolutions,thatis,thepercentageofthechangeinthenumberofrevolutionsisthepercentageofthechangeintherefrigerationcapacityofthepistonrefrigerationcompressor.

However,thecentrifugalrefrigerationcompressorisnot,becausetheenergyheadgeneratedbythecompressorandtheoutercircumferencespeedoftheimpeller(canalsobesaidtobeproportionaltothesquareofthecompressorrevolution),so,withthereductionoftherevolution,theenergyheadgeneratedbythecentrifugalrefrigerationcompressordecreasessharply,sotherefrigerationcapacitywillalsobesharplyreduced.

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