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ID:40384925
大小:2.45 MB
页数:70页
时间:2019-08-01
《5.Partload operation, impact of 3-D flow phenomena performance》由会员上传分享,免费在线阅读,更多相关内容在学术论文-天天文库。
1、5Partloadoperation,impactof3-DflowphenomenaperformanceApumpworkingsignificantlybelowthebestefficiencyflowrateissaidtooper-ateatpartload.Atlowspecificspeedsthiscanberoughlyassumedatq*<0.8,athighnqbelowq*<0.9.Sincebladeinletanglesandchannelcrosssectionsaretoolargeforthereducedflowr
2、ate,flowpatternsduringpartloadoperationfundamen-tallychangecomparedwiththedesignpoint.Theflowbecomeshighly3-dimensionalsinceitseparatesintheimpellerandthecollector.Finally,recircula-tionsareobservedatimpellerinletandoutletatsufficientlylowflow.Aneasymeanstoobtaininformationonthei
3、mpellerflowarestroboscopicobservationsoftufts.Flowpatternsinaradialimpellerofnq=22gainedinthiswayareshowninFig.5.1[B.20].Itcanbeseenthattheflowisattachedatq*>0.8whileincreas-inglylargezoneswithseparationandrecirculationareobservedatalowerflowrates.Similarflowpatternswerefoundonim
4、pellersofnq=26and33.Theinteractionbetweenimpellerandcasingatinletandoutletishighlysignifi-cantforthepartloadbehaviorofapump.ItlargelydeterminestheQ-H-curve,ra-dialandaxialforces,hydraulicexcitationforces,noiseandcavitation.Suchcom-plexflowsaredifficulttounderstand.Designingpumpsw
5、ithgoodpartloadbehavior,therefore,islargelybasedonexperience.Whendoingso,itishelpfultoclassifytheexperimentalobservationsaccordingtothephysicalmechanismsin-volved.Thisistheobjectiveofthefollowingdiscussion.Althoughlocalstallinimpellerandcollectoralsooccuratoperationsignifi-cantly
6、abovethebestefficiencypoint(q*>1),noflowrecirculationisobserved.5.1BasicconsiderationsLetusfirstanalyzewhichphysicalcharacteristicsofthepartloadbehaviorcanbededucedfrombasicprinciples,observationandexperience.5.1.1Well-designedpumpsachievehydraulicefficienciesof85to95%inthebestef
7、ficiencypoint–dependingonthespecificspeed,sizeandsurfacequality.Itcanthereforebeassumedthattheflownearthebestefficiencypointis“attached”.Thisimpliesthatnosignificantflowseparationsoccursincethesewouldbeasso-ciatedwithgreaterlosses.Measurementsandobservationsoftuftsinimpellersandc
8、ollectorsconfirmthisstatement.1885Partlo
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