salford-ventilation-noisedoc索尔福德noisedoc通风

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1、NOISEINVENTILATIONDUCTSSoundinductsTheprimarysourceofnoiseisthefan.Itwillradiatetonalsoundatfrequenciesrelatedtothemotor,rotational,frequencyandthebladefrequency.Itwillalsoradiatebroadbandsoundduetoanyturbulentairflowofftheblades.Thesoundpowerisconstrainedwithintheduc

2、ting.Thesoundpowerpropagatingalongtheductwillreduceonlywhereenergyhasbeen:·absorbedbytheductwalls(andpossiblythenradiatedoutsidetheduct)·reflectedbackuptheductbyasharpbend·dividedbetweenductswherebranchesdiverge·reflectedbackuptheductduetochangesinthecross-sectionalar

3、eaoftheductInthesimplestpossiblecaseofalongstraightductwithveryrigidwalls,thepowerwillbethesameatallpointsalongtheduct.FanNoiseNoiseenergygeneratedbythefanrotationisdependentonthediameterandtherotationalspeedofthefan,typicallyproportionaltothefifthorsixthpowerofthelin

4、earvelocityatthetipofthefanblades.Generallyalargediameterfanatlowrotationalspeedproduceslowfrequencyandcomparativelylownoiselevel.Thesamevolumeflowratecanbeachievedbyincreasingtherotationalspeedandreducingthediameter.Inthiscasethefrequencyandthelevelofthenoisearehighe

5、rbutthehigherfrequencynoisecanbemoreeffectivelyattenuatedbyliningtheductwithsoundabsorbingmaterials.IngeneraltheSWLoffansvariesgreatlywithtypes,sizes,andspeeds.Itshouldbechosencarefullytoensurelownoiselevels.Manufacturer’sdataonthesourceSWLofafanshouldalwaysbesought.F

6、lowgeneratednoise:·Inemptystraightductsnoisefromturbulenceisgenerallyverysmallcomparedwithotherfactors,especiallywithvelocty,u<10m/s.·Bends,Branches,JunctionsandTurnscauseabruptchangesinflowconditions.Noiselevelincreasesapproximately15(power%u5)to20(power%u7)dBperdoub

7、lingofflowspeeddependingheavilyontheductsizeandconfigurations.Noisecanbereducedbyroundingthebendsorintroducingstreamlinedturningvanes.·InteractionwithObstacles,e.g.silencersetccausesturbulencewakes.Noiselevelagaindependsapproximatelyonu5,andalsoonthesizeandgeometryoft

8、heobstacle.Shapesthatcreateabruptchangesintheflowarebesttobeavoided.·Inlet/OutletGrilles,(air)Diffusersanddampers.Similarnoi