離心風(fēng)機英文文獻

CentrifugalfanAcentrifugalfan(alsosquirrel-cagefan,asitlookslikea\o"Hamsterwheel"hamsterwheel)isamechanicaldeviceformoving\o"Air"airor\o"Gas"gases.Ithasa\o"Fan(mechanical)"fan\o"Wheel"wheelcomposedofanumberoffan\o"Blade"blades,or\o"Ribs"ribs,mountedaroundahub.AsshowninFigure1,thehubturnsona\o"Driveshaft"driveshaftthatpassesthroughthefanhousing.Thegasentersfromthesideofthefan\o"Wheel"wheel,turns90degreesand\o"Accelerate"acceleratesdueto\o"Centrifugalforce"centrifugalforceasitflowsoverthefanbladesandexitsthefanhousing.\o""[1]Figure1Centrifugalfanscangeneratepressurerisesinthegasstream.Accordingly,theyarewell-suitedfor\o"Industry"industrialprocessesand\o"Airpollution"airpollutioncontrolsystems.Theyarealsocommonincentralheating/coolingsystems.1.FancomponentsThemajorcomponentsofatypicalcentrifugalfanincludethefanwheel,fanhousing,drivemechanism,andinletand/oroutlet\o"Damper"dampers.2.TypesofdrivemechanismsThefandrivedeterminesthespeedofthefanwheel(impeller)andtheextenttowhichthisspeedcanbevaried.Therearethreebasictypesoffandrives.\o""[1]2.1DirectdriveThefanwheelcanbelinkeddirectlytotheshaftofan\o"Electricmotor"electricmotor.Thismeansthatthefanwheelspeedisidenticaltothemotor's\o"Rotation"rotationalspeed.Withthistypeoffandrivemechanism,thefanspeedcannotbevariedunlessthemotorspeedisadjustable.2.2.1BeltdriveFigure2:CentrifugalfanwithabeltdriveBeltdrivenfansusemultiplebeltsthatrotateinasetof\o"Sheave"sheavesmountedonthemotorshaftandthefanwheelshaft.Thistypeofdrivemechanismisdepictedinfigure2.Thebeltstransmitthemechanicalenergyfromthemotortothefan.Thefanwheelspeeddependsuponthe\o"Ratio"ratioofthediameterofthemotorsheavetothediameterofthefanwheelsheaveandcanbeobtainedfromthisequation:\o""[1]where:

rpmfan=fanwheelspeed,revolutionsperminuterpmmotor=motornameplatespeed,revolutionsperminuteDmotor=diameterofthemotorsheaveDfan=diameterofthefanwheelsheaveFanwheelspeedsinbelt-drivenfansarefixedunlessthebeltsslip.Beltslippagecanreducethefanwheelspeedseveralhundredrevolutionsperminute(rpm).2.2VariabledriveVariabledrivefansuse\o"Hydraulic"hydraulicor\o"Magnetic"magneticcouplings(betweenthefanwheelshaftandthemotorshaft)thatallowcontrolofthefanwheelspeedindependentofthemotorspeed.Thefanspeedcontrolsareoftenintegratedinto\o"Automate"automatedsystemstomaintainthedesiredfanwheelspeed.\o""[1]Analternatemethodofvaryingthefanspeedisbyuseofanelectronicvariable-speeddrivewhichcontrolsthespeedofthemotordrivingthefan.Thisoffersbetteroverallenergyefficiencyatreducedspeedsthanmechanicalcouplings.2.3FandampersFandampersareusedtocontrolgasflowintoandoutofthecentrifugalfan.Theymaybeinstalledontheinletsideorontheoutletsideofthefan,orboth.Dampersontheoutletsideimposeaflowresistancethatisusedtocontrolgasflow.Dampersontheinletsidearedesignedtocontrolgasflowandtochangehowthegasentersthefanwheel.Inletdampersreducefanenergyusageduetotheirabilitytoaffecttheairflowpatternintothefan.\o""[1]3.Backward-curvedbladesBackward-curvedblades,asinFigure3(b),usebladesthatcurveagainstthedirectionofthefanwheel'srotation.Thebackwardcurvaturemimicsthatofanairfoilcrosssectionandprovidesgoodoperatingefficiencywithrelativelyeconomicalconstructiontechniques.Thesetypesoffanwheelsareusedinfansdesignedtohandlegasstreamswithlowtomoderateparticulateloadings.Theycanbeeasilyfittedwithwearprotectionbutcertainbladecurvaturescanbepronetosolidsbuild-up.Backwardcurvedfanscanhaveahighrangeofspecificspeedsbutaremostoftenusedformediumspecificspeedapplications--highpressure,mediumflowapplications.Backward-curvedfansaremuchmoreenergyefficientthanradialbladefansandso,forhighhorsepowerapplicationsmaybeasuitablealternativetothelowercostradialbladedfan.4.StraightradialbladesRadialfanblades,asinFigure3(c),extendstraightoutfromthehub.Aradialbladefanwheelisoftenusedonparticulate-ladengasstreamsbecauseitistheleastsensitivetosolidsbuild-upontheblades,butitisoftencharacterizedbygreaternoiseoutput.Highspeeds,lowvolumes,andhighpressuresarecommonwithradialfans,andareoftenusedin\o"Vacuumcleaner"vacuumcleaners,pneumaticmaterialconveyingsystems,andsimilarprocesses.Figure35.CentrifugalfanratingsRatingsfoundincentrifugalfanperformancetablesandcurvesarebasedonstandardairSCFM.Fanmanufacturersdefinestandardairasclean,dryairwithadensityof0.075poundsmasspercubicfoot(1.2kg/m3),withthebarometricpressureatsealevelof29.92inchesofmercury(101.325kPa)andatemperatureof70°F(21°C).Selectingacentrifugalfantooperateatconditionsotherthanstandardairrequiresadjustmenttobothstaticpressureandbrakehorsepower.Thevolumeofairwillnotbeaffectedinagivensystembecauseafanwillmovethesameamountofairregardlessoftheairdensity.Ifacentrifugalfanistooperateatanon-standarddensity,thencorrectionsmustbemadetostaticpressureandbrakehorsepower.Athigherthanstandardelevation(sealevel)andhigherthanstandardtemperature,airdensityislowerthanstandarddensity.Centrifugalfansthatarespecifiedforcontinuousoperationathighertemperaturesneedtobeselectedtakingintoaccountairdensitycorrections.Again,acentrifugalfanisaconstantvolumedevicethatwillmovethesameamountofairattwodifferenttemperatures.If,forexample,acentrifugalfanmoves1,000ft3/min(28m3/min)at70°F(21°C)itwillalsomove1,000ft3/min(28m3/min)at200°F(93°C).Centrifugalfanairvolumedeliveredbythecentrifugalfanisnotaffectedbydensity.However,sincethe200°F(93°C)airweighsmuchlessthanthe70°F(21°C)air,thecentrifugalfanwillcreatelessstaticpressureandwillrequirelessbrakehorsepower.Selectingacentrifugalfantooperateatconditionsotherthanstandardairrequiresadjustmenttobothstaticpressureandpower.WhenacentrifugalfanisspecifiedforagivenCFMandstaticpressureatconditionsotherthanstandard,anairdensitycorrectionfactormustbeappliedtoselectthepropersizefantomeetthenewcondition.Since200°F(93°C)airweighsonly80%of70°F(21°C)air,thecentrifugalfanwillcreatelesspressure.Togettheactualpressurerequiredat200°F(93°C),thedesignerwouldhavetomultiplythepressureatstandardconditionsbyanairdensitycorrectionfactorof1.25(i.e.,1.0/0.8)togetthesystemtooperatecorrectly.Togettheactualpowerat200°F(93°C),thedesignerwouldhavetodividethepoweratstandardconditionsbytheairdensitycorrectionfactor.離心風(fēng)機離心風(fēng)機（也鼠籠式風(fēng)扇，因為它看起來像倉鼠輪）是一種機械裝置移動空氣或氣體。它有一個風(fēng)扇輪組成若干風(fēng)扇葉片，或肋骨，裝在一個樞紐。如圖1所示，該中心將在驅(qū)動軸，穿越風(fēng)扇住房。氣體進入從側(cè)面的風(fēng)扇方向盤，把90度，并加快由于離心力因為它流動的風(fēng)扇葉片和出口風(fēng)扇住房。[1]離心式風(fēng)機可產(chǎn)生壓力上升氣流。因此，他們非常適合工業(yè)加工和空氣污染控制系統(tǒng)。他們還共同在中央供暖/冷卻系統(tǒng)。圖11.風(fēng)機組件主要組成部分典型的離心式風(fēng)機包括風(fēng)扇輪，風(fēng)扇住房，驅(qū)動機制，進口和/或出口閘。2類型的驅(qū)動機制風(fēng)扇驅(qū)動器決定的速度，風(fēng)扇輪（葉輪）以及在何種程度上這樣的速度可以多種多樣。有三種基本類型的風(fēng)機驅(qū)動器。[1]

2.1直接驅(qū)動

風(fēng)扇輪可以直接聯(lián)系的骨干一個電動馬達(dá)。這意味著，風(fēng)扇輪速是相同的電機轉(zhuǎn)速。這種類型的風(fēng)機驅(qū)動機制，風(fēng)扇轉(zhuǎn)速不能更改，除非是可調(diào)的電機轉(zhuǎn)速。

2.1.1帶傳動圖2：離心風(fēng)機用皮帶驅(qū)動風(fēng)扇driveBelt使用多重皮帶旋轉(zhuǎn)的一套滑輪安裝在電機軸和風(fēng)扇輪軸。這種類型的驅(qū)動機制是描繪在圖2。皮帶傳遞機械能的電機風(fēng)扇。風(fēng)扇輪速取決于比例的直徑電機帶輪的直徑風(fēng)扇輪輪和可從該方程：[1]其中：rpmfan=范輪速，每分鐘的革命

rpmmotor=電機銘牌速度，每分鐘的革命

Dmotor=直徑電機輪Dfan=直徑風(fēng)扇輪輪范車輪速度皮帶驅(qū)動風(fēng)扇是固定的，除非帶滑。帶滑移可以降低風(fēng)扇輪速幾百革命每分鐘（每分鐘轉(zhuǎn)速）。圖22.2.變頻驅(qū)動器

可變液壓驅(qū)動風(fēng)扇使用或磁性聯(lián)軸器（范之間輪軸與電機軸），使控制風(fēng)扇輪速獨立的電機轉(zhuǎn)速。該風(fēng)扇轉(zhuǎn)速控制常常被納入自動化系統(tǒng)，以保持理想風(fēng)扇輪速。[1]替代的方法不同的風(fēng)扇速度是使用電子變速驅(qū)動器的速度控制的電機驅(qū)動風(fēng)扇。這提供了更好的整體能源使用效率，同時降低速度比機械聯(lián)軸器。2.3范減震器范減震器是用來控制氣體流量流入和流出的離心式風(fēng)機。他們可能會被安裝在入口旁或出口一側(cè)的風(fēng)扇，或兩者兼而有之。阻尼器的出口方面實行流動阻力，用于控制氣流。阻尼器的進氣口一側(cè)的目的是控制氣體流量和改變氣體進入風(fēng)機輪。范進閘減少能源使用量，由于他們有能力影響氣流的模式風(fēng)扇。[1]3.向后彎曲葉片后向彎曲的刀片，在圖3（b），使用該曲線對葉片的方向風(fēng)扇輪的自轉(zhuǎn)。落后的曲率模仿的翼型截面，并提供良好的運營效率相對經(jīng)濟的施工技術(shù)。這些類型的風(fēng)機輪轂中使用的風(fēng)扇設(shè)計來處理天然氣流與低到中