机械毕业设计英文外文翻译265节流阀操作状态在流量特性之上的有效实验研究Word文件下载.docx
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waterinsteadofminera1oi1asthepressuremediainhydraulic
powersystems，whichhasbecomemoreandmoreattractiveowingtothegreatadvantagessuchasenvironmenta1friendliness．
noflammability,cheapness，cleanlinessandeasydisposal.
However,comparedwithminera1oi1asakindofworkingmedia．
waterhaslowerviscosity，highervaporouspressure，higherdensityand1argerbulkmodulus，etc．Becauseofthese，theflow
Characteristicsusingwaterasworkingmediaareverydifferent
fromthecasewhenusingoilasworkingmedia．
Generally,therearetwokindsoffactorsexecutinggreateffectsontheflow—pressurecharacteristicsofthrottle．oneisgeo．
metricshapeandparameters．Whichincludetheshapeofpoppet
andseat，coneangle，thelengthoforifice，thelapbetweenpoppet
andseat，etc，andareunchangeablewhenthethrottleismanufactured．Manyresearcherspaidtheirmuchattentiontotheeffectsof
geometricshapeontheflowcharacteristicsofthrottleLJ．The
otherisoperatingconditions，whicharechangedwithvarious
workingcase．OperatingconditionsincludepoppetLift，working
media，backpressureandmediumtemperature，etc．Compared
withtheresearchesofeffectsofgeometricshapeonflowcharacteristics，previousresearchesareseldomconcentratedontheeffectsofoperatingconditionontheflowcharacteristicsofthrottle，
especiallyusingwaterasworkingmedia．In1991．D．N．Johnston
andcoworkerspublishedtheirexperimenta1investigationofflow
andforcecharacteristicsofhydraulicpoppetanddiscvalvesusing
waterasworkingfluidIntheirresearch．measuredflowcoefficientandforcecharacteristicsshowmarkeddifferencesdepending
onvalvegeometryandopening．However，intheirexperimental
andtheoretica1study．theeffectsofcapitation．whichisinevitable
inwaterhydraulicelements．onflowandforcecharacteristics
werenotunderconsideration．
Inthispaper,severalkindsofthrottle，includingconepoppet
valves，discvalves，bal1valvesanddumpingorifices，aretestedto
investigatetheinfluencesofoperatingconditionsonflowcharacteristicsofthrottle．Theoperatingconditionsincludepoppetlift，
backpressure，workingmediaandmediatemperature．Theworkingmediaistapwater．
FiglSchematicdiagramofexperimentalsystem
1．Pressuregauge2．15．Temperaturegauge3．16．2lConnectingblock4．Ⅵraterhydraulicpump
5Filter6．Watertank7．Displacementgauge
8．9．Pressuregaugel．Vla1veelementl1．Ⅷseat
l2．14．Adjustablerestrictivevalvel3．Reliefvalvel7．18．Shutoffvalve
l9．Measuringcup20．Flowmeter22．Cooler
Fig．2istheschematicdiagramofconepoppetvalve．Thetest
rigcanalsobeusedtomeasuretheflowcharacteristicsoforifice，
spoolvalve，ballvalveanddumpingorifice，etc．ifchangingthe
assemblyofpoppetandseat（seeFigs．3-5）．
Theflowcoefficient，whichisbasedonthedifference
betweentheupstreampressure，Pi，anddownstreampressure，P2，
canbegivenbytheequation
where（）istheflowareaofthrottleandPisthedensityofwater.
2．1effectsofpoppetliftontheflowcharacteristics
Inordertoresearchtheinfluencesofpoppetlitontheflow
andcavitationscharacteristics．thepapermakesexperimentalinvestigationonthethrottlesofa30~conepoppetwithsharpseat
（Fig．2，2a=30。
，2，，：
O，dz=l6．02irlln，calledthrottleA）anda30。
conepoppetwithchamferedseatf2a=30。
，2：
30o，d1：
l6．O4
mm，s=4．84mm，calledthrottleB1．Inexperiments，theinlet
pressureiskeptconstantat3Mpaandoutletpressureisreduced
gradually．Thetemperatureis20℃．Fig6istheflowcoefficient
andpressuredifferencecurvesoftwokindsOfthrottlewhenthe
poppet1itis0．5rifer．FromFig．6．itcanbeseenthattheflow
coefficientofsharpseatislargerthanthatofchamferedseat．That
isbecausealthoughthereissomepressurerecoveryinthecaseof
chamferedseat．whichleadstotheincreasingofflowcoefficient．
theviscousrestriction1ossofthrottleofchamferedseatis1arger
thanthatofsharpseat．
Whenthepoppetliftxis1．0mill（Fig．7），theflowcoefficient
ofchamferedseatislargerthanthatofsharpseat，whichis
oppositetothecaseofx=O．5mil1．
Inhydraulicthrottle，venacontractualisformedbecauseof
reattachmentflow．Thepressureofvenacontractualislowerthan
theotherplacesofflowinthethrottlebecausetheflowvelocity
thereishigher．Whenthepressureofvenacontractualislowerthan
thevaporpressureofwater（thevaporouspressureofwateris
l2kPaat50℃whichiseasytoreachinthrottle），vaporis
formedandthepressuretherewillnotdecreaseanymorewiththe
decreasingoftheoutletpressureofthrottle，andthusflow
coefficientcalculatedaccordingtoEq．f1）willdecreasesbecause
flowratedoesnotincreasewiththeincreasingofthepressure
differencesacrossthethrottle．Atthistimeflowsaturation
happens．ForthrottleA．theformationofvenacontractualisafter
throttleandtheformationofvaporisinthedownstreamofthe
throttle，whichhardlyinfluencestheflowthroughthethrottle．For
throttleB．theformationofvenacontractualisinthethrottleand
thusinfluencestheflowthroughthethrottlegreatly．Asflow
saturationisconceded．itiseasiertooccurinthrottleBthanA．
FromFig．7itcanbeseenthatthepressuredifferencesacross
thetwothrottleswhentheflowcoefficientdecreasesare2．75MPa
and2．O2MParespectivelywhenpoppetliftis0．5mm．en
poppetliftis1．0mm．thepressuredifferencesacrossthetwo
throneswhentheflowcoefficientdecreasesare2．04MPaand
ll36MParespectively,whicharelowerthanthecaseofx=0．5rills．
Fromhereitisknownthatflowsaturationoccursatlesserpres—
suredifferencewiththeincreasingofpoppetlitforboththrottles．
2．2Effectsofbackpressureontheflowcharacteristics
Generallyspeaking，increasingbackpressurecontributesto
inhibittheformationofbubbles．Cavitationsoccurrenceandflow
saturation．However，fromtheqv△curvesofthrottleB（2a=30。
，
2y=3o。
），atdifferentpoppetliftwithandwithoutbackpressure
respectively（Fig．8），itcanbeseenthatovertherangeofpressure
differenceconsidered．Whellthereisnobackpressure．Thereisno
flowsaturation；
whenthereisbackpressure．obviousflowsaturationisobservedatthesamepressuredrop．Thatisbecausewhen
thereisnobackpressure．thebubblesinthedownstreamchamber
ofthrottlearediculttocollapseandflowawaytoreturnline
directlyandsotheireffectsonflowcharacteristicsisslight．When
thereisbackpressure．becauseofpressureextrusion．bubbles
collapsebeforetheyflowawaytoreturnline．thusitiseasierto
formcavitationschokingorflowsaturation．
^H，ul￡．
Fig．9andFig．10aretheq△curvesoforificeanddisc
valvewithandwithoutbackpressurerespectively，itcanalsobe
seenthatthereisnoflowsaturationwhenwithoutbackpressure
andobviousflowsaturationisobservedwhenwithbackpressure
overtherangeofpressuredroptested．A1lthesethreethrottlesare
similartothecasewhenthereislapbetweenpoppetandseat．
Experimentalinvestigationsontheeffectsofoperatingconditionsontheflowcharacteristicsofthrottlearemadewhentap
waterisusedastheworkingmedia．Theresearchresultsshowthat
operatingconditionsinfluencetheflow．pressurecharacteristicsof
throttlegreatly．
Forvariouspoppetvalve，cavitationsandflowsaturationpc。
ourmoreeasilywiththeincreasingofpoppetlif1．
Backpressuremakesflowsaturationformmoreeasily．The
flowcoefficientwithbackpressureeislargerthanthatofwithout
Backpressureexertsmoreevidentinfluencesonflowcharacteristicswhenthereislapbetweenpoppetandseatthanthereisnolap
betweenthem．Theconepoppetvalvewithchamferedseat，orifice，
discvalve．andballvalvewithchamferedseatarethethrottlesof
thistype．Theinfluencesofbackpressureonflowcharacteristics
arenotverydistinctwhenthere1snolapbetweenpoppetandseat．
Theconepoppetvalvewithsharp．edgedseatandballvalvewith
sharp—edgedseatarethethrottlesofthistype．
WiththeincreasingofpoppetliftandReynoldsnumber,the
influencesofmediumtemperatureOBflowcharacteristicsarenot
verymarked．Whentheworkingmediumiswatertheflowcoefficientis
largerthanthatofusingoilasmedium．
节流阀操作状态
在流量特性之上的有效实验研究
抽象的实验：
研究操作状态对流量的效果
节流阀的特性是当自来水被当作研究节流阀的工作媒体使用的时候。
锥形提动阀．球装阀门．圆盘阀和倾销孔口．操作人员把工作媒体举升一定的高度，背压，煤质温度及其它．因为水的蒸汽的压力是比那油高出许多．水力是比较容易和方便在机械系统中发生操作，这些状态对节流阀的一般特性是有效果的研究．
关键字：
当压力媒介在水力系统中时，水力学是一种使用淡水或海水代替压力媒体的油技术，由于有很好的特性，水力的这些特性在系统中越来越有吸引力，被人们所用。
在外界有不可易燃，廉价，清洁和容易处理的特性。
然而,与油和其他的工作媒介的特性相比较，水因为有较低的黏性，较高的蒸汽压力，较高的密度和容积柔性模数的这些特性，等等，因为有这些特性的情况下，用水作为工作媒体和当以油作为工作媒体有很大的不同，通常，在节流阀的流量-压力特性上有很棒效果的因数的二个类型。
一个是几何形状参数，还有一个是位置形状，锥形体按某一角度转动，长孔口在长度之间重搭，等等，并且是当不变的节流阀被制作成很好效果的时候，花了研究员很多的精力。
在节流阀LJ的流量特性上的几何形状，另外是正在操作的状态，另一个是改变各种不同的操作状态的工作箱．
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