已阅读5页,还剩2页未读, 继续免费阅读
版权说明:本文档由用户提供并上传,收益归属内容提供方,若内容存在侵权,请进行举报或认领
文档简介
AbstractPressurewavevelocityinahydraulicsystemwasdeterminedusingpiezopressuresensorswithoutremovingfluidfromthesystem.Themeasurementswerecarriedoutinalowpressurerange(0.26bar)andtheresultswerecomparedwiththeresultsofotherstudies.Thismethodisnotasaccurateasmeasurementwithseparatemeasurementequipment,butthefluidisintheactualmachinethewholetimeandtheeffectofairistakenintoconsiderationifairispresentinthesystem.Theamountofairisestimatedbycalculationsandcomparisonsbetweenotherstudies.Thismeasurementequipmentcanalsobeinstalledinanexistingmachineanditcanbeprogrammedsothatitmeasuresinrealtime.Thus,itcouldbeusede.g.tocontroldampers.KeywordsBulkmodulus,pressurewave,soundvelocity.I.INTRODUCTIONRESSUREwavevelocity(soundvelocity)isanimportantfactorwhenhydraulicsystemsareanalyzedanddevised.Itisaparameterinmanyequationsthatmodelthedynamicsofhydraulicsystemsanditisalsoanimportantparameterwhendampersofhydraulicsystemsaredimensioned.Withthehelpofpressurewavevelocitythebulkmodulusofahydraulicsystemcanbedefined,orviceversa.Differentmeansformeasuringpressurewavevelocityarepresentedinmanystudies.Normallythesemeasurementsarecarriedoutinseparatemeasurementequipment,sothatthemeasuredfluidisremovedfromtheoriginalmachine.Thisaffectscertaincharacteristicsofthefluid,suchastheamountofairormoistureconcentration,andtheresultsofpressurewavevelocitymeasurementsmaydifferfromtheoriginalsituation.Separatewavevelocitymeasurementinstrumentationisveryoftendesignedinsuchawaythatatleastentrainedaircanberemovedfromthemeasuredfluid.Thus,theresultsofmeasurementdonottaketheeffectofairintoconsideration,oronlydissolvedairisnoticed.Thisdoesnotcorrespondtorealsystems,becauseairispresentinfluids,especiallyatlowpressures.Separatepressurewavemeasurementequipmentusuallycannotbeconnectedtothemachine,soreal-timemeasurementofwavevelocityisimpossible.Inmanyearlierstudiespressurewavevelocityhasbeenmeasuredwithultrasonictransducers.Theultrasoundtechniquemaybebasedon,e.g.time-of-flightorpulse-echoprinciples.Thismethodisveryaccurate;anaccuracyofeven0.005m/scanbeachieved,1althoughlargererrorshavealsobeenpresentedintheliterature2-4.Benefitsoftheultrasoundtechniqueare,e.g.long-termstability,precision,sensitivity,capabilityofapplyingtoopticallyopaque,concentratedandelectricallynon-conductingsystemsandthepossibilitytoautomatethemeasurement.However,instrumentationdesignandthesamplestudiedmayaffecttheaccuracyofthemethod.5.Anothermethodfordefiningpressurewavevelocityistomeasurethebulkmodulusofafluidusingamethodbasedondeterminationofthevolumechangeofthesampleundercompressionorexpansion.6-9.Useofthistechniquepreventsunwantedpressuregradientsbetweenthesampleandthesurroundingsystem.Theusefulpressurerangeofthemethodiswide(0.1-350MPa).Theamountofentrainedaircanalsobetakenintoconsideration.Drawbacksofthemethodaretheneedtofirstdeterminethespecificvolumeofthesampleunderatmosphericpressureandtheobviousrequirementofmeasuringthedensityofthesampleunderallthepressuresused.Thus,thismethodcannotbeusedforcontinuousreal-timemeasurements.Calculationofthebulkmodulusandfurthermorethepressurewavevelocity(soundvelocity)isshownin(1)and(2)inchapterII.Someresearchershaveusedpressuretransducerstodetectpressurewavevelocitiesinoils.HarmsandPrinke10presentedamethodbasedonphasedifference.Inthismethodexcitationshouldbeconstant,e.g.pumprippling,becausethesignaliscomparedattwopointsandthevalueofthewavevelocityiscalculatedfromthetimedifferenceofthesesignals10.Choetal.11andYuetal.12measuredthewavepropagationtimeandcalculatedacross-correlationfunctionofthepressuresignals.Methodsbasedonpressuremeasurementsmakereal-timemeasurementspossibleandtheinfluenceofaircanbetakenintoconsideration.YetanothermethodfordeterminingpressurewavevelocitywaspresentedbyApfel13.Thismethodisatechniquethatmeasurestheadiabaticcompressibilityanddensityofafluidwhenthesampleamountsareextremelysmall,4nl-4l.Pressurewavevelocitiescanbecalculatedfromthesedata.Thismethodisapplicable,e.g.forsupercooledorsuperheatedsamples,biologicalorhazardoussamplesorineverycasewhenthebulkpropertiesoffluidshavetobedeterminedfromsmallsampleamounts.Thefluidstudiedisacousticallylevitatedonanimmisciblehostliquidatacertainspotofthetestequipment.Areferencemeasurementofafluidwhosepropertiesarewell-knownismadeattheexactsamespot.Theresultsarerelativelyaccurate(withina2%margincomparedwiththesamevaluesdeterminedbytraditionalmethods).Inordertocalculatepressurewavevelocities,thedensityoftheMeasuringPressureWaveVelocityinaHydraulicSystemLariKela,andPekkaVhojaPWorldAcademyofScience,EngineeringandTechnology492009610samplehastobemeasuredusingdifferentequipment.Obviously,thismethodissuitableforlaboratoryexperimentsonly.13-14.Pressurewavevelocity(soundvelocity)canbeusedtoevaluatevariousimportantcharacteristicpropertiesoffluids.Forinstance,ithasbeenusedtodeterminetheconcentrationofsolventsinoils4,tocalculatethephysicalpropertiesofhydraulicandotherlubricatingfluids,aswellasfueloils7,15-17,toestimatethestructuralandmechanicalpropertiesoffats18andthephysicalpropertiesofpetroleumfractionsandpetroleumreservoirfluids3,5andtodeterminethecompositionofoil-watermixturesandemulsions2ortomeasurethepropertiesofmagnetorheological(MR)fluids19.Themostimportantaimofthisstudywastodevelopamethodformeasuringpressurewavevelocitythatenablesreal-timemeasurements,whicharenecessaryif,e.g.real-timecontrolsystemsforhydraulicsareconstructed.AnotheraimwastocollectdataforfutureresearchwithaHelmholtzresonatorattachedtothissystem.II.THEORETICALASPECTSOFPRESSUREWAVEVELOCITYDETERMINATIONSThebulkmodulusofelasticmaterialBisdefinedasthequotientofpressurevariationandrelativevolumevariationaffectedbypressurevariationB=VdVdP(1)wherePispressureandVisvolume20.Pressurewavesconsideredinthispaperaresimilartowavesthatproduceaudiblesound.Thus,pressurewavesarehandledaslongitudinalvibrationmoleculesmovingbackandforthinthedirectionofpropagationofthewave,producingsuccessivecondensationsandexpansionsinthemedium.Thesealterationsofdensitiesaresimilartothoseproducedbylongitudinalwavesinabar.Asseeninmanystudies,mentionedalsointhispaper,thedifficultyofthemathematicsissidesteppedbyrestrictingthewavesunderconsiderationtoonedimension.21.Itisworthnotingthatatravellingwavedoesnotcarrymaterial,justthewaveanditsenergymove.Choetal.11havepresentedthreedefinitionsforbulkmodulus,whicharewidelyusedinmanytextbooks.Thesedefinitionsareonlyapplicabletotheirownspecificconditions,andinthispaperthesonicbulkmodulus(2)isused,whichhasthesamevalueastheadiabaticbulkmodulus.ThesonicbulkmodulusBisderivedfromthesonicvelocityinthefluidandfluiddensity11,20B=a2(2)whereisdensityandaiswavevelocity(soundvelocity).Equation(2)canbesolvedforthebulkmodulusorwavevelocity,dependingonwhichoneistheknownfactor.Inthispaperdensityisknownandwavevelocityismeasured,sothebulkmoduluscanbecalculated.Butas(2)presents,thesameparametersthataffectthevalueofwavevelocityalsoaffectthebulkmodulusandthisistakenintoconsiderationinthetheoryreview.Themainfactorsthataffectthevalueoftheeffectivebulkmodulusofahydraulicsystemarefluidpressureandtemperature.TheireffectsarepresentedinFig.1.Otherfactorsthataffectthevalueoftheeffectivebulkmodulusare,e.g.theaircontentofthefluid,piperigidityandinterfaceconditionsbetweenthefluidandtheair12.Fig.1Effectoftemperatureandpressureonwavevelocityinanoilsample:335.1K,370.7K,402.1K5Partoftheaircontentdissolvesinamolecularformandtherestofit,entrainedair,existsintheformofsmallbubbles.Dissolvedairhasonlyalittleeffectonthebulkmodulus11,butthevolumetricpercentofentrainedairwithinafluidisoneofthemostinfluentialvariableswhenthebulkmodulusisevaluated.Ithasbeenprovedthatonepercententrainedaircanreducetheeffectivebulkmodulusofafluidbyasmuchas1085MPa,whichcorrespondstoa75percentdecreaseinthefluidmanufacturersvalue22.Itshouldbenotedthatalsoothergases,notonlyair,affectthebulkmodulusandsonicwavevelocity,andthetypeofgashasagreatereffectthandoesthequantityofthegas23.Thelowerthemolecularweightofthegas,thegreatertheeffectonthesonicwavevelocity23.Fluidpressurehasaneffectonthevalueofthebulkmodulus,particularlyinthelowerrangeofpressure.Onereasonfortheeffectofpressureonthebulkmodulusistherelationshipbetweenentrainedaircontentanddissolvedaircontentinafluid.Someentrainedairbecomesdissolvedairwhenpressureincreases.12.Theinfluenceofpressurecanbediscussedatthemolecularlevel,also.Ifthepressureofthefluidunderstudyislow,thefluidmoleculesfitamongeachothereasilyandasignificantamountoffreespaceisstillavailable.Whenthefluidiscompressed,thefreespacedecreasesquicklyatlowerpressures.Whenthepressureofthesystemishigh,thefreespaceisalmostnegligible.Atthispointafurtherdecreaseinvolumeisconnectedwithinteractionsbetweenfluidmoleculesandtheirneighbouringmolecules.24.IfahydraulicsystemspressureismorethanWorldAcademyofScience,EngineeringandTechnology49200961150bar,theeffectoffreeairisonlyminor9.Fluidtemperatureaffectsthedensityoftheaircontent,thesizeofairbubblesinthefluidandthereforetheequivalentcompressibilityofthefluid.Anincrementoftemperaturealsocauseschangesinthemolecularlevelofthefluid.Morevigorouscollisionsbetweenmoleculesareobserved,whichmayeventuallycausechangesinmolecularstructures,andadecreaseintheireffectivevolumeisprobable.24.Therebytemperaturehasanimportantinfluenceonthebulkmodulusandsonicwavevelocity,especiallyindynamicsituations.Theinfluenceoftemperaturehasbeenstudied,e.g.by23.Theirstudiesincludedatemperaturerangebetween-30Cand130C,andtheeffectoftemperatureonsonicwavevelocityseemedtobesignificant23.However,theeffectoffluidtemperaturecanbeignoredifthefluidtemperatureisapproximatelyconstant12,andinmanystudiesthishasbeendone.Inaddition,thebulkmodulusoflubricatingoilsatlowpressurescanbealmostindependentofthetemperature25.Thedensityandbulkmodulusofsolidparts(e.g.pipes)willnotvaryasmuchasthedensityofafluidwhentemperatureandpressurevary10.Thus,theeffectofpiperigidityonthebulkmoduluscanbeignoredifrigidpipesareassumedinahydraulicsystem12.Themoisturecontentofthefluidmayalsoplayaroleifpressurewavevelocitiesaredetermined;itslightlyreducesthevalueofthepressurewavevelocity23.Theviscosityofthefluidalsoaffectsthepressurewavevelocity26,butofcoursetheviscosityofafluiddependsonitsmolecularstructureinthefirstplace,hencetheeffectofviscosityonthepressurewavevelocityvarieswithdifferentfluids.III.TESTEQUIPMENTThetestequipmentandtheprincipleofmeasurementaredepictedinFigs.2and3,respectively.Themeasurementswerecarriedoutbyidentifyingapressurepulseattwopoints,P1andP2,usingpiezosensors.ThedistancebetweenpointsP1andP2(variableLinFig.3)isknownandtwodifferentdistanceswereusedinthetests.Theshorterdistancewas2.75mandthelongerwas4.26m.DistancesL1andL2werealways1.03mand0.11m,respectively.Apressurewavewasexcitedbymeansofapistoninsideapipe.Thisexcitationsystemenablesexcitationofapurepressurewave,becauseunnecessaryelbowsandinterfacesareavoided,sothatreflectionsandtransmissionsofthewaveareminimized.Thepistonwasmovedlightlybutrapidlywithahammer.Asphericalplugvalveandanadjustablevalvewereinstalledinthetestequipmentsothatflowandpressurecouldbecontrolledduringthemeasurements.Thispropertywasusedinthemeasurementssothattwomeasurementserieswerecarriedout.Thefirstonewasdoneunderconstantpressurewithoutflowwiththebothvalvesclosed.Thesecondonewasdonewithflow,sothatflow(andpressure)wascontrolledwiththeadjustablevalve.Theeffectofflowonwavevelocityisinsignificant,asseenlaterinthetext.Themeasurementswerecarriedoutovertwodayssothattemperaturecouldbeassumedtobeconstant.Thetestequipmentdidnotincludeatemperaturesensor,butthetestequipmentwasinsidealaboratorysothatthefluidtemperaturecouldbeassumedtobethesameasthesurroundingtemperature.Thelowestpressureusedwas0.2barandthehighestwas6.1bar,and545measurementswereexecutedbetweentheselimits.ExamplesofthemeasurementresultsaredepictedinFigs.4and5.ThemeasurementsystemincludedoneKyowaPG-20KUpressuresensor(forreferencepressure),twoKuliteHKM-375M-7barVGpressuresensors(forrecognizingapressurewaveattwopoints),aKyowaStrainAmplifierDPM-6H(fortheKyowapressuresensor),aThandar30V-2Aprecisionpowersupply(fortheKulitepressuresensors),aNationalInstrumentsUSB-621116-input(16bit250kS/s)DAQcard,aHPCompaqnx9010laptopcomputerwithMicrosoftWindowsXP,DasyLabv.8.00.004measurementsoftwareandMeasurement&AutomationExplorerv.001.Themeasurementfrequencywas25kHz(0.04ms)andtheblocksizewas1024bit.Fig.2TestequipmentFig.3PrincipleofthemeasurementsFig.4Responseofthepressurewaveatdetectionpointone(upper,dottedline)andtwo(lower,dashedline).NotethepressuredifferencebetweenthedetectionpointsbecauseofflowWorldAcademyofScience,EngineeringandTechnology492009612Fig.5Samecaseasabove.Thetimedifferencebetweenthedetectionpointscanbereadfromthesurveybox.NotethatthelinesaremodifiedforpublishingbydecreasingtheirresolutionsnotablyfromtheoriginalThevolumeflowofthetestequipmentQcanbeestimatedwiththeHagen-Poiseulleequation(3)27Q=)(128214ppld(3)wheredispipediameter,isdynamicviscosity,lispipelength,p1ispressureatpoint1andp2ispressureatpoint2.Duringthemeasurementspressurewillvaryfromzeroto0.5bar(pipelength2.75m)ortoalmostonebar(pipelength4.26m).Thismeansthattheabsolutemaximumflow,whichisevenoverestimatedhereonpurpose,isconstantlylessthan1.2l/min(0.4m/s)atatemperatureof18Canditseffectontheresultsisimpossibletonoticeinthisarrangement.FluidviscositywasmeasuredwithaBrookfieldDV-II+rotationviscometeranddensitybyusingthespecificweightmethod(weighinganaccuratevolumeofthefluidatthedesiredtemperature).Fluiddensitywas874kg/m3atatemperatureof18Cand864kg/m3atatemperatureof40C.Thedynamicfluidviscositiesatthecorrespondingtemperatureswere121cPand42cP.Thefluidwasacommercialmineraloil-basedhydraulicoil.IV.RESULTSOFMEASUREMENTSAltogether545measurementswereanalyzed.Theaveragepressureofthemeasurementswas2.9barandthemeasuredaveragepressurewavevelocity(soundvelocity),1377m/s.TheresultsofallthemeasurementsarepresentedinFig.6,whichindicatesthemagnitudeofthewavevelocityinthepressurerangebetween0.2barand6bar.InFig.6themeasuredresultsoftheflowsituationandnon-flowsituationaresep
温馨提示
- 1. 本站所有资源如无特殊说明,都需要本地电脑安装OFFICE2007和PDF阅读器。图纸软件为CAD,CAXA,PROE,UG,SolidWorks等.压缩文件请下载最新的WinRAR软件解压。
- 2. 本站的文档不包含任何第三方提供的附件图纸等,如果需要附件,请联系上传者。文件的所有权益归上传用户所有。
- 3. 本站RAR压缩包中若带图纸,网页内容里面会有图纸预览,若没有图纸预览就没有图纸。
- 4. 未经权益所有人同意不得将文件中的内容挪作商业或盈利用途。
- 5. 人人文库网仅提供信息存储空间,仅对用户上传内容的表现方式做保护处理,对用户上传分享的文档内容本身不做任何修改或编辑,并不能对任何下载内容负责。
- 6. 下载文件中如有侵权或不适当内容,请与我们联系,我们立即纠正。
- 7. 本站不保证下载资源的准确性、安全性和完整性, 同时也不承担用户因使用这些下载资源对自己和他人造成任何形式的伤害或损失。
最新文档
- 全球及中国乳胶密封剂行业市场现状供需分析及市场深度研究发展前景及规划可行性分析研究报告(2024-2030)
- 全球及中国三叶鼓风机行业市场现状供需分析及市场深度研究发展前景及规划可行性分析研究报告(2024-2030)
- 全球及中国一次性剃须刀行业市场现状供需分析及市场深度研究发展前景及规划可行性分析研究报告(2024-2030)
- 2024届河南省新乡市高三第二次模拟考试数学试题(解析版)
- 运营维护管理方案
- 2024年虚拟数字人行业运行状况及未来发展前景
- Visual Studio 2019(C#)Windows数据库项目开发 课件 第 09 章 系统完善
- 面包车管理台账表格模板
- 丰田汽车公司的核心竞争力
- 江苏省无锡市宜兴市2023-2024学年八年级下学期期中考试语文试题
- 超声科质量管理方案
- 运维审计报告
- 2024年内蒙古通辽市事业单位人才引进(130人)历年高频考题难、易错点模拟试题(共500题)附带答案详解
- 2024年江苏东台市国有资产经营有限公司招聘笔试参考题库含答案解析
- 虚拟现实技术在足球与体育训练中的应用
- 物业管理商业小区催费话术与技巧攻略
- 工业净水创业计划书
- 个人就业能力展示
- 俄乌谈判结果的分析报告
- 北师大版七年级数学下册高频考点专题突破 专题02 变量之间的关系 重难点题型-【高频考点】(原卷版+解析)
评论
0/150
提交评论