四川大学化工考研884复试面试英语题库翻译原文

四川大学化工考研884复试面试英语题库翻译原文四川大学化工考研884复试面试英语题库翻译原文四川大学化工考研884复试面试英语题库翻译原文资料仅供参考文件编号：2022年4月四川大学化工考研884复试面试英语题库翻译原文版本号：A修改号：1页次：1.0审核：批准:发布日期：Whenafluidflowsthroughaductoroverasurface,thevelocityoveraplaceatrightanglestothestreamisnotnormallyuniform.Thevariationofvelocitycanbeshownbytheuseofstreamlineswhicharelinessodrawnthatthevelocityvectorisalwaystangentialtothem.Theflowratebetweenanytwostreamlinesisalwaysthesame.Constantvelocityoveracross-sectionisshownbyequidistantstreamlinesandincreaseinvelocitybycloserspacingofstreamlines.Itisfoundtheheattransferrateperunitareaqisdependentonthosephysicalpropertieswhichaffectflowpattern.Thethermalpropertiesofthefluidandthevelocityofflowthefluidoverthesurface,thetemperaturedifferencetandafactordeternmingthenaturalcirculationeffectcausebyexpansionofthefluidonheating.Theoildistilledinaverylargesteeltower,thetechnicalnamesofwhichisthefractionatingtower.Thetoweristhirtytofiftymeterstallanditsdiameterisonetothreemeters.Itisdividedintochambers,eachofwhichcontainsalayeroftrays.Thereareholesinthetrays.Thechanbersareatdifferentheights,andtemperatureateachheightisdifferent.Agroupofoperationforseparatingthecomponentsofmixtureisbasedonthetransferofmaterialfromonehomogeneousphasetoanther.Unlikepurelymechanicalseparation,thesemethodsutilizedifferencesinvaporpressureorsolubility,notdensityorparticlesize.Thedrivingforcefortransferisaconoantrationdiffercetooraconcentrationgradient,muchasatemperaturedifferenceoratemperaturegradientprovidesthedrivingforceheattransfer.Thethreemostimportantcharacteristicsofanindividualparticleareitscomposition,itssizeanditsshape.Compositiondeterminesuchpropertiesasdensityandconductivity，providedthattheparticleiscompletelyuniform.Aparticleshapemayberegularsuchassphericalorcubic,oritmaybeirregularas,forexample,withapieceofbrokenglass.homogeneouscatalysisistheindustricaloxoprocessformanufacturingnormaliosobuty(异丁醛)。Ahomogeneouscatalysispressinvolvemorethanonephase，usuallythecatalystisasolidandthereactantsandproductsareinliquidorgaseousform.Whenthevaporsriseintothecoolerpartofthefractionatingtower,theyloseheat,thevaporsriseuntiltheyarejustbelowtheirownboilingtemperature.thentheycondenseonatrayandturnintoaliquidagain.Theliquidoneachtrayflowsintoaseparatesmalltowerwheretheliquidbreaksdownintosmallerfractions.Theseparationofthehydrocarbonsismoreaccurate.Thefunctionofdistillationistoseparate,byvaporization,aliquidmixtureofmiscible,andvolaulesubstancesintoindividualcomponentsor,insomecases,intogroupsofcomponents,theseparationofamixtureofalcoholandwaterintoitscomponentofliquidnitrogen,oxygenandargon,andofcrudepetroleumintogasoline,kerosence,fueloil,andlubricationstockareexamplesofdistillation.Forthepumpingofliquidsorgasesfromonevesseltoanotherorthroughlongpipes,somefromofmechanicalpumpisusuallyemployed.Theenergyrequirebythepumpwilldependontheheightthroughwhichtheliquidsraised,thepressurerequiredatdeliverypoint,thelengthanddiameterofthepipe,therateofflow,togetherwiththephysicalpropertiesoftheliquid,particularlyitsviscosityanddensity.Inthemajorityofchemicalprocesses,heatiseithergivenoutorabsorbed,andfluidsmustoftenbeheatedorcooleinawiderangeofplant,suchasfurnaces,evaporates,distillationunits,dryers,andreactionvesselswhereoneofthemajorproblemsisthatoftransferringheatatthedesiredrate.Inaddition,itmaybenecessarytopreventthelossofheatatthedesiresrateformsoneofthemostimportantareasofchemicalengineering.membranesciencehasreachedmaturity,andtheseparationprocesses,whicharebasedonthetechnologiesthatithasspawned,arenowcommonplace.Theycoversuchwiderangingapplicationasmicrofiltration,reserveosmosis,gasseparation,theartificialkidneyandcontrolled-releasepharmaceuticals,andtheyareusedextensivelyinindustry,medicineandtoprotecttheenvironment.Theremovalofoneormoreselectedcomponentsfromamixtureofgasesbyabsorptionintoasuitableliquidisthesecondmajoroperationofchemicalengineeringthatisbasedoninterphasemasstransfercontrolledlargelybyratesofdiffusion.Thus,acetonecanberecoverdfromanacetone-airmixturebtpassingthegasstreamintowaterinwhichtheacetonedissolveswhiletheairpassesout.Evaporationisachievedbyaddingheattothesolutiontovaporisethesolvent.Theheatissuppliedprincipallytoprovidethelatentheatofvaporization,and,byadoptingmethodsforrecoveryofheatfromthevepor,ithasbeenpossibletoachievegreateconomyinheatutilization.Whilstthenormalheatingmediumisgenerallylowpressureexhauststeamfromturbines,specialheattransferfluidsorfluegasesarealsoused.Manyorganicliquidarepurifiedbycrystallizationratherthanbydistillationsinceenthapiesofcrystallizationaregenerallymuchlowerthanenthalpiesofvaporizationandcaystallizationmaybecarrieoutclosertoambienttemperaturetherebyreducingenergyrequirements.Againstthis,crastallizationisrarelythelaststageinaprocessandsolventseparation,washinganddryingstagesareusuallyrequired.Theseparationofliquidmixtureintotheirvariouscomponentisoneofthemajoroperationsintheprocessindustries,anddistillation,themostwidelyusedmethodofachievingthisend,isthekeyoperatinginandoilrefinery.Inprocessing,thedemandforpurerproduct,coupledwiththeneedforgreatereffiency,haspromotedcontinuedresearchintothetechniquesofdistillation.Thisistheclassicreatorusedbyorganicchemists.Thetypicalvolumeinglasswareisafewhundredmilliliters.Reactantsarechargestothesystem,rapidlymixed,andrepidlybroughtuptotemperaturesothatreactionconditionsarewelldefined.Heatingiscarriedoutwithanoilbathoranelectricheatingmantle.Mixingiscarriedoutwithamagneticstirrerorasmallmechanicalagitator.Temperatureiscontrolledbyregulationthetemperatureorbyallowingasolventtoreflux.Inabatchreatorallmoleculesenterandleavetogether.ifthesystemsisoinermal,reactionyieldsdependonlyontheelapsedtimeandontheinitialcomposition,thesituationinflowsystemismorecomplicatebutnotimpossiblyso.Thecounterpartofthebatchreactiontimeistheageofamolecule.Agingbeginswhenamoleculeentersthereactorandceseswhenitleaves,thetotaltimespentwithintheboundariesofthereactionisknownastheexitage,orresidencetime.Severalpossiblemechanismshavebeensuggestedasthecauseofcrystalnucleationfromasupersaturatedsolution.Threerecognizednucleationprocessesare(1)homogeneousnucleation,whichoccursspontaneouslyanddoesnotrequirethepresenceofsurfacesofanykind;(2)heterogeneousnuclestion,usuallypromptedbythepresenceofacrystallinephaseofthesolutematerial.Enzymesarenature’scatalysts.Forthemomentitissufficienttoconsideranenzymeasalargeprotein,thestructureofwhichresultsinaveryshape-specificactivesite.Havingshapethatareoptimallysuitedtoguidereactantmolecules(usuallyreferredtoassubstrates)intheoptimumconfigurationforreaction,enzymesarehighltspecialandefficientcatalysts.Environmentalcatalysisisprojectedtogrowfasterthananyothersegmentofthecatalystmarketinthenext20years.Thisgrowthwillcomebothfromtraditionalareas,suchasemissionstreatment,andfromnewareasthatrangefromtheautomotiveindustrytopharmaceuticals.Tosustainthisgrowthandtomeetmorestringentenvironmentdemands,researcherswillrequireever-increasingcontrolandunderstandingofcatalyticmaterialandprocessesatthemolecularlevel.Processengineeringdesignistheappllicationofchemical,mechanical,petroleum,gasandotherengineeringtalentstotheprocess-relateddevelopment,planning,designsanddecisionsrequiresforeconomicalandeffectivecompletionofaprocessproject.Althoughtprocessdesignengineersareorganizationallylocatedinresearch,technicalservice,wconomicevaluation,theusualarrangementistohavethemavailabletotheengineeringgroupsconcernedwithdevelopingtheengineeringdetailsofaproject.Compressorsareusedforprovidinggaspressurerequiredtotransortgaswithpipelinesandtoliftoilingas-liftoperations.Thecompressorsusedintoday’snaturalgasproductionindustyfallintotwodistincttypes:reciprocatingandrotarycompressors.Reciprocatingcompressorsaremostcommonlyusedinthenaturalgasindustry.Theyarebuiltforpracticallyallpressuresandvolumetriccapacities.Hydrocarbonsconstitutetheessentialcomponentsofpetroleum,theirmoleculescontainonlycarbonandhydrogen;theyaregroupedintomanychemicalfamiliesaccoringtotheirstructu