熱能與動(dòng)力工程專(zhuān)業(yè)英語(yǔ)

......Chapter1IntroductiontoThermal.Chapter1IntroductiontoThermalScience第一章熱科學(xué)基礎(chǔ)Acousticflowmeter聲波流量計(jì)Corrugatedfin波狀散熱片Adiabatic[]絕熱的Crossproduct矢量積Aerodynamics空氣動(dòng)力學(xué)Denominator分母Affiliation聯(lián)系Developedflow充分發(fā)展流Airfoil機(jī)翼，螺旋槳Diffusion擴(kuò)散Alternative替代燃料Dopplereffect多普勒效應(yīng)Anemometer風(fēng)速計(jì)Double-pipeheatexchanger套管式換熱器Angularspeed角速度Drysaturatedvapor干飽和蒸汽Areadensity表面密度Electrode電極Baffle擋板Electrolyte電解，電解液Bifurcation分形Electrostatic靜電的Blackbody黑體Emissivity發(fā)射率Blade漿葉，葉片Equilibrium平衡Boiler鍋爐Fluidmechanics流體力學(xué)Boundarylayer邊界層Forcedconvection強(qiáng)制對(duì)流CarnotCycle卡諾循環(huán)Freeconvection自然對(duì)流Cartesiancoordinates笛卡爾坐標(biāo)系Frictionloss摩擦損失CelsiusDegree攝氏度Glassceramic微晶玻璃，玻璃陶瓷Compactheatexchanger緊湊式換熱器Heatengine熱機(jī)Composition成分，合成物Heatpump熱泵Compressedliquid壓縮液體Hydrofoil水翼Compressibility可壓縮性，壓縮率Hypersonicspeed高超音速Condensation凝結(jié)Infinitesimal無(wú)窮小的Condenser冷凝器Inflating/deflating充氣/壓縮Conduction導(dǎo)熱Internalcombustionengine內(nèi)燃機(jī)Controlvolume控制體Isentropic等熵的Convection對(duì)流 Isobaric等壓的Coriolis-accelarationflowmeter科Isolatedsystem孤立體系的氏加速流量計(jì)Isometric等容的Rough-walltube粗糙管Isothermal等溫的Saturation飽和Kinematicviscosity運(yùn)動(dòng)黏度Shearstress剪切力、切應(yīng)力Laminar層流Shell-and-tubeheatexchanger管殼式換熱器Manuscript手稿，原稿Specificvolume比容Moisture濕度，水分Steady穩(wěn)態(tài)的，定常的Molecule(化學(xué))分子Stiflingengine斯特林機(jī)Moltenpolymer熔融聚合物Strainrate變形速度，應(yīng)變率Muti-disciplinary多學(xué)科的Streamline流線NewtonianFluid牛頓流體Strut支撐，支柱Nominaltemperaturegradient法向Subcooledliquid過(guò)冷液體溫度梯度Numerator（數(shù)學(xué)）分子 Superheatedvapor過(guò)熱蒸汽Parallelflow平行流動(dòng)，并流 Surrounding環(huán)境，外界Pathline跡線 Thermalconductivity熱傳導(dǎo)率Phasechange相變 Thermalefficiency熱效率Planeflow平面流，二元流 Thermodynamics熱力學(xué)PlateandflameheatexchangerTorsional扭力的，扭轉(zhuǎn)的板式換熱器Polymersolution膠漿Trailingedge機(jī)翼后緣、尾緣Proof校樣Transmitter傳送裝置、發(fā)送器Propeller螺旋槳，推進(jìn)器Turbinemeter渦輪流量計(jì)Pump泵Turbulent湍流的Qulity干度Ultrosonic超聲波的Qusi-equilibrium準(zhǔn)平衡、準(zhǔn)靜態(tài)Uniformflow均勻劉Radiation輻射Vacuum真空RankinCycle朗肯循環(huán)Viewfactor角系數(shù)RegenerativeheatexchangerViscous黏性的蓄熱/再生式換熱器Reservoir水庫(kù)，蓄水池Cortexshedding漩渦脫落Reversible可逆的Waterfaucet水龍頭，水嘴Rotameter轉(zhuǎn)子流量計(jì)BiBiotnumber比澳數(shù)NPSH汽蝕余量CFD計(jì)算流體力學(xué)NTU傳熱單元數(shù)CHF臨界熱流量Nu努謝爾特?cái)?shù)COP制冷系數(shù)PE勢(shì)能Eu歐拉數(shù)Pr普朗特?cái)?shù)Fo富立葉數(shù)Ra瑞利數(shù)Fr弗勞德數(shù)Re雷諾數(shù)Gr格拉曉夫數(shù)Sc施密特?cái)?shù)KE動(dòng)能St斯坦頓數(shù)，斯特勞哈數(shù)LMTD對(duì)數(shù)平均溫差We韋伯?dāng)?shù)1.1FundamentalofEngineeringThermodynamics1.1工程熱力學(xué)基礎(chǔ)Thermodynamicsisascienceinwhichthestorage,transformationandtransferofenergyarestudied.Energyisstoredasinternalenergy(associatedwithtemperature),kineticenergy(dutomotion),potentialenergy(duetoelevation)andchemicalenergy(duetochemicalcomposition);itistransformedfromoneoftheseformstoanother;anditistransferredacrossaboundaryaseitherheatorwork.熱力學(xué)是一門(mén)研究能量?jī)?chǔ)存、轉(zhuǎn)換及傳遞的科學(xué)。能量以?xún)?nèi)能（與溫度有關(guān)）、動(dòng)能（由物體運(yùn)動(dòng)引起）、勢(shì)能（由高度引起）和化學(xué)能（與化學(xué)組成相關(guān)）的形式儲(chǔ)存。不同形式的能量可以相互轉(zhuǎn)化，而且能量在邊界上可以以熱和功的形式進(jìn)行傳遞。Inthermodynamics,wewillderiveequationsthatrelatethetransformationsandtransfersofenergytopropertiessuchastemperature,pressureanddensity.Substancesandtheirproperties,thus,becomeveryimportantinthermodynamics.Manyofourequationswillbebasedonexperimentalobservationsthathavebeenorganizedintomathematicalstatementsorlaws,thefirstandsecondlawsofthermodynamicsaremostwidelyused.在熱力學(xué)中，我們將推導(dǎo)有關(guān)能量轉(zhuǎn)化和傳遞與物性參數(shù)，如溫度、壓強(qiáng)及密度等關(guān)系間的方程。因此，在熱力學(xué)中，物質(zhì)及其性質(zhì)變得非常重要。許多熱力學(xué)方程都是建立在實(shí)驗(yàn)觀察的基礎(chǔ)之上，而且這些實(shí)驗(yàn)觀察的結(jié)果已被整理成數(shù)學(xué)表達(dá)式或定律的形式。其中，熱力學(xué)第一定律和第二定律應(yīng)用最為廣泛。1.1.1Thermodynamicsystemandcontrolvolume1.1.1熱力系統(tǒng)和控制體Athermodynamicsystemisafixedquantityofmattercontainedwithinsomeenclosure.Thesurfaceisusuallyanobviousone(likethatsurroundingthegasinthecylinder).However,itmaybeanimaginedboundary(likethedeformingboundaryofacertainamountofmassasitflowsthroughapump).熱力系統(tǒng)是一包圍在某一封閉邊界內(nèi)的具有固定質(zhì)量的物質(zhì)。系統(tǒng)邊界通常是比較明顯的（如氣缸內(nèi)氣體的固定邊界）。然而，系統(tǒng)邊界也可以是假想的（如一定質(zhì)量的流體流經(jīng)泵時(shí)不斷變形的邊界）。Allmatterandspaceexternaltoasystemiscollectivelycalleditssurroundings.Thermodynamicsisconcernedwiththeinteractionofasystemanditssurroundings,oronesysteminteractingwithanother.Asysteminteractswithitssurroundingsbytransferringenergyacrossitsboundary.Nomaterialcrossestheboundaryofasystem.Ifthesystemdoesnotexchangeenergywiththesurroundings,itisanisolatedsystem.系統(tǒng)之外的所有物質(zhì)和空間統(tǒng)稱(chēng)外界或環(huán)境。熱力學(xué)主要研究系統(tǒng)與外界或系統(tǒng)與系統(tǒng)之間的相互作用。系統(tǒng)通過(guò)在邊界上進(jìn)行能量傳遞，從而與外界進(jìn)行相互作用，但在邊界上沒(méi)有質(zhì)量交換。當(dāng)系統(tǒng)與外界間沒(méi)有能量交換時(shí)，這樣的系統(tǒng)稱(chēng)為孤立系統(tǒng)。Inmanycases,ananalysisissimplifiedifattentionisfocusedonaparticularvolumeinspaceintowhich,orfromwhich,asubstanceflows.Suchavolumeisacontrolvolume.Apump,aturbine,andaninflatingordeflatingballoonareexamplesofcontrolvolume.Thesurfacethatcompletelysurroundsthecontrolvolumeiscalledacontrolsurface.在許多情況下，當(dāng)我們只關(guān)心空間中有物質(zhì)流進(jìn)或流出的某個(gè)特定體積時(shí)，分析可以得到簡(jiǎn)化。這樣的特定體積稱(chēng)為控制體。例如泵、透平、充氣或放氣的氣球都是控制體的例子。包含控制體的表面稱(chēng)為控制表面。Thus,wemustchoose,inaparticularproblem,whetherasystemistobeconsideredorwhetheracontrolvolumeismoreuseful.Ifthereismassfluxacrossaboundary,thenacontrolvolumeisrequired;otherwise,asystemisidentified.因此，對(duì)于具體的問(wèn)題，我們必須確定是選取系統(tǒng)作為研究對(duì)象有利還是選取控制體作為研究對(duì)象有利。如果邊界上有質(zhì)量交換，則選取控制體有利；反之，則應(yīng)選取系統(tǒng)作為研究對(duì)象。1.1.2Equilibrium,processandcycle平衡、過(guò)程和循環(huán)Whenthetemperatureofasystemisreferredto,itisassumedthatallpointsofthesystemhavethesame,oressentiallythesametemperature.Whenthepropertiesareconstantfrompointtopointandwhenthereisnotendencyforchangewithtime,aconditionofthermodynamicequilibriumexists.Ifthetemperature,say,issuddenlyincreasedatsomepartofthesystemboundary,spontaneousredistributionisassumedtooccuruntilallpartsofthe教材1頁(yè)systemareatthesametemperature.對(duì)于某一參考系統(tǒng)，假設(shè)系統(tǒng)內(nèi)各點(diǎn)溫度完全相同。當(dāng)物質(zhì)內(nèi)部各點(diǎn)的特性參數(shù)均相同且不隨時(shí)間變化時(shí)，則稱(chēng)系統(tǒng)處于熱力學(xué)平衡狀態(tài)。當(dāng)系統(tǒng)邊界某部分的溫度突然上升時(shí)，則系統(tǒng)內(nèi)的溫度將自發(fā)地重新分布，直至處處相同。Whenasystemchangesfromoneequilibriumstatetoanother,thepathofsuccessivesatesthroughwhichthesystempassesiscalledprocess.If,inthepassingonestatetothenext,thedeviationfromequilibriumisinfinitesimal,aquasi-equilibriumprocessoccurs,andeachstateintheprocessmaybeidealizedasanequilibriumstate.Quasi-equilibriumprocessescanapproximatemanyprocesses,suchasthecompressionandexpansionofgasesinaninternalcombustionengine,withnosignificantlossofaccuracy.Ifthesystemgoesfromoneequilibriumstatetoanotherthroughaseriesofnon-equilibriumstates(asincombustion),anon-equilibriumprocessoccurs.當(dāng)系統(tǒng)從一個(gè)平衡狀態(tài)轉(zhuǎn)變?yōu)榱硪粋€(gè)平衡狀態(tài)時(shí)，系統(tǒng)所經(jīng)歷的一系列由中間狀態(tài)組成的變化歷程稱(chēng)為過(guò)程。若從一個(gè)狀態(tài)到達(dá)另一個(gè)狀態(tài)的過(guò)程中，始終無(wú)限小地偏離平衡態(tài)，則稱(chēng)該過(guò)程為準(zhǔn)靜態(tài)過(guò)程，可以把其中任一個(gè)中間狀態(tài)看作為平衡狀態(tài)。準(zhǔn)靜態(tài)過(guò)程可近似視為許多過(guò)程的疊加結(jié)果，而不會(huì)顯著減小其精確性，例如氣體在內(nèi)燃機(jī)內(nèi)的壓縮和膨脹過(guò)程。如果系統(tǒng)經(jīng)歷一系列不平衡狀態(tài)（如燃燒），從一個(gè)平衡狀態(tài)轉(zhuǎn)變?yōu)榱硪粋€(gè)平衡狀態(tài)，則其過(guò)程為非平衡過(guò)程。Whenasysteminagiveninitialstateexperiencesaseriesofprocessandreturnstotheinitialstate,thesystemgoesacycle.Attheendofthecycle,thepropertiesofthesystemhavethesamevaluestheyhadatthebeginning.當(dāng)系統(tǒng)從一個(gè)給定的初始狀態(tài)出發(fā)，經(jīng)歷一系列中間過(guò)程又回到其初始狀態(tài)，則稱(chēng)系統(tǒng)經(jīng)歷了一個(gè)循環(huán)。循環(huán)結(jié)束時(shí)，系統(tǒng)中的各參數(shù)又與初始參數(shù)相同。Theprefixiso-isattachedtothenamesofanypropertythatremainunchangedinaprocess.Anisothermalprocessisoneinwhichthetemperatureisheldconstant;inaniso-baricprocess,thepressureremainsconstant;anisometricprocessisaconstant-volumeprocess.在任一特性參數(shù)名稱(chēng)前加上前綴iso-，表示該參數(shù)在整個(gè)過(guò)程保持不變。等溫（isothermal）過(guò)程中溫度保持不變；等壓（isobaric）過(guò)程中壓強(qiáng)恒定；等容（isometric）過(guò)程中體積保持不變。1.1.3Vapor-liquidphaseequilibriuminpuresubstance純物質(zhì)的氣-液相平衡Considerasasystem1kgofwatercontainedinthepistonorcylinderarrangementshowninFig.1-1(a).Supposethepistonandweightmaintainapressureof0.1MPainthecylinderandthattheinitialtemperatureis20℃.Asheatistransferredtothewater,thetemperatureincreaseappreciably,thespecificvolumeincreaseslightly,andthepressureremainsconstant.Whenthetemperaturereaches99.6℃,additionalheattransferresultsinachangeofphase,asindicatedinFig.1-1(b).Thatis,someoftheliquidbecomesvapor,andduringthisprocessboththetemperatureandpressureremainconstant,butthespecificvolumeincreasesconsiderably.Whenthelastdropofliquidhasvaporized,furthertransferofheatresultsinanincreaseinbothtemperatureandspecificvolumeofthevapor,asshowninFig.1-1(c).如圖1-1(a)所示，由活塞和氣缸組成的裝置中裝有1kg水。假定活塞和其上的重物使氣缸內(nèi)壓強(qiáng)維持在0.1Mpa，初始溫度20℃。當(dāng)有熱量開(kāi)始傳遞給水時(shí)，缸內(nèi)水溫迅速上升，而比容略有增加，氣缸內(nèi)壓強(qiáng)保持恒定不變。當(dāng)水溫達(dá)到99.6℃時(shí)，如若再增加傳熱量，水將發(fā)生相變，如圖1-1(b)所示。也就是說(shuō)，一部分水開(kāi)始?xì)饣優(yōu)檎羝?，在此相變過(guò)程中，溫度和壓強(qiáng)始終保持不變，但比容卻有大幅度的增加。當(dāng)最后一滴液體被氣化時(shí)，進(jìn)一步的加熱將使蒸汽溫度和比容均有所增加，如同1-1(c)所示。圖1-1液體在常壓下的蒸發(fā)過(guò)程Thetermsaturationtemperaturedesignatesthetemperatureatwhichvaporizationtakesplaceatagivenpressure.Thispressureiscalledthesaturationpressureforthegiventemperature.Thus,forwaterat99.6℃,thesaturationpressureis0.1MPa,andforwaterat0.1MPathesaturationtemperatureis99.6℃.在給定壓強(qiáng)下發(fā)生氣化的溫度稱(chēng)為飽和溫度，壓強(qiáng)稱(chēng)為給定溫度下的飽和壓強(qiáng)。因此，99.6℃水的飽和壓強(qiáng)是0.1MPa，0.1MPa水的飽和溫度為99.6℃。Ifasubstanceexistsasliquidatthesaturationtemperature,itiscalledsaturatedliquid.Ifthetemperatureoftheliquidislowerthanthesaturationtemperaturefortheexistingpressure,itiscalledeitherasubcooledliquid(implyingthatthetemperatureislower教材2頁(yè)thanthesaturationtemperatureforthegivenpressure)oracompressedliquid(implyingthatthepressureisgreaterthanthesaturationpressureforthegiventemperature).如果某一工質(zhì)為液態(tài)并處于其飽和溫度和飽和壓強(qiáng)下，則稱(chēng)該液體為飽和液體。如果液體溫度低于當(dāng)前壓強(qiáng)下的飽和溫度，則稱(chēng)該液體為過(guò)冷液體（表明液體的當(dāng)前溫度低于給定壓強(qiáng)下的飽和溫度）或壓縮液體（表明液體的當(dāng)前壓強(qiáng)大于給定溫度下的飽和壓強(qiáng)）。Whenasubstanceexistsaspartliquidandpartvaporatthesaturationtemperature,itsqualityisdefinedastheratioofthemassofvaportothetotalmass.Thus,inFig.1-1(b),ifthemassofvaporis0.2kgandthemassofliquidis0.8kg,thequalityis0.2or20%.Qualityhasmeaningonlywhenthesubstanceisinasaturatedstate.若某一工質(zhì)在飽和溫度下以液、氣共存的形式存在，則稱(chēng)蒸汽質(zhì)量與總質(zhì)量之比為干度。因此，如圖1-1(b)所示，若蒸汽質(zhì)量為0.2kg，液體質(zhì)量為0.8kg，則其干度為0.2或20%。干度只有在飽和狀態(tài)下才有意義。Ifasubstanceexistsasvaporatthesaturationtemperature,itiscalledsaturationvapor(Sometimesthetermdrysaturationvaporisusedtoemphasizethatthequalityis100%).Whenthevaporisatatemperaturegreaterthanthesaturationtemperature,itissaidtoexistassuperheatedvapor.Thepressureandtemperatureofsuperheatedvaporareindependentproperties,sincethetemperaturemayincreasewhilethepressureremainsconstant.若某一工質(zhì)處于飽和溫度下并以蒸汽形態(tài)存在，則稱(chēng)該蒸汽為飽和蒸汽（有時(shí)稱(chēng)為干飽和蒸汽，意在強(qiáng)調(diào)其干度為100%）。當(dāng)蒸汽溫度高于其飽和溫度時(shí)，則稱(chēng)之為過(guò)熱蒸汽。過(guò)熱蒸汽的壓強(qiáng)和溫度是彼此獨(dú)立的，因?yàn)闇囟壬仙龝r(shí)，壓強(qiáng)可能保持不變。Letusplotonthetemperature-valuediagramofFig.1-2theconstant-pressurelinethatrepresentsthestatesthroughwhichthewaterpassesasitisheatedfromtheinitialstateof0.1MPaand20℃.LetstateArepresenttheinitialstate,Bthesaturated-liquidstate(99.6℃),andlineABtheprocessinwhichtheliquidisheatedfromtheinitialtemperaturetothesaturationtemperature.PointCisthe.....saturated-vaporstate,andlineBCistheconstant-temperatureprocess.saturated-vaporstate,andlineBCistheconstant-temperatureprocessinwhichthechangeofphasefromliquidtovaporoccurs.LineCDrepresents[]theprocessinwhichthesteamissuperheatedatconstantpressure.Temperatureandvolumebothincreaseduringthisprocess.在圖1-2所示的溫度-比容圖上作等壓線，表示水由初壓MPa0.1、初溫20℃被加熱的過(guò)程。點(diǎn)A代表初始狀態(tài)，點(diǎn)B為飽和液態(tài)（99.6℃），線AB表示液體由初始溫度被加熱至飽和溫度所經(jīng)歷的過(guò)程。點(diǎn)C表示飽和蒸汽狀態(tài)，線BC表示等溫過(guò)程，即液體氣化轉(zhuǎn)變?yōu)檎羝倪^(guò)程。線CD表示在等壓條件下蒸汽被加熱至過(guò)熱的過(guò)程，在此過(guò)程中，溫度和比容均增大。圖1-2溫度-比容曲線表1-1一些物質(zhì)的臨界參數(shù)Inasimilarname,aconstantpressureof10MPaisrepresentedbylineIJKL,forwhichthesaturationtemperatureis311.1℃.Atapressureof22.09MPa,representedbylineMNO,wefind,however,thatthereisnoconstant-temperaturevaporizationprocess.Instead,pointNisapointofinflectionwithazeroslope.Thispointiscalledthecriticalpoint.Atthecriticalpointthesaturated-liquidandsaturated-vaporstatesareidentical.Thetemperature,pressureandspecificvolumeatcriticalpointarecalledthecriticaltemperature,criticalpressureandcriticalvolume.Thecritical-pointdataforsomesubstancesaregiveninTable1-1.類(lèi)似地，線IJKL表示壓強(qiáng)為10MPa下的等壓線，相應(yīng)的飽和溫度為311.1℃。但是，在壓強(qiáng)為22.09MPa條件下（線MNO），不存在等溫蒸發(fā)過(guò)程。相反，點(diǎn)N是個(gè)轉(zhuǎn)折點(diǎn)，在該點(diǎn)上，切線斜率為零，通常把N點(diǎn)稱(chēng)為臨界點(diǎn)。在臨界點(diǎn)處，飽和液體和飽和氣體的狀態(tài)都是相同的。臨界點(diǎn)下的溫度、壓強(qiáng)和比容分別稱(chēng)為臨界溫度、臨界壓強(qiáng)和臨界比容。一些工質(zhì)的臨界點(diǎn)數(shù)據(jù)如表1-1所示。1.1.4ThefirstlawofthermodynamicsThefirstlawofthethermodynamicsiscommonlycalledthelawofconservationofenergy.教材3頁(yè).Inelementaryphysicscourses,thestudyofconservationofenergy.Inelementaryphysicscourses,thestudyofconservationofenergyemphasizeschangesinkineticandpotentialenergyandtheirrelationshiptowork.Amoregeneralformofconservationofenergyincludestheeffectsofheattransferandinternalenergychanges.Otherformsofenergycouldalsobeincluded,suchaselectrostatic,magnetic,strainandsurfaceenergy.1.1.4熱力學(xué)第一定律通常把熱力學(xué)第一定律稱(chēng)為能量守恒定律。在基礎(chǔ)物理課程中，能量守恒定律側(cè)重動(dòng)能、勢(shì)能的變化以及和功之間的相互關(guān)系。更為常見(jiàn)的能量守恒形式還包括傳熱效應(yīng)和內(nèi)能的變化。當(dāng)然，也包括其它形式的能，如靜電能、磁場(chǎng)能、應(yīng)變能和表面能。Historically,[]thefirstlawofthermodynamicswasstatedforacycle:thenetheattransferisequaltothenetworkdoneforasystemundergoingacycle.歷史上，用熱力學(xué)第一定律來(lái)描述循環(huán)過(guò)程：凈傳熱量等于循環(huán)過(guò)程中對(duì)系統(tǒng)所做的凈功。1.1.5ThesecondlawofthermodynamicsThesecondlawofthermodynamicscanbestatedinavarietyofways.Herewepresenttwo:theClausiusstatementandtheKelvin-Planckstatement.1.1.5熱力學(xué)第二定律熱力學(xué)第二定律有多種表述形式。在此列舉兩種：克勞修斯表述和凱爾文-普朗克表述。ClausiusstatementItisimpossibletoconstructadevicethatoperatesinacycleandwhosesoleeffectistransferofheatfromacoolerbodytoahotterbody.克勞修斯表述：制造一臺(tái)唯一功能是把熱量從低溫物體傳給高溫物體的循環(huán)設(shè)備是不可能的。圖1-3第二定律的違背Thisstatementrelatestoarefrigerator(oraheatpump).Itstatesthatitisimpossibletoconstructarefrigeratorthattransfersenergyfromacoolerbodytoahotterbodywithouttheinputofwork;thisviolationisshowninFig.1-3(a).以冰箱（或熱泵）為例，不可能制造一臺(tái)不用輸入功就能把熱量從低溫物體傳給高溫物體的冰箱，如圖1-3(a)所示。Itisimpossibletoconstructadevicethatoperatesinacycleandproducesnoothereffectthantheproductionofworkandthetransferofheatfromasinglebody.凱爾文-普朗克表述：制造一臺(tái)從單一熱源吸熱和做功的循環(huán)設(shè)備是不可能的。Inotherwords,itisimpossibletoconstructaheatenginethatextractsenergyfromreservoir,doeswork,anddoesnottransferheattoalow-temperaturereservoir.Thisrulesoutanyheatenginethatis100percentefficient,liketheoneshowninFig.1-3(b).換句話說(shuō)，制造這樣一臺(tái)從某一熱源吸熱并對(duì)外做功，而沒(méi)有與低溫?zé)嵩催M(jìn)行換熱的熱機(jī)是不可能的。因此，該表述說(shuō)明了不存在工作效率為100%的熱機(jī)，如圖1-3(b)所示。1.1.6TheCarnotCycleTheheatenginethatoperatesmostefficientlybetweenahigh-temperaturereservoirandalow-temperaturereservoiristheCarnotengine.Thisisanidealenginethatusesreversibleprocesstoformitscycleofoperation;suchacycleisCarnotcycle.TheCarnotengineisveryuseful,sinceitsefficiencyestablishesthemaximumpossibleefficiencyofanyrealengine.IftheefficiencyofarealissignificantlylowerthantheefficiencyofCarnotenginebetweenthesametemperaturelimits,thenadditionalimprovementsmaybepossible.1.1.6卡諾循環(huán)卡諾機(jī)是低溫?zé)嵩春透邷責(zé)嵩撮g運(yùn)行效率最高的熱機(jī)?？ㄖZ機(jī)是一個(gè)理想熱機(jī)，利用多個(gè)可逆過(guò)程組成一循環(huán)過(guò)程，該循環(huán)稱(chēng)為卡諾循環(huán)?？ㄖZ機(jī)非常有用，因?yàn)樗倪\(yùn)行效率為任何實(shí)際熱機(jī)最大可能的效率。因此，如果一臺(tái)實(shí)際熱機(jī)的效率要遠(yuǎn)低于同樣條件下的卡諾機(jī)效率，則有可能對(duì)該熱機(jī)進(jìn)行一些改進(jìn)以提高其效率。......圖1-4卡諾循環(huán)TheidealCarnotcycleinFig.1-4iscomposedoffourreversibleprocesses:12:Isothermalexpansion:23；Adiabaticreversibleexpansion:34；Isothermalcompression：41；Adiabaticreversiblecompression.TheefficiencyofaCarnotcycleis教材4頁(yè)T1LTHNotethattheefficiencyisincreasedbyraisingthetemperatureTHatwhichheatisaddedorbydecreasingthetemperatureTatwhichheatLisrejected.理想的卡諾循環(huán)包括四個(gè)可逆過(guò)程，如圖1-4所示：1→2等溫膨脹；2→3絕熱可逆膨脹；3→4等溫壓縮；4→1可逆絕熱壓縮?？ㄖZ循環(huán)的效率為T(mén)1L(1-1)TH注意，提高T（提高吸熱溫度）或降低T（降低放熱溫度）均可使循環(huán)效率提高。 H L1.1.7TheRankinecycleThefirstclassofpowercyclesthatweconsiderarethoseutilizedbytheelectricpowergeneratingindustry,namely,powercyclesthatoperatesinsuchawaythattheworkingfluidchangesphasesfromaliquidtovapor.Thesimplestvapor-powercycleiscalledtheRankinecycle,shownschematicallyinFig.1-5(a).Amajorfeatureofsuchcycleisthatthepumprequiresverylittleworktodeliverhigh-pressurewatertotheboiler.Apossibledisadvantageisthattheexpansionprocessintheturbineusuallyentersthequalityregion,resultingintheformationofliquiddropletsthatmaydamagetheturbineblades.1.1.7朗肯循環(huán)我們所關(guān)心的第一類(lèi)動(dòng)力循環(huán)為電力生產(chǎn)工業(yè)所采用的，也就是說(shuō)，動(dòng)力循環(huán)按這樣的方式運(yùn)行：工質(zhì)發(fā)生相變，由液態(tài)變?yōu)闅鈶B(tài)。最簡(jiǎn)單的蒸汽-動(dòng)力循環(huán)是朗肯循環(huán)，如圖1-5(a)所示。朗肯循環(huán)的一個(gè)主要特征是泵耗費(fèi)很少的功就能把高壓水送入鍋爐。其可能的缺點(diǎn)為工質(zhì)在汽機(jī)內(nèi)膨脹做功后，通常進(jìn)入濕蒸汽區(qū)，形成可能損害汽輪機(jī)葉片的液滴。圖1-5朗肯循環(huán)TheRankinecycleisanidealizedcycleinwhichfrictionlossesineachofthefourcomponentsareneglected.Thelossesusuallyarequitesmallandwillbeneglectedcompletelyininitialanalysis.TheRankinecycleiscomposedofthefouridealprocessesshownontheT-sdiagraminFig.1-5(b):12:Isentropiccompressioninapump；23:Constant-pressureheatadditioninaboiler;34:Isentropicexpansioninaturbine;41:Constantpressureheatrejectioninacondenser.朗肯循環(huán)是一個(gè)理想循環(huán)，其忽略了四個(gè)過(guò)程中的摩擦損失。這些損失通常很小，在初始分析時(shí)可完全忽略。朗肯循環(huán)由四個(gè)理想過(guò)程組成，其T-s圖如圖1-5(b)所示：1→2為泵內(nèi)等熵壓縮過(guò)程；2→3為爐內(nèi)定壓吸熱過(guò)程；3→4為汽輪機(jī)內(nèi)等熵膨脹做功過(guò)程；4→1為凝汽器內(nèi)定壓放熱過(guò)程。Thepumpisusedtoincreasethepressureofthesaturatedliquid.Actually,states1and2areessentiallythesame,sincethehigh-pressurelinesareextremelyclosetothesaturationcurve;theyareshownseparatedforillustrationonly.Theboiler(alsocalledasteamgenerator)andthecondenserareheatexchangersthatneitherrequirenorproduceanywork.泵用于提高飽和液體的壓強(qiáng)。事實(shí)上，狀態(tài)1和狀態(tài)2幾乎完全一樣，因?yàn)橛?點(diǎn)開(kāi)始的較高壓強(qiáng)下的吸熱過(guò)程線非常接近飽和曲線，圖中僅為了解釋說(shuō)明的需要分別標(biāo)出。鍋爐（也稱(chēng)蒸汽發(fā)生器）和凝汽器均為換熱器，它們既不需要功也不產(chǎn)生功。Ifweneglectkineticenergyandpotentialenergychanges,thenetworkoutputistheareaundertheT-sdiagram,representedbyarea1-2-3-4-1ofFig.1-5(b);thisistruesincethefirstlawrequiresthatW=Q.Theheattransfertotheworkingsubstanceisrepresentedbyareaout neta-2-3-b-a.Thus,thethermalefficiencyηoftheRankinecycleisarea12341areaa23baThatis,thedesiredoutputdividedbytheenergyinput(thepurchasedenergy).Obviously,教材5頁(yè)thethermalefficiencycanbeimprovedbyincreasingthenumeratororbydecreasingthenominator.Thiscanbedonebyincreasingthepumpoutletpressurep,increasingtheboileroutlettemperatureT,ordecreasing 2 3theturbineoutletpressurep.如果忽略動(dòng)能和勢(shì)能的變化，輸?shù)膬艄Φ扔赥-s圖曲線下面的面積，即圖1-5(b)中1-2-3-4-1所包圍的面積，由用熱力學(xué)第一定律可證明WQ。循環(huán)過(guò)程中工質(zhì)的吸熱量 net net對(duì)應(yīng)面積a-2-3-b-a。因此，朗肯循環(huán)的熱效率可表示為面積12341(1-2)面積a23ba即，熱效率等于輸出能量除以輸入能量（所購(gòu)能量）。顯然，通過(guò)增大分子或減小分母均可以提高熱效率。這可以通過(guò)增大泵出口壓強(qiáng)p，提高鍋爐出口溫度T，或降低汽機(jī)出口壓 2 3強(qiáng)p來(lái)實(shí)現(xiàn)。41.1.8TheReheatcycleItisapparentthatwhenoperatinginaRankinecyclewithahighboilerpressureoralowcondenserpressureitisdifficulttopreventliquiddropletsfromforminginthelow-pressureportionoftheturbine.Sincemostmetalcannotwithstandtemperaturesaboveabout600℃,thereheatcycleisoftenusedtopreventliquid-dropletformation:thesteampassingthroughtheturbineisreheatatsomeintermediatepressure,therebyraisingthetemperaturetostate5intheT-sdiagramofFig.1-6.Thesteamthenpassesthroughthelow-pressuresectionoftheturbineandentersthecondenseratstate6.Thiscontrolsorcompletelyeliminatesthemoistureproblemintheturbine.Thereheatcycledosenotsignificantlyinfluencesthethermalefficiencyofthecycle,butitdoesresultinasignificantadditionalworkoutput,representedinthefigurebyarea4-5-6-4’-4ofFig.1-6.Thereheatcycledemandsasignificantinvestmentinadditionalequipment,andtheuseofsuchequipmentmustbeeconomicallyjustifiedbytheincreasedworkoutput.Ifreheatisnotusedtoavoiddropletformation,thecondenserpressuremustbequitehigh,resultingrelativelylowcycleefficiency.Inthatsense,reheatsignificantlyincreasecycleefficiencywhencomparedtocyclewithnoreheatbutwiththehighercondenserpressure.1.1.8再熱循環(huán)對(duì)于一個(gè)處于高鍋爐壓強(qiáng)和低凝汽器壓強(qiáng)條件下的朗肯循環(huán)，顯然，很難阻止液滴在汽輪機(jī)低壓部分的形成。由于大多數(shù)金屬不能承受600℃以上的高溫，因此，通常采用再熱循環(huán)來(lái)防止液滴的形成。再熱過(guò)程如下：經(jīng)過(guò)汽輪機(jī)的部分蒸汽在某中間壓強(qiáng)下被再熱，從而提高蒸汽溫度，直至達(dá)到狀態(tài)5，如圖1-6所示。然后這部分蒸汽進(jìn)入汽輪機(jī)低壓缸，而后進(jìn)入凝汽器（狀態(tài)6）。再熱循環(huán)方式可以控制或者完全消除汽輪機(jī)中的濕蒸汽問(wèn)題，因此，通常汽輪機(jī)分成高壓缸和低壓缸兩部分。雖然再熱循環(huán)不會(huì)顯著影響循環(huán)熱效率，但帶來(lái)了顯著的額外的輸出功，如圖1-6中的面積4-5-6-4-4所示。當(dāng)然，再熱循環(huán)需要一筆可觀的投資來(lái)購(gòu)置額外的設(shè)備，這些設(shè)備的使用效果必須通過(guò)與多增加的輸出功進(jìn)行經(jīng)濟(jì)性分析來(lái)判定。如果不采用再熱循環(huán)來(lái)避免液滴的形成，則凝汽器出口壓強(qiáng)必須相當(dāng)?shù)馗撸蚨鴮?dǎo)致循環(huán)熱效率較低。在這種意義上，與無(wú)再熱循環(huán)且高凝汽器出口壓強(qiáng)的循環(huán)相比，再熱可以顯著提高循環(huán)效率。圖1-6再熱循環(huán)1.2FundamentalofFluidMechanicsFluidmotionsmanifestthemselvesinmanydifferentways.Somecanbedescribedveryeasily,whileothersrequireathoroughunderstandingofphysicallaws.Inengineeringapplications,itisimportanttodescribethefluidmotionsassimplyascanbejustified.Thisusuallydependsontherequiredaccuracy.Often,accuraciesof±10%areacceptable,althoughinsomeapplicationshigheraccuracieshavetobeachieved.Thegeneralequationsofmotionareverydifficulttosolve;consequently,itistheengineer’sresponsibilitytoknowwhichsimplifyingassumptionscanbemade.This,ofcourse,requiresexperienceand,moreimportant,教材6頁(yè)aunderstandingofthephysicsinvolved.1.2流體力學(xué)基礎(chǔ)流體運(yùn)動(dòng)表現(xiàn)出多種不同的運(yùn)動(dòng)形式。有些可以簡(jiǎn)單描述，而其它的則需要完全理解其內(nèi)在的物理規(guī)律。在工程應(yīng)用中，盡量簡(jiǎn)單地描述流體運(yùn)動(dòng)是非常重要的。簡(jiǎn)化程度通常取決于對(duì)精確度的要求，通?？梢越邮堋?0%左右的誤差，而有些工程應(yīng)用則要求較高的精度。描述運(yùn)動(dòng)的一般性方程通常很難求解，因此，工程師有責(zé)任了解可以進(jìn)行哪些簡(jiǎn)化的假設(shè)。當(dāng)然，這需要豐富的經(jīng)驗(yàn)，更重要的是要深刻理解流動(dòng)所涉及的物理內(nèi)涵。Somecommonassumptionsusedtosimplifyaflowsituationarerelatedtofluidproperties.Forexample,undercertainconditions,theviscositycanaffecttheflowsignificantly;inothers,viscouseffectscanbeneglectedgreatlysimplifyingtheequationswithoutsignificantlyalteringthepredictions.Itiswellknownthatthecompressibilityeffectsdonothavetobetakenintoaccounttopredictwindforcesonbuildingsortopredictanyotherphysicalquantitythatisadirecteffectofwind.Afterourstudyoffluidmotions,theappropriateassumptionsusedshouldbecomemoreobvious.Hereweintroducesomeimportantgeneralapproachesusedtoanalyzefluidmechanicsandgiveabriefoverviewofdifferenttypesofflow.一些常見(jiàn)的用來(lái)簡(jiǎn)化流動(dòng)狀態(tài)的假設(shè)是與流體性質(zhì)有關(guān)系的。例如，黏性在某些條件下對(duì)流體有顯著的影響；而在其它條件下，忽略黏性效應(yīng)的影響可以大大地簡(jiǎn)化方程，但并不會(huì)顯著改變計(jì)算結(jié)果。眾所周知，氣體速度很高時(shí)必須考慮其壓縮性，但在預(yù)測(cè)風(fēng)力對(duì)建筑物的影響程度，或者預(yù)測(cè)受風(fēng)力直接影響的其它物理量時(shí)，可以不計(jì)空氣的壓縮性。學(xué)完流體運(yùn)動(dòng)學(xué)之后，可以更明顯地看出采用了哪些恰當(dāng)?shù)募僭O(shè)。這里，將介紹一些重要的用來(lái)分析流體力學(xué)問(wèn)題的一般性方法，并簡(jiǎn)要介紹不同類(lèi)型的流動(dòng)。1.2.1LagrangianandEulerianDescriptionsofMotionInthedescriptionofaflowfield,itisconvenienttothinkofindividualparticlesofwhichisconsideredtobeasmallmassoffluid,consistingofalargenumberofmoleculesthatoccupiesasmallvolumethatmoveswiththeflow.Ifthefluidisincompressible,thevolumedoesnotchangeinmagnitudebutmaydeform.Ifthefluidiscompressible,asthevolumedeforms,italsochangesitsmagnitude.Inbothcasestheparticlesareconsideredtomovethroughaflowfieldasanentity.1.2.1拉格朗日運(yùn)動(dòng)描述和歐拉運(yùn)動(dòng)描述描述流場(chǎng)時(shí)，將著眼點(diǎn)放在流體質(zhì)點(diǎn)上是非常方便的。每個(gè)質(zhì)點(diǎn)都包含了微小質(zhì)量的流體，它由大量分子組成。質(zhì)點(diǎn)占據(jù)很小的體積，并隨流體流動(dòng)而移動(dòng)。對(duì)不可壓縮流體，其體積大小不變，但可能發(fā)生形變。對(duì)可壓縮流體，不但體積發(fā)生形變，而且大小也將改變。在上述兩種情況下，均將所有質(zhì)點(diǎn)看作一個(gè)整體在流場(chǎng)中運(yùn)動(dòng)。Inthestudyofparticlemechanics,whereattentionisfocusedonindividualparticles,motionisobservedasafunctionoftime.Theposition,velocityandaccelerationofeachparticlearelistedass(x,y,z,t),V(x,y,z,t)anda(x,y,z,t)andquantitiesofinterestcan 0 0 0 0 0 0 0 0 0becalculated.Thepoint(x,y,z)locatesthestartingpointthename-of 0 0 0eachparticle.ThisistheLagrangiandescription,namedafterJosephL.Lagrange,ofmotionthatisusedinacourseondynamics.IntheLagrangiandescriptionmanyparticlescanbefollowedandtheirinfluenceononeanothernoted.Thisbecomes,however,adifficulttaskasthenumberofparticlesbecomesextremelylarge,asinafluidflow.質(zhì)點(diǎn)力學(xué)主要研究單個(gè)質(zhì)點(diǎn)，質(zhì)點(diǎn)運(yùn)動(dòng)是時(shí)間的函數(shù)。任一質(zhì)點(diǎn)的位移、速度和加速度可表示為s(x,y,z,t)，V(x,y,z,t)，a(x,y,z,t)，其它相關(guān)參量也可計(jì) 0 0 0 0 0 0 0 0 0算。坐標(biāo)(x,y,z)表示質(zhì)點(diǎn)的起始位置，也是每個(gè)質(zhì)點(diǎn)的名字。這就是拉格朗日運(yùn)動(dòng)描 0 0 0述，以約瑟夫Ｌ拉格朗日的名字命名，該描述方法通常用于質(zhì)點(diǎn)動(dòng)力學(xué)分析。拉格朗日法跟蹤多個(gè)質(zhì)點(diǎn)的運(yùn)動(dòng)過(guò)程并考慮質(zhì)點(diǎn)間的相互作用。然而，由于實(shí)際流體包含質(zhì)點(diǎn)數(shù)目巨大，因而采用拉格朗日法研究流體流動(dòng)則非常困難。Analternativetofollowingeachfluidparticleseparatelyistoidentifypointsinspaceandthenobservethevelocityofparticlespassingeachpoint;wecanobservetherateofchangeofvelocityastheparticlespasseachpoint,thatis,V/x，V/y，V/zandwecanobserveifthevelocityischangingwithtimeateachparticularpoint,thatis,V/t.InthisEuleriandescription,namedafterLeonhardEuler,ofmotion,theflowproperties,suchasvelocity,arefunctionsofbothspaceandtime.Inrectangular,CartesiancoordinatesthevelocitiesexpressedasV=V(x,y,z,t).Theregionofflowthatisconsiderediscalledaflowfield.與分別跟蹤每個(gè)流體質(zhì)點(diǎn)不同的另一種方法是將著眼點(diǎn)放在空間點(diǎn)上，然后觀察質(zhì)點(diǎn)經(jīng)過(guò)每個(gè)空間點(diǎn)時(shí)的質(zhì)點(diǎn)速度，由此可以得到質(zhì)點(diǎn)流經(jīng)各空間點(diǎn)時(shí)的速度變化率，即V/x，V/y，V/z；還可以判斷某一點(diǎn)上的速度是否隨時(shí)間變化，即計(jì)算V/t。這種描述方法稱(chēng)為歐拉運(yùn)動(dòng)描述，以萊昂哈德歐拉的名字命名。在歐拉法中，速度等流動(dòng)參數(shù)是空間和時(shí)間的函數(shù)。在直角笛卡兒坐標(biāo)系中，速度表示為V=V(x,y,z,t)。我們所研究的流動(dòng)區(qū)域稱(chēng)為流場(chǎng)。1.2.2PathlinesandstreamlinesTwodifferentlineshelpusindescribingaflowfield.Apathlineisthefocusofpointstraversedbyagivenparticleasittravelsinafieldofflow;thepathlineprovidesuswitha“history”oftheparticle’slocations.Aphotographofapathlinewouldrequiredatimeexposureofanilluminatedparticle.教材7頁(yè)1.2.2跡線和流線可采用兩種不同的流動(dòng)線來(lái)幫助我們描述流場(chǎng)。跡線是某一給定質(zhì)點(diǎn)在流場(chǎng)中運(yùn)動(dòng)時(shí)所經(jīng)過(guò)的不同空間點(diǎn)形成的軌跡，它記錄了質(zhì)點(diǎn)的“歷史”位置。一定曝光時(shí)間下可以拍得發(fā)亮粒子的運(yùn)動(dòng)跡線。Astreamlineisalineintheflowpossessingthefollowingproperty:thevelocityvectorofeachparticleoccupyingapointonthestreamlineistangenttothestreamline,thatis,V×dr=0.SinceVanddrareinthesamedirection;recallthatthecrossproductoftwovectorsinthesamedirectioniszero.Aphotographofastreamlinescannotbemadedirectly.Forageneralunsteadyflowthestreamlinescanbeinferredfromphotographsofshortpathlinesofalargenumberofparticles.流線是流場(chǎng)中具有這樣特性的線：任一質(zhì)點(diǎn)在流線上某點(diǎn)處的速度矢量與該流線相切，即Vdr=0。這是因?yàn)閂和dr具有相同的方向，而具有相同方向的兩個(gè)矢量的叉乘積等于零。同跡線相比，流線不能直接由相機(jī)拍攝獲得。對(duì)于一般的非定常流動(dòng)，根據(jù)大量質(zhì)點(diǎn)的短跡線相片可以推斷出流線的形狀。1.2.3One-,two-,andthree-dimensionalflowsIntheEuleriandescriptionofmotionthevelocityvector,ingeneral,dependsonthreespacevariablesandtime,thatis,V=V(z,y,z,t).Suchaflowisathree-dimensionalflow,becausethevelocityvectordependsonthreespacecoordinates.Thesolutionstoproblemsinsuchaflowareverydifficultandarebeyondthespaceofanintroductorycourse.Eveniftheflowcouldbeassuredtobesteady[i.e,V=V(x,y,z)],itwouldremainathree-dimensionalflow.1.2.3一維、二維和三維流動(dòng)一般來(lái)說(shuō)，歐拉運(yùn)動(dòng)描述中的速度矢量取決于三個(gè)空間變量和時(shí)間變量，即V=V(x,y,z,t)。這樣的流動(dòng)稱(chēng)為三維流動(dòng)，因?yàn)樗俣仁噶恳蕾?lài)于三個(gè)空間坐標(biāo)。三維流動(dòng)的求解非常困難，并且也超出了序言的范圍。即使假設(shè)流動(dòng)為定常的（如，V=V(x,y,z)），該流動(dòng)仍為三維流動(dòng)。Oftenathreedimensionalfl