熱能與動(dòng)力工程專業(yè)英語(yǔ)

絕熱絕熱的Chapter1IntroductionThermal第一章

熱科學(xué)基礎(chǔ)Acousticflowmeter聲波流量計(jì)

Corrugatedfin波狀散熱片Adiabatic

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Crossproduct矢量積Aerodynamics空氣動(dòng)力學(xué)Affiliation聯(lián)系A(chǔ)irfoil機(jī)翼，螺旋槳Alternative替代燃料Anemometer風(fēng)速計(jì)ngularspeed角速度Areadensity表面密度Baffle擋板ifurcation分形Blackbody黑體Blade漿葉，葉片Boiler鍋爐

Denominator分母Developedflow充分發(fā)展流Diffusion擴(kuò)散Dopplereffect多普勒效應(yīng)Double-pipeheatexchanger套管式換熱器rysaturatedvapor干飽和蒸汽Electrode電極lectrolyte電解，電解液Electrostatic靜電的Emissivity發(fā)射率quilibrium平衡luidmechanics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Compactheatexchanger緊湊式換熱器Composition成分，合成物Compressedliquid壓縮液體Compressibility可壓縮性，壓縮率Condensation凝結(jié)Condenser冷凝器Conduction導(dǎo)熱Controlvolume控制體Convection對(duì)流

lassceramic微晶玻璃，玻璃陶瓷Heatengine熱機(jī)eatpump熱泵Hydrofoil水翼ypersonicspeed高超音速Infinitesimal無(wú)窮小的Inflating/deflating充氣/壓縮Internalcombustionengine內(nèi)燃機(jī)Isentropic等熵的sobaric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Kinematicviscosity運(yùn)動(dòng)黏度Laminar層流Manuscript手稿，原稿Moisture濕度，水分Molecule(化學(xué))分子Moltenpolymer熔融聚合物Muti-disciplinary多學(xué)科的NewtonianFluid牛頓流體

Saturation飽和Shearstress剪切力、切應(yīng)力Shell-and-tubeheatexchanger管殼式換熱器Specificvolume比容Steady穩(wěn)態(tài)的，定常的Stiflingengine斯特林機(jī)Strainrate變形速度，應(yīng)變率Streamline流線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Parallelflow平行流動(dòng)，并流Pathline跡線Phasechange相變Planeflow平面流，二元流Plateandflameheatexchanger板式換熱器Polymersolution膠漿Proof校樣Propeller螺旋槳，推進(jìn)器ump泵ulity干度usi-equilibrium準(zhǔn)平衡、準(zhǔn)靜態(tài)Radiation輻射ankinCycle朗肯循環(huán)Regenerativeheatexchanger蓄熱/再生式換熱器Reservoir水庫(kù)，蓄水池Reversible可逆的Rotameter轉(zhuǎn)子流量計(jì)BiBiotnumber比澳數(shù)

uperheatedvapor過(guò)熱蒸汽Surrounding環(huán)境，外界Thermalconductivity熱傳導(dǎo)率Thermalefficiency熱效率Thermodynamics熱力學(xué)Torsional扭力的，扭轉(zhuǎn)的railingedge機(jī)翼后緣、尾緣Transmitter傳送裝置、發(fā)送器Turbinemeter渦輪流量計(jì)Turbulent湍流的ltrosonic超聲波的niformflow均勻劉acuum真空Viewfactor角系數(shù)Viscous黏性的Cortexshedding漩渦脫落Waterfaucet水龍頭，水嘴NPSH汽蝕余量CFDCHF

計(jì)算流體力學(xué)臨界熱流量

NTU傳熱單元數(shù)Nu努謝爾特?cái)?shù)COP制冷系數(shù)Eu歐拉數(shù)Fo富立葉數(shù)Fr弗勞德數(shù)Gr格拉曉夫數(shù)

PE勢(shì)能Pr普朗特?cái)?shù)Ra瑞利數(shù)Re雷諾數(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

工熱學(xué)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)。能量以內(nèi)能（與溫度有關(guān)能（由物體運(yùn)動(dòng)引起能（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,andthus,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。1.1.1Thermodynamicsystemandcontrol1.1.1

熱力系和控制體Aaofsomeenclosure.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，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Allmatterandspacetoasystemiscollectivelycalleditssurroundings.Thermodynamicsisconcernedwiththeinteractionofasystemanditssurroundings,oronesysteminteractingwithanother.Asysteminteractswithitsbyenergyacrossitsboundary.Nomaterialcrossestheboundaryofasystem.thesystemdoesnotexchangeenergywiththesurroundings,itisanisolatedsystem.系統(tǒng)之外的所有物質(zhì)和空間統(tǒng)稱外界或環(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)稱為孤立系統(tǒng)。Inmanycases,ananalysisissimplifiedifattentionisfocusedonaparticularvolumeinspaceintowhich,fromwhich,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為控制表面。Thus,wemustchoose,inaparticularproblem,whetherasystemistobeconsideredorwhetheracontrolvolumeismoreIfmassfluxacrossaboundary,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,and平衡、程和循環(huán)Whenthetemperatureofasystemisreferredto,itisassumedthatallpointsofthesystemhavethesame,pertiesarefromandwhenthereisnotendencyforchangewithtime,aconditionofthermodynamicequilibriumIfissuddenlyincreasedatpartofthesystemboundary,spontaneousredistributionisassumedtooccuruntilallpartsofthe教材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。Whenafromoneequilibriumpathofsuccessivesatesthroughwhichthesystempassesiscalledprocess.If,intheonestatetonext,equilibriumisinfinitesimal,aquasi-equilibriumprocessoccurs,andeachstateintheprocessmaybeidealizedasanequilibriumstate.Quasi-equilibriumprocessescanapproximatemanyprocesses,suchasthecompressionandexpansionofannolossofaccuracy.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。Whenasystemagiveninitialstateaseriesprocessandreturnstotheinitialstate,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)程中溫度保持變；等壓（isobaric）程中壓強(qiáng)恒定；等容（isometric）過(guò)程中體積保持不變。1.1.3Vapor-liquidphaseequilibriumpuresubstance純物質(zhì)氣-液相平Considerasasystem1kgofwatercontainedinthepistonorcylinderarrangementshowninFig.1-1(a).Supposethepistonandweightmaintainapressureof0.1MPainthecylinderandthattheinitialtemperatureis20Astothewater,theincreaseappreciably,thespecificvolumeincreaseslightly,andthepressureremainsconstant.Whenthetemperaturereaches99.6,additionalheattransferresultsinachangeofphase,asindicatedinFig.1-1(b).Thatis,someoftheliquidbecomesvapor,andduringthisprocessboththetemperatureandpressureremainconstant,butthespecificWhendrophasvaporized,furthertransferofheatresultsinanincreaseinbothtemperatureandspecificvolumeofthevapor,asshowninFig.1-1(c).如圖1-1(a)所示，由活塞和氣缸組成的置中裝有水。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)步的加熱將使蒸汽溫度和比容均有所增加同1-1(c)所示。圖液體在常壓下蒸發(fā)過(guò)ThetermsaturationtemperaturedesignatesthetemperatureatwhichvaporizationataThisiscalledthesaturationpressureforgiventemperature.forwaterat

℃theis0.1MPa,waterat0.1MPathetemperatureis99.6

℃.在給定壓強(qiáng)下發(fā)生氣化的溫度稱為飽和溫度，壓強(qiáng)稱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的飽和溫度為99.6℃。Ifasubstanceexistsliquidatthesaturationitcalledsaturatedliquid.Ifthetemperatureoftheliquidislowerthantheisasubcooledliquid(implyingthatthetemperatureislower教材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),ifthemassofvaporis0.2kgandthemassofliquidiskg,qualityor20%.Qualityhasmeaningonlywhenthesubstanceisinasaturatedstate.若某一工質(zhì)在飽和溫度下以液、氣共存的形式存在，則稱蒸汽質(zhì)量與總質(zhì)量之比為干度。因此，如圖1-1(b)所，若蒸汽質(zhì)量為液體質(zhì)量為0.8kg，則其干度為0.220%。干度只有在飽和狀態(tài)下才有意義。Ifasubstanceexistsasvaporatthesaturationtemperature,itiscalleddrysaturationvaporisusedtoemphasizethatthequalityis100%).Whentheisatemperaturegreaterthanthesaturationtemperature,itissaidtoexistassuperheatedvapor.Thepressuretemperatureofsuperheatedvaporareindependentproperties,sincethetemperaturemayincreasewhilethepressureremainsconstant.若某一工質(zhì)處于飽和溫度下并以蒸汽形態(tài)存在，則稱該蒸汽為飽和蒸汽（有時(shí)稱為干飽和蒸汽，意在強(qiáng)調(diào)其干度為100%蒸汽溫度高于其飽和溫度時(shí)，則稱之為過(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-pressurelinerepresentsstateswhichwaterpassesasitisheatedfromtheinitialstateof0.1MPaandLetstateArepresenttheinitialstate,Bthesaturated-liquidstate(99.6℃),andlineABtheprocesswhichtheliquidisfromtheinitialtemperaturetothesaturationtemperature.PointCisthesaturated-vaporstate,andlineBCistheconstant-temperatureprocessinwhichthechangeofphasefromliquidtovaporoccurs.LineCDrepresents

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theprocessinwhichthesteamissuperheatedatconstantpressure.Temperatureandvolumebothincreaseduringthisprocess.在圖1-2所示的溫度-比容圖作等壓線，表示水由初壓0.1MPa初溫20℃被加熱過(guò)程。點(diǎn)A表初始狀態(tài)，點(diǎn)B飽和液態(tài)（99.6℃線AB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示飽和蒸汽狀態(tài)，線表示等溫過(guò)程，即液氣化轉(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。圖溫度比容線表1-1一些物質(zhì)的臨界參Inasimilarname,aconstantpressureof10MPaisrepresentedbylinetheis311.1Atapressureof22.09MPa,linewefind,however,thatthereisnoconstant-temperaturevaporizationprocess.Instead,pointNisapointofinflectionwithaslope.Thispointisthepoint.Atthecriticalpointsaturated-liquidandsaturated-vaporstatesareidentical.Thetemperature,pressureandspecificvolumeatcriticalpointarecalledthetemperature,pressureandcriticalvolume.Thecritical-pointdataforsomesubstancesaregiveninTable1-1.類似地，線IJKL表示壓強(qiáng)為下的等壓線，相應(yīng)的飽和溫度為311.1℃。但是，在壓強(qiáng)為22.09MPa條件下（線不存在等溫蒸發(fā)過(guò)程。相反，點(diǎn)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)如表示1.1.4ThefirstlawofthermodynamicsThefirstlawofthethermodynamicsiscommonlycalledthelawofconservationofenergy.教材Inelementaryphysicscourses,thestudyofconservationofenergyemphasizeschangeskineticpotentialenergytheirrelationshiptomoreformofenergyincludestheofinternalcouldalsobeincluded,suchaselectrostatic,magnetic,strainandsurfaceenergy.1.1.4熱力學(xué)第定律通常把熱力學(xué)第一定律稱為能量守恒定律。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,

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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。ClausiusstatementItisimpossibletoconstructadevicethatoperatesinacycleandwhoseofheattoa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。圖第二定的違背Thisstatementrelatesarefrigerator(oraheatpump).statesthatitisimpossibletoconstructarefrigeratorthattransfersenergyfromacoolerbodytoahotterbodywithouttheinputofwork;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。Itisimpossibletoconstructadevicethatoperatesinacycleandproducesnoeffectthanproductionofworkandthetransferofheatfromasinglebody.凱爾文-普克表述：制一臺(tái)從一熱源吸熱和做功的循環(huán)備是不可能的。Inotherwords,itisimpossibletoconstructaheatenginethatextractsenergyfromreservoir,work,anddoestransfertoalow-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)示。1.1.6TheCarnotCycleTheheatenginethatoperatesmostefficientlybetweenahigh-temperaturereservoirtheCarnotengine.Thisisanidealenginethatusesreversibleprocessitscycleofoperation;suchacycleisCarnotcycle.TheCarnotengineisveryuseful,sinceitsefficiencyestablishesthemaximumpossibleefficiencyofrealareallowerthantheefficiencyofCarnotenginebetweenthesametemperaturelimits,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)稱為卡諾循環(huán)?？ㄖZ機(jī)非常有用為它的運(yùn)行效率為任何實(shí)際熱機(jī)最大可能的效率此，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。圖卡諾循TheidealCarnotcycleinFig.1-4iscomposedoffourreversibleprocesses:12:Isothermalexpansion:23；reversibleexpansion:34；compression：41；Adiabaticreversiblecompression.TheefficiencyofaCarnotcycleis教材NotethattheefficiencyisincreasedbyraisingthetemperatureTHatwhichheatisaddedordecreasingthetemperatureTatwhichheatLisrejected.理想的卡諾循環(huán)包括四個(gè)可逆過(guò)程，如圖所：→2溫膨脹2→3絕熱可逆膨脹；→4等溫壓縮；4→1可逆絕熱壓縮。卡諾循環(huán)的效率為T(mén)LT

(1-1)注意，提高T（提高吸熱溫度）或降低（低放熱溫度）均可使HL環(huán)效率提高。1.1.7TheRankinecycleThefirstofthatconsiderarethoseutilizedbytheelectricpowergeneratingindustry,namely,powercyclesthatoperatesinsuchathattheworkingphasesliquidtovapor.Thesimplestvapor-powercycleiscalledtheRankinecycle,shownschematicallyinAmajorfeaturesuchthatthepumpverylittletodeliverhigh-pressuretheboiler.Apossibledisadvantageisthattheexpansionprocessintheturbinetheofliquiddropletsthatmaydamagetheturbineblades.1.1.7朗肯循環(huán)我們所關(guān)心的第一類動(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)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。圖朗肯循TheRankinecycleisanidealizedcycleinwhichfrictionlossesineachofthefourcomponentsareneglected.Thelossesusuallyarequitesmallandwillbeneglectedcompletelyininitialanalysis.TheRankinecycleiscomposedofthefouridealprocessesshownontheT-sdiagraminFig.1-5(b):12:Isentropiccompressioninapump；2Constant-pressureheatadditioninaboiler;Isentropicexpansioninaturbine;4Constantpressureheatrejectioninacondenser.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：1→2泵內(nèi)等熵壓縮過(guò)程；2→3為爐定壓吸熱過(guò)程；→4為汽輪機(jī)內(nèi)等熵膨脹做過(guò)程；4→1為凝汽器內(nèi)定壓放熱過(guò)程。Thepumpisusedtoincreasethepressureofthesaturatedliquid.Actually,2same,linesareextremelyclosetothesaturationcurve;theyareshownseparatedforillustrationonly.Theboiler(alsocalledasteamgenerator)heatthatproduceanywork.泵用于提高飽和液體的壓強(qiáng)事實(shí)上態(tài)1和狀態(tài)2幾乎完全一樣，因?yàn)橛?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.totheisrepresentedbyoutneta-2-3-b-a.Thus,thethermalefficiencyηoftheRankinecycleisThatdividedbytheenergyenergy).Obviously,教材thethermalefficiencybeimprovedthenumeratorbydecreasingthecandonebythepumpoutletpressurepincreasingtheboileroutlettemperatureT,or23theturbineoutletpressurep.4如果忽略動(dòng)能和勢(shì)能的變化出的凈功等于-s圖曲線下面的面積，即圖1-5(b)1-2-3-4-1所包圍的面積，由用熱力學(xué)第一定律可證明W

。循環(huán)過(guò)程中工質(zhì)的吸熱量對(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1面積

(1-2)即，熱效率輸出能量除以輸入能量（所購(gòu)能量然，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)提高鍋2爐出口溫度或降低汽機(jī)口壓強(qiáng)實(shí)現(xiàn)。341.1.8TheReheatcycleItisapparentwhenoperatingRankineboilerpressureoralowcondenserpressureitisdifficulttopreventliquiddropletsfromforminginthelow-pressureportionoftheturbine.Sincemostmetalcannotwithstandtemperaturesaboveabout℃,thereheatcycleistoformation:thethroughtheturbineisreheatatsomeintermediatepressure,therebyraisingdiagramofFig.1-6.Thethenpassesthroughthelow-pressuresectionoftheturbineandentersthecondenseratstate6.Thiscontrolsorcompletelyeliminatesthemoisturedoseinfluencesthethermalefficiencyofthecycle,butitdoesresultinasignificantadditionalworkoutput,representedinthefigurebyarea4-5-6-4’-4ofThereheatcyclesignificantinadditionalequipment,andtheuseofsuchequipmentmustbeeconomicallybytheoutput.notusedtoavoiddropletformation,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（狀態(tài)6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的面積4-5-6-4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?，因而?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。圖再熱循1.2FundamentalofFluidMechanicsFluidinmanySomebedescribedveryeasily,whileothersrequireathoroughunderstandingofphysicallaws.Inengineeringapplications,itisimportanttodescribetheassimplyascanbejustified.Thisusuallydependsontherequiredaccuracy.Often,accuraciesof±10%areacceptable,althoughinsometobegeneralequationsofmotionareverydifficulttosolve;consequently,itistheengineerresponsibilitytoknowwhichsimplifyingassumptionscanbemade.This,ofcourse,requiresexperienceand,moreimportant,教材aunderstandingofthephysicsinvolved.1.2流力基流體運(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，通常可以接受±10%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此程師有責(zé)任了解可以進(jìn)行哪些簡(jiǎn)化的假設(shè)。當(dāng)然需要豐富的經(jīng)驗(yàn)重要的是要深刻理解流動(dòng)所涉及的物理內(nèi)涵。Sometofluidproperties.Forexample,undercertainconditions,viscositycanaffecttheflowsignificantly;inothers,viscouseffectscanbeneglectedgreatlysimplifyingtheequationswithoutsignificantlyalteringthepredictions.Itiswellknownthatthecompressibilityeffectsdonothavetobetakenintoaccounttopredictwindforcesonbuildingsortoanythataofwind.Afterourstudyoffluidmotions,theappropriateassumptionsusedmoreHeresomeapproachesusedtoanalyzefluidmechanicsandgiveabriefoverviewofdifferenttypesofflow.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)要介紹不同類型的流動(dòng)。1.2.1LagrangianandEulerianDescriptionsMotionInthedescriptionofaflowfield,itisconvenienttothinkofindividualparticlesofwhichisconsideredtoasmallmassoffluid,consistingofalargenumberofmoleculesthatoccupiesasmallvolumethatmoveswiththeflow.Ifthefluidisincompressible,volumedoesnotmagnitudemaydeform.theiscompressible,thevolumedeforms,italsochangesitsmagnitude.Inbothcasestheparticlesareconsideredtomovethroughaflowfieldasanentity.1.2.1拉格朗日動(dòng)描述和歐運(yùn)動(dòng)描描述流場(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)生形變而大也將改變?cè)谏鲜鰞煞N情下，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,velocityandaccelerationofeachparticlearelistedas,y,z,t),V(x,y,zand,y,z,t)quantitiesinterest000000000becalculated.point(x,y,z)locatesthestarting000eachThisL.Lagrange,ofmotionisusedondynamics.Lagrangiandescriptionmanyparticlescanbefollowedandtheirinfluenceononeanothernoted.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(x,,t，(x,,t)，(xy,00000z,t)，其它相關(guān)參量也可計(jì)算。坐標(biāo)(x,,z)表示點(diǎn)的起始位置，00也是每個(gè)質(zhì)點(diǎn)的名字。這就是拉格朗日運(yùn)動(dòng)描述，以約瑟夫的名字命名，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,

wecanifthevelocityischangingtimeateachthatis,

InthisEuleriandescription,namedafterLeonhardEuler,ofmotion,sucharefunctionsofbothspaceandCartesiantheexpressedasV=(x,y,z,t).Theofflowthatconsiderediscalledaflowfield.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)算這種描述方法稱為歐拉運(yùn)動(dòng)描述，以萊昂哈字命名。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(,yz,)。我們所研究的流動(dòng)區(qū)域稱為流場(chǎng)。1.2.2PathlinesandstreamlinesTwodifferenthelpusdescribingafield.Apathlineistheittravelsofflow;thepathlineprovidesuswith“history”oftheparticle’slocations.Aphotographofapathlinewouldrequiredatimeexposureofanilluminatedparticle.教材1.2.2跡線和流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。Aintheflowpossessingthefollowingproperty:thevelocityvectorofeachparticleoccupyingapointthestreamlineisstreamline,thatV×drVandrareinthesamedirection;thatproductofvectorsinsamedirectioniszero.photographofacannotbemadeForageneralunsteadyflowthestreamlinescanbeinferredfromphotographsofshortpathlinesofalargenumberofparticles.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V=0。這是因?yàn)楹蛂具有相同的方向，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。1.2.3two-,three-dimensionalInofindependsonthreespacevariablesandtime,thatis,V=V(z,y,z,t).Suchaflowisathree-flow,becausevelocityvectoronthreecoordinates.solutionstoproblemsinsuchaflowverydifficultandarebeyondthespaceofanintroductorycourse.Eveniftheflowcouldbeassuredtobesteady[i.e,V=V(x,y,z)],itwouldremainathree-dimensionalflow.1.2.3一維、二和三維流動(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=(,y,,)。這樣的流動(dòng)稱為三維流動(dòng)，因?yàn)樗俣仁噶恳蕾囉谌齻€(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，=Vx,y,z)流仍為三維流動(dòng)。Oftenathreedimensionalflowcanbeapproximatedasatwo-dimensionalflow.Forexample,theflowoverawidedamisthree-dimensionalbecauseoftheendconditions,buttheflowinthecentralportionawayfromtheendsbetreatedastwo-dimensional.Ingeneral,atwo-dimensionalflowisaflowinwhichthevelocityvectordependsononlytwoAnexampleaplaneinwhichthedependstwospatialcoordinates,xandy,z[i.e.V=V(x,y)].三維流動(dòng)常?？梢越瞥啥S流動(dòng)。例如，對(duì)于一個(gè)很寬的大壩，受壩兩端條件的影響，水流經(jīng)大壩時(shí)的流動(dòng)為三維流動(dòng)；但遠(yuǎn)離壩端的中間部分的流動(dòng)可看作是二維的。一般來(lái)說(shuō)，二維流動(dòng)是指其速度矢量只取決于兩個(gè)空間坐標(biāo)的流動(dòng)。平面流動(dòng)即是如此，速度矢量只依賴于兩個(gè)空間坐標(biāo)，而與標(biāo)關(guān)（如，=V,)

x，Aflowainwhichvelocityononlyonespacevariable.Suchflowsoccurinlong,straightpipesorbetweenparallelplates.Thevelocityinthepipevariesonlywithri.e.,u=r(r).Thevelocitybetweenparallelplatesvariesonlywiththecoordinateyi.e.,Eveniftheunsteadysothatasduringthestartup,一維流動(dòng)的速度矢量只依賴于一個(gè)空間坐標(biāo)。這類流動(dòng)常發(fā)生在長(zhǎng)直管內(nèi)和平行平板間。管內(nèi)流動(dòng)的速度只隨到管軸的距離變化，即u=u(r)平行平板間的速度也只與坐標(biāo)有關(guān)uuy)使流動(dòng)為非定常流動(dòng)，如啟動(dòng)時(shí)的情形，=u(,)，但流動(dòng)仍是一維的。Asflows,thevelocitydorespecttothespacecoordinateinthedirectionofflow.Thisdemandsthattheregionofinterestbeasubstantialdistanceanorachangeinininwhichaflowfieldissimplifiedtoauniformflow:thevelocityandotherfluidproperties,areconstantoverthearea.Thissimplificationismadewhenvelocityisessentiallyoverthearathercommonsuchflowinapipesection,andflowinastream.Theaveragevelocitymaychangefromonesectiontoanother;theflowconditionsdependsonlyonthespacevariableintheflowdirection.對(duì)于完全發(fā)展的流動(dòng)，其速度輪廓線并不隨流動(dòng)方向上的空間坐標(biāo)而改變。這要求研究區(qū)域要遠(yuǎn)離入口處或幾何形狀突然改變的區(qū)域。有許多流體力學(xué)方面的工程問(wèn)題，其流場(chǎng)可以簡(jiǎn)化為均勻流動(dòng)：速度和其它流體特性參數(shù)在整個(gè)區(qū)域內(nèi)均為常數(shù)。這種簡(jiǎn)化只對(duì)速度在整個(gè)區(qū)域內(nèi)均保持不變時(shí)才成立，而且這種情況非常普遍。例如：管內(nèi)的高速流動(dòng)和溪水的流動(dòng)。平均速度可能從一個(gè)斷面到另一個(gè)斷面有所不同，而流動(dòng)條件僅取決于流動(dòng)方向上的空間變量。1.2.4Newtonianfluidandnon-NewtonianfluidANewtonianfluidisafluidwhosestressversusratestraincurveistheisknowntheAsimpletodescribeNewtonianbehaviorisτ=μdu/dy.τistheshearstressexertedbytheμisthefluidviscosity,du/dyisvelocitygradientperpendiculartothedirectionofshear.教材1.2.4牛頓流體非牛頓流體牛頓流體是指應(yīng)力與變形率關(guān)系曲線為過(guò)坐標(biāo)圓點(diǎn)的直線的流體。直線的斜率稱為黏度。用=μu/dy個(gè)單的關(guān)系式來(lái)描述牛頓流體的特性τ為流體施加的切向應(yīng)力μ流體的動(dòng)力黏度u/dy為垂直于切應(yīng)力方向上的速度梯度。Ifafluiddoesnotobeythisittermednon-Newtonianfluid,ofwhichthereareseveraltypes,includingpolymersolutions,moltenpolymers,manysolidsuspensionsandmosthighlyviscousfluids.Inanon-Newtonianfluid,therelationbetweentheshearstressandthestrainrateisnonlinear,andcanevenbetime-dependent.Thereforeaconstantcoefficientofviscositycannotbedefined.Aratiobetweenshearstressandrateofstrain(orshear-dependentviscosity)canbedefined,thisconceptbeingmoreusefulforwithouttime-dependentbehavior.如果流體不滿足上述關(guān)系式，則被稱為非牛頓流體，它包括以下幾種類型：聚合物溶液、聚合物熔體、固體懸浮物和高黏度流體。在非牛頓流體中，切向應(yīng)力和變形率成非線性關(guān)系，甚至可能是非定常的，因此不能定義恒定的黏度系數(shù)。但可以定義切向應(yīng)力和變形率的比值(或隨切向應(yīng)力變化的黏度)，這個(gè)概念對(duì)不具有時(shí)間相關(guān)性行為的流體非常有用。1.2.5andinviscidflowAfluidflowmaybebroadlyclassifiedaseitheraviscousfloworaninvisi