熱能專業(yè)英語Ch01教案解析

絕熱的絕熱的Chapterctionto一熱學(xué)基Acousticflowmeter聲波量

fin波狀熱

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product矢量積空動學(xué)Affiliation聯(lián)系A(chǔ)irfoil機Alternative替代燃風(fēng)速計ngular角速度density面密度Baffle擋板分形Blackbody體漿葉，葉片Boiler鍋爐

Denominator分母flow充分發(fā)Diffusion擴散Dopplereffect多普效應(yīng)Double-pipechanger套式換熱器rysaturatedvapor干和汽電極lectrolyte電解電液Electrostatic靜電的Emissivity發(fā)射率quilibrium平衡luidmechanics流力學(xué)er邊界層

Forced

強制對流Carnotcle卡諾循環(huán)Cartesian笛卡坐系攝氏度Compactex緊湊式熱器Composition成分合成物liquid壓縮液體可壓性，縮率凝結(jié)冷凝器導(dǎo)熱控制體Convection對流

Free自然對流rictionloss摩擦損lassceramic微晶璃，璃陶engine熱機eatpump熱泵Hydrofoil水翼y高速Infinitesimal無窮小的Inflating/deflating充氣/壓縮combustion內(nèi)燃機Isentropic等熵的sobaric等壓的flowmeter加Isolated的計33Isometric等容的等溫的viscosity動黏度層流手稿，原稿Moisture濕度，水分Molecule(化學(xué)分子polymer熔聚物Muti-disciplinary多學(xué)科的Fluid牛頓體

ough-walltube粗糙管Saturation飽和stress剪切、切應(yīng)力Shell-and-tubeheatex管殼式換熱器比容Steady穩(wěn)態(tài)的，定常的engine斯特林Strain變形速，應(yīng)變流線支撐，支柱法向溫度Subcooledliquid過冷體梯度Numerator（數(shù)學(xué)）分子Parallelflow平行流動，并跡線相變Planeflow平面，二元流andheatchanger板mer膠漿Proof校樣螺旋，推進器泵ulity干度準(zhǔn)平衡、準(zhǔn)態(tài)輻射RankinCy朗肯循環(huán)heatchanger蓄熱再式熱器水庫蓄池可逆的Rotameter轉(zhuǎn)子流量計

過蒸汽環(huán)境外傳導(dǎo)Thermalefficiency熱Thermodynamics熱學(xué)Torsional扭力的，扭的railing機翼后、尾緣Transmitter傳送裝、發(fā)器meter渦流計湍流的Ultrosonic超聲波的Uniformflow均勻劉真空View角數(shù)Viscous黏的Cortex漩渦脫落水龍頭水Abbrev33BiBiotnumber比澳數(shù)CFD計算流體力學(xué)CHF臨界流量制冷數(shù)歐數(shù)o富立葉數(shù)弗德數(shù)r格拉曉夫數(shù)KE動能LMTD對數(shù)均差

NPSH汽蝕量NTU傳熱單數(shù)Nu努謝爾特數(shù)勢能Pr普朗數(shù)Ra瑞利數(shù)雷諾數(shù)施密特數(shù)斯坦頓數(shù)勞哈數(shù)We韋伯?dāng)?shù)1.1FundamentalThermodynamics工礎(chǔ)Thermodynamicsasciencewhichthestorage,andenergystudied.Energyisstoredasenergy(associatedtemperature),(dutopotentialenergy(duetoelevation)and(duecomposition);itisfromoftheseformsanditistransferredacrossaaseitherheatwork.熱力學(xué)是一門研究能量儲存換及傳遞的科學(xué)以內(nèi)與溫度有物體運引起（由高度引）化學(xué)能（化組成相關(guān)）形儲存。不形的能量可以相互化，而且能量在界上可以熱和功形式進行傳遞。wewillequationsandtransfersofenergytosuchastemperature,pressuredensity.andbecomeinthermodynamics.Manyofourequationswillbeonobservationshaveintoorlaws,firstandsecondofthermodynamicswidely在熱學(xué)我們推有能轉(zhuǎn)化傳與性數(shù)如度壓及密度等關(guān)間的方程。因，在熱力學(xué)中物質(zhì)及其性質(zhì)得非常重要。多熱力學(xué)方程是建立在實驗察的基礎(chǔ)之上而這些實驗察的結(jié)果已被理成數(shù)學(xué)表達或定律的形式其中，熱力學(xué)一定律和第二律應(yīng)用最為廣。33Thermodynamicsystemcontrolvolume體AfixquantityofcontainedwithinsomeTheisusuallyobviousthatsurroundingthegastheHowever,itanimagineddeformingboundaryaamountofitflowsthroughpump).熱力統(tǒng)一圍某封邊界的有定量物。系邊通是較明顯的（氣體的而，統(tǒng)界也以是假的（如定質(zhì)量流體流經(jīng)泵時斷變形的邊界。AllmatterandextoaitsThermodynamicsconcernedinteractionastemanditssurroundings,onesystemwithAsywithitssurroundingsbytransferringitsboundary.crossestheofasyIfexenergytheitisanisolatedsystem.系之的有物質(zhì)和間稱界或環(huán)境熱學(xué)主要研系與界或系統(tǒng)系統(tǒng)之的互用統(tǒng)過在界上行量傳遞從與外界進行相作用但在界上有量換。當(dāng)系與界沒有量換，這樣的統(tǒng)為立系。Inmanycases,ansimplifiedifattentiononvolumespaceintowhich,fromasubstancevolumeiscontrolApump,pletelysurroundscontrolvolumecalledacontrolsurface.在許多情況下，當(dāng)我們只關(guān)心間有質(zhì)進流的個特定體積時，分析可以到簡這樣的特體積稱控體例泵透平氣或放氣氣球都控體的例子包控體的表面為制面。Thus,inasybeorisIfisfluxacrossboundary,aisotherwise,asyisidentified.因此，于具體的問題，我們須是取統(tǒng)為究象有利還是選取控制體作為究象利如果邊上有質(zhì)量交換則取制有反之，則應(yīng)選取系統(tǒng)作為33究對。Equilibrium,cycle、Whentemperatureareferredto,itisassumedthatallofsystemessentiallythetemperature.Whenthearetopointandisnotendencyforchangewithtime,conditionofthermodynamicIfsuddenlyofspontaneousisassumedtooccurparts教材systemare對某一參考系統(tǒng)，假設(shè)系統(tǒng)各溫完相當(dāng)物內(nèi)部各點的特性參數(shù)均相同不隨時間變化時系統(tǒng)處于熱力學(xué)平衡狀態(tài)統(tǒng)邊某分的度然升時，則系統(tǒng)的溫度將自發(fā)重新分布，直至處相同。changesfromoneequilibriumstatetothepathofsystempassesiscalledIf,intheonestatenext,thefrominfinitesimal,quasi-equilibriumeachprocessmayasanequilibriumQuasi-equilibriumprocessescanapproximateprocesses,asthecompressiongasesinternalcombustionwithsignificantofIffromoneequilibriumstateanotherthroughofnon-equilibrium(asinanon-equilibriumprocessoccurs.當(dāng)系統(tǒng)從一個平衡狀態(tài)轉(zhuǎn)變?yōu)橐缓鈶B(tài)時，系統(tǒng)所經(jīng)歷的一系列由中間狀態(tài)組成變化歷程稱為過程一狀態(tài)到達另一個狀態(tài)的過程中無小偏離平衡態(tài)，則稱該程為準(zhǔn)靜態(tài)過以其任一個間態(tài)看作平狀態(tài)靜過程近視為許過程的疊加結(jié)不會顯著減小其精確性例如氣體在內(nèi)燃內(nèi)的壓縮和膨脹過程。如果系統(tǒng)經(jīng)歷一系列不平狀（燃一平衡狀轉(zhuǎn)變?yōu)橐粋€平狀態(tài)，則其過程為非衡過程。Whengiveninitialprocessinitialsystemgoesacycle.Attheendthepropertiesof33thesystemthesamevaluesthebeginning.當(dāng)統(tǒng)從一個給定的初始狀態(tài)出發(fā)，經(jīng)歷一系列中間過程又回到其初始狀態(tài)，則稱系統(tǒng)經(jīng)了個環(huán)循結(jié)時，統(tǒng)的參又初參相同。cessthetemperatureheldintheremainsisometricprocessisconstant-volumeprocess.在任一特性參數(shù)稱前加上前綴，示該參數(shù)在整個過程保持不變。等溫（）過程中溫度保持不變；等壓isobaric）程中壓強恒定；等容isometric）過中體積保持不變。Vapor-liquidphaseequilibriuminpure-液相平衡assystem1oftheorarrangementshowninFig.1-1(a).Supposepistonweightaof0.1MPaand20.Asheatistothetheincreaseappreciably,specificandthepressurethereaches℃additionalheatresultsachangephase,inis,somethevapor,andduringprocessboththeandconstant,butspecificvolumeWhenthelastofvaporized,transferofheatanincreasebothtemperatureandspecificofFig.1-1(c).如1-1(a)所活塞氣缸成的置中有1kg假定活塞和其上的重使氣缸壓強維持在初始溫度20。熱始給，水速，而比容略有增加氣缸內(nèi)壓強保持定不變當(dāng)水溫達到99.6℃時，若加，將發(fā)相變?nèi)?-1(b)所示也就是說，一部分水開始氣化變?yōu)檎?，在此相變過程中，溫度和強始終保持不比容卻大幅度的增加當(dāng)后一滴液體被化時進一的加將蒸溫度和比均所加，同1-1(c)示。圖在常壓下的發(fā)程Thedesignatesthevaporization33takesplaceatagivenpressure.pressureiscalledthepressurethegiventemperature.water99.6

℃

,the0.1MPa,and℃.在給定壓下生化溫稱為飽和度壓稱給溫下的飽和強因，飽和壓強是0.1MPa，水的飽溫為99.6℃。Ifasubstanceexistsasattemperature,itiscalledsaturatedIftheofliquidlowerthanthetheexistingitiseitherliquidthatlower教材頁saturationtheacompressedliquid(implyingthatthepressureisgreaterthansaturationpressurefortemperature).如果某一工質(zhì)為液態(tài)并處于其和度飽壓下則該液體為飽和液體。如果液溫低當(dāng)前壓強的和度則稱該液體為過冷液表明液體的前溫度于定壓下飽溫）壓液體表液的前強于定溫下飽壓Whensubstancepartliquidandpartvaporatsaturationtemperature,isdefinedthemassvaportothemass.inifthemassis0.2kgandofis0.8qualityQualityhasmeaningonlysubstanceisasaturatedstate.若某一工質(zhì)在飽和溫度下以液氣存形存，稱汽質(zhì)量與總質(zhì)量之比為干度此圖1-1(b)示蒸質(zhì)量為體質(zhì)量0.8kg其干度為或。干度有在和態(tài)下才有意。Ifasubstanceexistsvaporattheitvapor(SometermdrysaturationvaporusedemphasizethatqualityisisatthesaturationitsaidThepressuretemperaturesuperheatedindependentmayincreaseremainsconstant.若某一工質(zhì)處于飽和溫度下并蒸形存，稱蒸為飽和蒸汽（有時稱為干33飽和蒸汽，意在調(diào)其干度為蒸汽溫度高于稱之為過熱蒸汽。過熱蒸的壓強和溫度彼此獨立的，因為度上升時，壓可能保持不。usonofFig.1-2constant-pressurelinethatthestatesthroughthewaterasitisheatedfromtheinitialstateof0.1MPaand20℃.LetAtheBthe℃ABtheprocessinwhichtheliquidistheinitialthesaturationtemperature.Cissaturated-vaporandistheprocesswhichthechangeoffromtovaporoccurs.CD

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theprocesswhichsteamatTemperatureandvolumeincrease在所的度-比容上作壓，表示水由壓、初溫℃被加的過程點A代初狀態(tài)點B為和液態(tài)（99.6℃AB表液由始度熱至飽和度所經(jīng)歷的過點表飽和蒸汽態(tài)線BC表示過即液化變?yōu)檎舻倪^程線表在等壓條下汽被加熱過的過程，此程中溫度和比均大。圖-2度-比容曲線表-1一臨similarname,ofMPaisbylinethetemperature311.1℃AtapressureofbyMNO,wefind,Instead,pointapointofinflectionzeroThisisthepoint.Atthepointthesaturated-liquidandidentical.Thetemperature,andspecificvolumepointarecalledthetemperature,pressureandcritical-pointforsomegivenin類地，線表示壓為下等壓相應(yīng)和溫為311.1。是，在壓為22.09MPa件下（線MNO在溫蒸過程相反點N轉(zhuǎn)折點在該上，切線斜為零，通常點稱為臨界點。在臨點處，飽和液體和飽和氣體的態(tài)都相同的臨界點的溫度、壓強和比容分別稱為臨界溫度界比容。一些質(zhì)的臨界點數(shù)據(jù)如表所示。33ThefirstofthermodynamicsThefirstlawoftheiscalledthelawofconservation教材頁Inphysicstheofconservationchangesrelationshiptowork.Amoregeneralformofconservationofincludeseffectsoftransferandinternalenergyformsofalsobesuchaselectrostatic,surfaceenergy.律通常把熱力學(xué)第一定律稱為能守定?；镎n中，能量守恒定律側(cè)重動能能的變化以和間互更為常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，包括其它形式的，如靜能、磁場、應(yīng)變能和表面。Historically,

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firstlawofthermodynamicswasstatedforcycle:isequaltothenetdonea歷史上，用熱學(xué)第一定律描述循環(huán)過：凈量于循環(huán)過程中對系統(tǒng)所做的凈功。1.1.5secondThesecondlawthermodynamicsstatedavarietyways.Herewepresenttwo:theandtheKelvin-Planck1.1.5二律熱力第二律多種表述形列舉兩種勞修表述凱爾文-普朗克述。ClausiusItisconstructdevicethatinaandsoleeffectisoffromhotter克勞修斯表一臺唯一功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。圖第二定律的statementrelatestoa(orapump).Itstatesthatitimpossibletoconstructa33hottertheinputofwork;in以冰（熱為例不可能制造一臺不用輸入就能把熱量從低溫體傳給高溫物體冰箱，如圖1-3(a)。Itisimpossibletoconstructdevicethatincyandproducesnoothereffectthantheofworkandtheofheatfrom.凱文-普克述：造一臺從單一熱源環(huán)設(shè)備是不可能的。Initisimpossibletothatenergyfromreservoir,doeswork,doestransfertorulesheatengineisefficient,liketheoneinFig.1-3(b).換句話說，制造這樣一臺從某熱吸并外功而有與低溫?zé)嵩催M行換熱的熱機不能。因此，表說了不在作率為的機圖1-3(b)所示。Carnotthatoperatesefficientlyreservoiralow-temperatureisengine.Thisisreversibleformitscycleofsuchacycleiscycle.TheCarnotengineisverysinceitsestablishesthemaximumpossibleofanyengine.Iftheofreallowerthantheefficiencythetemperaturethenadditionalimprovementsmaybepossible.卡環(huán)卡諾機是低溫?zé)岷透邷責(zé)嵩催\效最的機。諾機是一個理想熱，用多個可逆過程組成一循環(huán)過程循稱為諾循卡諾機常用因為它的運行率為任實際機大可能的效因此果臺實際機效率要低同樣條件下的諾效，有可能對熱進一些進提其效率圖卡cyiniscomposedofreversibleprocesses:12:23；Adiabaticex4；compression4；AdiabaticTheofCarnotcycleis教材33HLHLHLHLTLTthattheefficiencyisraisingtheTatwhichheataddedbydecreasingthetemperatureTatwhichis想循四過圖示12等溫膨脹23絕熱可逆膨脹34等溫；41可逆絕壓縮卡循環(huán)效率TLT

注，提高T（提高吸熱溫度）或降低T（低放熱溫度）均可使循環(huán)效率提高。RankinecycleThefirstclassofthatthosebyelectricgeneratingcyclesoperatestheworkingfluidchangesfromtovapor.simplestvapor-poweriscalledRankineshowninFig.1-5(a).AmajorfeatureofsuchisthattheverylittleworktodeliverwatertheApossibleexpansionprocessintheusuallytheregion,inthatmaydamagetheturbine朗環(huán)我們所心的第一類動力循環(huán)電生工采用，就是說，動力循環(huán)按這樣的式運行：工質(zhì)發(fā)生相變，液變氣。簡蒸-動力循是朗循，圖1-5(a)所。朗肯循環(huán)的一個主要特征是泵耗費很少的功就能把高壓水送入鍋爐。能的缺為工質(zhì)在汽機內(nèi)膨脹做功后，通常進入濕蒸汽區(qū)，形成可能損害汽輪機葉片的液滴。圖朗環(huán)RankinecycleisidealizedcyclewhichfrictionlosseseacharelossesusuallyareandwillcompletelyinitialThecycleiscomposedthefouridealshownT-sdiagramFig.1-5(b):1Isentropicin；23:Constant-pressureinboiler;34:Isentropicexpansioninaturbine;4Constantina朗肯循是一個理想循其了過的損這損失通常很小在33out以提。out以提。過出p，爐324始分析時可完全忽略。朗循環(huán)由四個理想過程組成，其s圖圖示2為泵內(nèi)等壓縮程3為爐內(nèi)壓吸過程4為汽機內(nèi)熵膨做功程41為凝汽器定壓放熱過程。pumpisusedtoincreaseofActually12thelinesexcurve;areseparatedforillustrationonly.Theboilercalledsteamandcondenserheatchangersneithernoranywork.泵于提高飽和液體的壓強。事實上，狀態(tài)狀態(tài)乎全一，為由點開始的高壓下吸熱過程線常接飽曲線中為解釋說明需分標(biāo)出鍋爐也蒸發(fā)生器）凝器為換器它既不需要也產(chǎn)功。Ifwepotentialchanges,workoutputisareatheT-sby1-2-3-4-1thissincelawrequiresthatW=theworkingsubstanceisbyareaThus,thethermalefficiencyηtheRankine

areaareaais,desiredoutputdividedbyinputpurchased,教材頁thethermalbyincreasingthenumeratorbydonebyoutletpressurepincreasingtheboileroutlettemperatureT,thepressure如果忽略動能和能的變化，輸出凈功等于圖曲線下面的面積，圖中所包圍的面積，由熱學(xué)一定律證明WQ。環(huán)程工質(zhì)吸熱量對應(yīng)積。此，肯循的熱率可示為

1積

即，熱率輸能量以輸入能量（所購能量然，通過增分子減分母均可這可以增大泵強口溫度T，或汽機出口壓強來現(xiàn)。331.1.8TheReheatcycleItiswhenoperatingwithahighboilerpressureoraitisdifficultpreventfromforminginlow-pressureportionoftheturbine.metalcannotwithstandtemperaturesabout600℃thereheatcycleusedpreventformation:thethroughturbinereheatatintermediatetherebyraisingthetostate5inT-sdiagramFig.1-6.Thethenpassesthroughlow-pressureofandstateThiscontrolscompletelyeliminatesthemoisturetheturbine.Thereheatdosenotinfluencesthethecybutitresultinsignificantadditionalworkoutput,inthefigureby’Thereheatcydemandsinequipment,andtheuseofbeeconomicallyjustifiedbytheworkoutput.Ifreheatisdropletformation,pressurebehigh,resultinglowcy.Inthatcycleefficiencywhencomparedwithnoreheatcondenserpressure.1.1.8再對于一個處高鍋爐壓強和低凝汽器壓強條件下的朗肯循環(huán)，顯然，很難阻止滴在汽輪機低部的成由大多數(shù)金不承600℃以的溫，此通常采用再循環(huán)來止液滴的形成再熱程如下經(jīng)過輪的部蒸在中間壓強被熱從提高溫度至達態(tài)，圖示然后這部分蒸壓，而后進凝器狀熱環(huán)式以控制或者完全消汽機的蒸汽問題，因此通常汽輪機分成高壓缸和低壓缸兩部分雖再熱循環(huán)不會顯著影響循環(huán)熱效率但來了顯著的額外的輸出功，如的面積4-5-6-4所。當(dāng)，熱循環(huán)需要筆觀的投資來購額外的備設(shè)備的使用效果必須通過與多增加的輸出功進行經(jīng)濟性分析判定如果不采用再熱環(huán)來避免液滴的形成則凝出強須相當(dāng)?shù)馗咭驅(qū)аh(huán)熱效率較低種上無再熱循且高凝汽出口壓強的循環(huán)比再熱可以顯提高循環(huán)效率。圖再環(huán)1.2FundamentalofFluidMechanicsFluidmotionsthemselvesmanydifferentwaybe33describedverywhileathoroughofphysicallaws.Inittodescribethefluidassimplyasbejustified.ThisOften,±10%althoughinapplicationshigheraccuraciesbemotionverydifficultsolve;consequently,ittheengineersresponsibilityknowwhichassumptionsThis,course,more教材頁aoftheinvolved.流體運動表現(xiàn)出多種不同的運形。些以單述而其它的則需要完全理解其內(nèi)的理律在程應(yīng)用中盡量簡單地描述流體運動是常重要的簡程度常決精度求常接左右誤，有工應(yīng)則要較的度述動的般性程通很求解因程師有責(zé)任了解可以進行哪些簡化的假設(shè)當(dāng)，需要豐富經(jīng)，重要是深理解流動涉的理內(nèi)。Someusedtosimplifyaflowarerelatedtofluidproperties.Forexample,certainviscositythesignificantly;inviscouseffectsgreatlysimplifyingequationswithoutsignificantlypredictions.Itisknowndotointoaccounttopredictwindonpredictotherphysicalquantityisadirectofwind.ouroffluidmotions,theassumptionsshouldbecomeobvious.Hereweintroduceimportantanalyzefluidmechanicsandgiveaoverviewofdifferenttypesofflow.一些常見的用來簡化流動狀態(tài)假是流性有系。例如，黏性在某些條件下對流有顯著的影響在它條件下黏應(yīng)響大地簡化方程但不會顯改變計算結(jié)果眾所知體速度很高時必須考慮其壓縮性但預(yù)測建筑物影響度者受直響它量可不計空氣的壓縮性學(xué)流體動學(xué)后以顯出了恰假這將介一些重要的用來分析流體力學(xué)問的一般性方法，簡要介紹不同類型的流動。3300000表為度可,tV0,0t，它可000000LagrangianofMotionIntheofaflowfield,itisthinkofparticlesofwhichsmallmassoffluid,consistinglargenumberofoccupiessmallmoveswiththeflow.IftheisinmayIfthefluidisasthevolumeititsbothcasesparticlesconsideredtoflowfieldentity.述描述流場時，將著眼點放在流質(zhì)上非方的每質(zhì)點都包含了微小質(zhì)量的流體，它由大量分子組成。質(zhì)占據(jù)很小的體積，并隨流體流動而移動。對不可壓縮流體，其體大小變能生形可壓縮體但體發(fā)生變且大小也將變。在述兩種情況下，均將所有質(zhì)點看作一個整體在流場中運動。Inthestudyofparticlewhereisonindividualparticles,motionisaoftime.position,andofarelisted(x,zV(x,y,z,t)anda,z,t)andquantitiesofcancalculated.point(x,y,z)thepointparticle.Thisisthedescription,namedafterJosephL.motionisinaLagrangianmanybefollowedinfluenceonenoted.Thishowever,difficultnumberofparticlesbecomesextremelylarge,asinfluid質(zhì)點力學(xué)主要研究單個質(zhì)點，點動時的數(shù)任質(zhì)點的位移速度和速(x,y,z,t)，其也(xyz)表示質(zhì)點置，也是每個質(zhì)點的名字。拉格朗述，以夫拉格日名命名該述法通常用質(zhì)動學(xué)分格朗日法跟蹤多個質(zhì)點的運動過程并考慮質(zhì)點間的相互作用而實流體包含質(zhì)點數(shù)目巨大因采拉格日法研究流體流則非常難。Analternativetofluidistopointsinspaceofparticlespassingeachpoint;canchangevelocityasparticlespoint,is,

x，，

and

wecanifthevelocityischangingwithtimepoint,is,

.

Inthisdescription,namedEuler,ofmotion,33flowasvelocity,arefunctionsofspaceandIncoordinatesexpressedasVy,t).Theofflowcalledaflowfield.V=(,z,t1.2.2PathlinesstreamlinesTwodifferentlineshelpusindescribingflowfield.Apathlinethefocusbyagivenittravelsinfieldoftheprovideswitha“historyofthelocations.Aphotographrequiredexposureofanparticle.1.2.2拍發(fā)粒子Athefollowingproperty:theofoccupyingapointonstreamlineisthatV×dr=0.Vandrinthesamedirection;thatthecrossofinthedirectionzero.Aphotographofbemadeaflowfromofpathlinesnumberof具有樣特性任處矢該相切V因Vdr相向有向矢叉乘積于零相比能接相攝于量One-,three-dimensionaltheEuleriandescriptionofmotionthevector,independs33variablesthatis,Suchaflowdimensionalflow,thevelocitydependsoncoordinates.solutionstoinsuchflowareverydifficultarethespaceancourse.Evenifthecouldto[i.e,V=V(x,y,z)],itwouldremaina、和流一來說拉動描述中的速度矢量取決于三個空間變量和時間變量VVx,,t。樣流動為維動因為度量賴于個間標(biāo)三維動求非常困難，并且也超出序言的范圍。即假設(shè)流動為定常的（，=(x,yz)流動三維流。threeflowbeapproximatedastwo-dimensionalflow.Fortheflowoverawideisbecauseofendflowtheportionawayfromtheastwo-dimensional.general,two-dimensionalflowisflowwhichthevelocityvectoronspacevariables.isflow,inthevectordependstwocoordinates,xnot三維流動常?？梢越贫S流。例如對于一個很寬的大壩，壩兩端件的影響水流經(jīng)大壩的流為三流但離壩端的中間部分的流動可作是二維的一來二流動是指其速度矢量只取決于兩空間坐標(biāo)的流動平流即如速度矢量依賴于，個空間坐標(biāo)，而坐標(biāo)無關(guān)，V=V(x)Aone-dimensionalflowisaflowinwhichtheonlyspaceflowslong,straightorbetweenparallelThevelocityonlywithu=r(r).Thebetweenparallelonlywithcoordinateyi.e.,u=u(y).ifflowissou=u(y,t),astheduringstartup,flowone-dimensional.一維流動的速度矢量只依賴于個空坐。類動發(fā)生在長直管內(nèi)和平行平板間管內(nèi)流動速只到軸距變，(r)平行板速也只與y坐標(biāo)有關(guān)，即=()。流非流如時形=uy,)，該流動仍是維的。Asfordevelopedflows,profilesdonotvarywiththespacecoordinateindirectionThisdemandsthebefromanentranceorasuddenchangeingeometry.are33influidinwhichaflowfieldauniformflow:thevelocityandfluidproperties,areoverthearea.Thissimplificationismadewhenisessentiallyconstantoverarea,rathersuchflowshighflowpipeflowaThechangefromonesectiontoanother;theflowconditionsdependsonlythevariabletheflowdirection.對于完全發(fā)展的流動，其速度廓并隨動向的間坐標(biāo)而改變。這要求研究區(qū)要遠入處或幾何形突然變區(qū)域許多體力方面工問題流場可簡化為均勻流動度和其流特性參在個區(qū)域均常數(shù)這種化只速度在整個區(qū)域內(nèi)保持不時成立而且種情況非常普遍例如內(nèi)高速動和水的流均速度能從一個斷面到另個斷面所同流動條件僅取決于流動方向上的空間量。1.2.4Newfluidandnon-NewtonianfluidAfluidisafluidrateisandpassesorigin.isknowntheviscosity.Asimplerelationdescribefluidbehaviorisτ=μτshearstressexertedbythefluid,μisthedu/dyisofshear.教材1.2.4牛牛流體牛頓流體是應(yīng)與變形率關(guān)曲為過坐標(biāo)圓點直的流體。直的斜率稱黏度用τ=uy這單系描頓體的特性。為流體施加的向應(yīng)力，為流體動力度duy為垂直于切應(yīng)力向上的速度梯度。Ifafluidrelation,itfluid,ofwhicharetyincludingpolysolutions,polysolidandhighlyviscousInfluid,therelationtheshearstressandstrainisandbeThereforeconstantofviscositybeAratiobetweenandofstrain(orshear-dependent)defined,usefulforfluidwithouttime-dependent如果流體不滿上述關(guān)式被為非頓流包括以下種類合物溶、33聚合物熔體懸物高度非頓流向和率線關(guān)系，甚可能是非定常的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，個念不有時相性為流非有用ViscousinviscidAfluidclassifiedeitherfloworflow.Aninviscidflowisoneinviscouseffectssignificantlyflowareflowtheeffectsofimportantandbeignored.黏流體的流動可大分為黏性流動和黏性流黏性流動指黏作用流的影很小、被忽略的流動而在黏性流動中，度的影響極為要，不容忽。modelinviscidflowanalytically,cansimplyletthewillobviouslymakezero.Itmoredifficultinviscidexperimentally,becausefluids(suchaswaterandair)questionthenflowsinis“iftheshearinflowsmallandoversmalldonotsignificantlyaffectthe”Thisstatementisverycourse,anditwillanalysistheinviscid為了模分析非黏性流簡讓為可顯略一切黏性作用在驗室中，制造非黏性流動則非水和空氣）都有黏性。然后問題變?yōu)槭欠翊嬖谖覀兣d趣的、且黏性影響微乎其微的動？答案是：存在只要動中的向力小且作用圍小不會著響流就可”當(dāng)這種描非籠統(tǒng)，需要大的分析證無黏性動設(shè)是正的experience,ithasbeenfoundtheprimaryofflows,flows,externalthatflowswhichexteriorbody.Inviscidprimaryflowsstreamlinedsuchflowaroundairfoilhydrofoil.thatexistaretothinlayer,calledaboundaryistotheboundary,asthatinFig.1-7;velocityinlayeralwayszeroa33fixedwall,aresultofmanyflowsituations,boundarythinsimplywhenthegrossofaroundForflowsolutionprovidesanexcellentpredictiontoflowaroundtheexceptinsidethepossiblyflowisencounteredcontractionsinsidepipingandshortflowswhereeffectsare圖圍據(jù)經(jīng)現(xiàn)以于擬黏流動基流為部動存在于體部流非性流動對于繞流線物體的研究非常重要如流或任能存的黏性影薄薄的，稱之為邊界，它緊貼物體面，如所示。黏的影邊層內(nèi)定面的速度始為對于許多流情界層非薄當(dāng)研究流線型流動總體特征時可忽略邊界層的影響例如，對繞翼型的流動除邊層內(nèi)可能近緣的區(qū)域之黏性流動解實際情況非常吻合管系中收段流動以內(nèi)流中性響均忽不的段域可化成黏流。Viscousflowsthebroadofinternalflows,flows

[]

andinInflowseffectssubstantial“”andaccountamountsthatbetooilandgasinpipelines.Theno-slipconditionresultinginvelocityatandtheresultingsheardirectlyto教材內(nèi)中很一部分情都于性流如流渠流以及明渠流些流動性作用造成相當(dāng)“”此解釋管道輸運石油和天然氣必定耗大量的能源無滑移條件使得壁面處的速度為零，由此產(chǎn)生的切應(yīng)力，直接導(dǎo)致這些損失的產(chǎn)生。LaminarturbulentflowsAviscousfloweitherlaminarflowturbulentflow.flowthefluidflowswithsignificantlymixingofneighboringfluidparticles.Ifdyewereinjectedintotheflow,itwouldmixtheneighboringfluidexceptbyactivity;itwouldidentityforarelativelylongperiodtime.shearaflow.flowmaybehighlytimedependentbesteady.層33黏性流動可分層流和流層流中流體流體質(zhì)顯的混如在流動注入染料了分子運動的影響外流質(zhì)點不與周圍體混合并將相的段時內(nèi)保持其狀黏切應(yīng)力始終影響層流是高度非定常的也可以定常。Inaflowfluidveryirregularlysuchasvelocityandshowarandomwithtimeandcoordinates.ThephyquantitiesaredescribedbyInthissensecan“”turbulentflow:flowinwhichthetime-averagesicalquantitieschangeinAeinjectedintowouldmixbytheactiontherandomlymovingparticles;itwouldloseitsidentitydiffusionAlaminarflowandflowobservedbyperformingasimpleexperimentawaterfaucet.TurnthefaucetsoflowsoutveryslowlyassilentThislaminarthefaucetslowlyandflowbecomingturbulent.Noteaturbulentflowwithrelativelysmallflow紊流流體運作不規(guī)則地變化速度和壓強等參數(shù)的大小時間和空坐標(biāo)上呈現(xiàn)隨機變化些物往均值來描這義上定“定?！蔽闪鳎杭淳挡浑S時變化的紊流入流的染在流質(zhì)隨機運動的用下速周圍流進行混料在此擴散過程中很快就會消散而變得無法識別流和流用個水龍頭進行簡單實驗來觀察其流動狀態(tài)開水龍頭時的流如靜靜的小一樣流動得常緩慢此的流動狀態(tài)就是流；慢慢大水龍頭觀到動漸得紊亂。注意，紊流從相對小的流量下開始展而成。flowdependsphysicaldescribingtheTheislengththeflowfield,thethicknessoflayerorthediameterIfisflowmaytheflowmaybeparameterisaspatialaverageofthe;forenoughflowturbulent.parameteriskineticviscosity;forasmallviscosityflowmayturbulent.流動狀態(tài)依賴于個描述流動條件物理參數(shù)第一個參數(shù)是流場的特征長度如邊層厚或道徑如果這個特征長度尺度夠大動中的擾動可會逐漸增大從使33動。crit動動。crit動如動critT得動變紊流第二個參是特征速度如空平流速足夠大流速將導(dǎo)致紊的產(chǎn)生第個數(shù)運黏，流的性小紊的能越大。threebeintosingleparameterastooltopredictflowThisquantityisReynoldsnamedafterOsborneaparameter,asRe=VL/ν,LandVarelengthνisthekinematic.Ifrelativelysmall，theisifitlarge,flowisturbulent.Thisbydefiningacriticalnumber,RethattheflowislaminariftheminimumcriticalReynoldsnumberisusedapplications.Iftheissmoothandvibration,criticalReynoldsnumberbelevelflowisdecreased;incessofcriticalReynoldsnumberisdifferentgeometry,e.g.itflowparallelusingaveragevelocityand上述三個參數(shù)可以整理成一個參數(shù)用預(yù)測流動狀態(tài)這個參就是雷諾數(shù)以斯本字名該數(shù)無綱數(shù)，義為/中，L和V分別為特長度和征速度度如管中L為徑，V為平均。雷數(shù)相對較，流雷諾數(shù)較大則紊流界雷諾數(shù)，可更精確地進表，Re<Re，流。流≈2000這是低的臨界雷諾數(shù)并適于大多數(shù)工程用如果管壁極為光滑且振動由流中脈動平減而臨雷數(shù)可增，經(jīng)測以的臨界值。采不同的特尺寸計算所得臨界雷諾數(shù)將有所不同如平均速度和平板之間的距離計算得到的平行板間流動臨界雷數(shù)為1500。Inboundarylayeristaflatduetoaconstant-velocityfluidstream,thelengthscalewithfromupstreamedge.Anoldsiscalculatedlengthxacertainx,Reand教材頁transitionfromlaminarturbulent.inuniformflowafluctuationlevel,valuesasRe=106Inweassumeroughwall,or33TcritTcrithighlevel,withannumberofapproximately×5.對于平板上的邊界層，由于來流為均勻來流，其特征長度隨到前緣點的離而化計雷諾數(shù)時采用長作特征長度在某一特定x下變，流動從層流過渡紊流處于均勻流中的光滑剛性平板且由來流的脈動水平較低時已觀的界雷數(shù)高達10。多數(shù)應(yīng)用中常假面為壁面者自的脈水平較時，應(yīng)臨界雷諾數(shù)為105。1.2.7IncompressibleandcompressibleAnincompressibleflowexistsifthefluidparticlerelativelyitmovesthroughtheflowfield,thatis,D/Dt=0.Thisdoesnotdemandthatisconstant.Ifthedensityisconstant,theflowisincompressible,butthatflow,inwhichρ=(z),height,andthatinvolveadjacentofandsaltashappensriversentertheocean,examplesofincompressibleinvaries.1.2.7不如果任流體質(zhì)點在通流場時密度保持相恒定即t則該流動可縮流并要求處的度均相等如果場中處的度均相明顯流是不壓縮的那是一更加嚴(yán)的況密度發(fā)生變化的不壓縮流的例子大氣流動，為垂直方向坐標(biāo)，以及江河入海洋時淡水與鹽水相鄰的分層流。Inflows,flows,flowtoabove,arealsonamedafteriswhereVthespeedandthespeedc=(κ0.5

.IfM<0.3,densityvariationare3%flowistoincompressible;standardthisaaboutIfdensityinfluencetheflowandcompressibilityeffectsshouldaccountedfor;are除液流動外速流被不縮例上文提到的大氣動馬赫數(shù)恩斯名字命名為M=V/是流速播為

c

。如＜0.3度最變化3%時可為縮標(biāo)態(tài)大，這種情況對應(yīng)氣體流低100。如果M，度變化影響動，必考33流體縮帶的響這的流就可縮動。Incompressiblegasflowsatmosphericflows,ofofcommercialandairflows,flowthroughandflowoftonameflowstheaerodynamicsofhigh-speedairflowthroughjetflowthroughtheturbineaplant,acompressor,flowairgastureinancombustionengine.不可壓的氣體流動包大氣流動用飛機著陸和起飛時的氣體流動暖和空調(diào)系統(tǒng)中的流繞流汽車周圍的流動通過散熱器氣流以及繞流建筑的氣體流動等不勝枚壓縮流動括高速行周圍的體動通過噴氣式發(fā)動機的氣體流動電中過汽輪機的蒸汽流動，壓縮機中的氣體流動以及內(nèi)燃機中空氣和燃氣混合物的流動。ndamentalsofHeatissciencethatseekstopredictenergytransfermaytakeplacematerialasaofdifference.Thermodyteachestransferisscienceoftransferseeksmerelyplainalsoproducttherateatwhichtheexwilltakeplacecertainspecifiedconditions.Thefactaheat-transferrateistheofanalythedifferenceheatandthermodynamics.Thermodydealswithsyequilibrium;itmaytopredictofenergyrequiredstemfromitmaynotpredicthowfastawilltakeplacesincethestemisnotequilibriumduringtheprocess.Heatsupplementsthefirstofthermodybyprovidingexrulesmaybeusedestablishenergy教材11頁transferrate.Hereweofheatdifferenttypesofchanger.傳熱學(xué)是一門研究在存在溫差物體間發(fā)生能量傳遞的科學(xué)學(xué)這式遞的能量定義為量熱學(xué)不僅可以解熱傳遞是何傳遞且可以算在特定條件下傳熱速率實傳熱速正一個析期的目標(biāo)它指了傳熱學(xué)熱學(xué)33的差熱力學(xué)處理的是平衡狀態(tài)下的系統(tǒng)計當(dāng)系統(tǒng)一個平衡狀態(tài)過到另一個平衡狀時所需要的能不能決統(tǒng)處過渡程的平衡態(tài)時量變的快程度熱提供了用計算傳熱速率實驗關(guān)式對熱力第一定律和第二定律進行補充。這里，們介紹熱量傳遞三種方和不同型的換熱器。ConductionWhenagradientaexperienceshownthatthereistransferfromreg