水和水蒸氣的性質(zhì)課件

Chapter6.ThepropertyofWaterandVapor

(第6章.水和水蒸氣的性質(zhì))6.1Basicconceptions(基本概念)6.2PhasechangeProcessofPureSubstance(純質(zhì)的相變過程)6.3PropertyTables(水蒸氣性質(zhì)表)6.4h-sdiagramsforWaterVapor(水蒸氣的h-s圖)6.5ThermodynamicProcessesofWaterVapor(水蒸氣的熱力過程)Chapter6.ThepropertyofW1水和水蒸氣是實(shí)際氣體的代表水蒸氣在空氣中含量極小，當(dāng)作理想氣體一般情況下，為實(shí)際氣體，使用圖表18世紀(jì)，蒸氣機(jī)的發(fā)明，是唯一工質(zhì)直到內(nèi)燃機(jī)發(fā)明，才有燃?xì)夤べ|(zhì)目前仍是火力發(fā)電、核電、供暖、化工的工質(zhì)優(yōu)點(diǎn):便宜，易得，無毒，膨脹性能好，傳熱性能好是其它實(shí)際氣體的代表水和水蒸氣是實(shí)際氣體的代表水蒸氣在空氣中含量極小，當(dāng)作理想氣2§6-1純物質(zhì)的熱力學(xué)面及相圖物質(zhì)三種聚集狀態(tài)：固態(tài)、液態(tài)、

氣態(tài)水的三態(tài)：冰、

水、

蒸汽Puresubstance

Solid

Liquid

Gas

Ice

Water

Steam

§6-1純物質(zhì)的熱力學(xué)面及相圖物質(zhì)三種聚集狀態(tài)：3

任何一種物質(zhì)都可以經(jīng)歷下列所述的相變.Anykindofsubstancemayundergovarioustypesofphasechangesasfollowing:

溶解(Fusion/melting)=solidtoliquid凝固(Freezing)=liquidtosolid氣化(Vaporization)=liquidtogas凝結(jié)(Condensation)=gastoliquid升華(Sublimation)=solidtogasPhasechanges(相變):任何一種物質(zhì)都可以經(jīng)歷下列所述的相變.Phasec4純物質(zhì)的p-T相圖ppTT液液氣氣固固水一般物質(zhì)三相點(diǎn)三相點(diǎn)臨界點(diǎn)臨界點(diǎn)流體流體升華線升華線融解線融解線汽化線汽化線純物質(zhì)的p-T相圖ppTT液液氣氣固固水一般物質(zhì)三相點(diǎn)三相點(diǎn)5p-Tdiagram

ofpuresubstancespTLiquidVaporSolidTriplepointCriticalpointFluidSublimationMeltingVaporizationp-Tdiagramofpuresubstances6Thesublimationline

separatesthesolidandvaporregions;Thevaporizationlineseparatestheliquidandvaporregions;itendsatthecriticalpoint.Themeltinglineseparatesthesolidandliquidregions;Thethreelinesmeetatthetriplepoint.Triplepoint(三相點(diǎn)）：allthreephasescoexistinequilibrium.(三種相態(tài)以平衡共存)Criticalpoint(臨界點(diǎn)):

Thepointatwhichthesaturatedliquidandsaturatedvaporstatesareidentical.

Nodistinctioncanbemadebetweenliquidandvaporphasesabovethecriticalpoint.(臨界點(diǎn)就是氣相與液相一致的狀態(tài)點(diǎn),溫度高于臨界點(diǎn)之上,氣相與液相沒有明顯的區(qū)別)

Thesublimationlineseparate7臨界點(diǎn)Criticalpoint水的臨界點(diǎn)狀態(tài)飽和液線與飽和氣線的交點(diǎn)氣液兩相共存的pmax,Tmax等溫線是鞍點(diǎn)臨界點(diǎn)臨界點(diǎn)Criticalpoint水的臨界點(diǎn)狀態(tài)飽和液線與8思考題3.有沒有500oC的水？1.溜冰冰刀2.北方冬天晾在外邊的衣服，是否經(jīng)過液相4.有沒有-3℃的蒸汽？5.一密閉容器內(nèi)有水的汽液混合物，對其加熱，是否一定能變成蒸汽？思考題3.有沒有500oC的水？1.溜冰9復(fù)習(xí)：純物質(zhì)的p-T相圖ppTT液液氣氣固固水一般物質(zhì)三相點(diǎn)三相點(diǎn)臨界點(diǎn)臨界點(diǎn)流體流體SubstancesthatexpandandcontractonfreezingdifferonlyinthemeltinglineontheP-Tdiagram.復(fù)習(xí)：純物質(zhì)的p-T相圖ppTT液液氣氣固固水一般物質(zhì)三相點(diǎn)10飽和線、三相線和臨界點(diǎn)pv飽和氣線三相線飽和液線飽和固線T臨界點(diǎn)飽和線、三相線和臨界點(diǎn)pv飽和氣線三相線飽和液線飽和固線T臨11VaporandLiquid(汽相和液相)鍋爐汽輪機(jī)發(fā)電機(jī)給水泵凝汽器過熱器因固相不流動，更關(guān)心汽液兩相冰蓄冷VaporandLiquid(汽相和液相)鍋汽輪機(jī)發(fā)電12§6-2汽化與飽和氣化(Vaporization):

由液態(tài)變成氣態(tài)的物理過程(不涉及化學(xué)變化)TheProcessof

Changingfromliquidintogas/vaporiscalled

vaporization.

凝結(jié)(Condensation)：

由氣態(tài)變成液態(tài)的物理過程

Theprocessofchangingfromgas/vaporintoliquidiscalled

Condensation6.2.1汽化與凝結(jié)

§6-2汽化與飽和氣化(Vaporization):凝結(jié)13Therateofcondensationdependsuponthedensityofvaporinthespaceabovetheliquid.(凝結(jié)的速率取決于液面上方氣相空間氣體分子的密度,即蒸氣壓力)Liquidmoleculehastoovercomethesurfacetensiontobecomevapor,thereforevaporizationconsumesenergy.(液相分子必須克服表面張力才能進(jìn)入氣相空間而氣化,因此氣化是要耗能的)TherateofVaporizationdependsontheliquidtemperature.(氣化的速率取決于液相的溫度)第六章水和水蒸氣的性質(zhì)課件14TheequilibriumiscalledSaturationState.(飽和狀態(tài)）

Thepropertiesatthisstateiscalled

SaturationProperties.(飽和參數(shù)）TheequilibriumiscalledSatu156.2.2飽和狀態(tài)Saturationstate飽和狀態(tài)：汽化與凝結(jié)的動態(tài)平衡Attheequilibriumstate,thepressurecorrespondingtoonlyonetemperature.Thatis,.飽和溫度Ts飽和壓力ps一一對應(yīng)放掉一些水，Ts不變，ps？TspsSaturationtemperatureSaturationpressure6.2.2飽和狀態(tài)Saturationstate飽和狀態(tài)16ps=1.01325barTs=100

℃青藏ps=0.6barTs=85.95℃高壓鍋ps=1.6barTs=113.32℃Thereisadefiniterelationbetween.ps=1.01325barTs=100℃青藏ps=0.6b176.2.3汽化Vaporization沸騰：表面和液體內(nèi)部同時發(fā)生的汽化Itisanintensivevaporizationphenomenonoccursintheliquid.(氣體和液體均處在飽和狀態(tài)下)汽化:由液態(tài)變成氣態(tài)的物理過程(不涉及化學(xué)變化)

蒸發(fā)：汽液表面上的汽化Itoccursabovethefreesurfaceofliquid

BoilEvaporation6.2.3汽化Vaporization沸騰：表面和液體18Evaporation

occursatanytemperatureandpressure.（蒸發(fā)可在任何溫度和壓力下發(fā)生．）Evaporationratedependsonthefreesurfacearea,thetemperature,theflowrateabove,etc.（蒸發(fā)的速度與自由液面表面積，液體溫度，液面風(fēng)速等有關(guān)．Boiling

canonlyoccurastemperaturereachesthesaturationtemperaturecorrespondingtothespecifiedpressureorthepressuredropsbelowthesaturationpressurecorrespondingtothespecifiedtemperature.（沸騰只能當(dāng)溫度達(dá)到給定壓力所對應(yīng)的飽和溫度或壓力降到給定溫度所對應(yīng)的飽和壓力時,才能發(fā)生)第六章水和水蒸氣的性質(zhì)課件19§6-3水蒸氣的定壓發(fā)生過程t<tst=tst=tst=tst>tsv<v’v=v’v=v’’v’<v<v’’v>v’’未飽和水飽和水飽和濕蒸汽飽和干蒸汽過熱蒸汽h<h’h=h’h=h’’h’<h<h’’h>h’’s<s’s=s’s=s’’s’<s<s’’s>s’’水預(yù)熱汽化過熱6.3.1P=constant(壓力p是定值)§6-3水蒸氣的定壓發(fā)生過程t<tst=tst=20PreheatStage(預(yù)熱階段)CompressedliquidtoSaturatedliquid.(未飽和液體飽和液體)Compressedliquid/subcooledliquidisnotabouttovaporization.Asheatadded,tslightly.WhenItbecomesSaturatedliquid.

Theliquidisabouttovaporize.Itisthestateatwhichitisstillaliquid,butanyheatadditionwillcausesomeoftheliquidtovaporize.PreheatStage(預(yù)熱階段)21VaporizationStage(氣化階段)SaturatedliquidtoSaturatedvapor(飽和液體飽和蒸氣)Saturatedvapor

isavaporabouttocondense.AsubstanceatstatebetweenSaturatedliquidandSaturatedVaporiscalledSaturatedliquid-vapormixture/wetvapor.

LatentheatofVaporization(氣化潛熱):TheamountofenergyabsorbedduringvaporizationVaporizationStage(氣化階段)22SuperheatStage(過熱階段)Superheatedvapor

isthevaporthatisnotabouttocondense.

tSuperheatStage(過熱階段)t23注意：水蒸氣定壓發(fā)生過程說明(1)(2)(3)理想氣體實(shí)際氣體汽化時，T＝Ts不變，但h增加汽化潛熱(4)未飽和水過冷度過冷水過熱蒸汽過熱度只有熵加熱時永遠(yuǎn)增加注意：水蒸氣定壓發(fā)生過程說明(1)(2)(3)理想氣體實(shí)24StateofLiquidandvapor未飽和液，過冷液飽和液飽和濕蒸氣飽和蒸氣過熱蒸氣SaturatedliquidSaturatedvaporSaturatedliquid-vapormixtureSuperheatedvaporCompressed

liquidSubcooledliquid汽化潛熱LatentheatofVaporization壓縮液6.3.2

定壓氣化過程的P-v圖和T-s圖P-vandT-sdiagramsStateofLiquidandvapor未飽和液，25sp-v圖，T-s圖上的水蒸氣定壓加熱過程一點(diǎn)，二線，三區(qū)，五態(tài)sp-v圖，T-s圖上的水蒸氣定壓加熱過程一點(diǎn)，二線，三區(qū)，26Saturatedliquidline,SLL

isformedbyconnectingaseriesofboilingpoints.

saturatedvaporline,SVL：Connectingaseriesofpointsatdrysaturatedvaporbuildsaline,knownassaturatedvaporline,SVL.Vaporizationcontinuesbyfurtherheatsupplytothesystemuntilnoliquidisleft.Thisstateisknownasdrysaturatedvapor,e.g.pointd.Ifthesystemisslightlycooledatthisstate,thendropletsofliquidwillbegintoform.

Thestateofsubstancebetweensaturatedliquidanddryvaporiscalledwetvapor.

Furtherheatingofadrysaturatedvaporatconstantpressurecausesariseofvaportemperatureanditbecomessuperheatedvapor.Thestateofsubstanceiscompletelydefinedbyitspressureandtemperatureifitisinliquidorsuperheatedvaporphase.Saturatedliquidline,SLLis27vv28Onepoint(一點(diǎn)):criticalpoint(臨界點(diǎn))Twolines(兩線):SLLandSVL(飽和液體線和飽和蒸氣線)Threeregions(三區(qū)):Subcooledliquidregion(未飽和液體區(qū))Saturatedliquid-vapormixture region(濕蒸氣區(qū))Superheatedvaporregion(過熱蒸氣區(qū))Fivestates(五態(tài)):Subcooledliquid(未飽和液體)Saturatedliquid(飽和液體)Saturatedliquid-vapormixture(濕蒸氣)Saturatedvapor(干飽和蒸氣)Superheatedvapor(過熱蒸氣)Onepoint(一點(diǎn)):criticalpoint29

6.4.1

TypesofPropertyTables(水蒸汽表的分類)

1.SaturatedwaterTables(飽和水和飽和蒸汽表)Saturatedwater---TTables(以溫度t為獨(dú)立變量排列)Saturatedwater---pTables(以壓力p為獨(dú)立變量排列)2.SubcooledwaterandSuperheatedvaporTable(未飽和水和過熱水蒸汽表)Pandtaredependentvariables(以p和t為自變量)§6.4水蒸氣性質(zhì)表PropertyTablesofWaterVapor6.4.1TypesofPropertyTable30

2、ReferenceStateandReferenceValues(基準(zhǔn)點(diǎn)的規(guī)定)Forwater,thesaturatedliquidat0.01℃istakenasreferencestate.(取水的三相點(diǎn)，即0.01oC為基準(zhǔn)點(diǎn)，規(guī)定在此溫度下液態(tài)水的熱力學(xué)能和熵為零。)

Theinternalenergyandentropyareassignedzero

atthisstate.

313.PropertiesofSaturatedliquid-vapormixtureatPressurep(壓力為p的濕飽和蒸汽)

Thestateofwetvaporcannotbedefinedbyjustpressureandtemperatureuntiloneotherpropertyisgiven.Theconditionorqualityofwetvaporisoftendefinedbyitsdrynessorwetnessfraction.定義干度x才可以確定濕蒸汽的狀態(tài)。Wedefinedrynessas

drynessfraction,x=themassofdryvaporin1kgofthemixture,

wetnessfraction,1-x=themassofliquidin1kgofthemixture.3.PropertiesofSaturatedliq32

第六章水和水蒸氣的性質(zhì)課件33第六章水和水蒸氣的性質(zhì)課件34注意:飽和表的起始點(diǎn)ptsv’(m3/kg)v’’s’s’’kJ/(kg.K)0.0061120.010.00100022206.1750.09.15621.099.630.00104341.69461.30277.36085.0151.850.00109280.374811.86046.821550.0263.920.00128580.039412.92095.9712221.29374.150.003260.003264.4294.429(bar)(℃)bdbd注意:飽和表的起始點(diǎn)ptsv’(m3/kg)v’’s’s’’35第六章水和水蒸氣的性質(zhì)課件364.Exercise.Consultingpropertytablesofwatervaportodeterminethestateofeachpointandtheirh，s，x.(利用水蒸氣表判斷下列各點(diǎn)的狀態(tài)，并確定其h，s，x的值。)

4.Exercise.Consultingprope37（1）由飽和水和飽和蒸汽表查得

p=2MPa時，顯然，可知該狀態(tài)為過熱蒸汽。查未飽和水過熱蒸汽表，得p=2MPa，t=300℃時對于過熱蒸汽，干度x無意義。（1）由飽和水和飽和蒸汽表查得

p=2MPa時，38（2）查飽和表得p=9MPa時可見，

該狀態(tài)為濕蒸汽，其干度為

又查飽和表得（2）查飽和表得p=9MPa時39=2489.0kJ/kg

按濕蒸汽的參數(shù)計(jì)算式得=2489.0kJ/kg

按濕蒸汽的參數(shù)計(jì)算式得40

(3)顯然，該狀態(tài)為濕蒸汽狀態(tài)。由已知參數(shù)查飽和水和飽和蒸汽表得

按濕蒸汽的參數(shù)計(jì)算公式得

41（4）由飽和水和飽和蒸汽表查得:當(dāng)p=1.0MPa時，ts=179.9℃，顯然t<ts，所以該狀態(tài)為未飽和水。通常t=175℃的狀態(tài)參數(shù)可利用t=170℃與t=180℃的對應(yīng)狀態(tài)參數(shù)內(nèi)插得到，但此處t=170℃與t=180℃跨越了未飽和表中的黑粗線，說明它們分別處于不同相區(qū)。應(yīng)使內(nèi)插在未飽和水區(qū)內(nèi)進(jìn)行，選取離最接近的t=170℃與ts=179.9℃的未飽和水參數(shù)內(nèi)插。

查未飽和水和過熱蒸汽表得

p=1.0MPa，t=170℃時

p=1.0MPa，t=179.9℃時

（4）由飽和水和飽和蒸汽表查得:當(dāng)p=1.0MPa時，ts=42于是t=175℃時

對于未飽和水干度x無意義。

于是t=175℃時對于未飽和水干度x無意義。43（5）

時，飽和蒸汽比體積

，該狀態(tài)為過熱蒸汽。查過熱蒸汽表得

t=260℃時，

,t=270℃時，

該狀態(tài)的溫度可由比體積值求得

（5）

時，飽和蒸汽比44討論

應(yīng)該注意，在利用未飽和水與過熱蒸汽作內(nèi)插時，不允許跨越表中的粗折線，如遇這種情況，應(yīng)選用更詳細(xì)的表，或使內(nèi)插計(jì)算在未飽和水（或過熱蒸汽）區(qū)內(nèi)進(jìn)行。

討論

應(yīng)該注意，在利用未飽和水與過熱蒸汽作內(nèi)插時，不允許跨越45 §6.5h-sdiagramofwatervapor

(水蒸汽的h-s圖)SLLandSVL(界限曲線，x=0、x=1兩條曲線)2.ConstantPressureLineandConstantTemperatureLine(定壓線和定溫線)InSaturatedliquid-vaporregion,constantpressurelineandconstanttemperaturelineareidentical.(在濕蒸汽區(qū)定壓線與定溫線重合。)3.ConstantVolumeLine（定容線。)4.ConstantDrynessLine(定干度線。)GivenTwoProperties,alltheotherstatepropertiescanbedeterminedfromtheDiagram.(給定兩個參數(shù)，即可查出其余全部參數(shù))。

§6.5h-sdiagramofwaterva46Priorities(優(yōu)點(diǎn))：Fastandconvenient.方便、快速。Drawbacks(缺點(diǎn))：NotsoaccurateasPropertytables精確性稍差。

。47第六章水和水蒸氣的性質(zhì)課件48s(kJ/kg*K)h(kJ/kg)s(kJ/kg*K)h(kJ/kg)496.6.1Characteristicsofwatervapor(水蒸汽的特點(diǎn))1.Watervaporcannotbetreatedasidealgas(水蒸汽不是理想氣體)pv=RTisnotsuitable.（理想氣體狀態(tài)方程不適用。）2.AnalysisandCalculationonWatervaporcanbesolvedbyusingTablesandDiagrams(水蒸汽的分析和計(jì)算采用水蒸汽圖和表。)3.TheFirstandtheSecondLawsmustbeobeyedduringprocessesofwatervapor(熱力學(xué)第一定律和第二定律成立)§6.6ThermodynamicProcessesofWaterVapor(水蒸氣的熱力過程)6.6.1Characteristicsofwater50

Forreversibleprocesses,(對于可逆過程：)Forreversibleprocesses,516.6.2Procedures(步驟)(1)Basedonthegivenconditions,determinetheinitialstateanditsproperties.(根據(jù)已知條件，確定初始狀態(tài)，查出其余參數(shù)。)(2)Basedonthecharacteristicsoftheprocessandoneofthepropertiesofthefinalstate,determinethefinalstateanditsproperties.(根據(jù)過程特點(diǎn)和一個終態(tài)參數(shù)，確定終態(tài)，再查出其余終態(tài)參數(shù)。)(3)Basedontheinitialandfinalstate,calculatetheq、Δu、wduringtheprocess。(根據(jù)初、終態(tài)參數(shù)，計(jì)算q、Δu、w等。)6.6.2Procedures(步驟)526.6.3Basicthermodynamicprocessofwatervapor(水蒸氣的基本熱力過程)(1)ConstantVolumeProcess(定容過程,v=定值。)ConstantvolumeProcess(定容過程)6.6.3Basicthermodynamicproc53(2)ConstantPressureProcess(定壓過程p=定值)Constant

PressureProcess(定壓過程)(2)ConstantPressureProcess54(3)ConstantTemperatureProcess(定溫過程T=定值)Isothermal

Process(定溫過程)(3)ConstantTemperatureProce55(4)AdiabaticProcess(絕熱過程)IsentropicProcess(定熵過程)(4)AdiabaticProcess(絕熱過程)I56Example:1kgwatervapor,initially,℃undertakesanisentropicexpansionprocessandreachesthefinalstateof

Calculatetheamountofworkdonebythewatervaporduringtheprocess.

Answer:Accordingtothevaluesof,theinitialstate1canbedetermined.Fromwatertablesorh-sDiagram,weknowthatthen

Example:57

Frompoint“1”,drawaverticalline,whichwillmeetwiththelineofatpoint“2”,thefinalstateisobtained.Thenfromh-sdiagram,wegettoknowthat第六章水和水蒸氣的性質(zhì)課件58

Chapter6.ThepropertyofWaterandVapor

(第6章.水和水蒸氣的性質(zhì))6.1Basicconceptions(基本概念)6.2PhasechangeProcessofPureSubstance(純質(zhì)的相變過程)6.3PropertyTables(水蒸氣性質(zhì)表)6.4h-sdiagramsforWaterVapor(水蒸氣的h-s圖)6.5ThermodynamicProcessesofWaterVapor(水蒸氣的熱力過程)Chapter6.ThepropertyofW59水和水蒸氣是實(shí)際氣體的代表水蒸氣在空氣中含量極小，當(dāng)作理想氣體一般情況下，為實(shí)際氣體，使用圖表18世紀(jì)，蒸氣機(jī)的發(fā)明，是唯一工質(zhì)直到內(nèi)燃機(jī)發(fā)明，才有燃?xì)夤べ|(zhì)目前仍是火力發(fā)電、核電、供暖、化工的工質(zhì)優(yōu)點(diǎn):便宜，易得，無毒，膨脹性能好，傳熱性能好是其它實(shí)際氣體的代表水和水蒸氣是實(shí)際氣體的代表水蒸氣在空氣中含量極小，當(dāng)作理想氣60§6-1純物質(zhì)的熱力學(xué)面及相圖物質(zhì)三種聚集狀態(tài)：固態(tài)、液態(tài)、

氣態(tài)水的三態(tài)：冰、

水、

蒸汽Puresubstance

Solid

Liquid

Gas

Ice

Water

Steam

§6-1純物質(zhì)的熱力學(xué)面及相圖物質(zhì)三種聚集狀態(tài)：61

任何一種物質(zhì)都可以經(jīng)歷下列所述的相變.Anykindofsubstancemayundergovarioustypesofphasechangesasfollowing:

溶解(Fusion/melting)=solidtoliquid凝固(Freezing)=liquidtosolid氣化(Vaporization)=liquidtogas凝結(jié)(Condensation)=gastoliquid升華(Sublimation)=solidtogasPhasechanges(相變):任何一種物質(zhì)都可以經(jīng)歷下列所述的相變.Phasec62純物質(zhì)的p-T相圖ppTT液液氣氣固固水一般物質(zhì)三相點(diǎn)三相點(diǎn)臨界點(diǎn)臨界點(diǎn)流體流體升華線升華線融解線融解線汽化線汽化線純物質(zhì)的p-T相圖ppTT液液氣氣固固水一般物質(zhì)三相點(diǎn)三相點(diǎn)63p-Tdiagram

ofpuresubstancespTLiquidVaporSolidTriplepointCriticalpointFluidSublimationMeltingVaporizationp-Tdiagramofpuresubstances64Thesublimationline

separatesthesolidandvaporregions;Thevaporizationlineseparatestheliquidandvaporregions;itendsatthecriticalpoint.Themeltinglineseparatesthesolidandliquidregions;Thethreelinesmeetatthetriplepoint.Triplepoint(三相點(diǎn)）：allthreephasescoexistinequilibrium.(三種相態(tài)以平衡共存)Criticalpoint(臨界點(diǎn)):

Thepointatwhichthesaturatedliquidandsaturatedvaporstatesareidentical.

Nodistinctioncanbemadebetweenliquidandvaporphasesabovethecriticalpoint.(臨界點(diǎn)就是氣相與液相一致的狀態(tài)點(diǎn),溫度高于臨界點(diǎn)之上,氣相與液相沒有明顯的區(qū)別)

Thesublimationlineseparate65臨界點(diǎn)Criticalpoint水的臨界點(diǎn)狀態(tài)飽和液線與飽和氣線的交點(diǎn)氣液兩相共存的pmax,Tmax等溫線是鞍點(diǎn)臨界點(diǎn)臨界點(diǎn)Criticalpoint水的臨界點(diǎn)狀態(tài)飽和液線與66思考題3.有沒有500oC的水？1.溜冰冰刀2.北方冬天晾在外邊的衣服，是否經(jīng)過液相4.有沒有-3℃的蒸汽？5.一密閉容器內(nèi)有水的汽液混合物，對其加熱，是否一定能變成蒸汽？思考題3.有沒有500oC的水？1.溜冰67復(fù)習(xí)：純物質(zhì)的p-T相圖ppTT液液氣氣固固水一般物質(zhì)三相點(diǎn)三相點(diǎn)臨界點(diǎn)臨界點(diǎn)流體流體SubstancesthatexpandandcontractonfreezingdifferonlyinthemeltinglineontheP-Tdiagram.復(fù)習(xí)：純物質(zhì)的p-T相圖ppTT液液氣氣固固水一般物質(zhì)三相點(diǎn)68飽和線、三相線和臨界點(diǎn)pv飽和氣線三相線飽和液線飽和固線T臨界點(diǎn)飽和線、三相線和臨界點(diǎn)pv飽和氣線三相線飽和液線飽和固線T臨69VaporandLiquid(汽相和液相)鍋爐汽輪機(jī)發(fā)電機(jī)給水泵凝汽器過熱器因固相不流動，更關(guān)心汽液兩相冰蓄冷VaporandLiquid(汽相和液相)鍋汽輪機(jī)發(fā)電70§6-2汽化與飽和氣化(Vaporization):

由液態(tài)變成氣態(tài)的物理過程(不涉及化學(xué)變化)TheProcessof

Changingfromliquidintogas/vaporiscalled

vaporization.

凝結(jié)(Condensation)：

由氣態(tài)變成液態(tài)的物理過程

Theprocessofchangingfromgas/vaporintoliquidiscalled

Condensation6.2.1汽化與凝結(jié)

§6-2汽化與飽和氣化(Vaporization):凝結(jié)71Therateofcondensationdependsuponthedensityofvaporinthespaceabovetheliquid.(凝結(jié)的速率取決于液面上方氣相空間氣體分子的密度,即蒸氣壓力)Liquidmoleculehastoovercomethesurfacetensiontobecomevapor,thereforevaporizationconsumesenergy.(液相分子必須克服表面張力才能進(jìn)入氣相空間而氣化,因此氣化是要耗能的)TherateofVaporizationdependsontheliquidtemperature.(氣化的速率取決于液相的溫度)第六章水和水蒸氣的性質(zhì)課件72TheequilibriumiscalledSaturationState.(飽和狀態(tài)）

Thepropertiesatthisstateiscalled

SaturationProperties.(飽和參數(shù)）TheequilibriumiscalledSatu736.2.2飽和狀態(tài)Saturationstate飽和狀態(tài)：汽化與凝結(jié)的動態(tài)平衡Attheequilibriumstate,thepressurecorrespondingtoonlyonetemperature.Thatis,.飽和溫度Ts飽和壓力ps一一對應(yīng)放掉一些水，Ts不變，ps？TspsSaturationtemperatureSaturationpressure6.2.2飽和狀態(tài)Saturationstate飽和狀態(tài)74ps=1.01325barTs=100

℃青藏ps=0.6barTs=85.95℃高壓鍋ps=1.6barTs=113.32℃Thereisadefiniterelationbetween.ps=1.01325barTs=100℃青藏ps=0.6b756.2.3汽化Vaporization沸騰：表面和液體內(nèi)部同時發(fā)生的汽化Itisanintensivevaporizationphenomenonoccursintheliquid.(氣體和液體均處在飽和狀態(tài)下)汽化:由液態(tài)變成氣態(tài)的物理過程(不涉及化學(xué)變化)

蒸發(fā)：汽液表面上的汽化Itoccursabovethefreesurfaceofliquid

BoilEvaporation6.2.3汽化Vaporization沸騰：表面和液體76Evaporation

occursatanytemperatureandpressure.（蒸發(fā)可在任何溫度和壓力下發(fā)生．）Evaporationratedependsonthefreesurfacearea,thetemperature,theflowrateabove,etc.（蒸發(fā)的速度與自由液面表面積，液體溫度，液面風(fēng)速等有關(guān)．Boiling

canonlyoccurastemperaturereachesthesaturationtemperaturecorrespondingtothespecifiedpressureorthepressuredropsbelowthesaturationpressurecorrespondingtothespecifiedtemperature.（沸騰只能當(dāng)溫度達(dá)到給定壓力所對應(yīng)的飽和溫度或壓力降到給定溫度所對應(yīng)的飽和壓力時,才能發(fā)生)第六章水和水蒸氣的性質(zhì)課件77§6-3水蒸氣的定壓發(fā)生過程t<tst=tst=tst=tst>tsv<v’v=v’v=v’’v’<v<v’’v>v’’未飽和水飽和水飽和濕蒸汽飽和干蒸汽過熱蒸汽h<h’h=h’h=h’’h’<h<h’’h>h’’s<s’s=s’s=s’’s’<s<s’’s>s’’水預(yù)熱汽化過熱6.3.1P=constant(壓力p是定值)§6-3水蒸氣的定壓發(fā)生過程t<tst=tst=78PreheatStage(預(yù)熱階段)CompressedliquidtoSaturatedliquid.(未飽和液體飽和液體)Compressedliquid/subcooledliquidisnotabouttovaporization.Asheatadded,tslightly.WhenItbecomesSaturatedliquid.

Theliquidisabouttovaporize.Itisthestateatwhichitisstillaliquid,butanyheatadditionwillcausesomeoftheliquidtovaporize.PreheatStage(預(yù)熱階段)79VaporizationStage(氣化階段)SaturatedliquidtoSaturatedvapor(飽和液體飽和蒸氣)Saturatedvapor

isavaporabouttocondense.AsubstanceatstatebetweenSaturatedliquidandSaturatedVaporiscalledSaturatedliquid-vapormixture/wetvapor.

LatentheatofVaporization(氣化潛熱):TheamountofenergyabsorbedduringvaporizationVaporizationStage(氣化階段)80SuperheatStage(過熱階段)Superheatedvapor

isthevaporthatisnotabouttocondense.

tSuperheatStage(過熱階段)t81注意：水蒸氣定壓發(fā)生過程說明(1)(2)(3)理想氣體實(shí)際氣體汽化時，T＝Ts不變，但h增加汽化潛熱(4)未飽和水過冷度過冷水過熱蒸汽過熱度只有熵加熱時永遠(yuǎn)增加注意：水蒸氣定壓發(fā)生過程說明(1)(2)(3)理想氣體實(shí)82StateofLiquidandvapor未飽和液，過冷液飽和液飽和濕蒸氣飽和蒸氣過熱蒸氣SaturatedliquidSaturatedvaporSaturatedliquid-vapormixtureSuperheatedvaporCompressed

liquidSubcooledliquid汽化潛熱LatentheatofVaporization壓縮液6.3.2

定壓氣化過程的P-v圖和T-s圖P-vandT-sdiagramsStateofLiquidandvapor未飽和液，83sp-v圖，T-s圖上的水蒸氣定壓加熱過程一點(diǎn)，二線，三區(qū)，五態(tài)sp-v圖，T-s圖上的水蒸氣定壓加熱過程一點(diǎn)，二線，三區(qū)，84Saturatedliquidline,SLL

isformedbyconnectingaseriesofboilingpoints.

saturatedvaporline,SVL：Connectingaseriesofpointsatdrysaturatedvaporbuildsaline,knownassaturatedvaporline,SVL.Vaporizationcontinuesbyfurtherheatsupplytothesystemuntilnoliquidisleft.Thisstateisknownasdrysaturatedvapor,e.g.pointd.Ifthesystemisslightlycooledatthisstate,thendropletsofliquidwillbegintoform.

Thestateofsubstancebetweensaturatedliquidanddryvaporiscalledwetvapor.

Furtherheatingofadrysaturatedvaporatconstantpressurecausesariseofvaportemperatureanditbecomessuperheatedvapor.Thestateofsubstanceiscompletelydefinedbyitspressureandtemperatureifitisinliquidorsuperheatedvaporphase.Saturatedliquidline,SLLis85vv86Onepoint(一點(diǎn)):criticalpoint(臨界點(diǎn))Twolines(兩線):SLLandSVL(飽和液體線和飽和蒸氣線)Threeregions(三區(qū)):Subcooledliquidregion(未飽和液體區(qū))Saturatedliquid-vapormixture region(濕蒸氣區(qū))Superheatedvaporregion(過熱蒸氣區(qū))Fivestates(五態(tài)):Subcooledliquid(未飽和液體)Saturatedliquid(飽和液體)Saturatedliquid-vapormixture(濕蒸氣)Saturatedvapor(干飽和蒸氣)Superheatedvapor(過熱蒸氣)Onepoint(一點(diǎn)):criticalpoint87

6.4.1

TypesofPropertyTables(水蒸汽表的分類)

1.SaturatedwaterTables(飽和水和飽和蒸汽表)Saturatedwater---TTables(以溫度t為獨(dú)立變量排列)Saturatedwater---pTables(以壓力p為獨(dú)立變量排列)2.SubcooledwaterandSuperheatedvaporTable(未飽和水和過熱水蒸汽表)Pandtaredependentvariables(以p和t為自變量)§6.4水蒸氣性質(zhì)表PropertyTablesofWaterVapor6.4.1TypesofPropertyTable88

2、ReferenceStateandReferenceValues(基準(zhǔn)點(diǎn)的規(guī)定)Forwater,thesaturatedliquidat0.01℃istakenasreferencestate.(取水的三相點(diǎn)，即0.01oC為基準(zhǔn)點(diǎn)，規(guī)定在此溫度下液態(tài)水的熱力學(xué)能和熵為零。)

Theinternalenergyandentropyareassignedzero

atthisstate.

893.PropertiesofSaturatedliquid-vapormixtureatPressurep(壓力為p的濕飽和蒸汽)

Thestateofwetvaporcannotbedefinedbyjustpressureandtemperatureuntiloneotherpropertyisgiven.Theconditionorqualityofwetvaporisoftendefinedbyitsdrynessorwetnessfraction.定義干度x才可以確定濕蒸汽的狀