第六章-水和水蒸气的性质课件

Chapter6.ThepropertyofWaterandVapor

(第6章.水和水蒸气的性质)6.1Basicconceptions(基本概念)6.2PhasechangeProcessofPureSubstance(纯质的相变过程)6.3PropertyTables(水蒸气性质表)6.4h-sdiagramsforWaterVapor(水蒸气的h-s图)6.5ThermodynamicProcessesofWaterVapor(水蒸气的热力过程)Chapter6.ThepropertyofW1水和水蒸气是实际气体的代表水蒸气在空气中含量极小，当作理想气体一般情况下，为实际气体，使用图表18世纪，蒸气机的发明，是唯一工质直到内燃机发明，才有燃气工质目前仍是火力发电、核电、供暖、化工的工质优点:便宜，易得，无毒，膨胀性能好，传热性能好是其它实际气体的代表水和水蒸气是实际气体的代表水蒸气在空气中含量极小，当作理想气2§6-1纯物质的热力学面及相图物质三种聚集状态：固态、液态、

气态水的三态：冰、

水、

蒸汽Puresubstance

Solid

Liquid

Gas

Ice

Water

Steam

§6-1纯物质的热力学面及相图物质三种聚集状态：3

任何一种物质都可以经历下列所述的相变.Anykindofsubstancemayundergovarioustypesofphasechangesasfollowing:

溶解(Fusion/melting)=solidtoliquid凝固(Freezing)=liquidtosolid气化(Vaporization)=liquidtogas凝结(Condensation)=gastoliquid升华(Sublimation)=solidtogasPhasechanges(相变):任何一种物质都可以经历下列所述的相变.Phasec4纯物质的p-T相图ppTT液液气气固固水一般物质三相点三相点临界点临界点流体流体升华线升华线融解线融解线汽化线汽化线纯物质的p-T相图ppTT液液气气固固水一般物质三相点三相点5p-Tdiagram

ofpuresubstancespTLiquidVaporSolidTriplepointCriticalpointFluidSublimationMeltingVaporizationp-Tdiagramofpuresubstances6Thesublimationline

separatesthesolidandvaporregions;Thevaporizationlineseparatestheliquidandvaporregions;itendsatthecriticalpoint.Themeltinglineseparatesthesolidandliquidregions;Thethreelinesmeetatthetriplepoint.Triplepoint(三相点）：allthreephasescoexistinequilibrium.(三种相态以平衡共存)Criticalpoint(临界点):

Thepointatwhichthesaturatedliquidandsaturatedvaporstatesareidentical.

Nodistinctioncanbemadebetweenliquidandvaporphasesabovethecriticalpoint.(临界点就是气相与液相一致的状态点,温度高于临界点之上,气相与液相没有明显的区别)

Thesublimationlineseparate7临界点Criticalpoint水的临界点状态饱和液线与饱和气线的交点气液两相共存的pmax,Tmax等温线是鞍点临界点临界点Criticalpoint水的临界点状态饱和液线与8思考题3.有没有500ºC的水？1.溜冰冰刀2.北方冬天晾在外边的衣服，是否经过液相4.有没有-3℃的蒸汽？5.一密闭容器内有水的汽液混合物，对其加热，是否一定能变成蒸汽？思考题3.有没有500ºC的水？1.溜冰9复习：纯物质的p-T相图ppTT液液气气固固水一般物质三相点三相点临界点临界点流体流体SubstancesthatexpandandcontractonfreezingdifferonlyinthemeltinglineontheP-Tdiagram.复习：纯物质的p-T相图ppTT液液气气固固水一般物质三相点10饱和线、三相线和临界点pv饱和气线三相线饱和液线饱和固线T临界点饱和线、三相线和临界点pv饱和气线三相线饱和液线饱和固线T临11VaporandLiquid(汽相和液相)锅炉汽轮机发电机给水泵凝汽器过热器因固相不流动，更关心汽液两相冰蓄冷VaporandLiquid(汽相和液相)锅汽轮机发电12§6-2汽化与饱和气化(Vaporization):

由液态变成气态的物理过程(不涉及化学变化)TheProcessof

Changingfromliquidintogas/vaporiscalled

vaporization.

凝结(Condensation)：

由气态变成液态的物理过程

Theprocessofchangingfromgas/vaporintoliquidiscalled

Condensation6.2.1汽化与凝结

§6-2汽化与饱和气化(Vaporization):凝结13Therateofcondensationdependsuponthedensityofvaporinthespaceabovetheliquid.(凝结的速率取决于液面上方气相空间气体分子的密度,即蒸气压力)Liquidmoleculehastoovercomethesurfacetensiontobecomevapor,thereforevaporizationconsumesenergy.(液相分子必须克服表面张力才能进入气相空间而气化,因此气化是要耗能的)TherateofVaporizationdependsontheliquidtemperature.(气化的速率取决于液相的温度)第六章-水和水蒸气的性质ppt课件14TheequilibriumiscalledSaturationState.(饱和状态）

Thepropertiesatthisstateiscalled

SaturationProperties.(饱和参数）TheequilibriumiscalledSatu156.2.2饱和状态Saturationstate饱和状态：汽化与凝结的动态平衡Attheequilibriumstate,thepressurecorrespondingtoonlyonetemperature.Thatis,.饱和温度Ts饱和压力ps一一对应放掉一些水，Ts不变，ps？TspsSaturationtemperatureSaturationpressure6.2.2饱和状态Saturationstate饱和状态16ps=1.01325barTs=100

℃青藏ps=0.6barTs=85.95℃高压锅ps=1.6barTs=113.32℃Thereisadefiniterelationbetween.ps=1.01325barTs=100℃青藏ps=0.6b176.2.3汽化Vaporization沸腾：表面和液体内部同时发生的汽化Itisanintensivevaporizationphenomenonoccursintheliquid.(气体和液体均处在饱和状态下)汽化:由液态变成气态的物理过程(不涉及化学变化)

蒸发：汽液表面上的汽化Itoccursabovethefreesurfaceofliquid

BoilEvaporation6.2.3汽化Vaporization沸腾：表面和液体18Evaporation

occursatanytemperatureandpressure.（蒸发可在任何温度和压力下发生．）Evaporationratedependsonthefreesurfacearea,thetemperature,theflowrateabove,etc.（蒸发的速度与自由液面表面积，液体温度，液面风速等有关．Boiling

canonlyoccurastemperaturereachesthesaturationtemperaturecorrespondingtothespecifiedpressureorthepressuredropsbelowthesaturationpressurecorrespondingtothespecifiedtemperature.（沸腾只能当温度达到给定压力所对应的饱和温度或压力降到给定温度所对应的饱和压力时,才能发生)第六章-水和水蒸气的性质ppt课件19§6-3水蒸气的定压发生过程t<tst=tst=tst=tst>tsv<v’v=v’v=v’’v’<v<v’’v>v’’未饱和水饱和水饱和湿蒸汽饱和干蒸汽过热蒸汽h<h’h=h’h=h’’h’<h<h’’h>h’’s<s’s=s’s=s’’s’<s<s’’s>s’’水预热汽化过热6.3.1P=constant(压力p是定值)§6-3水蒸气的定压发生过程t<tst=tst=20PreheatStage(预热阶段)CompressedliquidtoSaturatedliquid.(未饱和液体饱和液体)Compressedliquid/subcooledliquidisnotabouttovaporization.Asheatadded,tslightly.WhenItbecomesSaturatedliquid.

Theliquidisabouttovaporize.Itisthestateatwhichitisstillaliquid,butanyheatadditionwillcausesomeoftheliquidtovaporize.PreheatStage(预热阶段)21VaporizationStage(气化阶段)SaturatedliquidtoSaturatedvapor(饱和液体饱和蒸气)Saturatedvapor

isavaporabouttocondense.AsubstanceatstatebetweenSaturatedliquidandSaturatedVaporiscalledSaturatedliquid-vapormixture/wetvapor.

LatentheatofVaporization(气化潜热):TheamountofenergyabsorbedduringvaporizationVaporizationStage(气化阶段)22SuperheatStage(过热阶段)Superheatedvapor

isthevaporthatisnotabouttocondense.

tSuperheatStage(过热阶段)t23注意：水蒸气定压发生过程说明(1)(2)(3)理想气体实际气体汽化时，T＝Ts不变，但h增加汽化潜热(4)未饱和水过冷度过冷水过热蒸汽过热度只有熵加热时永远增加注意：水蒸气定压发生过程说明(1)(2)(3)理想气体实24StateofLiquidandvapor未饱和液，过冷液饱和液饱和湿蒸气饱和蒸气过热蒸气SaturatedliquidSaturatedvaporSaturatedliquid-vapormixtureSuperheatedvaporCompressed

liquidSubcooledliquid汽化潜热LatentheatofVaporization压缩液6.3.2

定压气化过程的P-v图和T-s图P-vandT-sdiagramsStateofLiquidandvapor未饱和液，25sp-v图，T-s图上的水蒸气定压加热过程一点，二线，三区，五态sp-v图，T-s图上的水蒸气定压加热过程一点，二线，三区，26Saturatedliquidline,SLL

isformedbyconnectingaseriesofboilingpoints.

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

Thestateofsubstancebetweensaturatedliquidanddryvaporiscalledwetvapor.

Furtherheatingofadrysaturatedvaporatconstantpressurecausesariseofvaportemperatureanditbecomessuperheatedvapor.Thestateofsubstanceiscompletelydefinedbyitspressureandtemperatureifitisinliquidorsuperheatedvaporphase.Saturatedliquidline,SLLis27vv28Onepoint(一点):criticalpoint(临界点)Twolines(两线):SLLandSVL(饱和液体线和饱和蒸气线)Threeregions(三区):Subcooledliquidregion(未饱和液体区)Saturatedliquid-vapormixture region(湿蒸气区)Superheatedvaporregion(过热蒸气区)Fivestates(五态):Subcooledliquid(未饱和液体)Saturatedliquid(饱和液体)Saturatedliquid-vapormixture(湿蒸气)Saturatedvapor(干饱和蒸气)Superheatedvapor(过热蒸气)Onepoint(一点):criticalpoint29

6.4.1

TypesofPropertyTables(水蒸汽表的分类)

1.SaturatedwaterTables(饱和水和饱和蒸汽表)Saturatedwater---TTables(以温度t为独立变量排列)Saturatedwater---pTables(以压力p为独立变量排列)2.SubcooledwaterandSuperheatedvaporTable(未饱和水和过热水蒸汽表)Pandtaredependentvariables(以p和t为自变量)§6.4水蒸气性质表PropertyTablesofWaterVapor6.4.1TypesofPropertyTable30

2、ReferenceStateandReferenceValues(基准点的规定)Forwater,thesaturatedliquidat0.01℃istakenasreferencestate.(取水的三相点，即0.01oC为基准点，规定在此温度下液态水的热力学能和熵为零。)

Theinternalenergyandentropyareassignedzero

atthisstate.

313.PropertiesofSaturatedliquid-vapormixtureatPressurep(压力为p的湿饱和蒸汽)

Thestateofwetvaporcannotbedefinedbyjustpressureandtemperatureuntiloneotherpropertyisgiven.Theconditionorqualityofwetvaporisoftendefinedbyitsdrynessorwetnessfraction.定义干度x才可以确定湿蒸汽的状态。Wedefinedrynessas

drynessfraction,x=themassofdryvaporin1kgofthemixture,

wetnessfraction,1-x=themassofliquidin1kgofthemixture.3.PropertiesofSaturatedliq32

第六章-水和水蒸气的性质ppt课件33第六章-水和水蒸气的性质ppt课件34注意:饱和表的起始点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:饱和表的起始点ptsv’(m3/kg)v’’s’s’’35第六章-水和水蒸气的性质ppt课件364.Exercise.Consultingpropertytablesofwatervaportodeterminethestateofeachpointandtheirh，s，x.(利用水蒸气表判断下列各点的状态，并确定其h，s，x的值。)

4.Exercise.Consultingprope37（1）由饱和水和饱和蒸汽表查得

p=2MPa时，显然，可知该状态为过热蒸汽。查未饱和水过热蒸汽表，得p=2MPa，t=300℃时对于过热蒸汽，干度x无意义。（1）由饱和水和饱和蒸汽表查得

p=2MPa时，38（2）查饱和表得p=9MPa时可见，

该状态为湿蒸汽，其干度为

又查饱和表得（2）查饱和表得p=9MPa时39=2489.0kJ/kg

按湿蒸汽的参数计算式得=2489.0kJ/kg

按湿蒸汽的参数计算式得40

(3)显然，该状态为湿蒸汽状态。由已知参数查饱和水和饱和蒸汽表得

按湿蒸汽的参数计算公式得

41（4）由饱和水和饱和蒸汽表查得:当p=1.0MPa时，ts=179.9℃，显然t<ts，所以该状态为未饱和水。通常t=175℃的状态参数可利用t=170℃与t=180℃的对应状态参数内插得到，但此处t=170℃与t=180℃跨越了未饱和表中的黑粗线，说明它们分别处于不同相区。应使内插在未饱和水区内进行，选取离最接近的t=170℃与ts=179.9℃的未饱和水参数内插。

查未饱和水和过热蒸汽表得

p=1.0MPa，t=170℃时

p=1.0MPa，t=179.9℃时

（4）由饱和水和饱和蒸汽表查得:当p=1.0MPa时，ts=42于是t=175℃时

对于未饱和水干度x无意义。

于是t=175℃时对于未饱和水干度x无意义。43（5）

时，饱和蒸汽比体积

，该状态为过热蒸汽。查过热蒸汽表得

t=260℃时，

,t=270℃时，

该状态的温度可由比体积值求得

（5）

时，饱和蒸汽比44讨论

应该注意，在利用未饱和水与过热蒸汽作内插时，不允许跨越表中的粗折线，如遇这种情况，应选用更详细的表，或使内插计算在未饱和水（或过热蒸汽）区内进行。

讨论

应该注意，在利用未饱和水与过热蒸汽作内插时，不允许跨越45 §6.5h-sdiagramofwatervapor

(水蒸汽的h-s图)SLLandSVL(界限曲线，x=0、x=1两条曲线)2.ConstantPressureLineandConstantTemperatureLine(定压线和定温线)InSaturatedliquid-vaporregion,constantpressurelineandconstanttemperaturelineareidentical.(在湿蒸汽区定压线与定温线重合。)3.ConstantVolumeLine（定容线。)4.ConstantDrynessLine(定干度线。)GivenTwoProperties,alltheotherstatepropertiescanbedeterminedfromtheDiagram.(给定两个参数，即可查出其余全部参数)。

§6.5h-sdiagramofwaterva46Priorities(优点)：Fastandconvenient.方便、快速。Drawbacks(缺点)：NotsoaccurateasPropertytables精确性稍差。

。47第六章-水和水蒸气的性质ppt课件48s(kJ/kg*K)h(kJ/kg)s(kJ/kg*K)h(kJ/kg)496.6.1Characteristicsofwatervapor(水蒸汽的特点)1.Watervaporcannotbetreatedasidealgas(水蒸汽不是理想气体)pv=RTisnotsuitable.（理想气体状态方程不适用。）2.AnalysisandCalculationonWatervaporcanbesolvedbyusingTablesandDiagrams(水蒸汽的分析和计算采用水蒸汽图和表。)3.TheFirstandtheSecondLawsmustbeobeyedduringprocessesofwatervapor(热力学第一定律和第二定律成立)§6.6ThermodynamicProcessesofWaterVapor(水蒸气的热力过程)6.6.1Characteristicsofwater50

Forreversibleprocesses,(对于可逆过程：)Forreversibleprocesses,516.6.2Procedures(步骤)(1)Basedo