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1、关于水和水蒸气的性质第1页，讲稿共59张，创作于星期二水和水蒸气是实际气体的代表水和水蒸气是实际气体的代表水蒸气水蒸气在空气中含量极小，当作在空气中含量极小，当作理想气体理想气体一般情况下，为一般情况下，为实际气体实际气体，使用图表，使用图表18世纪，蒸气机的发明，是唯一工质世纪，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、化工的工质目前仍是火力发电、核电、供暖、化工的工质优点优点:便宜，易得，无毒，便宜，易得，无毒，膨胀性能好，传热性能好膨胀性能好，传热性能好是其它实际气体的代表是其它实际气体的代表第2页，讲稿共59张，创作于
2、星期二 6-1 纯物质的热力学面及相图纯物质的热力学面及相图物质三种聚集状态：物质三种聚集状态：固态、固态、液态、液态、气态气态水的三态：水的三态：冰、冰、水、水、蒸汽蒸汽Pure substanceSolidLiquidGasIceWaterSteam第3页，讲稿共59张，创作于星期二 任何一种物质都可以经历下列所述的相变任何一种物质都可以经历下列所述的相变.Any kind of substance may undergo various types of phase changes as following:溶解溶解(Fusion/melting)=solid to liquid 凝固凝
3、固(Freezing)=liquid to solid 气化气化(Vaporization)=liquid to gas 凝结凝结(Condensation)=gas to liquid 升华升华(Sublimation)=solid to gas Phase changes(相变相变):第4页，讲稿共59张，创作于星期二The sublimation line separates the solid and vapor regions;The vaporization line separates the liquid and vapor regions;it ends at the cri
4、tical point.The melting line separates the solid and liquid regions;The three lines meet at the triple point.Triple point(三相点）：三相点）：all three phases coexist in equilibrium.(三种相态以平衡共存三种相态以平衡共存)Critical point(临界点临界点):The point at which the saturated liquid and saturated vapor states are identical.No d
5、istinction can be made between liquid and vapor phases above the critical point.(临界点就是气相与液相一致的状态点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温度高于临界点之上,气相与液气相与液相没有明显的区别相没有明显的区别)第7页，讲稿共59张，创作于星期二 思考题思考题3.有没有有没有500C的水的水？1.溜冰冰刀溜冰冰刀2.北方冬天晾在外边的衣服，北方冬天晾在外边的衣服，是否经过液相是否经过液相4.有没有有没有-3的蒸汽的蒸汽？5.一密闭容器内有水的汽液混合物，对其一密闭容器内有水的汽液混合物，对其
6、加热，是否一定能变成蒸汽？加热，是否一定能变成蒸汽？第9页，讲稿共59张，创作于星期二饱和线、三相线和临界点饱和线、三相线和临界点pv饱和气线三相线饱和液线饱和固线T临界点第11页，讲稿共59张，创作于星期二Vapor and Liquid(汽相和液相汽相和液相)锅锅炉炉汽轮机汽轮机发电机发电机给水泵给水泵凝凝汽汽器器过热器过热器因固相不流动，因固相不流动，更关心汽液两相更关心汽液两相冰蓄冷冰蓄冷第12页，讲稿共59张，创作于星期二6-2 汽化与饱和汽化与饱和气化气化(Vaporization):由液态变成气态的物理过程由液态变成气态的物理过程 (不涉及化学变化不涉及化学变化)The Proc
7、ess ofThe Process of Changing from liquid into Changing from liquid into gas/vapor is calledgas/vapor is called vaporizationvaporization.凝结凝结(Condensation)：由气态变成液态的物理过程由气态变成液态的物理过程 The process of changing from gas/vapor into liquid is calledThe process of changing from gas/vapor into liquid is calle
8、d CondensationCondensation6.2.1 6.2.1 汽化与凝结汽化与凝结 第13页，讲稿共59张，创作于星期二The rate of condensation depends upon the density of vapor in the space above the liquid.(凝结的速率取决于液面上方气相空间气体分子的密度凝结的速率取决于液面上方气相空间气体分子的密度,即蒸气压力即蒸气压力)Liquid molecule has to overcome the surface tension to become vapor,therefore vaporiz
9、ation consumes energy.(液相分子必须克液相分子必须克服表面张力才能进入气相空间而气化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因此气化是要耗能的)The rate of Vaporization depends on the liquid temperature.(气化的速率取决于液相的温度气化的速率取决于液相的温度)第14页，讲稿共59张，创作于星期二The equilibrium is called Saturation State.(饱和状态）饱和状态）The properties at this state is called Saturation Pr
10、operties.(饱和参数）饱和参数）第15页，讲稿共59张，创作于星期二6.2.2 饱和状态饱和状态Saturationstate饱和状态：汽化与凝结的动态平衡饱和状态：汽化与凝结的动态平衡At the equilibrium state,the pressure corresponding to only one temperature.That is,.饱和温度饱和温度Ts饱和压力饱和压力ps一一对应一一对应放掉一些水，放掉一些水，Ts不变，不变，ps？TspsSaturationtemperatureSaturationpressure第16页，讲稿共59张，创作于星期二ps=1.0
11、1325barTs=100青藏青藏ps=0.6barTs=85.95高压锅高压锅ps=1.6barTs=113.32There is a definite relation between There is a definite relation between.第17页，讲稿共59张，创作于星期二6.2.3 汽化汽化 Vaporization沸腾：沸腾：表面和液体内部同时发生的汽化表面和液体内部同时发生的汽化 It is an intensive vaporization phenomenon occurs in the liquid.(气体和液体均处在饱和状态下气体和液体均处在饱和状态下)
12、汽化汽化:由液态变成气态的物理过程由液态变成气态的物理过程 (不涉及化学变化不涉及化学变化)蒸发：蒸发：汽液表面上的汽化汽液表面上的汽化 It occurs above the free surface of liquidIt occurs above the free surface of liquid BoilEvaporation第18页，讲稿共59张，创作于星期二Evaporation occurs at any temperature and pressure.（蒸（蒸发可在任何温度和压力下发生）发可在任何温度和压力下发生）Evaporation rate depends on th
13、e free surface area,the temperature,the flow rate above,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（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 can only occur as temperature reaches the saturation temperature corresponding to the specified pressure or the pressure drops below the saturation pressure corresponding to the
14、specified temperature.（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（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和压力时,才能发生才能发生)第19页，讲稿共59张，创作于星期二6-3 水蒸气的定压发生过程水蒸气的定压发生过程t tsv vv=vv=vv v v未饱和水未饱和水饱和水饱和水饱和湿蒸汽饱和湿蒸汽饱和干蒸汽饱和干蒸汽过热蒸汽过热蒸汽h hh=hh=hh h hs ss=ss=ss s s水预热水预热汽化汽化过热过热6.3.1 P=constant(压力压力 p 是定值是定值)第20页，讲稿共59张，创
15、作于星期二 Preheat Stage(预热阶段预热阶段)Compressed liquid to Saturated liquid.(未饱和液体未饱和液体 饱和液体饱和液体)Compressed liquid/subcooled liquid is not about to vaporization.As heat added,t slightly .When It becomes Saturated liquid.The liquid is about to vaporize.It is the state at which it is still a liquid,but any hea
16、t addition will cause some of the liquid to vaporize.第21页，讲稿共59张，创作于星期二Vaporization Stage(气化阶段气化阶段)Saturated liquid to Saturated vapor(饱和液体饱和液体 饱和蒸气饱和蒸气)Saturated vapor is a vapor about to condense.A substance at state between Saturatedliquid and Saturated Vapor is calledSaturated liquid-vapor mixtu
17、re/wetvapor.Latent heat of Vaporization(气化潜热气化潜热):The amount of energy absorbed during vaporization第22页，讲稿共59张，创作于星期二Superheat Stage(过热阶段过热阶段)Superheated vapor is the vapor that is not about to condense.t第23页，讲稿共59张，创作于星期二注意：水蒸气定压发生过程说明注意：水蒸气定压发生过程说明(1)(2)(3)理想气体理想气体实际气体汽化时，实际气体汽化时，TTs不变，但不变，但h增加增加汽
18、化潜热汽化潜热(4)未饱和水未饱和水过冷度过冷度过冷水过冷水过热蒸汽过热蒸汽过热度过热度只有熵加热时永远增加只有熵加热时永远增加第24页，讲稿共59张，创作于星期二StateofLiquidandvapor未饱和液，过冷液未饱和液，过冷液饱和液饱和液饱和湿蒸气饱和湿蒸气饱和蒸气饱和蒸气过热蒸气过热蒸气SaturatedliquidSaturatedvaporSaturatedliquid-vapormixtureSuperheatedvaporCompressedliquidSubcooledliquid汽化潜热汽化潜热LatentheatofVaporization压缩液压缩液 6.3.2
19、定压气化过程的定压气化过程的P-v P-v 图和图和T-s T-s 图图 P-v and T-s diagrams第25页，讲稿共59张，创作于星期二sp-v图，图，T-s图上的水蒸气定压加热过程图上的水蒸气定压加热过程一点，二线，三区，五态一点，二线，三区，五态第26页，讲稿共59张，创作于星期二Saturated liquid line,SLLisformedbyconnectingaseriesofboilingpoints.saturated vapor line,SVL：Connectingaseriesofpointsatdrysaturatedvaporbuildsaline,k
20、nownassaturatedvaporline,SVL.Vaporizationcontinuesbyfurtherheatsupplytothesystemuntilnoliquidisleft.Thisstateisknownasdry saturated vapor,e.g.pointd.Ifthesystemisslightlycooledatthisstate,thendropletsofliquidwillbegintoform.Thestateofsubstancebetweensaturatedliquidanddryvaporiscalledwet vapor.Furthe
21、rheatingofadrysaturatedvaporatconstantpressurecausesariseofvaportemperatureanditbecomessuperheated vapor.Thestateofsubstanceiscompletelydefinedbyitspressureandtemperatureifitisinliquidorsuperheated vaporphase.第27页，讲稿共59张，创作于星期二v第28页，讲稿共59张，创作于星期二One point(一点一点):critical point(临界点临界点)Two lines(两线两线):
22、SLL and SVL(饱和液体线和饱和蒸气线饱和液体线和饱和蒸气线)Three regions(三区三区):Subcooled liquid region(未饱和液体区未饱和液体区)Saturated liquid-vapor mixture region(湿蒸气湿蒸气区区)Superheated vapor region(过热蒸气区过热蒸气区)Five states(五态五态):Subcooled liquid(未饱和液体未饱和液体)Saturated liquid(饱和液体饱和液体)Saturated liquid-vapor mixture(湿蒸气湿蒸气)Saturated vapor
23、(干饱和蒸气干饱和蒸气)Superheated vapor(过热蒸气过热蒸气)第29页，讲稿共59张，创作于星期二 6.4.1 Types of Property Tables (水蒸汽表的分类水蒸汽表的分类)1.Saturated water Tables(饱和水和饱和蒸汽表饱和水和饱和蒸汽表)Saturated water-T Tables(以温度以温度t为独立变量排列为独立变量排列)Saturated water-p Tables(以压力以压力p为独立变量排列为独立变量排列)2.Subcooled water and Superheated vapor Table(未饱和水和过未饱和水和
24、过热水蒸汽表热水蒸汽表)P and t are dependent variables(以以p和和t为自变量为自变量)6.4 水蒸气性质表水蒸气性质表 Property Tables of Water Vapor第30页，讲稿共59张，创作于星期二 2、Reference State and Reference Values(基准点的规定基准点的规定)For water,the saturated liquid at 0.01 is taken as reference state.(取水的三相点，即取水的三相点，即0.01 oC为基准点，规定在为基准点，规定在此温度下液态水的热力学能和熵为零
25、。此温度下液态水的热力学能和熵为零。)The internal energy and entropy are assigned zero at this state.第31页，讲稿共59张，创作于星期二3.Properties of Saturated liquid-vapor mixture at Pressure p (压力为压力为p的湿饱和蒸汽的湿饱和蒸汽)Thestateofwetvaporcannotbedefinedbyjustpressureandtemperatureuntiloneotherpropertyisgiven.Theconditionorqualityofwetv
26、aporisoftendefinedbyitsdrynessorwetnessfraction.定义干度定义干度x才可以确定湿蒸汽的状态。才可以确定湿蒸汽的状态。We define dryness as dryness fractiondryness fraction,x=the mass of dry vapor in 1 kg of the mixture,x=the mass of dry vapor in 1 kg of the mixture,wetness fractionwetness fraction,1-x=the mass of liquid in 1 kg of the
27、mixture.,1-x=the mass of liquid in 1 kg of the mixture.第32页，讲稿共59张，创作于星期二 第33页，讲稿共59张，创作于星期二第34页，讲稿共59张，创作于星期二第36页，讲稿共59张，创作于星期二4.Exercise.Consulting property tables of water vapor to determine the state of each point and their h，s，x.(利用水蒸气表判断下列各点的状态，并确定其利用水蒸气表判断下列各点的状态，并确定其h，s，x的值。的值。)第37页，讲稿共59张，创
28、作于星期二o（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。第38页，讲稿共59张，创作于星期二o（2）查饱和表得查饱和表得p=9MPa时时 可见可见，该状态为该状态为湿蒸汽湿蒸汽，其干度为，其干度为 又查饱和表得又查饱和表得第39页，讲稿共59张，创作于星期二=2489.0kJ/kg按湿蒸汽的参数计算式得按湿蒸汽的参数计算式得第40页，讲稿共59张，创作于星期二(3)显然，该状态为湿蒸汽状态。由已知参数查饱和水和饱和显然，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蒸汽表得
29、按湿蒸汽的参数计算公式得按湿蒸汽的参数计算公式得第41页，讲稿共59张，创作于星期二（4）由饱和水和饱和蒸汽表查得）由饱和水和饱和蒸汽表查得:当当p=1.0MPa时，时，ts=179.9，显然显然tts，所以该状态为，所以该状态为未饱和水未饱和水。通常通常t=175的状态参数可利用的状态参数可利用t=170与与t=180的对应状态的对应状态参数内插得到，参数内插得到，但此处但此处t=170与与t=180跨越了未饱和表中的黑粗线，跨越了未饱和表中的黑粗线，说明它们分别处于不同相区。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，选取离最接近的应使内插在未饱和水区内进行，选取离最接近的t=1
30、70与与ts=179.9的未饱和水参数内插。的未饱和水参数内插。查未饱和水和过热蒸汽表得查未饱和水和过热蒸汽表得p=1.0MPa，t=170时p=1.0MPa，t=179.9时第42页，讲稿共59张，创作于星期二于是t=175时对于未饱和水干度对于未饱和水干度x无意义。无意义。第43页，讲稿共59张，创作于星期二（5）时，饱和蒸汽比体积时，饱和蒸汽比体积，该状态为该状态为过热蒸汽过热蒸汽。查过热蒸汽表得查过热蒸汽表得t=260时，时，,t=270时，时，该状态的温度可由比体积值求得该状态的温度可由比体积值求得第44页，讲稿共59张，创作于星期二o讨论讨论应该注意，在利用未饱和水与过热蒸汽作应该
31、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。计算在未饱和水（或过热蒸汽）区内进行。第45页，讲稿共59张，创作于星期二6.5 h-s diagram of water vapor (水蒸汽的水蒸汽的h-s图图)1.SLL and SVL 2.(界限曲线，界限曲线，x=0、x=1两条曲线两条曲线)2.Constant Pressure Line and Constant Temperature Line (定压线和定温线定压线和
32、定温线)In Saturated liquid-vapor region,constant pressure line and constant temperature line are identical.(在湿蒸汽区定压线与定温线重合。在湿蒸汽区定压线与定温线重合。)3.Constant Volume Line（定容线。（定容线。)4.Constant Dryness Line(定干度线。定干度线。)Given Two Properties,all the other state properties can be determined from the Diagram.(给定两个参数，即
33、可查出其余全部参数)。第46页，讲稿共59张，创作于星期二Priorities(优点优点)：Fastandconvenient.方便、快速。方便、快速。Drawbacks(缺点缺点)：NotsoaccurateasPropertytables精确性稍差精确性稍差。第47页，讲稿共59张，创作于星期二第48页，讲稿共59张，创作于星期二s(kJ/kg*K)h(kJ/kg)第49页，讲稿共59张，创作于星期二6.6.1 Characteristics of water vapor (水蒸汽的特点水蒸汽的特点)1.Water vapor can not be treated as ideal gas
34、(水蒸汽不是水蒸汽不是理想气体理想气体)pv=RT is not suitable.（理想气体状态方程不适用。）（理想气体状态方程不适用。）2.Analysis and Calculation on Water vapor can be solved by using Tables and Diagrams(水蒸汽的分析和计算采用水蒸汽图和表。水蒸汽的分析和计算采用水蒸汽图和表。)3.The First and the Second Laws must be obeyed during processes of water vapor(热力学第一定律和第二定律成立热力学第一定律和第二定律成立)
35、6.6 Thermodynamic Processes of Water Vapor (水蒸气的热力过程水蒸气的热力过程)第50页，讲稿共59张，创作于星期二 For reversible processes,(对于可逆过程：对于可逆过程：)第51页，讲稿共59张，创作于星期二6.6.2 Procedures(步骤步骤)(1)Based on the given conditions,determine the initial state and its properties.(根据已知条件，确定初始状态，查出其余参数。根据已知条件，确定初始状态，查出其余参数。)(2)Based on the
36、 characteristics of the process and one of the properties of the final state,determine the final state and its properties.(根据过程特点和一个终态参数，确定终态，再查出其余终态参数。根据过程特点和一个终态参数，确定终态，再查出其余终态参数。)(3)Based on the initial and final state,calculate the q、u、w during the process。(根据初、终态参数，计算根据初、终态参数，计算q、u、w等。等。)第52页，讲
37、稿共59张，创作于星期二6.6.3 Basic thermodynamic process of water vapor(水蒸气的基本热力过程水蒸气的基本热力过程)(1)Constant Volume Process(定容过程定容过程,v=定值。定值。)Constant volume Process(定容过程定容过程)第53页，讲稿共59张，创作于星期二(2)Constant Pressure Process(定压过程定压过程p=定值定值)Constant Pressure Process(定压过程定压过程)第54页，讲稿共59张，创作于星期二(3)Constant Temperature P
38、rocess (定温过程定温过程 T=定值定值)Isothermal Process(定温过程定温过程)第55页，讲稿共59张，创作于星期二(4)Adiabatic Process(绝热过程绝热过程)Isentropic Process(定熵过程定熵过程)第56页，讲稿共59张，创作于星期二Example:1 kg water vapor,initially,undertakes an isentropic expansion process and reaches the final state of Calculate the amount of work done by the wate
39、r vapor during the process.Answer:Accordingtothevaluesof,theinitialstate1canbedetermined.Fromwatertablesorh-sDiagram,weknowthatthen第57页，讲稿共59张，创作于星期二Frompoint“1”,drawaverticalline,whichwillmeetwiththelineofatpoint“2”,thefinalstateisobtained.Thenfromh-sdiagram,wegettoknowthat第58页，讲稿共59张，创作于星期二感感谢谢大大家家观观看看第59页，讲稿共59张，创作于星期二