chapter2PropertiesofPureSubstances2-1PureSubstance2-1-1DefinitionofPureSubstanceAhomogeneoussubstanceispuresubstance2-1-2PhasesofPureSubstance

SolidLiquidGas

2-2PhaseChangeProcessofPureSubstance2-2-1ConstantPressureProcessofWaterpv123455’1’2’3’4’5”1”2”3”4”cTv123451’2’3’4’5’1”2”3”4”5”cT=constantvaporLiquid+VaporCriticalpointLiquidLiquid+solidSolid+VaporsolidpTTripleline2-2-1PropertiesofWater1.Onepoint：CriticalpointC2.Twolines：Saturatedwaterline,Saturatedvaporline3.ThreeRegions:Compressedwaterregion,Saturatedmixtureregion,superheatedvaporregion4.Fivestates:Compressedwater,Saturatedwater,Saturatedmixture,Saturatedvapor,superheatvapor2-3-1p-v-TSurface

2-3P-v-TsurfaceandP-Tdiagram2-3-2p-Tdiagram

PTSolidVaporliquidMeltinglineVaporizationSublimationExpandonfreezingExtractonfreezingCriticalpoint2-4PropertyTables2-4-1SaturatedLiquidandVaporOnepropertyisenoughtoCalculateotherproperties.

t℃P,MPav’v”h’h”s’s”1000.10130.001041.6738419.062676.31.30697.35642001.55510.001160.12714352.42791.42.33076.4289Enthalpy----thecombinationproperty:H=U+PV

Or,perunitmassh=u+Pv2-4-2SaturatedMixtureOne

propertytocalculatesaturatedproperties,buthowtodeterminethepropertiesofsaturatedmixture?Onespecialpropertytocalculatethefractionofliquidandvapor,thequality2-4-3SuperheatedVapor

TwoindependentpropertiesareusedtoCalculateotherpropertiesT℃P=0.1MPav,m3/kgh,kJ/kgs,kJ/kg.K1001.69582676.27.36281501.93642776.47.54382-4-4ReferencestateandreferencevalueWater:Saturatedliquidat0.01℃istakenasthereferencestate,whereu=0s=0R-12:Saturatedliquidat-40℃istakenasthereferencestate,whereu=0s=0Notice:

Thereferencestatedifferwithdifferenttables2-5-1TheIdeal-GasThemoleculesofideal-gashavenovolumeTherearenoattractionamongmoleculesofideal-gas2-5-2TheIdeal-GasEquationofState

2-5TheIdeal-GasEquationofState

(1).pV=mRT

pv=RT

R------Thegasconstant(2)

pVm=μRμTpvm=RμT

Rμ-----Theuniversalgasconstant=8.314kJ/kmol.K

2-6RealGases2-6-1CompressibilityFactor

Pv=RTcanonlybeemployedforthegasunderhightemperatureorlowpressureForrealgas,frompv=RT:z-------CompressibilityFactor:ameasureofdeviationfromideal-gasbehaviorz=1:Ideal-Gasz>1orz<1:Real-Gas2-6-2Vander

WaalsEquationofState

(1)considerthevolumeoccupiedbythemoleculesthemselvesfrompv=RT:Sincethesmallerspaceforthemoleculesflyingwillleadtomorechanceofhitonitscontainer,thepressureofthegaswillincreasethen.Correctthisbyreplacingvasv-b(2)considercontractionamongthemoleculesThecontractionwillleadtoadecreaseonpressure,socorrecttheequationasfollowing:Thecontractionshouldbeinproportiontoρ2whichcanbewriteas

1/v2.‘a(chǎn)’isproportionalcoefficientdecided