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时间:2021-04-01
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1、masstransferwater:solidgasphaseheattransferhotairwetmaterialmomentumtransferwateristransferfromsolidtogasphaserelativemovementbetweenhotairandwetmaterialwatervaporizationbroughtoutbyairDRYINGThePropertyOfWet-Air(Air-Water)wet-air:dryair+humidity----idealgasHu
2、midificationtermsdryairisconstoverdryingprocessunitmassofdryairisasbasisHumidityHMassratioofwatervaportodryairkgwater/kgdryairForidealgas:nv,na---kmolSaturatedHumidityHsPartialpressureofhumidityinwetairisequaltovaporpressurepsatfixedtemperaturePercentagerelativ
3、ehumidityreflectsunsaturationofwetair,anddryingpower↓,dryingpower↑=1,nodryingpowert↑,pS↑,↓,dryingpower↑p=101.3kN/m2HumidvolumeH(m3/kgdryair)HumidheatcH(kJ/kgdryairC)basis:at0Cwaterinliquidphasedryairr0:latentheatofwatersteamat0C,2490kJ/kgEnthalpyI(kJ/k
4、gdryair)tas,tw,tt:dry-bulktemperaturetw:wet-bulktemperaturetas:adiabaticsaturationtemperatureAdiabaticsaturationtemperaturetasadiabaticsaturationprocess:massandheattransfertoequilibriumair,tas,Hasair,t,HtaswaterIentry=Iexporttwisnotstatefunctiontw=f(t,H)tfixed,
5、H↓,tW↓,unsaturateddegree↑Wet-bulbtemperaturetwDewpointtdHisfixed,tsaturationt=tdPd:vaporpressureattd,=partialpressureofairatinitialstatepvunsaturatedair:t>tas=tw>tdsaturatedair:t=tas=tw=tdtfixed,tas、tw↓unsaturateddegree↑Relationamongtas,tw,tAir-watersystem湿
6、度HumiditychartCharttoexpressvariationofwetair1.Heatingandcoolingprocess2.Adiabaticsaturationprocess3.Non-adiabaticwettingprocess4.GasmixingprocessFlowSheetofDryingblowerdryerHeatexchangerExpressionofmoistureinwetmaterialwetbasis:wdrybasis:XMoistureevaporatedkg
7、干空气/kg水amountofdryairkg/sHeatbalance1.preheaterH=const,t2.dryerIdealprocessP-X*curve(orP*-Xcurve)-XcurveEquilibriummoistureFreemoistureBoundmoistureNon-boundmoisturemoisturepresentedintwoformsdryingcurveX~τ*dryingratecurveR~XMechanismOfMoistureTransferredInWe
8、tMaterialdiffusiontheoryofdryingcapillarytheoryofdryingWetmaterialporositymaterialnon-porositymaterialmechanismofmoisturetransferredinwetmaterialDryingTimeForConstantDryingP
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