大学课件-化工原理-干燥english.ppt

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1、masstransferwater:solidgasphaseheattransferhotairwetmaterialmomentumtransferwateristransferfromsolidtogasphaserelativemovementbetweenhotairandwetmaterialwatervaporizationbroughtoutbyairDRYINGThePropertyOfWet-Air(Air-Water)wet-air:dryair+humidity----idealgasHu

2、midificationtermsdryairisconstoverdryingprocessunitmassofdryairisasbasisHumidityHMassratioofwatervaportodryairkgwater/kgdryairForidealgas：nv,na---kmolSaturatedHumidityHsPartialpressureofhumidityinwetairisequaltovaporpressurepsatfixedtemperaturePercentagerelativ

3、ehumidityreflectsunsaturationofwetair,anddryingpower↓，dryingpower↑=1，nodryingpowert↑，pS↑，↓，dryingpower↑p=101.3kN/m2HumidvolumeH(m3/kgdryair)HumidheatcH（kJ/kgdryairC）basis:at0Cwaterinliquidphasedryairr0:latentheatofwatersteamat0C，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，tsaturationt=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,t2.dryerIdealprocessP-X*curve(orP*-Xcurve)-XcurveEquilibriummoistureFreemoistureBoundmoistureNon-boundmoisturemoisturepresentedintwoformsdryingcurveX~τ*dryingratecurveR~XMechanismOfMoistureTransferredInWe

8、tMaterialdiffusiontheoryofdryingcapillarytheoryofdryingWetmaterialporositymaterialnon-porositymaterialmechanismofmoisturetransferredinwetmaterialDryingTimeForConstantDryingP