transport_and_adsorption

《transport_and_adsorption》由会员上传分享，免费在线阅读，更多相关内容在学术论文-天天文库。

1、SolvedwithCOMSOLMultiphysics5.0TransportandAdsorptionIntroductionThisexampledemonstrateshowyoucanmodelphenomenadefinedindifferentdimensions(2Dand1Dinthisexample)inafullycoupledmannerusingCOMSOLMultiphysics.Inthisparticularcase,themodelinvolvesasmallparallel-platereactor

2、withacatalyticsurface.Similarapplicationswheresurfaceprocessesareofcriticalimportanceincludebiochipdevicesandasemiconductorcomponents.Whenmodelingchemicalreactionsthereactionratesarecommonlyfunctionsoftheconcentrationsofthereactantsinthephasethattransportsthechemicals.H

3、owever,forsurfacereactionsitisalsonecessarytoaccountforthesurfaceconcentrationsoftheactivesitesandsurfaceadsorbedspecies.Themassbalancesinthebulkofthereactormustthereforebecoupledtothemassbalancesforspecies,presentonlyatthesurfaceofthedevice.ModelDefinitionThefirstappro

4、ximationyoucanmakeistoreducethe3Dgeometryto2D,whichisreasonableifthevariationsinconcentrationaresmallalongthedepthofthedomain.Figure1showshowthe2Dmodeldomainisrelatedtothefull3Dreactorgeometry.1

5、TRANSPORTANDADSORPTIONSolvedwithCOMSOLMultiphysics5.03D2DGasoutletActivesur

6、faceActivesurfaceAsAGasinletModeledcross-sectionplaneFigure1:Themodeleddomainisaparallelplatereactorwithanactivesurfacewhereyouwanttomodeltheconcentrationofsurfacespecies.AdenotesmolecularspeciesdissolvedingasandAsthesamespeciesadsorbedonthesurface.MODELEQUATIONSTheadso

7、rption/desorptionreactionatthesurfaceisdescribedbykfAASkrwherekfandkrareforwardandreverserateconstants.AandAsarethemolecularspeciesinthegasandadsorbedonactivesitesonthesurface,respectively.Letθbethefractionofactivesitesoccupiedbyadsorbedmolecules.Thefractionoffreesitesi

8、sthen1−θ.Langmuirderivedthattherateofdesorptionofmolecules,rdes2(mol/(m·s)),isproportionaltoθandequaltokrθwherekrisaconstantatconstanttemperature.Furthermore,therateofadsorptionofmoleculesisproportionaltoboththefractionoffreesurfacesites,1−θ,andtotherateofwhichmolecules

9、strikethesurface.Thecollisionrateisinturndirectlyproportionalthepartialpressureofthespecies,pA(Pa).Therateofad