Monte Carlo modeling of the thermal conductivity of porous cometary ice.pdf

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1、Icarus157,219–227(2002)doi:10.1006/icar.2002.6815,availableonlineathttp://www.idealibrary.comonMonteCarloModelingoftheThermalConductivityofPorousCometaryIceYossiShoshany,DinaPrialnik,andMorrisPodolakDepartmentofGeophysicsandPlanetarySciences,TelAvivUniversity,RamatAviv69978,IsraelE-mail:din

2、a@planet.tau.ac.ilReceivedJuly1,2001;revisedNovember13,2001Weshouldstressthatporeswillbeassumedtobeempty,Thebasicstructureofcometnucleiisanaggregationofgrains,whereasinreality,whenthesolidmatrixismadepredominantlywithasizedistributionthatextendsoverseveralordersofmagni-oficeandtemperaturesa

3、renottoolow,vapormayfilltheporestudeandasimilardistributionofpores.Althoughattemptshaveandflowthroughthem.Suchisthecaseintheouterlayersofbeenmadetoassesstheeffectofporosityonthethermalconductiv-cometarynuclei,forexample.Often,heattransportbyvapority,theeffectofporesizedistributionhasbeenignor

4、ed.Modelingcanbemoreefficientthanheatconductionbythesolid(e.g.,aporousstructurewithawidesizedistributionwouldrequireaSmoluchowski1982,SteinerandK¨omle1991).Rigorously,suchveryfine3-Dgrid,soastoaccommodatethesmallestandlargestsituationsshouldbedescribedbysimultaneoussolutionsofthevoids.Inorder

5、tocircumventthisdifficulty,weadoptahierarchicalmassandheattransportequationsandthenheattransferbyprocedure.Thusweassumearandomandfractalporousstructurevaporarisesindependentlyofheatconductionbythesolid(e.g.,andusea3-DMonteCarlomodel.Thebasicconfigurationisacubemadeofunitcellsoftwotypes,(ice)fi

6、lledandvoid,randomlydis-Espinasseetal.1991,Prialnik1992,BenkhoffandHuebnertributed.Theirrelativenumbercorrespondstoaprescribedporosity.1995).Onlyifmasstransportisomitted,inordertosimplifyWesolvetheheattransportequationforthiscubeuntilasteadystatethecalculations,doesitbecomenecessarytoparame

7、trizeheatisobtained,andfromthissolutiontheeffectivethermalconductiv-transportbyvaporandaddittothethermalconductivitycoef-ityisderived.Thecalculationsarerepeatedforarangeofporositiesficient,whichresultsinaneffectivethermalconductivity(e.g.,andtemperatures,