A computational study of convective heat transfer for turbulent flows in multi-channel, narrow-gap fuel element has been carried out, using a general marching procedure. The fluid distribution adjustment among seven annular-sector channels is based on the assumption of the same pressure drop in these passages. It was found that the inlet velocities of the bilateral channels are lower than these of the middles, and the axial local heat transfer coefficients for the seven channels do not approach the fully developed constant value. At each cross section, the periphery temperature distribution is not uniform, while the local temperature distribution along axial coordinate is of sinuous type with the peak at x=0.7-0.8m. At the same Reynolds number, the averaged Nusselt numbers of water in Channel 1 and Channel 7 are higher than those in the middles. The maximum surface temperature increases almost linearly with the inlet water temperature, whereas it decreases almost asymptotically with the inlet average velocity.

Inthefirstpartofthiswork(PartI),wepresentedandvalidatedtheDSMC-HFSmethod,whichcanbeusedtodealwithheatfluxspecifiedboundaryconditionsinDSMCsimula-tions.Inthisarticle,themethodisappliedtodemonstratethegeneralpropertiesofrarefieddiatomicgaseousflowinamicrochannelunderuniformheatfluxboundaryconditions.Theeffectsofwallheatfluxongaseousflowandheattransfercharacteristicsareinvestigatednumericallyanddiscussedindetail.Itcanbeconcludedfromthepresentresearchthatgaseousrareficationandcompressibilityincreasewiththeincreaseofthewallheatflux.Gasaccelerationathigherwallheatfluxismoreobviousthanthatatlowerwallheatflux.Thehighwallheatfluxreducesthemassflowrateandelevatestheheattransferabilityexceptatthechannelinlet.

Forflowsassociatedwithmicroelectromechanicalsystems(MEMS),theheatfluxspeci-fied(HFS)boundaryconditionexistsbroadly.However,problemswiththeHFSboundaryconditionhavenotbeenwellrealizedinthesimulationsofmicrochannelflowsusingthedirect-simulationMonteCarlo(DSMC)method.Inthepresentwork,inversetemperaturesampling(ITS)isusedtodealwithdiatomicgaseousflowandheattransferinamicrochan-nel.Thistechniqueprovidesanapproachtocalculatethemolecularreflectivecharacteristictemperaturefromthemolecularincidentenergyandtheheatfluxatthewallboundary.CoupledwiththeDSMCmethod,thisdiatomicmoleculeITStechniquecanbeusedtotreattheHFSboundaryconditionsintheDSMCmethod.Verificationindicatesthatthepro-poseddiatomicmoleculeITSmethodcanaccuratelysimulatethegaseousflowandheattransfer.InPartIIofthiswork,theproposedmethodisappliedtodemonstrategeneralmicrochannelgaseousflowpropertiesunderuniformheatfluxboundaryconditions.atthesametime,thenewmethodisadoptedtonumericallyinvestigatetheeffectsofwallheatfluxongaseousflowandheattransferproperties.

Numerical computations were performed for the average Nusselt number at an internal vertical plate situated in a square enclosure, with the inner plate and the bounding wall of the enclo-sure maintained at uniform but different temperatures. Natural con-vection occurred in the air which occupied the enclosure space. The position of the inner vertical plate within the enclosure was varied parametrically. The plate height-cavity height ratio was 0.513. For narrow distance between the inner plate and the bounding wall the inner plate Nusselt number was enhanced. Aside from this, the plate average Nusselt number was remarkably insensitive to the plate position. The effect of the Rayleigh number on the velocity and temperature fields and local Nusselt numbers are also discussed. The agreement between the predicted flow pattern for Ra=1.1

Three-dimensionalturbulentflowandheattransferinaninternallyfinnedtubewithablockedcore-tubehavebeennumericallystudiedbytherealizablek−εturbulencemodelwiththewall-functionmethod.Thenumericalmethodisvalidatedbycomparingthecalculatedresultswithexperimentaldata.Therangeofratioofblockedcore-tubeoutsidediametertoouter-tubeinsidediameter(d0/Di)isfrom0.25to0.75.Thecomputationalresultsdemonstratedthatthereexistsanoptimalratioof(d0/Di)underbothidenticalmassflowrateandidenticalpressuredrop.Theoptimalratioof(d0/Di),whichisreducedwiththeincreaseofmassflowrate,isapproximately0.5to0.625atgivenmassflowrateforbothconstantwalltemperatureanduniformwallheatflux.Theoptimalratioof(d0/Di)atagivenpressuredropisfrom0.44to0.50,whichisalsoslightlyreducedwiththeincreaseofpressuredrop.Furthermore,theoptimalratioof(d0/Di)isnotsensitivetothenumberofcross-sectionwavyfinsofaninternallylongitudinalfinnedtube,intherangeofafinwavenumberof15–25.