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.

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.

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.

Effective boundary condition is one of the most critical problems in the computation of micro-channel flows with direct simulation Monte-Carlo (DSMC) method. In the present work, the implementation of DSMC with specified pressure boundary condition (PBC) was discussed in detail. The variations of gaseous local pressure, temperature and number density of the particles caused by the temperature difference between channel walls and gas were presented. It was found that with the increase of both gaseous compressibility and rarefaction, the pressure distribution along micro-channel became more nonlinear. Heat transfer occurred almost only at channel inlet and outlet, and the average wall heat flux increased almost linearly to the inlet-to-outlet pressure ratio. The computational results also showed that PBC was more suitable for the simulation of micro-channel flow problems than the conventional velocity boundary condition (VBC).

Natural convection in a cubic inclined enclosure with three isolated plates was investigated experimentally. The influences of the plates' spacing, the inclination angles of the enclosure, and the Rayleigh number on the heat transfer of the plate group were obtained. It was found that under a fixed Rayleigh number, there is a plate spacing at which the heat transfer rate of the three plates is approximately the same for the horizontal plate group. Under the range of Rayleigh numbers considered, the heat transfer rate of the plate group is less than that of the natural convection of the plate group in infinite space. The heat transfer rate of the plates increases with the plate inclined angle tilting from θ=90 deg to θ=0 deg, with the most steep increase occurring in the range of θ=90 deg to 45 deg. A global correlation of the heat transfer results for all the inclination between 0 deg and 60 deg can be obtained as Nul,m=0.5360 (Ra1cos) 0.25 with a spread of ±8.9 percent.