采用高效紧凑式换热器是近年来微型燃气轮机发展取得成功的关键技术之一。本文在燃机参数给定情况下，通过对三种换热表面进行热力计算和分析，结果表明，CC原表面在紧凑式换热器中具有较强的应用潜力。此外，还就温差对压损的影响及燃气旁通量对回热度的影响进行了研究。

Analysis and simulation of rarefied nitrogen gas flow and heat transfer were performed with the Knusden number ranging from O.05 to 1.O, using the direct simulation of Monte Carlo (DSMC) method, The influences of the Kn number and the aspect ratio on the gas temperature and wall heat flux in the microchannels were studied parametrically. The total and local heat fluxes of the microchannel walls varying with the channel inlet velocities were also investigated in detail. It was found that the Kn number and the aspect ratio greatly influence the heat transfer performance of microchan-nels, and both the channel inlet and outlet have higher heat fluxes while the heat flux in the middle part of channels is very low. It is also found that the inlet free stream flow velocity has small affect on the wall total heat flux while it changes the distribution of local heat flux.

Twoshell-and-tubeheatexchangers(STHXs)usingcontinuoushelicalbafflesinsteadofsegmentalbafflesusedinconventionalSTHXswereproposed,designed,andtestedinthisstudy.ThetwoproposedSTHXshavethesametubebundlebutdifferentshellconfigura-tions.Theflowpatternintheshellsideoftheheatexchangerwithcontinuoushelicalbaffleswasforcedtoberotationalandhelicalduetothegeometryofthecontinuoushelicalbaffles,whichresultsinasignificantincreaseinheattransfercoefficientperunitpressuredropintheheatexchanger.Properlydesignedcontinuoushelicalbafflescanreducefoulingintheshellsideandpreventtheflow-inducedvibrationaswell.TheperformanceoftheproposedSTHXswasstudiedexperimentallyinthiswork.TheheattransfercoefficientandpressuredropinthenewSTHXswerecomparedwiththoseintheSTHXwithsegmentalbaffles.Theresultsindicatethattheuseofcontinuoushelicalbafflesresultsinnearly10%increaseinheattransfercoefficientcomparedwiththatofconventionalsegmentalbafflesforthesameshell-sidepressuredrop.Basedontheex-perimentaldata,thenondimensionalcorrelationsforheattransfercoefficientandpres-suredropweredevelopedfortheproposedcontinuoushelicalbaffleheatexchangerswithdifferentshellconfigurations,whichmightbeusefulforindustrialapplicationsandfur-therstudyofcontinuoushelicalbaffleheatexchangers.ThispaperalsopresentsasimpleandfeasiblemethodtofabricatecontinuoushelicalbafflesusedforSTHXs.

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

In this paper, a SIMPLE-like algorithm on collocated grid system has been developed. The ability to suppress the spurious pressure field is achieved via introducing the pressure difference between adjacent two grid points into the convection-diffusion finite difference scheme, and the interfacial velocity is obtained by simple linear interpolation. The differencing scheme, discretization of governing equations and solution procedure of the algorithm are described in detail. In order to check the validity of the algorithm, several test cases which have analytical or benchmark solutions are presented. Good agreements are obtained between the numerical and the corresponding analytical or benchmark solutions. The ability of the improved algorithm to suppress the spurious pressure field is demonstrated via a 3-D example.