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).

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.

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.

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.