Study On Heat Transfer And Fluid Flow Around A Pair Of Hot And Cold Microtubes

With the rapid development of MEMS, microbial engineering and aerospace inrecent years, it is getting great interesting to research the heat transfer performanceand fluid flow characteristic in these miniaturization equipments. Heat transfer andfluid flow in these miniaturization equipments is a very complex issue. Manyinternational scholars have devoted to this problem by both theoretical andexperimental investigations, however, there is little common accepted conclusion sofar.In the miniaturization process of traditional tube shell heat exchanger, there havebeen some difficult problems to be solved, such as intensive hole welding difficulty,large flow resistance of shell side and flow maldistribution, etc.. Therefore to exploreand research a new heat exchange mode and organization structure of cold and hotfluid in micro scale has both significances in technical application and academictheory.A strengthening heat transfer model, the stagger arrangements consisting of acold and hot horizontal microtubule inside a shell tube, was proposed in the paper andthe heat transfer performance and fluid flow characteristic of this model wasresearched by both experiment and simulation via Lattice Boltzmann Method.Two fine stainless steel pipes with outside diameter1.0mm, inside diameter0.75mm, and tube spacing1.5Do were arranged in the center of a inside diameter20.0mmshell tube. The experimental results show that natural convection between the coldand hot tube increses with the increasing of the Rayleigh number firstly thendecreases, and there is a peak. The results also indicate that the arrangement of hottube under cold tube is the optimal, and the case of hot tube above cold tube is theworst.In the Reynolds number range of Re=50-4000, the friction coefficients werefound to be considerably higher than those predicted by the conventional correlations,but the trend of the friction coefficient varying with the Re number in thesemicrotubes is similar to the conventional laws for large tubes.Meanwhile, the Natural convection around a pair of hot and cold horizontalisothermal microtubes in an isothermal square enclosure, which side length is equal to the inside diameter of the shell tube in the experiment, was numerically studied usingLattice Boltzmann Method (LBM). The temperature profiles, streamline patterns andthe local and averaged Nu numbers of the hot tube, cold tube and the overall twotubes for different Ra numbers were given and discussed. It is found that thenumerically calculated Nusselt numbers were in general agreement with theexperimental results and the differences becomes obvious at low Rayleigh number.Finally, the improvement and some proposals for future study on this subjecthave been outlined.