Research And Development Of A New Type Of Enhanced Tube Under Low Reynolds Number

Heat exchangers are universal equipments used in many industrial fields such as chemical industry, petroleum refining industry, power industry, food industry, light industry, atomic energy installation, medicine manufacturing industry, aerospace industry and so on. In the thermodynamic system, the investment of heat exchangers is in higher proportion in the gross investment of an enterprise, and the performance of heat exchangers directly influences the thermal cost. In recent years, because of many factors such as process requirements, energy crisis etc, the research on heat transfer enhancement techniques has been an important way to save energy nowadays.The shell-and-tube heat exchanger has many advantages such as reliable structure, mature techniques, wide application and so on, so it is the most frequently used structure in the thermodynamic system presently. It gets improved and developed continuously with the great progress of the research method on heat transfer enhancement techniques and modern design. The research on heat transfer enhancement for the tube-side of the shell-and-tube heat exchanger is carried out by theoretical analysis, numerical simulation and experiments in this dissertation. Concretely, the issue of heat transfer augmentation is researched in allusion to the widely existed problem of the low heat transfer coefficient of laminar convective heat transfer in tubes. A new type of tube is firstly introduced under the direction of the Field Synergy Principle, which can be manufactured directly by rolling the traditional smooth pipe. The manufacturing procedure is so simple that it costs low. The new structure can markedly enhance the laminar convective heat transfer of the tube side with less additional increase of flow resistance and thus has an excellent integrated performance of heat transfer enhancement. The multi-longitudinal vortex flow in the new tube is induced by alternating change of its cross-section, which is the optimal velocity field for laminar convective heat transfer in tubes and doesn't easily attenuate along axial direction. That's why the new tube can remarkably enhance heat transfer. Meanwhile, the flow resistance is relatively low. So the new structure is a sensational kind of heat transfer augmentation element and will have a broad application in engineering fields.Numerical simulation are performed for the flow and heat transfer characteristics in the 3D model of the new structure using the FLUENT software based on the numerical method. The impact of Reynolds number, Prandtl number and the tube's geometry size on the tube side flow and heat transfer characteristics is investigated. The results indicate that the new structure has a good effect of heat transfer enhancement with a relatively low increase of flow resistance, especially for the fluid with high Prandtl number and low Reynolds number. According to the data of the numerical simulation, the correlation equations of Nusselt number and flow friction factor are obtained respectively, which are useful to take the new structure into practice.The new tube is also studied by experiments in the latter part of this dissertation. The results of the experiments have proved the excellent performance of heat transfer enhancement of the new tube. The experimental research can provide a reference for the performance perfection, structure optimization and engineering application of the new tube. The results of the numerical simulation are validated credible compared with that of the experiments. In a word, the new tube has a simple structure, which makes the manufacture convenient, and thus it is easy for it to be produced in a large scale in industries. So it will have a bright application and a broad developmental prospect.