Characteristic Research And Analysis Of Shellside With Different Support Structures In Heat Exchangers With Longitudinal Flow Of Shellside Fluid

Heat transfer is a universal equipment in many industrial fields such as chemical industry, petroleum refining industry, power industry, food industry and light industry etc. In thermodynamic system, the investment of heat exchanger is in higher proportion in gross investment of an enterprise, and the performance of heat exchanger directly influences thermal cost. In recent years, because of many factors as process requirements, energy crisis, and environment protection etc, enhancement technology of heat transfer and the modern design & research methods of heat exchangers have made great progress.One of the important topics for heat transfer enhancement in shellside of shell-and-tube heat exchanger currently are to revise the structural style, improve the flow condition and increase heat transfer coefficient. Many countries commit themselves to researching new types of heat exchangers with longitudinal flow of shellside fluid(HELFSF). HELFSF makes its shellside fluid flow longitudinally through new type of bundle support structure instead of conventional baffle. The notable characters of HELFSF are shellside fluid flows through bundle longitudinally, achieves entire adverse current with tube fluid, results in large effective temperature difference and less heat transfer dead space, and the flow disturbance caused by the support structure enhances heat transfer, prevents flow-induced vibration of tubes when fluid flows across tube bundle transversely.It is an important topic to carry out further study on HELFSF. The analysis and research of shellside fluid flow and heat transfer in heat exchangers are helpful in the development of safe, high efficiency and economical heat exchanger structure. In conventional research of heat exchangers, experimental method is mostly employed. However, it cannot keep pace with the requirement of research and development of heat exchangers because of its intrinsic disadvantages. As numerical simulation method is used more widely with the advancement of computational fluid dynamics, computational heat transfer and computer technology. Numerical simulation has lots of virtues relative to experimental method, such as easy to change calculational condition, convenient use, capacity of calculating fluid flow and heat transfer on complex conditions, less limits, short period, low experimental expense, easy repetition and modification, capacity of getting detailed information, etc. It is one of important research directions to employ numerical simulation method to analyze and study heat exchangers and to accelerate development of heat exchangers.In the dissertation, the numerical simulation method is selected. FLUENT, CFDsoftware with strong function, is employed to calculate 3-dimentional fluid flow and heat transfer of HELFSF bundle supported by rod-baffle, big round-hole baffle, small round-hole baffle, plum-hole baffle, rectangle-hole baffle and ring-baffle. By the analysis and comparison of fluid flow and heat transfer under different flow rates, the distribution conditions of flow field and temperature field are obtained and some software as Excel and Origin are used to analyze and compare the results in detail. The main work and innovative points of the dissertation are as follows:(1) The software Fluent and the periodic unit duct model are employed to carry out numerical simulation. Based on previous work and empirical formula for heat transfer, the numerical simulation of fluid flow and heat transfer for rod-baffle supporting periodic unit duct model is implemented and the results are verified. Meanwhile, in order to ensure the correctness and accuracy of numerical simulation, models with different mesh densities and different periodic lengths are calculated to determine mesh density and periodic length.(2) By the numerical simulation of fluid flow and heat transfer in shellside with different support structures and the post processing of results, the conditions of velocity, pressure and temperature on different sections are obtained and the detailed analysis of fluid flow and heat transfer are carried out.(3) Based on the analysis of various support structure, it is catched out and concluded that the vortex and reverse flow and near-wall jet flow when fluid flows across support structure such as big round hole, plum hole and so on scours the boundary layer and decreases the thickness of fluid film, which enhance the heat transfer together with the effect of disturbance flow and turbulence flow.(4) Based on the analysis of various support structure, the simulation results are compared with rod-baffle. The increment percent of different shellside support structures versus rod-baffle support is tabled to discuss the characteristics of various support structure comprehensively.The method of numerical simulation can be used to research and develop other HELFSF with different support structures. And the simulation results can provide reference for the selection and application of different support structures of HELFSF.