The Study On Fluid Induced Vibration Of Tube Bundles In Heat Exchanger

Heat exchanger, which is widely used in petroleum, electric power, chemical industry, central heating and other various fields, is one of the main industrial equipment to achieve energy recycling and improve energy efficiency. In recent years, heat transfer efficiency of the heat exchanger is being improved by increasing the span of the tube bundle which has decreased the rigidity of the tubes, at the same time the fluid flow velocity is more and more fast, flow induced vibration phenomenon has become more and more obvious, bundle failure cases caused by vibration that brought serious harm have continued increasing. Therefore, flow induced vibration of heat exchanger tube bundles is a significant research topic.Firstly, the heat exchanger modal analysis is carried out to determine the natural frequency, investigate the vibration modes and vibration characteristics; Then, through the combination of theoretical analysis and numerical simulation, several common mechanisms of fluid induced vibration, vortex shedding around a circular cylinder, turbulent flow and fluid elastic excitation, are analyzed, the vibration of tube bundles under three kinds of induced mechanism is explored in detail. The results show that the possibility of the vibration induced by vortex shedding and the fluid elastic excitation is large, and the vibration response of the tube bundle at the entrance of the shell side is larger than that of the other locations.In the modal analysis, three kinds of finite element models of heat exchanger are chosen to calculate and contrast. The natural frequency of each order is obtained, and the results provide the basis for choosing suitable numerical simulation model of the heat exchanger. The results also show the different vibration characteristics of the different vibration orders. In the analysis of flow field in shell side, porous medium model in Fluent software is used to simulate the fluid, the velocity field and pressure field distribution are obtained.In the vibration analysis of tube bundles induced by vortex shedding in shell side of heat exchanger, numerical simulation of the flow around a circular cylinder is carried out, and the lift coefficient and drag coefficient of the three heat exchange tubes are obtained, based on which the lift and drag force effect on heat transfer tubes are calculated and applied to the get the corresponding of the tubes through transient response analysis. The results show that tubes at the center and exit of the shell side is less than that of tubes at the entrance of the shell side. The tubes are subjected to larger stress at the baffle plate, where the stress concentration is easy to occur.In the vibration analysis of tube bundles induced by turbulence buffeting and fluid elastic excitation, through the calculation, it is determined that the tube bundle vibration may be due to fluid elastic excitation, but the possibility of vibration due to turbulence buffeting is small. By using the dynamic mesh model in Fluent software to simulate, the displacement curve of the vibration response of the cylinder is obtained.In summary, the heat exchanger tube bundles may vibrate induced by fluid flow, and the mechanism of vibration is mainly caused by vortex shedding and fluid elastic excitation. Compared with the other position of the heat exchange tube, the response and the possibility of the vibration of the tubes at the entrance of the shell side are larger. Therefore, the heat transfer tubes at the entrance of the shell side are more likely to be failure due to fluid induced vibration.