Research Of Natural Vibration Mode Of Bimetallic Heat Exchange Tube

With the development of industrial technology, petroleum, chemical, energy and nuclear industry for heat requirements continue to increase, which makes the structure of heat transfer equipment more complex and construction bigger. In order to improve wear or corrosion resistance of heat transfer tubes, while meeting the requirements of structural rigidity, strength and stability, the heat transfer tubes from the original development of a single metal pipe to double metal composite pipe. The inner tube of bi-metal heat transfer tubes of is generally steel, outer tube is generally aluminum or brass which have higher ductility and heat transfer. In order to further improve the heat transfer efficiency, usually rolling the extruded material such as copper or aluminum outer tube into fins, which form the current widely used bimetallic finned heat transfer tubes. Bimetal finned tube has many advantages, such as excellent corrosion resistance and excellent thermal conductivity. However, due to the bi-metal composite fin tube is a combination of the inner and outer tubes of different pipe material, and the outer tube fin rigidity led to its computational complexity, so it is not easy to solve the vibration characteristics.Currently, Domestic and foreign researches of tube vibration modes on bimetal composite fin is less. For effective prevention and control of dual-metal composite fin tube damage due to fluid-induced vibration, in this paper will do depth research on inherent vibration modes of bimetal finned tube. Methods used in this paper are mainly theoretical analysis, experimental testing and finite element simulation, as follows:(1) Bimetallic smooth tube is the simplified structure of bimetal composite fin tube. Natural frequencies of the bimetallic smooth tube were accurately analyzed on this article. In the theoretical analysis, the bi-metallic tube is considered as a connected in parallel system in which the equivalent section stiffness and the equivalent mass method is used to obtain the theoretical analysis formula of bimetallic smooth tube inherent frequency. And by Finite Element Modal analysis of bimetal composite tube and experimental testing methods for the natural frequency of copper- steel- copper metal composite tube verify the theoretical analysis.(2) According to the composition in the form of double-metal composite fin tube structure which was reduced to a series with the parallel combination of stiffness system. The calculation methods of equivalent sectional stiffness, equivalent mass and equivalent inertia are derived. So the theory analytical expressions of bimetal finned tube natural frequency of bending vibration and the natural frequency of torsional vibration and the natural frequency of axial vibration. The method was validated by experiments and numerical simulations. The research on the effect of the fin geometry which include fin height, fin width and fin thickness on natural frequency is done.(3) Bimetallic finned heat transfer tubes in shell and tube heat exchangers are often used in the U-shaped structure in the form of installation, in order to predict and control U-bimetallic finned heat transfer tubes of flow-induced vibration damage, it needs to accurately analyze its vibration mode. In this paper, the vibration modes of the surface and the outer surface of U-shaped steel-aluminum bimetal composite fin tube were tested and numerical simulated, and the effect of the U-bend radius R of the arc tube on the characteristics of its natural frequency is analyzed.