Study On The Integrity Of High-efficienct Heat Exchange Tubes

Heat exchanger plays an important role in industrial process equipment.With the continuous progress of society and the depletion of natural resources,high-energy conservation and environmental protection are increasingly required.At the same time,in order to improve the heat transfer efficiency,high-efficient heat exchangers have been widely used.As important components,high-efficient heat exchange tubes,which are rolled from plain tubes by forming periodical corrugations or inner and outer fin structures,have been studied extensively.Due to the special structures,high-efficient heat exchange tubes are of higher heat transfer efficiency.A lot of researches on the heat transfer performance of high-efficient heat exchange tubes have been conducted domestically or abroad.However,in order to ensure the safety of high-efficient heat exchange tubes in service,their mechanical integrities should also be studied.In this thesis,the axial stiffness,load carrying capacity,fatigue performance,metallographic structure and residual stress of converging-diverging tubes,spiral grooved tubes,T-finned tubes,diamond-finned tubes and threaded tubes have been studied.The main contents are as follows:(1)The axial stiffness of five kinds of high-efficient heat exchange tubes was studied numerically and experimentally.Finite element method was used to stimulate the axial deformation of five kinds of high-efficient heat exchange tubes under axial tension load and thus,the axial stiffness of these tubes were calculated.The results were compared with the axial stiffness of plain tubes with the same specification and the stiffness equivalent coefficients were defined.Relationship between the structural parameters of the high-efficient heat exchange tubes and the stiffness equivalent coefficient was explored.With sufficient numerical results,the formulas of the stiffness equivalent coefficient of the high-efficient heat exchange tubes were fitted and verified through the axial tensile tests.(2)The axial,circumferential,radial stresses at the five kinds of high-efficient heat exchange tubes under the axial tension load were numerically computed and the stress distributions were obtained.The influence of structural parameters on the stresses of high-efficient heat transfer tubes was investigated.By comparing the axial,circumferential and radial stresses of five kinds of high-efficient heat exchange tubes with the axial stress of plain tubes with the same specifications under the same axial tension load,the so-called stress enlarge coefficients were defined and fitted as functions of the structural parameters of the high-efficient heat exchange tubes for the engineering applications.(3)Fatigue tests,metallographic analysis experiments and residual stress measurements of the five kinds of high-efficient heat exchange tubes were carried out to find the change of the anti-fatigue performance,metallographic structures and surface residual stresses before and after rolling processing in order to provide references for the safety assessments and formulation of rolling processes of these high-efficient heat exchange tubes.