Research On The Influence Of Tube Joint Structure And Tube Bundle On The Strength And Rigidity Of Tube Sheet

As the scale of the process industry becomes larger and larger large-scale,more and more large-scale tubular heat exchangers are used.Tubesheet is an important part in the tubular heat exchangers,and its reasonable design is of great significance to ensure the safe operation of the equipment and reduce the cost.At present,in the simulation of large-scale tubular heat exchangers,the actual tube joint structure and the role of baffles are often ignored,which reduces the accuracy of the simulation.In addition,for large-diameter thin tubesheets with complex forces and deformations,the tube bundle has a more prominent support effect on the tubesheet.It is difficult to get an accurate solution based on the existing standards.For this reason,this thesis conducted a large number of numerical simulations and analyses on the tubular heat exchanger.The main work of the thesis is as followed:(1)Numerical analysis models with different tube-to-tubesheet joint structures were established,deflection and stress distribution at the tubesheet center were analyzed and compared with the simulation results at the simplified tube-to-tubesheet joint that fully connects the tube to the tubesheet.It is found that in terms of tubesheet stiffness and strength,tightly expanded tube-to-tubesheet joints are better than welded tube-to-tubesheet joints.The results obtained by the simplified model are less conservative than welded joints.However,the simplified model can be used to simulated the fully expanded joints.For the hydraulic expanded tube-to-tubesheet joints,the larger the expansion length,the stronger the supporting effect of the tube on the tubesheet.In addition,the effect of the gap between the tube and the tube hole on the tubesheet is negligible.(2)A finite element analysis model was established for a large fixed tubesheet heat exchanger where the tubes were welded with the tubesheet.Influences of the tubesheet thickness and the number of tubes on the strength and stiffness of the tubesheet were investigated and compared with the calculated results with the code JB4732.Results show that although the deflection waveform of the thintube sheet is complicated,the wave amplitude in the middle of the tubesheet is small and has little effect on the stress of the tube.Thinning of the tubesheet as well as reduce of the number of tubes will increase the change of the deflection and stress at tubesheet.The theoretically calculated values of tubesheet stress and deflection are relatively low which may present dangerous in the engineering design of tubesheets.(3)Limit load analysis of the fixed tubesheet heat exchanger with welded tube-to-tubesheet joints was carried out.Load-bearing capacity of the tube joint structure under different load conditions was investigated,and the influence of the tubesheet thickness on the limit load was analyzed.Results show that the thinner the tubesheet,the more of the joint structures that produce plastic hinges.The tube-to-tubesheet joints are highly possible locations occuring damage to heat exchnagers.The simplified model that fully connects the tube to the tubesheet overestimates the load-bearing capacity of the heat exchanger.(4)The fixed tubesheet heat exchanger model was established by the combination of tube-shell elements,and the eigenvalue buckling analysis of the fixed tubesheet heat exchanger under the pressure of the tube side and the shell side was carried out.The influences of the tubesheet and shell thickness,number of baffles on the critical instability load of the tube bundle were examined.Results show that for the large-diameter thin tube-sheet heat exchangers,instability of the tubes located at the edge of the tube bundle may occur even under the shell-side pressure.Without the baffle,the heat exchanger will buckle before the strength failure occurs.