Stress Analysis And Structure Optimization Of Shell-and-Tube Heat Exchangers Under Thermal-Mechanical Load

In the process of using tube-and-shell heat exchanger,the excessive stress of tube plate and heat exchange tube is one of the main reasons for the structural damage of the heat exchanger.According to the load condition of tube-and-shell heat exchanger,this thesis analyzes the stress of tube-and-shell heat exchanger under the action of thermal-mechanical load,and puts forward the structural optimization scheme of the heat exchanger.This thesis mainly studies the stress of heat exchanger from two aspects.One is to explore the method of reducing the residual stress by studying the welding residual stress of heat exchanger.The second is to study the working stress of heat exchanger,and put forward the measures to reduce the working stress.The service life of heat exchanger is improved by studying and optimizing the residual stress and working stress.In this thesis,the residual stress caused by welding is simulated by using external moving heat source.The simulation results show that the residual stress of different welded structures is different.The welded structures with protruding Angle,open groove and protruding Angle open groove can reduce the welding residual stress,and the form stress of protruding Angle open groove can reduce the maximum.It is found that with the increase of welding speed,the maximum stress value will decrease slightly.By analyzing the power intensity of different welding heat sources,the maximum value of welding residual stress will decrease correspondingly when the power intensity of welding heat sources is reduced.The welding residual stress of heat exchange tube plate was studied by making welding model.Four different forms of welding models were made,namely flat welding,protruding Angle,open groove and protruding Angle open groove.The residual stress of four kinds of welding specimens was detected by X-ray method.The test results were close to the simulated values in Chapter 2,which confirmed the correctness of the residual stress simulation results.Four kinds of welding specimens were subjected to ultrasonic impact.By comparing the size of the residual stress before and after ultrasonic impact,it is found that ultrasonic impact can reduce the welding residual stress,and can change the welding tensile stress before ultrasonic impact into compressive stress,which proves the feasibility of ultrasonic impact in reducing the residual stress.The stress of tube-and-shell heat exchanger is analyzed by the method of heat-fluid-solid coupling under the thermal-mechanical load.The numerical simulation is carried out under the condition of adding temperature load,pressure load and residual stress load.Through the finite element analysis,it is found that the maximum stress value of the heat exchanger is located at the joint of tube plate and heat exchange tube,and the stress value is particularly large at the joint of tube plate and shell.The effects of residual stress load and ultrasonic impact on heat exchanger stress are compared.It is found that the existence of residual stress has a great impact on heat exchanger stress.The value of residual stress decreases after ultrasonic impact,and the maximum value of heat exchanger stress also decreases.In order to solve the problem of excessive stress of heat exchanger,three kinds of structural optimization schemes are put forward,which are reasonable selection of materials of heat exchanger tube and shell,changing the thickness of heat exchanger tube plate and changing the welding structure of heat exchanger tube and tube plate.Through finite element analysis of the optimized heat exchanger and comparison with the original structure heat exchanger,the overall maximum stress of the optimized heat exchanger is greatly reduced,and the structure optimization of the heat exchanger is realized.The thesis contains 88 figures,6 tables and 88 pieces of references.