| The fixed tube-sheet heat exchanger is commonly used in practical engineering because of its simple structure, strong bearing ability, wide adaptability, high reliability and so on. But the traditional large size and high parameterization fixed tube-sheet heat exchangers are often affected by thermal stress, thus greatly restricting its application.The pre-stressed technology can effectively reduce the thermal stress. The methods can improve the safety reliability of the traditional fixed tube-sheet heat exchanger and expand their flexible operating range. Therefore, it is of great importance to study the heat transfer and related strength properties of the pre-stressed fixed tube-sheet heat exchanger. This paper mainly includes the followings:1. According to the symmetries of the structural model and loads, a half axial symmetry finite-element model of the fixed tube-sheet heat exchanger is built in this paper. With full consideration of the effect of temperature on the materials properties, the temperature boundary conditions of the coupled wall obtained by FLUENT software are applied to the structural analysis model in ANSYS. Then, the stress characteristics of the fixed tube-sheet heat exchanger are studied and analyzed. The analysis results show that the most dangerous areas of the fixed tube-sheet heat exchanger under temperature load tend to appear in the junction between the tubes and the tube-sheet, the shelland the tubr-sheet. The most serious damage parts of the fixed tube-sheet heat exchanger under the operating condition are consistent with the analysis results.2. After studying the influence of pressure load and temperature load on the stress characteristics of the tube sheet individually, the stress intensity on the defined path is evaluated by the method of ANSYS equivalent stress linearization. It is concluded that the influence of temperature load on the stress intensity of the defined path is very significant. On this basis, the pre-deformation technology which is used to reduce the thermal stress caused by the temperature difference between the tubes and the shell is proposed. According to the principle of stress superposition and the indirect coupling evaluation analysis, it is further proved that the pre-deformation load can improve the stress condition of the tube-sheet and enhance the safety, reliability and operation flexibility.3. Taking into account of all these factors related to the strength of tube sheets, the united method combining the finite element simulation analysis and the theory of plates and shells is put forward. Besides the method should based on the calculation formula of the bending stress of the tube sheet in GB151.Based on this method, the formula for computing the maximum bending stress of the tube sheet is deduced. And it is expected to improve the stress strength calculation of the tube sheets. According to the relevant design parameters of the fitting formula, the influence of the relevant parameters on the maximum bending stress of the tube sheet is studied separately. The results of the analysis are consistent with the classical theory and engineering experiences.According to the GB151 standard specification,the maximum bending stress of the tubesheet under different combination conditions are calculated. And the relevant simulation analysis are carried out to calculate the stress intensity of the tube sheet.Compared with the computational formula for the maximum bending stress of the tube sheets and the results of simulation analysis, it has been proved to be effective and reasonable.4. The experimental platform has been built in this paper and the testing scheme is confirmed. The stress distribution of the tube sheet will be tested by using the TDS303 static strain indicator. The simulated results agree well with experimental results within acceptable error range of engineering. Therefore, the experimental results prove the accuracy of the finite element simulation analysis results. |
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