Numerical Simulation Of Flow&Heat Transfer And FSI Analysis Of Expansion Joint In A Superheater

The superheater plays a pivotal role in the marine steam power plant, one of the most important components of marine boiler. Due to the high smoke temperature and the convection heat transfer coefficient, which is lower than the boiling heat transfer coefficient in the evaporate surface, the heat transfer condition in superheater is unfavorable relatively. When a higher thermal load meets relatively lower steam flow, while the steam temperature in the tube is higher, easy to cause the tube explosion. At the same time, the connection strength and tightness of the junction of the superheater tubes and collector are also pivotal indicators to investigate the superheater security. During the operation of marine boiler, the operating conditions change frequently. Because of the influence of thermal stress in cyclic thermal loading, the residual contact stress and tightness may decrease, which is likely to cause leakage.Attribute to the working characteristic mentioned above, the superheater is one of the most fragile parts in the marine steam power plant. This dissertation, started from the basic theory, is mainly concentrated on the numerical simulation of Flow&Heat transfer and Fluid-Structure-Interaction (namely FSI) analysis of the expansion joint in a superheater. The software used in the projects is Fluent and ANS YS respectively. The main contents include:(1)Based on the theory of Fluid Mechanics and Heat transfer, a simplification principle for the numerical simulation in Fluent software is deduced and obtained in the treatise. The author deems that given the certain boundary condition, the factors which influence the characteristic of flow and heat transfer in superheater can attribute to the parameters of nd2/D2,L/(√nl) and v1m-1dm/s1. The simplified model possesses a lower amount of grid, and can correctly reflect the feature of Flow&Heat transfer simultaneously.(2)The normal condition and faults of rupture and clapboard collapse are realized in Fluent through the modification of boundary condition, which in ture, the laws of flow and heat transfer are deduced. In light of the working feature, the optimization design is carried out in the treatise. While the risk of faults can be lessen in the optimized superheater, the dominant parameters can be remained the same.(3)Through the numerical simulation of cold expansion process of materials of12Cr1MoVg and1Cr19Ni11Nb, the results of analysis indicates that these2kinds of materials mentioned above both have a relatively high-quality cold expansion performance relatively abominable working condition(4)Based on the results achieved, a FSI analysis is carried out in the dissertation, where the influence of temperature load and the ES in straight tube are considered simultaneously. The expansion feature of tube(materials of12CrlMoVg and1Cr19Nil1Nb)and sheet(12Cr1MoVg), the structure analysis of U-shape tube and the influence of thermal expansion coefficient are involved in this part. According to the results, the tube material of12CrlMoVg reflects a better expansion performancea while leakage in joint may happen when the tube material is1Crl9Ni11Nb because of the discrepancy of thermal expansion coefficient between tube and sheet; when the discrepancy is between-0.2×10-5and0.2×10-5, a considerable residual contact stress and the tightness in expansion joint can be guaranteed after cyclic thermal loading; the U-shape section can absorb the thermal stress stems from the thermal loading in some degree.This treatise is a improvement and extension of past analysis work. In the meanwhile, the experience can be offered to the future FSI analysis.