超超临界锅炉水冷壁管传热恶化对横向裂纹影响的有限元分析

FEM Analysis of Heat Transfer Crisis of Water Wall Tube on Transverse Crack in Ultra-Supercritical Pressure Boiler

为研究不同传热条件下水冷壁管的温度及热应力分布特征,以某1 000 MW超超临界锅炉水冷壁管为对象,建立了水冷壁管的三维有限元模型,分正常传热和传热恶化2种情况进行了计算。计算结果显示,向火侧壁面热负荷、管内传热系数对传热恶化后的温度和热应力有显著影响,在尚未达到屈服前,水冷壁管的热应力与温度基本呈线性关系。传热正常时,水冷壁管鳍片处温度和热应力值大于水冷壁管向火侧顶点相应值,而向火侧顶点发生破坏的可能性较小;在传热恶化时,水冷壁管向火侧顶点的温度和热应力迅速增大,并明显高于水冷壁管鳍片处,传热恶化的反复出现引起的交变应力最终导致水冷壁管横向裂纹的产生。

In order to study the features of the temperature and the thermal stress distribution in water wall tubes under different conditions, the 3D FEM model of a water wall tube of a 1 000-MW ultra-supercritical pressure boiler is built and the computation is taken in the scenarios of the normal heat transfer and the deteriorated heat transfer. The computation results show that the temperature and the thermal stress are strongly affected by the fire-side heat nux and the tube internal heat transfer coefficient, and there is a linear relationship between the temperature and the thermal stress before the water wall tube yields. In the normal heat transfer scenario, the temperature and the thermal stress in fins are bigger than that in the fire-side apex, while in the deteriorated heat transfer scenario, the temperature and the thermal stress in the fire-side apex grow greatly, and they are much bigger than that in fins. The alternating stress caused by the repeated heat transfer crisis will make transversal cracks in the tube.