自然循环蒸汽发生器二次侧流动与传热特性数值模拟

Numerical simulation on flow and heat transfer characteristics in secondary side of natural circulation steam generator

为研究与传热管破损紧密相关的二次侧横流能量等流动与传热特性,使用Fluent软件中的多孔介质模型,模拟传热管束、汽水分离器和支撑板阻力。一次侧向二次侧的放热以内热源的形式加载到模型中,基于k-ε湍流模型,并结合两相漂移流模型计算,得到了立式自然循环蒸汽发生器二次侧流体温度、空泡份额、速度沿轴向高度的变化规律,同时分析了直管区和弯管区二次侧流体的横流速度和横流能量。结果表明:直管区第二块支撑板(2.3 m高度)处和弯管区沿圆周由热侧向冷侧80°和100°附近横流能量较大,分别约为300、550 J/m3,传热管破损几率较大;在进行蒸汽发生器设计时,建议减小第二块支撑板处的二次侧流动阻力,增加最内层汽水分离器和蒸汽发生器中心轴线之间的距离,从而减小传热管破损几率。

To study the flow and heat transfer characteristics of secondary side,such as cross flow energy,which closely related to the failure of tube,the resistances of tube bundles,separators and support plates were simulated by the porous medium model of Fluent.Heat transfer from primary to secondary side was loaded to the model in the form of internal heat source,variations of secondary side fluid temperature,void fraction.Velocity along the axial height in vertical natural circulation steam generator were calculated based on the k-εturbulence model and combined with two-phase drift flow model.The cross flow velocity and energy in the straight and bend regions were also analyzed.The results show that,cross flow energy was larger at the secondary support plate(2.3 m)in straight region,as well as around 80°and 100°of the circumference from hot to cold side in bend region,about 300 and 500 J/m3,respectively,and the failure rate of tube was larger.When the steam generator is designed,it is suggested to reduce flow resistance of secondary side at the secondary support plate and increase the distance between innermost steam separator and central axis of steam generator,so as to reduce the failure rate of tube.