低参数条件下并联多通道间汽-水两相流密度波不稳定性分析

Analysis of Steam-Water Density Wave Instability Among Parallel Multiple Channels Under Low Parameter Conditions

建立了适用于并联任意多通道间汽液两相流密度波不稳定性分析的时域法计算模型,将并联通道内流动区域划分为一系列网格,建立质量、动量、能量守恒离散方程,考虑沿程两相工质物性变化。参考深度调峰低负荷条件下锅炉水冷壁相关参数,对低压力(p=8~10 MPa)、低质量流速(G=300~500 kg/(m^(2)·s))下并联多通道间密度波脉动特性开展计算分析。采用先增大后减小的线性分布规律近似模拟水冷壁管道壁面的轴向热流密度分布。结果表明:随着系统压力、入口工质质量流量的降低,系统稳定性逐渐降低;随着轴向热流密度分布不均匀度的增大,系统密度波脉动趋于发散,系统临界热负荷逐渐降低,系统趋于不稳定;系统临界热负荷随轴向热流密度分布不均匀度的变化趋势是非线性的。

A time-domain calculation model was developed to study the density wave instability of steam-water two phase flow in parallel multiple channel system.Based on the collocated mesh method,the flow domain along each channel was split into a series of sections,and the discretized mass,momentum,and energy equations were established for each section with consideration of the property variation.According to relevant parameters of boiler water wall under low load conditions during deep peak shaving,the model was used to study the density wave oscillation characteristics among parallel multiple channels under low system pressure(p=8-10 MPa)and low system mass flow rate(G=300-500 kg/(m^(2)·s)).The axial heat flux distribution on the pipe wall was simplified,and it followed a linear distribution law that increases first and then decreases along the pipe.Results show that the stability of the system is gradually weakened with the decrease of system pressure and system mass flow rate.With the increase in the non-uniformity of the axial heat flux distribution,the density wave oscillation of the flow rate tends to diverge,and the corresponding threshold heat power gradually decreases,indicating that the system tends to be unstable.The change trend of the threshold heat power with the non-uniformity of the axial heat flux distribution is nonlinear.