开式自然循环流动不稳定性的频域法分析

Instability Analysis of Open Natural Circulation System Using Frequency Domain Method

非能动安全壳热量导出系统依靠自然循环导出事故后排入安全壳内的热量,但在运行过程中也可能发生流动不稳定性现象。本文以某开式自然循环非能动安全壳热量导出系统为对象,建立了描述该系统行为的数学模型和本构关系,运用小扰动法对守恒方程进行线性化,通过Laplace变换获得系统质量流速随加热段进口焓变化的传递函数。基于Nyquist稳定性判据,分析了热工参数变化对该自然循环系统稳定性的影响。结果表明:系统的流动稳定性本质上受空泡份额随质量含气率的变化关系的制约,在一定范围内,随着质量含气率的增大,空泡份额对质量含气率的敏感性减弱,系统趋于稳定。

The passive containment cooling system may serve to remove the heat from the containment after some accidents by means of natural circulation.However,it may also suffer from the two-phase flow instability during the operation.The mathematical model and constitutive relationships were set up for an open natural circulation system.The conservation equations were linearized by using the perturbation method.The transfer function of the mass flow rate of the system was derived in terms of the enthalpy change of the heating section through Laplace transformation.Based on the Nyquist stability criterion,the influence of thermal-hydraulic parameters on the stability of the natural circulation system was analyzed.The results show that the flow stability of thesystem is mainly dominated by the relationship between the void fraction and the quality of the two-phase flow.In the studied range,with the increase of the quality,the sensitivity of the void fraction to the quality is weakened,and the system tends to be stable.