开式自然循环闪蒸不稳定的线性均相流模型

Linear homogeneous-flow model of flashing instability in open natural circulation system

针对开式自然循环闪蒸不稳定边界的判定问题,本文运用状态空间方法对其进行研究,提出了描述该过程的线性均相流模型,导出了判断系统稳定性的状态空间表达式,并求解得到了闪蒸不稳定的边界。模型计算结果和实验结果符合较好,仅在高加热功率工况下存在一定偏差,而形成偏差的原因是加热段内沸腾喷发过程对闪蒸过程产生强烈的干扰,使其无法形成稳定的闪蒸流动。同时实验中通过注气诱导法排除了对闪蒸过程的影响,得到新的闪蒸不稳定边界,与模型计算得到的下边界符合很好,证明了本模型结果具有较高的准确性。

With respect to judging the flashing instability boundary in an open natural circulation system,we use a state-space method and develop a linear homogeneous-flow model to describe its physical process. From the statespace analysis results,we deduce a state space expression for estimating the stability of the system. We then determine the flashing instability boundary by solving these equations. The calculation result shows good agreement with the experimental result,with only a slight deviation under the condition of high heating rate. This deviation is mainly due to the interference effect of a boiling eruption in the steady flashing flow process in high heating power conditions,and this interference makes it difficult to establish a stable flashing flow. Next,we use a gas-injection method on the up-leg to avoid this interference effect in the experiments,and obtain an accurate lower boundary for the flashing instability. This boundary agrees well with the calculated lower boundary,which verifies the accuracy of this model.