自然循环条件下,蒸汽发生器并联U型管束内存在单相流动不稳定性,部分U型管内存在倒流现象,对反应堆非能动安全产生负面影响.本文通过对基本守恒方程无量纲处理,采用线性扰动分析理论,获得了U型管内流动不稳定性判断准则(特征格拉晓夫数).结果表明,当U型管格拉晓夫数高于特征格拉晓夫数时,管内流动是不稳定的,会出现倒流现象.以某型蒸汽发生器为对象,对U型管束流动不稳定性进行判断,通过与现有判别方法进行对比,验证了建立的U型管内流动不稳定性的判别方法.在此基础上,分析了蒸汽发生器一次侧流体入口密度对倒流现象的影响,发现当入口密度降低时,倒流现象更容易发生.本文结论可为蒸汽发生器优化设计提供一定的理论支持.%Under the natural circulation conditions ,it is shown that the single phase flow instability in parallel U-tubes of steam generator (SG ) can exist and the reverse flow occurs within some U-tubes ,which have negative effect on nuclear power plant passive safety .In this paper ,the dimensionless analysis was used to deduce the non-dimensional conservation equations and the flow instability criterion (critical Grashof number) was derived according to the linear instability analysis .The results show that for a certain U-tube , w hile the Grashof number is higher than the critical Grashof number ,the flow in the U-tube is instable ,and the reverse flow will occur .Aiming at a certain type of steam generator ,the flow instability in the U-tubes was analyzed and the flow instability criterion was verified by comparing with current existing methods .The effect of inlet density on the flow instability in U-tubes was studied .The result shows that the lower the inlet density is ,the easier the reverse flow happens .The conclusions can be used in the optimal design of the steam generator .
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