中文摘要：

本文以模拟压水反应堆一回路系统在自然循环条件下运行时的蒸汽发生器为对象，提出了分析蒸汽发生器并联倒U型管内单相水的流动及传热流特性的数学模型及相应的数值计算方法，计算结果表明，在一定的回路系统自然循环流动条件下，并联倒U型管内会同时发生正流和倒流。并发现，蒸汽发生器倒U型管内的倒流对一回路系统的自然循环流量有重要影响。

英文摘要：

A mathematical model and numerical calculation method to analyze the single phase water flow and heat transfer behavior in inverted U-tubes of a steam generator with natural circulation have been presented. The calculation results show that normal flow and reverse flow can simultaneously exist in the inverted U-tubes of the steam generator with natural circulation. It is also found from the calculation results that the reverse flow in the inverted U-tubes of the steam generator has great influences on the mass flow rate in the natural circulation system.