用于缓减UTSG倒流的U型管改进研究

针对自然循环条件下蒸汽发生器部分并联U型管出现的倒流现象，以增强自然循环能力和减少倒流为目的，提出非对称U型管改进方案。基于基本守恒方程，建立了非对称U型管流动传热计算模型和自然循环冷热源位差计算模型。在此基础上，以某型核动力装置U型管为原型，对改进前后U型管倒流临界流量与回路冷热源位差的变化进行了计算分析。计算结果表明：非对称U型管改进使倒流临界流量明显减小，回路冷热源位差明显提升。适当调整U型管上升段与下降段长度比可减少倒流发生，提高自然循环能力。

Improvement of U-tube for Easing Reverse Flow in UTSG

For the reverse flow to occur within partial U-tubes of U-tube steam generator (UTSG) under natural circulations, a new asymmetric U-tube was proposed to enhance the natural circulation capacity and ease the reverse flow. Based on the basic conservation equations, the mathematical model was developed for calculating the pressure drop in U-tube and elevation difference between cold and heat sources. On this basis, taking a nuclear power plant U-tube as prototype, the changes of critical mass flux and elevation difference between heat and cold sources were calculated before and after improvement. The results show that the new asymmetric U-tube can reduce critical mass flux significantly and increase the elevation difference between heat and cold sources. The appropriate adjustment of the length ratio between up section and down section can ease reverse flow and improve the natural circulation capacity.