自然循环工况下倒U型管蒸汽发生器的一次侧流量反转机理

Flow Inversion Mechanism in the Primary Side of an Inverted U-tube Steam Generator Under Natural Circulation

在自然循环工况下,倒U型管蒸汽发生器(UTSG)的进出口存在负压降,使得UTSG内的部分倒U型管易发生倒流现象.针对特定的UTSG,定量地建立倒U型管进出口压差随一次侧质量流量变化的水动力曲线,并采用最佳估算程序Relap5对UTSG进行建模分析.针对同一给定的自然循环工况,分别采用UTSG入口总质量流量从高到低和从低到高两种质量流量加载方式趋近.研究发现,自然循环工况的质量流量加载方式对UTSG倒流的发生有显著影响;从低到高的质量流量加载方式会导致更多倒U型管发生倒流,产生更大的流动阻力;在其他运行参数相同的情况下,UTSG倒流反转为正流的临界质量流量远高于正流反转为倒流的临界质量流量;采用从高到低的质量流量加载方式到达自然循环工况更有利于避免UTSG倒流的发生.

For natural circulation,it is shown that the negative drop of pressure in the primary side of a inverted U-tube steam ge-nerator（UTSG）caused by the density difference of the fluid inside may result in reverse flows within some inverted U-tubes.A model of a given UTSG with nine parallel U-tubes is established using the best estimate code Relap5.Two conditions with different UTSG inlet mass flow rate loading methods are compared.Results show that mass flow rate loading methods significantly affect UTSG reverse flow phenomenon.Approaching the natural circulation by decreasing the inlet mass flow rate leads to less reverse flow U-tubes and flow resistance than increasing the inlet mass flow rate from zero.And the critical mass flow rate of flow inversion for the former condition is smaller than that for the later.In conclusion,reaching natural circulation by decreasing inlet mass flow rate of UTSG may avoid reverse flow.