Investigation on Factors Affecting Reverse Flow in Inverted U-Tubes of Steam Generator Under Natural Circulation

For natural circulation, it is shown that reverse flow occurs in the inverted U-tubes of steam generator (SG) at certain low power levels. A flow model based on one-dimensional Oberbeck-Boussinesq equation was formulated to analyze this phenomenon. Two SGs of different scales were calculated. The results show that the reverse flow phenomenon occurs easily in the shorter U-tubes in small SG, but the phenomenon occurs easily in the longer U-tubes in large SG. The inlet temperature has great influence on the occurrence of reverse flow.