Experimental research on space distribution of reverse flow U-tubes in steam generator primary side

Abstract

For the phenomenon of single-phase reverse flow in the parallel U-tubes of the steam generator (SG), the occurrence and disappearance of the reverse flow are systematically analyzed by experimental methods, as well as the reverse flow rate and the space distribution of the reverse flow U-tube. The experimental results show that there are different critical values corresponding to the occurrence and the disappearance of reverse flow. The reverse flow occurs as the pressure drop of U-tube is reduced to the reverse flow critical pressure drop. Also the flow becomes normal flow as the pressure drop of U-tube is above the normal flow critical pressure drop. When the reverse flow occurred in parallel U-tubes, the flow distribution will have several states. The space distribution of reverse flow U-tube has a certain randomness to a single experiment, but there are also statistical rules with amounts of repeated experiments. In this study, the changes of critical mass flow rate corresponding to the occurrence and disappearance of reverse flow with the inlet temperature are obtained, by which the operation regions of the parallel U-tubes are divided into three parts, namely normal flow region, reverse flow region and blending region, respectively. These research results could be helpful in the development of the reverse flow theories.