Flow Pattern of Gas-Liquid Two-Phase Flow in a U Bend Pipeline with Upper and Lower Horizontal Pipes.

For next-generation nuclear reactors, hybrid safety systems which consist of active and passive safety systems have been planned. Steam generators using U bend pipelines with upper and lower horizontal pipes will be used as one of the passive safety systems. Liquid is generated due to condensation of steam in pipelines if these pipelines are used as condensers. It is supposed that flow patterns in the horizontal parts of these pipelines are different from those in horizontal pipes without U bend. An experimental study was carried out using a U bend pipeline with upper and lower horizontal pipe which has a lower tank and a water supply section at midway of lower horizontal pipe. Flow patterns were observed at four parts, and their maps were compared with those in the previous studies.