(An) experimental investigation of the three modes of reflux condensation and their transition criteria

Abstract

The reflux condensation phenomenon in steam generator U-tubes, which may be an important heat removal mechanism in a certain phase of small break loss of coolant accident in nuclear power plants, has been investigated. The flow pattern is an important factor of heat removal capability. In the present work, a series of experiment have been performed to establish the basic modes of reflux condensation. Basically, three modes have been identified which is in complete agreement with the previous workers. Three basic modes are the filmwise reflux condensation mode, the complete reflux condensation mode and the thermosyphoning mode. Experimental results that have been obtained under the filmwise reflux condensation mode are compared with the Nusselt condensation theory. In addition, to examine the effect of cooling water temperature on the reflux condensation lengths, two series of tests were made at two different coolant temperature levels. Finally, transition criteria between the three reflux condensation modes were experimentally investigated while changing the inlet steam flow rate.