The role of flooding phenomena in reflux condensation in a vertical inverted U-tube

Reflux condensation in a vertical inverted U-tube inside steam generators form an important heat removal mechanism in loss of coolant accidents in nuclear power plants. The role of flooding on reflux condensation in a single inverted U-tube was studied. The range of reflux condensation covered in the present paper is the ''complete reflux condensation'' range, which consists of an oscillating single-phase water column sustained by a condensing two-phase countercurrent churn-annular flow region. The analysis based on the Wallis type of flooding correlation was carried out by postulating that the formation of the single-phase water column on top of the two-phase region was governed by ''flooding'' conditions at the entrance. The analytical results were compared with the experimentally measured rate of condensation for the range of operating conditions