Evaluating the two-phase flow through upward branches in horizontal vessels or large tubes

The accurate prediction of the mass flux through a small break or a branch at the bottom, the top or the side of a horizontal coolant pipe with stratified flow is of great importance in various fields of the industrial technology, both in case of normal operation or accidental situations. Examples can be found in chemical or nuclear technologies. On this subject, various Authors carried out extensive experimental and theoretical studies in order to determine the beginning of liquid or vapour entrainment and proposed correlations for the evaluation of the exit quality. As in case of upward branch the proposed correlations show some weakness, we have set up a new formulation which overcames such a difficulty. Such a formulation has been tested by implementing it in two codes of the well known RELAPS series and then by performing the simulation of a blowdown transient carried out in the Joint Research Centre horizontal vessel COLUMBUS plant. Excellent results have been obtained.