Experimental investigation on dominant waves in upward air-water two-phase flow in churn and annular regime.

This paper describes new measurements on the characteristics of waves in churn and annular flow. The measurements were for air-water flow in an 11 mm diameter vertical tube, a diameter close to the equivalent diameter of nuclear reactor channels. These measurements extend the parameter space of previous publications into the low and gas and liquid mass flow rates important for nuclear reactor fault studies. Detailed measurements of the flow characteristics are reported, including the identification of a new regime we designate ‘pre-annular flow’, in which the liquid film between the waves appears to be stationary. The results of these measurements at low mass fluxes are compared with predictions in this low mass flux region using the principal literature correlations, all of which were actually obtained from elsewhere in the parameter space. Reassuringly, the broad conclusion is that despite this, these correlations obtained from elsewhere are safe to continue to be used in this low mass flux region. A new interpretation of the criteria for onset of entrainment was also obtained from the study. [ABSTRACT FROM AUTHOR]