Two-phase counter-current flow in a large diameter vertical pipe with internal pipes: experiments and numerical simulations

Counter-current two-phase flow is met in several industrial plants in the chemical, nuclear and oil industry fields. This paper presents experimental and numerical results obtained in a circular column of 240 mm diameter with two inner pipes. An upward flow of air and a downward flow of water at ambient conditions is considered. Superficial air velocities up to 26 cm/s and superficial water velocities up to 11 cm/s are analysed, corresponding to global void fractions up to 28.7%. In the first part of the paper, global void fraction data are obtained using the gas disengagement technique while local data are acquired from a double fibre optical probe. Firstly, global void fraction have been analysed and compared with literature correlations. Secondly, local data have been used for a better understanding of the local phenomena. Thirdly, global and local data have been compared. In the second part of the paper, a numerical model of the experimental facility has been developed within the commercial code ANSYS Fluent Release 14.5.7. Numerical results are compared with experimental data for the case of two superficial air velocities. The effects of turbulence modelling, drag modelling and turbulent dispersion coefficient are studied. The inclusion of a correction to the drag force, in order to take into account turbulence, is found to be necessary to obtain results consistent with the experimental measurements.