Experimental investigation of counter current air-water flow in a large Diameter vertical pipe with inners

Counter current two phase flow is encountered in a wide variety of industrial applications. This paper describes the experimental results obtained in a circular column of 240 mm diameter with two inner pipes. The counter current flow studied concerns an upward flow of air and a downward flow of water at ambient temperature and pressure. The following range of operating conditions was analysed: superficial air velocities up to 26 cm/s and superficial water velocities up to 11 cm/s, corresponding to global air volume fractions up to 29%. The experimental investigations concerned (i) flow visualization, (ii) local data from a double fibre optical probe and (iii) global void fraction data. Images obtained from an optical camera were used to observe the general flow patterns. Data obtained from the double fibre optical probe were used to study local flow characteristics. In particular, bubble velocity, bubble mean diameter, bubble diameter distribution and local void fraction are presented and discussed. Gas disengagement technique was used to obtain the volume averaged air fraction over a range of superficial air velocities. Global void fraction results are discussed, compared with existing correlations and used for investigating flow regime transition. Finally, global and local data are compared and used for understanding hydrodynamics