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 23 cm/s and superficial water velocities up to - 11 cm/s, corresponding to a global air volume fractions (gas holdup) up to 29%. The experimental investigation concerned (i) flow visualization, (ii) local data from a double fibre optical probe and (iii) gas holdup measurements. The images obtained from an optical camera were used to observe the general flow patterns. The data obtained from the double fibre optical probe were used to study the local flow characteristics. In particular, the local void fractions, the bubble velocities, the bubble mean diameters and the bubble diameter distributions and are presented and discussed. The bed expansion technique was used to obtain the gas holdup measurements for every operating condition. The gas holdup measurements are discussed, compared with existing correlations and used for investigating the flow regime transitions. Finally, the gas holdup and the local void fraction measurements data are compared and used for understanding the local hydrodynamics.