Mean and turbulent fluctuating velocities in oil–water vertical dispersed flows

Experiments of oil–water upward and downward flows have been carried out in a 38 mm ID pipe to investigate the modifications of turbulent flow characteristics by the presence of dispersed phase, i.e., mean and turbulent velocity profile of the continuous phase and mean velocity profile of the dispersed phase. Results for both oil-in-water (o/w) and water-in-oil (w/o) dispersions are presented. In o/w upward flow, the axial mean velocity profiles are found to be flatter than in single-phase flow and then change to centre peaked as the input oil fraction increases; a flatter profile is seen in w/o upward flow. In downward flow, the presence of oil drops always tends to flatten the continuous phase velocity profile in o/w dispersions, while a slightly centre peaked profile is observed in all cases of w/o systems. For both upward and downward flows, the presence of the dispersed phase tends to flatten the turbulence intensity profile and to result in a more uniform distribution of the turbulent energy over the pipe cross-section. It is also found that turbulence is more likely to be enhanced in the pipe centre area, where the volume fraction and the size of the dispersed phase are larger, while suppressed in the area close to the wall. Turbulence intensity is increased with mixture velocity and is slightly higher in upward than in downward flows. The current study suggests that local dispersed phase fraction and size as well as dispersed phase velocity seem to affect turbulence characteristics in oil–water flows. Previous models based on particle-laden flows for the prediction of turbulence enhancement or suppression were examined and agreement was found to depend on the type of dispersion (i.e., whether oil or water constitute the continuous phase).