Experimental determination and modeling of bubble size distributions in bubble columns

Using a five point conductivity technique local values of bubble size, bubble velocity and gas fraction have been experimentally determined in a 288 mmID and 4.3 m high bubble column as a function of axial and radial position for the air/water and CO2/N-2/aqueous MDEA systems. The experimental results are compared with predictions from a fundamental two-fluid model. The implementation of a non-steady lateral drag term in the two-fluid model has been shown. In addition to improving the physical realism of the model, it is found to give slight improvements in the predictions of the distributions of local bubble size. Predictions of bubble size are found in reasonable agreement with experimental values in the heterogeous flow regime, whereas they are still found to be unreliable at low gas velocities. Local void predictions are found in reasonable agreement with experimental values, but deviations occur in the homogeneous flow regime towards the wall. This is attributed to deficiencies in the simplified bubble size model, suggesting improvements of that. It is shown how the Sauter mean diameter as a measure for bubble size is a more sensitive parameter to the radial bubble structure variations in a bubble column than the number averaged diameter. An equation for the calculation of local volumetric gas flow rates, based on conductivity probe data, has been developed and is shown to give improved predictions compared to previous methods in the heterogeneous regime.