Evaluation of micro-bubble size and gas hold-up in two-phase gas-liquid columns via scattered light measurements

In this paper, potential use of an elliptically polarized light scattering (EPLS) method to monitor both bubble size and gas hold-up in a bubble-laden medium is explored. It is shown that with the use of the new EPLS system, normalized scattering matrix elements (M-ij's) measured at different side and back-scattering angles can be used to obtain the desired correlations between the bubble sizes and input flow parameters for a gas-liquid (GL) column, including gas flow rate and surfactant concentrations. The bubble size distributions were first evaluated experimentally using a digital image processing system for different gas flows and surfactant concentrations. These images showed that the bubbles were not necessarily spherical. We investigated the possibility of modeling the bubbles as effective spheres. The scattering matrix elements were calculated using the Lorenz-Mie theory and the results were compared against the experimentally determined values. It was observed that the change in the bubble size yields significant changes in M-11, M-33, M-44, and M-34 profiles. An optimum single measurement angle of theta = 120 degrees was determined for a gas velocity range of 0.04-0.35 cm/s (ID = 4.5 cm). The choice of the optimum angle depends on frit pore size, column diameter, gas pressure, and surfactant concentration. These results suggest that a simplified version of the present EPLS system can effectively be used as a two-phase flow sensor to monitor bubble size and liquid hold-up in industrial systems. (c) 2006 Elsevier Ltd. All rights reserved.