Journal of Quantitative Spectroscopy & Radiative Transfer 101 (2006) 527–539 Evaluation of micro-bubble size and gas hold-up in two-phase gas–liquid columns via scattered light measurements Mustafa M. Aslan a , Czarena Crofcheck b , Daniel Tao c , M. Pinar Mengu¨c - a,Ã a Department of Mechanical Engineering, University of Kentucky, Lexington, KY 40506, USA b Department of Biosystems and Agricultural Engineering, University of Kentucky, Lexington, KY 40506, USA c Department of Mining Engineering, University of Kentucky, Lexington, KY 40506, USA Abstract 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 y ¼ 120  was determined for a gas velocity range of 0.04–0.35 cm/s (ID ¼ 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. r 2006 Elsevier Ltd. All rights reserved. Keywords: Light scattering; Two-phase flow; Bubbles; Scattering matrix; Bubble size; Flow rate 1. Introduction Two-phase gas–liquid (GL) tanks/columns/flows are extensively used in chemical, biochemical, petroleum, and mining industries [1–3]. Efficiency of mass transfer between liquid and gas depends on the total surface area of bubbles in the liquid. Therefore, determination of characteristics of the bubble population in a GL flow, such as bubble size distribution and gas hold-up in the liquid, is critical for evaluation of column performances. There are many experimental methods devised over the years to characterize GL flows in columns [2]. The parameters concerning column mass transfer efficiency are numerous, including bubble size distribution, ARTICLE IN PRESS www.elsevier.com/locate/jqsrt 0022-4073/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jqsrt.2006.02.068 Ã Corresponding author. Fax: +1 859 257 3304. E-mail address: menguc@engr.uky.edu (M. Pinar Mengu¨c - ).