| Liquid foams being dynamic systems with a wide variety of industrial applications require continuous and non-intrusive diagnostics for monitoring of their bulk properties. The utility of polarized light scattering for characterizing liquid foams has been investigated with a vision for developing in-line diagnostic systems that can be used to monitor the foam properties and provide a basis for process control. A theoretical understanding of the polarized light propagation in foams was obtained through Monte Carlo ray tracing simulations by coupling a statistical model based on foam physics with a vector Monte Carlo scheme. The effects of the average bubble size and polydispersity on the depolarization of incident polarized laser beam were investigated. The results showed that depolarization ratios were sensitive to these parameters.; An elliptically polarized light scattering set up was used to determine the six Mueller matrix elements (S11, S12, S 22, S33, S34, and S44) of a slow decaying stable foam (shaving foam) as function of backscattering angle and time. The elements S11, S 12, and S33 are observed to be sensitive to the foam age. A qualitative agreement between the predictions from Monte Carlo simulations and measurements is observed and the elements S11, S12, and S 33 at scattering angles 120° to 135° are identified as useful parameters to measure foam properties.; The Mueller matrix elements (S11, S12, and S33) were used to study the dynamic evolution of foams generated from four different solutions using a kitchen blender. The polarized intensities (S11+/- S12 and S11+/- S33) were monitored as the foam drained freely and coarsened. The drainage and coarsening models were used to correlate the polarized intensities to bubble size and gas to liquid content. S11+ S12 at scattering angles 120° and 130° were found to correlate the best.; The polarized light scattering is applied to the case of foam fractionation to investigate its usefulness in monitoring the process performance. The enrichment parameter, which has a strong dependence on the bubble size distribution and liquid content, is treated a metric representative of foam properties. Three different gas flow rates (35 ml/min, 52 ml/min, and 80 ml/min) are used with four pH values (4.8, 5.5, 6.5, and 7.5) for the foam fractionation of a dilute solution of bovine serum albumin (0.1 mg/ml). The light scattering data S11+S12 and the enrichment values are measured over a period of 90 min. and correlated using a linear model. The predictive power of the model is analyzed by comparing the observed enrichment to the one predicted by the model from light scattering data. Statistically, no significant difference was observed, suggesting the utility of S11+S12 for monitoring the performance of the foam fractionation process.; Keywords. Bubble size, liquid hold up, drainage, coarsening, Mueller matrix. |
