| A comprehensive experimental and theoretical investigation of the mass transfer processes in the extrusion devolatilization of polymer solutions has been completed. The analysis covers the violently foaming regime of mass transfer where the supersaturation of the system far surpasses viscous and surface forces that might retard volatile phase growth, the simpler case of bubble free mass transfer where solvent concentrations are extremely low and the comprehensive transition which exists between these two regimes. Experiments have been performed with three dissimilar polymer/solvent systems on a laboratory scale (20 mm) counter-rotating, non-intermeshing twin screw extruder. A novel stochastic modeling approach has been applied to the foaming regimes to combine the numerous fundamental physical processes associated with the existence of bubbles into a usable, realistic model. The bubble free mass transfer areas have been modeled using a penetration theory/surface renewal model specifically tailored for this extrusion geometry. Overall good agreement and consistency between the experimental and theoretical results have been observed. The modeling has given insight into surface area, residence time and average mass transfer coefficients dependencies on operating conditions. The effects of screw configuration on the various mass transfer regimes are also considered. |
