Design and analysis of a mixer incorporating lateral mixing to laminar convective mixing for polymer melts

This study is intended to understand and emphasize the importance of incorporating lateral mixing to laminar convective mixing.;The concept of randomization of laminar flow patterns by introducing a periodic flow in the direction perpendicular to the direction of bulk flow, i.e., lateral motion, was proposed, incorporated in a novel mixer design, experimentally tested and partially theoretically analyzed.;The Enhanced Mixing Cell (EMC) Batch Internal Mixer, which was designed, constructed and used throughout this study, consists of two concentric cylinders. The inner one is rotationary with a step barrier on it; the outer one is stationary containing a slot with a piston inside it moving periodically up and down, which allows the fluid to flow in and out of the main annular chamber in the lateral direction. The contribution of lateral motion, which abstracts and reintroduces the fluid from and into the main circulation, is to improve laminar convective mixing and to eliminate the lateral nonuniformities. This lateral flow mixing mechanism can be ideally explained in terms of rearranging of the highly ordered laminar flow streamlines by repeatedly "splitting and mismatching" them.;Extensive mixing is improved by reducing the two-dimensional scale of segregation, instead of the striation thickness, which is not necessarily decreased. Intensive mixing is improved, simply as the result of improvement of extensive mixing, or, in other words, by giving all the material in the main mixing chamber through lateral flow an equal chance to go through the tip region and be broken up.;Experimental results show a great deal of difference between the cases of absence and presence of the lateral mixing. The combination of the periodic lateral and steady laminar flow results in a homogeneous mixture, while laminar mixing alone inevitably produces samples with a strong texture, which have some unique pattern that can be readily visually recognized.;Compared to the Banbury Mixer, the EMC Batch Internal Mixer is superior because of its geometric simplicity, its ability to impose a controllable degree of randomness, and its large mixing capability.;The design and application aspects of this concept for a real mixer are also discussed.