No abstract

This study attempts to investigate the kinematics of the mixing occurring in the lenticular kneading disc section of the co‐rotating twin screw extruder, employing the tools of dynamics. The Eulerian velocity field distributions, generated by a two‐dimensional isothermal and creeping flow of Newtonian fluid under the periodic co‐rotation of the kneading discs, were obtained by Finite Element Method. A simple and novel particle tracking technique based on the FEM solution of the velocity field was employed to follow individual particles, and to produce the Poincare section mapping. Furthermore, fingerprints of chaotic motion were revealed essentially through the Lyapunov exponents, which were positive. The results suggest that the dynamics in the two‐dimensional kneading disc section of the twin screw extruder can be characterized as capable of imparting chaotic motion. The tools developed in this study should facilitate a better understanding of the mixing capabilities of the twin screw extrusion process.

The separation features of a new type of PLOT U column are presented through many applications. This type of PLOT U column is coated with a divinylbenzene-ethylene glycol dimethacrylate copolymer. It has an increased polarity when compared with a conventional PLOT Q type column. The stationary phase of the PLOT U column is truly bonded, thus providing column rinsability and low column bleed.

SummaryAlumina-coated porous layer open tubular (PLOT) columns are widely used for analyses of light hydrocarbons (Ci to C6). There is, however, a need for improved selectivity for complex analyses such as the determination of impurities in high purity petrochemical products. Some commercial alumina PLOT columns do not have sufficient selectivity for such analyses. The selectivity of four commercial alumina PLOT columns is evaluated for analyses of propylene and ethylene, and differences in column selectivity discussed. Requirements of column selectivity and retention are presented for several applications including the analysis of refinery gas, transformer oil gas, and fuel gas.

Slip at the wall is often encountered during the flow of polymeric materials and during the mixing of multiphase systems, such as concentrated suspensions. This article is concerned with the development of a numerical method to simulate flows that show such slip. The flow of a generalized Newtonian fluid with Bingham-like viscosity curve is considered and a linear relation between the slip velocity and the shear stress at the wall is used. A novel method based on a penalty parameter is developed to implement the slip boundary conditions into the finite element method. The flow in the conveying elements of the extruder is used as an example of the application of this method. It is shown that the wall slip decreases the pressurization capability of the extruder and increases the leakage flow occurring over the flight tips, as well as its mixing efficiency by reducing the rate of recirculation and the stress levels. The technique developed in this article can be applied to many flows that show slip phenomena and may be used to gain better understanding of the dynamics of mixing of commercially important materials.