Flow field analysis of batch and continuous mixing equipment.

摘要

Banbury mixers and corotating, intermeshing twin screw extruders are widely used in polymer processing. The flow field in both these mixing equipments is difficult to analyze due to the complex geometry and highly transient character of the flow. In this work, a fluid dynamics analysis package--FIDAP, using the finite element method was employed to simulate the flow patterns of a BB-2 type Banbury mixer and the kneading disc region of a Werner & Pfleiderer ZSK-30 corotating twin screw extruder. The problem of time dependent flow boundaries was solved by selecting a number of sequential geometries to represent a complete mixing cycle. The flow field was characterized in terms of velocity profiles, pressure distributions, shear stresses generated and a parameter {dollar}lambda{dollar} quantifying the elongational flow components. The influence of processing conditions and design variables on the flow characteristics. The influence of processing conditions and design variables on the flow characteristics was analyzed. The results obtained are important for a better understanding of the influence of design and processing conditions on mixing efficiency.; Based on the results of flow simulations in the kneading disc region, methods were proposed to investigate laminar and dispersive mixing. Following the trajectories of trace elements, the changes in interfacial areas were monitored. This quantity is reflective of laminar mixing efficiency. The change of interfacial area is strongly affected by the total strain and the value of the parameter {dollar}lambda.{dollar} The initial position and orientation of the trace elements in the flow field play important roles in their deformation.; A method was developed to predict possible droplet sizes based on Grace's (47) experimental results. The possible droplet sizes in our calculations are about one order of magnitude smaller than the actual sizes. This is due to the residence time effect, which was not considered in our calculations. A better methodology was proposed for studying dispersive mixing efficiency. However, the new approach could be very tedious and time consuming.