Chaotic Advection
“The process of chaotic advection is characterized by recursive stretching and folding of compounds in a fluid-like state. When generally immiscible plastics or plastic-like materials are processed, the resulting composite may develop encapsulation as a function of the chaotic advection.
A twin-rod, continuous flow smart blender device consists of a barrel in which the conditions for chaotic advection are developed. Twin stir rods in the barrel rotate independently, but in the same direction to develop chaotic advection. The number of rotations of the rods and the time a melt- remains in the barrel (the residence time) determinate the extent of the chaotic advection.
When a master batch comprising a melt-processable material and particles is subjected to chaotic advection, the particles may become oriented in the melt-processable material (as is the case with clay), or form inter-connecting networks (as is the case with carbon black). The degree of orientation or network formation and interconnectivity among particles depends on the degree of chaotic advection to which the master batch is exposed.
A second, melt-processable material may be introduced to the smart blender separately from but simultaneously with a master batch. In such examples, the particles either are oriented or form networks in the melt-processable material of the master batch, and the second, melt-processable material exists as alternating layers of material, effectively free of the particles.
The extent of particle orientation and particle network characteristics in a melt and processing time are related to the number (N) of chaotic advection periods. One period can comprise the separate and sequential rotation of individual stir rods that can be rotated in the same direction. Perturbation strength (u) equals the fraction of a complete rotation for each rod during one period. In the following examples, in which the continuous chaotic advection blender was used, unless otherwise noted, u=3.0. Chaotic advection was induced by the rotation of stir rods. In a preferred configuration (embodiment), rods were rotated by separate stepper motors independently controlled by a computer interface.
Recent US Patents
4/7/2009
7,514,2009
Composites with oriented particles and particle networks with method
Zumbrunnen of Clemson University, South Caroling used chaotic advection to plastis with high barrier properties for food packaging. Clay is especially a good filler forming very thin platelets (approximately 1 nm) and having high frontal area with low mass diffusively. (RDC 3/14/2011)
Recent Journal Articles
The influence of cam geometry and operating conditions on chaotic mixing of viscous fluids in a twin cam mixer
( 581–598) AIChE Journal 57 #3 (2011)
Robinson and Cleary of CSIRO Mathematics, Australia used smooth particle hydrodynamica (SPH) simulations to better understand the mixing performance of a class of two-dimensional Twin Cam mixers. The chaotic manifolds of the flow are used to describe the mixing and to identify isolated regions. For an equilateral triangle cam geometry, a figure-eight manifold structure traps a layer of fluid against the cam boundaries. Changes in the differential rotation and phase offsets between the cams results in modest improvements in the mixing rate across the manifold barrier. Reducing the apex angle of the triangle changes the manifold structure and allows the trapped layer of fluid to mix more effectively with the rest of the domain. Examining the chaotic manifolds within a typical industrial mixer can provide valuable insight into both the transient and long-term mixing processes, leading to a more focused exploration of possible mixer configurations and to practical improvements in mixing efficiency. (RDC 2/10/20110