Optimization of a static mixer using dynamical systems techniques

To improve upon the mixing performance of the Kenics mixer, variations on the standard mixer geometry are investigated using techniques from dynamical systems analysis, including Poincare sections, tracking of fluid tracers, and the development of stretching histories for tracer elements. A more traditional mixing measure, the variation coefficient, is also computed. Three geometric parameters are investigated: the twist direction of adjacent elements: the element length to diameter ratio, and the amount of twist per element. The flow in a mixer with the standard configuration where elements have alternating twist direction is globally chaotic; the flow in a mixer where all elements have the same twist direction displays large segregated regular regions which act as a barrier to uniform mixing and make the latter configuration undesirable for most mixing applications. Extent of mixing per element and energy efficiency are independent of element length to diameter ratio, allowing shorter elements to be used advantageously to obtain equivalent mixing in a smaller space or shorter residence time. A substantial increase in mixer efficiency is achieved using elements with less twist than the standard 180 degrees Kenics configuration. (C) 1998 Elsevier Science Ltd. All rights reserved.