A static mixer is a stationary in line device installed in a pipe or flow channel to accomplish mixing and related effects as a fluid flows through its structure. The concept is simple and very attractive for the continuous processing of fluids because without moving parts there are none of the sealing problems and maintenance concerns which are typically associated with agitators and other mechanical mixing devices. Additionally, static mixers are very compact and energy efficient. The benefits are especially attractive in the textile fibers industry where the production of man-made fiber involves many continuous and semi-continuous processes operating at high temperature and high pressure.
Static mixing has a long history in the textile fibers industry. In the very early days of synthetic or chemical fiber production various baffles and flow guides were inserted into reactor and transfer lines to promote mixing and improve flow homogenization. Many designs, some very simple and 'homemade', some very complex and 'expensive to make' and some proprietary to the individual producer were used. Well over one hundred patents have been issued for static mixing devices, and today about thirty five designs are commercially available. Their use in synthetic fiber production has greatly accelerated since the late 1960's early 1970's when technically sophisticated designs which could be reliably manufactured, and applications know-how became readily available. Simultaneously during this period the major
Static mixer design requirements differ depending on the mixing service, and the fluid flow characteristics. In the textile fibers industry the most significant area of application involves the processing of high viscosity fluids, and consequently the static mixers are required to operate in the laminar flow regime. These mixers operating at low fluid Reynolds numbers must accomplish their task without the benefit of local eddy activity which promotes homogenization of flow components in turbulent flow.
STATIC MIXING FUNDAMENTALS
Static mixers are very compact relative to the scale of fluid flow being processed. The best designs are basically continuous radial mixing devices which operate at a uniform shear rate. Additionally, they are characterized by an effective degree of plug flow, dependent on the specific design and application. Static mixing applications require either blending or dispersion of feed components. The difference between these two fundamental requirements is shown in Figure 1. Blending or simple mixing to achieve a homogeneous mass requires that the materials are miscible—each can be infinitely folded into the other. Dispersion on the other hand is applicable to immiscible materials