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| CSIRO | SOLVE | Issue 3 - May 05 | |
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ARTICLE
MANUFACTURING:
Science Masters the Mix By BRAD COLLIS
A MIX OF MATHS, SCIENCE AND CREATIVE THINKING COMES UP WITH THE ULTIMATE STIRRER. Viscous fluids like food mixes, paints, polymers (plastics), when molten during manufacture, cosmetics and other industrial substances have always been difficult to mix using conventional 'beat and stir' machinery.
Some highly theoretical dabbling into the mathematical equations of different flow fields gradually progressed to computer modelling and eventually to a whole new mixer concept. They have now developed and patented a revolutionary mixer - the Rotated Arc Mixer (RAM) - that introduces programmable chaos into a mixing process. On the face of it, the mixer is a surprisingly simple-looking device - two tubes, one inside the other. The inner tube, through which the fluid passes, has a series of small openings running in a spiral pattern down its length. As the fluid moves through the inner tube, the outer tube rotates on its axis. This creates a drag on the inner flow near each opening, forcing the fluid to also rotate as it moves through the inner tube. When the fluid passes by the next opening, this flow is reoriented. By programming the sequence of openings, a much more thorough mix can be achieved at much lower energy input compared to conventional rotors and beaters. Importantly, explains Dr Rudman, this mixer only works with viscous fluids: "It wouldn't work with something like water." He says target applications for the RAM mixer include molten polymer mixes, the food industry and biotechnology. "In the manufacture of plastics, the bulk of polymeric materials are not single polymers but blends of several polymers and/or additives such as fibres or powders. The physical properties of many composite materials are achieved this way, including strengthened plastics, and the enhancement of properties (such as electrical or thermal) in plastics and glasses. "Also, many new biotechnology processes require ingredients like bacteria, yeast and nutrients being mixed in large fermentation tanks. These mixtures are often quite viscous and need thorough but careful mixing of nutrients to maintain the cultures. If you stir too fast you can kill the cells you are trying to grow by beating them to death. The RAM mixer doesn't place the same stress on the cells being grown." Dr Rudman says the new mixer also suits applications in which the material being mixed is prone to clogging: "For example, static mixers used in the manufacture of a range of products (including cosmetics and pastes) have baffles, plates and constrictions that cause fibrous materials, chemical scale or viscous fouling to build up, slowing production and demanding frequent cleaning." Although the researchers have had the technology for several years, industry inquiries have only recently begun to trickle in. A Scandinavian fish-food manufacturer has shown interest in the technology's potential for improving the homogeneity of bacterial fermentations for aquaculture feed. A confectionary manufacturer has trialled the RAM for mixing powder into viscous sugar syrups. Several companies have expressed interest in mixing nano-particles and fibres into viscous polymeric liquids to increase strength and durability of materials. More recently, the RAM mixer is showing potential as a heat exchange facilitator. Heat exchange technology has been around for some time - a car radiator being one simple example - but heating and cooling processes in manufacturing often need critical control to make production safe, reliable and cost effective. "This is a new area that we have just started to explore with the RAM mixer. Where heating or cooling needs to be carefully managed, which is usually the case with viscous fluids, this could be a very useful tool," says Dr Rudman. He likens the process to using cold milk to cool a cup of coffee: "If you place the milk on the surface it will eventually cool the coffee, but not as uniformly and quickly as when you stir in the milk. And if you have a situation where that blending and cooling needs to be carefully managed, perhaps computerised, the RAM mixer has this capability because the set-up, such as placement of the openings, flow rate and rotation rate, can be customised." Dr Rudman says a typical competitor for through-flow applications is the static mixer, against which the RAM has been benchmarked. Some demonstrated advances of the RAM are:
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