Mix it up better than before

Australian scientists have produced a new mixer that they claim is five times more energy efficient than traditional industrial mixing for everything from explosives to cosmetics.

They also claim that the patented 'Rotated Arc Mixer' (RAM), as it is called, can also mix thick fluids better than anything that has been developed previously.

Inventors Dr Guy Metcalfe and Dr Murray Rudman of CSIRO Thermal & Fluids Engineering say, 'The RAM overcomes many mixing problems. For example, static mixers used in cosmetics manufacture, have baffles, plates and constrictions that result in regions that clog and cause material build-up.'

'Stirred tank mixers used in the dairy industry, can suffer from large stagnant regions (badly mixed regions leading to waste raw material) and high energy consumption. Stirred-tank mixers are also normally characterised by regions of high shear (turbulence).'

Dr Rudman says that these regions of high shear may destroy delicate products or reagents, such as the biological reagents involved in fermentation in food processing.

Similarly, regions of high shear may produce poor mixing in explosives resulting in inferior explosive performance.

Regions of high shear may also disrupt the formation and growth of particles or aggregates in a crystalliser (sugar cane processing). Alternatively, fibrous pulp suspensions may catch on the baffles or plates of a static mixer leading to blockage and regular production downtime.

No such problems with the RAM, though.

It comprises an outer cylinder that rotates around a fixed inner cylinder, which has flow apertures cut at strategic locations depending on the material being mixed.

As the outer cylinder rotates, fluid is moved axially through the inner cylinder. The viscous drag from the outer cylinder, which acts on the fluid in the region of each flow aperture, sets up a secondary (transverse) flow in the fluid.

Dr Metcalfe says, 'The key to the RAM mixer's success is these forces that produce very effective chaotic mixing of highly viscous fluids in either batch or continuous (through-flow) modes.'

'Depending on the specific application, suitable combinations of flow rate, rotation rate and flow aperture are chosen, based on the mathematical models and methods developed by our team.'

Dr Metcalfe says, 'The concept for the RAM came out of blue sky mathematical research aimed at overturning traditional mixing design.'

'We had an idea about an ideal mixer, and developed mathematical models to see how it would perform and then we produced the real thing..'

CSIRO Thermal & Fluids Engineering is currently designing an industrial scale RAM Mixer for a specific industrial operation to demonstrate its effectiveness to industry.

'Now that we have moved past the development of a successful laboratory prototype we are keen to find industry partners to commercialise this exciting new technology,' says Dr Rudman.