News | December 27, 2000

Experimental fluid mixer said to best conventional designs

Investigators at CSIRO (Highett, Victoria), Australia's government-funded research organization, have produced a new type of mixer they say is five times more energy efficient than traditional industrial mixing for everything from explosives to cosmetics. They also claim that the patented device, known as the Rotated Arc Mixer, can mix thick fluids better than any other mixer.

The new mixer's inventors, Guy Metcalfe and Murray Rudman of CSIRO Thermal & Fluids Engineering, note that static mixers used, for example, in cosmetics manufacture, have baffles, plates and constrictions that result in regions that clog and cause material build-up. And stirred-tank mixers used in the dairy industry can suffer from large stagnant regions and high energy consumption, they add. They also note that stirred-tank mixers are normally characterized by regions of high shear, which can destroy delicate products or reagents.

The RAM has been configured to sidestep these problems. The device consists of 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.

In a CSIRO press release, 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."

CSIRO cites the following advantages of the RAM over static mixers in through-flow applications. It

  • can mix twice as well as an equivalent commonly used static mixer;
  • consumes five times less energy;
  • has very low shear, but effective mixing;
  • has no stagnant regions;
  • is easy to clean;
  • has no internal surfaces (baffles, plates, etc.) for material to build up on;
  • is easy to scale-up to plant scale, since flow fields are the same, regardless of size; and
  • is designed for very high-viscosity fluids.

    • CSIRO Thermal & Fluids Engineering reports that it is now designing an industrial-scale RAM device to demonstrate its effectiveness. The organization is looking for industrial partners to commercialize the technology.

    Contact Ken Anderson, CSIRO, Construction & Engineering. Tel: +61-3-9252-6172; E-mail: ken.anderson@dbce.csiro.au.

    Edited by Gordon Graff
    Managing Editor, Laboratory Network.com