Cat's eye flip flow to improve industrial mixing

In the domestic kitchen, mixing is a crucial step when baking. Mix too little and ingredients will not be evenly distributed; mix a soufflé too much and it will fall flat. In commercial operations, mixing becomes even more critical. Every batch must meet the same exacting standards but be created in the least amount of time to minimise costs.

Researchers in the UK claim to have developed a new recipe for industrial mixing that has the potential to optimise mixers. Fluid mechanics expert Lionel Rossi, a researcher at the French Alternative Energies and Atomic Energy Commission (CEA), and colleagues from Imperial College London have published a paper that describes what they call a ‘cat’s eye’ mixing sequence.

Instantaneous illustration of the lamination observed during a cat’s eyes flip mixing sequence. [Image: L.Rossi/CEA]

The process uses magnets to generate synchronised flows of jets that move in opposite directions and whose positions are slightly offset from each other. By controlling the timing of the jets and their strength and position, the researchers created a promising mixing sequence called a ‘cat’s eyes flip flow’, named because the resulting pattern, as visualised with coloured dyes added to the solution, resembles the almond shape of a cat’s eye. They studied the flows created by this sequence and compared them to other patterns, and found that the cat’s eyes flip flows were most efficient at mixing solutions.

“The new sequence is both robust and fast, and its relative simplicity makes it transferable to mixing devices at all scales,” Rossi said.

At very small scales, Rossi noted, the sequence should help reduce mixing times and possibly even the space required for mixing. This would be of interest for lab-on-a-chip applications “that require numerous manipulations in a minimum of time and space”, Rossi said.

At larger scales, he said, “the sequence should increase performance while reducing energy consumption”; for example, by reducing the stirring of saturated regions, making the process more environmentally friendly.

The researchers now plan to develop tailored mixing strategies applicable to almost any mixing need by using different sequences of synchronised flows as building blocks.

The article, Lamination, stretching and mixing in cat’s eyes flip sequences with varying periods, by Lionel Rossi, Denis Doorly and Dimitri Kustrin, is published in the journal Physics of Fluids.