Strange pentagon is the best shape for mixing two liquids together

According to a series of simulations, not only should your stirring tool be shaped like a bizarre pentagon, but you should also use two of them and move them in a jagged half-circle before allowing fluid vortices to do the rest.

Peter Schmid and Maximilian Eggl of the King Abdullah University of Science and Technology in Saudi Arabia and the University of Mainz Medical Center in Germany used simulations and an algorithm to figure out what shape is the most effective at combining two liquids.

Researchers found new way to mix coffee effectively.

In the simulation, two fluids with consistency similar to water were placed in a cylinder and stirred by two stirrers. Initially, the stirrers were cylindrical and programmed to move in smooth circles, one on the container's rim and one near its center, as is typical for large-scale mixing processes in the food and pharmaceutical industries.

The stirrers' shape and motion were then iteratively improved by the researchers using an optimization algorithm, resulting in a stirrer that mixed the liquids more quickly and thoroughly each time.

The algorithm discovered that the best stirrer had a pentagon shape that was uneven and curved. It also found that the stirring technique could be improved upon too, using a jagged, start-and-stop motion. To compare the various methods, the researchers used a common measurement of how well two liquids are blended. When using the algorithm's preferred stirrers and stirring method, liquids were up to 2.3 times more thoroughly mixed than when using conventional cylinder-shaped stirrers that moved in a circular motion.

Schmid asserts that the new stirrer design is effective because, when combined with the new mixing motion, it generates a large number of vortices, or small whirlpools, as the stirrer rotates. Vortices can move away from the stirrer and act as their own tiny swirling mixers, he says. Stirrers primarily influence the behavior of liquids immediately adjacent to them.

Two stirrers mix together two liquids.

 

He and Schmid claim they have no plans to produce coffee stirrers. Instead, they hope that the findings will be useful in industrial settings for mixing liquids.

Even slightly more angular stirring implements could be very helpful, according to Jean-Luc Thiffeault at the University of Wisconsin, who claims that stirrers and motions that create many vortices improve mixing processes.

In the future, Eggl says, the researchers want to take into account liquids like toothpaste and ketchup that thicken or thin as they are stirred. To see if mixing with shaking could be more energy-efficient than stirring alone, they also plan to include shaking of the container in the simulations.

Journal reference: Physical Review Fluids, DOI: 10.1103/PhysRevFluids.7.073904