In fact, fast or lengthy stirring could result in powdered ingredients separating out of the mixture, according to a new study by engineering researchers at Rutgers University in the US.
They suggest that applying the findings to manufacturing of drugs, foods and other materials make better products with less manufacturing waste. The findings are published in the current issue of Nature.
"While mixing dry ingredients would seem to be a simple undertaking, getting uniform batches on a large scale can in fact be a challenge for industries," said Ben Glasser, professor of chemical and biochemical engineering at Rutgers, The State University of New Jersey.
In the pharmaceutical arena, uneven blending can have serious consequences, For example, a tablet could be produced with either too much or too little of an active pharmaceutical ingredient (API).
Glasser said that for years researchers have studied how liquids and gases act when stirred and discovered that uniform flow can actually degrade into turbulence. This concept has already been applied to such diverse areas as manufacturing, aviation, pollution control and weather prediction, he added. "But we still don't know that much about powder or granular mixing dynamics."
The most striking finding reported by Glasser et al was the tendency of fine particles to separate into distinct layers under conditions that would otherwise seem to cause thorough mixing.
In their paper titled A Taylor vortex analogy in granular flows, they noted that at lower mixing speeds, fine glass beads of different sizes started to mix uniformly. But as the speed increased, the beads started forming distinct layers, the number and thickness varying with rotation speed. The researchers were able to identify patterns of granular motion that promoted layer formation and interfered with achieving uniform mixing.
While the researchers did their work under controlled laboratory conditions, they believe they have uncovered principles about mixing behavior in solid particles that could be useful not only for manufacturing, but also in understanding and manipulating "particle" flow on a larger scale, such as rock slides and avalanches.