Spray tuning

If you've ever splattered paint on a canvas or sprayed a cookie sheet with oil, you likely created - aside from a minor mess - a shower of droplets, ranging from dime-sized splotches to pencil-point specks. Such droplet sizes may seem random, but now engineers at MIT can predict a liquid's droplet size distribution, including the likelihood of producing very big and very small droplets, based on one main property: the liquid's viscoelasticity, or stickiness. What's more, the team has found that, past a certain stickiness, fluids will always exhibit the same relative range of droplet sizes. Knowing how big or small a liquid spray's droplets may be can help researchers identify optimal fluids for a number of industrial applications, from preventing defects in automotive paint jobs, to fertilizing farm fields via aerial spraying. The researchers' The paper's lead author is Bavand Keshavarz, a graduate student in the lab of Gareth McKinley, who is the School of Engineering Professor of Teaching Innovation at MIT and the paper's senior author. Their co-authors include Eric Houze, John Moore, and Michael Koerner of Axalta Coating Systems, a Philadelphia-based manufacturer of paints for commercial vehicles. A thickening ingredient The ways in which liquids fragment, or break up into droplets, has been a fascination for centuries and an active field of study for the past few decades.