Next time grab a coffee before you have to run to work it might be a good idea to reach for a latte than a regular drip coffee. According to a study recently reported in “Physics of Fluids,” published by AIP Publishing, the extra foam manages to dampen the sloshing effect of the coffee, making it much less likely that you will spill your morning joe all over yourself. Even just a few layers of foam will your groggy journey much safer.
EurekAlert reported on Feb. 24, that the idea for the study first came to Emilie Dressaire, an assistant professor of mechanical and aerospace engineering at the New York University Polytechnic School of Engineering, when she was picking up her latte at a coffee shop. Dressaire said that when she reached for a stopper, she was informed that she wouldn’t need one for her latte, which got her thinking about how bubbles could work as a dampener. Later, when Dressaire joined the complex fluids group at Princeton University, she realized that she was not alone in noticing the peculiar effect of bubbles, though her colleagues admitted that it was beer that gave them the idea.
Alban Sauret, currently a researcher at the French National Center for Scientific Research, said described how he first noticed the dampening effect of bubbles while in a bar. “While I was studying for my Ph.D. in the south of France, we were in a pub, and we noticed that when we were carrying a pint of Guinness, which is a very foamy beer, the sloshing almost didn’t happen at all.”
As neither cafes nor pubs are particularly scientific places for research, the scientists decided they needed to move their experiments to the lab. To accurately test the dampening effect of foam, the researchers built an apparatus that consisted of a narrow rectangular glass container filled with water, glycerol (which increases fluid viscosity) and dishwashing detergent. Using a needle at the bottom of the container, the scientists injected a stream of air into the solution producing layers of 3-millimeter bubbles.
The scientists then experimented by having the machine go through several types of motion, including a rapid side-to-side motion and a slowly rocking the container back and forth. Because the bubbles produced by the laundry detergent were very stable, the scientists were able to record the resulting waves with a high-speed camera without out the bubbles dissipating. After examining the sloshing waves of the solution with the number of bubble layers on top, the scientists realized that is was friction of the bubbles rubbing against the sides of the container that dampened the waves. While the bubbles towards the middle of the cup did little to affect the waves, it only took five layers of bubbles along the side to decrease height the sloshing waves by a factor of ten.
Although preventing coffee and beer spills is a noble cause, the study might have serious implications as well. Sloshing can be a potentially dangerous issue when transporting large quantities of dangerous fluids like liquefied gas in tankers or propellants in rocket engines. The waves produced by such a large quantity of liquid can put a lot of pressure on the side of the tankers or even tip over a vehicle.
“The potential applications are much bigger than just beer,” claims Sauret. Hopefully, this research might lead to a safer way and cheaper way of moving large quantities of dangerous fluids.