How can a latte be less messy than a regular black coffee? New York University Polytechnic School of Engineering researchers have discovered the reason and believe their results could be useful for industry. Prof Emilie Dressaire, along with her colleagues discovered that coffee’s sloshing motion can be significantly dampened by just a few bubble layers. Their findings were published in Physics of Fluids, citation below. Their research may be useful to companies in a variety of industries, such as those looking for safer transportation of liquefied gases in trucks or propellants in rocket engine engines. Professor Dressaire recalls thinking of foam first as a sloshing dampener. She picked up her Starbucks latte and was informed that a stopper wouldn’t be necessary to prevent it from leaking. The experiment was drawn. The experiment shows that waves without foam were larger than those with foam (b). (Image: http://scitation.aip.org/) When she started working in the complex fluids group at Princeton University, colleagues mentioned the same thing with foamy beer. Alban Sauret (a French researcher) said that while she was doing her Ph.D., she noticed something similar with foamy beer. The team of researchers took the observations of the café and lab and created a test device to measure foam’s dampening ability. The researchers created a rectangular, narrow glass container that they filled with water, Dawn, and glycerol to make it viscous. The foam was created by forcing air through a needle at the bottom the rectangular cell. The bubbles were flattened to a thickness of three millimeters. Francois Boulogne, a member of the team said that they were able to create flat layers of 3mm-diameter bubbles. Two types of movement were tested by the scientists: The device was jolted with fast, side-toside movements. 2. You rock it back and forth. One-tenth of waves with foam on top Researchers believe that foam helps dissipate the energy from the sloshing solutions by friction with the containers sides. They found that five layers of bubbles are sufficient. Additional layers didn’t add any dampening. Because the foam’s top layer did not move, this is why it appears that five layers are sufficient. The dampening effect was only caused by bubbles that came in contact with containers’ walls. The problems that energetic sloshing can create in liquids can go beyond the inconvenience of spilled beverages in cafes or bars. They can also affect safety for hazardous liquids such as oils and liquefied gases when transported in large tanksers. According to the authors, sloshing can cause significant pressure on tanker walls, which could lead to ruptures and disrupt vehicle motion. According to Mr. Boulogne: “The possibilities are more than beer.” Citation: “Damping liquid sloshing with foams,” A. Sauret and F. Boulogne. J. Cappello, E. Dressaire, H. A. Stone. Physics of Fluids. Publised February 24, 2015. DOI: 10.1063/1. 4907048.
