If you’ve ever splashed water on a hot pan, you’ve probably seen how the droplets appear to dance and levitate above the surface. Although it may seem like a visual trick, these drops actually levitate thanks to a phenomenon known as the Leidenfrost effect.
This effect, named after the German physician Johann Gottlob Leidenfrost, has been studied by physicists since the 18th century. It occurs when a surface is hot enough to vaporize the base of water droplets, creating a cushion of vapor that keeps them floating.
Generally, this phenomenon is observed at temperatures above 230 degrees Celsius, but recent research, published in Nature Physics, has questioned these established limits.
A team led by Jiangtao Cheng, associate professor of Mechanical Engineering at Virginia Tech, has managed to induce the Leidenfrost effect at much lower temperatures, around 130 degrees Celsius.
This has been possible thanks to the development of surfaces covered with micropillars. These microscopic structures, just 0.08 millimeters tall (about the thickness of a human hair), are arranged in a regular pattern 0.12 millimeters apart, according to a press release.
Each drop of water spreads over 100 or more of these micropillars. These small pillars increase the heat transfer towards the water droplets, allowing them to boil faster and making the phenomenon observed in a matter of milliseconds.
“Like the papillae of a lotus leaf, the micropillars do more than just decorate the surface,” Cheng explained. “They give the surface new properties.”
Efficient heat transfer
This innovation not only redefines the Leidenfrost effect, but also has important practical implications, especially in fields that require efficient heat transfer, such as industrial machinery cooling and nuclear cooling towers.
According to Wenge Huang, a doctoral student and member of the research team, the micropillar surface allows for a more efficient heat transfer mechanism, which could prevent incidents such as steam explosions.
“We thought that micropillars would change the behavior of this well-known phenomenon, but our results defied even our own expectations,” said Professor Jiangtao Cheng, director of the study.
These explosions pose a serious risk in industrial and nuclear environments, as they occur when vapor bubbles within a liquid expand rapidly due to an intense heat source. The surface structure of heat exchangers can significantly influence the growth of these bubbles.
Cleaning in industrial environments
Furthermore, this micropillar surface strategy not only improves heat transfer but also makes the surfaces easier to clean. The steam bubbles generated can dislodge particles and debris from surface textures, improving the efficiency of cleaning processes in industrial environments.
“We thought that micropillars would change the behavior of this well-known phenomenon, but our results defied even our own expectations,” Cheng said. “The observed interactions between bubbles and droplets are a great discovery for heat transfer in boiling,” she added.
