The Leidenfrost effect, where a drop of water seems to float above a hot surface, usually happens above 230 degrees Celsius. The team of Jiangtao Cheng, associate professor in the Virginia Tech Department of Mechanical Engineering, has discovered a method to create the aquatic levitation at a much lower temperature, and the results have been published in Nature Physics. Alongside first author and Ph.D. student Wenge Huang, Cheng’s team collaborated with Oak Ridge National Lab and Dalian University of Technology for sections of the research.
The discovery has great potential in heat transfer applications such as the cooling of industrial machines and surface fouling cleaning for heat exchangers. It also could help prevent damage and even disaster to nuclear machinery. Currently, there are more than 90 licensed operable nuclear reactors in the U.S. that power tens of millions of homes, anchor local communities, and actually account for half of the country’s clean energy electricity production. It requires resources to stabilize and cool those reactors, and heat transfer is crucial for normal operations.
The traditional measurement of the Leidenfrost effect assumes that the heated surface is flat, which causes the heat to hit the water droplets uniformly. Cheng’s team has found a way to lower the starting point of the effect by producing a surface covered with micropillars. These tiny pillars press into a water droplet, releasing heat into the interior of the droplet and making it boil more quickly.
When the textured surface was heated, the team discovered that the temperature at which the floating effect was achieved was significantly lower than that of a flat surface, starting at 130°C.
The Leidenfrost effect is more than an intriguing phenomenon to watch, it is also a critical point in heat transfer. When water boils, it is most efficiently removing heat from a surface. In applications such as machine cooling, this means that adapting a hot surface to the textured approach presented by Cheng’s team gets heat out more quickly, lowering the possibility of damages caused when a machine gets too hot.
“Our research can prevent disasters such as vapor explosions, which pose significant threats to industrial heat transfer equipment,” said Huang. “Vapor explosions occur when vapor bubbles within a liquid rapidly expand due to the present of intense heat source nearby. One example of where this risk is particularly pertinent is in nuclear plants, where the surface structure of heat exchangers can influence vapor bubble growth and potentially trigger such explosions. Through our theoretical exploration in the paper, we investigate how surface structure affects the growth mode of vapor bubbles, providing valuable insights into controlling and mitigating the risk of vapor explosions.”