Structured Thermal Armor
Researchers from City University of Hong Kong have developed a structured thermal armor (STA) that can achieve efficient liquid cooling even over 1,000°C, thereby solving a 266-year-old challenge presented by the Leidenfrost effect. The Leidenfrost effect is a physical phenomenon in which a liquid, close to a surface that is significantly hotter than the liquid’s boiling point, produces an insulating vapor layer that keeps the liquid from boiling rapidly. Because of this repulsive force, a droplet hovers over the surface, rather than making physical contact with it. The Leidenfrost effect dramatically slows down heat transfer to a liquid, which makes liquid cooling on the hot surface ineffective. This effect is detrimental in many situations. This innovation can potentially be used for different testing related challenges in material testing labs.
The researchers developed a multi-textured material with components that have contrasting thermal and geometrical properties. The design superimposes 1. Conductive pillars, which promote heat transfer, 2. Thermally insulating membrane, which sucks and evaporates the liquid, and 3. Underground U-shaped channels, which evacuate the vapor. The researchers were able to inhibit the Leidenfrost effect up to 1,150 °C and achieved controllable cooling from 100°C to over 1,150°C in a metrology testing lab. This level of liquid cooling can be used in aero and space engines, and to improve the safety and reliability of next-generation nuclear reactors with the help of material testing labs.
“This multidisciplinary research project is truly a breakthrough in science and engineering, since it mixes surface science, hydro- and aerodynamics, thermal cooling, material science, physics, energy, and engineering. Searching for novel strategies to address the liquid cooling of high-temperature surfaces has been one of the holy grails in thermal engineering since 1756. We are fortunate to fundamentally suppress the occurrence of the Leidenfrost effect and thereby provide a paradigm shift in liquid thermal cooling at extremely high temperatures, a mission that has remained uncharted to date,” said Professor Wang
The current thermal cooling strategies under extremely high temperatures adopt air cooling measures rather than effective liquid cooling owing to the occurrence of the Leidenfrost effect, especially for applications in aero and space engines and next-generation nuclear reactors. “The designed STA can be fabricated to be flexible, eliminating the need for additional manufacturing, especially for those surfaces that are hard to be textured directly. This is why the STA possesses huge potential for practical applications,” added Professor Wang. All types of materials used in such research activities need to be evaluated in material testing labs.
The findings were published in the latest issue of the scientific journal Nature. The research was led by Professor Wang Zuankai from CityU’s Department of Mechanical Engineering (MNE), Professor David Quéré from the PSL Research University, France, and Professor Yu Jihong, Director of the International Center of Future Science, Jilin University and Senior Fellow of the Hong Kong Institute for Advanced Study at CityU.
Mengnan Jiang, Yang Wang, Fayu Liu, Hanheng Du, Yuchao Li, Huanhuan Zhang, Suet To, Steven Wang, Chin Pan, Jihong Yu, David Quéré, Zuankai Wang. Inhibiting the Leidenfrost effect above 1,000 °C for sustained thermal cooling. Nature, 2022; 601 (7894): 568 DOI: 10.1038/s41586-021-04307-3