Water beats air in Hong Kong-led scientific heat transfer breakthrough
- Research team says its development can even be used in rocket launches to cool surfaces simply by water-spraying
- Low-cost film solves a physics problem first identified by a German doctor in the 18th century
A Hong Kong-led research team has cracked a centuries-old problem that has made it impossible to use water for cooling extremely hot surfaces, from rocket engines to frying pans.
Lead researcher Wang Zuankai, a chair professor of mechanical engineering at City University of Hong Kong, first came across the phenomenon as a 10-year-old in his hometown in China’s eastern province of Shandong.
“A magician came to our village and performed walking barefoot on red-hot iron pillars. I didn’t dare to watch,” Wang said.
“Now I know it’s the Leidenfrost effect – he wasn’t hurt because he dipped his feet in water before dashing across the pillars, creating a layer of vapour which served as protection.”
Named after the German doctor Johann Gottlob Leidenfrost, who first described it in the 18th century, the effect is often observed in kitchens – when water droplets bounce like beads on hitting a hot pan.
A vapour barrier is formed between the liquid and surface which prevents the water from boiling and evaporating, reducing heat transfer at high temperatures.
While the effect is a boon to firewalkers, it has been a costly problem in steelmaking, aerospace industries and nuclear plants, where rapid cooling from extremely high temperatures is a common need, usually solved by using air.