Australasian Science: Australia's authority on science since 1938

Boiling Water that Never Bubbles

By Stephen Luntz

Water can be made to boil without bubbling by using textured surfaces, an Australian/American collaboration has proved in Nature.

The discovery is an application of the Leidenfrost effect, which is best known for causing drops of water to appear to dance on a hot metal plate. In this case an evaporative vapour film suspends the drops above the metal. The vapour has much lower thermal conductivity than either the plate or the water, preventing the drops from boiling away.

The Leidenfrost effect breaks down as the hot surface cools. The water can enter a nucleate-boiling regime, more commonly known as bubbling, which potentially includes vapour explosions.

However, Prof Derek Chan of Swinburne University’s Faculty of Life and Social Sciences has helped demonstrate that textured hydrophobic surfaces cause the vapour layer to relax gradually while cooling occurs, preventing bubble formation. If smooth hydrophobic surfaces are used, vapour collapse still occurs but at lower temperatures than for surfaces that do not repel water.

Chan has previously demonstrated that hot bodies travel more easily through liquids than cold ones (AS, September 2011, p.13). “Both arise from the fact that above the Leidenfrost point you get a sustained vapour layer, which gives either drag reduction or initiates boiling without the formation of bubbles,” Chan says.

Water-repelling surfaces are in widespread use, and Chan says his team demonstrated the effect using several brands of car paint that were manufactured to prevent splashes sticking to the car.

It is not clear whether the discovery will have practical applications. Explosive boiling is a major problem when attempting to reintroduce water to nuclear reactors after disasters such as Fukushima. However, Chan says the same surfaces will reduce heat transfer in nuclear reactors under normal operation – which is the point of using water in the first place.

“I’m not a nuclear engineer so I’m not sure if they would want to use this,” says Chan. “It would be useful in a disaster, but less efficient under normal circumstances.”

More prosaically, coating the inside of household kettles with suitable textured surfaces could prevent splashing as they boil.