Boiling Without Explosive BubblesCategory: Science & Technology
Posted: September 14, 2012 11:11AM
There are a few classic experiments that dramatically demonstrate the Leidenfrost effect, including holding liquid nitrogen on ones tongue and dipping a wet hand in molten lead (which I have witnessed). The reason the hand is not burned and the tongue is not frozen is because a vapor barrier forms between the two things of greatly different temperatures. Now researchers at Northwestern University have introduced a new element to the mix and it may have far reaching impacts.
Typically when a hot enough object is placed in water, the water will boil and produce a prodigious amount of bubbles that actually explode out of the liquid. This is an extremely bad situation and can happen at chemical plants and nuclear reactors. However, the vapor barrier of the Leidenfrost effect inhibits the formation of these bubbles, and thus prevents the explosion. Sadly the vapor barrier only forms at high temperatures that do not stretch all the way down to the boiling point of water, but by making the hot object superhydrophobic, the researchers discovered they could cool the object, without forming any bubbles. The key is that the superhydrophobic surface is also rough, so the vapor can exist within the surface's cavities, and keep the liquid water from directly touching the hot object.
When the researchers tested this they were able to get a 400 ºC steel sphere all the way down to 100 ºC without an explosion of bubbles. Hopefully this experiment will evolve into a safety feature for those situations that could use it soon.