Leidenfrost Effect Ring

The Leidenfrost ring is a metal ring that demonstrates the Leidenfrost effect. It has a precise shaped pattern on the surface that causes the water to be propelled across the surface. Drop a single drop of water on the surface and it quickly builds up speed. Side walls retain the water inside the ring. Different sized droplets of water and temperatures cause slightly different results. While developing the product it was discovered that it is even possible to have a loop of water spinning around in the ring. A spellbinding yet intrinsically simple device utilising one of those often overlooked bits of science. You can see a similar device being shown on the BBC TV programme QI here, the whole section of the programme can be viewed here

More detail on the Leidenfrost effect

The Leidenfrost effect occurs when a liquid comes into contact with something hot; with the correct temperature difference between the two. This causes rapid state change on the surface of the liquid resulting in a thin layer of insulating gas between the object and liquid. This boundary layer between the two results in some interesting phenomenon.

The easiest way to see the Leidenfrost effect is to heat up a frying pan. For comparison first heat it to 100C to 160C put a drop water in the pan, you will see it boil, spit and turn to steam fairly quickly (at 160C it is pretty quick). Now increase the temperature of the frying pan to at least 200C, this is when the Leidenfrost effect will take place. Put another drop of water in the frying pan and you will see it takes much longer to turn into steam. It hovers around on a tiny cushion of steam about 0.1mm high. This separates out the water and frying pan, insulating the water and increasing the time it remains as a water droplet. It is quite impressive how long the water drop takes to boil off.

Leidenfrost effect is named after Johann Gottlob Leidenfrost, who wrote and discussed the effect in his work entitled “A Tract About Some Qualities of Common Water” in 1756.

Warnings

• To stop lime scale build-up on the ring use distilled water
• Lime scale does regrade performance
• This product requires temperature over 200C
• For adults only (18+)
• Boiling water can spilt
• Risk of burns from water, steam and apparatus
• Check cooking apparatus or hotplate can handle temperatures
• If you use a sauce pan be sure it can take the higher temperatures
• Use safety goggles

For further information I highly recommend the excellent work done by the University of Bath. More information can be found here http://www.bath.ac.uk/research/news/2015/05/19/leidenfrost-thermostat/