Scientists have understood how to make frozen ice-free ice records on a metal surface with patterns, according to a new article published in the journal ACS Applied Materials and Interfaces. This is the last breakthrough to get out of the Virginia Tech Lab of the mechanical engineer Jonathan Boreyko.
A few years ago, the Boreyko laboratory experimentally demonstrated an effect of Leidenfrost in three phases in water vapor, liquid water and ice. Leidenfrost’s effect is what is happening when you pull a few drops of water on a very hot and sizzling pan. The drops levitate, sliding around the pan with wild abandonment. If the surface is at least 400 ° Fahrenheit (well above the boiling point of the water), cushions of water or steam vapor are formed under them, keeping them levities. The effect also works with other liquids, including oils and alcohol, but the temperature at which it manifests will be different.
Boreyko’s laboratory has discovered that this effect can also be made of ice simply by placing a flat and flat ice record on a heated aluminum surface. When the plate was heated above 150 ° C (302 ° F), the ice did not levity on a vapor as does the liquid water. Instead, there was a significantly higher threshold of 550 ° Celsius (1,022 ° F) so that the levitation of the ice occurs. Unless this critical threshold is reached, cast iron under the ice is only boil in direct contact with the surface. Cross this critical point and you will get a Leidenfrost effect in three phases.
The key is a temperature differential in cast iron water just under the ice disc. The bottom of the melting water is boiling, but the top of the cast iron water glue to the ice. It takes a lot to maintain such an extreme temperature difference, and this consumes most of the heat of the surface of aluminum, which is why it is more difficult to reach the levitation of an ice record. The ice can remove the effect of Leidenfrost even at very high temperatures (up to 550 ° C), which means that the use of ice particles instead of liquid droplets would be better for many applications involving spray extinction: rapid cooling in nuclear power plants, for example, the fight against fires or rapid hot calibration when shaping metals.
