When a droplet is put on a heated surface it evaporates and eventually boils, but what if the surface temperature is much higher than the boiling point of water?

Our experiments use a hot turbine-like substrate to instantaneously vaporise a surface layer of water when a droplet touches it. This levitates a droplet on a cushion of its own vapour. The turbine-like surface shape rectifies the direction of flow of the vapour and causes a droplet to rotate.

The rotation of the droplet can be used to couple the rotation of a solid. Alternatively, a disk of solid dry ice can be placed directly onto the turbine-like surface and a thin layer of solid dry ice will directly sublimate to vapour. We have used this to create the first example of a sublimation heat engine.

Publications

• A sublimation heat engine
  G.G. Wells, R.L. Aguilar, G. McHale and K. Sefiane
  Nature Communications 6 (2015) art. 6390.
  View open access version

• How energy from dry ice could power human colonies on Mars
  R.L. Aguilar
  The Conversation online, 3rd March 2015