Leidenfrost Ratchets

Properties such as asymmetry and disequilibrium can be exploited in order to obtain useful work from a physical system. Our group is investigating one particularly interesting manifestation of the ``ratchet'' effect. We find that film-boiling (leidenfrost) drops of liquid placed on an asymmetrically-structured surface experience acceleration significant enough for transport to occur even against small inclines. We believe that a viscous drag force is the mechanism for this net flow of fluid, which is supported by a thin layer of vapor. Because heat is the primary input of energy into the system, this effect could prove useful in cooling applications where a classical ``pump'' may not be ideal.