Leidenfrost Engine: Dynamics of rotating disks on turbine-like surfaces

When a liquid droplet is placed on a surface heated to a temperature significantly higher than the liquid’s boiling point, the droplet levitates on a cushion of its own vapor due to the Leidenfrost effect. This vapor layer provides a virtually frictionless motion of liquid droplets (and sublimating solids), which can be directed by asymmetrically texturing the substrate, which forces a preferential vapour flow direction. Here we investigate the rotation of a liquid pool, supporting glass disks, on heated turbine-like asymmetrically textured substrates. The transparent disk allows us to visualise the liquid distribution over the turbine, which informs our assessment of the torque losses and rotation stability of the supported disk. We also demonstrate that by replenishing the liquid, sustained rotation can be achieved. Experimental observations are supported by an analytical model. The dynamic analysis of the rotation of such Leidenfrost liquid (and solid) rotors paves the way for developing mm and sub-mm scale heat engines. The concepts here can be extrapolated to alternative liquid and solids to develop applications in extreme environments where temperature differences are common.