Self-propelled Wetted Paper Leidenfrost Object

We investigated the self-propulsion of two new Leidenfrost objects on hot flat plate.We define a Leidenfrost object as a designed device which is able to remain in a stable Leidenfrost state.As far as we know,it is the first time that self-propulsion is acquired for a water based object in Leidenfrost state on a hot flat plate.In this study we demonstrated experimentally and theoretically that by deforming a drop of water,the non-uniform distribution of mass leads to a non-homogeneous vapour layer.The lubrication flow inside generates a lateral force being able to propel the body.The influences of filter paper and the mass repartition have been studied.The latter exhibits a great influence.Experiences show the evaporation rate of the water-paper composite is different from that of pure water.The difference can be seen as the existence of a maximum thickness of the vapour underneath the liquid.An analytical model,which explains the condition of emergence and the dynamic of the self-propulsion during a complete evaporation,was set up.Moreover,the analytical resolution allows simple Computational Fluid Dynamics simulations.This frictionless water based Leidenfrost object,if welldeveloped,can meet a wide range of engineering applications from generation of electricity to nano-deposition.A roadmap leading to the optimization of the device for electricity generation has been drawn.