  In this Letter, we systematically investigate the Leidenfrost temperature for
hot solid substrates with various thermal diffusivities and surface
roughnesses. Based on the experimental results, we build a phenomenological
model that considers the thermal diffusivity of a solid substrate and derive a
relationship between the surface roughness and the resulting vapor film
thickness. The generality of this model is supported by experimental data for
different liquids and solid substrates. Our model thus allows for a theoretical
prediction of the Leidenfrost temperature and develops a comprehensive
understanding of the Leidenfrost effect.
