  In this study the Leidenfrost temperature during spray cooling of very hot
substrates is experimentally measured. The spray parameters, i.e. the drop
diameters and velocities and the mass flux, are very accurately measured.
Astonishingly, the measured Leidenfrost temperature is independent of any of
the spray impact parameters, but is determined exclusively by the materials of
the liquid and the substrate. The mechanism of film boiling is explained by the
formation of a fast propagating vaporizing front, when the inertial forces in
the associated liquid flow are comparable with the viscous stresses. This leads
to a theoretical prediction for the Leidenfrost temperature which agrees well
with the experimental data.
