  Spray cooling a hot target is characterized by strong heat flux density and
fast change of the temperature of the wall interface. The heat flux density
during spray cooling is determined by the instantaneous substrate temperature,
which is illustrated by boiling curves. The variation of the heat flux density
is especially notable during different thermodynamic regimes: film,
transitional and nucleate boiling. In this study transient boiling curves are
obtained by measurement of the local and instantaneous heat flux density
produced by sprays of variable mass flux, drop diameter and impact velocity.
These spray parameters are accurately characterized using a phase Doppler
instrument and a patternator. The hydrodynamic phenomena of spray impact during
various thermodynamic regimes are observed using a high-speed video system. A
theoretical model has been developed for heat conduction in the thin expanding
thermal boundary layer in the substrate. The theory is able to predict the
evolution of the target temperature in time in the film boiling regime.
Moreover, a remote asymptotic solution for a heat flux density during the fully
developed nucleate boiling regime is developed. The theoretical predictions
agree very well with the experimental data for a wide range of impact
parameters.
