Study of droplet sprays prior to impact on a heated horizontal surface

This paper concerns a quantitative assessment of the heat and mass transfer behavior of spray droplets, downward oriented prior to their impact on a heated horizontal surface. An experimental and theoretical investigation of the coupling effects between a downward oriented spray and a rising saturated buoyant jet that results from evaporation of the spray an a heated surface has been successfully completed. A model describing the coupled thermal and hydrodynamic behavior of both the spray and the saturated buoyant jet has been developed. An experimental set-up involving a high speed photographic apparatus has been used to observe in-flight monodispersed sprays and to measure the diameter and the velocity of droplets as they approach the heated surface. The theoretical and experimental results indicate that the temperature of the saturated buoyant jet is highly affected by the presence of a subcooled spray and small droplet sprays, vertically projected, experience high condensation rates as they pass through the saturated buoyant jet, reaching the saturation temperature before impacting on the heated surface, as well as experience acceleration as a consequence of an increase in mass due to the condensation.