Measurement of the Heat Flux During a Drop Impact onto a Hot Dry Solid Surface Using Infrared Thermal Imaging

Abstract

The interaction of a drop and a hot wall is an important process encountered in a large number of industrial applications, mainly associated with spray cooling. If the wall temperature is high enough the drop impact, its spreading and breakup are influenced by micro-scale thermodynamic phenomena caused by the intensive drop evaporation, bubble or vapor film formation. These phenomena influence also the local distribution of heat flux at the drop/substrate interface. In this study an infrared (IR) technique has been used for measurements of the contact temperature at the drop/substrate interface during the drop impact. These measurements allow distributions of the heat flux at this interface to be calculate with high temporal and spatial resolution. Different drop outcome regimes (evaporation, break-up and rebound) have been characterized and the relationship between the heat flux and the regimes has been described. In particular, partial wetting, emergence and expansions of bubbles in the nucleate boiling regime and the vapor film formation during the Leidenfrost regime have been observed. The system leads to better understanding of the mechanisms of drop breakup and rebound. Finally, the temporal evolution for the total heat flow from the hot substrate has been determined for various substrate temperatures.