Unsteady temperature fields of evaporating water droplets exposed to conductive, convective and radiative heating

In this paper, we present the rates and typical durations of high-temperature heating and evaporation of water droplets determined for the dominating conductive, convective or radiative energy supply. We developed three setups for heating a water droplet: on a substrate (conduction), in a muffle furnace (radiation), and in a heated airflow (convection). The heating temperature is up to 1000 °C to correspond high-temperature technologies, namely thermal cleaning of fluids, polydisperse fire extinguishing with low water consumption, etc. With the help using of a high-speed video recording system, we determine the water droplet lifetimes (the times of their complete evaporation). Using Planar Laser Induced Fluorescence, we establish the quantitative differences between the water droplet heating rates (heating time to lifetime ratios) on the three setups. Maximum temperatures are determined that the water droplets reach when exposed to different heating mechanisms. Furthermore, we obtain the criterial dependences to connect the main attributes of temperature field generation of an evaporating water droplet with the heating conditions. Finally, we identify possible implications of the research findings and ways to further improve the newly developed experimental approach.