Heating and evaporation of suspended water droplets: Experimental studies and modelling

The results of a series of experiments focused on investigation of the heating and evaporation of suspended water droplets in a hot air flow (at temperatures up to 800 C) are described. The temperatures inside droplets were estimated based on Planar Laser-Induced Fluorescence (PLIF) imaging. The advantages and limitations of this method are investigated. Typical distributions of temperatures inside droplets at the initial stages of their heating and evaporation are presented. These distributions at various cross-sections are compared. They are shown to be strongly inhomogeneous during the whole period of observation. A new model for heating and evaporation of a suspended droplet, taking into account temperature gradient and recirculation inside the droplet and the effect of a supporting rod, is suggested. It is assumed that the heat transferred from the rod to the suspended droplet is homogeneously distributed inside the droplet; its effect is modelled similarly to the effect of external thermal radiation, using the previously developed model for droplet heating in the presence of this radiation. It is shown that a reasonable agreement between the model predictions and experimental data can be achieved if the reduction of the ambient gas temperature due to the presence of an evaporating droplet is taken into account. The effect of the rod on droplet heating is shown to be most significant for ambient gas temperature equal to 100 C and becomes negligibly small when the gas temperature reaches 800 C.