Oblate spheroidal droplet evaporation in an acoustic levitator

The modelling of evaporation in which droplet geometry deviates from sphericity, i.e., oblate spheroid, when the droplet experiences high dynamic stresses or a high Weber number, is important in many applications. The validation of such theoretical models is often difficult to achieve experimentally. The acoustic levitation technique was used to investigate the evaporation of an oblate spheroid for different liquids. Evaporation of oblate droplet at constant aspect ratio is realized through the course of evaporation in the acoustic levitator by continuously adjusting the applied acoustic force on the droplet. A Two-dimensional axisymmetric computational model in oblate coordinate system is presented to predict droplet evaporation driven by the acoustic boundary layer, the model calculates the vapor flux at each grid point on droplet surface. The evaporation follows the d2-law and a good agreement between model prediction and experiments is demonstrated. The acoustic levitator allows for the study of the evaporation of freely suspended deformed droplets and validates the theoretical model of oblate droplet evaporation.