Acoustic-driven droplet evaporation: beyond the role of droplet-gas relative velocity

Abstract

Acoustic waves can be used for high-precision evaporation of droplets, allowing for fine control over the droplet diameter. Previous works considered the acoustic field as simply a means for generating relative velocity u1 between a droplet and its surrounding gas, which convects heat and mass from the droplet while oscillating. In the present work, we experimentally examine the effects of an acoustic field fundamental characteristics – pressure and velocity distribution and the phase between them – on a droplet evaporation rate. Our results clearly show that the pressure and phase contribute to the evaporation, with the latter dramatically affecting the process. We propose a generalization to existing models that account only for variations in u1, and demonstrate how the new model outperforms its counterpart when fitted to the experimental data. Our generalized correlation increases R2 for fitting the experimental data from 0.82 to 0.94, when compared with a standard model that only accounts for relative velocity. The new insight may be utilized for enhancement and fine-tuned control over droplet evaporation via acoustics, to be used over a wide range of applications, including lab-on-a-droplet reactions and vapor transport in thermoacoustic devices.