Effect of nonisothermal gas absorption on drying of acoustically levitated wet porous granules

A transient model of drying of acoustically levitated slurry droplets at the stage when solid particles have formed wet porous granules is proposed. The model is formulated by a system of transient nonlinear energy and mass conservation equations utilizing an anelastic approximation. The filtration process of the vapor–gas mixture within the porous granule is described using Darcy’s law. The model takes into account the effects of acoustic flow, forced convection, absorption/desorption of soluble gases, filtration, and compressibility of the vapor–gas mixture inside the porous crust. It has been shown that the drying rate increases in the presence of active gas. It follows from numerical calculations that in a gas mixture containing air with an ammonia mass fraction of 0.3, at a temperature of 288K and a humidity of 50%, with an acoustic field frequency of 55 kHz and an SPL of 160 dB, the time of porous shell formation of a silica–water slurry droplet with the initial radius of 250 µm is half shorter than that in a gas mixture free from an active gas. We also found that drying time increases with increasing frequency and decreases with increasing sound pressure. The numerical analysis showed that the drying rate of an acoustically levitated porous agglomerate increases by about 10% with increasing intensity of the applied acoustic field from 158 dB to 162 dB. The predictions of the proposed model are in good agreement with the available experimental data. Based on the proposed concept, alternative drying technologies can be developed.