Acoustic-induced flow on the evaporation dynamics of twin drops

The present study aims to investigate the effect of an acoustic field on the internal circulation and evaporation of three distinct combinations of twin methanol drops. The drop combinations used for making twin drops are (i) methanol and water (i.e., 15% and 75% of methanol), (ii) pure methanol, (iii) one pure methanol, and methanol-water (15 % and 75 % of methanol). The studies are conducted for two different drop spacings of 0.5 and 1.5 cm. The results suggest that the higher spacing (i.e., 1.5 cm) produced a stronger acoustic streaming effect than the lower one (i.e., 0.5 cm) for all the twin drop combinations, which indicates higher internal circulation at a larger spacing of 1.5 cm. For all the spacings, the evaporation rate is observed to be proportional to the internal circulation at all twin drop combinations. Further, empirical correlations are developed to predict the evaporation rate and internal circulation for twin drops with different combinations. The study shows that the evaporation and internal circulation follow a universal behavior for all the combinations of twin drops at both the drop spacings, while the higher values are observed at a larger spacing of 1.5 cm compared to the smaller one of 0.5 cm. The paper clearly demonstrates the complex interplay of variables involved in the evaporation / internal circulation of twin methanol drops under the influence of an acoustic field, thus producing a universal behaviour that is independent of their composition for both the drop spacings.