Numerical investigation of coalescence phenomena, affected by surface acoustic waves

We investigate numerically the coalescence dynamics of two same droplets on a wettable substrate when the droplets are subjected by the surface acoustic waves (SAW). For this purpose, dynamics of the flow is simulated using Lattice Boltzmann method. At first, the coalescence phenomena are studied. Then, the effects of SAW on behaviors of droplets are illustrated. The results show that in the pumping mode, regardless of the location, the droplets coalesce when the SAWs are applied. Also, we can reduce the connection time about 60% by increasing the wave amplitude. Based on the results, the coalescence time is minimized to a certain wave amplitude that in our study occurs in the wave amplitude number (ASAW) about 16. In the jetting mode, three different dynamical behaviors are observed and are categorized with wave amplitude number. When ASAW < 8, the coalescence of two droplets and the detachment of the formed droplet occurs, while we observe the periodic detachment and connection of droplets for 8 < ASAW < 10. Then, two droplets affected by SAWs are removed from the surface for ASAW > 10. Also, we show that ASAW ≈ 14 is the optimum situation for removal of the droplets from the surface.