Controlling and regulating droplet impact dynamics on a heated surface via electrowetting

The potential application of droplet rebound suppression includes improved spray cooling performance due to prolonged liquid-wall interaction and reduced energy loss. It is also advantageous for preventing cross-contamination, disseminating germs, hazardous chemicals, and many other things. Even though the electrowetting-induced droplet impact has great potential in controlling and regulating the droplet dynamics, to date, there has been no research on electrowetting-assisted droplet impalement on a heated surface. The present work aims to explore the electrowetting-assisted droplet impalement dynamics and corresponding heat transfer characteristics. A Cahn–Hilliard phase field method-based numerical model is developed to analyze the behavior and evolution of the interfaces during the temporal dynamics of droplet impalement. A molecular kinetic theory-based dynamic contact angle model precisely tracks the three-phase contact line dynamics. The impact dynamics are studied for several voltage waveforms, including square, sinusoidal, and triangle, at various applied frequencies in the 5–150 Hz range. Moreover, the static contact angle—voltage waveform and applied frequency—voltage waveform regime map reveals the different droplet rebound behavior and bubble entrapment for a wide range of contact angles (100°–160°). In contrast to the sinusoidal and triangle waveforms, the square waveform effectively eliminates the bubble entrapment during impingement with a high impact velocity of 0.9 m/s. It also exhibits droplet rebound suppression for all contact angles and frequencies within the range of 5–150 Hz. The electrowetting-assisted cooling effectiveness for the square waveform is enhanced by 213.6% and 112.7% for static contact angles of 100° and 160° respectively.