In order to improve dropwise condensation (DWC), droplets must be efficiently shed from the surface to avoid a film formation and low heat transfer rates. Coatings and nanostructured surfaces have been used to achieve better droplet shedding, but they face problems of poor long-term durability and affordability. Thus, active methods relying on external stimuli must be explored. A vibration study using three substrates (copper, PTFE and Saphir) was undertaken to understand the effects of vibration parameters on droplet mobility. The substrates ranged from being hydrophilic to hydrophobic. The first objective was to determine the resonant frequencies of droplets on these surfaces for a range of droplet sizes, ranging from 3.3 ?l to 6.8 ?l. The experimental resonant frequencies were measured and compared to the ones obtained from the Celestini's model for validation purposes. A discrepancy of about 20 % was observed. In the next part of the study, the droplets were vibrated with increasing accelerations until sliding was observed. The acceleration and frequency at sliding were recorded, and the amplitude and vibration intensity was calculated. These parameters were compared across each surface and droplet volume. In all the experiments, it was noticed that amplitude, acceleration, and vibration intensity depended on droplet volume and the hydrophobicity of the surface. Droplets of smaller volume needed greater vibrational energy to slide due to relatively high magnitude of the corresponding adhesive force. For droplets of the same volume, it was observed that hydrophobic substrates are better than hydrophilic substrates in promoting sliding. It was also observed that roughness of the substrate plays a significant role in reducing the sliding of the droplet. Finally, across any droplet size-substrate combination, it was observed that vibrations at resonant frequency of the droplet led to easier sliding with the least consumption of energy, as indicated by the vibration intensity. Thus, it is advisable to use resonant frequency of droplets to promote droplet shedding in a host of applications including dropwise condensation.
