| dc.description.abstract | In recent years, enhancements in dropwise condensation have been achieved by
formulating, fabricating, and using hydrophobic coatings with all sorts of surface features. Reduction in contact angle hysteresis and better droplet sliding properties have been achieved by incorporating nanoscale features on surfaces. However, most recently developed coatings still face considerable implementation challenges due to their lack of long-term durability and affordability. Therefore, methods that rely on external stimuli for faster droplet shedding during dropwise should be explored. Recently, the use of vibrations to promote droplet shedding in DWC has been studied. However, it is important to identify the corresponding resonance frequencies to keep vibration amplitudes low for optimal system performance.
In the first part of this study, four droplets within 3 - 5 μL and five different vertically oriented surfaces with contact angles ranging from 70⁰ - 110⁰ were used. Experiments were conducted to determine the resonance frequencies for each droplet-surface combination. In the second stage, the surface was imposed with the resonance frequencies and frequencies within ± 8 Hz of the resonance frequencies for the respective droplet volumes. The acceleration of the surface was adjusted until droplet sliding occurred. It was observed that minimum acceleration values required for droplets to slide were at their corresponding resonance frequencies.
In the study, condensation experiments were conducted under constant subcooling conditions for copper and PTFE without vibration and under resonant vibrations. The effects of imposing a single frequency and amplitude as well as frequency sweeps on condensation rates were explored. It was found that for both surfaces, vibrations led to enhancement in condensation rates with maximum enhancement achieved when high-to-low frequency sweep was imposed.
In summary, vibrations at resonant frequencies have led to efficient drop mobility on the surface and improved dropwise condensation rates. The potential use of resonant vibrations in condensation systems should improve their overall thermal performance considerably. | |
