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Abstract Droplet impact on substrates is the cornerstone of several processes relevant to many industrial applications. Imposing substrate oscillation modifies the impact dynamics and can, therefore, be used to control the ensuing heat, mass, and energy transfer between the substrate and the impacting droplet. Previous research has shown that substrate oscillation strongly influences the spreading behavior of the droplet. In this study, we extend this understanding to examine how substrate oscillations can further modulate the retraction dynamics of the droplet, consequently affecting its long-term behavior, with a particular focus on induced jetting and subsequent breakup. We systematically examine the breakup of jets formed by the recoiling droplet through experimental investigations across a range of oscillation frequencies and amplitudes. Our findings reveal two distinct jet breakup modes: early and late, each governed by different time scales. Subsequently, we present a mechanistic description of the jetting process. Furthermore, we derive a simple scaling analysis based on energy balance to identify the critical condition required for jet breakup. Finally, we compare the experimental data with the scaling analyses to show its efficacy.
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Jet Formation After Droplet Impact on Microholed Hydrophilic Surfaces
Droplet impacts on solid surfaces produce a wide variety of phenomena such as spreading, splashing, jetting, receding, and rebounding. In microholed surfaces, downward jets through the hole can be caused by the high impact inertia during the spreading phase of the droplet over the substrate as well as the cavity collapse during recoil phase of the droplet. We investigate the dynamics of the jet formed through the single hole during the impacting phase of the droplet on a micro-holed hydrophilic substrate. The sub-millimeter circular holes are created on the 0.2 mm-thickness hydrophilic plastic films using a 0.5 mm punch. Great care has been taken to ensure that the millimeter-sized droplets of water dispensed by a syringe pump through a micropipette tip can impact directly over the micro-holes. A high-speed video photography camera is employed to capture the full event of impacting and jetting. A MATLAB code has been developed to process the captured videos for data analysis. We study the effect of impact velocity on the jet formation including jet velocity, ejected droplet volume, and breakup process. We find that the Weber number significantly affects outcomes of the drop impact and jetting mechanism. We also examine the dynamic contact angle of the contact line during the spreading and the receding phase.
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- Award ID(s):
- 1701339
- PAR ID:
- 10359535
- Date Published:
- Journal Name:
- IMECE2022
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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