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In this work, we experimentally studied bubble formation on the superhydrophobic surface (SHS) under a constant gas flow rate and at quasi-static regime. SHS with a radius RSHS ranging from 4.2 to 19.0 mm was used. We observed two bubbling modes A and B, depending on RSHS. In mode A for small RSHS, contact line fixed at the rim of SHS, and contact angle (θ) initially reduced, then maintained as a constant, and finally increased. In mode B for large RSHS, contact line continuously expanded, and θ slowly reduced. For both modes, during necking, contact line retracts, and θ was close to the equilibrium contact angle. Moreover, the pinch-off of bubble at the early stage was similar to the pinch-off of bubble from a nozzle and followed a power-law relation Rneck ∼ τ0.54, where Rneck is the minimum neck radius and τ is the time to detaching. Furthermore, we calculated the forces acting on the bubble and found a balance between one lifting force (pressure force) and two retaining forces (surface tension force and buoyancy force). Last, we found a waiting time for a finite volume to be detected for large RSHS. The detached volume was well predicted by Tate volume, which was derived based on balance between buoyancy and surface tension and was a function of bubble base radius.
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Effect of gas flow rate on bubble formation on superhydrophobic surface
Abstract We experimentally studied the effect of gas flow rateQon the bubble formation on a superhydrophobic surface (SHS). We variedQin the range of 0.001 < Q/Qcr < 0.35, whereQcris the critical value for a transition from the quasi‐static regime to the dynamic regime. The bubble geometrical parameters and forces acting on the bubble were calculated. We found that asQincrease, the bubble detached volume (Vd) increased. After proper normalization, the relationship betweenVdandQgenerally agreed with those observed for bubbles detaching from hydrophilic and hydrophobic surfaces. Furthermore, we found thatQhad a minor impact on bubble shape and the duration of bubble necking due to the negligible momentum of injected gas compared to surface tension and hydrostatic pressure. Lastly, we explained the primary reason for the largerVdat higher flow rates, which was increased bubble volume during the necking process. Our results enhanced the fundamental understanding of bubble formation on complex surfaces and could provide potential solutions for controlling bubble generation and extending the application of SHS for drag reduction, anti‐fouling, and heat and mass transfer enhancement.
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- PAR ID:
- 10564948
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Droplet
- Volume:
- 4
- Issue:
- 1
- ISSN:
- 2769-2159
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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