Forced convection in the wakes of impacting and sliding bubbles

Meehan, R. O’Reilly; Williams, N. P.; Donnelly, Brian; Persoons, Tim; Nolan, Kevin; Murray, Darina B.

doi:10.1007/s00231-017-2165-6

Cited by 4 publications

(6 citation statements)

References 30 publications

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“…• to the horizontal, which allows for direct comparison to our previous IR and PIV work [1,3,29]. The regime map of Tsao and Koch [37] broadly classifies rising air bubbles of these diameters in water as oblate ellipsoids, although the presence of the sliding surface dramatically alters the bubble shape and behavior.…”

Section: Resultsmentioning

confidence: 92%

“…While it is true that Tomographic PIV could provide 3D information on the flow, its implementation would likely prove extremely challenging in this case, since the bubble would block much of the laser light. Figure 5(c) presents the convective heat flux enhancement relative to free convection from our previous thin-foil IR thermography measurements [29] for the same bubble size. These findings are in excellent agreement with our Schlieren measurements, revealing complex, elliptical-shaped "packets" of cooling [3,29] within the wake structure itself.…”

Section: Resultsmentioning

confidence: 97%

“…Figure 5(c) presents the convective heat flux enhancement relative to free convection from our previous thin-foil IR thermography measurements [29] for the same bubble size. These findings are in excellent agreement with our Schlieren measurements, revealing complex, elliptical-shaped "packets" of cooling [3,29] within the wake structure itself. Small regions of maximum convective heat flux enhancement are found to occur on the outside of the bubble path, which is consistent with the advection and motion of the hairpin loops within the wake structure observed using Schlieren measurements.…”

Section: Resultsmentioning

confidence: 97%

“…A significant portion of this enhancement stems from the turbulent mixing of the surrounding fluid, which is induced by the unsteady wake [3]. Previous work has sought to capture the dynamics of the sliding bubble and its associated wake by means of infrared (IR) thermography [3,29], bubble interface tracking [1], and particle image velocimetry (PIV) [1,30]. To date, a wake structure has been detected that is broadly consistent with the hairpin vortex structure observed behind freely rising bubbles [15,17,31] and near-wall bluff bodies [32,33].…”

Section: Introductionmentioning

confidence: 99%

“…• C, convective heat transfer enhancement 7-8 times that of natural convection has been shown to occur in small, discrete "packets" within the wake structure [3,29]. This wake structure has also been found to alter the dynamics of a subsequent trailing sliding bubble, for which the mechanism of heat transfer enhancement is more complex [2].…”

Section: Introductionmentioning

confidence: 99%

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Visualization of the wake behind a sliding bubble

et al. 2017

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In this work, Schlieren measurements are presented for the wake of an air bubble sliding under a heated, inclined surface in quiescent water to provide new insights into the intricate sliding bubble wake structure and the associated convective cooling process. This is a two-phase flow configuration that is pertinent to thermal management solutions, where the fundamental flow physics have yet to be fully described. In this work, we present an experimental apparatus that enables high-quality Schlieren images for different bubble sizes and measurement planes. By combining these visualizations with an advanced bubble tracking technique, we can simultaneously quantify the symbiotic relationship that exists between the sliding bubble dynamics and its associated wake. An unstable, dynamic wake structure is revealed, consisting of multiple hairpin-shaped vortex structures interacting within the macroscopic area affected by the bubble. As vorticity is generated in the near wake, the bubble shape is observed to recoil and rebound. This also occurs normal to the surface and is particularly noticeable for larger bubble sizes, with a periodic ejection of material from the near wake corresponding to significant shape changes. These findings, along with their implications from a thermal management perspective, provide information on the rich dynamics of this natural flow that cannot be obtained using alternate experimental techniques.

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