Flow structures and dynamics in the wakes of sliding bubbles

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

doi:10.1016/j.ijmultiphaseflow.2016.03.010

Cited by 22 publications

(21 citation statements)

References 23 publications

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“…• to enable comparison to our previous studies [1][2][3]. A custom experimental structure is therefore constructed with all of these components mounted onto an aluminium frame with an adjustable angle.…”

Section: Methodsmentioning

confidence: 99%

“…High-speed images are acquired at 1 kHz using a Phantom V311 high-speed camera (1280 × 800 CMOS sensor, 20 μm pixel size). Following recording, the raw images are postprocessed in MATLAB using the interface tracking algorithm outlined in our previous work [1,2]. This method enables not only the bubble shape and path but the dynamics of its interface to be tracked, thereby linking the fluid shed by the bubble into its near wake to changes in its interface.…”

Section: Methodsmentioning

confidence: 99%

“…Observation of the dynamics of a gas bubble moving through a liquid provides insight into a complex natural phenomenon that is important to a diverse range of applications in chemical engineering, water treatment, and thermal management [1][2][3][4]. Regarding thermal management, it is well established that two-phase flows can offer significant performance advantages, including extremely high heat transfer coefficients, temperature homogenization, and passive and low-power consumptions [5].…”

Section: Introductionmentioning

confidence: 99%

“…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%

“…While 2D PIV provides quantitative in-plane velocity measurements, these are integrated over interrogation windows. Additionally, each window is limited to two dimensions, although it is possible to step the laser position to obtain a pseudo-three-dimensional (3D) representation of the flow field [1]. Thin-foil thermography provides higher resolution measurements but only at the heated surface.…”

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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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Visualization of the wake behind a sliding bubble

et al. 2017

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Mechanisms of heat transfer for axisymmetric bubble impingement and rebound

et al. 2017

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Heat transfer enhancement resulting from the impingement and rebound of bubbles in confined geometries can play an important role in heat transfer applications. Limited studies exist on the impact behaviour of large ellipsoidal bubbles against a horizontal surface, while the associated fluid flow field has received even less recognition. To address this, the current study investigates the dynamics of a single large ellipsoidal bubble impinging on a horizontal heated surface.The bouncing dynamics have been explored by utilising synchronised high-speed and IR photography. Due to the large bubble size in the present study only a bubble with a low release to surface distance was found to have a symmetric bouncing event. The results showed that separated wake structures initially cooled the surface before the wake structures become counter productive and convect warm fluid onto the previously cooled surface. Two cooling zones were observed; the inner region due to the bubble and the outer region due to the bubble's wake.

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