L. Pavlov, M. D'Angelo, M. Cachile, V. Roig, P. Ern
{"title":"OSCILLATING BUBBLES RISING IN A DOUBLY CONFINED CELL","authors":"L. Pavlov, M. D'Angelo, M. Cachile, V. Roig, P. Ern","doi":"10.31527/analesafa.2022.fluidos.66","DOIUrl":null,"url":null,"abstract":"The motion of bubbles rising in confined geometries has gained interest due to its applications in mixing and mass transfer processes, ranging from bubble column reactors in the chemical industry to solar photobioreactors for algae cultivation. In this work we performed an experimental investigation of the behavior of air bubbles freely rising at high Reynolds numbers in a planar thin-gap cell of thicknessh=2.8 mm filled with distilled water. The in-plane width of the cell W is varied from 2.4 cm to 21 cm. We focus on the influence of lateral confinement on the motion of bubbles in the regimes with regular path and shape oscillations of large amplitude, that occur for the size range 0.6 cm<d<1.2cm. In addition, a rise regime that consists of a vertical rise path with regular shape oscillations, that does not appear in the laterally unconfined case, is uncovered. In the presence of lateral walls, the mean rise velocity of the bubble Vb becomes lower than the velocity of a laterally unconfined bubble of the same size beyond a critical bubble diameterdcVthat decreases as the confinement increases(i.e. as W decreases). The influence of the lateral confinement on the bubble mean shape can be determined from the change in the mean aspect ratio χ of the ellipse that best fits the bubble contour at each instant. It is observed that bubbles become closer to circular (χcloser to 1) as the confinement increases. The departure from the values of χ of the laterally unconfined case occur at a critical diameter dcχ that is lower for greater confinement and also greater than dcV for each confinement, thus indicating that the effect of the lateral confinement is seen earlier (i.e. on smaller bubbles) on the velocity than on the aspect ratio. Assuming that the wall effect is related to the strength of the downward flow generated by the bubble, we introduce the mean flow velocity in the space let free for the liquid between the walls and the bubble, Uf, that can be estimated by mass conservation as Uf=dVb/(W−d). We further introduce the relative velocity between the bubble and the downward fluid in its vicinity Urel=Vb+Uf=Vb/ξ, whereξ=1−d/Wis the confinement ratio of the bubble. We found that, for a given bubble size in the oscillatory regime, Urel is approximately constant for all the studied values of W, and matches closely the value in the absence of lateral confinement. This provides an estimation, at leading order, of the bubble velocity that generalizes the expression proposed by Filella et al. (JFM, 2015) and accounts for the additional drag experienced by the bubble due to the lateral walls. We then show that, for givendandξ, the frequency and amplitudes of the oscillatory motion can be predicted using the characteristic length and velocity scalesdandUrel.","PeriodicalId":41478,"journal":{"name":"Anales AFA","volume":"18 3 1","pages":""},"PeriodicalIF":0.1000,"publicationDate":"2022-08-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Anales AFA","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.31527/analesafa.2022.fluidos.66","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q4","JCRName":"PHYSICS, MULTIDISCIPLINARY","Score":null,"Total":0}
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Abstract
The motion of bubbles rising in confined geometries has gained interest due to its applications in mixing and mass transfer processes, ranging from bubble column reactors in the chemical industry to solar photobioreactors for algae cultivation. In this work we performed an experimental investigation of the behavior of air bubbles freely rising at high Reynolds numbers in a planar thin-gap cell of thicknessh=2.8 mm filled with distilled water. The in-plane width of the cell W is varied from 2.4 cm to 21 cm. We focus on the influence of lateral confinement on the motion of bubbles in the regimes with regular path and shape oscillations of large amplitude, that occur for the size range 0.6 cm
由于气泡在混合和传质过程中的应用，从化学工业中的气泡柱反应器到藻类培养的太阳能光生物反应器，气泡在受限几何形状中上升的运动引起了人们的兴趣。在本工作中，我们进行了实验研究气泡在厚度=2.8 mm的平面薄间隙池中充满蒸馏水时在高雷诺数下自由上升的行为。电池的面内宽度W从2.4 cm到21 cm不等。我们重点研究了侧向约束对气泡运动的影响，这些气泡在0.6 cm
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