OSCILLATING BUBBLES RISING IN A DOUBLY CONFINED CELL

The motion of bubbles rising in confined geometries has gained interest due to its applications mixing and mass transfer processes, ranging from bubble column reactors the chemical industry solar photobioreactors for algae cultivation. In this work we performed an experimental investigation behavior air freely at high Reynolds numbers a planar thin-gap cell thicknessh=2.8 mm filled with distilled water. in-plane width W is varied 2.4 cm 21 cm. We focus on influence lateral confinement regimes regular path shape oscillations large amplitude, that occur size range 0.6 cm<d<1.2cm. addition, rise regime consists vertical oscillations, does not appear laterally unconfined case, uncovered. presence walls, mean velocity Vb becomes lower than same beyond critical diameterdcVthat decreases as increases(i.e. decreases). can be determined change aspect ratio χ ellipse best fits contour each instant. It observed become closer circular (χ 1) increases. departure values ofχof case diameterdcχthat greater also greaterthandcVfor confinement, thus indicating effect seen earlier (i.e. smaller bubbles) ratio. Assuming wall related strength downward flow generated by bubble, introduce space let free liquid between walls Uf, estimated conservation asUf=dVb/(W−d). further relative fluid vicinityUrel=Vb+Uf=Vb/ξ, whereξ=1−d/Wis bubble. found that, given oscillatory regime, Urel approximately constant all studied W, matches closely value absence confinement. This provides estimation, leading order, generalizes expression proposed Filella et al. (JFM, 2015) accounts additional drag experienced walls. then show givendandξ, frequency amplitudes predicted using characteristic length scales d Urel.