Experimental Assessment of an Innovative Device to Mimic Bubble Swarm Turbulence

Abstract

The local mass transfer of a bubble under swarm turbulence influence is the key to the performance of gas-liquid contactors. For measurements, optical accessibility is reduced due to an increased void fraction. The performance of a flexible grid of rigid particles to mimic the hydrodynamic conditions of bubble-induced swarm turbulence is assessed using spectral energy density distribution and an approach to connect the turbulent intensity to the according length scale of the flow. Despite the significant physical property differences to real bubbly flow the flexible grid is found to realistically mimic the swarm turbulence of a cocurrent bubble column. Hence, a single bubble approaching the proposed flexible grid experiences hydrodynamic conditions comparable to real bubble-induced turbulence.

Emulation of Bubble‐Induced Turbulence Using Randomly Moving Particles in a Grid Structure

“…Furthermore, different length scales are generated by the randomly moving particles and constantly changing entrainment of the free stream between the particle strings. These length scales were measured and characterized by EDM and discussed in detail in . The devices induce a range of length scale, while on the lower half of the considered range the grids produce smaller values while in the higher frequency ranges larger scales.…”

“…Comparable grids are used and the results evaluated with the measurements in a real bubble column. Mießner et al compared the energy spectra taken in real high dense bubble swarms with that under the elliptical particle grids ( d p = 4.6 mm, 4 and 10 vol %). Both a real bubble column in co‐flow ( u = 8 cm s −1 ) with a volume fraction α = 4.24 vol % and the free‐moving particle grids are characterized with the time‐resolved EDM.…”

“…The transition is between the initial turbulent energy, and the onset of the energy cascade can serve as a reference length L since the wake structures of swarm turbulence arise in the bubble dimension ( d b ∼ 5 mm). In , a deduction of this scaling is provided. The largest eddies that need to be considered for the bubble motion and deformation are on the order of three times the diameter.…”

“…The similar time scale describes the longest periodic flow structure that can in turn be used to describe the length scales by applying the Taylor hypothesis. In , a detailed analysis regarding the length scale and turbulence level is given. Mießner et al described that the particles introduce turbulences with the initial length scale of swarm turbulence.…”

Modeling the Excess Velocity of Low-Viscous Taylor Droplets in Square Microchannels

“…The specific flow conditions can furthermore serve for cell isolation [7], genetic analysis [8] and reaction screening in a droplet chain [9]. In contrast to large scale multiphase flows, microscopic flows are much easier to predict as there are no complex interactions such as swarm turbulence [10,11] commonly found in bubble columns. In fact, the reproducibility of e.g.…”