1. Mixing induced by a bubble swarm rising through incident turbulence
- Author
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Varghese Mathai, Chao Sun, Detlef Lohse, Elise Alméras, and Physics of Fluids
- Subjects
Bubble ,Mixing (process engineering) ,UT-Hybrid-D ,General Physics and Astronomy ,FOS: Physical sciences ,02 engineering and technology ,Thermal diffusivity ,01 natural sciences ,010305 fluids & plasmas ,Physics::Fluid Dynamics ,symbols.namesake ,0203 mechanical engineering ,0103 physical sciences ,Diffusion (business) ,Fluid Flow and Transfer Processes ,Physics ,Turbulence ,Mechanical Engineering ,Isotropy ,Fluid Dynamics (physics.flu-dyn) ,Reynolds number ,Mechanics ,Physics - Fluid Dynamics ,22/4 OA procedure ,020303 mechanical engineering & transports ,Turbulence kinetic energy ,symbols - Abstract
This work describes an experimental investigation on the mixing induced by a swarm of high Reynolds number air bubbles rising through a nearly homogeneous and isotropic turbulent flow. The gas volume fraction $\alpha$ and the velocity fluctuations $u'_0$ of the carrier flow before bubble injection are varied, respectively, in the ranges $0\leq \alpha \leq 0.93\%$ and 2.3 cm/s $\leq u'_0 \leq 5.5$ cm/s, resulting in a variation of the bubblance parameter $b$ in the range [0, 1.3] ($b = \frac{V_r^2 \alpha}{{u'}_0^2}$, where $V_r$ is the relative rising velocity). Mixing in the horizontal direction can be modelled as a diffusive process, with an effective diffusivity $D_{xx}$. Two different diffusion regimes are observed experimentally, depending on the turbulence intensity. At low turbulence levels, $D_{xx}$ increases with gas volume fraction $\alpha$, while at high turbulence levels the enhancement in $D_{xx}$ is negligible. When normalizing by the time scale of successive bubble passage, the effective diffusivity can be modelled as a sole function of the gas volume fraction $\alpha^* \equiv \alpha/\alpha_c$, where $\alpha_c$ is a theoretically estimated critical gas volume fraction. The present explorative study provides insights into modeling the mixing induced by high Reynolds number bubbles in turbulent flows., Comment: 8 pages, 6 figures (submitted manuscript)
- Published
- 2019