Bubble mediated transfer of dilute gas in turbulence

Publication Year
2021

Type

Journal Article
Abstract

Bubble-mediated gas exchange in turbulent flow is critical in bubble column chemical reactors as well as for ocean-atmosphere gas exchange related to air entrained by breaking waves. Understanding the transfer rate from a single bubble in turbulence at large Péclet numbers (defined as the ratio between the rate of advection and diffusion of gas) regimes is important as it can be used for improving the models on a larger scale. We characterize the mass transfer of dilute gases from a single bubble in a homogeneous isotropic turbulent flow in the limit of negligible bubble volume variations. We show that the mass transfer occurs within a thin diffusive boundary layer at the bubble-liquid interface, whose thickness decreases with an increase in turbulent Péclet number, Pe. We propose a suitable time scale θ for Higbie (1935) penetration theory, θ = d 0 /ũ, based on d 0 the bubble diameter andũ a characteristic turbulent velocity, hereũ = √ 3 u rms , where u rms is the large-scale turbulence fluctuations. This leads to a non-dimensional transfer rate Sh = 2(3) 1/4 Pe/π, from the bubble in the isotropic turbulent flow. The theoretical prediction is verified by direct numerical simulations of mass transfer of dilute gas from a bubble in homogeneous and isotropic turbulence, and very good agreement is observed as long as the thin boundary layer is properly resolved.

Journal
Journal of Fluid Mechanics
Volume
920
Pages
A34
Date Published
May 2021
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