Bubble-mediated transfer of dilute gas in turbulence
Bubble-mediated transfer of dilute gas in turbulence
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DOI：
10.1017/jfm.2021.447
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发表时间：
2021-06
影响因子：
3.7
通讯作者：
P. K. Farsoiya;S. Popinet;L. Deike
中科院分区：
文献类型：
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作者：
P. K. Farsoiya;S. Popinet;L. Deike
摘要在鼓泡塔化学反应器中，湍流中气泡介导的气体交换是至关重要的，对于与破碎波携带的空气有关的海洋-大气气体交换也是如此。了解在大Péclet数(定义为气体的平流率和扩散率之间的比率)时湍流中单个气泡的传输率很重要，因为它可以用于在更大范围内改进模型。在气泡体积变化可以忽略的范围内，研究了均匀各向同性湍流中单个气泡产生的稀薄气体的传质过程。结果表明，传质发生在气泡-液体界面的薄扩散边界层内，扩散边界层厚度随湍流Péclet数的增加而减小。我们为Higbie(Trans.Aiche，Vol.31,1935，pp.365-389)穿透理论，它基于气泡直径和特征湍流速度，其中$u是大尺度的湍流涨落。这导致了各向同性湍流中气泡的无量纲传递速率${Sh}=2(3)^{1/4}\Sqrt{\widetilde{{Pe}}/{\Rm\pi}}$。通过对均匀各向同性湍流中气泡中稀薄气体传质的直接数值模拟，验证了理论预测的正确性，并且只要对薄边界层进行适当的分辨，就能得到很好的一致性。
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) is important as it can be used for improving 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, $\widetilde {{Pe}}$. We propose a suitable time scale $\theta$ for Higbie (Trans. AIChE, vol. 31, 1935, pp. 365–389) penetration theory, $\theta = d_0/\tilde {u}$, based on $d_0$ the bubble diameter and $\tilde {u}$ a characteristic turbulent velocity, here $\tilde {u}=\sqrt {3}\,u_{{rms}}$, where $u_{{rms}}$ is the large-scale turbulence fluctuations. This leads to a non-dimensional transfer rate ${Sh} = 2(3)^{1/4}\sqrt {\widetilde {{Pe}}/{\rm \pi} }$ 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.