Suppression of electroconvective and morphological instabilities by an imposed cross flow of the electrolyte
Suppression of electroconvective and morphological instabilities by an imposed cross flow of the electrolyte
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DOI：
10.1103/physrevfluids.6.033701
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发表时间：
2021-03-10
影响因子：
2.7
通讯作者：
Koch, Donald L.
中科院分区：
文献类型：
--
作者：
Li, Gaojin;Townsend, Alex;Koch, Donald L.
电对流（EC）不稳定性及其对表面形态扰动（Morph）的影响在许多应用中很重要，包括电渗析、电池和燃料电池。在这项工作中，我们使用两种方法研究了二维通道流对EC和Morph不稳定性的影响。在体分析中，我们通过忽略空间电荷层和在电中性体区域上施加第二类电渗滑移速度边界条件，得到了小波数和大波数的渐近解。在全分析中，使用超球面光谱方法分析了液体电解质的整个区域的不稳定性。这两项研究表明，流动显着影响EC不稳定性。所施加的流扭曲的浓度场，造成的遮蔽效果，阻碍了从低到高浓度区域的离子传输，因此抑制EC不稳定性低于一定的波数。结合空间电荷层对高波数模的粘性稳定作用，足够强的外加流可以完全抑制EC不稳定性。不稳定性开始的临界电压的增量大致与施加的速度和双层厚度的乘积的平方根成比例。施加的流动对Morph不稳定性的影响较小，除了它可以去除EC不稳定性导致的形态模式，从而改变最不稳定模式的波数。
Electroconvective (EC) instability and its influence on surface morphological perturbations (Morph) are important in many applications, including electrodialysis, batteries, and fuel cells. In this work, we study the effects of a two-dimensional channel flow on the EC and Morph instabilities using two approaches. In the bulk analysis, we derive the asymptotic solutions for small and large wave numbers by neglecting the space charge layer and imposing a second kind electroosmosis slip velocity boundary condition on the electroneutral bulk region. In the full analysis, the instability of the entire region of the liquid electrolyte is analyzed using the ultraspherical spectral method. Both studies show that the flow significantly affects the EC instability. The imposed flow distorts the concentration field, causing a sheltering effect which hinders the ion transport from low- to high-concentration regions, and therefore suppresses the EC instability below a certain wave number. In combination with the viscous stabilization of the high wave number modes by the space charge layer, a sufficiently strong imposed flow can fully suppress the EC instability. The increment in the critical voltage for the instability onset is roughly proportional to the square root of the product of imposed velocity and double layer thickness. The imposed flow has a smaller effect on the Morph instability, except that it may remove the morphological modes resulting from the EC instability and thereby change the wave number of the most unstable mode.