Growth and detachment of single hydrogen bubbles in a magnetohydrodynamic shear flow
Growth and detachment of single hydrogen bubbles in a magnetohydrodynamic shear flow
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DOI：
10.1103/physrevfluids.2.093701
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发表时间：
2017-09-15
影响因子：
2.7
通讯作者：
Cierpka, Christian
中科院分区：
文献类型：
--
作者：
Baczyzmalski, Dominik;Karnbach, Franziska;Cierpka, Christian
本文研究了磁流体动力学（MHD）剪切流对单个亚毫米级氢气泡生长和分离的影响。这些气泡在酸性环境（1M H2SO4）中在水平Pt微电极（直径100 μ m）处电解产生。固有的电场被一个均匀的电极平行的磁场叠加，高达700 mT，在电解质中产生洛伦兹力，驱动MHD流。氢气泡的生长和运动的微观高速成像和电流的测量进行了分析，而粒子跟踪测速（μ PTV）和粒子图像测速（μ PIV）被施加到测量周围的电解质流。此外，根据实验条件进行了数值模拟。结果表明，随着磁感应强度的增加，气泡的生长时间和脱离直径显著减少，这被认为是提高水电解效率的原因。为了进一步了解气泡分离机制，对作用在气泡上的力进行了分析。强烈的磁流体动力学诱导的拖曳力导致气泡在脱离之前缓慢地滑离微电极的中心。这种运动增加了活性电极面积并提高了气泡生长速率。结果进一步表明，在大电流密度下，主气泡底部形成的微小气泡的合并可能对气泡的脱离起重要作用。此外，讨论了气液界面Marangoni应力的产生。
This study investigates the effect of a magnetohydrodynamic (MHD) shear flow on the growth and detachment of single sub-millimeter-sized hydrogen gas bubbles. These bubbles were electrolytically generated at a horizontal Pt microelectrode (100 mu m in diameter) in an acidic environment (1 M H2SO4). The inherent electric field was superimposed by a homogeneous electrode-parallel magnetic field of up to 700 mT to generate Lorentz forces in the electrolyte, which drive the MHD flow. The growth and motion of the hydrogen bubble was analyzed by microscopic high-speed imaging and measurements of the electric current, while particle tracking velocimetry (mu PTV) and particle image velocimetry (mu PIV) were applied to measure the surrounding electrolyte flow. In addition, numerical flow simulations were performed based on the experimental conditions. The results show a significant reduction of the bubble growth time and detachment diameter with increasing magnetic induction, which is known to improve the efficiency of water electrolysis. In order to gain further insight into the bubble detachment mechanism, an analysis of the forces acting on the bubble was performed. The strong MHD-induced drag force causes the bubble to slowly slide away from the center of the microelectrode before its detachment. This motion increases the active electrode area and enhances the bubble growth rate. The results further indicate that at large current densities the coalescence of tiny bubbles formed at the foot of the main bubble might play an important role for the bubble detachment. Moreover, the occurrence of Marangoni stresses at the gas-liquid interface is discussed.