B8.2 - Simultaneous Measurements of the Liquid Phase Velocity and Gas Bubble Trajectories in a Two-Phase Flow at Gas- Evolving Electrodes

AMA Conferences 2015
2015-05-19 - 2015-05-21
Nürnberg, Germany
Proceedings SENSOR 2015
B8 - Fluid-Structure Interaction Sensing
D. Baczyzmalski, C. Kähler, C. Cierpka - Universität der Bundeswehr München, Neubiberg (Germany), T. Weier - Helmholtz-Zentrum Dresden – Rossendorf, Dresden (Germany)
329 - 333


In water electrolysis the efficiency is related to the free area of the electrodes, which is limited by hydrogen gas bubbles evolving at the cathode. Therefore, a fast transport of the hydrogen bubbles away from the electrodes into the bulk is beneficial. The detachment and transport of bubbles from the electrode is affected by the convection of the electrolyte surrounding the bubble. In order to characterize the flow close to the electrode’s surface, simultaneous measurements of the fluid velocities of the electrolyte and the size and trajectories of hydrogen bubbles were carried out in an undivided water electrolyzer at the Helmholtz-Zentrum Dresden – Rossendorf. The liquid phase velocity was measured by particle image velocimetry (PIV) as well as particle tracking velocimetry (PTV) using fluorescent tracer particles and laser light illumination. Gas bubble trajectories were determined using particle tracking on bubble shadow images obtained by a second camera in conjunction with a background illumination. The images were separated by the different wavelengths of the illumination/fluorescence. However, the uncertainty of the fluid and gas bubble velocity is strongly affected by the high void fraction in the vicinity of the electrode. As a result, liquid phase velocities determined with PIV are substantially biased in the near-wall region. The application of advanced PTV methods allows for more precise measurements closer to the electrode. Thus, an improved characterization of the evolving wall jet can be achieved by a combination of both PIV and PTV methods. Furthermore, the effect of large rising bubble with path oscillations on fluid velocities has been investigated. The wake generated by these bubbles can have a strong impact on the nearwall fluid velocities and their fluctuations and thus influence the mass transfer near the electrodes and the performance of the water electrolyzer.