Modelling the two-phase flow and current distribution along a vertical gas-evolving electrode

Abstract

The bubbly two-phase flow and electric current density distribution along a single, vertical, gas-evolving electrode are modelled and the results of a boundary layer analysis are presented. Existing empirical models for particle transport in sheared and sedimenting suspensions are adopted for the bubble mixture to close the two-phase model. Ionic species concentrations are shown to be essentially homogeneous as the mixing effect of the bubble suspension usually is much larger than dispersion by molecular diffusion even at laminar flow conditions. The non-uniformity of the bubble distribution along the electrode results in a non-uniform current density distribution, which agrees well with existing experimental findings in the literature.

Dynamic modelling of hydrogen evolution effects in the all-vanadium redox flow battery

“…The first two assumptions can be justified by the fact that the bulk of the fluid is water. Bubble formation at electrodes evolving H 2 and other gases is believed to result from supersaturation of dissolved gas in the liquid adjacent to the electrode surface [14,19]. The bubbles form at so-called 'nucleation sites' on the electrode surface.…”

“…The formation and effects of gas bubble evolution on planar electrodes, particularly from H 2 evolution, has been investigated fairly extensively [14][15][16][17][18]. Analytical and numerical models have been developed, notably by Dahlkild and co-workers [19,20], Ziegler and Evans [15] and Mat and co-workers [21,22], all based on the multi-phase mixture (or 'drift-diffusion') model [23,24]. The same approach towards bubble formation and gas/liquid transport is adopted in this paper.…”

Modelling the effects of oxygen evolution in the all-vanadium redox flow battery

“…3. The oxygen gas forms spherical bubbles that maintain their shape when detaching from the electrode surface and do not coalesce [10,[18][19][20]. Small bubbles remain spherical as a result of high surface tension and their coalescence can be neglected [21].…”

A Coupled Electrochemical and Hydrodynamical Two-Phase Model for the Electrolytic Pickling of Steel

“…31 and 38, in order to take account of the reduction of electrode surface area due to blockage by bubbles, we use the approach of Dahlkild 16 and Wedin and Dahlkild, 17 among others, and introduce a multiplicative factor ͑1 − ␥͒ for the current density.…”