Experimental investigation of gas bubble effects on electrolyte conductivity in alkaline water electrolyser stack manifolds and evaluation of the theoretical two-phase correlation models

Abstract

In bipolar alkaline water electrolyser (AWE) stacks, gas bubbles in outlet manifolds reduce electrolyte conductivity and thereby affect shunt-current losses. Correlation models such as Bruggeman are widely used to predict this loss but remain unvalidated for manifold-like geometries. This thesis experimentally quantifies the impact of gas bubbles on electrolyte conductivity across a void-fraction range not previously investigated and evaluates five conductivity correlation models against these measurements.

Conductivity was measured in an acrylic test section with pin electrodes, using a circulating 25 wt % KOH loop with nitrogen injected to generate void fractions up to about 0.97. Single-phase measurements over 25–60 °C agreed with the Gilliam correlation. A dispersed gas regime could not be sustained in a horizontal tube, so measurements were conducted vertically, where the flow developed as bubbly near the inlet and evolved into slug, then churn, downstream.

Conductivity behaviour falls into three void-fraction ranges. Measurements appeared to agree with the correlation models only at very low void fraction, though data here were limited and require further confirmation. At intermediate void fractions, conductivity deviated progressively above the models; bubbly flow showed higher conductivity than slug flow at the same void fraction, tentatively linked to liquid continuity, though this needs further verification. At high void fractions, relative conductivity levelled off at 0.2–0.25 rather than collapsing toward zero, showing a continuous liquid path persists even at near-unity void fraction. Electrolyte flow rate increased conductivity significantly in bubbly flow but had minimal effect in slug and churn flow. The theoretical correlations fail beyond low void fraction, indicating the need for an improved empirical correlation accounting for flow regime and void fraction for reliable shunt-current modelling in scaled-up AWE systems.