Two models of electrical impedance for electrodes with tap water and their capability to record gas volume fraction

Bubble columns are devices for simultaneous two-phase or three-phase flows. Phase interactions produce several flow
patterns where the void fraction is an important variable involved in the behavior and fundamental in flow pattern transitions.
Electrical impedance sensors (EIS) determine void fraction and perform as fast response, passive elements, exhibiting
resistive, capacitive and inductive behaviors highly dependent upon the excitation frequency. A simple electrical model
frequently used is a set of a resistance and a capacitor connected in parallel. Same elements can also be arranged in series,
as we do here. We identify three behaviors in the series and parallel arrangements, as well as in the experimental data.
While the ones of the series arrangement are coincident with experimental data, the ones of the parallel model are only
partially coincident at high frequencies. Moreover, while the parallel model is insensitive to changes in gas volume fraction
in the resistive range, the series model presents sensitivity to changes in the gas volume fraction. Therefore, on these
grounds the series arrangement exhibits a better performance than the parallel model.