Measurement of near-wall stratified bubbly flows using electrical impedance

The impedance measurement between a pair of flush-mounted electrodes was used to measure the characteristics of a stratified near-wall bubbly flow. The variation in cross electrode impedance with liquid layer thickness and mixture void fraction was examined using numerical simulations and static experiments. The experimental realization of the measurement system was used to measure the solid fraction of a water–glass sphere mixture to an uncertainty of ±2.4%, where the diameter of the glass spheres ranged from 0.1 to 0.2 of the electrode diameter. A stratified bubbly flow was produced over a flat surface, and optical measurements of the bubble distributions were used to understand the measured impedances across the electrode pair. Comparison between the computed impedance change (based on the observed void fraction and liquid layer height) and the inferred quantities from the impedance measurement alone yielded a variation from 12 to 28% on average. The use of multiple electrode pairs is discussed.