Abstract

In this study, the electric field generated by axial ring electrode conductivity cells is investigated. It is shown that the geometric parameters of such cells (mainly electrode separation, diameter and width) have a large effect on the resulting electric field uniformness. To quantify this effect, a parameter termed the effective measurement volume (EMV) is introduced which quantifies the measurement volume within the conductivity cell that contains 90% of the total current, normalized to that of an ideal conductivity cell (which generates a uniform electric field). The effects of a conductivity cells EMV on bulk conductivity measurements are both simulated and experimentally confirmed for emulated annular two-phase flow conditions. The results show that measurements performed with conductivity cells of high EMV tend towards true void fraction values, whereas cells of low EMV tended towards larger measurement error. This is quantified in the sum of squared residuals of the measurement, where a conductivity cell with an EMV of 0.19 has a sum of squared residual that is 638.4 times larger than a cell with an EMV of 1.00. Understanding the limitations of geometric parameters, a new axial conductivity profiling sensor was developed that uses one pair of electric field generating electrodes, and multiple measurement electrodes to create an axial conductivity profile with an axial measurement resolution of 10 mm.