Experimental Comparison Between Conductive and Capacitance Wire-Mesh Sensors to Predict Gas Void Fraction and Flow Regimes in Vertical Pipes

Abstract

A comparative study of conductive and capacitance wire-mesh sensors was carried out for a wide range of gas velocities and for a fixed liquid velocity of 1.5 m/s. The two instruments were mounted on the vertical pipe at the highest and lowest positions of the downward and upward orientations in order to predict the gas void fraction and establish various flow regimes. The principle of conductive WMS is based on the discrepancies between the conductivity of the gas and liquid, while the principle of capacitance WMS is based on the variation of the permittivity between the two-phase. During the run of the experiments, the frequency was set at 1,000 Hz for one minute.

Averaged time traces of gas void fraction and its probability density function (PDF) and distributions of gas void fraction were applied to confirm the similarities or discrepancies between the two techniques. It was observed that the gas void fractions obtained by both techniques displayed similar behavior. Although conductive WMS exhibited higher void fraction values than those measured by capacitance WMS.

The cross-sectional and sliced images (i.e., reconstructed images) were also extracted from conductive and capacitance wire-mesh sensors at higher and lower locations of the upward section, which were used as another means to confirm the above-mentioned results. It was noted from the images that both devices depicted similar flow patterns for each particular flow rate.