Sectional water fraction measurement for gas-water two-phase flow containing a conductive water phase utilizing capacitance sensor

Abstract

To apply an electrical capacitance sensor to sectional water fraction measurement for gas-water (salinity) two-phase flow, this paper investigates the effect of medium's conductivity on the measurement for capacitance sensors and its elimination. Firstly, mechanism of how medium's conductivity influences the capacitance measurement of a capacitance sensor is analyzed by combining the physical model of the sensor with its conditioning circuit. The theoretical analysis indicates that the applied exciting frequency is a key factor influencing the conductivity effect; the effect can be restrained by increasing the excitation frequency. Then, an exciting frequency optimization rule is proposed accordingly. Besides, sensor configuration and geometry optimization (based on FEM simulation) are discussed to achieve a more satisfying performance. Dynamic and static calibration experiments were carried out for stratified gas–liquid (salinity) two-phase flow for the purpose of validating the proposed method. The experimental results confirm the effectiveness of the proposed method. This work is constructive to the design for the capacitive sensing technologies applied to conductive objects, and offers insights into structure design and optimization for capacitance sensors.