A dual-modality electrical tomography sensor for measurement of gas–oil–water stratified flows

• A new ECT/ERT dual-modality sensor is proposed and investigated.
• The voltage-excitation and current-measurement strategy is adopted for ERT.
• A simple data fusion method is introduced for multiphase flow measurement.
• Experimental verification of the proposed measurement scheme.

Multiphase flow measurement is a challenging work, especially for the measurement of gas–oil–water flows. In the past, researchers tried to measure gas–oil–water flows by using two separate electrical tomography (ET) sensors, e.g. electrical capacitance tomography (ECT) and electrical resistance tomography (ERT). In this paper, a typical ECT sensor with inner electrodes, as an ECT/ERT dual-modality sensor, is investigated for the measurement of gas–oil–water stratified flows. With this ECT sensor, the voltage-excitation and current-measurement strategy is adopted for both ECT and ERT measurement unlike the conventional ERT with current-injection and voltage-measurement, which cannot provide quantitative measurements because of serious fringe effect. To validate the effectiveness of the proposed measurement strategy, experiment was conducted with an impedance-analyser-based data acquisition system, which can take both capacitance and conductance measurements simultaneously. Based on the measured capacitance and conductance, the corresponding permittivity and conductivity distributions can be reconstructed for the same cross section. A simple data fusion method is proposed to extract the information regarding the oil distribution from the reconstructed images, which was proved to be effective. In the experiment, different excitation frequency and different conductivities of the water phase were examined to investigate their influence on the three-phase flow imaging and measurement. The proposed measurement strategy has advantages of simplified sensor design, reducing the complexity of the related electronics as well as acquiring all information from the same cross section.