Multiphase flow is a commonly seen transient and complex dynamic system in many industrial processes. The phase fraction and velocity are two of the most important parameters for flow monitoring and measurement. Due to the advantages of simplicity in sensor structure, low fabrication costs and fast response, conductance sensors have received broad attentions in horizontal, vertical and inclined multiphase pipe flow measurement. A conductance sensor measures the multiphase mixture conductivity between two electrodes in contact with the fluid to determine the phase fraction. Combined with cross-correlation technique, the velocity can also be acquired. This paper presents a review on the basic sensing principle, different types of conductance sensors and their applications in flow monitoring, flow pattern identification, phase fraction determination and velocity measurement of multiphase flow. Finally, based on the conclusion of the disadvantages, advantages and limitations of this technique, the insight into trends for future development are given.

Capacitive sensors are found in numerous applications, and they are capable of sensing several parameters. Multiphase flows occur in many industrial processes that require proper monitoring to improve the efficiency and safety of plants and equipment. Detailed (high-resolution) flow information is required from dedicated flow experiments at a laboratory scale to develop and validate flow modelings. In both cases, capacitive flow sensors have been applied to have a varying degree of flow detailing, e.g., from simple capacitive probes up to capacitive flow imaging and tomography. This article reviews the different capacitive sensors applied to multiphase flow measurement and imaging. Operating principles, sensor geometries, and capacitive measuring circuits are presented and discussed along with advantages and disadvantages, focusing on flow applications and possible flow parameters yielded from sensors. Some new trends in capacitive flow sensors are also presented.

Three-phase gas–liquid–liquid flows are very common in petroleum extraction, production, and transport. In this work a dual-modality measuring technique is introduced which may be well applied for three-phase flow visualization. The measuring principle is based on simultaneous excitation with two distinct frequencies to interrogate each crossing point of a mesh sensor, which in turn are linked to conductive and capacitive parts of fluid impedance. The developed system can operate eight transmitter and eight receiver electrodes at a frame repetition frequency up to 781 Hz. The system has been evaluated by measuring reference components. The overall measurement uncertainty was 8.4%, which considering the fast repetition frequency of measurements is suitable for flow investigation. Furthermore, a model-based method to fuse the data from the dual-modality wire-mesh sensor and to obtain individual phase fraction of gas–oil–water flow is introduced. Here a parametrized model is fitted to the measured conductivity and permittivity distributions enabling one to obtain phase fraction from measured data. The method has been applied and tested to the acquired data from a mesh sensor in static and dynamic three-phase mixtures of gas, oil, and water. Fused images and quantitative values show good agreement with reference values. The newly developed dual-modality wire-mesh sensor has the potential to investigate three-phase flows to a good degree of detail, being a valuable tool to investigate such flows.

From wells to refining plants and distribution networks, operations in the oil and gas industry involve the transport of multiphase mixtures through long pipelines. One of the most representative patterns is the so-called slug flow, which is characterized by the intermittent passage of gaseous and liquid structures. The monitoring of slug flows allows for proper control and safety in many operations in the oil and gas industry. In recent years, Distributed Acoustic Sensing (DAS) has emerged as a promising technology for industrial use and is applied here for flow monitoring. Namely, this paper introduces the use of DAS for the measurement of slug flow. A number of flow configurations under controlled conditions are investigated. Measurements were carried out in a 9 m-horizontal pipeline section in a flow-loop laboratory. Fiber-optics were helically wrapped along the outer surface of the pipeline to promote higher sensitivity at a higher spatial resolution space. The velocity of the gas-phase given by the elongated bubbles velocity is estimated from DAS data through radial integration in k-f space and distributed cross-correlation methods. Using measurements from a commercial conductance-based sensor as a reference, the results showed RMSD% of 8.34% and 12.18%, respectively. The cross-correlation method has the clear advantage of being able to yield (spatial) distributed data.

We introduce a flow meter to monitor the flow rate of individual phases in gas-liquid flows. The meter combines pressure data from a Venturi tube and void fraction data from a twin-plane capacitive sensor. By the twin geometry of the capacitive sensor it is possible cross-correlate the two signals to estimate gas flow rate. A simple algebraic approach, which considers no-slip condition between phases and disregards influence of gas phase, combines pressure fluctuations of the Venturi meter with the measured phase fraction to estimate liquid flow rate. The proposed meter has been tested in horizontal air-water flow loops, 1-inch and 2-inches internal pipe diameter, in permanent and transient regimes. Calculated values were compared to reference measurements. The proposed meter performs well determining liquid flow rate, independent of the flow pattern, in the whole measured range with some more discrepancies at lower values of liquid flow rate. Gas flow rate presented good agreement with reference measures whereas here mainly slug flow pattern has been investigated. RMSD% of 6.4% for liquid and 15.6% for gas are found, being satisfactory for many applications, considering the fact the introduced flow rate meter operates without the need for any adjustment based on reference measurements or previous knowledge/assumption of the gas/vapor quality parameter, as has been usual for other similar recent developments.