M.J. Da Silva

Capacitance wire-mesh sensor for fast measurement of phase fraction distributions

We introduce a new wire-mesh sensor based on capacitance (permittivity) measurements. The sensor can be used to measure transient phase fraction distributions in a flow cross-section, such as in a pipe or other vessel, and is able to discriminate fluids having different relative permittivity (dielectric constant) values in a multiphase flow. We designed and manufactured a prototype sensor which comprises two planes of 16 wires each. The wires are evenly distributed across the measuring cross-section, and measurement is performed at the wire crossings. Time resolution of the prototype sensor is 625 frames per second. Sensor and measuring electronics were evaluated showing good stability and accuracy in the capacitance measurement. The wire-mesh sensor was tested in a silicone oil/water two-phase bubbly flow.

Design of an optical tomograph for the investigation of single- and two-phase pipe flows

We describe a fast optical tomography sensor which has been designed for the investigation of single- and two-phase flows in smaller flow cross-sections, such as pipes and bubble columns. It enables image acquisition at frame rates of up to 4.5 kHz at roughly 2 mm image resolution. The sensor works similar to a conventional CT of the fourth generation with 256 light emitters and 32 light receivers arranged about the objects cross-section. The light emitters are sequentially flashed while the light receiver intensities are recorded synchronously. A primary area of application is single-phase flows with dye tracers. Another potential application is the investigation of bubbly two-phase flows at low gas fractions. Principle tests have been made for both problems.

Comparison between wire mesh sensor and gamma densitometry void measurements in two-phase flows

Wire mesh sensors (WMS) are fast imaging instruments that are used for gas–liquid and liquid–liquid two-phase flow measurements and experimental investigations. Experimental tests were conducted at Helmholtz-Zentrum Dresden-Rossendorf to test both the capacitance and conductance WMS against a gamma densitometer (GD). A small gas–liquid test facility was utilized. This consisted of a vertical round pipe approximately 1 m in length, and 50 mm internal diameter. A 16 × 16 WMS was used with high spatial and temporal resolutions. Air–deionized water was the two-phase mixture. The gas superficial velocity was varied between 0.05 m s−1 and 1.4 m s−1 at two liquid velocities of 0.2 and 0.7 m s−1. The GD consisted of a collimated source and a collimated detector. The GD was placed on a moving platform close to the plane of wires of the sensor, in order to align it accurately using a counter mechanism, with each of the wires of the WMS, and the platform could scan the full section of the pipe. The WMS was operated as a conductivity WMS for a half-plane with eight wires and as a capacitance WMS for the other half. For the cross-sectional void (time and space averaged), along each wire, there was good agreement between WMS and the GD chordal void fraction near the centre of the pipe.

A Novel Needle Probe Based on High-Speed Complex Permittivity Measurements for Investigation of Dynamic Fluid Flows

For the investigation of multiphase or multicomponent flows, which are of interest, for instance, in oil extraction and processing or in chemical engineering, there are only few suitable measuring techniques. For this reason, we have developed a high-speed complex permittivity needle probe. Such probes are able to distinguish the different phases or components of a flow by measuring the complex value of the electrical permittivity at a high data rate (up to 20 000 samples/s). The performance of the system, as well as its ability to differentiate organic substances, has been analyzed. A time-resolved experiment in an oil-water-gas flow, as well as a two-substance mixing experiment in a stirred tank, is presented.

Phase fraction distribution measurement of oil-water flow using a capacitance wire-mesh sensor

In this paper, a novel wire-mesh sensor based on permittivity (capacitance) measurements is applied to generate images of the phase fraction distribution and investigate the flow of viscous oil and water in a horizontal pipe. Phase fraction values were calculated from the raw data delivered by the wire-mesh sensor using different mixture permittivity models. Furthermore, these data were validated against quick-closing valve measurements. Investigated flow patterns were dispersion of oil in water (Do/w) and dispersion of oil in water and water in oil (Do/w&w/o). The Maxwell–Garnett mixing model is better suited for Dw/o and the logarithmic model for Do/w&w/o flow pattern. Images of the time-averaged cross-sectional oil fraction distribution along with axial slice images were used to visualize and disclose some details of the flow.

Capacitance Planar Array Sensor for Fast Multiphase Flow Imaging

In this paper, we introduce a novel planar array sensor based on electrical capacitance (permittivity) measurements to visualize flows of multiphase mixtures along the surface of objects. The prototype sensor is formed by 32 times 32 interdigital sensing structures. It can be mounted onto the wall of pipes or vessels and thus has minimal influence on the flow. An associated electronics measures the capacitance of the fluid at each sensing structure in a multiplexed manner at high sampling rate. This way, images of the fluid distribution are produced. The electronics is able to generate up to 15 000 images/s. Results of system evaluation and results of two exemplary flow experiments are presented and discussed.

Dual-modality wire-mesh sensor for the visualization of three-phase flows

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.

Enhanced Local Void and Temperature Measurements for Highly Transient Multiphase Flows

We introduce a novel combined temperature and conductivity needle probe measuring system for local void fraction measurements in two-phase flow experiments. The system is able to deal with direct sheathed micro thermocouples as well as open thermocouples. It consists of a thermo needle probe connected to a special electronic circuit using AC measuring technique for the conductivity measurements and a high gain instrumentation amplifier with very high common mode rejection for the amplification of the Seebeck voltage generated by the micro thermocouple. After system build up and calibration, the system has been tested in different experiments. In a dropping experiment the time constant of the temperature measurement of the needle probe system was determined as 3.6 ms. Additionally, steam-water experiments have been carried out to demonstrate the system performance

Fluid turbulence monitoring by means of FBG mesh

Single-phase flow turbulence monitoring by means of the utilization of an optical fiber Bragg grating (FBG) mesh is presented in this work. Present device is immune to electromagnetic interferences and independent of the fluid dielectric constant or pipe transparency. The kinetic energy of the flow produces a wavelength shift associated to the strain, which is the basis of the detection mechanism. Spatial resolution inside the pipes is obtained by arranging the FBGs in a 8×8 matrix shape with a total of 16 FBGs multiplexed within the same single mode fiber (SMF), which reduces considerably the size and connections of the device. The results show differentiated patterns as a function of time and flow speed, which can be directly associated to velocity distributions inside the tube. Different regions can be differentiated as a function of the force induced strain: core, annular and wall regions.

Development of a high-speed capacitive surface sensor for fluid distribution imaging

Experimental investigation of multiphase flows plays an important role in many research and industrial application areas, such as chemical and petroleum industry and nuclear engineering. We introduce a novel surface sensor based on electrical capacitance (permittivity) measurements to visualize flows along the surface of objects. The prototype sensor is formed by a 32times32 pixel interdigital sensing structure and can be mounted onto the wall of pipes or vessels and thus has a minimal influence on the flow. An associated electronics measures the capacitance of the fluid on each sensing structure in a multiplexed manner. This way, images of the fluid distribution can be achieved directly without the need for any reconstruction procedure. Images at up to 10,000 frames per second can be obtained. The system was evaluated showing good reproducibility and accuracy. Initial results of a two-component mixing experiment are presented.