Marco Jose da Silva

Planar Array Sensor for High-speed Component Distribution Imaging in Fluid Flow Applications

A novel planar array sensor based on electrical conductivity measurements is presented which may be applied to visualize surface fluid distributions. The sensor is manufactured using printed-circuit board fabrication technology and comprises of 64 × 64 interdigital sensing structures. An associated electronics measures the electrical conductivity of the fluid over each individual sensing structure in a multiplexed manner by applying a bipolar excitation voltage and by measuring the electrical current flowing from a driver electrode to a sensing electrode. After interrogating all sensing structures, a two-dimensional image of the conductivity distribution over a surface is obtained which in turn represents fluid distributions over sensors surface. The employed electronics can acquire up to 2500 frames per second thus being able to monitor fast transient phenomena. The system has been evaluated regarding measurement accuracy and depth sensitivity. Furthermore, the application of the sensor in the investigation of two different flow applications is presented.

Experimental investigation of horizontal gas-liquid slug flow by means of wire-mesh sensor

The monitoring and visualization of two-phase flow is of great importance either from technical/practical point of view for process control and supervision or from scientific/theoretical point of view, for the understanding of physical phenomenon. A wire-mesh sensor was applied to experimentally investigate two-phase horizontal pipe flow. Furthermore, some physical flow parameters were extracted based on the raw measured data obtained by the sensor. In this article, first, the work principle of wire-mesh sensors is revised and, second, the methodology of flow parameter extraction is described. A horizontal flow test section comprising of a pipe of 26 mm i.d. 9 m long was employed to generate slug flows under controlled conditions. An 8 × 8 wire-mesh sensor installed at the end of the test section delivers cross-sectional images of void fraction. Based on the raw data, mean void fraction, time series of void fraction and characteristic slug frequency are extracted and analyzed for several experiments with different liquid and gas superficial velocities.

Autonomous sensor particle for parameter tracking in large vessels

A self-powered and neutrally buoyant sensor particle has been developed for the long-term measurement of spatially distributed process parameters in the chemically harsh environments of large vessels. One intended application is the measurement of flow parameters in stirred fermentation biogas reactors. The prototype sensor particle is a robust and neutrally buoyant capsule, which allows free movement with the flow. It contains measurement devices that log the temperature, absolute pressure (immersion depth) and 3D-acceleration data. A careful calibration including an uncertainty analysis has been performed. Furthermore, autonomous operation of the developed prototype was successfully proven in a flow experiment in a stirred reactor model. It showed that the sensor particle is feasible for future application in fermentation reactors and other industrial processes.

Quantitative cross-sectional measurement of solid concentration distribution in slurries using a wire-mesh sensor

Wire-mesh sensors have so far been widely applied in gas–liquid flows where resistance or capacitance distributions are measured and converted into gas or liquid holdup distributions. In this work we report on the qualification of the wire-mesh imaging technique for the measurement of cross-sectional solid concentrations in solid–liquid mixtures. As the dielectric constants of solid particles are different from those of gas, water or oil in the flow, measuring this property can be used as an indication of solid distribution. Experiments were performed in a stirred tank of 100 mm diameter equipped with a capacitance wire-mesh sensor. The wire-mesh sensor was operated at an acquisition speed of 4000 frames per second and has a spatial resolution of 6.25 mm. As solids we used silica sand particles (diameter ~250 μm) which were suspended in water in a volume concentration range of 1% to 35% to form slurries. By varying the stirring speed, different solid concentration distributions were produced and investigated. In order to convert the measured relative permittivity distribution into a solid concentration distribution, an empirical approach was employed.

Single and Multiphase Flow Characterization by Means of an Optical Fiber Bragg Grating Grid

This study introduces a new approach to characterize single and multiphase flow of water and air/water blends, respectively, by means of the utilization of optical fiber Bragg gratings (FBGs) arranged in a grid pattern. Here, the FBGs act as transducers between the force applied on the optical fiber surface by the liquid or air/liquid flow and the strain-induced Bragg wavelength shift. Since the force is proportional to the square of the velocity, associated to the kinetic energy, it is possible to establish a relationship between the Bragg wavelength shift and flow speed for single-phase flow monitoring. When multiphase flows are taken in consideration, a sudden Bragg wavelength shift represents an abrupt change in the force applied onto the fiber, which means a transition between liquid and air. It is hard to localize turbulences in single phase flow or establish the bubble position for multiphase flow from the response of a single FBG. Therefore, the sensors in this study have been arranged forming an 8 × 8 grid, with a total of 16 different FBGs multiplexed in wavelength. FBG grid enables the detection of turbulences or air bubbles within the pipe by means of an adequate aggregation and processing of the response of the FBGs at each crossing point, with a total of 64 crossings (12 crossings are out of the cylindrical shape pipe). Different flow speeds and void conditions with distinct void fractions and flow rates have been studied. The optical fiber sensors performance agreed with that of a wire-mesh system, which is conventionally used as a reference high performance measurement tool for multiphase flow. Results showed the great potential of this technique that reduces in more than a half the costs, complexity and size of actual devices used for the same purpose.

Multiphase flow characterization using optical fiber Bragg gratings

Optical fiber Bragg grating strain sensors are used to characterize the multiphase flow of water and air in a laboratory test bed. The load applied by the fluid flow on the fiber gratings is the underlying mechanism of the sensor and different flow conditions with distinct void fractions and flow rates were investigated. The optical fiber sensors performance was compared against that of a wire-mesh system which is conventionally used as a reference high performance measurement tool for multiphase flow. Results are in good agreement showing the potential of the technique.

Design of a neutrally buoyant self-powered multi-parameter sensor for data logging in flow applications

Experimental acquisition of spatially distributed parameters in large scale vessels and containers is of great interest for investigation and optimization of plants and processes such as stirred tanks, chemical reactors or bioreactors. For the measurement of process parameters in a stirred fermentation biogas reactor we developed the concept of neutrally buoyant self-powered sensor particles. The prototype sensor performs logging of temperature, absolute pressure and 3D-acceleration data and is integrated in a robust capsule which gives a balance between buoyancy and gravitation with respect to the liquid process substrate. In an initial test of the developed prototype its autonomous operation has been successfully proved showing feasibility for future application in a biogas reactor.

Advanced image processing of wire-mesh sensor data for two-phase flow investigation

Two-phase gas-liquid flows, the simultaneous flow of a gas and liquid in a pipe, are commonly found in several industrial activities, among them during the extraction and processing of crude oil. Wire-mesh sensors are flow imaging devices which are able to generate images of phase distribution of two-phase flows within a pipe cross section at high spatial and temporal resolutions. Appropriated image processing algorithms are however necessary in order to extract important flow parameter from raw data. In this paper, we describe a bubble identification algorithm based on three-dimensional image segmentation. Results of bubbles velocity and flow rate measurement based on the development algorithm are validated against reference models showing good agreement.

Development of NIR optical tomography system for the investigation of two-phase flows

Two-phase flows are present in many processes in nature as well as in industrial activities such as exploration, production and transportation of oil and gas. In many cases, flow monitoring determines the efficiency and safety of processes and equipment. Thus, this paper presents a preliminary study about developing an optical tomography system for real-time monitoring of gas-liquid two-phase flows. The system comprises 16 optical sources and 16 optical receivers operating at near-infrared wavelength. Time response of single channels is optimized allowing for fast frame rate measurements up to 1000 frames/s. Initial tests in a two-phase flow loop show promising results.

Neuartige kapazitive Sensoren für die Visualisierung von MehrphasenströmungenNovel Capacitive Sensors for the Visualization of Multi-Phase Flows

Zusammenfassung In diesem Beitrag werden zwei neuartige bildgebende Sensoren zur Untersuchung von Mehrphasenströmungen beschrieben – der kapazitive Gittersensor und der kapazitive Flächensensor. Beide Sensoren basieren auf einer matrixförmigen Anordnung von Messelementen, mit denen die elektrische Kapazität eines umgebenden Fluides sehr schnell abgetastet wird. Dadurch sind diese Sensoren in der Lage, zeitlich und räumlich hochaufgelöste Bilder der Phasenverteilung einer Mehrphasenströmung zu erzeugen. Die Sensoren und die zugehörige Messelektronik werden präsentiert. Darüber hinaus werden ausgewählte Ergebnisse von Strömungsvisualisierungen dargestellt und diskutiert.