Eduardo Nunes dos Santos

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.

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.

Capacitive Multielectrode Direct-Imaging Sensor for the Visualization of Two-Phase Flows

In this paper, a novel capacitive array–sensor to visualize two-phase flow by measuring liquid holdup in pipe cross-section is introduced. The measuring principle is based on the difference between electrical permittivity of the phases. The sensor consists of two copper rings being an emitter and one receiver ring. The receiver ring is divided into segments, which are individually interrogated by the measuring electronics in a fast manner. In this way, flow images are directly generated from acquired signals of electrodes in a way that it visually represents the investigated flow, avoiding the use of image reconstruction algorithms as usual in tomographic techniques. The sensor is fabricated in a flexible printed-circuit board, which is flush-mounted in the inner pipe wall. A measuring electronics is responsible to detect the capacitance changes in the electrodes. The introduced sensor along with the associated electronics has been tested in static and dynamic two-phase flow, both horizontally and vertically. Direct images were generated in these different situations, showing satisfactory results when compared with a reference wire-mesh sensor.

Bubble shape estimation in gas-liquid slug flow using wire-mesh sensor and advanced data processing

Wire-mesh sensors produce three-dimensional data of void fraction distribution at high resolution thus being an appropriate tool to investigate two-phase gas-liquid flows. Slug flow is typically found in petroleum production lines. This type of flow is characterized by the intermittent occurrence of gas bubbles and liquid slugs along the pipe. An important issue of these flows is the existence of a variety of regimes, depending on the flow rates of gas and liquid. The quantitative and qualitative information about shapes of the bubble nose and tail allows to study and to model the flow characteristics in order to increase safety and profit margins in operation of pipelines. In this paper we investigate two methods to estimate typical bubble shape of gas-liquid slug flow, which are based on ensemble mean and median approaches, for a set of identified bubbles in a given experiment. Results show that both approaches produce similar estimations, however since median is a type of robust estimator, contours of bubbles are better defined. Three-dimensional images of typical bubbles, for five different operational conditions, are generated and reveal some details about bubble shape.

Optical fiber Bragg grating mesh for multiphase flow sensing

This work introduces a new approach to characterize the multiphase flow by means of the utilization of optical fiber Bragg gratings. Here, the force applied by the air/liquid flow on the fiber gratings is the underlying mechanism of these sensors. Flow images are constructed from the response of a 8x8 mesh of sensors, with a total of 16 different FBGs multiplexed in wavelength. The data from each sensor has been processed in order to obtain a 2D plot of the air/liquid phase as well as a 3D plot of the air bubbles inside the tube for each time interval.

Capacitive direct-imaging sensor for two-phase flow visualization

This paper introduces a direct-imaging sensor based on multiple capacitance (permittivity) measurements. The sensor is fabricated in a flexible printed-circuit board (PCB) technology and comprises a driving ring electrode and a number of detecting electrodes flush-mounted into pipe peripheral. Direct images are generated representing the cross-sectional distribution of the phases in a two-phase flow. A prototype sensor was built and the system was tested in three different ways. Firstly in an air-water stratified mixture, secondly in an air-oil stratified mixture and then in a dynamic two-phase flow. Results were compared with a reference sensor showing good agreement.

Two-Phase Flow Imaging by means of an 8x8 Optical Fiber Bragg Grating Grid

Two-phase flows characterization by means of the utilization of an optical fiber Bragg grating (FBG) grid is presented. The force applied by the air/liquid flow on the FBGs is the underlying mechanism of this sensor.

Images Analysis of Horizontal Two-Phase Slug Flows

Multi-phase flow measurements are very common in industrial applications especially of the oil and gas industry. In order to study such pattern one can apply many different techniques such as capacitive probes, X-ray and gamma ray tomography, ultrasound transducers, wire-mesh sensors and high speed videometry. This article describes experimental study of water-air slug in horizontal pipes through non-intrusive image analysis technique. A flow test section comprising of a pipe of 26 mm internal diameter and 9 m long was employed to generate slug flows under controlled conditions. The behavior of the flow was studied using gas and liquid velocities between 0.3 m/s and 2 m/s with 6000 images (500×232 pixels) for each case. The algorithm comprises the automatic analysis of a sequence of frames in MatLab to measure flow characteristics such as Taylor bubble velocity and frequency applying morphological treatment. Finally, the parameters measured through the high speed videometry were compared with theoretical predictions showing that such method can be used to validate other types of sensors in experimental conditions.Copyright