Capacitance Wire Mesh Sensor Research Articles

Numerical analysis and structural optimization of a DLC coated capacitance wire-mesh sensor for measuring liquid metal-gas two-phase distribution

The detection of liquid metal-gas two-phase distribution in lead-cooled fast reactor once steam generator tube rupture occurs is vital to the security assessment of the reactor core. In this paper, considering the high temperature, corrosiveness and high conductivity of the liquid metal, a diamond-like carbon coated capacitance wire-mesh sensor is proposed to detect the two-phase distribution in liquid metal. Based on the software COMSOL, a numerical model is firstly established that is quantificationally verified by experiment to study and optimize the performance of the coated WMS. The measurement accuracy of the sensor is investigated by ranging the AC excitation frequency and structure parameters of the system. The results show that the liquid metal has blocking effect on the small bubbles and the sensor has great measurement accuracy when the transverse and vertical interval are 2 mm while the exitation frequecy, coat thickness and electrode diameter show little effect. This research could guide the measurement in liquid metal-gas two-phase flow.

Comparative Analysis of Riser Base and Flowline Gas Injection on Vertical Gas-Liquid Two-Phase Flow

Gas injection is a frequently used method for artificial lift and flow regime rectification in offshore production and transportation flowlines. The flow behaviour in such flowlines is complex and a better understanding of flow characteristics, such as flow patterns, void fraction/hold up distributions and pressure gradient is always required for efficient and optimal design of downstream handling facilities. Injection method and location have been shown to strongly affect downstream fluid behaviour that can have important implications for pumping and downstream facility design, especially if the development length between pipeline and downstream facility is less than L/D = 50 as reported by many investigators. In this article, we provide the results of an experimental investigation into the effects of the gas injection position on the characteristics of the downstream upwards vertical gas flow using a vertical riser with an internal diameter of 52 mm and a length of 10.5 m. A horizontal 40-m-long section connected at the bottom provides options for riser base or horizontal flow line injection of gas. The flowline gas injection is performed 40 m upstream of the riser base. A 16 by 16 capacitance wire mesh sensor and a gamma densitometer were used to measure the gas-liquid phase cross-sectional distribution at the riser top. A detailed analysis of the flow characteristics is carried out based on the measurements. These include flow regimes, cross-sectional liquid holdup distributions and peaking patterns as well as analysis of the time series data. Our findings show that flow behaviours differences due to different gas injection locations were persisting after a development length of 180D in the riser. More specifically, core-peaking liquid holdup occurred at the lower gas injection rates through the flowline, while wall-peaking holdup profiles were established at the same flow conditions for riser base injection. Wall peaking was associated with dispersed bubbly flows and hence non-pulsating as against core-peaking was associated with Taylor bubbles and slug flows. Furthermore, it was found that the riser base injection generally produced lower holdups. It was noted that the circumferential injector used at the riser base promoted high void fraction and hence low liquid holdups. Due to the bubbly flow structure, the slip velocity is smaller than for larger cap bubbles and hence the void fraction is higher. The measurements and observations presented in the paper provides valuable knowledge on riser base/flowline gas introduction that can directly feed into the design of downstream facilities such as storage tanks, slug catchers and separators.

Tuning capacitance wire-mesh sensor gains for measurement of conductive fluids

Abstract In this paper, the front-end circuit of a capacitance wire-mesh sensor (WMS) is analyzed in detail and a new methodology to tune its feedback gains is reported. This allows, for the first time, a capacitance WMS to be able to provide linear measurements of multiphase fluids with electrical conductivity greater than 100 𝜇S/cm, which is particularly important for tap water, where the conductivity is typically in between 100 S/cm and 500 𝜇S/cm. Experimental and numerical results show that the selected gains using the proposed methodology contribute to suppress cross-talk and energy losses, which in turn, reduces considerably the deviation of the conductivity measurement and the estimation of derived flow parameters, such as local and average phase fraction.

Identification of Oil-Gas Two Phase Flow in a Vertical Pipe using Advanced Measurement Techniques

The characteristics of flow configuration in pipes are very important in the oil industry due to its role in governing equipment design. In vertical risers, many flow configurations could be observed such as bubbly, slug, churn, and annular flow. In this project, two tomographic techniques have been applied simultaneously to the flow in a vertical riser: the Electrical Capacitance Tomography (ECT) technique and the Capacitance Wire Mesh Sensor (WMS) technique. The employed pipe diameter was 50mm and the superficial studied velocities were 0.06-3.0m/s for gas and 0.06-0.4m/s for oil. Several techniques have been used to analyze the output data of the two tomography techniques such as time series of cross-sectional averaged void fraction, Probability Density Function (PDF), image reconstruction, and liquid hold-up profile. The averaged void fractions were calculated from the output signal of the two measurement techniques and plotted as functions of the superficial velocity of the gas. The flow patterns were identified from the PDF of the averaged void fraction. In addition, it was found that both tomographic techniques are reliable in identifying the flow regimes in pipes.

Pressure drop, void fraction and flow pattern of vertical air–silicone oil flows using differential pressure transducer and advanced instrumentation

New data for pressure drop, void fraction and flow pattern in a vertical riser using air–silicone oil as the system fluid are reported in this work. A differential pressure cell (DP cell) was used to measure the pressure drop. Also, void fraction data were recorded simultaneously by an electrical capacitance tomography (ECT) and wire mesh sensor (WMS). The observed flow patterns are the spherical cap bubble, slug and churn flows. However, only the slug flow without the presence of churn flow is seen within the transition line as predicted by the map. The characteristic probability density function (PDF) derived from void fraction data was used to determine the flow patterns. A comparison between present experimental results and the air–water data reported in the literature was carried out and various levels of agreement were achieved. The PDFs obtained from the DP cell signals for spherical cap bubble and slug flows significantly differ from those derived from the ECT and WMS outputs. Current void fraction and pressure gradient results were compared with the values predicted by ten empirical correlations selected from the literature. Statistical tools such as Mean Square Error (MSE), Root Mean Square Error (RMSE) and Mean Absolute Percentage Error (MAPE) were applied in the comparison. The Greskovich and Cooper correlation gave the least MSE, RMSE and MAPE values of 0.0007908, 0.013 and 3.05%, respectively for slug flow.

Investigating the effect of pressure on a vertical two‐phase upward flow with a high viscosity liquid

AbstractThis article presents void fraction and pressure gradient data for sulfur hexafluoride (SF6) with gas densities of 28 and 45 kg/m3 and oil (with viscosity 35 times that for water) in a 127 mm diameter pipe. The superficial velocities of gas ranged from 0.1 to 3 m/s and those for liquid from 0.1 to 1 m/s, respectively. Measurements of void fraction data were recorded using a capacitance wire mesh sensor (WMS) system, which permits the 3D visualization of the flow patterns. All the data were obtained with a data acquisition frequency of 1,000 Hz. A differential pressure transducer was used to measure the pressure drops along the length of the pipe. The WMS provide time and cross‐sectionally resolved data on void fraction and from an analysis of its output, flow patterns were identified using the characteristic signatures of probability density function (PDF) plot of time series of void fraction. The PDF plots showed the single peak shapes associated with bubbly and churn flows but not the twin‐peaked shape usually seen in slug flows. This confirms previous work in larger diameter pipes but with less viscous liquids. For the bubble and churn flows investigated, the pressure gradient was observed to decrease with an increase in gas superficial velocity. Nevertheless, there was an insignificant observed effect of pressure on void fraction below certain transitional flow rates, the effect however became significant beyond these values. In the present work, wisps appear to be smaller, which might be due to the different fluid properties of the working fluids employed. In addition, wisps are easily revealed as long as there is a transition between churn and annular flows regardless of the pressure. Experimental data on void fraction and pressure gradient are compared against existing data. Reasonably good agreements were observed from the results of the comparison.

Prediction of entrained droplet fraction in co-current annular gas–liquid flow in vertical pipes

The entrained droplet fraction is an important parameter in annular two-phase flow, as its correlations are key inputs in flow simulation codes for the prediction of pressure drop and critical heat flux or dryout. Investigators have stressed the importance of extending the validity range of current correlations so that more conditions are covered. This could be achieved for example by including fluids with higher viscosities, a wider range of operating pressures, and increase in the size of pipes used for experiments (most of the data in the literature are from pipes of 50mm diameter and below). In attempt to improve the latter, experiments were conducted in a 101.6mmgas–liquid flow loop at Cranfield University’s Oil and Gas Engineering Laboratory and data on the fraction of droplets were collected in the annular flow regime by measuring the film velocity, from which the droplet fraction was calculated. Comparison of the film velocity by this method and by a mass balance showed close agreement. A capacitance Wire Mesh Sensor was used for flow visualisation in order to distinguish between annular and churn flow. In order to arrive at an improved correlation, over 1300 data points were gathered from other published works. These include air–water studies where large pipes of up to 127mm in diameter were used. The others were from small-diameter pipes and for refrigerant, steam–water, air–water, and air–glycerine flows. Since in the annular regime, the gas flow entrains liquid droplets into the core, their presence alters the properties of the gas core. Therefore, accurate predictions are pivotal for the energy efficient design and operation of facilities in the petroleum and nuclear power industry. The correlation obtained here showed good agreement with the collected databank.

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.

Capacitance wire mesh imaging of bubbly flows for offshore treatment applications

The impact of ship motion on bubbly flow was emulated using a swell simulator to expose flow structure changes emerging in bubble columns relevant to offshore floating applications. Roll, roll+pitch, yaw, heave and sway were implemented at various frequencies and changes in bubbly flow resulting from the imposed motions were monitored for the first time by means of a dual capacitance wire mesh sensor to measure local gas holdup and velocity. Visualizations of the two-phase flow revealed that roll, roll+pitch, and high-frequency sway were the most impactful in terms of bubble zigzag and swirl, and bubble-clustering and segregation due to vessel dynamic inclinations. As a consequence of these motions, lateral migration of bubbles and their clustering enhanced liquid recirculation and local streamwise gas velocity. Compared to static vertical bubble column, bubbly flow pattern was barely altered by yaw and low-frequency sway except the heave displacements which tended to slowdown the bubble rise.

Hydrodynamics of gas–liquid cocurrent downflow in floating packed beds

An innovative experimental setup combining a robot with six-degree-of-freedom motions (translational: surge, sway, heave, and rotational: roll, pitch, yaw) and an embarked column instrumented with a capacitance wire mesh sensor was built to investigate experimentally the two-phase flow hydrodynamics in porous media within inclined stationary and oscillating packed beds under gas–liquid cocurrent descending flows. The hydrodynamic deviations with respect to the stationary straight column were thoroughly analyzed in terms of bed pressure drop, liquid saturation, regime changeover, and pulse flow properties. Non-tilting oscillations had marginal effects on the packed bed hydrodynamics which remained practically similar to the one prevailing in stationary vertical trickle beds. Conversely, tilting oscillations profoundly influenced the flow regime inside the packed bed as a result of the time-dependent nature of the gravitational and inertial (acceleration/deceleration) forces brought about by the hexapod rotational oscillations which caused important secondary transverse displacements of the fluids in the bed. Using moment analysis of the probability density functions of the registered liquid saturation time series, it was found that due to the periodic gravity-driven stratification, the transition to pulse flow shifted towards higher fluid velocities as the oscillation periods of roll or roll+pitch motions were increased.

Comparison of experimental and Computational Fluid Dynamics (CFD) studies of slug flow in a vertical riser

This paper presents a comparison of the results obtained from experiments and CFD studies of slug flow in a vertical riser. A series of two experimental investigations were carried out on a 6m vertical pipe with a 0.067m internal diameter charged with an air–silicone oil mixture. For the first set of experiments, the riser was initially full of air, and then liquid and gas flows set to liquid and gas superficial velocities=0.05 and 0.344m/s, respectively, electrical capacitance tomography (ECT) and wire mesh sensor (WMS) transducers were employed. In the second one, the riser was initially full of (static) liquid, and then liquid and gas flows set to liquid and gas superficial velocities=0.05 and 0.344m/s, respectively, only ECT was used. A characterisation of the observed slug flow regimes was carried out. This includes the evaluation of the instantaneous distribution of the phases over the pipe cross-section, the Probability Density Function (PDF) of void fraction, time series of cross-sectional void fraction, Power Spectral Density (PSD), structure velocity of the Taylor bubble, lengths of the liquid slug and Taylor bubble and void fractions in the liquid slug and Taylor bubble. The simulation results were validated both qualitatively and quantitatively against experimental data. A reasonably good agreement was observed between the results of the experiment and CFD.

Detailed analysis of phase distributions in a vertical riser using wire mesh sensor (WMS)

This paper looks into the results of an experimental study concerned with the phase distributions of gas–liquid multiphase flows experienced in a vertical riser. Scale experiments were carried out using a mixture of air and silicone oil in a 6m long riser pipe with an internal diameter pipe of 67mm. A series of pipe flow experiments were performed for a range of injected air superficial velocities over the range 0.05–4.73m/s, whilst the liquid superficial velocities ranged from 0.05 to 0.38m/s. Measurements of cross-sectional void fraction and radial time averaged void fraction across a pipe section located 4.92m from the pipe flow injection were obtained using a capacitance wire mesh sensor (WMS). The data were recorded at a frequency of 1000Hz over an interval of 60s. For the range of flow conditions studied, the average void fraction was observed to vary between 0.1 and 0.83. An analysis of the data collected concluded that the observed void fraction was strongly affected by the gas superficial velocity, whereby the higher the gas superficial velocity, the higher was the observed average void fraction. The average void fraction distributions observed were in good agreement with the results obtained by other researchers. The accuracy and performance of void fraction correlations were carried out in terms of percentage error and Root Mean Square (RMS) error. Reasonably symmetric radial void fraction profiles were obtained when the air–silicone oil was fully developed, and the shape of the symmetry profile was strongly dependent on the gas superficial velocity. The data for air/water and air/silicone oil systems showed reasonably good agreement except at gas superficial velocity of 0.05m/s. A comparison of the experimental data was performed against a published model to investigate the flow structure of air–water mixtures in a bubble column. A satisfactory report was observed for radial void fraction profile (mean relative error is within 5.7%) at the higher gas superficial velocities.

Two-Phase Upward Flow in a Slightly Deviated Pipe

This study was undertaken to look at the effect of a slight inclination of pipe on upward flow characteristics especially at 10 deg from vertical position. Air-silicone oil flows in a 67 mm diameter pipe have been investigated using a capacitance wire mesh sensor (WMS) and electrical capacitance tomography (ECT). They provide time and cross-sectionally resolved data on void fraction. Superficial gas and liquid velocities of 0.05–1.9 and 0.05–0.5 were studied. Statistical methods and visual observation methods were used to characterize the fluid flows obtained into different flow patterns. From the output results from the tomography instruments, flow patterns were identified using both the reconstructed images as well as the characteristic signatures of Probability density function (PDF) plots of the time series of cross-sectionally averaged void fraction. Bubbly, cap bubble, slug, and churn flows were observed when the pipe was deviated by 10 deg from vertical pipe for the range of superficial gas velocities considered.

Capacitance wire-mesh sensor applied for the visualization of three-phase gas–liquid–liquid flows

This short communication describes the application of a capacitance wire-mesh sensor for the investigation of a gas–liquid–liquid three-phase flow in a laboratory setup. Experiments with air, silicone oil and water are performed first in static and second in dynamic flow conditions. The capacitance mesh sensor is capable of generating images of the cross-sectional distribution of relative permittivity values, which in turn is an indication to the phases present in the multiphase mixture. Initial tests show that the sensor is a valuable tool to investigate three-phase flows, which are very common in the oil industry.

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.

Comparison between Electrical Capacitance Tomography and Wire Mesh Sensor Output for Air/Silicone Oil Flow in a Vertical Pipe

Two tomographic techniques have been applied simultaneously to the flow of air and silicone oil in 67 mm internal diameter vertical pipe. A twin plane electrical capacitance tomgraphy (ECT) electrode system driven by Tomoflow electronics was positioned below a new capacitance wire mesh sensor (WMS) system. The former used 8 electrodes around the pipe in each plane, the latter employed two arrays of 24 evenly spaced wires stretched over the pipe cross-section. The ECT measurement was triggered from the WMS electronics. High speed videos were also taken simultaneously through the transparent pipe wall. Gas superficial velocities of 0.05−5.5 m/s and liquid superficial velocities of 0−0.7 m/s were studied. These gave bubbly, slug, and churn flow in the pipe. The outputs of the two techniques have been compared at a number of levels. At its most basic, the time averaged cross-sectionally averaged void fractions were compared. They showed excellent agreement. At the next level, the time series of the cross-sect...

Kapazitäts-Gittersensor: Prinzip und AnwendungCapacitance Wire-Mesh Sensor: Principle and Application

Zusammenfassung Gittersensoren ermöglichen räumlich und zeitlich hochaufgelöste Untersuchungen von Mehrphasenströmungen und können für viele strömungsdiagnostische Probleme eingesetzt werden. Dieser Beitrag beschreibt den neu entwickelten Kapazitäts-Gittersensor, welcher auf der Messung der elektrischen Permittivität (Kapazität) basiert. Neben der Beschreibung des Messprinzips und der dazugehörigen Messelektronik sowie Datenanalyse wird auch ein ausgewähltes Anwendungsbeispiel präsentiert. Der Gittersensor wurde bei der Untersuchung einer zweiphasigen Öl-Gas-Rohrströmung eingesetzt, wobei die Strömungsregime visualisiert und einige wichtige quantitative Strömungsparameter aus den gemessenen Rohdaten extrahiert wurden.

Measurement of Dynamic Liquid Distributions in a Fixed Bed Using Electrical Capacitance Tomography and Capacitance Wire-Mesh Sensor

An intricate problem associated with fixed bed operation is liquid maldistribution, which denotes the fact that the liquid does not homogeneously flow through the bed. In a comparative study we evaluated two capacitance imaging methods—capacitance wire-mesh sensor and electrical capacitance tomography (ECT)—with respect to their capability of measuring static and dynamic liquid holdup in a fixed bed. The capacitance wire-mesh sensor as an invasive instrument is able to disclose flow structures at higher spatial resolution and was therefore considered the reference instrument for liquid holdup measurement. We found that both methods predict dynamic liquid holdup in the column in a similar way with only small systematic deviation. The results therefore prove that noninvasive electrical capacitance tomography can reliably measure cross-sectional dynamic liquid holdup in a fixed bed, even with a simple and fast linear back projection reconstruction algorithm.

High-resolution gas–oil two-phase flow visualization with a capacitance wire-mesh sensor

The application of a novel wire-mesh sensor based on electrical capacitance (permittivity) measurements for the investigation of gas–oil two-phase flow in a vertical pipe of 67 mm diameter under industrial operating conditions is reported in this article. The wire-mesh sensor employed can be operated at up to 5000 frames per second acquisition speed and at a spatial resolution of 2.8 mm. By varying the gas and liquid flow rates, different flow patterns, such as bubbly, slug and churn flow, were produced and investigated. From the images of gas void fraction distribution, quantitative flow structure information, such as time series of cross-sectional void fraction, radial void fraction profiles and bubble size distributions, was extracted by special image-processing algorithms.