Measurement of vertical oil-in-water two-phase flow using dual-modality ERT–EMF system

Oil-in-water two-phase flows are often encountered in the upstream petroleum industry. The measurement of phase flow rates is of particular importance for managing oil production and water disposal and/or water reinjection. The complexity of oil-in-water flow structures creates a challenge to flow measurement. This paper proposes a new method of two-phase flow metering, which is based on the use of dual-modality system and multidimensional data fusion. The Electrical Resistance Tomography system (ERT) is used in combination with a commercial off-the-shelf Electromagnetic Flow meter (EMF) to measure the volumetric flow rate of each constituent phase. The water flow rate is determined from the EMF with an input of the mean oil-fraction measured by the ERT. The dispersed oil-phase flow rate is determined from the mean oil-fraction and the mean oil velocity measured by the ERT cross-correlation velocity profiling. Experiments were carried out on a vertical upward oil-in-water pipe flow, 50 mm inner-diameter test section, at different total liquid flow rates covering the range of 8–16 m³/hr. The oil and water flow rate measurements obtained from the ERT and the EMF are compared to their respective references. The accuracy of these measurements is discussed and the capability of the measurement system is assessed.     

Non-intrusive measurements of shallow water discharge

Waste-water channels or physical hydraulic models often convey shallow water flows with depths around 5 cm. Such free surface flows can in principle be measured using standard measuring flumes or thin-plate weirs, but proper employment of these is often practically impossible, e.g. due to limited space. To avoid this, various flow meters with contact probes (i.e. »area-velocity« probes) are employed instead, but in reality this often results in inaccurate measured values of discharge. This paper presents an effective way to determine discharge of very shallow flow without intruding the flow. Our approach is based on computer aided visualization, namely on the quantification of the field of vectors representing local velocities on the water surface of the flow. In contrast to other studies, this method does not require complex measuring equipment, special lights or special devices for the seeding of particles. Experiments were conducted in 0.5 m and 1.06 m wide rectangular channels, made of glass and concrete, respectively, and they show that this method could be employed both in hydraulic laboratories and in the field. Measurements showed that velocity on the surface of the shallow water flow differs from theoretical average mean flow velocity in the observed cross section, and further that this difference increases with the decrease of water depth. This suggests that the assumption, which states that in shallow water flows the surface velocity is similar enough to the mean flow velocity, is not necessarily correct.     

Flow imaging for multi-component flow measurement

For pseudo-homogeneous flows, measurements of density and mean velocity can give the component mass flow rate of a two-component mixture. However, for accurate measurement of non-homogeneous flow rate, the density and velocity distribution across the cross-section of the pipe must be known. The most practical way of obtaining this information is by using the flow imaging technique.

A recently developed capacitance system gives 60 frames per second images of oil/water flow in a 78 mm pipe. The target spatial resolution is one part in 20 by distance (one in 400 by area). The electrical properties of each imaged boundary are functionally related to the imaged value, so the component ratio of a two-component mixture within a boundary can be measured, although individual particles cannot be imaged. Design data shows how the basic system can be part of a complete system for component mass flow measurement.     

Reliable in-plane velocity measurements with magnetic resonance velocity imaging

Magnetic resonance (MR) imaging is a well-known diagnostic imaging modality. In addition to its high-quality imaging capabilities, hydrogen-based MR can also provide non-invasively the velocity of water-based fluids in all three spatial directions (through-plane and in-plane) in an image. Many previous studies showed that MR velocity imaging can accurately measure the through-plane velocity. The aim of this study was to evaluate how reliable are the in-plane velocity measurements in an image. The axial velocity of water in horizontal tubes (inner diameter: 14.7–26.2 mm) was measured with segmented (fast) and non-segmented (slow) k-space MR velocity imaging using: (a) an imaging slice placed perpendicular to the tube axis with through-plane velocity-encoding; and (b) an imaging slice placed parallel to the tube axis with in-plane velocity-encoding. The two planes intersected along the vertical tube-centerline. The flow rate was accurately quantified (mean error <10%) and the in-plane velocity profiles were not significantly different from the through-plane profiles (mean difference =6%, correlation coefficients >0.98). There was no significant difference between the velocity profiles from the segmented and the non-segmented sequences (mean difference <1%, correlation coefficients >0.95). The results of this study suggest that fast MR velocity imaging can measure the in-plane velocity in an image with reliability.     

Adaptive filtering techniques for velocity estimation of tomographic electric capacitance signals of two-phase gas/oil flows

The development of adaptive real-time flow velocity estimation algorithms for two-phase flows can contribute to monitoring the pipelines of various complex processes, such as energy, chemical, petroleum and nuclear industries. Among the different non-invasive tomography techniques, electrical capacitance tomography (ECT) is gaining increasing attention for its potential use in real-time imaging and characterization of multiphase flow systems. The nature of ECT signals for two-phase flows can significantly degrade the velocity estimation process with cross-correlation approaches. We address the unique challenges of such signals and propose a preprocessing technique to improve the performance and robustness of the velocity estimation algorithm. Two adaptive filters are used to estimate the velocity of a two-phase type flow. A least mean square (LMS) and a fast block LMS (FBLMS) are used to model the time delay between the two signals captured by the twin sensor (ECT). Performance of the proposed technique is assessed by applying it to ECT data obtained from an experimental flow rig. The computed estimates are then compared with the calculated velocity from tracking motion of bubbles captured by a high speed camera monitoring the two phase flow in the pipe. Results show that the proposed technique provides consistent results across various flow patterns, and is advantageous compared to cross-correlation based techniques, specially for chaotic flow conditions. Furthermore, the proposed estimation algorithms can be applied to other electric based tomographic techniques.     

Experimental and numerical research on portable short-throat flume in the field

The use of portable short-throat flume in the field is an emerging technique developed for water discharges measurement of inlet in the field. Based on the principle of critical flow and RNG k–ε three-dimensional turbulence model along with the TruVOF technique, experiments and corresponding simulations were performed for 16 working conditions on the 76 mm width flume with discharges up to 40.01 L/s to determine its hydraulic performance. Hydraulic performance of the flume obtained from simulation analyses were later compared with observed results based on time-averaged flow field, flow pattern, Froude number and velocity distribution. Comparison yielded a solid agreement between results from two methods with relative error below ±10%. Regression models developed for upstream depth versus discharge under different working conditions were satisfying with the relative error of 9.16%, which met the common requirements of flow measurement in irrigation areas. Compared to the long-throat flume, head loss of portable short-throat flume in the field was significantly less. Further, head loss under the free flow condition was less than that under the submerged flow condition of portable short-throat flume with a flat base in the field.     

Effects of flow patterns and salinity on water holdup measurement of oil-water two-phase flow using a conductance method

This research investigates the effects of flow pattern and salinity of oil-water two-phase flow on water holdup measurement using a conductance method. Firstly, vertical upward oil-water two-phase flow experiment is conducted in a 20 mm inner diameter (ID) pipe, in which the salinities of aqueous solutions are set as 151 ppm, 1003 ppm, 2494 ppm and 4991 ppm respectively. Experimental water-cut and mixture velocity are set as 80–100% and 0.0184–0.2576 m/s. In the experiment, three different flow patterns, i.e., dispersed oil-in-water slug flow (D OS/W), dispersed oil-in-water flow (D O/W) and very fine dispersed oil-in-water flow (VFD O/W) are observed and recorded by a high speed camera. Meanwhile, we collect the response of Vertical Multiple Electrode Array (VMEA) conductance sensor excited by a sine voltage signal. The result shows that, for VFD O/W, the water holdup from VMEA sensor shows a satisfied agreement with that of quick closing valve (QCV) method under certain salinities, i.e., 1003 ppm as well as 2494 ppm. For D OS/W flow and D O/W flow characterized by dispersed oil droplets with various sizes, considerable deviations of water holdup between VMEA sensor and QCV method under four kinds of salinity aforementioned are presented. Afterward, according to experimental analysis along with theoretical deviation, it is concluded that the deviation of the measurement system reaches its minimum when reference resistance in the measurement circuit and salinity of the aqueous solution satisfy constraint conditions, and the accuracy of water holdup using the conductance method can be improved through adjusting reference resistance to match the salinity of water phase. Finally, the recurrence plot algorithm is utilized to identify typical flow patterns mentioned above and it shows satisfied results on comprehending the discrepancies among different flow patterns, demonstrating that the recurrence plot algorithm can be effectively applied in flow pattern identification regarding oil-water flows.     

Imaging stratifying liquid–liquid flow by capacitance tomography

Electrical capacitance tomography offers a non-intrusive technique for on-line visualisation of two-phase liquid–liquid flows. It has been applied on a facility which provides metered flows of water and kerosene to a test section at the start of which they pass through a dispersing multi-hole orifice plate. The test section consists of a sudden expansion with an internal diameter of 63 mm inlet and 100 mm outlet and which can be inclined. Beyond this the mixture is separated into the two constituents and returned to their individual tanks. Tomography measurements were made using a PTL-300 electronic system coupled to a 12-electrode sensor which was built in-house. The sensor is fitted on the outside of one of the plastic pipe lengths of the test section. By varying the input oil fractions from 20% to 70%, using mixture velocities of 0.2, 0.3, and 0.4 m/s and positioning the pipe at angles of +6,+3,0, −4 and −7 to the horizontal, different flow patterns were established in the test section. A specially developed calibration method is used in all experiments and tomographic images of the stratifying liquid–liquid flow were obtained. These images show clearly that the spatial distribution in a pipe cross-section is strongly dependent on the mixture velocity and the distance from expansion in the range studied. Concave interfaces were observed in horizontal and downward inclination flow for all cases while convex interfaces were identified only in an upward inclination flow at the high input oil fractions and high mixture velocities. This application illustrates very clearly the capability of the ECT for on-line imaging of liquid–liquid two-phase flows.     

Capacitance sensor for hold-up measurement in high-viscous-oil/conductive-water core-annular flows

Capacitance sensors are widely used in multiphase flows, for example, to estimate the hold-up in a given section of the pipe, taking advantage of the different permittivity values of the two liquids. The estimation is obtained by capacitance measurements between two electrodes, flush mounted on the external surface of the experimental pipe. Usually, capacitance sensors are used to investigate flows with non-conductive fluids, but they have the possibility to work also when, for example, conductive water is used. However, the capacitance technique applied to conductive fluids develops some issues. In this paper, we present a concave electrode sensor system developed for oil/conductive-water flows. A key contribution is to propose a modelization to the problem of capacitive sensing in presence of conductive fluids, based on a new approach to the parasitic couplings outside the measurement section. Thanks to this modelization, we propose a new design method for the working frequency and the electrode measurement head.     

Characterization of gas-liquid two phase flows using dielectric Sensors

Two phase flow regime identification and void fraction measurement is an area of considerable interest because of its wide applications in process industries. The principle involved in dielectric measurement is that the two phase flow regime is characterized by the changes in effective permittivity of the two phase fluid mixture. In the present work, a pair of parallel copper electrodes on the two sides of a glass tube acts as a dielectric sensor. As the void fraction in the glass tube changes, the effective permittivity of the medium changes. This causes a variation in the capacitance value across the electrodes. A standard IC, Oscillator 555 is employed as a tool to generate a rectangular wave. The variation in dielectric constant is analyzed based on the change in time period of the trough (T₀) of the rectangular wave that is recorded online by a data acquisition system. Experiments were performed in a 4.7 mm diameter tube with air-water, air-palmolein oil two phase fluids to study the variation in dielectric constant which is indicated as a change in time period of trough. The effect of conductivity of water on the capacitance variation is examined with water having Total dissolved solids (TDS) which is a measure of movable ions in the range 10-4000 ppm (16 µS/cm–6.3 mS/cm). The novelty in the present work is the determination of changes in capacitance value based on the change in time of trough of the rectangular wave. The technique does not require amplification or a filtering circuit, thereby leading to a precise identification of two phase flow regime.     

Application of GMDH neural network technique to improve measuring precision of a simplified photon attenuation based two-phase flowmeter

Multiphase flowmeters have an important role to play in the industry and any attempts that lead to improvements in this field are of great interest. In the current study, group method of data handling (GMDH) technique was applied in order to increase measuring precision of a simple photon attenuation based two-phase flowmeter that has the ability to estimate the gas volumetric percentage in a two-phase flow without any dependency to flow regime pattern. The simple photon attenuation based system is comprised of a cobalt-60 radioisotope and only one 25.4 mm × 25.4 mm sodium iodide crystal detector. Four extracted features from recorded photon spectrum in sodium iodide crystal detector were used as the inputs of GMDH neural network. Equations related to the combination of the features and the error rate of each approximation is also reported in this paper. Applying the mentioned technique, the gas volumetric percentage in an oil-gas two phase flow was determined with the root mean square error of less than 2.71 without any dependency to the flow pattern. The obtained measuring precision in this study is at least 2.1 times better than reported in previous studies.     

Characterization of slug flows in horizontal piping by signal analysis from a capacitive probe

The slug flow is a common occurrence in gas–liquid piping flows. Usually it is an undesirable flow regime since the existence of long lumps of liquid slug moving at high speed is unfavorable to gas–liquid transportation, so that considerable effort has been devoted to study its hydrodynamic characteristics. In this work, a capacitive probe was used for dynamic measurements in the horizontal air–water slug flows, for several flow rates. The acquired signals were representative of the effective liquid layer thickness near every cross sectional area of the flow, instead of merely the holdup or void fraction in a finite volume of the flow. This was possible because probe had a thin sensing electrode that minimizes the axial length effect on the measurements. Tests were performed in a 34 mm i.d. acrylic pipe, 5 m long; in which slug flows as well as stratified-smooth and stratified-wavy flows were generated. Signal analysis techniques were applied for flow regime identification and toward characterization of these two-phase flows: Power Spectrum Density (PSD) from Fourier Transform and Probability Density Function (PDF) from Statistical Analysis. Therefore, PSD and PDF graphs were taken as signatures of each flow under test and a correlation was calculated for each PSD and PDF set of data, which showed to be a robust parameter for correct flow regime identification.     

Pattern recognition and signal processing of ultrasonic echo signal on two-phase flow

This paper presents a novel measurement method using ultrasonic echo signals on the flow of air–water mixtures. This method has the capability of measuring an instantaneous echo intensity profile along an ultrasonic beam, so it is expected to apply to pattern recognition of two-phase flow. Additionally, this method has an advantage compared with conventional techniques because of the clump-on type. The principle of the flow pattern recognition is based on the delay time and strength of the pulse echo. In this paper, first of all, the transmission of ultrasound through solid plates, which are made of plexiglass and carbon steel, has been investigated and the effective incidence angles for these materials were found. Then, echo signals reflected off a boundary between water and air in a vertical pipe, having a diameter of 50 mm, were obtained using an ultrasound system, and the effects estimated of a two-phase pattern, from bubbly to slug flow, on the signals. In addition, water flows down the inner surface of a pipe as annular flow, and the echo signals then also investigated.     

Experimental assessment on the performance of hot wire anemometry in and around a permeable medium by comparison with Particle Image Velocimetry

The air flow through a test section partially obstructed by a permeable array of wires was measured simultaneously by Hot Wire Anemometry (HWA) and Particle Image Velocimetry. The objective of the study was the assessment of the suitability of HWA for the measurement of flow velocities amid and adjacent to groups of small obstacles. In the present case the obstacles are set in a regular array configuring a highly permeable structure. The probe was placed at three characteristic positions: in the free flow close to the wire array, inside the permeable medium, and at the interface between the permeable structure and the free flow. The measurements were performed with the hot wire operating under natural convection and mixed convection heat transfer, and operating the hot wire at different overheat ratios. Natural convection plumes extending over several permeable volume elements were detected when the hot wire was under natural convection, in some cases reaching velocities up to 60 mm/s downstream from the hot wire position. For low velocity flows, natural convection can be regarded as a flow velocity offset, which becomes negligible at local velocities higher than 0.03 m/s. For higher velocities, in the mixed convection regime, the intrusivity of the HWA probe becomes relevant. Furthermore, the flow in the test section used in the study presents a linear instability that produces velocity fluctuations. Availing ourselves of this phenomenon we verified the dynamic response of the HWA at the lowest velocity where the flow shows periodic fluctuations; for a local mean velocity of (0.131 ± 0.012) m/s the HWA showed a satisfactory dynamic response up to 20 Hz.     

Spray characterization in air-assist atomizers using flow-induced acoustic vibrations and multivariate analysis

This feasibility study investigated a new non-intrusive approach employing acoustic chemometrics. The method includes acoustic/vibration data recording obtained utilizing two clamp-on piezoelectric accelerometers and two electret condensers-type microphones mounted on an arc. Principal Component Analysis (PCA) classification models were based on the acoustic FFT spectra from four sensors. The non-dimensional number (X) values correspond to the different breakup regimes comprising a range of air and liquid (water) flow rates in this air-assisted atomizer (one-analyte system). PCA classification model discerns the clusters belonging to similar non-dimensional number (X) values with the maximum variance in the first principal component (PC1) direction for both sensors combined. This study also assesses the utility of the acoustic chemometrics approach for predicting the flow parameter, such as Sauter mean diameter (SMD) based on the Partial Least Squares-Regression (PLS-R). The PLS-R prediction models work best for the 550 mm location with a low root mean square error of prediction (RMSEP) value of 5.443 and a high Pearson correlation coefficient (R²) value of 0.856 when validated using 50% independent data (test set validation). The comparison between the two sensor types demonstrated superior prediction performance for accelerometers for all the prediction models.     

A novel tomographic sensing system for high electrically conductive multiphase flow measurement

Electrical resistance tomography (ERT) has been widely applied in order to extract flow information from various multiphase flows, e.g. the concentration and velocity distributions of the gas phase in gas–water two phase flows. However, the quality of measurement may become very poor from a multiphase flow whose continuous phase has a considerably high electrical conductivity, e.g. seawater (5.0 S/m), using a conventional current-injected ERT system. It is known that a large current excitation is necessary in order to enhance the measurement sensitivity. In practice, it will be very challenging to build a current source with a large amplitude (more than 75 mA) and a high output impedance at a high excitation frequency. This paper presents an implementation of an ERT system with a voltage source and current sensing to overcome the limits of the current source. The amplitude of the current output can reach more than 300 mA. A logarithmic amplifier is used to compress the signal’s dynamic ranges from 18.32 dB to 1.66 dB. The structure and features of this system are presented in this paper and the performances of key circuits are reported. Finally the experimental results from a highly conductive flow (1.06 S/m) are analysed and compared with the measurements obtained from a low conductive flow.     

Validation of magnetic resonance velocimetry for mean velocity measurements of turbulent flows in a circular pipe

Magnetic resonance velocimetry (MRV) is a versatile flow visualization technique that has been utilized for medical applications. Recently, MRV has been used to visualize engineering flows, but most engineers are still unfamiliar with the technique. In this paper, we introduce the basic principles and experimental configurations of MRV in detail and evaluate the accuracy of MRV applied to measure the mean velocity fields of turbulent flows in a circular pipe. A Philips Achieva 3.0 T Tx MRI scanner is used to provide a magnetic field and acquire resonance signals for flow visualization. Fully developed turbulent flows with Reynolds numbers of 6800, 9900 and 19400 were measured, and the axial mean velocity vectors were obtained with a spatial resolution of 0.5 mm for the three directions. Results show that the mean velocity profiles are in good agreement with reference data sets when properly scaled in both the inner and outer layers.

     

Measurement of velocity profiles in multiphase flow using a multi-electrode electromagnetic flow meter

This paper describes an electromagnetic flow meter for velocity profile measurement in single phase and multiphase flows with non-uniform axial velocity profiles. A Helmholtz coil is used to produce a near-uniform magnetic field orthogonal to both the flow direction and the plane of an electrode array mounted on the internal surface of a non-conducting pipe wall. Induced voltages acquired from the electrode array are related to the flow velocity distribution via variables known as ‘weight values’ which are calculated using finite element software. Matrix inversion is used to calculate the velocity distribution in the flow cross section from the induced voltages measured at the electrode array. This paper presents simulations and experimental results including, firstly the effects of the velocity profile on the electrical potential distribution, secondly the induced voltage distribution at the electrode pair locations, and thirdly the reconstructed velocity profile calculated using the weight values and the matrix inversion method mentioned above. The flow pipe cross-section is divided into a number of pixels and, in the simulations, the mean flow velocity in each of the pixels in single phase flow is calculated from the measured induced voltages. Reference velocity profiles that have been investigated in the simulations include a uniform velocity profile and a linear velocity profile. The results show good agreement between the reconstructed and reference velocity profiles. Experimental results are also presented for the reconstructed velocity profile of the continuous water phase in an inclined solids-in-water multiphase flow for which the axial water velocity distribution is highly non-uniform. The results presented in this paper are most relevant to flows in which variations in the axial flow velocity occur principally in a single direction.     

Application of ultrasonic multi-wave method for two-phase bubbly and slug flows

This paper proposes a measurement technique for two-phase bubbly and slug flows using ultrasound. In order to obtain both liquid and gas velocity distributions simultaneously, a new technique for separating liquid and gas velocity data is developed. The technique employs a unique ultrasonic transducer referred to as multi-wave transducer (TDX). The multi-wave TDX consists of two kinds of ultrasonic piezoelectric elements which have different resonant frequencies. The central element of 3 mm diameter has a basic frequency of 8 MHz and the outer element has a basic frequency of 2 MHz. The multi-wave TDX can emit the two ultrasonic frequencies independently. In our previous investigations, both elements were connected with two ultrasonic velocity profile (UVP) monitors to measure liquid and bubble velocity distributions. However, the technique was limited to the measurement of bubbly flows at low void-fraction. Furthermore, it was impossible to synchronize the instantaneous velocities of liquid and bubbles because of the facility limitation. In order to overcome these disadvantages, cross-correlation method is employed for the measurements in this study. In order to apply the technique to flow measurements, ultrasound pressure fields are measured. As a result, it is found that the TDX must be set 20 mm away from the test section. The technique is applied to measuring bubbly and slug flows. By the combination of 2 and 8 MHz ultrasonic echo signals, the echo signals are distinguished between reflected from particles and bubbles. Compared with the results of obtaining with the multi-wave method and a high-speed camera, it is confirmed that the technique can separate the information of liquid and gas phases at a sampling rate of 1000 Hz.