Measurement Of Two-phase Flow Parameters Research Articles

An Image Construction Based on the VTLF Fusion Technique for Oil–Water Two-Phase Flow of Noncontact Electrical Impedance Tomography

Electrical tomography (ET) has attracted extensive attention in the petroleum multiphase flow field due to its advantages of nonintrusion, nonradiation, and simple equipment structure. Some contactless impedance imaging methods, such as capacitively coupled electrical resistance tomography (CCERT) and phase-based dielectric spectroscopy tomography, or displacement current phase tomography (DCPT), have been studied for the parameter measurement of two-phase flow. The mentioned research mainly focuses on the separate imaging by real part, imaginary part, or phase information of the voltage/current. However, the distribution change of media in the region of interest (RoI), especially the presence of high permittivity and conductivity materials, involves the distribution change of conductivity, permittivity, and loss factor. Developing a proper image fusion technique based on the three components can provide more comprehensive image information for tomographic imaging. This article proposed an improved logic filter image fusion algorithm based on a variable threshold (VTLF), and a noncontact electrical impedance tomography (NEIT) system for imaging water–oil two-phase flow is carried out. Image reconstruction is implemented by the VTLF image fusion algorithm under different media distributions, conductivities, and excitation frequencies, and the image fusion algorithms of a weighted average (WA) and logic filter (LF) are also used for comparison. The simulation results show that the reconstructed images by the proposed fusion method of VTLF had the lowest artifacts and the highest correlation coefficient (above 0.7) compared with other methods. Also, in the experiment, the VTLF also got the best performance, so it is effective to improve the reconstruction accuracy.

Phase-isolation of upward oil–water flow using centrifugal method

Phase-isolation is a process of isolating each phase to a respective space within the transmission pipe by applying various kinds of lateral forces to the two-phase mixture. Once the phase-isolation is completed, two phases will flow concurrently and have a substantially clear interface between them which will greatly benefit for the measurement of two-phase flow parameters and for the separation of two-phase flow. In this study, a simple and optimized style of centrifugal device was employed for producing a swirling motion to the oil–water flow in a vertical upward pipe. The phase-isolation characteristics which influenced by various flow parameters (density, viscosity, oil diameter, inlet oil cut (λo) and velocity etc.) was simulated. Experiments were carried out in an oil–water two-phase flow loop to verify the simulation results and the encouraging agreement is obtained. It is showed that oil–water two-phase flow can be effectively isolated in the vertical upward pipe as predicted in the ranges of oil superficial velocity below 0.2m/s and water superficial velocity between 0.4 and 1.5m/s and the D O/W flow pattern performs the best phase-isolation effect. When λo≤10%, the cross section oil holdup after phase-isolation (Po) measured by visual observation is approximately equal to λo and the relative error is within the accepted error range of 0.25–8.5%.

Experiments on the Effects of a Spacer Grid in Air-Water Two-Phase Flow

Understanding the effects of spacer grids on the coolant flow through a nuclear reactor core is required for best-estimate design and analysis of the plant. The impact of a spacer grid on two-phase flows is of particular importance because the geometric effects of the grid can alter the two-phase flow structure and, consequently, the mass, momentum, and energy transfer characteristics. Therefore, a scaled separate-effects test facility is constructed to investigate the effects of a spacer grid on the hydrodynamics of air-water two-phase flow through a rod bundle. The test facility is scaled to maintain hydrodynamic and geometric similarity to single- and two-phase flows in a conventional pressurized water reactor and to facilitate detailed local measurements of two-phase flow parameters around the simulant fuel rods with a four-sensor conductivity probe. This paper presents measurements of local time-averaged two-phase flow parameters acquired upstream and downstream of the spacer grid with the conductivity probe in a representative subchannel of a 1×3 rod bundle for eight flow conditions. Characteristic features of the development of the two-phase flow parameters along the test section are discussed.

An accurate wall temperature measurement using infrared thermometry with enhanced two-phase flow visualization in a convective boiling system

This paper presents an experimental strategy to achieve the accurate wall temperature measurement using infrared (IR) thermometry with the enhanced flow visualization. Our particular interest is focused on the measurement of two-phase flow parameters in a convective boiling system which involves a large heated area. For the present application, the important issues such as the design of test section and material selection were discussed along with our decision-making process. Then, the IR-based temperature tracking algorithm was established based on the multi-layer heater wall design proposed. To apply this algorithm, however, the optical properties of materials must be identified first. Thus, the optical features of selected materials, e.g., soda-lime glass and indium-tin-oxide (ITO) were investigated and the measured values were validated through experiments.The wall temperature tracking algorithm on the proposed heater wall design was validated both for steady-state and transient conditions. Also, such algorithm was proved to be applicable for the heat flux measurement. Finally, the feasibility of the present approach was demonstrated through a subcooled flow boiling experiment. The results showed that both the hydrodynamic motions of bubble and the corresponding wall temperature can be captured with high fidelity using the measurement strategy presented, from which the interrelation between the sliding vapor bubbles and the wall heat transfer were discussed.

Two-phase flow measurements at high void fraction by a Venturi meter

An experimental investigation of a vertical upward annular two-phase flow across a Venturi flow meter has been performed for the measurement of two-phase flow parameters with reference to the experimental simulation of nuclear accidents, as LOCA, characterized by very high void fraction. The pressure drops between the inlet and throat section and between inlet and outlet (irreversible pressure losses) have been measured and analyzed. The Venturi flow meter is characterized by an inlet diameter of 80 mm and a throat diameter of 40 mm (β = 0.5), with equal convergent and divergent angles (θ = 21°). The instrument has been tested in a test section having an internal diameter (Di) of 80 mm and a total length (L) of about 4 m, with air–water two-phase flow at ambient pressure. The air superficial velocity ranged between 14 and 18 m/s while the water superficial velocity ranged between 0.0008 and 0.005 m/s, so that the flow pattern was annular and the corresponding flow quality ranged between 0.78 and 0.96. The dependence of the pressure drops on the phases velocities has been analyzed and modeled as a function of the superficial velocities of the phases, and the mass flow rate of the two phases has been derived from the present test data when the annular flow pattern does not change in a significant way. The flow quality can be evaluated with an accuracy of 5% and the mass flow rate of air and water can be estimated with an accuracy better than 2% and 30% respectively.

Electrical Capacitance Probe Characterization in Vertical Annular Two-Phase Flow

The paper presents the experimental analysis and the characterization of an electrical capacitance probe (ECP) that has been developed at the SIET Italian Company, for the measurement of two-phase flow parameters during the experimental simulation of nuclear accidents, as LOCA. The ECP is used to investigate a vertical air/water flow, characterized by void fraction higher than 95%, with mass flow rates ranging from 0.094 to 0.15 kg/s for air and from 0.002 to 0.021 kg/s for water, corresponding to an annular flow pattern. From the ECP signals, the electrode shape functions (i.e., the signals as a function of electrode distances) in single- and two-phase flows are obtained. The dependence of the signal on the void fraction is derived and the liquid film thickness and the phase’s velocity are evaluated by means of rather simple models. The experimental analysis allows one to characterize the ECP, showing the advantages and the drawbacks of this technique for the two-phase flow characterization at high void fraction.

Suitability of an MRMCE (multi-resolution minimum cross entropy) algorithm for online monitoring of a two-phase flow

The flow regimes are important characteristics to describe two-phase flows, and measurement of two-phase flow parameters is becoming increasingly important in many industrial processes. Computerized tomography (CT) has been applied to two-phase/multi-phase flow measurement in recent years. Image reconstruction of CT often involves repeatedly solving large-dimensional matrix equations, which are computationally expensive, especially for the case of online flow regime identification. In this paper, minimum cross entropy reconstruction based on multi-resolution processing (MRMCE) is presented for oil–gas two-phase flow regime identification. A regularized MCE solution is obtained using the simultaneous multiplicative algebraic reconstruction technique (SMART) at a coarse resolution level, where important information on the reconstructed image is contained. Then, the solution in the finest resolution is obtained by inverse fast wavelet transformation. Both computer simulation and static/dynamic experiments were carried out for typical flow regimes. Results obtained indicate that the proposed method can dramatically reduce the computational time and improve the quality of the reconstructed image with suitable decomposition levels compared with the single-resolution maximum likelihood expectation maximization (MLEM), alternating minimization (AM), Landweber, iterative least square technique (ILST) and minimum cross entropy (MCE) methods. Therefore, the MRMCE method is suitable for identification of dynamic two-phase flow regimes.

Measurement of Two-Phase Flow Parameters and Image Reconstruction Based on Weighted SVD Truncated Conjugate Gradient Algorithm

Taking into account the effect of sensitivity field and ill-posed problem in ERT, a weighted SVD truncated conjugate gradient image reconstruction algorithm (WSTCG) and its mathematical model were developed based on singular value decomposition of the sensitivity matrix theory. Simulation and experimental results show the proposed algorithm has two excellent characters of high quality and fast convergence speed compared with the LBP algorithm and CG algorithm.

Comparison of differential pressure model based on flow regime for gas/liquid two-phase flow

Gas/liquid two-phase flow in horizontal pipe is very common in many industry processes, because of the complexity and variability, the real-time parameter measurement of two-phase flow, such as the measurement of flow regime and flow rate, becomes a difficult issue in the field of engineering and science. The flow regime recognition plays a fundamental role in gas/liquid two-phase flow measurement, other parameters of two-phase flow can be measured more easily and correctly based on the correct flow regime recognition result. A multi-sensor system is introduced to make the flow regime recognition and the mass flow rate measurement. The fusion system is consisted of temperature sensor, pressure sensor, cross-section information system and v-cone flow meter. After the flow regime recognition by cross-section information system, comparison of four typical differential pressure (DP) models is discussed based on the DP signal of v-cone flow meter. Eventually, an optimum DP model has been chosen for each flow regime. The experiment result of mass flow rate measurement shows it is efficient to classify the DP models by flow regime.

Comparison between wire-mesh sensors and conductive needle-probes for measurements of two-phase flow parameters

Measurements of two-phase flow parameters such as void-fraction, bubble velocities, and interfacial area density have been performed in an upwards air–water flow at atmospheric pressure by means of a four-tip needle-probe and a wire-mesh sensor. For the first time, a direct comparison between the two measuring techniques has been carried out. Both techniques are based on the measurement of the fluid conductivity. For void-fraction and velocity measurements, similarity exists between the two methodologies for signal analysis. A significantly different approach is followed, instead, for the estimation of the interfacial area concentration: while the evaluation based on the needle-probe signal is carried out by using projections of the gas–liquid interface velocity, the evaluation based on the wire-mesh signals consist in a full reconstruction of the bubbles interfaces. The comparison between the two techniques shows a good agreement.

Finned Fuel Element Two-Phase Flow Parameter Measurements Using Real-Time Neutron Radiography

The measurement of two-phase flow parameters for development of constitutive relationships for the HANARO/MAPLE type finned fuel using Real-Time Neutron Radiography (RTNR) is discussed in this paper. A single element finned Fuel Element Simulator (FES) was used with Freon 134a as the working fluid. To observe the effect of a spacer device on void distribution, single pin tests were performed with and without a spacer present. By analyzing the RTNR images using image processing, the effects of the spacer on the time-averaged and instantaneous void fraction distribution were studied. For the experimental results without a spacer, the time-averaged local void distribution is radially asymmetric and the degree of void fluctuation increases with a decreasing frequency along the heated channel, where the observed asymmetry may be caused by flow induced vibration. For the experimental results with a spacer, the spacer clearly limits any significant vibration and the local void distribution becomes more symmetrical. The spacer however does generate an axial void fraction maximum at the upstream of the spacer with a small depletion zone at the exit of the spacer. By analysis of the instantaneous local void distribution, void fluctuation at the heated wall due to boiling was clearly observed. Also, the agglomeration and breakup of the cold-wall void was evident. The dynamic effects of the local void transients will be discussed in detail.

Local instrumentation for the investigation of multi-phase parameters in a packed bed

Local two-point conductivity probe and film-thickness probes were developed for measurement of two-phase flow parameters in a packed bed containing spherical packing. The probes were calibrated and installed in a packed bed with minimal flow disturbance. A flush and two parallel wire film-thickness probes were used to measure the liquid film thickness on the packing. The conductivity probe and impedance meter were used to measure local and bed wise void fraction, respectively, for trickle, wavy, transitional, pulsing, and bubbly flow.

Terahertz PT technology for measurement of multiphase flow and its infrared simulation

Terahertz process tomography (PT) is a new technology for multiphase flow measurement. T-ray PT prototype based on analysis of the T-ray's merits was proposed and an NIR PT simulation system was developed in this paper. The architecture, algorithm and characteristics of the simulation system were studied through experimental test. Evaluations of the simulation system performance and corresponding promotional approach were made. It was shown that the solution of simulation system could be adapted for THz PT technology, and that the experimental results proved that the simulation system itself is suitable for parameter measurement of two-phase flow.

Near infrared laser computed tomography test–system design and application

A new near infrared laser computed tomography test system is developed. The characteristics, construction, algorithm and performance of this system are analyzed. Simulation experiment results show that the image reconstruction speed and the resolution of this system can be improved easily. Research works also prove that the proposed near infrared computed tomography system is suitable for the parameter measurement of two-phase flow.

Laboratory Measurement of Two-Phase Flow Parameters in Rock Joints Based on High Pressure Triaxial Testing

The accurate flow measurement of each individual phase is important in unsaturated flow through rock joints, where both air and water phases flow together. An increase in the quantity of one fluid phase decreases the relative permeability of the other phase. The relative permeability is important in numerical models to analyze the risk of ground-water inundation and uncontrollable gas flows in underground excavations in jointed rock. A new apparatus, the High Pressure Two-Phase Triaxial Apparatus (HPTPTA), has been designed for examining the strength and coefficient of permeability characteristics of fractured and intact rocks under two-phase flows. In single-phase triaxial equipment, the rock specimen is subjected to a single fluid flow (either water, oil, or gas) through the fractures. In the HPTPTA, two fluids (e.g., water + air, water + oil, and oil + air) can be forced to flow through the specimen, and the flow rates of the fluids can be measured independently. The scope of tests that can be carried out in this apparatus is wide, including the evaluation of (1) stress-strain behavior subject to internal fluid flow; (2) relative permeability of each fluid phase under different degrees of saturation; and (3) the associated volume change of the specimen. In this paper, the design concepts of the HPTPTA and the results based on the testing of fractured rock specimens are discussed. The laboratory results are compared to a simplified mathematical model developed by the writers. Based on the laboratory results, it is shown that the well-known Darcy's law can be modified for estimating the two-phase flow rates using the relative permeability concept.