Void Fraction Measurements Research Articles

Tailorable regulation of mass transfer channel in environmentally friendly calcium alginate membrane for dye removal

Environmentally friendly polymer membranes for dye contamination removal were prepared from edible calcium alginate. The stable gel structure was formed by molecular chains of sodium alginate cross-linked by chelate-formation with calcium ions. To improve the water permeability of the membranes and make them suitable for membrane separation processes, their mass transfer channels were precisely regulated to form fine voids via the addition of oligoethylene glycol (OEG) or polyethylene glycol (PEG) to a casting polymer solution and subsequent removal of the OEG or PEG from the membranes by a washing process after cross-linking. Fourier transform infrared spectroscopy confirmed that the chemical properties of the membranes with voids formed by OEG or PEG were the same as the properties of the original calcium alginate membrane without void forming. Despite their same chemical properties, the performance of the membranes clearly differed. The effect of the different void structures on the mass transfer channels was investigated using pure water permeation, Methyl Orange dye rejection, and volumetric void fraction measurements, as well as morphological observations by field-emission scanning electron microscopy. The membrane with voids formed by OEG exhibited to an increase in water permeability compared with the original membrane, whereas the molecular separation performance was maintained within the nanofiltration region. Meanwhile, the membrane with voids formed by PEG was suitable for use in high-flux ultrafiltration processes for pretreating wastewater. The biocompatible membranes with tailorable separation ability presented herein are candidates for use in purification processes for recovering dye-polluted water resources.

Capacitance sensor for measuring void fraction in small channels

The paper presents a method for the measurement of void fraction in two-phase flow of liquid and gas phases in small channels by means of capacitance sensor. It was assumed arbitrarily that the small channels are those of diameter less than 10 mm. The capacitance sensor investigated in this paper consisted of two electrodes mounted on the outer wall of a glass pipe, and an electronic circuit for signal detection. The capacitance of two electrodes depends on the mean electric permittivity of the medium between them. The mean permittivity is a function of permittivity of the channel material and the percentage of both phases of different dielectric constants: liquid and gas. In this paper, the void fraction in two-phase flow was determined from frequency deviation of a high-frequency oscillator, in which the capacitance sensor was connected to a resonant circuit with an inductance in parallel. The advantage of this method over other methods based on the direct capacitance measurement (for example, LCR bridge) is that the intermediate steps for the determination of void fraction from the capacitance changes are omitted, and the void fraction can be directly determined from the calibration curve. Changes in the capacitance of electrodes for various void fractions have been determined numerically from the distribution of electric field in this geometry.

Performance comparison of capacitance-based flowmeter with gamma-ray attenuation-based two-phase flowmeter for determining volume fractions in an annular flow regime’s components

Precise metering of the void fraction is one of the important problems in the oil, chemical and petrochemical industries. For void fraction measurement, there are different kinds of sensors with different configurations. In this regard, the capacitance-based sensor and gamma-ray attenuation-based sensor are very well known as two most accurate and widely used sensors. In this paper, we report, to the best of our knowledge, for the first time a comparison between these two sensors in an annular air–oil flow. Simulations were accomplished with benchmarked COMSOL Multiphysics software and MCNPX code. Results show that the general sensitivity of gamma-ray sensor is ~ 90% higher than the general sensitivity of capacitance-based sensor. For a more accurate comparison, momentary sensitivity factors for a variety void fractions in both sensors were obtained. In the low void fraction range, the gamma-ray sensor has much better performance; however, in the high void fraction range, the capacitance-based sensor has a better performance. In the range of 0.9–1 void fractions, the momentary sensitivity of capacitance-based sensor is ~ 67% higher than that of gamma-ray attenuation-based sensor.

Study on Measure Approach of Void Fraction in Narrow Channel Based on Fully Convolutional Neural Network

Void fraction is one of the key parameters for gas-liquid study and detection of nuclear power system state. Based on fully convolutional neural network (FCN) and high-speed photography, an indirect void fraction measure approach for flow boiling condition in narrow channels is developed in this paper. Deep learning technique is applied to extract image features and can better realize the identification of gas and liquid phase in channels of complicated flow pattern and high void fraction, and can obtain the instantaneous value of void fraction for analyzing and monitoring. This paper verified the FCN method with visual boiling experiment data. Compared with the time-averaged experimental results calculated by the energy conservation method and the empirical formula, the relative deviations are within 11%, which verifies the reliability of this method. Moreover, the recognition results show that the FCN method has promising improvement in the scope of application compared with the traditional morphological method, and meanwhile saves the design cost. In the future, it can be applied to void fraction measurement and flow state monitoring of narrow channels under complex working conditions.

High-resolution high-speed void fraction measurements in helically coiled tubes using X-ray radiography

Helical coil heat exchangers are known for their superior heat transfer, compactness and robustness against thermal expansion compared to systems with straight pipes. Due to all these benefits, they became quite popular in the last few decades in various industries such as pharmaceutical, chemical or nuclear. Generally, they are used in a single-phase environment or with evaporation taking place on the shell side. However, in most of the steam generator designs adopted in advanced nuclear reactors, the two-phase mixture flows upward within the vertically oriented helical coils. In addition, physical two-phase phenomena taking place inside helical tubes differ significantly from those in straight pipes due to inherent centrifugal and torsion effects. To improve the computational models used to predict the thermal hydraulic performance of such steam generators, experimental characterization and identification of different two-phase flow patterns in helical coils are essential. In the present paper, high-resolution measurements of the void fraction distribution for an adiabatic upward air–water two-phase flow were conducted in a transparent helically coiled acrylic pipe by means of high-speed X-ray radiography at ambient conditions. Various void fraction based features such as probability density function estimates, profiles over the height of the pipe cross-section and temporal evolutions were used to identify and characterize flow regimes. A total of 13 measurements are presented in this paper, classified into six flow regimes, namely: bubbly, plug, wavy, slug, slug-annular and annular flow. The obtained flow regimes are in accordance with flow regime characterizations and transition criteria already reported in literature.

Flow induced vibration of two-phase flow passing through orifices under slug pattern conditions

Flow restricting orifices are important components for flow and pressure control in the oil, gas, and power generation industries. In many situations, the piping systems are operating under two-phase flow conditions. These orifices affect the redistribution of the two phases and induce vibrations in the piping structures. These vibrations often occur during a slug flow pattern and can severely affect the integrity of a structure; therefore, in the present work, both the vibrations of the piping structure and the characteristics of the two-phase flow dynamics are experimentally investigated in the presence of an orifice. In this study, an air–water​ two-phase flow mixture was utilized at different superficial velocities ranging from 0.12 m/s to 1.7 m/s for air and 0.46 m/s to 1.3 m/s for water. Synchronized flow visualization images, along with local void fraction and vibration measurements, were used to evaluate the response of the structure as the slug flow passed through the orifices. Detailed instantaneous local void fraction measurements were carried out to understand the underlying physics of the phenomenon and their effect on the vibration response of the structure. The results showed that not all slug flow cases excited the piping at the slug frequency. The amplitude of vibration around the slug frequency was found to increase as the superficial velocity of the gas phase increased.

Simulation and experiments on the feasibility of using gamma tomography for void fraction measurements in nuclear fuel bundle mock-ups

The High-Resolution Gamma Tomography System (HRGTS) facility is under development at the University of Michigan. This system is planned generally for application to two-phase flow loops representing nuclear fuel bundles. These measurements should provide insight into fluid dynamics phenomena and high resolution data for validation of computational fluid dynamics (CFD) codes. The HRGTS is planned to be deployed in the Michigan Advanced Rod Bundle fLow Experiment (MARBLE). an adiabatic test loop consisting of an 8x8 square lattice arrangement. Simulations modeling MARBLE were performed to study how the counting statistics of the imaging process propagate into void fraction uncertainty. The simulation results showed that an accuracy of around 1% is expected with imaging times of 1 min. Computed tomography measurements were performed on partial mockups of the bundle geometry, which confirmed that the technique can be used to obtain accurate subchannel void fraction data in complicated and challenging measurement scenarios.

Study on water damage mechanism of asphalt pavement based on industrial CT technology

Abstract It is impossible to study the relationship between water damage and voidage of asphalt pavement because the voidage of pavement core sample cannot be determined accurately. Based on the industrial computed tomography (CT) scanning technology for core samples of real void fraction measurement, dynamic water flushing apparatus to water damage damage of core samples, the CT scan void fraction and destruction after the relationship between splitting strength and CPN rutting depth of core samples, respectively, set up different lanes of void fraction and cleavage strength and the fitting formula of rut depth.

The Influence of Drying Conditions of Clay-Based Polymer Coatings on Coated Paper Properties

Coatings based on pigment and polymer binders are applied on paper surfaces to improve their surface, optical, and printing properties. Besides the coating composition, the structure and properties of the coated papers are influenced by the coating layer consolidation upon drying. In this study, the influence of drying conditions on the structure and properties of coating layers based on natural pigments (clay) and polymer binders (butadiene acrylonitrile latex) has been analyzed. Using a laboratory rod Mayer device, the coatings were applied as thin layer (about 15–16 g/m2) on the paper surface and samples of coated paper were dried at 20 and 105 °C temperatures. The optical, structural, and water absorption properties of the coating layer were evaluated by the measurement of gloss, opacity, void fraction, light scattering, and contact angle. The obtained results highlighted that both the drying temperature and latex content in the coating color have a synergic effect on the coated paper quality.

Evaluation of flow pattern recognition and void fraction measurement in two phase flow independent of oil pipeline’s scale layer thickness

The main objective of the present research is to combine the effect of scale thickness on the flow pattern and characteristics of two-phase flow that is used in oil industry. In this regard, an intelligent nondestructive technique based on combination of gamma radiation attenuation and artificial intelligence is proposed to determine the type of flow pattern and gas volume percentage in two phase flow independent of petroleum pipeline’s scale layer thickness. The proposed system includes a dual energy gamma source, composed of Barium-133 and Cesium-137 radioisotopes, and two sodium iodide detectors for recording the transmitted and scattered photons. Support Vector Machine was implemented for regime identification and Multi-Layer Perceptron with Levenberg Marquardt algorithm was utilized for void fraction prediction. Total count in the scattering detector and counts under photo peaks of Barium-133 and Cesium-137 were assigned as the inputs of networks. The results show the ability of presented system to identify the annular regime and measure the void fraction independent of petroleum pipeline’s scale layer thickness.

Determination of void fraction in a bed of solid particles by the method of flow cutoff

The paper presents a new method for determining the void fraction of two-phase flow with a condensable vapor phase. This method relies on the known technique of blocking the flow and allows measuring void fraction in the pore space of solid particle packings. The paper presents the results of experiments with packed beds of steel balls with diameters of 2 mm and 4 mm, 250 mm high. A comparison with some techniques for calculation of void fraction for empty vertical pipes is made.

Measurement of void fraction in pipes by nuclear transmission based techniques

In this study, the application of nuclear transmission based techniques to the measurement of two-phase flow was evaluated and the experiment setup was described. Because neutrons are appreciably affected by interaction with hydrogen atoms, techniques based on transmission of thermal and fast neutron are particularly suitable for use with water or any other hydrogenous fluids. Based on the effective of water for gamma-rays attenuation on mass basis, transmission technique based on measuring of total gamma-rays has been examined. The beams of fast neutrons, thermal neutrons and gamma-rays emitted from 252Cf neutron source of strength 1.3 × 107 n/s were used. Void fraction is measured for steady-flow regimes in a horizontal air–water flow. Results are evaluated and the strength and limitations for each technique are given and discussed.

Overview of Void Fraction Measurement Techniques, Databases and Correlations for Two-Phase Flow in Small Diameter Channels

Void fraction is one of the most important parameters for the modeling and characterization of two-phase flows. This manuscript presents an overview of void fraction measurement techniques, experimental databases and correlations, in the context of microchannel two-phase flow applications. Void fraction measurement techniques were reviewed and the most suitable techniques for microscale measurements were identified along its main characteristics. An updated void fraction experimental database for small channel diameter was obtained including micro and macrochannel two-phase flow data points. These data have channel diameter ranging from 0.5 to 13.84 mm, horizontal and vertical directions, and fluids such as air-water, R410a, R404a, R134a, R290, R12 and R22 for both diabatic and adiabatic conditions. New published void fraction correlations as well high cited ones were evaluated and compared to this small-diameter void fraction database in order to quantify the prediction error of them. Moreover, a new drift flux correlation for microchannels was also developed, showing that further improvement of available correlations is still possible. The new correlation was able to predict the microchannel database with mean absolute relative error of 9.8%, for 6% of relative improvement compared to the second-best ranked correlation for small diameter channels.

Localization and quantification of radical production in cavitating flows with luminol chemiluminescent reactions

Hydrodynamic cavitation experiments in microfluidic systems have been performed with an aqueous solution of luminol as the working fluid. In order to identify where and how much reactive radical species are formed by the violent bubble collapse, the resulting chemiluminescent oxidation reaction of luminol was scrutinized downstream of a constriction in the microchannel. An original method was developed in order to map the intensity of chemiluminescence emitted from the micro-flow, allowing us to localize the region where radicals are produced. Time averaged void fraction measurements performed by laser induced fluorescence experiments were also used to determine the cavitation cloud position. The combination void fraction and chemiluminescence two-dimensional mapping demonstrated that the maximum chemiluminescent intensity area was found just downstream of the cavitation clouds. Furthermore, the radical yield can be obtained with our single photon counting technique. The maximum radical production rates of 1.2*107 OH/s and radical production per processed liquid volume of 2.15*1010 HO/l were observed. The proposed technique allows for two-dimensional characterisation of radical production in the microfluidic flow and could be a quick, non-intrusive way to optimise hydrodynamic cavitation reactor design and operating parameters, leading to enhancements in wastewater treatments and other process intensifications.

Measurement of Heat Transfer Performance and Void Fraction of Dimple Type Heat Transfer Surface with Low Pressure Pool Boiling

Measurement of Heat Transfer Performance and Void Fraction of Dimple Type Heat Transfer Surface with Low Pressure Pool Boiling

A novel complex network-based deep learning method for characterizing gas\u2013liquid two-phase flow

Gas–liquid two-phase flow widely exits in production and transportation of petroleum industry. Characterizing gas–liquid flow and measuring flow parameters represent challenges of great importance, which contribute to the recognition of flow regime and the optimal design of industrial equipment. In this paper, we propose a novel complex network-based deep learning method for characterizing gas–liquid flow. Firstly, we map the multichannel measurements to multiple limited penetrable visibility graphs (LPVGs) and obtain their degree sequences as the graph representation. Based on the degree distribution, we analyze the complicated flow behavior under different flow structures. Then, we design a dual-input convolutional neural network to fuse the raw signals and the graph representation of LPVGs for the classification of flow structures and measurement of gas void fraction. We implement the model with two parallel branches with the same structure, each corresponding to one input. Each branch consists of a channel-projection convolutional part, a spatial–temporal convolutional part, a dense block and an attention module. The outputs of the two branches are concatenated and fed into several full connected layers for the classification and measurement. At last, our method achieves an accuracy of 95.3% for the classification of flow structures, and a mean squared error of 0.0038 and a mean absolute percent error of 6.3% for the measurement of gas void fraction. Our method provides a promising solution for characterizing gas–liquid flow and measuring flow parameters.

Void fraction measurement of gas–liquid two-phase flow with a 12-electrode contactless resistivity array sensor under different excitation patterns

This work focuses on the void fraction measurement of gas–liquid two-phase flow by a 12-electrode contactless resistivity array sensor. Such a sensor, which can realize different excitation patterns, is developed here. Five different excitation patterns (with 1, 2, 3, 4 or 5 electrodes) and three two-phase distributions (bubble flow, stratified flow and annular flow) are investigated. Two data processing approaches, the data average method and the principal component regression (PCR) method, are used to establish models of void fraction measurement and hence to implement it. Experiments on void fraction measurement are carried out with the 12-electrode contactless resistivity array sensor. The results show that the void fraction measurement performances are different under different excitation patterns. Among the five different excitation patterns studied, the one with five electrodes has the best performance and the absolute values of void fraction measurement errors of the three two-phase distributions are all less than 5.0% (using the data average method) and 3.0% (using the PCR method). Research results indicate that the 5-electrode excitation pattern + PCR combination is a new effective way to implement void fraction measurement of gas–liquid two-phase flow with the 12-electrode contactless resistivity array sensor.

Signal characteristics of IR transceiver pair during two phase flow of varying liquid film thickness in a mini-channel

Taylor bubble/slug flow is a type of multiphase flow that is predominant in many natural and industrial applications. A thorough understanding of two phase flows and void fraction measurement is essential to understand thermal hydraulic behavior during accident conditions in nuclear reactors. The performance of mini-reactors/microreactors and microthrusters requires a complete knowledge on shape and size of the void fraction distribution, which governs the flow characteristics in mini-channels/microchannels. The present study focuses on analyzing the signal characteristics of two IR transceivers simultaneously during two-phase bubble/slug regime having varying liquid film thickness. The transceivers are positioned at 90° and 0° to the axis of a tube of 1.5 mm diameter and 2.5 mm thickness. The experimental signal output is compared with the results obtained from a numerical model developed using COMSOL Multiphysics package. The present study exposes the critical parameters that need to be considered while developing a 3D reconstruction methodology based on IR transceivers for volumetric void fraction measurement.

Sectional void fraction measurement of gas-water two-phase flow by using a capacitive array sensor

The sectional void fraction measurement for multiphase flow is usually influenced by flow patterns. Inspired by electrical capacitance tomography (ECT) devices applied to flow imaging (whose measured capacitance data contain both the flow pattern and sectional void fraction information), a capacitive array sensor is developed to realize two functions, flow pattern recognition and void fraction measurement, simultaneously; so that the void fraction measurement can be conducted for a certain flow pattern and the measurement accuracy can be expected to be improved. The main idea of the proposed method can be described as: firstly, the proper feature vectors are extracted from the electrical signal to identify the flow pattern (the BPNN model with GDX learning algorithm is used for flow pattern identification); and then the average of electrical signal is applied to estimates the void fraction by the corresponding calibration curve. An experimental platform of air/water two-phase flow is built (on which 3 flow patterns can be generated stably) to test the performance of the proposed method. The results support the correctness and effectiveness of the proposed method.

Liquid flow measurement using phase isolation and an imaging method in horizontal gas–liquid two-phase flow

A new imaging method based on phase isolation for the liquid flow measurement of gas–liquid two-phase flow is proposed in this study. A swirler is arranged upstream to isolate two-phase fluids. As the two-phase mixture passes through it, a strong swirl flow is generated. The gas is concentrated into the center of the tube and forms a gas core while the liquid phase is pushed to the tube wall and forms a uniform liquid film, which is where the swirl core-annular flow occurs. After phase isolation, many microbubbles, which are small enough to neglect their body force, appear in the liquid film. These phase-isolation-induced microbubbles are used as tracers to represent the local velocity of the liquid flow. A CCD camera is employed to track the motion of the bubbles at the focal plane and determines the velocity at this position. Then this measured local velocity is converted to the mean velocity of the liquid film by a velocity coefficient based on the similitude principle of the velocity profile. After the flow area of the liquid film is derived from the void fraction measurement by another CCD camera, the flowrate of liquid film is determined. The velocity coefficients which express the relation between local velocity and mean velocity of liquid film are obtained by a calibration experiment. Two conventional industry CCD cameras and corresponding individual LED illuminations constitute the imaging system. The image-processing algorithm was developed using the MATLAB image toolbox. AAir and tap water are used and their superficial velocity are in the range of 3.41 m s−1 ∼ 45.15 m s−1 and 0.022 m s−1 ∼ 0.265 m s−1, respectively. The thickness of liquid film ranges from 72.75 μm to 423.11 μm and the diameter of microbubbles ranges from 11 μm to 35 μm.