Two-phase Flow Test Research Articles

A Multiscale and Multiphysics PWR Safety Analysis at a Subchannel Scale

A high-fidelity safety analysis method for pressurized water reactors (PWRs) is presented using a multiscale and multiphysics coupled code. Computational resolution of the conventional safety analysis can be greatly improved using this method in which the whole reactor vessel is modeled at a subchannel scale with around 5 million calculation meshes. Three-dimensional thermal hydraulics inside the reactor vessel is simulated using CUPID-RV with subchannel-scale thermal-hydraulic models for the reactor core. The subchannel models were validated using the legacy rod bundle experiments including single- and two-phase flow tests that were used in the validation of other subchannel analysis codes. The three-dimensional mesh was generated for the reactor vessel. Structured meshes were used in the core region for the subchannel model, and body-fitted unstructured meshes were applied for the downcomer, lower and upper plenums, and hot and cold legs. The number of meshes was optimized for a practical calculation. A three-dimensional core kinetics code (MASTER) and a one-dimensional system analysis code (MARS) were coupled with CUPID-RV for an accident analysis of PWRs. Subchannel-scale full-core steam line break accident analysis of the OPR1000 PWR was realized using the coupled code (MASTER/CUPID-RV/MARS) with a reasonable computation time, and thus, the present method can be used as a practical tool for three-dimensional safety analysis of PWRs.

Experimental Investigation for Flow Regime Identification Using Probability Density Function of Void Fraction Signals

Abstract In this study, upward air–water two-phase flow tests were carried out in a 3 cm diameter pipe under atmospheric pressure, and over 3000 data points were collected from a wide range of superficial gas and liquid velocities (⟨jg⟩ ≈ 0.02–30 m/s and ⟨jf⟩ ≈ 0.02–2 m/s) for the investigation of flow regime identification. The probability density function (PDF) of transient void fraction signals and its full-width at half-maximum (FWHM) were obtained and used for analysis and data classification. Considering the features of PDF profiles, the flow conditions can be classified into four regions, which show a fair agreement with the existing flow regime maps in general trends. Furthermore, by examining the FWHM distributions, two more regions with high-FWHM (HF) values were identified as the transitions of higher-flow bubbly-to-slug and slug-to-churn flows as well as most portion of churn flow, and a valley region next to the HF regions can express the transition of churn-to-annular flows. Overall, six groups of flow conditions can be classified based on the present methodology, and each group can be corresponding to specific flow regimes or transition regions. This study can provide a simple and efficient way for flow regime identification.

Electrical and Optical Probe for Two-Phase Flow Monitoring

Two-phase flows of gas and liquid streams in pipes are used in various industries, such as the pharmaceutical, energy, petrochemical, and food industries. Therefore, monitoring and investigation of phenomena related to the flow are of significance for various applications. The construction and evaluation of an electrical and optical probe for the monitoring of two-phase flows in industrial environments are presented in this paper. The probe consists of two stainless-steel electrodes positioned transverse to the flow to measure the fluid electrical conductance. One of the electrodes is hollow. An optical fiber Bragg grating sensor is used to measure the strain. In order to verify the probe performance, two calibration techniques (static and dynamic) along with a mathematical model for strain measurement are employed. The experimental data from the two calibrations are in good agreement with the theoretical values. The developed probe is applied in a two-phase flow test bench to monitor different two-phase flows in the slug flow regime. The obtained results demonstrate its capability to monitor specific parameters of this flow regime. Therefore, the proposed sensor is very promising for flow monitoring.

Two-phase flow pressure loss through packed particle bed for wide void fraction range

The understanding of the two-phase flow phenomena in porous media is a critical issue for debris bed coolability assessment in severe nuclear power plant accidents. Hence, two-phase-flow friction force modeling has been extensively attempted, based on pressure-loss measurement data. However, most previous two-phase flow pressure loss experiments were conducted at a restricted void-fraction range up to approximately 0.6, which is considerably lower than the dryout condition. Therefore, in this research, two-phase flow tests in packed particle beds are conducted to gather two-phase pressure loss data in the high-void-fraction region. The test beds are constructed by packing mm-scale particles, 3–7 mm in diameter. The experimental data are analyzed and compared with the predicted values of the previous two-phase friction models in term of not only the pressure gradient but also the interfacial friction force between the liquid and gas phases. As there was no valid data for the high-void-fraction region during the previous model development processes, an appropriate model for the interfacial friction force at void fractions greater than approximately 0.6 is unavailable. However, the interfacial friction force plays a significant role in the coolability assessment of the ex-vessel debris bed because it determines the water ingression rate under a cocurrent flow condition. The obtained experimental results in this research indicate the necessity to further improve the model in order to decrease the uncertainty in severe accident risk quantification.

Pressure Drops and Dryout Heat Fluxes of Packed Beds with Cylindrical Particles

Motivated by reducing the uncertainties in coolability analysis of a debris bed formed in severe accident of nuclear reactors, the pressure drops of single-/two-phase flow and dryout heat fluxes of the packed beds with non-spherical particles are investigated in the present study. Both adiabatic single-/two-phase flow tests and boiling tests are performed on a particulate porous bed packed with cylindrical particles separately, the pressure drops and dryout heat fluxes under different conditions are measured to identify and validate the debris coolability analysis models. The results show that for a particulate bed packed with non-spherical particles such as cylinders, the effective particle diameter can be represented by the equivalent diameter of the particles, which is the product of Sauter mean diameter and the shape factor. Given this diameter, the measured pressure drops and the dryout heat fluxes are comparable with the predictions of Reed model. Comparing with the cooling scheme of top-flooding case, the bottom injection improves the dryout heat flux significantly.

Experimental investigation on heat transfer performance of C-shape tube immerged in a water pool

The Passive Residual Heat Removal Heat Exchanger (PRHR-HX) is one of the key equipment of the Passive Residual Heat Removal System (PRHRS) adopted in third-generation (GEN-III) nuclear power plants. Heat transfer process of the C-shape tube applied in PRHR-HX is the combination of inside-tube condensation and outside-tube pool boiling, which is complicated and relatively differ from the most previous studies. In this paper, a high temperature and pressure two-phase flow test loop was built to investigate the heat transfer performance of an actual-size C-shape tube immerged in a water pool. The results show that both the pressure and the mass velocity influence the heat transfer characteristics significantly, while the effect of water pool temperature is not remarkable. Temperature stratifications are observed in both the water pool and the C-shape tube. Specifically, an assessment of four pool boiling heat transfer correlations is carried out to predict the experimental results of the outside-tube pool boiling. Based on the summary of the shortages of those correlations, a new correlation for the C-shape tube is developed, and also proved to be reasonable due to the experimental results.

Particle size estimation of pulverized fuel in pneumatic pipelines using electrostatic sensing techniques

Particle size measurement of pulverized fuel (PF) provides useful data for efficiency improvement of a pulverizing system, optimization of fuel combustion and emission reduction on a fired power plant. This paper presents an experimental study of particle size estimation of pneumatically conveyed PF through electrostatic sensing. An electrostatic sensor head consisting of two narrow and one wide ring-shaped electrodes is designed and implemented to measure the PF velocity and quantify the features of the sensor signals. Experimental tests using particles with three different size ranges were conducted on the vertical pipe section of a 74 mm bore gas–solid two-phase flow test facility under various flow conditions. Test results show that the root-mean-square magnitude and power spectral density of electrostatic signals vary with particle size. For the same air velocity, the small change in particle velocity is an indication of particle size as the particle velocity decreases when the particle size is larger. The proposed method is capable of estimating PF particle size and has the potential to offer considerable advantages over its counterparts in power plant applications.

A compact x-ray system for two-phase flow measurement

In this paper, a compact x-ray densitometry system consisting of a 50 kV, 1 mA x-ray tube and several linear detector arrays is developed for two-phase flow measurement. The system is capable of measuring void fraction and velocity distributions with a spatial resolution of 0.4 mm per pixel and a frequency of 1000 Hz. A novel measurement model has been established for the system which takes account of the energy spectrum of x-ray photons and the beam hardening effect. An improved measurement accuracy has been achieved with this model compared with the conventional log model that has been widely used in the literature. Using this system, void fraction and velocity distributions are measured for a bubbly and a slug flow in a 25.4 mm I.D. air–water two-phase flow test loop. The measured superficial gas velocities show an error within ±4% when compared with the gas flowmeter for both conditions.

Investigations on two-phase flow resistances and its model modifications in a packed bed

During severe core melting accidents of light water reactors with failures of all cooling systems, the molten core fuel (corium) would meet and interact with residual coolant water (FCI), then break up and fragment into a porous debris bed. Therefore, the debris bed coolability depending mainly on the flow friction laws, will be in great significance to nuclear reactor safety. Motivated by reducing the uncertainties in debris coolability assessment, this paper reports an experimental study on two-phase flow resistance in porous packed beds, and a modified model is proposed to predict the pressure drops of two-phase flow through packed beds with coarse particles. The tests are performed on the DEBECO-LT facility which is constructed to investigate the friction laws of adiabatic single and two-phase flow in a particulate bed. The spherical particles of 1.5 mm, 2 mm, 3 mm, 4 mm, 6 mm and 8 mm in diameter are packed separately in the cylindrical test section with the inner diameter of 120 mm and the height of 600 mm. The quality of experimentation and instrumentation can be ensured by the good agreement between the measured pressure drops of single phase flow tests and the predictions of Ergun equation. Then air-water co-current two-phase flow tests are conducted to investigate the flow resistance characteristics, providing the basic data for verifying, analyzing and modifying the existing models. The results show that: 1) when two-phase fluids flow upward through the porous beds packed with the smaller particles (e.g. 1.5 mm and 2 mm), the flow resistance increases gradually with the fluid flowrate, and the predictions of Reed model are more comparable with the measured pressure drops. While for the beds with larger size parties (e.g. 4 mm, 6 mm, and 8 mm), the flow resistances of two phase flow show a down-up tendency and hardly be predicted well by previous models; 2) it is believed that the interfacial drag plays non-ignorable role to the flow resistances for the beds packed with larger size particles, and should be considered specifically in the analysis models; 3) A modified model is proposed to predict the two-phase flow resistance in the packed bed with coarse particles. Compared with the previous models, the predictions of modified model show a favorable agreement with the experimental data under different conditions.

Gas-Liquid Two-Phase Flow Measurement Using Coriolis Flowmeters Incorporating Artificial Neural Network, Support Vector Machine, and Genetic Programming Algorithms

Coriolis flowmeters are well established for the mass flow measurement of single-phase flow with high accuracy. In recent years, attempts have been made to apply Coriolis flowmeters to measure two-phase flow. This paper presents data driven models that are incorporated into Coriolis flowmeters to measure both the liquid mass flowrate and the gas volume fraction of a two-phase flow mixture. Experimental work was conducted on a purpose-built two-phase flow test rig on both horizontal and vertical pipelines for a liquid mass flowrate ranging from 700 to 14500 kg/h and a gas volume fraction between 0% and 30%. Artificial neural network (ANN), support vector machine (SVM), and genetic programming (GP) models are established through training with the experimental data. The performance of backpropagation-ANN (BP-ANN), radial basis function-ANN (RBF-ANN), SVM, and GP models is assessed and compared. Experimental results suggest that the SVM models are superior to the BP-ANN, RBF-ANN, and GP models for two-phase flow measurement in terms of robustness and accuracy. For liquid mass flowrate measurement with the SVM models, 93.49% of the experimental data yield a relative error less than ±1% on the horizontal pipeline, while 96.17% of the results are within ±1% on the vertical installation. The SVM models predict the gas volume fraction with a relative error less than ±10% for 93.10% and 94.25% of the test conditions on the horizontal and vertical installations, respectively.

Effects of moisture content on electrostatic sensing based mass flow measurement of pneumatically conveyed particles

Mass flow rate measurement of pneumatically conveyed particles is desirable for the optimal control of many industrial processes. The unpredicted variation of moisture content in particles affects the accuracy of mass flow measurement of particles in enclosed pipelines using electrostatic electrodes. In this study, the characteristics of measured electrostatic signals from particle flow under different flow conditions are analysed to study the effect of moisture content on the mass flow rate measurement. The measurement principle of ring-shaped electrostatic electrodes, the effects of moisture content on electrification of solid particles, and the experimental setup used in the study are presented. Two types of electrostatic electrodes with different axial widths and structure are adopted to measure the electrostatic signals of nonporous glass beads and porous activated carbon powder on the vertical pipeline of a 74mm bore gas–solid two-phase flow test rig under various moisture content, mass flow rate and conveying velocity conditions. The experimental results indicate that the amplitude and frequency characteristics of the electrostatic signals change with the moisture content. The deviation of mass flow measurement that caused by the variation of moisture content is analysed, and a recalibration process is demonstrated to be effective for the improvement of measurement accuracy.

A novel experimental facility for measuring internal flow of Solid-liquid two-phase flow in a centrifugal pump by PIV

PIV is one of the most effective flow measurement methods, but for solid-liquid two-phase flow in a centrifugal pump with complex internal structure and high speed rotation, many problems exist in the experimental facility design, such as solid particle releasement, synchronization issues among camera, laser and pump impeller, and methods of avoiding introducing bubbles into flow passage, etc. To solve these critical problems, a new experimental facility without agitation was designed for internal solid-liquid two-phase flow test in a centrifugal pump by PIV. The facility was tested by measuring two-phase flow of water-glass beans and water-rape seeds in a centrifugal slurry pump. The new test facility has many obvious advantages, such as the simpler structure without the agitating device, less noise in the test process, less power consumption, less number of particles to get a certain particle volume concentration, and the decrease of the experiment cost. The result shows that the new facility can realize a stable solid-liquid two-phase flow measurement with high reliability in a centrifugal pump.

Measurements of translational slug velocity and slug length using an image processing technique

Slug flow is a common flow regime that occurs in various industries, such as oil, gas, and power generation industries. In this study, the mean slug translational velocity and slug liquid length were measured using Phantom 9.2 software and an image processing analysis technique. The adopted image processing technique involved the analysis of video frames recorded from a high-speed camera (Phantom 9.2) in a horizontal transparent pipe using a combination of the approximate median method and blob analysis, along with an additional morphological process for detecting and segregating individual slugs. The experimental data were obtained from a designed two-phase flow test section, in which sets of superficial water and air velocities were selected to generate numerous slug flows. A good agreement with a maximum deviation of 6.7% between the estimated slug parameters from the adopted technique and the Phantom cine view controller software was achieved. Additionally, the developed technique provided precise results with a high processing speed of 10 frames per second.

A new algorithm for segmentation of ultrafast X-ray tomographed gas–liquid flows

The ultrafast electron beam X-ray computed tomography was developed during the last years to obtain detailed data on two-phase flows. In a recent study we investigated different gas–liquid flow regimes in a vertical pipe at the Transient Two-phase Flow test facility (TOPFLOW). The study includes experiments on gas–liquid flows with varied superficial velocities for both phases and different flow directions. The obtained data is required for understanding fundamental physics of two-phase flow phenomena and for the development and validation of CFD codes.To extract quantitative data from the reconstructed three-dimensional data array, a new segmentation algorithm was developed, due the results of existing segmentation algorithms aren't satisfyingly. The originality of this new algorithm bases on a stepwise creation of new bubbles using pixel agglomeration in shrinking steps without defining markers or starting points. The results were compared with threshold and gradient methods using two different bubble phantoms and real two-phase flow measurements. The new algorithm shows the best qualitative and quantitative results.

Reduced order modeling of transient two-phase flows and its application to upward two-phase flows in the under-balanced drilling

In this paper, reduced order modeling (ROM) of transient two-phase flow equations is performed based on the four-equation two-fluid model, using an equation-free/Galerkin-free proper orthogonal decomposition (POD) method. The AUSMDV∗ method is used to provide the required snapshots for the construction of the reduced basis vectors. The singular value decomposition method is employed to obtain the POD basis functions. An equation-free projective integration method is used to compute the flow variables. To validate the results, two two-phase flow test cases are solved using the presented POD method including two-phase shock tube and water–air separation problems. ROM of the governing equation for upward transient two-phase flow in the annulus of the drilling well is also performed using the POD method. The results show that the presented methodology can reduce the computational costs of the standard two-phase flows problems up to 35%. The time saving for upward two-phase flow in the drilling well may vary between 36% and 62% depending on the initial and boundary conditions of the problem under study.

IDENTIFICATION OF TWO-DIMENSIONAL VOID PROFILE IN A LARGE SLAB GEOMETRY USING AN IMPEDANCE MEASUREMENT METHOD

Multi-dimensional two-phase phenomena occur in many industrial applications, particularly in a nuclear reactor during steady operation or a transient period. Appropriate modeling of complicated behavior induced by a multi-dimensional flow is important for the reactor safety analysis results. SPACE, a safety analysis code for thermal hydraulic systems which is currently being developed, was designed to have the capacity of multi-dimensional two-phase thermo-dynamic phenomena induced in the various phases of a nuclear system. To validate the performance of SPACE, a two-dimensional two-phase flow test was performed with slab geometry of the test section having a scale of 1.43 m × 1.43 m × 0.11 m. The test section has three inlet and three outlet nozzles on the bottom and top gap walls, respectively, and two outlet nozzles installed directly on the surface of the slab. Various kinds of two-dimensional air/water flows were simulated by selecting combinations of the inlet and outlet nozzles. In this study, two-dimensional two-phase void fraction profiles were quantified by measuring the local gap impedance at 225 points. The flow conditions cover various flow regimes by controlling the flow rate at the inlet boundary. For each selected inlet and outlet nozzle combination, the water flow rate ranged from 2 to 20 kg/s, and the air flow rate ranged from 2.0 to 20 g/s, which corresponds to 0.4 to 4 m/s and 0.2 to 2.3 m/s of the superficial liquid and gas velocities based on the inlet port area, respectively.

Equal quality distribution of gas–liquid two-phase flow by partial separation method

This paper proposes a new method for equal quality distribution of gas–liquid two-phase flow by partial separate-phase distribution with a dual-header distributor. The upper and liquid (lower) headers are interconnected with five vertical downward arms. A gas–liquid two-phase mixture enters the distributor from the upper header where most of the liquid of the mixture is removed through the downward arms into the liquid header. Hence, firstly, the remaining gas-rich fluid can be uniformly distributed into the outlet branches, and then secondly, the liquid collected in the liquid header can be uniformly re-distributed into the individual outlet branches. Because both distribution processes are conducted in the condition of single or near single-phase flow, mal-distribution of the two-phase flow is essentially eliminated, and a satisfactory equal quality distribution of gas–liquid two-phase flow is reached. Experiments were conducted in an air–water two-phase flow test loop. The inner diameter of the inlet pipe was 60mm, the superficial velocity ranges of gas and liquid were 3–32m/s and 0.02–0.17m/s respectively, and the quality ranged from 0.02 to 0.44. The flow pattern in the inlet pipe included stratified flow, wavy stratified, slug flow, and annular flow. The experimental results showed that this new method could significantly improve the distribution performance of the two-phase flow. The maximum quality deviation between each outlet branch and the inlet pipe is less than ±1% under the conditions of stratified, wavy stratified and slug flows in the upper header, and less than ±5% in annular flow.

Development of drift-flux model based on 8 × 8 BWR rod bundle geometry experiments under prototypic temperature and pressure conditions

The drift-flux model is one of the imperative concepts used to consider the effects of phase coupling on two-phase flow dynamics. Several drift-flux models are available that apply to rod bundle geometries and some of these are implemented in several nuclear safety analysis codes. However, these models are not validated by well-designed prototypic full bundle test data, and therefore, the scalability of these models has not necessarily been verified. The Nuclear Power Engineering Corporation (NUPEC) conducted void fraction measurement tests in Japan with prototypic 8 × 8 BWR (boiling water reactor) rod bundles under prototypic temperature and pressure conditions. Based on these NUPEC data, a new drift-flux model applicable to predicting the void fraction in a rod bundle geometry has been developed. The newly developed drift-flux model is compared with the other existing data such as the two-phase flow test facility (TPTF) data taken at the Japan Atomic Energy Research Institute (JAERI) [currently, Japan Atomic Energy Agency (JAEA)] and low pressure adiabatic 8 × 8 bundle test data taken at Purdue University in the United States. The results of these comparisons show good agreement between the test data and the predictions. The effects of power distribution, spacer grids, and the bundle geometry on the newly developed drift-flux model have been discussed using the NUPEC data.

Multiphysics Simulations of Entrained Flow Gasification. Part I: Validating the Nonreacting Flow Solver and the Particle Turbulent Dispersion Model

In this two-part paper, we describe the construction, validation, and application of a multiscale model of entrained flow gasification. The accuracy of the model is demonstrated by (1) rigorously constructing and validating the key constituent submodels against relevant canonical test cases from the literature and (2) validating the integrated model against experimental data from laboratory scale and commercial scale gasifiers. In part I, the flow solver and particle turbulent dispersion models are validated against experimental data from nonswirling flow and swirling flow test cases in an axisymmetric sudden expansion geometry and a two-phase flow test case in a cylindrical bluff body geometry. Results show that while the large eddy simulation (LES) performs best among all tested models in predicting both swirling and nonswirling flows, the shear stress transport (SST) k–ω model is the best choice among the commonly used Reynolds-averaged Navier–Stokes (RANS) models. The particle turbulent dispersion model is accurate enough in predicting particle trajectories in complex turbulent flows when the underlying turbulent flow is well predicted. Moreover, a commonly used modeling constant in the particle dispersion model is optimized on the basis of comparisons with particle-phase experimental data for the two-phase flow bluff body case.

Experimental Visualization of Two-Phase Flow Inside an Electrical Submersible Pump Stage

Dynamic multiphase flow behavior inside a mixed flow electrical submersible pump (ESP) has been studied experimentally and theoretically for the first time. The overall objectives of this study are to determine the flow patterns and bubble behavior inside the ESP and to predict the operational conditions that cause surging. An experimental facility has been designed and constructed to enable flow pattern visualization inside the second stage of a real ESP. Special high-speed instrumentation was selected to acquire visual flow dynamics and bubble size measurements inside the impeller channel. Experimental data were acquired utilizing two types of tests (surging test and bubble diameter measurement test) to completely evaluate the pump behavior at different operational conditions. A similarity analysis performed for single-phase flow inside the pump concluded that viscosity effects are negligible compared to the centrifugal field effects for rotational speeds higher than 600 rpm. Therefore, the two-phase flow tests were performed for a rotational speeds of 600, 900, 1200, and 1500 rpm. Results showed formation of a large gas pocket at the pump intake during surging conditions.