Phase Fraction Distribution Research Articles

A Comparative Study on the Influence of Chromium on the Phase Fraction and Elemental Distribution in As-Cast High Chromium Cast Irons: Simulation vs. Experimentation

The excellent abrasion resistance of high chromium cast irons (HCCIs) stems from the dispersion of the hard iron-chromium eutectic carbides. The surrounding matrix on the other hand, provides sufficient mechanical support, improving the resistance to cracking deformation and spalling. Prior knowledge of the microstructural characteristics is imperative to appropriately design subsequent heat treatments, and in this regard, employing computational tools is the current trend. In this work, computational and experimental results were correlated with the aim of validating the usage of MatCalc simulations to predict the eutectic carbide phase fraction and the elemental distribution in two HCCI alloys, in the as-cast condition. Microstructural observations were carried out using optical microscopy and SEM. The chemical composition and fraction of each phase was measured by electron probe microanalysis and image analysis, respectively. In all cases, the values predicted by the pseudo-equilibrium diagrams, computed with MatCalc, were in accordance with the experimentally determined values. Consequently, the results suggest that time and resource intensive experimental procedures can be replaced by simulation techniques to determine the phase fraction and especially, the individual phase compositions in the as-cast state.

Predicting Welding Residual Stress of a Multi-pass P92 Steel Butt-Welded Joint with Consideration of Phase Transformation and Tempering Effect

A three-dimensional finite element model based on thermal–metallurgical–mechanical coupling theory was developed to simulate temperature field, phase fraction and residual stress distribution of a multi-pass P92 steel butt-welded joint. In the FE model, the influences of volume change, yield strength variation and plasticity induced by phase transformation on welding residual stress were carefully taken into account. In addition, an attempt was made to consider the effect of tempering on residual stress. In the current study, the hole-drilling method was employed to measure the residual stress distribution on the surface of P92 steel butt-welded joint, while optical microscope and Vickers hardness tester were used to characterize the microstructure and hardness, respectively. The comparison between the simulation results and the measured data shows that the developed computational approach could accurately predict welding residual stress for multi-pass P92 steel joint. Moreover, the results of Satoh test indicate that the tempering effect has influence on the stress evolution and the final magnitude to a certain extent.

Influence of heat treatment under hot isostatic pressing (HIP) on microstructure of intermetallic-reinforced tool steel manufactured by laser powder bed fusion

Microstructure and properties of as-built laser powder bed fusion (LPBF) steels differ from the conventional ones, and they may contain some porosity and lack of fusion. Therefore, post-treatments, including hot isostatic pressing (HIP), are used to densify the material, and tailor the properties of the final product. Usually, HIP is performed as an operation separate from heat treatment. In the present investigation a new approach was used, in which the whole cycle of the heat treatment was carried out in HIP under pressure, and the influence of HIP on microstructure of an advanced stainless maraging tool steel manufactured by LPBF was investigated. For a comparison, a conventional steel grade of the same chemical composition, after a heat treatment at the same temperature-time conditions, was also characterized. The microstructure of the steel was investigated by means of advanced microscopy and atom probe tomography. The influence of the manufacturing route, heat treatment and HIP on microstructure, austenitic phase fraction and size distribution of precipitates was investigated, and the role of high pressure in stabilization of austenite in the microstructure was discussed. It was concluded that since HIP influences phase transformations, a fundamental understanding of the influence of HIP on microstructure is necessary, and development of new post processing regimes guaranteeing the best performance of the material is required.

Application of extended quadrature method of moments for simulation of bubbly flow and mass transfer in gas‐liquid stirred tanks

In the present paper, two gas‐liquid stirred tanks, one agitated by a radial impeller and another by an axial impeller, are modelled using the open‐source computational fluid dynamic (CFD) package OpenFOAM (open source field operation and manipulation). The combined effect of the bubble break‐up and coalescence in the tank is considered by a population balance model (PBM) called extended quadrature method of moments (EQMOM). The three‐dimensional simulation is made using a multiple reference frame (MRF), a well‐established method for the modelling of mixers. Dispersed gas and bubble dynamics in the turbulent flow are modelled using the Eulerian‐Eulerian approach (E‐E) with mixture k‐epsilon turbulent model and the modified Tomiyama drag coefficient for the momentum exchange. The model is developed to predict the spatial distribution of gas phase fraction, Sauter mean bubble diameter (), number density function (NDF), dissolved oxygen (DO) evolution, and flow structure. The numerical results are compared with experimental data and a fair agreement is achieved. The results of the axial impeller are discussed based on four impeller rotational speeds with different volumetric mass transfer coefficients.

Gas–Liquid Flow Pattern Analysis Based on Graph Connectivity and Graph-Variate Dynamic Connectivity of ERT

Two-phase flow is widely encountered in process engineering and related scientific research. Understanding flow patterns and their transitions is important to discover the fluid mechanics of two-phase flow. In order to investigate the complexity of horizontal gas–water two-phase flow and accurately identify the flow pattern, a 16-electrode electrical resistance tomography was used to collect the spatial distribution of phase fraction. The experimental data are compressed and treated as a 16-D time series corresponding to the average response of the phase distribution in the field of each exciting electrode, which can be studied with graph-based techniques. Three connectivity metrics—correlation, coherence, and the phase-lag index are extracted from the multivariate time series, which correspond to the amplitude, power, and phase-based connectivity among signals, respectively. Together, these connectivity metrics make a comprehensive description of the characteristics of each flow pattern and reveal the transition process of flow patterns. The dynamic characteristics of typical flow patterns are then analyzed using the method of graph-variate signal analysis named graph-variate dynamic connectivity.

Numerical investigation of jet agitation in a nuclear liquid waste storage tank

Radioactive liquid waste is often stored in a large capacity (150 m3) horizontal cylindrical tanks. It is necessary to keep the contents of the tank agitated to prevent the settling of fine solids in the tank. In extreme cases, solids settled at the tank base may invoke the system malfunction. This paper deals with the Computational Fluid Dynamic (CFD) modeling of the agitation mechanism considering the turbulent dispersion effects. The simulations are conducted on a standard tank geometry to arrive the optimum jet velocity required to suspend the settled solid particles thoroughly. The distribution of volume phase fraction, velocity magnitude, turbulence kinetic energy (TKE) and eddy dissipation of each phase for different inlet jet velocities (v = 10–25 m/s) have been presented. The spatial variation of these quantities are measured at three different planes in the vessel mainly in the vicinity of the nozzle exit. The results indicate that the jet velocity is a significant parameter that influences the particle suspension. Parametric studies have also been carried out for four different particle sizes, viz. dp = 5, 10, 50 and 100 μm. The present study revealed that, for the range of parameters covered, the smallest (dp = 5 μm) and the largest (dp = 100 μm) particle sizes has least effect in terms of solids suspension.

Modeling and analysis of residual stress distribution in butt welded joint with thorough penetration taking into account influence of groove weld

A chamfering of the joining sheet edges is often used in welding practice. In work, the analysis of groove weld input on residual stress distribution in single-pass butt welded joints with thorough penetration is presented. For this purpose, comparative calculations of instantaneous and residual stresses in two steel flat bars were made. The butt welded joints of S235 steel elements put to the analysis. Numerical simulations were conducted for joint with welding groove and for joint without chamfering of flats. The calculations include strains caused by temperature changes as well as the effect of phase transformations. For calculations are used authors’ programs made in Borland Delphi. The results are presented in the form of temperature, volume phase fraction and stress distributions in the element’s cross section as well as welding thermal cycles and stress history at selected points. The analysis of the results of the calculations showed slight differences in the stress distributions in the heat-affected zones of the considered flat bars, while it did not show significant differences in stress levels outside these areas.

Energy-resolved neutron tomography of an unconventional cultured pearl at a pulsed spallation source using a microchannel plate camera

A non-destructive neutron analysis technique performed at the IMAT beamline of the STFC (Science and Technology Facility Council), UK, is presented. In this experiment, neutrons of different energy have been exploited to obtain a tomographic reconstruction of a biomineralic sample, more specifically a cultured pearl, by using a time-resolving pixel camera, the MicroChannel Plate (MCP) detector, utilizing an array of 2×2 Timepix readout chips. The MCP camera is capable of energy-resolved two-dimensional mapping of neutron transmission with a spatial resolution of ~55μm. By using a Simultaneous Iterative Reconstruction Technique (SIRT), virtual sections of the internal part of the sample have been created, thus revealing several features inside its bulk. The crystallographic phase map via Bragg edge analysis, showing a phase fraction distribution on the entire specimen, has been generated as well. Finally, 3D volume rendering of the pearl is presented.

Experimental investigations on a common centrifugal pump operating under gas entrainment conditions

This paper presents an experimental study on the effects of additional gas entrainment in centrifugal pumps designed for conveying liquid phases only. The pump performance has been evaluated for several gas entrainment conditions, and for various operational settings of the pump, such as its alignment and the rotational speed of the impeller. As a main performance indicator the impact of entrained gas on the hydraulic power of the pump has been analyzed using experimental data. Additionally, high-resolution gamma-ray computed tomography (HireCT) operated in time-averaged rotation-synchronized scanning mode has been applied to quantify local phase fraction distributions inside the rapidly rotating pump impeller. Based on these quantitative tomographic measurements, gas holdup profiles along selected streamlines have been calculated and gas accumulation areas inside the impeller chambers have been visualized. Thus, various internally accumulated gas holdup patterns have been identified and, eventually, associated with characteristic pump performance behaviors. Moreover, the tomographic measuring method allowed an enhanced gas holdup analysis in specified pump compartments. As a result, the related specific gas and liquid phase holdup profiles have been evaluated.

The measurement of stress and phase fraction distributions in pre and post-transition Zircaloy oxides using nano-beam synchrotron X-ray diffraction

Zircaloy-4 oxide stress profiles and tetragonal:monoclinic oxide phase fraction distributions were studied using nano-beam transmission X-ray diffraction. Continuous stress relief and phase transformation during the first cycle of oxide growth was observed. The in-plane monoclinic stress was shown to relax strongly up to each transition, whereas in-plane tetragonal stress-relief (near the metal-oxide interface) was only observed post transition. The research demonstrates that plasticity in the metal and the development of a band of in-plane cracking both relax the monoclinic in-plane stress.The observations are consistent with a model of transition in which in-plane cracking becomes interlinked prior to transition. These cracks, combined with the development of cracks with a through-thickness component (driven primarily by plasticity in the metal) and/or a porous network of fine cracks (associated with phase transformation), form a percolation path through the oxide layer. The oxidising species can then percolate from the oxide surface to the metal/oxide interface, at which stage transition then ensues.

Modeling of Heat Affected Zone in Multipass GMAW Surfacing S235 Steel Element

The paper presents the model of heat affected zone in a steel element during multipass Gas Metal Arc Weld surfacing. The temperature field is described analytically assuming a volumetric model of heat source and a semi-infinite body model of the surfacing workpiece. The solution takes into consideration the heating during overlaying subsequent weld beads and self-cooling of already padded areas. The critical temperatures A1 and A3 are used to determine partial and full austenitic transformation zones, while the temperature of solidus is used to determine the fusion line. Kinetics of phase transformations during cooling is determined on the basis of TTT-welding diagram. In description of phase transformations progress the J-M-A-K law for diffusive transformations, and the K-M law for martensitic transformation are used. The results of calculations are presented in the form of temperature and volume phase fraction distributions.

Refined reconstruction of liquid–gas interface structures for stratified two-phase flow using wire-mesh sensor

Wire-mesh sensors (WMS), developed at HZDR [13,4], are widely used to visualize two-phase flows and measure flow parameters, such as phase fraction distributions or gas phase velocities quantitatively and with a very high temporal resolution. They have been extensively applied to a wide range of two-phase gas–liquid flow problems with conducting and non-conducting liquids. However, for very low liquid loadings, the state of the art data analysis algorithms for WMS data suffer from the comparably low spatial resolution of measurements and from boundary effects, caused by e.g. flange rings – especially in the case of capacitance type WMS. In the recent past, diverse studies have been performed on two-phase liquid–gas stratified flow with low liquid loading conditions in horizontal pipes at the University of Tulsa. These tests cover oil–air flow in a 6-inch ID pipe and water–air flow in a 3-inch ID pipe employing dual WMS with 32×32 and 16×16 wires, respectively. For oil–air flow experiments, the superficial liquid and gas velocities vary between 9.2m/s≤νSG≤15m/s and 0.01m/s≤νSL≤0.02m/s, respectively [2]. In water–air experiments, the superficial liquid and gas velocities vary between 9.1m/s≤νSG≤33.5m/s and 0.03m/s≤νSL≤0.2m/s, respectively [17,18]. In order to understand the stratified wavy structure of the flow, the reconstruction of the liquid–gas interface is essential. Due to the relatively low spatial resolution in the WMS measurements of approximately 5mm, the liquid–gas interface recognition has always an unknown uncertainty level. In this work, a novel algorithm for refined liquid–gas interface reconstruction is introduced for flow conditions where entrainment is negligible.

Influences of Microstructure Characteristics on Forming Limit Behavior of Dual Phase Steels

In the automotive sector, dual phase (DP) steel grades have been increasingly used for various car body parts due to their good combination of strength and formability. To control mechanical and fracture characteristics of the DP steels, effects of martensitic phase fraction, morphology, and phase distribution must be understood. In this work, DP steel sheets with different martensitic phase fractions and ferritic grain sizes were produced through the intercritical annealing process. Likewise, FE simulations of 2D representative volume elements (RVEs) based on real micrograph were performed for all generated DP microstructures. Flow behaviors of single individual phases in the DP steels were described by a dislocation theory and local chemical compositions. Calculated stress–strain responses were verified with experimental results from tensile tests. Subsequently, stretch-forming tests under different states of stress using the Nakajima samples were carried out for the examined DP steels. Micromechanics RVE models were then applied to predict failure occurrences in the DP microstructures by considering plastic strain instability. Influences of morphologies and properties of constituent phases on localization due to incompatible deformation between martensite and ferrite were discussed with regard to governing stress states.

Neutron Bragg Edge Tomography for Phase Mapping

This paper describes non-destructive three-dimensional (3D) mapping of crystallographic phase distributions within the bulk (centimeter range) of samples with micrometer-scale resolution. The technique leverages diffraction contrast due to Bragg scattering and the large penetration power of neutrons through high-atomic-number-element-based structural materials. Our tomographic approach overcomes critical limitations of existing techniques by allowing spatially resolved phase mapping in bulk samples and offers a wide range of potential applications. The technique is demonstrated for (metastable 304L stainless) steel samples that exhibit strain-induced martensitic phase transformation after being subjected to tensile and torsional deformation. The distribution of phase fractions within the 3D reconstructed volumes was verified at select locations using neutron diffraction as well as EBSD, and results agree with transformation kinetics theory.

Experiments with a Wire-Mesh Sensor for stratified and dispersed oil-brine pipe flow

Two-phase oil–water flow was studied in a 15m long horizontal steel pipe, with 8.28cm internal diameter, using mineral oil (having 830kg/m3 density and 7.5mPas viscosity) and brine (1073kg/m3 density and of 0.8mPas viscosity). Measurements of the holdup and of the cross-sectional phase fraction distribution were obtained for stratified flow and for highly dispersed oil–water flows, applying a capacitive Wire-Mesh Sensor specially designed for that purpose. The applicability of this measurement technique, which uses a circuit for capacitive measurements that is adapted to conductive measurements, where one of the fluids is water with high salinity (mimicking sea water), was assessed. Values for the phase fraction values were derived from the raw data obtained by the Wire-Mesh Sensor using several mixture permittivity models. Two gamma-ray densitometers allowed the accurate measurement of the holdups, which was used to validate the data acquired with the capacitive Wire-Mesh Sensor. The measured time-averaged distribution of the phase fraction over the cross-sectional area was used to investigate the details of the observed two-phase flow patterns, including the interface shape and water height. The experiments were conducted in the multiphase-flow test facility of Shell Global International B.V. in the Netherlands.

3D Mapping of Crystallographic Phase Distribution using Energy‐Selective Neutron Tomography

Nondestructive 3D mapping of crystallographic phases is introduced providing distribution of phase fractions within the bulk (centimeter range) of samples with micrometer-scale resolution. The novel neutron tomography based technique overcomes critical limitations of existing techniques and offers a wide range of potential applications. It is demonstrated for steel samples exhibiting phase transformation after being subjected to tensile and torsional deformation.

Numerical and experimental study of the electrofusion welding process of polyethylene pipes

The electrofusion welding process is widely used to join polyethylene components in gas distribution networks. This article provides experimental and 3D‐finite element tools capable of reproducing the major phenomena that occur during an electrofusion process. A specific version of the 3D‐ finite element model simulation software Forge® has been developed to take into account the fitting parameters such as polyethylene thermal properties (i.e., melting and crystallization kinetics, phase transition, and thermal contact resistance) and the electrical and geometrical settings (i.e., welding input parameters). From a numerical point of view, a well refined highly anisotropic mesh adaptation is applied to well capture the contact condition between the heat source and the polyethylene. The computed results (temperature, melted, and cold areas) were compared with experimental data and gave very good agreement in terms of temperature and liquid phase fraction distribution. POLYM. ENG. SCI., 55:123–131, 2015. © 2014 Society of Plastics Engineers

Domain Size Distribution in Phase Separated Cholesterol/Phospholipid Langmuir Monolayers: Line Tension and Transition Kinetics

Multicomponent phase separated phospholipid monolayer systems of a canonical cholesterol and DMPC (∼30/70 mole percent) have been used to study several aspects of cholesterol/phospholipid interaction and phase behavior. Despite the successful characterization and theoretical approaches applied to these systems there are still important details of monolayer morphology that are not fully understood. Here, we address the role of transition kinetics on domain size distributions. For our experiments, three different barrier speeds were chosen (4, 40, 400 cm squared per minute) as the monolayer passed through the miscibility phase transition (8.4 mN/m transition pressure). Average domain size was observed to decrease as the barrier speed increased (transition rate). The detailed size distribution measurements also provide the opportunity to measure changes in phase fraction and size distribution with monolayer surface pressures (2, 4, and 6, mN/m). Careful study of factors influencing the size distribution of phase separated domains is particularly relevant to the recently proposed line tension measurement technique (Lee et al., vol. 108 pp. 9425, PNAS 2011). We have implemented this method for the monolayer system studied here. A comparison to previously implemented line tension measurements based on a Fourier analysis of boundary fluctuations approaches will be presented. Finally, a brief comparison on the role of dyes and dye quality will be presented. Comparison among one year old Texas Red and new Texas Red, showed an impact in the sizes of domains.

Characterization of multiphase flow in bubble columns using KT-1 signature and fractal dimension

This work presents the analysis of phase fraction distribution in bubble column reactor using KT-1 signature and fractal dimension. The experiment was carried out using X-ray CT scanner at Leibniz University Hannover. Convolution back projection algorithm is used to obtain the cross-sectional attenuation coefficient distribution. Individual phase distributions of the three phases (air, water and PVC), across the column cross-section, have been obtained using dual energy X-ray tomography. This paper reports measurement of phase fraction distribution at a cross-section level located at 3.2m from the inlet. The effect of variation of PVC concentration on phase fraction distribution of air and PVC has been investigated. Analysis of reconstructed phase fraction using KT-1 signature and fractal dimension reveals interesting information regarding the flow regime transition and mixing phenomenon in the bubble column.

Characteristics of horizontal liquid–liquid flows in a circular pipe using simultaneous high-speed laser-induced fluorescence and particle velocimetry

This paper describes a set of experiments on liquid–liquid flows in a horizontal circular tube. The liquids used in the experiments were an aliphatic hydrocarbon oil (Exxsol D80) and an aqueous solution of glycerol. The concentration of glycerol in the solution was adjusted so that the two liquids had the same refractive index, and optical distortions due to the curvature of the (transparent) circular tube test section were corrected for with the use of a graticule technique. The test section was far downstream of an inlet section that established an initially stratified co-current flow of the two immiscible liquids, with the Exxsol D80 oil flowing over the glycerol/water solution. The flows were investigated at the test section with the application of laser-based optical diagnostic methods, which included high-speed simultaneous Planar Laser Induced Fluorescence (PLIF), Particle Image Velocimetry (PIV) and Particle Tracking Velocimetry (PTV). These techniques allowed the reliable evaluation of the nature of the investigated horizontal liquid–liquid flows (i.e., the flow patterns from phase distribution information), together with the detailed spatiotemporally resolved measurement of key flow characteristics such as phase and velocity distributions, and also of important parameters such as droplet size. The resulting PLIF images provide a clear indication of the distribution of the phases within a plane that passed through the channel centreline, and are used to obtain qualitative information about the arising flow patterns. The images were also used quantitatively to generate data on phase distribution, in situ phase fraction, interface level and droplet size distribution. Much of the PLIF data on in situ phase fraction and interface level agrees well with predictions from a simple stratified laminar–laminar flow model. The particle velocimetry methods (PIV and PTV) provide data on the velocity profiles in the investigated flows. Over the range of superficial velocity conditions investigated, the velocity profile in the lower (heavier and more viscous) glycerol/water solution phase was typically characteristic of laminar flow, whereas in the upper (lighter and less viscous) Exxsol D80 oil phase the profile often showed a shape characteristic of turbulent flow.