Dispersed Region Research Articles

Deformation behavior of high speed steel/low Carbon steel composite with harmonic structure by MM/SPS process

The harmonic-structured composite that consists of a network fine grain region with a high speed steel and a dispersed coarse grain region with a low carbon steel was fabricated prepared using a mechanical milling, which is one of the severe plastic deformation method, and spark plasma sintering process. The microstructure and mechanical properties harmonic- structured composite compact were evaluated by a scaning electron microscope and a tensile test, respectively. The harmonic-structured composite exhibited high strength and enough ductility compared with a conventional particle-dispersed composite with the same weight ratio of high speed steel/low carbon steel. The microstructure observation of harmonic-structured composite revieals that the superior elongation of the harmonic-structured composite is attributed to the plastic deformation around the cracks which initiate at the network area.

Annealing Effect on Mechanical Properties of Ti-Al Alloy/Pure Ti Harmonic-Structured Composite by MM/SPS Process

The Ti-Al alloy/pure Ti harmonic-structured composite was produced by mechanical milling and spark plasma sintering process for improvement of low ductility at room temperature of Ti-Al alloy. The harmonic-structured composite with the dispersed area having coarse grained titanium and the network area having fine-grained Ti-48mol%Al alloy demonstrates high strength and high ductility at room temperature. The annealing effect of the microstructure on the mechanical properties in the Ti-Al alloy/pure Ti harmonic-structured composite are investigated. The microstructure of the Ti-Al alloy/pure Ti harmonic-structured composite annealed at 873K, 973 K and 1073 K are maintained the Ti-Al network structure and pure Ti dispersed regions, the average grain size of pure Ti dispersed region is only coarsen by annealing. The harmonic-structured composite annealed at 873K, 973K and 1073 K are maintained the high hardness. The tensile results reveal that the Ti-Al alloy/pure Ti harmonic- structured composite annealed at 873K exhibits high strength and especially high ductility.

MM/SPS プロセスにより作製したハイス鋼／炭素鋼複合調和組織材料の変形挙動

The harmonic-structured composite that consists of a network fine grain region with a high speed steel and a dispersed coarse grain region with a mild steel was fabricated prepared using a mechanical milling and spark plasma sintering process. The microstructure of harmonic-structured composite compact was observed by a scanning electron microscope and mechanical properties were evaluated by a tensile test and Vickers hardness test. The harmonic-structured composite exhibited high strength and enough ductility compared with a conventional particle-dispersed composite with the same volume fraction of high speed steel/mild steel. The work-hardening rate of harmonic-structured composite is higher than the conventional particle-dispersed composite so that the harmonic-structured material demonstrates a high elongation. The microstructure observation of harmonic-structured composite reveals that the superior elongation of the harmonic-structured composite is attributed to the plastic deformation of the dispersed area around the cracks which initiate at the network area.

Experimental investigation on the performance of drag reducing polymers through two pipe diameters in horizontal oil–water flows

In this paper, experiments were conducted to understand the influence of a small change of pipe diameter in the effectiveness of drag reducing polymer (DRP) in horizontal oil–water flow. Two pipe diameters were used in this study; 19 and 25.4mm pipes. The results showed a remarkable influence of pipe diameter on the polymer efficiency in modifying flow patterns and drag reduction. The results from both pipes showed that only 10ppm polymer concentration is needed to achieve the maximum drag reduction for each investigated condition. The presence of DRP extended the region of stratified and dual continuous flows. However, the percentage increase in the stratified region is more significant in the 25.4-mm pipe while the extent of the dual continuous pattern in the 19-mm pipe is larger than that in the 25.4-mm pipe. Regardless of the pipe diameter, annular flow changed for all the investigated conditions to dual continuous flow. The dispersed region (water continuous or oil continuous) decreased after introducing DRP but the decrease is larger for the 19-mm pipe especially for dispersion of oil in water. The results for both pipes revealed that the maximum drag reduction is achieved when the flow is dispersed oil in water; however, higher drag reduction was obtained in the larger pipe diameter. Drag reductions up to 60% were observed in the 25.4-mm pipe in comparison with up to 45% achieved in the 19-mm pipe.

調和組織構造を有するハイス鋼／炭素鋼複合材料の微細組織と機械的性質

Harmonic structured materials with fine and coarse grains demonstrate not only enhanced strength but also enough ductility simultaneously. The harmonic structured material consists of a network like a fine grain region and a dispersed coarse grain region. The high strength and enough ductility are attributed to the network fine grain region and the dispersed coarse grain region, respectively. In this study, the harmonic structured metallic composite with high speed steel (HSS) and low carbon steel (LCS) is fabricated by mechanical milling and spark plasma sintering process. The harmonic structured HSS/LCS composite consists of the network like fine grain region with HSS and dispersed coarse grain region with LCS. The hardness of the harmonic structured composite with HSS and LCS is higher than the conventional particle dispersed composite with the same HSS volume fraction.Furthermore, the harmonic structured composite with HSS and LCS indicates high tensile strength without ductility loss, compared to the conventional HSS particle dispersed composite with the same HSS volume fraction. The harmonic structure control of composite materials is effective to improve the mechanical properties with enough ductility maintained.

MM/SPS プロセスにより作製した純チタンおよび Ti-48 mol%Al 合金の複合調和組織材料の機械的性質

Ti-Al alloy demonstrates high strength in high-temperature environments. Thus, the Ti-Al alloys are expected in an application as high temperature materials. However, the Ti-Al alloys demonstrate limited ductility at room temperature. Harmonic-structured materials with a network fine grain structure and a dispersed coarse grain structure show high strength and sufficient ductility at room temperature. In addition, a composite of different materials is also effective in improving both strength and ductility. Therefore, the harmonic-structured composite with pure titanium (Ti) and Ti-48 mol%Al alloy (Ti-48Al) were fabricated by the combination of the mechanical milling (MM) and the spark plasma sintering (SPS) process. The harmonic-structured composite consists of a fine grained network Ti-Al alloy and a dispersed coarse grain Ti region. The XRD result reveals that the harmonic-structured composite is composed of Ti, TiAl, and Ti3Al phases. The harmonic-structured composite demonstrates high strength and sufficient ductility compared with the conventional compact consisting of only Ti-48Al. Advanced ductility of the harmonic-structured composite is attributed to an obstruction of the crack propagation by the dispersed coarse grain region. After heat treating the Ti/Ti-48Al harmonic-structured composite, its hardness decreased to much lesser than that of the pure Ti compact.

Experimental and numerical investigation of solid behavior in a gas–solid turbulent fluidized bed

The solid behavior in a turbulent fluidized bed was studied by combination of experimental measurements and computational fluid dynamics (CFD) simulations. Solid fractions were measured by optical fiber probe under three different superficial gas velocities and three different static bed heights at different axial levels. The experimental results showed that the lateral distribution of solid fraction is core-annulus and the operating conditions can influence the shape of the axial bed void profiles. In the CFD simulations, an Eulerian–Eulerian two-fluid model that incorporates the kinetic theory of granular flow was used to describe the gas–solid two-phase flow in a turbulent fluidized bed. A modified drag model was proposed using a scaling factor to reduce the universal drag laws, which accounts for the effect of particle clustering. The drag model can predict the coexisting regions, the bottom dense, bubbling region and the dilute, dispersed flow region observed in experiments. No significant difference was observed between results after application of laminar and turbulence model. The simulated axial bed void and radial solid fraction fit well with experimental data. The transient local solid fraction and the particle velocity were also investigated.

Horizontal liquid–liquid flow characteristics at low superficial velocities using laser-induced fluorescence

Horizontal flows of two immiscible liquids with the same refractive index, a kerosene-like hydrocarbon and a glycerol–water solution, have been instigated with planar laser-induced fluorescence in a square duct. Four flow regime categories were observed, these being: (1) stratified flow; (2) mixed flow (i.e., two distinct continuous phase regions with droplets in each); (3) two-layer flow, comprised of a dispersed region and a continuous, unmixed region (i.e., oil-dispersed flow over glycerol solution flow and, oil flow over a glycerol solution dispersion); and (4) dispersed flows (i.e., continuous oil phase dispersion and continuous glycerol solution dispersion. The flow can be described as occupying three zones; an oil phase at the top, a glycerol–water phase at the bottom, with a mixed zone between them. The vertical height covered by the mixed zone increased for increasing superficial mixture velocity, and the vertical height of the glycerol–water phase decreased for increasing input oil fraction. At low oil fractions the interface level separating the two phases was not affected by changes to the superficial mixture velocity. However, at higher oil fractions the interface height from the bottom of the channel decreased progressively as the superficial velocity was increased. Higher velocities also gave rise to increasingly fluctuating interface level heights. The mean droplet size increased initially, reached a maximum and then decreased as the oil fraction was increased, and was largest at intermediate and smallest at high superficial velocities.

CD45lowc-Kithigh cells have hematopoietic properties in the mouse aorta-gonad-mesonephros region

Long-term reconstituting hematopoietic stem cells first arise from the aorta of the aorta-gonad-mesonephros (AGM) region in a mouse embryo. We have previously reported that in cultures of the dispersed AGM region, CD45lowc-Kit+ cells possess the ability to reconstitute multilineage hematopoietic cells, but investigations are needed to show that this is not a cultured artifact and to clarify when and how this population is present. Based on the expression profile of CD45 and c-Kit in freshly dissociated AGM cells from embryonic day 9.5 (E9.5) to E12.5 and aorta cells in the AGM from E13.5 to E15.5, we defined six cell populations (CD45−c-Kit−, CD45−c-Kitlow, CD45−c-Kithigh, CD45lowc-Kithigh, CD45highc-Kithigh, and CD45highc-Kitvery low). Among these six populations, CD45lowc-Kithigh cells were most able to form hematopoietic cell colonies, but their ability decreased after E11.5 and was undetectable at E13.5 and later. The CD45lowc-Kithigh cells showed multipotency in vitro. We demonstrated further enrichment of hematopoietic activity in the Hoechst dye-effluxing side population among the CD45lowc-Kithigh cells. Here, we determined that CD45lowc-Kithigh cells arise from the lateral plate mesoderm using embryonic stem cell-derived differentiation system. In conclusion, CD45lowc-Kithigh cells are the major hematopoietic cells of mouse AGM.

Properties of energetic particle bursts at dawnside magnetosheath: Cassini observations during the 1999 Earth swing-by

[1] During Cassini's Earth swing-by in 1999, the Low-Energy Magnetospheric Measurement System (LEMMS) detected energetic particles at the distant dawn magnetosheath. LEMMS identified 9 electron bursts and continuous proton flux surges at least up to 100 keV at X = −72 Re to −102 Re during the southward turning of the interplanetary magnetic field. All bursts were anti-field-aligned and correlated with the Bz directions streaming away from the magnetosphere, indicating that they are originated in the magnetosphere. The different source locations of protons and electron bursts were suggested from the magnetic field direction during the flux enhancement owing to the high time resolution mode of LEMMS: electrons were from flank low-latitude boundary layer and protons were from wide and dispersed region in the magnetopause. Although the energy spectra of the particles in the magnetosheath were similar to that in the plasma sheet, the proton spectra showed a bend around 5 keV possibly due to scatterings and accelerations by large amplitude waves. Most of these proton spectra were well described by the kappa distributions. The fact that the electron bursts were identified only at limited locations suggested that the reconnection on the magnetopause was required at the source, while protons could leak out both from the magnetic reconnection and the continuous gradient drift with wave scatterings at the magnetopause. Within the short time snapshot of the magnetosheath, extremely active feature of the particle leakage throughout the magnetopause was revealed.

Comparison of Particle Image Velocimetry and Laser Doppler Anemometry measurement methods applied to the oil–water flow in horizontal pipe

In this work, a comparison of Particle Image Velocimetry (PIV) and Laser Doppler Anemometry (LDA) measurement methods was made applied to oil–water two-phase flow in a horizontal pipe. The experiments were conducted in a 15 m long, 56 mm diameter stainless steel pipe using Exxsol D60 oil (density 790 kg/m 3 and viscosity 1.64 mPa s) and water (density 996 kg/m 3 and viscosity 1.0 mPa s) as test fluids. The experiments were performed at different mixture velocities and water cuts. Mixture velocity and water cut vary up to 1.06 m/s and 0.75, respectively. The instantaneous local velocities were measured using PIV and LDA, and based on the instantaneous local velocities mean velocities and turbulence profiles are estimated. The measurements are performed in the vertical plane through the pipe center. A double-pulsed Nd:yttrium aluminium garnet (YAG) laser and a high-speed camera with 1260×1024 px resolution (1.3 Mpx) were used for the PIV measurements. The LDA set-up is a two-colour backscatter system with 3 W Argon-Ion Laser. The time averaged cross-sectional distributions of oil and water phases were measured with a traversable gamma densitometer. The measured mean axial velocity and turbulence profiles using PIV were observed to compare favourably well with LDA measurements. Nevertheless, the PIV measurements are more sensitive for optical disturbances in the dispersed region close to the oil–water interface. Hence, this region cannot be confidently analyzed using PIV, whereas LDA offers full-field measurements even at higher mixture velocities.

Mass Transfer in a Rotor−Stator Spinning Disk Reactor with Cofeeding of Gas and Liquid

This paper presents a new type of spinning disk reactor configuration for gas−liquid operations. It combines the features of a classical spinning disk with a liquid film on the rotor [e.g., Aoune, A.; Ramshaw, C. Int. J. Heat Mass Transfer 1999, 42, 2543−2556] and those of a rotor−stator spinning disk unit with a single gas inlet in the bottom stator [Meeuwse, M.; van der Schaaf, J.; Kuster, B. F. M.; Schouten, J. C. Chem. Eng. Sci. 2010, 65 (1), 466−471]. In this new configuration, gas and liquid are cofed through an inlet in the top stator. It is shown that gas−liquid mass transfer mainly takes place in the dispersed region between the rotor and the bottom stator. kGLaGLVR in this region is up to a factor of 6 larger than in the region with the liquid film on the rotor. Simulation of gas desorption from a saturated liquid shows that the gas−liquid mass transfer in this cofed configuration is considerably improved in comparison to the separate reactors, at similar operating conditions. The new reactor ha...

Surface and rheological properties of as-received colloidal goethite (α-FeOOH) suspensions: pH and polyethylenimine effects

The yield stress and zeta potential ( ζ) of slurries prepared from as-received goethite were evaluated as a function of pH, solids concentration, cationic polyethylenimine (PEI) concentration and molecular weight (Mw). The goethite slurries displayed a maximum yield stress at the isoelectric point ( pI). These slurries do not have a low pH dispersed region. The yield stress obeyed the yield stress–DLVO force model. The maximum yield stress displayed a dependence on the solids volume fraction to a power of 3.8. PEI adsorbed and changed both the surface chemistry and rheological yield stress of the slurries. At most additive concentration ranging from 0.1 to 0.4dwb% for PEI of Mw 600, 1800 and 70,000, the maximum yield stress of the slurries is larger than that with no adsorbed additives. At low PEI concentration of 0.1dwb%, the same maximum yield stress of 30 Pa was obtained for three Mws; 600, 1800 and 70,000 representing a 1.5-fold increase. The increased attraction between particles was attributed to charge patch attraction at low surface coverages and hydrogen bonding at high coverages. Adsorbed PEI decreased the yield stress at low pH. However complete dispersion was observed only for 0.4dwb% PEI with Mw 70,000, at pH below 7. Complete dispersion was not observed at high pH for the same polymer at all concentrations.

CFD modeling and validation of the turbulent fluidized bed of FCC particles

AbstractAn experimental and computational study is presented on the hydrodynamic characteristics of FCC particles in a turbulent fluidized bed. Based on the Eulerian/Eulerian model, a computational fluid dynamics (CFD) model incorporating a modified gas‐solid drag model has been presented, and the model parameters are examined by using a commercial CFD software package (FLUENT 6.2.16). Relative to other drag models, the modified one gives a reasonable hydrodynamic prediction in comparison with experimental data. The hydrodynamics show more sensitive to the coefficient of restitution than to the flow models and kinetics theories. Experimental and numerical results indicate that there exist two different coexisting regions in the turbulent fluidized bed: a bottom dense, bubbling region and a dilute, dispersed flow region. At low‐gas velocity, solid‐volume fractions show high near the wall region, and low in the center of the bed. Increasing gas velocity aggravates the turbulent disorder in the turbulent fluidized bed, resulting in an irregularity of the radial particle concentration profile. © 2009 American Institute of Chemical Engineers AIChE J, 2009

Micro-CT characterization of structural features and deformation behavior of fly ash/aluminum syntactic foam

The structure of a fly ash/aluminum syntactic foam was characterized using X-ray microcomputed tomography. Microstructural features, such as size, morphology and distribution of fly ash microballoons, were quantitatively related to the deformation behavior using interrupted compression tests. The syntactic foam was found to exhibit four distinct stages of deformation: (i) elastic; (ii) dispersed collapse of the fly ash microballoons; (iii) unification of the dispersed collapse region forming a band of densification, usually normal to the loading axis, via localized plasticity; and (iv) final densification. The tomographic observations show that deformation is initially controlled by the fragmentation and collapse of dispersed individual fly ash particles. After significant strain, sufficient microballoons have collapsed, localizing the stress and hence damage, and forming densification bands through severe plastic deformation of the aluminum matrix. A peak stress of 73 MPa and an energy absorption capacity of 27 MJ m −3 at 47% strain were obtained.

Numerical modeling of cryogenic chilldown process in terrestrial gravity and microgravity

In this paper, a numerical model is developed to predict the cryogenic chilldown process of a vertical tube for both terrestrial and microgravity conditions. The flow field is covered by four distinct regions, which are single-phase vapor region, dispersed flow region, inverted annular flow region, and single-phase liquid region. Heat transfer mechanisms are dictated by the flow patters. A two-fluid model is employed to analyze the dispersed flow region and the inverted annular film boiling region. Gravity effect on the chilldown process is also investigated. Model results indicate that film boiling heat transfer decreases with decreasing gravity level for the bottom flooding condition. The model results show a good agreement with the experimental data.

Modelling mass transfer in an aerated 0.2m3 vessel agitated by Rushton, Phasejet and Combijet impellers

Abstract We assembled a set of models that allows investigation of local variables that are difficult to measure, validation of mechanistic physical models, and comparison of different numerical solutions. Population balances (PB) for bubbles were combined with local flow modelling in order to investigate G–L mass transfer in an air–water system. Performance of three different impeller geometries was investigated: Rushton (RT), Phasejet (PJ) and Combijet (CJ). Simulations were compared against experimental mixing intensity, gas hold-up, vessel-averaged volumetric mass transfer rates ( k L a ), and local bubble size distributions (BSDs). The simulations qualitatively predict k L a 's with different impellers at the fully dispersed flow region and gave new insight on how k L a is formed and distributed in the stirred vessels. The used bubble breakage and coalescence models are able to describe both air–water and viscous non-Newtonian G–L mass transfer. Difference between experimental mass transfer rates of the three impellers was within experimental error, even trough the flow patterns, gas distribution, and local BSDs differ considerably. The population balance for bubbles was modelled in two different ways, with multiple size groups (MUSIGs) and with the bubble number density (BND) approach. MUSIG calculations took over twice as much computational time than BND, but there was little difference in the results. The Rushton turbine k L a was described with best accuracy, which is not surprising since most phenomenological models are fitted based on RT experiments. We suggest that these models should be validated over a wider range of vessel geometries and operating conditions.

Three-phase upward flow in a vertical pipe

In this paper we develop an approach to design a three-phase, gas–solid–liquid flow system that transports pneumatically scarified solid particles, including sticky ones, through a vertical pipe. The proposed system permits the introduction and maintenance of a liquid film that coats the pipe’s inner wall and acts as a lubricant that ensures sticky particles continue to move upward without permanently adhering to the pipe wall. The system’s operating conditions fall within the boundaries of the annular dispersed region on a typical flow pattern map of vertical flow of a gas–liquid mixture. High gas superficial velocities combined with low liquid superficial velocities characterize such a region. A combination of a modified one-dimensional, two-fluid annular dispersed flow model and a one-dimensional pneumatic conveying model is shown to describe this transport process satisfactorily. Solution of the combined models produces all the necessary design parameters including power requirements and superficial velocities of the two-fluid media needed to transport a given amount of solid particles. Results of model calculations are compared with rare three-phase flow data obtained prior to the development of the present model, by an independent experimental team that used the physical conditions of the present approach. Reasonable agreement justifies the use of the combined model for engineering design purposes.

Characterization of Hematopoietic Stem/Progenitor Property of Cells in the Culture of the Mouse Aorta-Gonad-Mesonephros Region.

The aorta-gonad-mesonephros (AGM) region is a primary source of definitive hamotopoietic cells in the midgestation mouse embryo. In the culture of the dispersed AGM region with cytokines such as stem cell factor, basic fibroblast growth factor, and oncostatin M, adherent cells containing the endothelial cells were firstly observed, and then nonadherent hematopoietic cells were produced. In the present study, we report on the characterization of hematopoietic cells that emerge in the AGM culture. Based on the expression profile of CD45 and c-Kit examined by flow cytometry, we defined three cell populations: CD45low c-Kit+ (population 1), CD45low c-Kit− (population 2), and CD45high c-Kitlow/− (population 3) cells. Cells in the population 1 exhibited immature morphology with a large nucleus and cells in populations 2 and 3 displayed morphology characteristic to granulocytes and macrophages, respectively. Expression levels of the CD31, GATA-2, and AML-1 genes were higher in cells in population 1 than in cells in the other two populations. The number of colonies formed in the semi-solid culture of cells in the above-mentioned three populations was assessed. The semi-solid colony-forming activity was much higher in cells in the population 1 than those in the other two populations. It has been reported that hematopoietic stem/progenitor cells can be detected in cobble stone area forming cells in the coculture system with stromal cells. Only the population 1 cells had cobble stone area-forming activity when cultured with OP9 stromal cells. A part of the population 1 was positive for Sca-1. Among the population 1 cells, cobble stone area-forming activity of Sca-1+ cells (i.e., CD45low c-Kit+ Sca-1+ cells) was 6-fold higher than that of Sca-1− cells (i.e., CD45low c-Kit+ Sca-1− cells). When the population 1 cells were plated and cultured on a monolayer of OP9 stromal cells, three types of cells whose characters fitted all the above-mentioned population 1, 2, and 3, in terms of the CD45/c-Kit expression profile and microscopically observed morphology, emerged again. In contrast, cells in the populations 2 and 3 had no such features. Similarly, when GFP+ population 1 cells from the GFP retrovirus-infected AGM culture were cultured again with the freshly prepared dispersed AGM region, we found all populations 1, 2, and 3 with GFP expression. These results suggested that immature hematopoietic cells in the AGM culture were highly enriched in the population 1. We next performed intrahepatic injection of the population 1 cells into irradiated newborn mice. Four months after transplantation, myeloid reconstitution was found in the spleen, bone marrow, and peripheral blood of mice transplanted with population 1 cells. Lymphoid reconstitution was also observed in the spleen and thymus of the same recipients. These results indicate that the CD45low c-Kit+ cells produced in the AGM culture have the potential to reconstitute multi-lineage hematopoietic cells.

Elementary processes of soil–water interaction and thresholds in soil surface dynamics: a review

AbstractElementary processes of soil–water interaction and the thresholds to these processes are important to understand as they control a range of phenomena that occur at the soil surface. In particular processes involved with wetting by rainfall that lead to particle breakdown are critical. This breakdown causes soil detachment and crust formation, which are both key elements in erosion.This paper reviews the range of approaches that have been taken in describing the processes associated with the wetting of a soil surface by rainfall. It assembles the studies that emphasize soil physics, soil chemistry, and erosion mechanics in a framework to enable a balanced consideration of important processes and management strategies to control erosion for a particular situation. In particular it discusses the factors associated with the two basic processes of soil structural breakdown, i.e. slaking and dispersion, and how these processes are critical in particle detachment, transport and surface crust formation. Besides the balance between the exchangeable cation composition and electrolyte concentration (measured as the sodium adsorption ratio (SAR) and total cation concentration (TCC) respectively) of the soil, the importance of energy input and soil organic matter content in controlling clay dispersion is emphasized.Based on the balance between these factors, the soil can be in one of three different regions, i.e. a dispersed region, a flocculated region and one where the resilience of the soil is variable. The implications of each of these regions to soil erosion management are briefly outlined, as are the critical roles that soil cover levels and organic matter have in controlling erosion. Finally, the relationship between various laboratory measures of aggregate stability, and corresponding field erosion characteristics, is discussed. Copyright © 2004 John Wiley & Sons, Ltd.