Heterogeneous Distribution Of Particles Research Articles

Insight into particle size distribution and particle-scale reactions in a supercritical water fluidized bed reactor by CPFD method

Supercritical water gasification (SCWG) provides a promising solution for converting coal into hydrogen-rich gaseous. However, the modelling of the coal SCWG process still poses challenges due to the heterogeneous particle distribution, large quantity of particles, and complex chemical reactions. This study presents a novel three-dimensional numerical model based on computational particle fluid dynamics (CPFD) to study coal particle gasification in the reactor. The model integrates realistic coal particle size distribution, heat and mass transfer phenomena alongside heterogeneous/homogeneous chemical reactions across phases, elucidating multi-scale reacting flow behaviors and illustrating particle volume fraction, size, and velocity distributions. The obtained results reveal the evolution of coal composition, particle scale gasification process, and distribution of gaseous product components in the supercritical fluidized bed reactor. This work aims to serve as a reference for understanding the flow and heat transfer phenomena between supercritical water and coal particles in SCWG reactors.

Understanding the differential precipitation behavior of friction stir welded Al-Zn-Mg-Fe alloy during long-term natural aging

Al-Zn-Mg-Fe (HE700) is a new generation cast alloy based on dilute Al-Fe hypoeutectic system. Being a new member, the precipitation behavior of the HE700 alloy is not fully understood unlike its conventional 7xxx series counterparts. Moreover, presence of Fe and friction stir welding (FSW) used to join such alloys add to the complexity of the precipitation phenomenon. The present study captured the microstructural features with atomic-scale resolution that provided new insights into the nature, distribution, and evolution of precipitates in this alloy. The stir zone (SZ) and heat-affected zone (HAZ) exhibited significantly different natural aging behavior. Finer precipitates identified as GPI and GPII (Guinier Preston zones) were found to coexist with very fine zinc-rich solute clusters in the SZ. The GP zones evolved gradually and transitioned into strengthening precipitates. The HAZ, on other hand, exhibited heterogeneous distribution of coarse pre-existed particles and fine MgZn2 precipitates that were heterogeneously nucleated by localized solute supersaturation and thermally induced dislocations. Hardness variations can be correlated to precipitates evolution thereby helping design a suitable post-weld heat treatment (PWHT) process.

Effect of particle size distribution variability on the permeability of hydrate-bearing sediments: A CFD study

Natural gas hydrates (NGH) are considered as a future clean energy in the era of carbon neutrality. The seepage behaviour of hydrate-bearing sediment (HBS) and its controlling factors are significant for developing effective production strategies. In this study, we aim to elucidate how the heterogeneous spatial distribution of clayey-silty sediment particles, particularly the non-uniform particle size distribution (PSD) affects the permeability of HBS. An algorithm was developed to generate the heterogeneous spatial distribution of sediment particles based on the PSD of hydrate-bearing cores extracted from Japan Nankai Trough (D50 = 122 μm). A series simulation of fluid flow in porous media based on CFD was conducted for the HBS with varying hydrate saturations (SH). The watershed segmentation algorithm was employed for the identification of pore structure, including pore space and pore throat with a detailed analysis on the pore structure evolution with SH. Host sediments with higher uniformity result in initial high permeability but the permeability reduction with increasing SH is more significant compared with that of lower uniformity. Pore throat width reduced to less than 5 μm with SH above 50% compared with its original width of ∼30 μm. Tortuosity exhibits a linear increase with SH, while permeability decreases exponentially with increasing tortuosity. We propose an improved permeability model (KCpro) based on the classical Kozeny-Carman model accounting for the change in specific surface area for non-uniform PSD in HBS with good agreement. This study confirmed the applicability of CFD modelling as a promising tool to study the seepage behaviour of HBS complementary to classical permeability experimental tests. Results of this study provide fundamental understanding on how permeability evolves in HBS with significant PSD variations in natural gas hydrate reservoirs in nature.

Displacement Mechanism and Flow Characteristics of Polymer Particle Dispersion System Based on Capillary Bundle Model

During the development of oil reservoirs, a rapid increase in water cut following reservoir flooding leads to inefficient or ineffective circulation of injected water, rendering a significant portion of the remaining oil in the reservoir inaccessible. The displacement method using polymer particle dispersion systems effectively solves the issue of rapid water breakthrough in oil reservoirs. Owing to the particle phase separation phenomenon, polymer particles can selectively penetrate into the larger pores where water circulation is inefficient, enhance their flow resistance, and thereby achieve equilibrium displacement along with an increased swept volume. This paper investigates the heterogeneous distribution of polymer particles within a porous medium, incorporates the red blood cell dendrite concentration distribution theory from biological fluid mechanics, and develops a mathematical model to delineate the viscosity characteristics of polymer particle dispersion systems, taking into account the phase separation phenomenon. Building on this foundation, it formulates a capillary bundle model for the polymer particle dispersion system specifically designed for oil displacement and proceeds to determine its relative permeability curve. Simulation outcomes reveal that at a water saturation level of 0.063, the concentration of polymer particles in fractured large pore capillaries is markedly elevated, yet capillaries with a pore size under 26 μm remain devoid of polymer particles. With the increase of water saturation, the concentration of polymer particles in large pore capillaries reduces, whereas it progressively augments in medium pore capillaries. Upon reaching a peak water saturation of 0.751, capillaries smaller than 18 μm are entirely free of polymer particles. These findings suggest that the heterogeneous distribution of polymer particles markedly inhibits the percolation capabilities of the dispersed system following a water phase breakthrough, facilitating the entry of more dispersion into oil-laden capillaries and thus enhancing the flow capacity of the oil phase.

Nonempirical fractal permeability model and experimental verification of hydrate-bearing sediments based on heterogeneous distribution of particles

The one of the factors limiting production of gas-water is affected by sediments' permeability. Evaluating the normalized permeability (Kn) of sediments containing hydrates is necessary for analyzing the saturation (decomposition level) and flow capacity. The mistakes in Kn prediction are frequently brought about by the assumption such as homogenous particles distribution and ignoring microscopic pore structure. To address the issue, a fractal-based nonempirical prediction model of Kn was developed by modeling, parameter acquisition using SEM and Analyzer, experiment validation, error comparison with published data, and sensitivity analysis for evolution, respectively. Assuming that sediment skeleton particles were misaligned spherical particles of equal diameter. The heterogeneity of sediments was described by the vertical and horizontal distance ratio (m) and offset angle (θ) of the particles. This led to a novel approach for determining average tortuosity (τav,0) and tortuosity fractal dimension (Dτ,0). The viability of the model was confirmed by permeability measurement experiments. Additionally, using the measuring function of SEM, the maximum pore diameter of sediments was obtained. Furthermore, a comparison with earlier data demonstrated the effect. Considering heterogeneity, the average accuracy of Geometric Mean Variance in Kn has increased to 9.66%. Finally, each parameter's impact on prediction was examined. At m = 1.357, Dτ,0 grows symmetrically. Kn,GC varies 15 times more with an increase in Dτ,0 than Kn,PF. All findings indicate that the new model is more likely to be forecasted Kn for a variety of systems, including clayey-silt, sand, and silty-sand system, and especially in reflecting the heterogeneity.

Implementation and Validation of a Numerical Method for Concentrated Suspensions in Large Flows Based on the Particle Diffusion Equation

This work presents the development of an OpenFOAM solver aimed at correctly predicting dynamics of concentrated suspensions when subjected to non-uniform shear flows. The newly implemented solver is able to predict the behavior of a heterogeneous mixture whose characteristics depend on the solid particle local concentration. To simulate such behavior, the conservation equation expressing the time variation of the particle volume fraction has been implemented in OpenFOAM; this was achieved by modifying a pre-existing solver, pimpleFoam, which discretizes the Navier–Stokes system of equation through the PIMPLE algorithm. As a first step, the formulation of the momentum equation has been adapted to correctly solve cases with non-Newtonian fluids. Successively, the Krieger’s correlation has been used to model the viscosity variation in the domain to take in account heterogeneous particle distributions. Finally, the iterative cycle for the solution of the migration equation has been included within the time loop. The above-mentioned code has been successfully validated by comparing the numerical results with the measured data provided by experiments reported in literature.

Numerical investigations on water entry and/or exit problems using a multi-resolution Delta-plus-SPH model with TIC

As a classical Fluid-Structure Interaction (FSI) problem, water entry and/or exit of marine structures involve large deformations of free-surface and splashing, which have long been a great challenge for numerical modeling. Smoothed Particle Hydrodynamics (SPH) is a meshless Lagrangian particle method that has natural advantages in dealing with the non-linear variation of free-surface and moving interfaces. However, the characteristics of weakly-compressible SPH itself may lead to deficiencies such as pressure noise, tensile instability, heterogeneous particle distributions and computational inefficiency. Therefore, in this work, an acoustic damper term is formulated in the momentum equation to eliminate the amount of acoustic pressure waves induced by liquid impacts. Meanwhile, the Adaptive Particle Refinement (APR) is applied to obtain sufficiently fine particle resolution and reduce the computational cost. For the tensile instability issues induced by negative pressures, especially at the water exit stage, the Tensile Instability Control (TIC) is adopted into the SPH simulations to suppress its adverse impact. Furthermore, the Particle Shifting Technique (PST) is beneficial to the two schemes above, and it is also employed in this study. That is to say, PST can effectively solve the problem of particle disorder, which increases the accuracy and robustness of APR and reduces the momentum conservation error caused by TIC. Finally, we propose an improved Free-Surface Detection Method (FSDM) to allow the flow separation from the structure surface at the water entry stage that is impacted by PST. The fairly good agreements between the numerical results and the experimental data indicate the present SPH model can be treated as a reliable numerical tool for accurately solving such problems of structures penetrating fluid interfaces.

Effect of microstructure on mechanical, electrochemical, and biological properties of Ti/HA surface composites fabricated by FSP method

This study investigated the effect of microstructure on the mechanical, electrochemical, and biological properties of Ti/HA surface composites fabricated using the FSP method. The microstructure was altered by various traverse speeds of 30–75 mm/min. Microstructural studies revealed that lower traverse speeds (30–45 mm/min) resulted in fewer defects like voids and cracks compared to higher speeds (60–75 mm/min). A more heterogeneous distribution of HA particles in the Ti matrix was observed at higher traverse speeds due to a higher stirring effects and cooling rates. Mechanical investigations showed that ultimate tensile strength decreased with increasing traverse speed. The values for samples at 30, 45, 60, and 75 mm/min were obtained as 855 MPa, 746 MPa, 754 MPa, and 542 MPa, with a ± 4% standard deviation respectively. Electrochemical tests showed that the corrosion resistance decreased with increasing traverse speed due to more pitting corrosion occurring specifically at the interfaces between Ti/HA phases. All samples exhibited high biocompatibility, but cell viability was highest in the sample produced at a speed of 75 mm/min which had a higher amount of defects and surface agglomeration of HA particles affecting cell growth and proliferation. These findings demonstrate how processing conditions can significantly impact material properties including susceptibility to localized forms of corrosion as well as cell response over time.

Modelling of ductile failure in materials with heterogeneous particle structure using localization analysis

In this study, we evaluate the use of strain localization analysis based on the imperfection band approach to model the effect of heterogeneous particle distribution on the ductile failure of structural metallic materials. To this end, tensile tests are performed on smooth and notched samples made of aluminium alloy AA6110 with an equiaxed grain structure and an inhomogeneous distribution of the constituent particles. The constituent particles are assumed to be the main contributors to the ductile failure of the alloy. By varying the heat treatment of the alloy, three different materials are considered with different strength, work hardening, and ductility, while the grain structure and constituent particle distribution are unaltered. Finite element simulations of the tension tests are conducted using both metal and porous plasticity models and the stress–strain histories of the elements in the minimum section of the specimen are used in strain localization analyses. In these analyses, ductile failure is assumed to occur when the strain rate inside a thin, planar imperfection band becomes infinite. The imperfection band is modelled with porous plasticity, using either a higher initial porosity than in the bulk material or by adding void nucleation. It is found that the ductility of the materials is most accurately captured by modelling the imperfection band by stress-enhanced nucleation.

Cracking during freeze‐drying in dense freeze cast ceramics: Role of drying rate

AbstractCracks can form during the freeze‐drying of freeze cast ceramic suspensions while attempting to produce dense ceramics. The suspensions contain alumina particles dispersed in cyclohexane. The rate of drying is controlled by the pressure and temperature during drying (slow drying at atmospheric pressure and −15°C and fast drying under vacuum while the temperature slowly increases from −80°C to room temperature). X‐Ray micro‐computed tomography was used to characterize internal crack formation. Cracks were found to occur during freeze‐drying rather than during freezing. Both slow and fast drying produced cracks, although two different morphologies were observed. Mechanistic models are proposed for the formation of both types of cracks. The rate of freezing was found to influence the formation of cracks. Slow freezing tended to reduce the formation of drying cracks because the slower freezing produced a more heterogeneous distribution of particles and porous regions, which tends to allow stress to be relieved by opening up existing pores rather than forming cracks in the more homogeneous fast frozen bodies.

Effect of heterogeneity on interphase heat transfer for gas–solid flow: A particle-resolved direct numerical simulation

Particle-resolved direct numerical simulation (PR-DNS) of flow past a particle cluster is conducted to analyze the influence of heterogeneous particle distribution on the gas–solid heat transfer calculation. Then, the heat transfer rates calculated using Gunn's correlation are systematically compared with the DNS results for virtual computational fluid dynamics-discrete element method (CFD-DEM) grids with different levels of heterogeneity. The results show that, for a grid located at the interface between the dense cluster region and dilute region, Gunn's correlation significantly overestimates the heat transfer rate, especially at small Reynolds numbers. This is caused by the large temperature difference between the dense and dilute regions in the heterogeneous CFD-DEM grid. The value calculated by Gunn's correlation can be up to ten times the DNS result. For a homogeneous grid inside a dense region, the conventional Nusselt correlation fails to capture the rapid increase in the fluid temperature gradient around the near-interface particles when the grid approaches the cluster–fluid interface. Furthermore, even if the size of the CFD-DEM grid is reduced to twice the particle diameter, the heterogeneous particle distribution still leads to a remarkable error in the heat transfer calculation. Finally, modifications to Gunn's correlation are proposed for three typical cross-interface cases, which can well reflect the influence of the heterogeneous distribution of particles and yield a heat transfer rate close to the PR-DNS results. The mean relative deviations of the three fitted correlations are 5.8%, 14.3%, and 22.4%, respectively.

The Impact of Hidden Structure on Aggregate Disassembly by Molecular Chaperones.

Protein aggregation, or the uncontrolled self-assembly of partially folded proteins, is an ever-present danger for living organisms. Unimpeded, protein aggregation can result in severe cellular dysfunction and disease. A group of proteins known as molecular chaperones is responsible for dismantling protein aggregates. However, how protein aggregates are recognized and disassembled remains poorly understood. Here we employ a single particle fluorescence technique known as Burst Analysis Spectroscopy (BAS), in combination with two structurally distinct aggregate types grown from the same starting protein, to examine the mechanism of chaperone-mediated protein disaggregation. Using the core bi-chaperone disaggregase system from Escherichia coli as a model, we demonstrate that, in contrast to prevailing models, the overall size of an aggregate particle has, at most, a minor influence on the progression of aggregate disassembly. Rather, we show that changes in internal structure, which have no observable impact on aggregate particle size or molecular chaperone binding, can dramatically limit the ability of the bi-chaperone system to take aggregates apart. In addition, these structural alterations progress with surprising speed, rendering aggregates resistant to disassembly within minutes. Thus, while protein aggregate structure is generally poorly defined and is often obscured by heterogeneous and complex particle distributions, it can have a determinative impact on the ability of cellular quality control systems to process protein aggregates.

Droplet impact-induced molten pool dynamics and particle migration patterns during TIG-assisted droplet deposition manufacturing of SiC particle-reinforced Al–Si alloy

A three-dimensional droplet-pool coupled model with dispersed phase was developed to simulate the TIG-assisted droplet deposition manufacturing (DDM) of silicon carbide (SiC) particle-reinforced aluminum (Al) matrix composites (AMCs), which was employed to calculate the surface morphology of the deposited layer, the thermal-flow fields and the distribution state of reinforcing particles in the molten pool. The cross-section profile of a single-track SiC-reinforced AMC deposit and the distribution state of reinforcements were examined and compared with the findings predicted by simulation, a good agreement was achieved. It is found that the falling Al droplet produces an obvious crater on the curved surface of molten pool. The viscous damping and simultaneous solidification are the main factors that dissipate the kinetic energy of the droplet. In addition, we discuss quantitatively how impact-induced thermodynamic within molten pool can change the migration behaviors and the distribution state of SiC reinforcement. The heterogeneous distribution of reinforcement particles can be attributed to the thermocapillary micro-convection and the velocity difference in the spreading and recoiling stages.

Impact of highly phospholipid-containing lipid nanocarriers on oral bioavailability and pharmacodynamics performance of genistein

Oxidative stress is a leading cause of different diseases. Genistein is a valuable bioflavonoid possessing antioxidant and anti-inflammatory activity but unfortunately, it suffers from low aqueous solubility, extremely poor bioavailability and first pass effect when used in its pure state. The aim of this work was to formulate and characterize genistein-loaded highly phospholipid-containing lipid nanocarriers to improve oral bioavailability and pharmacodynamic performance. Lipid nanocarriers were prepared by the emulsification/sonication technique. The influence of phospholipid percentage (1%–10%) on physicochemical properties, drug release and stability was investigated. The particle size, zeta potential and EE% were in ranges from 211.9 ± 21.6 to 342.3 ± 7.9 nm, −11.6 ± 1.7 to −19.4 ± 3.1 mV and 78.5 ± 4.7% to 92.2 ± 1.9%, respectively. Drug release was less predominant in the case of SLN formulations when compared to corresponding NLC formulations. High phospholipid percentage produced less stable formulations in terms of particle size growth, gelation and heterogeneous particle distributions. DSC, FT-IR and XRD tools revealed that genistein has existed in an amorphous form in NLC4. The bioavailability of NLC4 was approximately 2.6-fold greater than that of conventional suspension. Additionally, lipid peroxidation in liver homogenate and histopathological alterations in liver and kidney sections were particularly improved, providing a promising strategy for oral administration of genistein.

Copper matrix composite with bimodal microstructures fabricated by liquid nitrogen temperature rolling

Liquid nitrogen temperature (LNT) rolling at a high strain rate was applied to in-situ TiB2/Cu composites fabricated by powder metallurgy. An artificially controlled heterogeneous distribution of TiB2 particles in a Cu matrix leads to bimodal microstructures in the LNT-rolled composites, i.e. reinforcement-rich regions are constituted by in-situ formed TiB2 particles and nano-Cu grains (about 25 nm), while reinforcement-poor regions are mainly composed of heavily deformed ultrafine Cu grains (about 0.5 µm). Compared with TiB2/Cu composites processed by normal rolling, LNT-rolled TiB2/Cu composites with heterogeneous microstructures exhibit good overall performance with high ultimate tensile strength (594 MPa), high elongation (6.3%), high electrical conductivity (82.6% International Annealed Copper Standard) and improved thermal stability, which is favourable for electrical and electronic device applications.

An investigation on the permeability of hydrate-bearing sediments based on pore-scale CFD simulation

The distribution pattern of CH4 hydrate in hydrate-bearing sediments (HBS) significantly impacts the permeability, which is one of the critical flow properties controlling the fluid production in the exploitation of natural gas hydrate (NGH) reservoirs. Thus, it warrants investigation on the key influencing factors, i.e., (a) hydrate saturation; (b) hydrate distribution patterns; (c) sediment particle size on the associated permeability of HBS especially at pore-scale. In this study, a series of two-dimensional geometric models were constructed that best represent the commonly-observed hydrate distribution patterns. The pore-scale flow behavior of the resulting models was simulated through computational fluid dynamics. The simulation results suggest that the reduction of permeability is dependent on the distribution pattern of hydrate. The permeability of grain-coating HBS decreases by a maximum of five orders of magnitude at SH = 0.3. Additionally, increasing SH results in new pore throats and induces clogging in fluid flow that controls permeability reduction. A strong log-log linear relationship was identified between sediment particle size and the simulated permeability. A modified empirical model for the estimation of HBS permeability was proposed considering both tortuosity and effective porosity. Moreover, a heterogeneous sediment particle distribution model was constructed for the first time that accurately described the particle size distribution of a hydrate-bearing core sample recovered from Japan Nankai Trough. Compared to the homogeneous model, a heterogeneous model results in a more substantial reduction of permeability with SH and better represents the permeability of the HBS core sample. The finding of this study can be significant in understanding the pore-scale flow behavior in HBS and are meaningful for the design of safe and effective production methods in the exploitation of NGH reservoirs.

Electrochemical behaviour of friction stir welded joints: Effect of tool shoulder diameter

In the present research work, the effect of shoulder diameter on the corrosion rate of stir zones (SZs) of dissimilar joints exposed to 3.5 M NaCl solution fabricated via friction stir welding (FSW) was studied in detail. In FSW, the tool shoulder diameter as one of the important process parameters significantly affects frictional heat input and material flow leading to the heterogeneous distribution of second phase particles (precipitates) that alters the electrochemical behaviour of FSWed joints. The influence of shoulder diameter on corrosion rate was analyzed via macro and microstructural characterization and open circuit potentiodynamic testing. The surface morphology and microstructural analysis of specimens reveal the occurrence of both pitting and intergranular corrosion (IGC) in base materials and SZs of welded specimens. Among the welded specimens, the SZ of weld I fabricated under shoulder size of 18 mm revealed the lower corrosion resistance. The potentiodynamic test revealed that weld I having very fine grains as compared to other joints exhibits the highest current density and corrosion rate.

Characterisation and structural transformation of yttria dispersed austenitic steel through VHP

Two different alloys were developed from the mixtures of pre-alloyed powders consisting of ferroalloys to get the required composition of austenitic stainless steel via the powder metallurgy technique along with the presence and absence of Y2O3. The subsequent mechanical alloyed powders were subject to vacuum hot pressing at 1200°C. The samples were subject to microstructural characterisation post-vacuum hot pressing process. With the addition of yttria, the structure of the grains was fine for the mechanical alloyed vacuum hot pressed samples. The TEM analysis revealed the presence of heterogeneous distribution of yttria particles along the grain boundaries. With the addition of yttria within the metal matrix, the hot pressed density was increased marginally.

A shock-capturing scheme with a novel limiter for compressible flows solved by smoothed particle hydrodynamics

There are many compressible flows involving strong discontinuities in nature and engineering applications. Their behaviors are complicated by the existence of shock waves, rarefaction waves and contact discontinuities. To investigate these flows, a shock-capturing scheme based on smoothed particle hydrodynamics (SPH) is proposed. In this scheme, Roe’s approximate Riemann solver cooperated with a novel limiter is embedded into the SPH governing equations to capture shocks. This limiter is simple and effective to control numerical dissipations, and the use of this limiter eliminates the tunable artificial viscosity as required by the conventional SPH. Additionally, to restore the accuracy limited by heterogeneous particle distribution that is usually encountered in the simulation of strongly-compressible flows, the gradient operator in the continuity equation is corrected by a renormalization procedure. Last but not least, for initial particle distribution, unlike the equal mass particle distribution commonly used in compressible SPH simulations, the equal spacing particle distribution is adopted in this scheme, which makes it much easier to model multidimensional problems. The present scheme has been verified by a set of benchmark tests involving contact discontinuities, extreme shock waves and strong rarefaction waves, some of which are firstly simulated by the SPH method.

Wellbore characteristics of air drilling with hammer in thick conglomerate and its influence on hole deviation

Air drilling with hammer is generally recognized as an effective drilling method, but the hole obtained in thick conglomerate formation is very irregular, and the control of hole deviation is very difficult. Although many studies have been carried out, the mechanism of this phenomenon has not been found out yet. In this paper, based on the numerical simulation of rock breaking process of air hammer, the influence of the heterogeneity of conglomerate on the wellbore regularity and hole deviation is analyzed. The results show that the direction of the bit will be changed due to the heterogeneous distribution of gravel particles, which make the wellbore with a severely irregular shape. On this basis, the finite element models of BHA in regular and irregular wellbores are established respectively, and the influence of wellbore irregularity on the stress of BHA is analyzed. It can be found the irregular wellbore is easy to form additional fulcrum, shorten the effective swing distance of pendulum bottom hole assembly. The additional fulcrum greatly changes the mechanical characteristics of the BHA, reducing the angle dropping force on bit, or even produce the angle building force.