Mixed Particles Research Articles

Vertical Variability in morphology, chemistry and optical properties of the transported Saharan air layer measured from Cape Verde and the Caribbean.

The structural properties of the Saharan air layer (SAL) including chemical, morphological and optical properties were measured during the Saharan Aerosol Longrange TRansport and Aerosol Cloud interaction Experiment (SALTRACE- June/July 2013). Flight measurements were done from Cape Verde and the Caribbean. Changes happening with the chemical composition, mixing, shape and absorption of aerosol single particles (particle diameter range 0.5-3.0 µm) inside SAL during its transport are detailed. Dust-dominated SAL (relative number abundance >90%) and generally low mixing (<1% with sea-salt and sulphates) are observed at both locations. The change in shape (determined as aspect ratio (AR)) after transatlantic transport was statistically not significant. The iron oxide fraction, important for light absorption, contributed 6.0-6.8% to SAL dust. A lower amount of Fe oxides was observed in transported SAL, especially for the size range 0.5-1.5 µm. This reduction in Fe oxide content resulted in a 4% decrease (0.0046-0.0044) in dust imaginary refractive index and a 1% decrease in single scattering albedo (0.802-0.809) at 520 nm. Our work suggests including the size distribution of iron oxides and their particular behaviour in future experiment/model studies.

Study on the resistance of basalt fiber concrete to erosion of building structure by wind gravel flow

Concrete structures in the windy regions of the Gobi face constant erosion from wind gravel flow, leading to severe surface damage and significantly reduced durability. This paper investigates the erosion resistance of basalt fiber (BF) concrete under various erosion conditions using the air-flow sand injection method. The results indicate that adding 0.15% BF to concrete reduces its erosion rate by 20.7% to 21.5% compared to concrete without BF. Therefore, a BF content of 0.15% provides optimal erosion resistance for the concrete. The correct amount of BF bonds tightly with the cement mortar, forming a mesh structure inside the concrete that absorbs the kinetic energy of gravel impacts. The concrete erosion process can be divided into an early accelerated phase and a later stabilized phase. Throughout these phases, the erosion rate of concrete increases with the erosion angle (EA), erosion wind speed (EWS), and gravel flow rate (GFR). In particular, the erosion rate of BF15 concrete increased by 35.6 to 46.4mg/cm² when the EA changed from 15° to 90°. Notably, surface damage from low-angle erosion mainly consists of cut scratches, while high-angle erosion primarily results in erosion pits. As the grain size of the eroded gravel increases, the erosion rate of the concrete decreases. However, when a single large gravel particle impacts the concrete, it creates a larger and deeper erosion pit. Furthermore, the erosion rate of BF concrete exhibits a strong negative linear correlation with its mechanical properties, with an R² value exceeding 0.88. Moreover, erosion reduces both compressive and splitting tensile strengths of concrete. For BF15 concrete, however, the decreases are minimal: compressive strength drops by just 1.2MPa, and splitting tensile strength decreases by only 0.2MPa. Building on Bitter and Neilson’s theoretical erosion model, an improved erosion model for BF concrete has been developed under wind gravel flow. This model incorporates the BF mixing factor and particle size function while considering other erosion parameters comprehensively. The enhanced model provides a theoretical foundation and scientific basis for safeguarding concrete structures in Gobi wind-prone regions.

GPU based discrete element modeling for convex polyhedral shape particles: Development and validation

Particle dynamics simulations face a significant challenge in understanding the intricate behaviors of convex polyhedral particles due to their complex geometries and interactions. DEM emerges as a key method, illuminating the concealed intricacies of these geometric entities. Traditional algorithms often require cumbersome processes to check each type of contact individually. However, Gilbert-Johnson-Keerthi’s (GJK) and the expanding polytope algorithm (EPA) provide efficient numerical solutions for polyhedral contact detection and contact resolution. These Minkowski difference-based methods streamline contact detection and overlap computation, paving the way for deeper exploration of three-dimensional contact theory within DEM simulations. By leveraging GPU computational power, this paper outlines key algorithmic steps and verifies the code’s accuracy through comparison with simulated and experimental data, with an average deviation of less than 5%. This study explores the impact of particle shape on the dynamics and mechanical behavior of densely packed systems, particularly in hoppers and tumblers. Spherical particles discharge faster but mix more slowly than polyhedral shapes, with icosahedrons achieving quicker full mixing. These results align with experimental findings, further validating the simulation approach.

Numerical study of the effects of unmatched pressure on the supersonic particle-laden mixing layer

The dispersion of monodisperse, inertial particles in a supersonic mixing layer consisting of two sheared flows with differing pressures (P1 for the particle-laden jet flow and P2 for the airflow) is numerically investigated using large Eddy simulation and Euler–Lagrange methods. The calculations reveal the following insights: The pressure disparity between the two flows induces a transverse gas flow effect, which swiftly deflects the mixing layer from the high-pressure side to the low-pressure side. The growth rate of mixing layer increases with the ratio of P2/P1 and while the deflected displacement correlates with the pressure difference |P2-P1|. However, the particles exhibit delayed tracking characteristics to the deflected mixing layer because of their relative relaxation to the transverse gas velocity, particularly in the upstream region of the mixing layer (also known as the Kelvin–Helmholtz instability developing zone or KH zone). Notably, when the P2 exceeds that of the P1, particles can more easily penetrate into the vortices of KH zone, significantly enhancing the downstream gas–particle mixing. This mixing enhancement is particularly pronounced for larger particles due to their increased inertia, which allows them to advance into the vortices of KH zone more effectively than smaller ones.

How Porosity Influences the Heterogeneous Ice Nucleation Ability of Secondary Organic Aerosol Particles

AbstractDuring processing in deep convective cloud systems, highly viscous or glassy secondary organic aerosol (SOA) particles can develop a porous structure through a process known as atmospheric freeze‐drying. This structural modification may enhance their heterogeneous ice nucleation ability under cirrus conditions through the pore condensation and freezing mechanism. Pristine, compact SOA particles, on the other hand, are recommended to be treated as ice‐inactive in models. This recommendation also applies to internally mixed particles, where a coating layer of secondary organic matter (SOM) deactivates the intrinsic ice nucleation ability of the core, which may be a mineral dust grain. Ice cloud‐processing may also improve the ice nucleation ability of such a composite particle by inducing structural changes in the coating layer, which can release active sites on the mineral surface. In this work, we investigated the change in the ice nucleation ability of pure SOA particles from the ozonolysis of α‐pinene and two types of internally mixed particles (zeolite and coal fly ash particles coated with SOM) after being subjected to the atmospheric freeze‐drying process simulated in an expansion cloud chamber. For pure α‐pinene SOA, we found only a slight improvement in the ice nucleation ability of the ice cloud‐processed, porous particles compared to their pristine, compact counterparts at 221 and 217 K. In contrast, the zeolite and coal fly ash particles, which were initially deactivated by the organic coating, became significantly more ice‐active after atmospheric freeze‐drying, emphasizing that such composite particles cannot be excluded from model simulations of heterogeneous ice formation.

Influence of mixed particle sizes on shear yield stress of magnetorheological fluid

AbstractThis study investigated the effect of magnetic particle size and volume fraction on the shear yield stress and dynamic viscosity of magnetorheological fluids. Magnetorheological fluids with varying volume fractions of micro‐ and nanoscale magnetic particles were prepared. A plate‐on‐plate shear test bench was constructed to evaluate the fluids under a constant shear rate, with the applied current ranging from 0 A to 1.2 A. Results indicated that the shear yield stress initially increased and then decreased as the volume fraction of magnetic nanoparticles increased, reaching a maximum of 47 kPa at a volume fraction of 7 %. However, the excessive addition of magnetic particles or large‐diameter particles led to settling and reduced stability of the fluids. The findings suggest that optimizing the size and volume fraction of magnetic particles is crucial for maximizing the shear yield stress of magnetorheological fluids.

Nanoparticle integration in adhesive and hybrid single lap joints: effect on strength and fatigue life under environmental aging

Examining the mechanical performance of CFRP and aluminum samples subjected to environmental aging is crucial. Additionally, it is essential to develop methods to enhance their mechanical properties. This research investigates the impact of fullerene and single-walled carbon nanotubes (SWCNT) on the fatigue life and static strength of bonded and bonded/bolted joints. The study focuses on composite-to-composite (CTC) and composite-to-aluminum (CTA) substrates under three-point bending, both before and after hygrothermal aging. The samples were divided into four categories: (1) neat specimens, (2) specimens with added fullerene, (3) specimens with added SWCNT, and (4) specimens with a combination of 50% SWCNT and 50% fullerene. The experimental results indicated that the optimal nanoparticle ratio for bonded joints differs from that for bonded/bolted joints. Adding nanoparticles to the adhesive increased the fatigue life of SLJs, particularly in samples containing mixed particles and SWCNT. In some cases, nanoparticles amplified the effect of hygrothermal conditions, enhancing fatigue life further. The integration of nanoparticles into the adhesive and the use of bonded/bolted joints significantly improved joint strength, with the combination of both techniques yielding the best results. These modified joints offer a promising alternative to traditional joints in terms of strength and fatigue life. The study enhances understanding of the aging of adhesive and hybrid joints, especially dissimilar joints (composite to metal), and provides insights into their behavior under various environmental aging conditions. These methods show potential for optimizing joints and composite structures, improving durability, and reducing the likelihood of operational failures.

Combustion synthesis and photoluminescence of Ca2SrWO6:Dy3+ double perovskite: An approach for white light emission

Luminescent Ca2SrWO6:Dy3+ double perovskites are synthesized via the combustion route of material synthesis, wherein urea is taken as fuel. The as-prepared phosphor series comprehensively characterized for their structural and photoluminescence (PL) properties. The Rietveld refinement of XRD data revealed monoclinic crystallized microcrystals with mixed particles of the size of less than 1 µm, studied via SEM. Ca2SrWO6:Dy3+ displayed standard Dy3+ transitions 4F9/2–6H15/2 (blue emission) and 4F9/2–6H13/2 (yellow emission) collectively resulted in white light emission, confirmed via CIE study. Under 278 and 388 excitations, 2 mol% doping of Dy3+ found to be optimum concentration, beyond which concentration quenching is observed due to dipole–dipole interaction. The Y/B ratio ∼1 shows potential to produce white light and make phosphor suitable for WLED applications. The Ca2SrWO6:Dy3+ phosphor displayed notably high thermal stability with PL intensity persisted 77.6 % at LED burning temperature (150 °C) when compared to PL intensity attained at room-temperature, which is basically due to the rigid perovskite structure. In addition, the PL decay lifetime of 4F9/2 state was calculated by utilizing decay curves. Subsequently, the PL quantum efficiency and non-radiative relaxation rate are determined. The theoretical model of Auzel’s fit function is used to calculate to quantum efficiency and was found to be 93.27 % for Ca2SrWO6:2 % Dy3+ phosphor. Moreover, the photometric results reveals that the CIE points are lies in white region of CIE diagram with comparable CCT. The collective results indicated the utility of the phosphor for potential WLED applications.

Organic Carbon Reaction Kinetics in Bioturbated Sediments

AbstractMost organic carbon delivered to the seafloor is degraded within the bioturbated layer. Theory and empirical evidence have shown that organic carbon reactivity relates to the age of a particle. However, due to particle mixing, the age‐depth linear relation induced by sediment accretion is obfuscated. Here we combine a Lagrangian particle tracking model that resolves the age distribution of particles in the bioturbated zone and couple it to age‐dependent organic carbon degradation. Depth profiles for organic carbon concentration, reactivity and degradation rate are presented for sediments receiving low and high reactivity organic carbon in coastal, continental slope and deep‐sea environments. Our results show that a simple first‐order kinetics model suffices for well‐mixed sediments and systems receiving pre‐processed materials. A reactive continuum approach is needed for poorly mixed sediments receiving highly reactive organic carbon and for sediments below the bioturbated layer.

Power production characteristics of binary particles pulsed anaerobic fluidized bed microbial fuel cell

A novel binary particulate pulsating anaerobic fluidized bed microbial fuel cell (BPFB-MFC) was designed and constructed in order to improve the efficiency of low-grade energy conversion in sewage. The effects of pulsed liquid flow rate and bed filling rate on the electricity production performance and effluent treatment characteristics of the BPFB-MFC were investigated experimentally. The results showed that when the pulsed liquid flow was u=1.95sin(π/3)t cm·s-1 and when the bed materials in the anode chamber consisted of 10% bed height activated carbon particles and 10% bed height ceramic particles, the highest voltage produced was 519.7mV, the highest power density was 587.5mW·m-2, and the lowest internal resistance was 171.2Ω, which was the optimal experimental working condition. It was found that the electricity production performance and effluent treatment efficiency of the mixed particles system were better than those of a system with single particles. This work held promise of promoting the industrialization of MFC.

A CFD and experimental study of hydrodynamic and heat transfer behavior in ribbed fluidized beds

Abstract The study focuses on enhancing the performance of fluidized bed systems, which are widely used in industrial processes requiring efficient heat and mass transfer. By integrating ribs at angles of 135, 150, and 165° on the riser wall, the research assesses their impact on hydrodynamic behavior and heat transfer using CFD simulations. The simulations, confirmed through experimental data, revealed that the 150° ribbed model outperforms others by improving particle mixing and achieving the highest heat transfer coefficient. The investigation also covered static pressure, solid volume fraction, and particle velocities at different bed heights (30, 60, 90, and 120 mm), showing that ribbed models significantly enhance turbulence and particle distribution, with the 150° ribs providing a balance between dynamic mixing and stable flow.

Shear characteristics of nonuniform distribution of granular materials in ring shear test and impact on landslides

Knowledge of the shear behavior of landslide soil is very important for understanding landslide dynamics. This study investigated the shear behavior of base soil particle materials using ring shear tests with glass beads. Samples with varying particle sizes and distributions were examined to explore how particle size affects shear behavior at different shear velocities. Analysis of the samples included assessment of shear stress, displacement-shear stress fluctuations, and changes in the shear stress standard deviation. Results showed that with increasing shear displacement, shear stress fluctuations stabilize. Rather large difference particle size differences lead to more uniform particle mixing and a lower shear stress standard deviation. Conversely, when smaller particles predominate, particle mixing is less uniform, resulting in a higher shear stress standard deviation. Additionally, this study discussed the shear dilation and compaction mechanisms of samples under large displacement shear.

An experimental setup for studying conduction and radiation heat transfer in a rotary drum

This study presents the development of a novel heating system that aims to bridge the experimental gap for analyzing both radiation and conduction heat transfer in a rotary drum. The experiments were conducted by loading the drum with 4 mm silica glass beads at varying fill levels (10 %, 17.5 %, and 25 %) and rotation rates (2, 5, and 10 RPM), and monitoring the temperature evolution with an infrared camera. Higher fill levels resulted in lower average particle bed temperatures, while rotation rate influenced the contact time between particles and the drum wall and the exposure to radiative heat. A rotation rate of 5 RPM resulted in the highest average bed temperature due to optimal contact and exposure time for conduction and absorption of radiative heat, respectively. Thus, a balance between adequate particle mixing and optimal contact/exposure time is crucial for maximizing heat transfer efficiency in rotary drums exhibiting conduction and radiation.

Configuration optimization of a biomass chemical looping gasification (CLG) system combined with CO2 absorption

Biomass chemical looping gasification (CLG) combined with CO2 absorption in a dual circulating fluidized bed (DCFB) has emerged as an advanced technology for clean and efficient biomass utilization, yet the reactor design for achieving higher gasification performance and the in-depth understanding of physical-thermal-chemical characteristics is still lacking. This study presents an optimized design aimed at enhancing hydrogen production and carbon reduction in the biomass CLG process with a DCFB reactor by employing the multiphase particle-in-cell (MP-PIC) method integrated with thermochemical sub-models. The proposed reactor is comprehensively compared with the original reactor from the experimental setup in terms of particle mixing, heat transfer, and gasification behaviors. The results indicate that compared to the original setups, the proposed CLG system demonstrates: (i) an improved gas-solid mixing, as evidenced by the particle mixing index rising from 0.23 to 0.34; (ii) an enhanced particle heat transfer coefficient, which boosts heat and mass transfer process; (iii) a 10.11 % increase in H2 concentration alongside a 23.71 % decrease in CO2 concentration; (iv) a particle distribution characterized by higher concentration at the bottom and lower concentration at the top, along with intensified particle back-mixing. The pressure drop inside the combustor is higher than that in the gasifier. A smaller absorbent mean particle diameter and lower-positioned biomass feeding port contribute to the improvement of the CLG performance.

Particle Dynamics Study on Influencing Factors of Ice Slurry Flow Characteristics in District Cooling Systems

In district cooling systems, substituting the conventional cooling medium with ice slurry represents an ideal approach to achieve economical operation. During pipeline transportation, ice slurry exhibits heterogeneous flow characteristics distinct from those of pure fluids. Consequently, investigating the flow field characteristics of non-homogeneous ice slurry, quantitatively analyzing the rheological variations and flow resistance laws due to the uneven distribution of ice particles, and standardizing the comprehension and depiction of flow patterns within ice slurry pipes hold significant theoretical importance and practical value. This study analyzes the heterogeneous isothermal flow characteristics of ice slurry in a straight pipe by employing particle dynamics and the Euler–Euler dual-fluid model. Taking into account the impact of ice particles’ non-uniform distribution on the rheological properties of ice slurry, a particle concentration diffusion equation is incorporated to develop an isothermal flow resistance model for ice slurry. The flow behavior of ice slurry with initial average ice particle fractions (IPFs) ranging from 0% to 20% in DN20 horizontal straight and elbow pipes is examined. The findings reveal that the degree of heterogeneous flow in ice slurry is inversely proportional to the initial velocity and directly proportional to the initial concentration of ice particles. When the flow velocity is close to 0.5 m/s, the flow resistance of ice particles exhibits a linear positive correlation with changes in flow velocity, whereas the flow resistance of the fluid-carrying phase displays a linear negative correlation. As the flow rate increases to 1 m/s, the contribution of each phase to the total flow resistance becomes independent of the initial velocity parameter. Additionally, the drag fraction of the ice particle phase is positively associated with the initial concentration of ice particles. Furthermore, the phenomenon of “secondary flow” arises when ice slurry flows through an elbow, enhancing the mixing of ice particles with the carrier fluid. The extent of this mixing intensifies with a decrease in the turning radius and an increase in the initial velocity.

Impact of axial segregation characteristics on the particle collision energy in rotating drums

The particle mixture in rotating drums is not always in a completely mixed state, resulting in a complex relationship between the particle mixing and segregation characteristics and the overall collision energy. Based on existing experimental validation, the rotary drums with axial adjacent segments are numerically simulated via the discrete element method to investigate the axial segregation mechanism of the particle mixtures in rotary drums. The results show that the rotational direction of the adjacent axial segments changes the axial flow configuration, resulting in a transformation of the overall particle mixing and segregation characteristics. Based on the proposed novel relative regional total energy (RRTE) index, this work further evaluates the impact of the axial segregation characteristics on the collision energy of binary and ternary particle mixtures within rotary drums. The axial segregation phenomenon makes the RRTE of each radial surface inconsistent, resulting in difficultly reflecting the particle collision energy through the individual radial surface. Compared with the radial drum surface, the RRTE represented by the axial surface can better reflect the particle collision energy in rotating drums. In summary, the more obvious the presence of axial segregation characteristics in rotary drums, the lower the total collision energy used for overall grinding process of the media and abrasive particles.

Prediction of rod-like particle mixing in rotary drums by three machine learning methods based on DEM simulation data

The mixing of non-spherical particles in rotary drums exhibits significant complexity, particularly when density segregation and size segregation occur simultaneously. Three machine learning models: artificial neural network (ANN), extremely randomized trees (ERT), and particle swarm optimized support vector regression (PSO-SVR) were developed to predict the mixing time and mixing degree at the steady mixing state of rod-like particles in rotary drums. The training, validation, and test data for the machine learning models were generated from 121 discrete element method (DEM) simulations with four independent variables: revolution frequency, particle density ratio, particle size ratio, and drum length. All three models predicted the mixing degree accurately with R2≥ 0.94. The ERT and PSO-SVR models also predicted the mixing time well with R2≥ 0.88. Building machine learning models is hundreds of times faster than running DEM simulations, making these models highly promising for predicting larger-scale simulations with more complex-shaped particles.

Recycling mixed polymer particles using a spiral tube tribo‐electrostatic separation device

AbstractAt present, research on the electrostatic separation of polymers is primarily concentrated in the WEEE field, with limited studies addressing the electrostatic separation of vehicle polymers. In this study, tribo‐charging separation of PA66/PP (modified)/PE three‐component vehicle polymer mixed particles was investigated using a spiral tube tribo‐charged separation device. Firstly, a force model of particle movement in the spiral tube was established, and the theoretical analysis determined that the critical rotational speed of particle centrifugal movement is 70 rpm. Secondly, the optimal charging parameters were determined by single‐factor experiments and orthogonal experiments, and the effect of the blanking baffle on the particle charging was also investigated. Finally, high‐voltage electrostatic separation simulations and experiments were carried out, achieving separation purities of 92.8% for PA66, 80.7% for PP (modified), and 86.6% for PE, respectively. Results provide both theoretical and experimental reference for one‐pass electrostatic separation of three kinds of plastic particles by spiral tube turbo‐charged separation device.Highlights Separation of vehicle polymers is crucial for its high‐value‐added recycling. A spiral tube tribo‐electrostatic separation device is developed. The critical rotational speed of particle centrifugal movement is analyzed. The influence of the blanking baffle on the particle charge is investigated.

Investigations into the flow dynamics of mixed biomass particles in a fluidized bed through Hilbert-Huang transformation and data-driven modelling

Flow dynamics of binary particles are investigated to realize the monitoring and optimization of fluidized beds. It is a challenge to accurately classify the mass fraction of mixed biomass, considering the limitations of existing techniques. The data collected from an electrostatic sensor array is analyzed. Cross correlation, empirical mode decomposition (EMD), Hilbert-Huang transform (HHT) are applied to process the signals. Under a higher mass fraction of the wood sawdust, the segregation behavior occurs, and the high energy region of HHT spectrum increases. Furthermore, two data-driven models are trained based on a hybrid wavelet scattering transform and bidirectional long short-term memory (ST-BiLSTM) network and a EMD and BiLSTM (EMD-BiLSTM) network to identify the mass fractions of the mixed biomass, with accuracies of 92% and 99%. The electrostatic sensing combined with the EMD-BiLSTM model is effective to classify the mass fraction of the mixed biomass.

Investigation and prediction of impact of aggregate size and shape on porosity and compressive strength of pervious concrete

ABSTRACT Pervious concrete is proven to environmentally benefit urban pavement construction. Optimising compaction energy evidently reduces uncertainty in the mass production of pervious concrete with uniform characteristics. The distribution of compaction energy in wet mix and rearrangement of binder-coated aggregate particles are affected by the size and shape of aggregates. This study analyses the impact of aggregate size and shape on porosity and compressive strength prediction from mix-design parameters. Aggregate-to-cement ratio (3, 4 and 5), compaction (0, 30 and 60 blows from standard Proctor rammer), aggregate sizes (5–12 mm, 12–18 mm and 18–25 mm) and aggregate shape (0, 200 and 1000 revolutions of milling in Los Angeles Abrasion Value) were used to cast a total number of 486 samples. Constituents were mixed in an electrically powered drum of capacity 96 L, for 20 min. Porosity was computed from constituent ratios (theoretical porosity) and apparent weight (measured porosity). The compressive strength of samples was recorded using a Universal Testing Machine. The measured porosity and theoretical porosity relationship was significantly affected by the shape of the aggregate and not by the size. Modified Ryshkewitch’s model predicted compressive strength from porosity, aggregate-to-cement ratio, compaction and aggregate size and shape with an accuracy of 0.92 (R2). Two of six arbitrary constants depended on aggregate shape and size.