In a powdery layer, the shear mechanical response to impact dictates whether particles roll, slide, deposit. Existing engineering models struggle to balance computational efficiency with physical fidelity, whereas DEM remains computationally prohibitive. To address this challenge, this study develops a macroscopic constitutive model for the shear mechanical response of impact-grown powdery layers based on fractal continuum-based mechanics. Through fractal coordinate transformation, the discrete fractal layer is mapped into an equivalent continuum, from which a linear elastic constitutive relation is derived. In this model, directional codimensions , harmonic index and position-dependent intercept term serve as key links between microstructure and macroscopic response, with their evolution calibrated via DEM simulations. Results show that declines from 0.9 to 0.7 with increasing relative layer height. The harmonic index , calibrated via least-squares optimization, exhibits high sensitivity and decreases with layer height. The intercept term increases with relative layer height and load position factor, reflecting the position-dependent initial shear resistance. Validation against DEM data confirms the model's accuracy in capturing shear force-deflection behavior across varying particle sizes (20–90 ), layer heights, loading positions, and material types (copper and glass). Small particles show near-linear force-deflection relationships, while large particles exhibit rapid initial stiffening followed by nonlinear hardening. This framework provides theoretical and practical tools for macro-scale analysis of ash deposit stability under flue gas shear stress, offering a theoretical basis for predicting crack initiation and spalling.
Sewage sludge poses a major challenge for resource utilization and thermal disposal because of its high moisture content, low calorific value, and the slagging and corrosion risks associated with alkali and alkaline earth metals (AAEMs). Synergistic incineration with organic-rich fermentation residue offers a potential route for improving sludge thermal treatment; however, the particle-scale evolution and in-flame transformation behavior of AAEMs during this process remain insufficiently understood. In this study, the synergistic incineration of sludge and fermentation residue was investigated using phase-selective laser-induced breakdown spectroscopy (PS-LIBS) and OH planar laser-induced fluorescence (OH-PLIF), combined with offline X-ray diffraction and fluorescence measurements. PS-LIBS was used to track the relative spatial evolution of particle-phase Na, K, Ca, and Al, while OH-PLIF provided information on flame structure and reaction-zone distribution. The results suggest a possible particle-evolution pathway involving volatile release, fragmentation, alkali vaporization, downstream re-capture, and agglomeration, ultimately leading to the formation of composite inorganic phases. The roles of AAEMs, S, and Cl were further discussed to interpret alkali redistribution and particle-phase signal evolution. Finally, the NOx emissions during the co-combustion of sludge and fermentation residues are examined which showed a certain degree of reduction. These findings provide particle-scale insight into AAEM transformation during sludge–fermentation residue synergistic incineration and offer a useful reference for clean thermal treatment of heterogeneous organic wastes.
The cigarette rod is a typical porous medium, and its complex internal pore structure has a significant influence on draw resistance. Conventional permeability models, such as the Kozeny–Carman (K–C) model, primarily rely on bulk structural parameters and idealized assumptions. They have limited ability to characterize the heterogeneous pore networks and pore size distributions of cigarette rods, making it difficult to accurately predict draw resistance. To accurately predict cigarette draw resistance, this study used computed tomography (CT) to reconstruct the three-dimensional (3D) pore structure of cigarette rods. A machine learning (ML) model was then developed based on the extracted pore structure parameters, followed by interpretability analysis to reveal their relationship with draw resistance. First, draw resistance was measured for 12 types of cigarette samples. Then, 12 cigarettes from each category were scanned by CT to reconstruct the 3D pore structure and extract porosity, specific surface area (SSA), tortuosity, pore-scale structure parameters, including average pore diameter and pore length-to-diameter ratio, and pore size distribution parameters. Based on these data, a random forest (RF) model was developed to map pore structure features to draw resistance, and feature importance analysis with ablation studies was used to evaluate the effect of different feature combinations on prediction accuracy. The results show that, compared with the traditional K–C model, the RF method significantly improved the prediction accuracy of cigarette draw resistance. After introducing pore-scale structure parameters, the model performance was further improved. The R2 of the selected multi-parameter model reached 0.925. Further interpretability analysis indicated that average pore diameter, porosity, and the pore size distribution parameter Q90/Q10 were the key structural factors affecting draw resistance. Accordingly, incorporating Q90/Q10 into the traditional permeability model effectively improved the prediction accuracy by up to 26.6%. This study reveals the relationship between pore structure and draw resistance using an ML method, providing an effective approach for predicting cigarette draw resistance.
Mechanochemical activation (MA) uses mechanical energy to drive transformations in solids, offering a solvent-free alternative to thermal and solution-based processing. This review synthesizes the fundamentals, milling technologies, modeling approaches, and industrial applications of MA, emphasizing critical comparison rather than description. The literature was assembled through a defined search-and-screening protocol, and the resulting corpus of 182 sources is characterized bibliometrically. The fundamentals are framed as a causal chain linking mechanical energy input to defect generation, structural disorder, surface activation, and enhanced reactivity. Conventional milling systems (planetary ball mills, stirred media mills, and high-pressure grinding rolls) and emerging field-assisted approaches (plasma-, ultrasonic-, and microwave-assisted milling) are compared quantitatively by specific energy, particle size, throughput, activation efficiency, and scalability. The modeling section evaluates analytical, empirical, and computational tools—energy-size laws, population-balance kinetics, the discrete element method, computational fluid dynamics, the finite element method, and molecular dynamics—comparing their cost, accessible scales, coupling limitations, and validation, and assessing how each serves MA-specific questions. Machine learning is examined as a cross-cutting accelerator alongside its data and physical-constraint bottlenecks. Industrially, MA improves leaching, enables low-temperature synthesis, and supports waste valorization; its economic and life-cycle dimensions and scale-up barriers are discussed, and categorized research priorities conclude the review.
Transient non-local rheology in dense granular systems is governed by the coupled evolution of flow localization, dilation, stress transmission, and contact network structure. A three-dimensional discrete element model of annular shear is used to investigate the complete transition from shear start-up to statistically steady flow over a range of inertial numbers. Boundary-driven motion evolves through boundary nucleation, dilation-driven expansion, structural adjustment, and steady localization. During start-up, the localized flowing layer expands while broadly distributed weak motion contracts into a shorter creeping tail. At steady state, the flow penetration depth first increases and then decreases with inertial number, whereas the non-local decay length shows the opposite trend, confirming that appreciable flow penetration and creep attenuation characterize complementary aspects of non-local propagation. Axial stress undergoes near-surface concentration, dilation-induced release, and force chain mediated recovery, while the velocity field remains localized even after stress homogenization. Dilation transforms the initially dense contact network into a sparse and spatially differentiated load-bearing structure. Strong contacts carry the dominant and nearly constant share of the normal load and govern stress transmission and shear resistance, whereas weak contacts maintain geometric connectivity and buffer disturbances in the creeping bulk. Normal force anisotropy is dominant and remains nearly coaxial with the deviatoric stress, while geometric fabric anisotropy shifts from the creeping skeleton toward the localized flowing layer as inertia increases. These findings provide a micromechanical basis for non-local constitutive models incorporating compressibility, dynamic fabric, and the differentiated roles of localized flow and creep.
A cold-model circulating fluidized bed is used to investigate gas–solid flow behavior in tapered-in risers with inclined angles of 0.3°, 0.5°, and 0.7°, with a conventional cylindrical riser as a reference. Local solids holdup and particle velocity are measured using optical fiber probes. The tapered-in risers exhibit a distinct S-shaped axial solids holdup profile and a continuously decreasing particle velocity along the axial direction, in contrast to the typical C-shaped solids holdup profile and bottom particle-acceleration region observed in the cylindrical riser. The bottom section of the tapered-in riser remains in a dilute fast-transport state because of the high local gas velocity, whereas the middle section becomes the main flow-transition region. In this region, the decrease in local gas velocity caused by cross-sectional expansion is not followed immediately by particle deceleration, leading to near-wall accumulation, back-mixing, local internal circulation, and the highest solids holdup. Radially, the cylindrical riser shows a core–annulus structure that weakens after the bottom acceleration region, while the tapered-in risers develop stronger core–annulus structures in the middle and upper sections. A mechanistic analysis based on the Kutta–Joukowski (K-J) force further indicates that the radial non-uniformity of local solids holdup is closely related to the K-J force acting on particles. The K-J force analysis helps explain the development of near-wall solids accumulation and core–annulus structures, and its magnitude is jointly affected by slip velocity and particle-velocity gradient. Mesoscale analysis further shows that near-wall clusters in the middle and upper sections of the tapered-in riser are denser and more persistent, although their occurrence frequency is lower. These results clarify the geometry-induced flow restructuring in tapered-in risers and provide hydrodynamic guidance for the design of tapered-in riser–turbulent bed coupled reactors for PDH.
In underground tunnelling, it is essential to prevent sedimentation and clogging of the slurry circulation pipelines in slurry shields, as otherwise a series of consequences will occur that eventually lead to failure of the tunnel working face. The present study proposes a method to induce swirling motions in the slurry-stone transport pipeline using swirl induction pipes to sweep the accumulated stones at the pipe bottom into the mainstream and sustain their suspension, thereby minimizing the risk of clogging. We established a CFD-DEM (Computational Fluid-Discrete Element Method) coupled simulation, together with an Archard wear model, to predict the complex slurry-stone interaction, the inter-particle and particle-wall interactions during the transport of excavated coarse stones in non-Newtonian bentonite slurry within the circulation system. We validated the model against available experimental data and employed the validated model to evaluate the enhancement of hydraulic transportation by swirl pipes with various pitch-to-diameter (PD) ratios at different slurry inlet velocities, in terms of slurry flow pattern, particle distribution, slip factor, particle accumulation rate, pressure loss and pipeline wear. Special attention was paid to the potential of swirl pipes to operate at a fraction of the conveying velocity required for conventional circular pipe systems without the risk of clogging. The study demonstrates that a suitable fraction of the conventional conveying velocity and an optimal PD ratio for the swirl pipe can be achieved to reduce pumping energy, pressure loss and wear, thereby saving operation and maintenance costs.
Steelmaking produces large quantities of iron-rich by-products and their recycling improves resource efficiency and reduces waste generation. This work investigates the potential for utilizing mill scale to produce self-reducing briquettes assessing the effectiveness of recycled Arabic gum as a sustainable binder compared to conventional starch. The briquettes were produced by combining the mill scale with different reducing agents: olive pomace biochar pyrolyzed at 750 (OP750) and 350 °C (OP350), and cupola furnace dust (CFD). By using Arabic gum instead of starch, an improved resistance to impact was observed for each mixture (1000 for OP750 and CFD versus 767 and 191, respectively). Recycled Arabic gum, also, limited the swelling of each mixture and promoted the sintering of the briquettes. On the contrary, the starch favored an increase in volume (maximum 153.62%) until 1200 °C. Furthermore, the Arabic gum enhanced the reduction capacity of the mixture while preventing chemical or morphological variations in the reduction products and leading to an increase of up to 9.06% in the degree of metallization with OP350. Overall, most the results obtained using Recycled Arabic gum exceeded the industrial benchmark, confirming the feasibility of its usage as a substitute for starch in self-reducing briquettes.
We present the development of a cost-effective detector system for positron emission particle tracking (PEPT) inside dense granular media [1, 2, 3]. The detector is based on the coincident detection of the two back-to-back 511keV gamma rays produced by electron-positron annihilation. In contrast to most PET systems, which typically employ inorganic crystal scintillators, our design uses elongated organic scintillator bars that are read out at both ends by 2 × 2 arrays of silicon photomultipliers (SiPMs). The detector consists of four modular walls, each comprising 22 scintillator bars, surrounding an observation volume of approximately 0.5m × 0.5m × 1m.In this work, the position of a stationary radioactive positron source is reconstructed using the first commissioned detector configuration, consisting of two opposing walls with every second scintillator bar instrumented. The complete detector readout chain and the data processing and reconstruction algorithms are presented in detail. By exploiting precise timing information from the scintillation signals, the annihilation position is reconstructed using consecutive time-of-flight (ToF) analyses. The experimental results are compared with previously published Monte Carlo simulations of the same detector configuration.Although only one quarter of the final detector is currently operational, the reconstructed source position exhibits a root mean square deviation below 3.2mm. These results demonstrate the feasibility of the proposed detector concept and provide a strong experimental foundation for the completion of the full four-wall PEPT system.
