Initial Solid Volume Fraction Research Articles

Packing properties assessment of cement and alternative powders: Artefacts and protocols

This paper introduces three major recommendations for the assessment of the maximum packing fraction of mineral powders through compressive rheology. First, our results show that a minimum compressive stress is required for the measured solid volume fraction to tend towards a constant jamming fraction. Second, we show that the modification of the particles surface properties, especially their friction coefficient, by polymer adsorption, allows for this jamming fraction to get closer to the particle maximum packing fraction. Finally, we show that a minimal value of the initial solid volume fraction of a sample is necessary to prevent particle size separation during testing. We moreover show that the measured jamming fraction depends on the initial solid volume fraction of cement-based samples. We suggest that such a peculiar behavior finds its origin in the dependency of early hydrates volume or morphology on the initial supersaturation.

Understanding the thixotropic structural build-up of C3S pastes in the presence of polycarboxylate superplasticizers

Due to the physical and chemical effect of polycarboxylate (PCE) ether superplasticizers on the simultaneous hydration of aluminate phase and silicate phase, the structural build-up of cement paste with PCE remains a much-complicated process. In order to reveal the underlying mechanism, this study reports the thixotropic structural build-up of C3S paste with PCE in the early stage (stage I before initial setting, within 1500 s). It should be subdivided into stage I′ (rapid non-linear increase) and stage I″ (slow linear development), since PCE significantly prolongs the duration of stage I′ from ∼10 s to ∼1000 s. Although PCE does not alter the origins of thixotropy (CSH/C3S cohesive forces and colloidal interactions), it can change the magnitude of driving forces, greatly depending on its adsorption in the pseudo-contact region. Consequently, the dominant driving force in stage I′ is C3S cohesive force, while it is colloidal interactions in stage I″. The quantitative models of colloidal percolation characteristic time (tperc) and thixotropic structural build-up rate (Gthix) are developed, both of which are determined by the surface coverage and initial solid volume fraction. Increasing PCE dosage augments tperc and diminishes Gthix, until reaching the maximum adsorption threshold (not full surface coverage), beyond which further PCE increase has a minimal effect on tperc and Gthix.

CFD-DEM numerical investigation of the effects of water content and inclination angle on interactions between debris flows and slit dam

Debris flows, composed of sediment–water mixtures, can pose significant risks to downstream populations and infrastructure in mountainous regions. Slit dams have been demonstrated as being effective measures for decreasing the destructivity of debris flows. Reliable evaluations of the interactions between debris flows and slit dams are challenging if the complicated component characteristics of debris flows, such as the water content, are not considered. Here, a multi-scale study of debris flows impacting a slit dam is conducted via computational fluid dynamics and discrete element method (CFD-DEM) simulations to understand the influences of the water content (controlled by solid volume fraction in this study) and the channel inclination angle on flow–slit dam interactions. The results indicate that both the initial solid volume fraction and the channel inclination angle have significant effects on the impact kinematics of flow–slit dam interactions and regulation functions of the slit dam: (i) For gentle slopes, the deposition of debris flows is primarily influenced by flume basal friction, and the normalized peak total impact forces have little difference for a given inclination angle, whereas for steep slopes, an overtopping can occur, further result in the increasing of the normalized peak total impact forces with the increase of solid volume fraction. (ii) The run-up height and retention efficiency are also analyzed to provide a scientific reference for optimizing the design of slit dams.

Particle sedimentation models for a commercial lithium extraction process from brine

This work assesses and examines particle sedimentation behaviors for magnesium removal process in a commercial lithium recovery plan with the aid of a lab-scale stirred tank reactor in the presence and absence of rotational stirring. The effects of stirrer agitation rate on the sediment height and induction period were investigated in the range of 280–390 RPM. A one-dimensional unsteady-state model was utilized, capable of describing the main phenomena observed in experimental particle sedimentation tests. The model showed fair agreement with experimental results obtained for the batch-wise sedimentation at different agitation rates. Moreover, the model was further used to assess the particle sedimentation behaviors in batch-wise and continuous stirred tank reactors. A critical boundary, based on a critical Peclet number and initial solid volume fraction, was proposed to avert/decelerate particle sedimentation in both reactor configurations, which could provide operation guidelines for batch and continuous reactors.

Modeling submerged granular flow across multiple regimes using the Eulerian–Eulerian approach with shear-induced volumetric behavior

The behavior of submerged granular flow is strongly dependent on the solid volume fraction and the viscosity discontinuity over a wide range of flow regimes. To obtain a general description of this type of flow, this study proposes a new model to compute solid effective stresses of submerged granular materials across multiple flow regimes. Here, based on the critical state soil mechanics framework, a new equation is proposed to describe the evolution of elastic reference of materials caused by elastoplastic deformation. The evolution of elastic reference subsequently informs the development of static pressure, and together with the dynamic pressure computed using a well-established blended model, resulting in a new approach to compute the solid pressure induced by both dynamic and static effects. The proposed model is then implemented in the Eulerian–Eulerian approach using the finite volume method to simulate the collapses of submerged granular columns, covering different flow regimes from quasi-static to viscous depositions. Simulation results agreeing well with experimental and numerical data in the literature are a testament to the performance of a well-developed constitutive law. In addition, the simulation results comprehensibly demonstrate the important role of interstitial fluid flow as well as the initial solid volume fraction in the collapsing process across different flow regimes with different packing densities. Furthermore, the effects of initial volume fraction, fluid pressure, and phase interaction forces on the flow responses are also discussed.

CFD-DEM Simulation of the Transport of Manganese Nodules in a Vertical Pipe

The present study aims to describe the characteristics of the hydraulic transport of manganese nodules in a vertical pipe. The solid–liquid two-phase flows were simulated using a numerical technique that combines the computational fluid dynamics (CFD) method and the discrete element method (DEM). Manganese nodules with diameters of 5.0 mm, 15.0 mm, and 30.0 mm were selected. The effects of the initial solid volume fraction and the initial mixture velocity were investigated. The results show that with increasing initial solid volume fraction, the liquid and solid velocities decrease but the total pressure drop over the pipe increases. Small particles are responsible for high particle collision frequency, which causes decreases in both the liquid velocity and the total pressure drop. Energy loss is aggravated by increasing the initial mixture velocity, manifesting in the increase of the total pressure drop. The retention ratio of manganese nodules varies inversely with the initial mixture velocity. A formula is proposed to describe the pressure drop due to the presence of solid particles and collisions.

Study of the Dilatancy/Contraction Mechanism of Landslide Fluidization Behavior Using an Initially Saturated Granular Column Collapse Simulation

AbstractFluidlike and integral sliding behaviors can be partly attributed to the dilatancy/contraction behavior of granular materials. A three‐dimensional two‐phase model and smoothed particle hydrodynamics method are applied to study the fluidization behavior by simulating the collapse of an initially fully saturated granular column. The dimensionless numbers (the initial aspect ratio, initial solid volume fraction, and Stokes number associated with the grain size) are varied to examine the collapse process and deposition characteristics. The profiles and front location during collapse highlight that the mechanism changes with the Stokes number and initial solid volume. The granular migration and pore pressure evolution characteristics are presented to clarify the differences in the collapse procedures and mechanisms pertaining to the simulation cases. The dimensionless final runout length and deposition height present monotonically increase and decrease following power laws with increasing initial aspect ratio, respectively; the dimensionless final runout length and deposition height also have monotonically decreasing and increasing relationships with increasing initial solid volume fraction and strongly increasing and decreasing characteristics during the transfer from the viscous flow regime to the inertial flow regime with increasing Stokes number, respectively. The simulation results indicate that the dynamic mechanism of the fluidization transformation is controlled by the Stokes number and initial solid volume fraction. Moreover, the coupling effect of the Stokes number, initial solid volume fraction and initial aspect ratio controls the collapse process of the initially saturated granular column.

Study on dynamic and static structural build-up of fresh cement paste with limestone powder based on structural kinetics model

The structural build-up of fresh cement-based materials is of great significance to the early forming and later performance. A structural kinetics model (SKM) used to indicate the structural build-up was developed by combining a kinetic equation described by structural parameter (λ) and a relationship between yield stress (τy) and λ in the paper. SKM transforms the structuration rate (Athix) in linear Roussel model and the characteristic time (tc) in non-linear Perrot model into more specific indicators such as initial solid volume fraction (ϕ0), rate of hydration during induction period (α̇ind), and shear rate (γ.). The yield stress (τy) obtained by RHEOLAB QC rotary viscometer was explored the dynamic and static structural build-up of fresh cement paste. The yield stress of fresh cement paste (W/C = 0.4) exhibits a quasilinear pattern with rate of 0.42 Pa/s for 210 min of mixing, with rate of 0.88 Pa/s for 100 min of resting after 4 min of mixing. The static yield stress of fresh cement paste evolves from linear to non-linear patterns within 100 min of resting after beyond 30 min of mixing. The fitting results show that SKM can well fit the evolution of yield stress including linear and nonlinear phases. Comparing with the dynamic structural build-up, the effect of limestone powder on the static structural build-up of cement paste is more obvious. When the mixing process is longer than 60 min, the content of limestone powder less than 20 wt% is beneficial to the structural build-up of fresh paste. Additionally, a declined rate of cement hydration in the induction period with increasing mixing time indicates that the rising yield stress, in this case, cannot be attributed entirely to the contribution of hydration to structural build-up.

Simulation of particles dissolution in the shear flow: A combined concentration lattice Boltzmann and smoothed profile approach

In the present study, the combination of the Concentration Lattice Boltzmann Method and the Smoothed Profile Method (CLBM–SPM) was used to simulate the dissolution of circular particles between parallel plates moving in opposite directions. The hydrodynamics and fluid concentration simulation were performed based on the single relaxation time Lattice Boltzmann Method. LBM convection–diffusion equation was then used to solve the concentration of the solute in the fluid phase. Additionally, SPM was employed to apply the no-slip boundary condition at the solid–fluid interface and to calculate the concentration forces. Initially, the results of the numerical solution were compared with the ones presented in the literature. Then the effects of the initial solid volume fraction, the Schmidt number, the Reynolds number, and particle size were studied to examine the behavior of particles dissolution. The results showed that the smallest dissolution time in the systems with different volume fractions was in a one with the least solid volume fraction. As the volume fraction was increased, the solid–fluid mass transfer driving force was decreased in the system. Also, with the rise of the Schmidt number, the dissolution time was increased, due to the decrease of the diffusion coefficient of the fluid flow. Moreover, by increasing the Reynolds number, the time required for the volume fraction ratio to reach 0.05 of its initial value was reduced. Finally, the particle size in this system was studied. The results indicated that with the decrease in particle size (or increase in the surface area), we could significantly alter the dissolution time.

Some Simulation Results and Parameter Analyses of a Generalized Quasi Two-Phase Bulk Mixture Model

Here, we consider a newly constructed generalized quasi two-phase bulk model for a rapid flow of a debris mixture consisting of viscous fluid and solid particles down a channel. The model is a set of coupled partial differential equations with new mechanical description of generalized bulk and shear viscosities, pressure, velocities and effective friction. The dynamical variables, physical parameters, inertial and dynamical coeffcients and drift factors involved in the equations contain certain important physics of mixture flow. So, we analyze the behaviour of some inertial and dynamical coeffcients involved in the model. These coeffcients strongly depend upon the initial material composition. We also simulate the evolution of the dynamical variables so as to reveal their strong non-linear behaviours. Through simulations, we also analyze the front position of the debris material, bottom-slip velocity and maximum velocity, which show fundamentally different dynamics for varied material compositions, from dilute to dense flows. Generalized mixture viscosity decreases as the ow moves downslope, and the rate at which it decreases depends upon the initial solid-volume fraction. We also compare the effective viscosity and the bulk mixture viscosity with respect to the norm of the strain rate tensors to reveal different non-linear behaviours.

Landslide damage incurred to buildings: A case study of Shenzhen landslide

Construction solid waste (CSW) landslides are always characterized by high mobility, and thus pose much danger to surrounding residents and buildings. In this study, a back in situ analysis of the catastrophic CSW landslide occurred in Shenzhen in December 2015 is presented, in which the motion-accumulation evolution process of the landslide and damage to structures are reproduced, and reasonable agreement between the simulation and actual conditions is obtained. In landslide process modeling, a depth-averaged model that can undergo dilation and contraction during deformation is adopted to simulate the behavior of the landslide assuming different conditions of initial solid volume fraction. The results show that a small initial solid volume fraction of a water-laden landslide undergoes small resistance caused by dilatancy. On the basis of landslide process analysis, the fluid–solid interaction is decoupled and considered to be a one-way action of the landslide on structures, which is reflected in the form of impact force. Structural response is evaluated by 3D finite element modeling. The failure process presents a type of plastic hinge formation at the beam–column connection positions, followed by local destruction of the impacted columns, and final structural failure is the cumulative result of this damage over time. This integrated approach could be implemented in quantitative risk assessment procedures pertaining to landslides.

Numerical investigation of particle–blast interaction during explosive dispersal of liquids and granular materials

Experiments show that when a high-explosive charge with embedded particles or a charge surrounded by a layer of liquid or granular material is detonated, the flow generated is perturbed by the motion of the particles and the blast wave profile differs from that of an ideal Friedlander form. Initially, the blast wave overpressure is reduced due to the energy dissipation resulting from compaction, fragmentation, and heating of the particle bed, and acceleration of the material. However, as the blast wave propagates, particle–flow interactions collectively serve to reduce the rate of decay of the peak blast wave overpressure. Computations carried out with a multiphase hydrocode reproduce the general trends observed experimentally and highlight the transition between the particle acceleration/deceleration phases, which is not accessible experimentally, since the particles are obscured by the detonation products. The dependence of the particle–blast interaction and the blast mitigation effectiveness on the mitigant to explosive mass ratio, the particle size, and the initial solid volume fraction is investigated systematically. The reduction in peak blast overpressure is, as in experiments, primarily dependent on the mass ratio of material to explosive, with the particle size, density, and initial porosity of the particle bed playing secondary roles. In the near field, the blast overpressure decreases sharply with distance as the particles are accelerated by the flow. When the particles decelerate due to drag, energy is returned to the flow and the peak blast overpressure recovers and reaches values similar to that of a bare explosive charge for low mass ratios. Time–distance trajectory plots of the particle and blast wave motion with the pressure field superimposed, illustrate the weak pressure waves generated by the motion of the particle layer which travel upstream and perturb the blast wave motion. Computation of the particle and gas momentum flux in the multiphase flow generated during explosive particle dispersal indicates that the particle momentum flux is the dominant term in the near field. Both the gas and particle loading must be taken into account when determining the damage to nearby structures following the detonation of a high-explosive charge surrounded by a material layer.

The effect of compaction of a porous material confiner on detonation propagation

The fluid mechanics of the interaction between a porous material confiner and a steady propagating high explosive (HE) detonation in a two-dimensional slab geometry is investigated through analytical oblique wave polar analysis and multi-material numerical simulation. Two HE models are considered, broadly representing the properties of either a high- or low-detonation-speed HE, which permits studies of detonation propagating at speeds faster or slower than the confiner sound speed. The HE detonation is responsible for driving the compaction front in the confiner, while, in turn, the high material density generated in the confiner as a result of the compaction process can provide a strong confinement effect on the HE detonation structure. Polar solutions that describe the local flow interaction of the oblique HE detonation shock and equilibrium state behind an oblique compaction wave with rapid compaction relaxation rates are studied for varying initial solid volume fractions of the porous confiner. Multi-material numerical simulations are conducted to study the effect of detonation wave driven compaction in the porous confiner on both the detonation propagation speed and detonation driving zone structure. We perform a parametric study to establish how detonation confinement is influenced both by the initial solid volume fraction of the porous confiner and by the time scale of the dynamic compaction relaxation process relative to the detonation reaction time scale, for both the high- and low-detonation-speed HE models. The compaction relaxation time scale is found to have a significant influence on the confinement dynamics, with slower compaction relaxation time scales resulting in more strongly confined detonations and increased detonation speeds. The dynamics of detonation confinement by porous materials when the detonation is propagating either faster or slower than the confiner sound speed is found to be significantly different from that with solid material confiners.

High-fidelity modeling and numerical simulation of cratering induced by the interaction of a supersonic jet with a granular bed of solid particles

The dynamics of cratering caused by a supersonic jet on a granular bed of solid particles is investigated using a high fidelity, two-phase model and numerical simulations. To model the gas phase, the Large Eddy Simulation (LES) approach is used and a kinetic theory based model is employed for the solid phase. Three-dimensional time-dependent simulations are conducted for the purpose of elucidating the morphological features of the crater and their evolution with time. Parametric variations of the initial conditions are performed to understand the effect of the initial solid volume fraction in the bed, of the coefficient of restitution, of the jet Mach number, of the particle diameter, and of the particle material density. Simulation snapshots of the craters are in qualitative agreement with images from the Mars Science Laboratory (MSL) mission and from Earth-based experiments. Analysis of the results shows that solid particle compaction at the crater base and side walls increases with increasing volume fraction of the undisturbed particle bed and reaches solid volume fractions close to 0.65. The coefficient of restitution is shown to have no effect on the large scale dynamics of the crater but affects the small scale features, particularly the shape of elongated bursts of solid particle clouds as well as radially aligned structures on the outer crater walls. A smaller jet Mach number results in a smaller crater characterized by ridge-like structures and walls at an angle of approximately 45° with respect to the undisturbed bed whereas larger Mach number jets create craters with walls approximately perpendicular to the undisturbed bed. A smaller particle size and a lighter particle material density also result in wider and deeper craters. The formation of all morphological structures is explained in detail and is related to the physical phenomena from which they originate. Power law curve fits are also presented for the crater outer diameter as well as for the depth. The mean and rms profiles of the solid volume fraction are computed, and it is found that the peak rms in the solid volume fraction does not occur at the surface but rather in the depth of the crater. In addition, the mean and rms of the particle momentum flux are also computed and discussed. Furthermore, the sources of particle momentum are evaluated, and the viscous drag as well as the gas pressure gradient are observed to be the prominent effects. The results show that the model developed is robust and is able to simulate craters due to a range of external conditions operating over particle beds having different characteristics.

Dynamic process simulation of construction solid waste (CSW) landfill landslide based on SPH considering dilatancy effects

Construction solid waste (CSW) landfill landslides, such as the Guangming New District landslide, which occurred in Shenzhen (hereafter the Shenzhen landslide), occur when the material is loose and saturated. They usually exhibit characteristics such as abrupt failure and whole collapse. During the propagation of landslides, dilatation behavior plays an important role in causing liquefaction, resulting in high velocity and exceptionally long run-out dynamics. We propose a dynamic model for describing fluidized CSW landslides by integrating the dilatancy model into smoothed particle hydrodynamics (SPH). The dilatancy model implies that the occurrence of dilation or the contraction of the granular-fluid mixture depends on the initial solid volume fraction. The dynamic model is used to simulate the Shenzhen landslide, and special attention is paid to the effects of different initial solid volumes on the mobility of the CSW landslide. The results show that when the solid volume fraction is higher than the critical value, contraction occurs, the excess pore water pressure increases, and the basal friction resistance is reduced. CSW landslide mobility is based on the initial solid volume fraction (or initial void ratio) of the granular-fluid mixture; a slight change in the initial volume fraction significantly affects the mobility of the CSW landfill landslide.

Applying Infrared Thermography and Image Analysis to Dilute 2-phase Particulate Systems: Hot Particle Curtains

Particle curtains occur in industrial drying and in solar particle receivers and are defined as a stream of particles falling a fixed distance through a gas or fluid phase. In industrial drying optimising heat and mass transfer between the cascading particles and the drying medium is essential for enhancing energy efficiency and reducing emissions. Modelling these devices via pragmatic process systems models and/or with computational fluid dynamics models can contribute to enhanced design and a better understanding of the fundamental processes that occur. Validation of curtain modelling is critical to building confidence in the resultant predictions, but unfortunately traditional methods such as discrete temperature measurement using probes are time consuming and can disturb the flow field. Infrared thermography is an image-based technique with the potential to alleviate some of these issues and to generate whole of field temperature data, well-suited to model validation. In this paper infrared thermographic images of hot particle curtains falling through still air are presented. Image analysis methods for adjusting and scaling images as well as detecting the curtain edges are also described. Experiments involving hot particle curtains (403k-413K) falling through a narrow slot (150×20-60 mm) in a room filled with still air (295K-300K) are presented. Curtain widths were varied by varying the slot width (20 mm and 60 mm) and a range of mass flow rates (0.04 kg/s-0.155 kg/s) and particle diameters (290 μm and 400 μm) were examined. Curtain shape, as defined by the edges of the curtains, was determined using methods adapted from image analysis. The 2D thermal images showed that the shapes of the curtains are strongly dependent on slot width or initial solids volume fraction, which has implications for maximising heat transfer in particle curtain processes.

Simulation of concentrated suspensions in free surface systems

AbstractThis study deals with the numerical simulation of free‐surface concentrated suspensions using the finite volume method. The numerical procedure, based on the particle diffusion‐flux model, is implemented in a computational fluid dynamic platform for estimating the particle volume fraction in three‐dimensional flows with arbitrary geometry and boundary conditions. The Volume of Fluid (VOF) method has been applied to track the flow interface between liquid and gas, with the solid particles dispersed in the liquid phase, in the free coating process. A finite length cylinder is dip coated, where the substrate is pulled out of a concentrated suspension bath. In the current work, the initial solid particle volume fraction range is 0.1–0.4 and the withdrawal velocity varies in the range of 0.05–0.15 m/s. Comparisons are made between numerical simulation predictions and experimental results for coating layer thickness, with close agreement achieved.

Mathematical modelling of batch sedimentation subject to slow aggregate densification

This paper considers an initially networked suspension in a batch settler subjected to very slow aggregate densification. The so-called pseudo-steady state aggregate densification theory developed by van Deventer (2012) has been extended to the case of initially networked suspensions. The solids behaviour and the evolutions of the suspension height and the consolidated bed height in the batch settler have been predicted using the extended pseudo-steady state theory. Different formulae for the weight-bearing strength of the consolidated bed (so-called weak gel and strong gel formulae, which differ near the top of the bed) are considered. The suspension height approaches the consolidated bed height far more quickly when using the weak gel formula than when using the strong gel one. This paper also investigates how the initial feed solids volume fraction and the initial suspension height affect the evolutions of the heights of the suspension and the consolidated bed, as well as the determinations of the solids volume fractions obtained at the bottom of the batch settler. When the initial feed solids fraction is sufficiently large and/or the initial suspension is sufficiently tall, the densification process has little effect on the solids fraction observed at the bottom of the settler.

Analysis of mesoscale heating by piston supported waves in granular metalized explosive

Deformation-induced heating of explosive composites is influenced by the material microstructure (i.e. porosity and particle sizes, shapes and packing), and component-specific thermomechanical properties and mass fractions. In this study, an explicit, 2D, Lagrangian finite and discrete element technique is used to examine thermomechanical fields in mixtures of explosive (HMX, C4H8N8O8) and metal particles (Al) induced by piston-supported deformation waves (piston speed 50 ⩽ Up ⩽ 500 m s−1). The mesoscale description uses a plane strain, thermoelastic–viscoplastic and friction constitutive theory to describe the motion and deformation of individual particles, and an energy consistent, penalty based method to describe inter-particle contact. The deformation response of material having an initial solid volume fraction of φs0 = 0.835 (porosity 1 − φs0 = 0.165) is characterized for different metal mass fractions and wave strengths. Transition from a strength-dominated to a pressure-dominated wave structure is predicted to occur with increasing wave strength due to the elimination of porosity. Average thermomechanical fields that define the effective wave structure differ both qualitatively and quantitatively for the two types of structures. Explosive component mass locally heated to elevated temperature behind waves is shown to be affected by the wave structure and the value of friction coefficient.

A Study of Interaction of Clouds of Inert Particles with Detonation in Gases

Interaction of a cloud of inert particles with a detonation in gaseous mixture is simulated and studied. The structure of both two- and three-dimensional detonations are modeled using a simplified chemical model with Arrhenius kinetics. Particle clouds are characterized based on the initial solid phase volume fraction () of the particle cloud and the initial cloud length (L 0). The results show that the minimum average detonation speed decreases with increase in at fixed L 0, and with an increase in L 0 at fixed . The detonation propagation through inert particle clouds is observed to fall into three regimes based on and L 0. In the first regime, the detonation speed is suppressed, but the reaction zone and leading shock remain coupled, and the triple points are nearly unaffected. In the second regime, the detonation is temporarily quenched but restored as the particle cloud moves away from the detonation front. In the third regime, the detonation is quenched permanently or at least does not get restored within the time available for the detonation propagation. It is also shown that the effects of inert particle clouds on the detonation front in three-dimensional studies are qualitatively similar to the results from two dimensional simulations. However, in post-detonation flow where transverse velocity components are important, simulations in three dimensions are necessary, especially to estimate particle dispersion.