Cohesive Particles Research Articles

A novel force balance model for predicting defluidization of ilmenite in a fluidized bed reactor

Ilmenite particles are readily defluidized when they are reduced in a fluidized bed reactor because nano-micro iron nuclei that precipitate on the particle surface are adhesive and tend to aggregate. We propose herein a novel force balance model with which to predict defluidization phenomena. This model is based on the particle cohesion force comprising the sum of the cohesion forces for surface asperities. As the surface coverage of iron particles increases with the extent of reduction, the cohesion forces of the particles gradually increase and eventually trigger defluidization. The surface coverage predicted by the model agrees well with experimental results for 88.4 ∼ 154.7 μm particles and the temperature range 700 ∼ 850 °C. The new force balance model reveals that particle size, sphericity, and temperature play key roles in defluidization of ilmenite during reduction. Defluidization occurs readily for fine and irregular particles, especially at high temperatures. Our model combines asperity, surface coverage, and particle sphericity to make a more general prediction.

Valuable reutilization of Basic Oxygen Furnace (BOF) slag for the CO2 sorption from oxy-fuel combustion in a fluidized bed reactor

Fossil fuel burning in numerous activities causes atmospheric CO2 concentration elevation and leads to environmental issues. Oxy-fuel combustion is considered as the effective strategy to improve CO2 capture since concentrated CO2 will be produced. In this study, basic oxygen furnace (BOF) slag was applied as sorbent for CO2 removal from oxy-fuel combustion in a fluidized bed reactor. BOF slag was applied under different operating conditions including particle size, calcination process, operating temperature, superficial velocity, and gas concentration. Calcination process improved the utilization of BOF slags and reached to 24.8 % and 24.5 % for 150–300 µm and 75–106 µm, respectively. The water vapor content in flue gas initiated the conversion of CaO into Ca(OH)2 and further improved the utilization value. However, 10 % water vapor caused higher particle cohesion and formed a laminar flow for smaller calcined BOF slag. Furthermore, the presence of SO2 reduced the utilization of BOF slag. Kinetics study and the properties change were also examined in this study. Carbonation process in this reaction was well fitted with the type I deactivation model. The CO2 absorption was proven by the formation of CaCO3 after carbonation process in each case of the operating conditions. Application of BOF slag not only reduced the cost but also became the strategy for waste recycle.

Flow loop study of a cold and cohesive slurry. Pressure drop and formation of plugs

Slurries of cohesive particles constitute a significant risk during subsea petroleum production due to their potential to plug the flow. This article describes a flow loop study of a slurry consistent with 0.23-mm ice particles in decane. The experiments were conducted for the concentration of particles up to 20.3% vol. and Re < 25000. The cohesion of ice was suggested by controlling the temperature of the slurry. The relative viscosity of the slurry was computed as a function of particle concentration using pressure drop measurements. The relative viscosity was 3.1 for the concentration of 20.3%. The Bingham-fluid model agreed with the empirical calculations within the discrepancy of 15.5%. Increased viscosity of slurry led to a higher pressure drop in the flow loop compared to the single-phase case. Pressure drops for 20.3% slurry flow were 5.2% and 44.4% higher than for pure decane at Reynolds numbers of 24778 and 4956, respectively. The test section of the loop was equipped with an orifice to induce the formation of plugs. The plugs were observed at particle concentrations below 7.0%. The article presents detailed experimental logs depicting the process of plug formation. The observed blocking cases partially agreed with flow maps from the literature. In addition, we note the applicability of the blockage risk evaluation technique from the Colorado School of Mines.

Effects of hydrate occurring mechanisms and saturation on the mechanical properties of hydrate-bearing sediments: Numerical study based on simplified DEM simulation

Natural gas hydrate is a strategic alternative energy source which are widely founded in seabed sediments. The study of the mechanical properties of hydrate-bearing sediments is the key content to ensure the safe exploitation of gas hydrate. Hydrate occurring mechanisms and saturation are important factors affecting the mechanical properties of hydrate-bearing sediments. In this work, simplified discrete element models that consider the hydrate occurring mechanism, hydrate saturation and confining pressure, were generated based on PFC code. Three main hydrate occurring mechanisms including pore filling, load bearing and cementation were characterized. The triaxial compression simulation was then conducted to investigate the model mechanical properties. The results show that the hydrate of cementation mode has the most obvious strength-enhancing effect on sediments, followed by the load bearing model and pore filling model. Hydrate occurring mechanism also affect the increasing trend of sediment strength and deformation modulus with hydrate saturation and confining pressure. The influence of hydrate occurrence mechanism on the mechanical behavior of sediment is largely controlled by the interaction between hydrate and sand particles interface. The hydrate of cementation mode increases the cohesion of the sediment particles, the hydrate of pore filling mode increases the friction between particles, and the hydrate of load bearing mode has the combined effects of the above two.

Biofilm producing Bacillus vallismortis TR01K from tea rhizosphere acting as plant growth promoting agent

Microbial biofilms are an aggregation of single or multi-species bacteria that acquires the capacity to adhere to any surface where they can act like a wholesome system chemically “speaking with” each other through quorum sensing. This synergism is very prominently noticed in the rhizospheric regions of plant roots subsequently forming a dome which can protect the root-rhizospheric niche from various biotic and abiotic stress. The bacterial EPS have a number of roles like adhesion, cohesion and aggregation of soil particles, retaining water molecules, acts as a potential barrier on the rhizospheric regions, facilitating ionic and genetic information exchange within the matrix component, enhanced production of plant readily available nutrients etc. Keeping this scenario in mind, this study was formulated on to isolate and explore novel rhizobacteria with colossal biofilm forming ability showing great potential as a source of lignocellulolytic plant growth promoting agent.The crop chosen for this study was tea or Camellia sinensis, a quintessential beverage that is consumed across the globe. The rhizospheric region of a woody plant like tea, acts as a hub for lignocellulosic enzyme producing bacteria. The novel rhizobacteria isolated from cultivated tea soil, Bacillus vallismortis TR01K [NCBI Genbank Accession Number MT672714], was found to have an immense biofilm forming potential that ranged approximately 40x times higher than normal standard bacterial biofilm forming potentials when tested under laboratory conditions. Further in vitro characterizations of the novel strain showed it's immense potential to make plant nutrient available, to produce plant growth hormones (IAA, GA3, Cytokinin) and produce plant stress mitigating hormone (ACC deaminase). Lignocellulolytic enzymes are a vital part of lignocellulosic biomass degradation-a sustainable biotechnological approach for enzymes, organic acids, feed and biofuel production. The selected bacteria was tested elaborately for the family of lignocellulolytic enzymes (cellulase, laccase, lignin peroxidase, pectinase, amylase, chitinase, beta glucanase etc.) which showed promising results. Thus, proving the entire set of experiments in compliance with the aforementioned hypothesis that the novel bacterial isolate from tea rhizosphere has a significant biofilm forming potential with a colossal potency for being lignocellulolytic plant growth promoting agent.

Inverting the Paradigm: From Art to Granular Science

Abstract The interface between art and science is an increasingly recognized source of innovation, yet explorations tend to skew toward art reaping the benefits of scientific developments. While, today, art is often freely embraced within scientific fields, it is rarely afforded the freedom to transform scientific research. The authors explore a new paradigm of “art-inspired science” by reimagining and computationally simulating an existing artwork as a dynamic body of cohesive particles. In the process, hanging forms of “granular stalactites” are identified and subsequently reproduced in an idealized simulated system. A theoretical “stickiness” model was then developed to predict their maximum height, which could have wide technological application. Artworks may therefore serve as catalysts for distinctive scientific research, allowing a mutually productive relationship between the disciplines.

On the fluidization of cohesive powders: Differences and similarities between micro‐ and nano‐sized particle gas–solid fluidization

AbstractThe fluidization of cohesive powders has been extensively researched over the years. When looking at literature on the fluidization of cohesive particles, one will often find papers concerned with only micro‐ or only nano‐sized powders. It is, however, unclear whether they should be treated differently at all. In this paper, we look at differences and similarities between cohesive powders across the size range of several nanometres to 10s of micrometres. Classification of fluidization behaviour based on particle size was found to be troublesome since cohesive powders form agglomerates and using the properties of these agglomerates introduces new problems. When looking at inter‐particle forces, it is found that van der Waals forces dominate across the entire size range that is considered. Furthermore, when looking into agglomeration and modelling thereof, it was found that there is a fundamental difference between the size ranges in the way they agglomerate. Where the transition between the types of agglomeration is located is, however, unknown. Finally, how models are made and agglomerate sizes are measured is currently insufficient to accurately predict or measure their sizes consistently.

Investigating the effects of material properties on the mixing dynamics of cohesive particles in a twin screw mixer using a discrete element method approach

A discrete element method (DEM) model was developed for a co-rotating twin-screw mixer (TSM) consisting of conveying and kneading elements. This model was used to simulate the mixing of a cohesive binary system of particles (P1 and P2). The particles were calibrated using angle of repose and dynamic yield strength simulations. Properties of P1 were kept constant throughout the study while properties of P2 were varied. The TSM model was used to study the influence of particle size, density, and flowability of P2 on process outputs such as powder holdup, mean residence time (MRT), and degree of mixing along the length of the TSM. All the three particle properties were varied at three-factor levels with flowability ranging from good flow (GF), poor flow (PF), and very very poor flow (VVPF) based on Carr’s classification. The model provides fundamental insights into the differences in mixing in the conveying sections of the mixer for materials with different flowability. Due to the co-rotating nature of the screws, the majority of the material in the conveying sections was carried on one side of the TSM for GF and PF particles, while both the screws carried VVPF particles. The total steady-state holdup and the mean residence time (MRT) of particles inside the TSM were heavily influenced by particle flowability compared to the other two tested particle parameters. The holdup in the conveying compartments ranged from 11%–15% of the total holdup, while the kneading compartment comprised 40% of the total holdup in the mixer. The simulations found that VVPF particles mixed the fastest and that the GF particles had the highest tendency to demix. The model was also used to suggest and test other screw design configurations to improve mixing. A screw design with kneading elements closer to the mixer outlet resulted in better mixing of GF particles. A screw design consisting only of conveying elements achieved the same degree of mixing as the original screw design for VVPF particles. • A model for a co-rotating twin-screw mixer was developed using DEM. • Holdup and mean residence time was influenced by the particle flowability. • Particles were transported mainly on one of the conveying screws. • The model was also used to suggest changes to screw design configurations.

Mechanical properties and mechanism of soil treated with nano-aqueous adhesive (NAA)

The loose structure and low mechanical strength of the surface soil make it vulnerable to damage under erosion conditions. Slope ecological protection is one of the effective methods to improve the stability of slope soil. Although it has been proved that polymer modified materials can effectively improve the soil properties and the environmental protection effect of slope, so far, the improvement mechanism has not been fully understood, especially the chemical mechanism of the material on the enhancement of soil mechanical properties is not clear. In the present study, the effects of nano-aqueous adhesive (NAA) on unconfined compressive strength, shear strength and aggregate characteristics of soil were studied by a series of laboratory experiments. The results show that NAA can increase the strength, aggregate number and stability of the soil, to effectively improve the stability of surface soil. In addition, through infrared spectroscopy and SEM test, it was found that NAA molecules were mainly distributed in the interlayer position of flaky clay minerals, mainly connected with clay minerals through hydrogen bonds, thereby effectively enhancing the cohesion of soil particles.

Modelling Deaggregation Due to Normal Carrier–Wall Collision in Dry Powder Inhalers

Powder deaggregation in Dry Powder Inhalers (DPI) with carrier-based formulations is a key process for the effectiveness of drug administration. Carrier-wall collisions are one of the recognised mechanisms responsible for active pharmaceutical ingredient (API) aerosolisation, and DPI geometries are designed to maximise their efficacy. The detachment of fine and cohesive API particles is investigated at a fundamental level by simulating with DEM the normal collision of a carrier sphere with an API particle attached. The impact velocity at which detachment occurs (escape velocity) is determined as a function of key parameters, such as cohesiveness, coefficient of restitution, static and rolling friction. An analytical model for the escape velocity is then derived, examining the role of the initial position of the particle, cohesion model and particle size. Finally, the results are framed in the context of DPI inhalers, comparing the results obtained with impact velocities typically recorded in commercial devices.

Research on the Macro-Mesoscopic Response Mechanism of Multisphere Approximated Heteromorphic Tailing Particles

Abstract The shape of tailing particles is essential factors of their macroscopic mechanical properties. Scholars have studied the effects of controllable factors, such as loading method, confining pressure, and strain rate, on the strength of tailing sand. However, research on the tailing particle structure and shape through laboratory tests has proved to be difficult due to the uncertain and discrete tailing particle distribution. Thus, the macro-mesoscopic response of heteromorphic tailing particles is rarely investigated. In this paper, the macro-mesoscopic response of heteromorphic tailing particles is studied using multisphere approximation, and numerical simulation of triaxial tests on the particles is conducted. Nonlinear evolution patterns of porosity, internal friction angle, and cohesion of heteromorphic tailing particles with the variation of angularity were investigated using the flexible boundary program developed in this study, which revealed the intrinsic relationship between the mesostructure evolution mechanism and the macroscopic engineering characteristics of heteromorphic tailing particles. The research results showed that (1) changes in angularity led to tailing particle rearrangements and, in turn, porosity changes. With increased angularity and confining pressure, particle sphericity decreased, and the deviatoric and peak stress increased accordingly. In the meantime, the softening was more significant as the peak stress was exceeded, while the cohesive force generally increased. (2) With fixed particle shape and angularity, the internal friction angle decreased slightly as the effective confining pressure increased. (3) In the shearing process, the simulated contact force chain evolution of tailing particles with different shapes was similar. The disordered contact force chains gradually undergo directional connection, i.e., the increased confining pressure reduced the number of free tailing particles and increased the number of stressed particles. (4) The triaxial stress-strain and peak stress in rigid boundary simulations under different confining pressures were slightly lower than those in the flexible boundary simulations. However, the difference was insignificant, indicating the good feasibility and reasonability of rigid boundary simulations for the macroscopic mechanical behaviors in triaxial tests. The research results could offer more direct insights into the macro-mesoscopic response and mechanical mechanisms of nonspherical particles and provide references for the simulation of tailings at the microscopic levels.

Floc Size Distributions of Cohesive Sediment in Homogeneous Isotropic Turbulence

Floc size distribution is one of the key parameters to characterize flocculating cohesive sediment. An Eulerian–Lagrangian framework has been implemented to study the flocculation dynamics of cohesive sediments in homogeneous isotropic turbulent flows. Fine cohesive sediment particles are modeled as the dispersed phase by the discrete element method, which tracks the motion of individual particles. An adhesive contact model with rolling friction is applied to simulate the particle–particle interactions. By varying the physicochemical properties (i.e., stickiness and stiffness) of the primary particles, the dependence of the mathematical form of the floc size distribution on sediment properties is investigated. At the equilibrium state, the aggregation and breakup processes reach a dynamic equilibrium, in which construction by aggregation is balanced with destruction by breakup, and construction by breakup is balanced with destruction by aggregation. When the primary particles are less sticky, floc size distribution fits better with the lognormal distribution. When the primary particles are very sticky, both the aggregation of smaller flocs and breakup from larger flocs play an equally important role in the construction of the intermediate-sized flocs, and the equilibrium floc size distribution can be better fitted by the Weibull distribution. When the Weibull distribution develops, a shape parameter around 2.5 has been observed, suggesting a statistically self-similar floc size distribution at the equilibrium state.

Predicting the flocculation kinetics of fine particles in a turbulent flow using a Budyko-type model.

Through an analogy with the Budyko curves in catchment hydrology science, this study defines the supply and demand limits for the flocculation system of cohesive particles (the supply limit can be represented by the potential floc size growth, whereas the demand limit can be represented by the steady-state floc size) and attempts to adopt Budyko-type models to estimate the temporal evolution of floc size during flocculation. Seventeen experimental datasets are collected to test the accuracy of the Budyko model with an average high correlation coefficient of 0.9784 and average low relative error and root mean squared error values of 0.1304 and 0.0605, respectively. Either the potential floc size growth or the steady-state floc size is a monotonic function of the flow shear rate, and a simple empiric power law function can be used to describe them. Other Budyko-type models are also found to show good prediction accuracies against the experimental datasets. This study indicates that Budyko-type models have potential as a good addition to existing flocculation models for predicting the temporal variation in the size population of flocs in a turbulent flow, provided that some coefficients have been calibrated by limited data points prior.

Wet mono-sized granular packing: effects of initial clusters and filling strategy

Cohesive particles have been demonstrated to affect packing structures that sometimes inhibit applications while helpful in others. Therefore, accurately tailoring the cohesive granular packing, e.g., wet particles, is very rewarding nowadays. We adopt the discrete element method (DEM) and present a packing strategy by falling different size clusters containing mono-sized particles with varying cohesion to tailor the packing structure. We demonstrate the strategy's effectiveness by comparing the result with previous experiments, and we found the larger cluster tends to form a looser packing. We evidence that a dimensionless number, l⁎, evaluating the competing importance between kinetic energy and capillary potential, can precisely describe the cohesion effect. We combine l⁎ with several key indices, e.g., packing fraction, granular temperature, coordination number and force network distribution, to describe packing formation. Meantime, we found the different characterisation of cohesion effect throughout packing stages, which can shed light on the understanding of wet granular packing.

A new potential interface tension model for MPS method avoiding unphysical particle cohesion

Improvement of the capability to accurately track the interface between immiscible phases/components is of great importance to the numerical analysis with complex multi-component and multi-phase flow dynamics, which might be involved in severe accidents of light water reactors, such as Molten Core-Concrete Interaction (MCCI). In order to model the interface tension between immiscible phases/components, Zhu et, al., precedingly developed a potential interface tension model in MPS method based on Kondo et al.‘s earlier model for surface tension and succeeded to stably model the interface tension qualitatively by introducing different attractive forces for different pairs of particle types. However, it has been known that pressure is overestimated in Zhu et, al.‘s potential interface tension model. Moreover, this study has shown that the fluid flow can be numerically hindered with Zhu et al.‘s potential interface tension model. These issues of Zhu et al.‘s potential interface tension model is caused by unphysical particle cohesion due to the inter-particle attractive forces determined by the surface tension coefficients, which are required even when the free surface is not considered. Meanwhile, in the framework of SPH method, Zhou et, al., proposed to model interface tension by introducing the repulsive force between different phases. Hence, this study aimed to develop a new potential interface tension model for MPS method which can overcome the conventional drawbacks of pressure overestimation or unphysical flow hindrance, by incorporating the repulsive force between immiscible fluid phases referring to Zhou et, al.‘s idea within SPH method.The interface tension in the present method is modeled as the repulsive force derived from the “repulsive potential” and is considered only near the interface to avoid the unphysical particle cohesion due to the inter-particle attractive forces. The amplitude coefficient in the repulsive potential is determined by the methodology similar to that proposed by Kondo, et, al.With the newly developed interface tension model, the common issue of numerical flow hindrance that occurred in the previous interface tension models in MPS method has been resolved. The validation of the newly developed interface tension model shows good agreement with theoretical evaluations of Laplace pressure and the droplet deformation ratio in a shear flow. Moreover, the new interface tension model has been validated against a 3-dimensional immiscible fluid stratification test, in which the new interface tension model shows good agreement with the test results and improvement of the pressure profile evaluations compared to that by Zhu et al.‘s model. Further extension of the present model so as to incorporate surface tension and wall wetting is one of the most important issues which require future development.

Elasto-plastic and adhesive contact: An improved linear model and its application

An improved linear model is developed for elasto-plastic and adhesive contact. New correlations are proposed and validated to estimate the key parameters of the model, including contact stiffness, yield point, maximum pull-off force and time step. The newly proposed contact model is applied to the analysis of single particle contact behaviour upon impact and bulk particle flow behaviour by DEM simulations. The results show that both single particle and bulk powder behave more “cohesively” if contact plastic deformation is considered. A cohesion yield number is proposed to describe the extent of yielding when cohesive particles are in contact with each other. There is a critical particle size, below which the effect of plastic deformation becomes prominent and must be considered. This provides a new framework and criteria for elasto-plastic and adhesive contact model, and a step towards understanding the effect of plastic deformation on the behaviour of cohesive particles.

Comparison between sand and clay clogging mechanisms of pervious concrete pavement

Pervious concrete (PC) pavement has been widely accepted as a green infrastructure but is prone to clogging. This study comparatively investigated sand and clay clogging mechanisms of PC and vertical sediment distributions of sand-clogged and clay-clogged PCs. Clay and three sizes of sand were used to clog PC under two exposure methods (no drying and drying). X-ray computed tomography (CT) was used to scan the clogged samples before and after 30 pressure washing cycles. The clogged permeability and permeability after each washing cycle were measured. The clogging patterns of sand depend mainly on sand particle sizes relative to PC pore sizes. The applied fine sand, coarse sand, and medium sand cause easy-passing clogging, surface clogging, and full-depth clogging, respectively. After clay clogging, more than 77% of the total retained clay occurs within the vertical region 24–72 mm below the sample surface; the most clogging (the lowest-permeability layer) occurs at a depth of approximately 48 mm. The dried clay retained within the region 40–120 mm below the surface (especially within the lowest-permeability layer) is hard to wash away because the drying process increases the cohesion of internal clay particles and clay adhesion to the rough, tortuous pore wall of PC. The clogged normalized permeability of 0.154 and permeability recovery ratio of 4.91% in dried clay-clogged samples are lowest among all the samples. However, pressure washing readily washes away the retained undried clay. Accordingly, it is recommended that pressure washing is used to eliminate the clogging effect of dried clay before hot, sunny exposure conditions dry the retained clay. This study provides evidence for developing effective pavement maintenance strategies.

Modeling the thermodynamics and kinematics of spherical particle dispersion in polymer melts: Model derivation and simulation analysis

AbstractA cohesive binding‐force‐based model has been developed to predict solid particulate agglomerate break up in fluids sheared volumes leading to particle dispersion in polymer melt extrusion processes. Particle—particle, particle—polymer, and particle—modifier—polymer interactions are modeled using adaptions from Hamaker's approach. This leads to an analytical molecular attraction approach that captures the effects of: (1) particle‐particle agglomerate cohesion based on material properties and structure, (2) the effect of surface modifiers on cohesive strength and particle separation, (3) polymer wetting and melt adhesion leading to medium‐agglomerate stress transfer, (4) applied fluid mechanical stress and melt temperature, and (5) residence time. In this paper, the model is evaluated, and several predicted effects of processing parameters on reduction of agglomerate size are calculated and graphically presented from this phase of the research. The predicted trends are consistent with the published data in the literature.

The Effect of Particle Cohesiveness and Plastic Deformability on the Powder Compression Process

The Effect of Particle Cohesiveness and Plastic Deformability on the Powder Compression Process

Geometric similarity on interparticle force evaluation for scaled-up DEM particles

The scaled-up particle model, which is also commonly known as the coarse grain model or discrete parcel model, is frequently used to reduce the computational cost in Discrete Element Method (DEM). In the direct force scaling approach, the forces acting on original particles are first estimated and then directly scaled to apply to scaled-up particles. It is therefore crucial to appropriately evaluate the variables of the original particles, e.g. overlap and separation distance, from the scaled-up particles particularly when estimating complex interparticle forces. The present work proposes the use of geometric similarity for the evaluation of the original particle overlap and separation distance. It is demonstrated that the proposed method can provide an almost identical stress-strain curve between the original and scaled-up particles during uniaxial compression of a packed particle bed, whilst the conventional method in the literature gives significant overestimation of the stress. In addition, the scaled-up particles can reasonably replicate the original velocity distributions of cohesive particles with both liquid bridge and JKR surface adhesion forces in a dynamic flow system (vertical mixer). The simulation results suggest that the method proposed can be applied to any type of interparticle forces. A scaling of time step limit is also derived theoretically and discussed.