Sticky Particles Research Articles

Geometrical frustration yields fiber formation in self-assembly.

Controlling the self-assembly of supramolecular structures is vital for living cells, and a central challenge for engineering at the nano- and microscales [1, 2]. Nevertheless, even particles without optimized shapes can robustly form well-defined morphologies. This is the case in numerous medical conditions where normally soluble proteins aggregate into fibers [3, 4]. Beyond the diversity of molecular mechanisms involved [5, 6], we propose that fibers generically arise from the aggregation of irregular particles with short-range interactions. Using a minimal model of ill-fitting, sticky particles, we demonstrate robust fiber formation for a variety of particle shapes and aggregation conditions. Geometrical frustration plays a crucial role in this process, and accounts for the range of parameters in which fibers form as well as for their metastable character.

Slagging and fouling of Zhundong coal at different air equivalence ratios in circulating fluidized bed

Circulating fluidized bed (CFB) with low operating temperatures may become an appropriate solution to the utilization of high-Na Zhundong coal. In this paper, one kind of Zhundong coal with 3.92% Na2O in coal ash was used as fuel, and its slagging and fouling characteristics at different air equivalence ratios (ERs) were systemically investigated in 0.4t/d CFB test system to determine a better utilization scheme of Zhundong coal. The results show that ash-related problems still occurred when this high-Na coal was used in CFB, which was greatly influenced by ER. At the reducing atmosphere (ER<1.0), slagging obviously occurred in the riser at ∼940°C. Na-based species reacted with the SiO2-rich bed material to form low-melting-temperature sodium silicates (Na2O·nSiO2). The formed sodium silicates covered bed material particles and increased their stickiness. These sticky particles agglomerated and adhered onto the high-temperature metal surfaces by adhesion force or inertial force, resulting in slagging. During slagging process, Ca, Mg and Fe acted as fluxing agents. This type slagging related to the SiO2-rich bed material might be reduced or even avoided via the replacement of the bed material. At the oxidizing atmosphere (ER>1.0), fouling on tail heating surfaces at medium-low temperatures (607–735°C) was the main ash-related problem. The released AAEM-based species were transported towards low-temperature surfaces by the mechanisms of diffusion, condensation and aggregation, or thermophoresis, resulting in a layered deposition. The inner layer of deposits with micron grain sizes, which was mainly composed of Na2SO4 and K2SO4, played a key role at the initial deposition stage. Besides, two kinds of aggregated particles separately rich in alkali silicates and Ca-based species were also important for fouling.

Agglomeration of celecoxib by quasi-emulsion solvent diffusion method without stabilizer: effect of good solvent

Aim: The aim of the present research is to investigate the feasibility of agglomeration of crystals by the quasi-emulsion solvent diffusion method without using a stabilizer.Method: Two solvent systems comprising a solvent and an antisolvent (water) were used to prepare celecoxib agglomerates. To this end, seven solvents including propanol, methyl acetate, methyl ethyl ketone, butanol, ethyl acetate, isopropyl acetate, and pentanol were examined. The agglomerates were evaluated by micromeritic properties (e.g., size, density, flowability), yield, drug physical state, friability, and dissolution behavior.Results: In the present study the clear trend was observed experimentally in the agglomerate properties as a function of physical properties of the solvent such as miscibility with water. Solvents with high water miscibility (25% v/v) resulted in sticky and hollow particles, while solvents with low water miscibility (3%v/v) led to the formation of agglomerates with low strength. However, the agglomerates made from the solvents with intermediate water miscibility (10% v/v), may reflect a greater integrity of the agglomerates regarding yield and strength.Conclusion: Results of this study offer a useful starting point for a conceptual framework to guide the selection of solvent systems for the quasi-emulsion solvent diffusion method without using a stabilizer.

Global Convergence of a Sticky Particle Method for the Modified Camassa--Holm Equation

In this paper, we prove convergence of a sticky particle method for the modified Camassa--Holm equation (mCH) with cubic nonlinearity in one dimension. As a byproduct, we prove global existence of weak solutions $u$ with regularity: $u$ and $u_x$ are space-time BV functions. The total variation of $m(\cdot ,t)=u(\cdot, t)-u_{xx}(\cdot,t)$ is bounded by the total variation of the initial data $m_0$. We also obtain $W^{1,1}(\mathbb{R})$-stability of weak solutions when solutions are in $ L^\infty(0,\infty;W^{2,1}(\mathbb{R}))$. (Notice that peakon weak solutions are not in $W^{2,1}(\mathbb{R})$.) Finally, we provide some examples of nonuniqueness of peakon weak solutions to the mCH equation.

A multitype sticky particle construction of Wasserstein stable semigroups solving one-dimensional diagonal hyperbolic systems with large monotonic data

This paper is devoted to the study of diagonal hyperbolic systems in one space dimension, with cumulative distribution functions or, more generally, nonconstant monotonic bounded functions as initial data. Under a uniform strict hyperbolicity assumption on the characteristic fields, we construct a multi-type version of the sticky particle dynamics and we obtain the existence of global weak solutions via a compactness argument. We then derive a [Formula: see text] stability estimate on the particle system which is uniform in the number of particles. This allows us to construct nonlinear semigroups solving the system in the sense of Bianchini and Bressan [Vanishing viscosity solutions of nonlinear hyperbolic systems, Ann. of Math. (2) 161(1) (2005) 223–342]. We also obtain that these semigroup solutions satisfy a stability estimate in Wasserstein distances of all order, which extends the classical [Formula: see text] estimate and generalizes to diagonal systems a result by Bolley, Brenier and Loeper [Contractive metrics for scalar conservation laws, J. Hyperbolic Differ. Equ. 2(1) (2005) 91–107] in the scalar case. Our results are established without any smallness assumption on the variation of the data, and we only require the characteristic fields to be Lipschitz continuous and the system to be uniformly strictly hyperbolic.

Modeling of ash deposition in a pulverized-coal boiler by direct simulation Monte Carlo method

In this paper, a mathematical model of the fly ash deposition in a 660MW supercritical once-through boiler was developed. The mechanism of particle-particle and particle-wall collisions has been considered. Particle collision is modeled by a direct simulation Monte Carlo (DSMC) method. Three submodels (impaction, thermophoresis, and sticking) were included in the mathematical model. In the ash deposition model, the critical velocity model was used to calculate the ash sticking rate during initial deposition, and the viscosity model was used for the outer layer deposition. An ash deposition probe was inserted into the peephole and ash deposits were collected. The morphology of these samples was analyzed using SEM. The deposit thickness and the distributions of adhesion particle size were obtained by mathematical model. The mean deposit thickness calculated by the DSMC method agreed with the value measured by the ash deposition probe with the relative error within 3.79%. The simulation results show that the deposition inner layer consists of fine particles less than 10μm in size and sticky fine particles were selectively captured during the initial deposition stage. The DSMC method may be a practical alternative for studies of ash deposit formation.

Vibration Level Improvement of Id Fan in a Cement Plant Based On CFD Study of Incoming Dust Particles Streamline

This paper presents numerical study of aerosol flow inside of the induce draft (ID) fan inlet duct of a cement plant and the field observation of the proposed guide plate implementation as vibration reducer. Since ID fan sucks the flow from the outlet of cyclone separator, that is normally swirling flow, and the geometry of the duct tends to produce unbalance fine particles distribution over the duct cross section, the vibration of ID fan increases periodically due to unbalance built-up of the fine particles over fan blades surface. Numerical result shows that, at the ID fan inlet, the distribution of fine particles is unbalance. The ratio of particles concentration in the gas entering fan side and motor side of the ID fan is 1.4 to 1 which influences on the unbalance deposition of sticky particles over related blades surface. Using proper guide plate installed in the last duct elbow before entering to the fan, the ratio of unbalance fine particles concentration reduces to 1.05 to 1 and is kept up to the fan free side and motor side inlets. The proposed guide plate has also already installed in a cement plant ID fan duct and vibration characteristic was also observed during 4 months after tie-in period. The plant vibration observation shows that its level is practically unchanged and maintained at low level (around 2 mm/s at fan side and 0.5 mm/s at motor side) which is still lower than maximum limit (11 mm/s). This condition reduces significantly vibration level and eliminates practically plant stop due to over vibration of ID fan along last 4 months operation which was normally suffered every 1.5 months before implementation of this study.

Microwave Scattering and Medium Characterization for Terrestrial Snow With QCA–Mie and Bicontinuous Models: Comparison Studies

Comparison studies are made between the QCA–Mie model and the bicontinuous model in microwave scattering from terrestrial snow. Both the scattering properties and the medium characterization are compared. For QCA, we use the multisize and the sticky particle models. For the bicontinuous model, we use the probability distribution function for the wavenumber. We compare the scattering rate and the angular distribution of scattering using the mean cosine of scattering and show that the two models have similar properties. In medium characterization, we use the pair distribution functions used in QCA to derive the correlation functions. We show that both the Percus–Yevick pair functions and the bicontinuous model have tails in the correlation functions that are distinctly different from the traditional exponential correlation functions. The methodologies of using ground measurements of grain size distributions and correlation functions to obtain model parameters are addressed.

Optimal convergence rate of the multitype sticky particle approximation of one-dimensional diagonal hyperbolic systems with monotonic initial data

Brenier and Grenier [SIAM J. Numer. Anal., 1998] proved that sticky particle dynamics with a large number of particles allow to approximate the entropy solution to scalar one-dimensional conservation laws with monotonic initial data. In [arXiv:1501.01498], we introduced a multitype version of this dynamics and proved that the associated empirical cumulative distribution functions converge to the viscosity solution, in the sense of Bianchini and Bres-san [Ann. of Math. (2), 2005], of one-dimensional diagonal hyperbolic systems with monotonic initial data of arbitrary finite variation. In the present paper, we analyse the L 1 error of this approximation procedure, by splitting it into the discretisation error of the initial data and the non-entropicity error induced by the evolution of the particle system. We prove that the error at time t is bounded from above by a term of order (1 + t)/n, where n denotes the number of particles, and give an example showing that this rate is optimal. We last analyse the additional error introduced when replacing the multitype sticky particle dynamics by an iterative scheme based on the typewise sticky particle dynamics, and illustrate the convergence of this scheme by numerical simulations.

Evaluation of the Efficiency of Filtration Processes Using Precoat Materials

AbstractThe highly efficient filtration of ultrafine dust emitted by biomass combustion processes with a baghouse filter has been successfully tested in the last years. To protect the filter material from the very small and sticky fine dust particles and to guarantee very high total collection efficiencies (&gt; 99 %) in a long‐term stable process, the use of a precoat is necessary. Tests done in a laboratory and a real‐application plant show that the reuse of precoat materials can lead to significant savings. Considering the influences of different combustion processes, the associated precoat efficiencies could be calculated. With these characteristic ratios, it is possible to evaluate different process settings. Hence, the amount and the cost of the needed precoat could be reduced significantly.

Implementation and Verification of Linear Cohesive Viscoelastic Contact Model for Discrete Element Method

PURPOSES: Implementation and verification of the simple linear cohesive viscoelastic contact model that can be used to simulate dynamic behavior of sticky aggregates. METHODS: The differential equations were derived and the initial conditions were determined to simulate a free falling ball with a sticky surface from a ground. To describe this behavior, a combination of linear contact model and a cohesive contact model was used. The general solution for the differential equation was used to verify the implemented linear cohesive viscoelastic API model in the DEM. Sensitivity analysis was also performed using the derived analytical solutions for several combinations of damping coefficients and cohesive coefficients. RESULTS : The numerical solution obtained using the DEM showed good agreement with the analytical solution for two extreme conditions. It was observed that the linear cohesive model can be successfully implemented with a linear spring in the DEM API for dynamic analysis of the aggregates. CONCLUSIONS: It can be concluded that the derived closed form solutions are applicable for the analysis of the rebounding behavior of sticky particles, and for verification of the implemented API model in the DEM. The assumption of underdamped condition for the viscous behavior of the particles seems to be reasonable. Several factors have to be additionally identified in order to develop an enhanced contact model for an asphalt mixture.

One-Dimensional Pressureless Gas Systems with/without Viscosity

A general global existence result for one-dimensional pressureless Euler/Euler-Poisson systems with or without viscosity is obtained by employing the “sticky particles” model. We first construct entropy solutions for some appropriate scalar conservation laws, then we show that these solutions encode all the information necessary to obtain solutions for the pressureless systems. Another novel contribution is the stability and uniqueness of solutions, which is obtained via a contraction principle in the Wasserstein metric.

Multiphase flow patterns in entrained-flow slagging gasifiers: Physical modelling of particle–wall impact at near-ambient conditions

Particle–wall interaction phenomena relevant to multiphase flow in entrained-flow slagging coal gasifiers have been investigated. The micromechanical patterns of particle impingement on the reactor walls have been characterized in a model system by high speed imaging and tracking of wax particles impacted onto a flat surface at near-ambient conditions. The solid/plastic versus fluid state of the wax particles was controlled by proper selection of the particle, ambient and target temperatures. Particle–wall collision was described in terms of normal and lateral restitution coefficients and capture efficiency. The influence of the particle stickiness, impact velocity and angle, and surface properties and structure of the target on the rebound patterns was studied. Results indicate that the elastic–plastic adhesive model provides an adequate representation of the non sticky particle–wall collisions. Moreover, the presence of a powder layer on the target favours energy dissipation and accumulation of particles close to the surface. This pattern promotes the establishment of a dense-dispersed phase in the near-wall zone of entrained-flow slagging gasifiers. Increasing the temperature, particles shift from the solid/plastic to the fluid state and the coefficient of restitution drops to vanishingly small values, confirming that deposition is the prevailing phenomenon during the collision of sticky particles on a wall.

Modeling radiative properties of air plasma sprayed thermal barrier coatings in the dependent scattering regime

A theoretical model on radiative properties of air plasma-sprayed (APS) 8wt% yttria stabilized zirconia (8YSZ) thermal barrier coatings (TBCs) is proposed and validated. Starting from analysis of microstructures, pores inside the coating are regarded as scatterers. Dependent scattering effects among scatterers are thoroughly considered in the framework of quasicrystalline approximation (QCA) and Percus–Yevick (P–Y) pair distribution function for sticky hard spherical particles, in which large nonspherical pores are treated as clusters of the elemental pores. Afterwards, the Monte Carlo (MC) method is used to solve the radiative transfer problem inside TBCs based on the radiative properties. The predicted optical responses including reflectance, transmittance and absorptance of TBC slabs with different thicknesses agree well with the experimental data. The widely used independent scattering assumption in conventional studies is also investigated and examined to be inapplicable in the semitransparent spectral region of TBCs, especially between around 3.2 and 5.6μm. This study provides a simple and physically robust direct prediction on radiative properties of TBCs solely based on their microstructures and bulk optical properties of the material. Moreover, the present method can be easily applied to the studies on radiative properties of other semitransparent porous media.

Highly efficient filtration of ultrafine dust in baghouse filters using precoat materials

The precipitation of sticky and ultrafine particles has become increasingly important. Biomass burners are one important example for ultrafine dust emission sources with ever growing importance. Therefore, a baghouse filter has been developed, which combines excellent separation efficiency (>99%, clean air dust loading of <1mg/m3) with convenience in operation. However, in order to prevent clogging of the filter cloth by sticky and ultrafine particles, it is necessary to use a precoat layer (e.g. hydrated limestone powder). If this technology is applied to larger scale processes, e.g. biomass burning for industrial drying processes, the reuse of the precoat material can generate significant savings.Therefore, extended tests on recycling of used precoat material have been performed. Particularly, the influence of precoat injection parameters and various mixing strategies of used and virgin powder for refreshing the precoat material have been investigated. Different mixtures have been characterised by their ability to disintegrate, flowability and filtration behaviour. It is clearly demonstrated that upon redispersing the used precoat fine dust mainly adheres to the coarse precoat with only a limited number of dust agglomerates being produced in addition. For each kind of precoat a minimum amount is determined in order to ensure a long-term stable process. This way a saving potential of between 40–67% has been found.An economic and ecologic process has been developed to precipitate ultrafine dust in a baghouse filter system using precoat materials.

Synthesis and Redispersibility of Poly(styrene-block-n-butyl acrylate) Core–Shell Latexes by Emulsion Polymerization with RAFT Agent–Surfactant Design

A coagulatable and redispersible poly(styrene-block-n-butyl acrylate) (PS-b-PnBA) copolymer latex system was developed. A series of PS-b-PnBA diblock copolymers with the PnBA content up to 70 wt % were prepared via a reversible addition–fragmentation chain transfer (RAFT) emulsion polymerization. An amphipathic poly(acrylic acid-b-styrene) trithiocarbonate was synthesized and employed as macro-RAFT agent and surfactant. The resulted latex particles contained a soft poly(n-butyl acrylate) core and a hard polystyrene shell. The hard plastic shell could prevent the elastomer core from deformation and fusion at room temperature. It was found that the latex particles with the nBA content ⩽60 wt % could be easily coagulated by HCl and redispersed by NaOH with some ultrasound treatment. The coagulation and redispersion processes were repeatable. When the nBA content reached 70 wt %, the plastic shell became too thin, resulting in collapsed sticky particles. The critical shell thickness for redispersible latexes was about 8 nm.

A Simple Proof of Global Existence for the 1D Pressureless Gas Dynamics Equations

Sticky particle solutions to the one-dimensional pressureless gas dynamics equations can be constructed by a suitable metric projection onto the cone of monotone maps, as was shown in recent work by Natile and Savare. Their proof uses a discrete particle approximation and stability properties for first-order differential inclusions. Here we give a more direct proof that relies on a result by Haraux on the differentiability of metric projections. We apply the same method also to the one-dimensional Euler--Poisson system, obtaining a new proof for the global existence of weak solutions.

Deformation propagation in responsive polymer network films

We study the elastic deformations in a cross-linked polymer network film triggered by the binding of submicron particles with a sticky surface, mimicking the interactions of viral pathogens with thin films of stimulus-responsive polymeric materials such as hydrogels. From extensive Langevin Dynamics simulations we quantify how far the network deformations propagate depending on the elasticity parameters of the network and the adhesion strength of the particles. We examine the dynamics of the collective area shrinkage of the network and obtain some simple relations for the associated characteristic decay lengths. A detailed analysis elucidates how the elastic energy of the network is distributed between stretching and compression modes in response to the particle binding. We also examine the force-distance curves of the repulsion or attraction interactions for a pair of sticky particles in the polymer network film as a function of the particle-particle separation. The results of this computational study provide new insight into collective phenomena in soft polymer network films and may, in particular, be applied to applications for visual detection of pathogens such as viruses via a macroscopic response of thin films of cross-linked hydrogels.

Wall effects in entrained particle-laden flows: The role of particle stickiness on solid segregation and build-up of wall deposits

Particle–wall interaction is relevant to the performance of entrained-flow slagging gasifiers. Different micromechanical char–slag interaction patterns may establish, depending on the stickiness of the wall layer and of the impinging char particle. The main goal of this study is to improve the mechanistic understanding of particle–wall interactions, by using the tool of physical modeling. The idea behind this research campaign is to use molten wax as a surrogate of fuel ash. The wax had rheological/mechanical properties resembling those of a typical coal slag. Experiments have been carried out in a 0.10m-ID lab-scale cold entrained-flow reactor, optically accessible, and equipped with a nozzle whence molten wax atomized into a mainstream of air. Reactor lengths in the range 0.1–0.6m were investigated, while the wax was atomized at a temperature of 100–110°C. Two interaction regimes were investigated: the “sticky wall–sticky particle” regime was simulated by setting the air mainstream and the wall temperatures at values beyond the wax melting range (160°C and 140°C, respectively); the “nonsticky wall–nonsticky particle” regime was simulated by setting both temperatures at 30°C, i.e. well below the wax softening range. Assessment of the flow and segregation patterns was based on direct visual observation by means of a progressive scan CCD video camera, while the partitioning of the wax droplets into the different phases was characterized by their selective collection at the reactor exhaust. The micromechanics of particle–wall interactions in the “nonsticky–nonsticky” regime was analyzed on the basis of particle impact and of hydrodynamics of gas mainstream and jet flows. Threshold gas velocities for particle detachment were evaluated for the characterization of particle resuspension phenomena.

Equation of state of sticky-hard-sphere fluids in the chemical-potential route.

The coupling-parameter method, whereby an extra particle is progressively coupled to the rest of the particles, is applied to the sticky-hard-sphere fluid to obtain its equation of state in the so-called chemical-potential route (μ route). As a consistency test, the results for one-dimensional sticky particles are shown to be exact. Results corresponding to the three-dimensional case (Baxter's model) are derived within the Percus-Yevick approximation by using different prescriptions for the dependence of the interaction potential of the extra particle on the coupling parameter. The critical point and the coexistence curve of the gas-liquid phase transition are obtained in the μ route and compared with predictions from other thermodynamics routes and from computer simulations. The results show that the μ route yields a general better description than the virial, energy, compressibility, and zero-separation routes.