Deviation Of Particle Size Distribution Research Articles

Upscaling polydispersed particle transport in porous media using pore network model

Understanding particle transport in porous media is critical in the sustainability of many geotechnical and geoenvironmental infrastructure. To date, the determination of the first-order rate coefficients in the advection–dispersion equation for simulating attachment and detachment of particles in saturated porous media typically has been relied on the result of laboratory-scale experiments. However, to determine attachment and detachment coefficients under varied hydraulic and geochemical variables, this method requires a large experimental matrix because each test provides only one set of attachment and detachment coefficients. The work performed in this study developed a framework to upscale the results obtained in pore-scale modeling to the continuum scale through the use of a pore network model. The developed pore network model incorporated variables of mean particle size, the standard deviation of particle size distribution, and interparticle forces between particles and sand grains. The obtained retention profiles using the pore network model were converted into attachment coefficients in the advection–dispersion equation for long-term and large-scale simulation. Additionally, by tracking individual particles during and after the simulation, the pore network model introduced in this study can also be employed for modeling the clogging phenomenon, as well as fundamental investigation of the impact of particle size distribution on particle retention in the sand medium.

Theoretical analysis of particle size re-distribution due to Ostwald ripening in the fuel cell catalyst layer

AbstractThe limited durability of hydrogen fuel cells is one of the main obstacles in their wider adoption as a clean alternative technology for small scale electricity production. The Ostwald ripening of catalyst material is recognized as one of the main unavoidable degradation processes deteriorating the fuel cell performance and shortening its lifetime. The paper systematically studies how the modeling approach towards the electrochemically driven Ostwald ripening in the fuel cell catalyst differs from the classical diffusion driven models and highlights how these differences affect the resulting evolution of particle size distribution. At moderately low electric potential, root-law growth of mean particle size is observed with linear relation between mean particle size and standard deviation of particle size distribution, similar to Lifshitz-Slyozov-Wagner theory, but with broader and less skewed distribution. In case of high electric potential, rapid particle growth regime is observed and qualitatively described by redeposition of platinum from a highly oversaturated solution, revealing the deficiencies of the existing platinum degradation models at describing the Ostwald ripening in the fuel cells at high electric potentials. Several improvements to the established models of platinum degradation in fuel cell catalysts are proposed, aimed at better description of the diffusion processes involved in particle growth due to Ostwald ripening.

Grain size distribution uncertainty quantification in volcanic ash dispersal and deposition from weak plumes

AbstractWe present the results of uncertainty quantification and sensitivity analysis applied to volcanic ash dispersal from weak plumes with focus on the uncertainties associated to the original grain size distribution of the mixture. The Lagrangian particle model Lagrangian Particles Advection Code is used to simulate the transport of inertial particles under the action of realistic atmospheric conditions. The particle motion equations are derived by expressing the particle acceleration as the sum of forces acting along its trajectory, with the drag force calculated as a function of particle diameter, density, shape, and Reynolds number. Simulations are representative of a weak plume event of Mount Etna (Italy) and aimed at quantifying the effect on the dispersal process of the uncertainty in the mean and standard deviation of a lognormal function describing the initial grain size distribution and in particle sphericity. In order to analyze the sensitivity of particle dispersal to these uncertain variables with a reasonable number of simulations, response surfaces in the parameter space are built by using the generalized polynomial chaos expansion technique. The mean diameter and standard deviation of particle size distribution, and their probability density functions, at various distances from the source, both airborne and on ground, are quantified. Results highlight that uncertainty ranges in these quantities are drastically reduced with distance from source, making them largely dependent just on the location. Moreover, at a given distance from source, the distribution is mostly controlled by particle sphericity, particularly on the ground, whereas in air also mean diameter and sorting play a main role.

Bubbling to turbulent bed regime transition of ternary particles in a gas–solid fluidized bed

The transition from bubbling to turbulent flow regime of a wide particle size distribution (PSD) powder was investigated in a circulating fluidized bed riser with an internal diameter and a height of 0.1 and 3.7m, respectively. Iron ore and limestone particles were used as the wide PSD powder. To study the effect of particle size distribution on the flow regime transition, five types of mono size glass bead were used. Binary and ternary mixtures were made from the mixture of mono size glass beads. The regime transition of the wide PSD powder was studied by means of overall pressure drop and pressure fluctuation analysis. By gradually increasing the superficial gas velocity, a bed of a wide PSD powder changed from a fixed bed state to partial fluidization and then to complete fluidization. The transition from bubbling to turbulent fluidization occurred in the complete fluidization state. The effects of fine particle concentration, coarse particle size, and particle size distribution on bubbling-to-turbulent regime transition velocity were also studied. A correlation expressed in terms of Rec, Ar, and standard deviation of particle size distribution (σp) was proposed to predict the transition velocity (Uc). The predicted Uc values were in close agreement with the experimental data of mono, binary, and ternary mixtures.

Effects of phase and chemical composition of precursor on structural and morphological properties of (Lu0.95Eu0.05)2O3 nanopowders

Europium-doped lutetium oxide nanopowders have been synthesized by the co-precipitation technique using ammonium hydrogen carbonate as a precipitant. Effects of chemical and phase composition of carbonate precursors on the morphology and sinterability of (Lu0.95Eu0.05)2O3 nanopowders have been studied. Two types of precursors have been obtained differing by the molar ratio R=NH4HCO3/Lu3+: a mixture of crystalline Lu0.95Eu0.05(OH)(CO3)·4H2O and unidentified amorphous phases at R=4–7 and crystalline Lu0.95Eu0.05(H2O)x(HCO3)3·nH2O precursor at R=8–20. The two-phase precursor consists of spherulite-like aggregates, while the crystalline one is characterized by plate-like morphology. Calcination of Lu0.95Eu0.05(H2O)x(HCO3)3·nH2O leads to formation of (Lu0.95Eu0.05)2O3 nanopowders that inherit the precursor morphology, while no morphology succession is observed for (Lu0.95Eu0.05)2O3 nanopowders obtained by heat treatment of the two-phase precursor. Calcination of the two-phase mixture leads to breakdown of the spherulites and to formation of equiaxed particles with an average diameter of 40nm with the standard deviation of particle size distribution of about 15%. The obtained low-agglomerated nanopowders were used in vacuum sintering to produce (Lu0.95Eu0.05)2O3 optical ceramics with in-line transmittance of 41% at 611nm.

Prediction of pressure drop in multi-size particulate pipe flow using correlation and neural network techniques

In this paper, we demonstrate how ANN based frameworks can be designed for prediction of pressure drop. First, Galerkin finite element method is used to simulate fully developed near-homogeneous multi-size slurry flow in horizontal pipe flow. After validating the finite element results with published data, two models (ANN) for the pressure drop are developed. The first model uses individual diameters and concentrations of each class size as inputs, and the second model uses the concentration-weighted mean diameter and standard deviation of particle size distribution as inputs. In comparison to the ANN models, the accuracy of predictions using correlations is found to be significantly inferior.

Clear-water scour at bridge piers in fine and medium gravel beds

An experimental investigation on scour at circular and square piers in uniform and non-uniform gravels (fine and medium sizes) under clear-water scour at limiting stability of gravels is presented. From the experimental results, it is observed that the equilibrium scour depth increases with decrease in gravel size. The variation of equilibrium scour depth with gravel sizes departures considerably from that with sand sizes. Consequently, the resulting sediment size factors for gravels, obtained from envelope curve fitting, are significantly different from the existing sediment size factor for sands. The influence of gravel gradation on scour depth is also prominent in non-uniform gravels. The time scales to represent the time variation of scour depth in uniform and non-uniform gravels are determined. For uniform gravels, the non-dimensional time scale increases with increase in pier Froude number and gravel size, whereas for non-uniform gravels, it decreases with increase in geometric standard deviation of particle size distribution of gravels.Key words: bridge pier, gravel beds, scour, erosion, sediment transport, open channel flow, hydraulic engineering.

Preparation of submicron-sized Mg(OH) 2 particles through precipitation

Fiber and lamellar-like nanosized Mg(OH) 2 particles were synthesized by precipitation of different magnesium salts with sodium hydroxide. An experimental design procedure was used to investigate the effects of salt concentration, base concentration, feed rate, and mixing rate on the mean particle size and the standard deviation of particle size distribution. The products prepared from MgSO 4 were found to be different from those from MgCl 2 and Mg(NO 3) 2. We concluded that the salt and the base concentrations were the key factors influencing the morphology of the final product, its particle size, however, was controlled mainly by the feed rate and the mixing rate.

Pad Surface Roughness and Slurry Particle Size Distribution Effects on Material Removal Rate in Chemical Mechanical Planarization

The ability to predict material removal rates in chemical mechanical planarization (CMP) is an essential ingredient for low cost, high quality IC chips. Recently, models that address the slurry particles have been proposed. We address three such models. The first two differ only in how the number of active particles is computed. Both assume that pad asperities are identical and nonrandom. The third is dynamic in accommodating changing pad properties. For larger mean particle size (diameter), the role of the standard deviation of particle size distribution is uncertain. The dynamic behavior of the third model is compared with experimental observations.

Electrical conduction of anisotropic conductive adhesives: effect of size distribution of conducting filler particles

The force–resistance relationship is investigated by considering for the first time the effect of size distribution of metallic filler particles in anisotropic conductive adhesives. It is shown, for both the elastic and plastic interactions between the metallic particle and the conducting plate, that the relationships between the applied force ( F) and the resistance can be described as power–laws (i.e. ∝ F − n ). The universal power–law relationships are found to be independent of both the mean particle size and the standard deviation of the particle size distribution. However, the exponent constant n is much larger for a non-monosized filler particle distribution than that for a monosized one. Although the power–law relationships are independent of the standard deviation of the particle size distribution and the mean particle size, a large standard deviation of particle size distribution leads to a large resistance. The theoretical prediction of the power–law relationship is found to be supported by available experimental observations.

カスケードインパクターのデータ処理

Numerical studies of the data reduction by a cascade impactor are conducted for specific conditions. It is clearly shown that the Twomey's method is superior to the conventional method which uses a 50% cut size, when nearly monodispersed particles are measured. It is impossible to estimate the true particle size distribution by the conventional method when the geometric standard deviation of the particle size is smaller than the geometric standard deviation of partial separation efficiency.It is possible to estimate the true particle size distribution by use of a Twomey's method, which uses a virtual stage and increases the division of the particle size, even if the geometric standard deviation of particle size distribution is less than 1.1.

A precise method to determine the diameter of airborne latex particles

To determine the diameter of spherical monodisperse latex particles, the following accurate and simple methods have been examined: (1) the balance method; (2) the gravitational sedimentation method; and (3) the electrical mobility method. Among these methods, it was found that the first one was very useful for particles having diameters around 1 μm and the third one which had been well calibrated by the first method was useful for smaller particles. Although the standard deviation of particle size distribution could not be determined in this study, the methods to determine mode and arithmetic mean diameters will be useful for calibration of size analyzers including electron microscopies.

Investigation of Sodium Mist Trapping Efficiency in Mesh-Packed Trap

An analysis is made on the trapping efficiency of a sodium mist trap brought by change in the mist particle size distribution. The trapping efficiency is represented in terms of the rate of mist adhesion onto the mesh wires. A log-normal distribution function is assumed for the particle size distribution in the mist at trap inlet. The analytical results yield the following conclusions: 1. The trapping efficiency is greatly influenced by [dbar]p , the mean particle diameter of the mist, and reduces to a minimum in the region of [dbar]p =1–10 μnm, for a trap packed with mesh of diameter currently practiced (−0.1 mm). Compared with [dbar]p , change in the standard deviation of particle size distribution exerts a much smaller influence on the trapping efficiency.2. The efficiency also depends on the flow rate of the mist through trap, represented by the Reynolds number Re expressed in reference to the wire diameter. With the trap configuration and other factors adopted in the analysis, lowering Re to 0.01, improves almost to unity the trapping efficiency, which is governed in this condition principally by the rate of mist diffusion.3. The calculated trapping efficiency agrees well with the corresponding values determined from the measured sodium concentrations in the inlet and the outlet gases.

Investigation of sodium mist trapping efficiency in mesh-packed trap.

An analysis is made on the trapping efficiency of a sodium mist trap brought by change in the mist particle size distribution. The trapping efficiency is represented in terms of the rate of mist adhesion onto the mesh wires. A log-normal distribution function is assumed for the particle size distribution in the mist at trap inlet. The analytical results yield the following conclusions: 1. The trapping efficiency is greatly influenced by [dbar]p , the mean particle diameter of the mist, and reduces to a minimum in the region of [dbar]p =1–10 μnm, for a trap packed with mesh of diameter currently practiced (−0.1 mm). Compared with [dbar]p , change in the standard deviation of particle size distribution exerts a much smaller influence on the trapping efficiency. 2. The efficiency also depends on the flow rate of the mist through trap, represented by the Reynolds number Re expressed in reference to the wire diameter. With the trap configuration and other factors adopted in the analysis, lowering Re to 0.01, i...