Phenomenological model‐based analysis of lithium batteries: Discharge,charge, relaxation times studies,and cycles analysis

The operation of lithium ion batteries in discharge and charge processes is addressed. A simple phenomenological model is developed to predict all variables values. A set of algebraic and differential equations is derived taking into account salt and lithium balances in electrodes, in the separator, and in particles. Balances are developed for finite volumes and appropriate average values of several variables such as concentrations, current densities, and electrochemical reaction rates are introduced. Definitions of current densities as volume fraction functions are critical issues in the computations. Experimental values taken from the literature for discharge processes are predicted very accurately. Constant salt concentration in the separator can be assumed and consequently, the model can be analytically solved. Charge and discharge times, initial cell capacity, lost capacity, and relaxation times are easily estimated from simple equations and cell parameters. The limiting processes taking place during cell discharge can be determined. Energy efficiency and capacity usage are quantified for cycles. © 2014 American Institute of Chemical Engineers AIChE J, 61: 90–102, 2015     

Prediction of particle charging in a dilute pneumatic conveying system

When particles are transported in pipelines, they acquire electrostatic charges as they come into contact with the pipe wall. Charged particles can cause problems such as particle agglomeration, blockage, and explosion. Understanding the particle charge can help to prevent these issues. This study investigates a technique for predicting the particle charge in a straight pipe of any given length, as well as the pipe length at which electrostatic equilibrium occurs, through experimentation in a short 1‐m pipe section. Experimentation with five different types of particles and four pipe wall materials at longer pipe lengths were used to validate the technique. This predictive technique is applicable to a range of particle shapes and sizes under the restriction that charge transfer is due to impact charging. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2308–2316, 2013     

Measurements by MRI of the settling and packing of solid particles from aqueous suspensions

This study extends the application of existing magnetic resonance imaging methods to measure the settling of solid particles from aqueous suspensions. The acquisition of one‐dimensional multiecho projections allowed the direct measurement of initial magnetizations (M₀), from which solid volume fractions along the sedimentation column were inferred. For polystyrene beads, it was found that monoexponential curves accurately fitted the transverse relaxation decays. In contrast, for the other four solids investigated (activated carbon, talc, calcium carbonate, and glass beads), the single exponential model did not suffice and additional terms in the fitting function significantly improved the calculation of solid concentrations. Additional information about particle sizes was obtained by comparing volume fractions with the spin–spin relaxation times of the hydrogen protons as a function of the vertical height through the sedimenting suspensions of activated carbon and polystyrene beads. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Preparation of Pt–Ru bimetallic anodes by galvanostatic pulse electrodeposition: characterization and application to the direct methanol fuel cell

The electrodeposition of platinum and ruthenium was carried out on carbon electrodes to prepare methanol anodes with different Pt/Ru atomic ratios using a galvanostatic pulse technique. Characterizations by XRD, TEM, EDX and atomic absorption spectroscopy indicated that most of the electrocatalytic anodes consisted of 2 mg cm^–2 of Pt–Ru alloy particles with the desired composition and with particle sizes ranging from 5 to 8 nm. Electrochemical tests in a single DMFC show that these electrodes are very active for methanol oxidation and that the best Pt/Ru atomic ratio in the temperature range used (50–110 °C) is 80:20. The influence of the relaxation time t _off was also studied and it appeared that a low t _off led to smaller particle sizes and higher performances in terms of current density and power density.     

Multiscale Lattice–Boltzmann Approach for Electrophoretic Particle Deposition

In this work, a gas-particle flow over a structured sensor surface is numerically investigated. A system of parallel electrodes with an applied voltage is distributed on top of a nonconducting flat surface. The considered submicron particles (size range 25–200 nm) are electrically charged. The simulation takes into account the interaction between particle motion, fluid flow and electrical field causing the particles to deposit on the surface. As a result, dendrite microstructures of particles start growing on the electrode surface. To model these effects in detail the numerical simulations are carried out on a mesh with very high resolution of up to Δx = 0.5 μm. The fluid-flow is calculated with the Lattice–Boltzmann method incorporating automatic local grid refinement. The Laplacian equation describing the electrical field is solved by a finite-difference-scheme. The particle movement is calculated by the Lagrangian point-particle approach, accounting for drag force, Brownian motion, and Coulomb forces. Results of particle transport and dynamics of particle deposition are presented for different applied voltage, electrode configurations, flow velocities, and particle sizes.     

Particle‐laden liquid jet impingement on a moving substrate

The impingement of high speed jets on a moving surface was studied. The jet fluids were dilute suspensions of neutrally buoyant particles in water–glycerin solutions. At these low particle concentrations, the suspensions have Newtonian fluid viscosity. A variety of jet and surface velocities, solution properties, nozzle diameters, mean particle sizes, and volume fractions were studied. For each case the splash‐deposition threshold was quantified. It was observed that for jets with very small particles, addition of solids to the jet enhances deposition and postpones splash relative to a particle‐free water–glycerin solution with the same viscosity. In contrast, jets with larger particles in suspension were more prone to splash than single phase jets of the same viscosity. It is speculated that the change in character of the splash response for the jets with larger particles in suspension occurs when the particle diameter is comparable to the lamella thickness. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4673–4684, 2017     

Controllable crystallite and particle sizes of WO3 particles prepared by a spray‐pyrolysis method and their photocatalytic activity

Information about correlation of material properties parameters (i.e., crystallite and particle sizes) and photocatalytic activity of tungsten trioxide (WO₃) particles are still lacking. For this reason, the purpose of this study was to synthesize WO₃ particles with controllable crystallite (from 18 to 50 nm) and particle sizes (from 58 to 677 nm) using a spray‐pyrolysis method and to investigate correlation of crystallite/particle size and photocatalytic activity. To gain control of crystallite/particle size, synthesis temperature (120–1300^°C) and initial precursor concentration (2.5–15 mmol/L) were investigated, which were then compared with the proposal of the particle formation mechanism. The results showed that both crystallite and particle sizes played an important role in photocatalytic activity. In this research, the optimum condition to produce the highest photocatalytic performance of WO₃ particles was at the temperature of 1200^°C (crystallite size: 25 nm), and initial concentration of 10 mmol/L (particle size: 105 nm). © 2013 American Institute of Chemical Engineers AIChE J, 60: 41–49, 2014     

Gas Recombination in Sealed Ni–MHx Cells

This paper focuses on investigation of gas recombination in a positive-limited-sealed Ni–MH_x cell. The positive electrodes were prepared by electrochemical impregnation of fibrous nickel plaques. The metal hydride negative electrodes were made by pasting the mixture of rare-earth hydrogen storage alloy powders, conducting and binding agents on foamed nickel substrates. The measurement of the positive capacity at different charge times was used to estimate the partial current for oxygen evolution at the same time. The effects of charge rate, electrolyte saturation level and initial state of charge of the positive electrodes on the recombination were investigated in sealed Ni–MH_x cells. By determining the differential capacity of nickel hydroxide electrodes, an improved mathematical model was used to evaluate the gas recombination parameters during charge, overcharge, rest and discharge of the positive-limited-sealed Ni–MH_x cell. The gas recombination during rest, discharge and overdischarge was also examined. The oxygen recombination on the nickel hydroxide electrodes can be neglected due to the consumption of water when the nickel hydroxide electrodes were discharged. The longer overdischarge produced an increase in cell pressure for the sealed Ni–MH_x cell at an electrolyte unsaturated level and the evolving gas can be recombined by a following recharge operation. © 1997 SCI.     

A system‐size independent validation of CFD‐DEM for noncohesive particles

For the first time, CFD‐DEM simulations of small‐scale fluidized beds are quantitatively validated against large‐scale experiments. Such validation is possible via the identification of a measurement independent of system size, namely defluidization. CFD‐DEM inputs (particle properties and operating conditions) are measured directly. Sphericity is found to be critical, even for highly spherical particles. This size‐independent method of validation is valuable since it allows for validation of CFD‐DEM models without restrictions on system sizes or particle sizes. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4051–4058, 2015     

A soft‐sphere‐imbedded pseudo‐hard‐particle model for simulation of discharge flow of brick particles

A novel hybrid approach of soft‐sphere‐imbedded pseudo‐hard‐particle model is proposed to cope with the complex collision of nonspherical particles. In this approach, the boundary of a host hard particle is covered by a series of soft‐spheres, which are allowed to oscillate about the equilibrium position according to the position, orientation, and shape configuration of the host particle. The collision processes are twofold: as a predictive process, particle‐particle interaction takes place through the collision between the distributed soft‐spheres, which causes subspheres to deviate from the equilibrium positions; as a corrective process, relaxation is superposed to allow the soft‐spheres to move back toward the equilibrium positions quickly. Consequentially, this process generates the force and torque on the host particle and determines its movement. Finally, after validation, this new model is used to explore the effects of aspect ratio and base angle on the discharge of brick particles in hoppers. © 2016 American Institute of Chemical Engineers AIChE J, 62: 3562–3574, 2016     

The effect of cohesive forces on the fluidization of aeratable powders

The effects of cohesive forces of van der Waals type in the fluidization/defluidization of aeratable type A powders in the Geldart classification are numerically investigated. The effects of friction and particle‐size distribution (PSD) on some design‐significant parameters, such as minimum fluidization and bubbling velocities, are also investigated. For these types of particles, cohesive forces are observed as necessary to fully exhibit the role friction plays in commonly observed phenomena, such as pressure overshoot and hysteresis around minimum fluidization. This study also shows that a full‐experimental PSD consisting of a dozen particle sizes may be sufficiently represented by a few particle diameters. Reducing the number of particle types may benefit the continuum approach, which is based on the kinetic theory of granular flow, by reducing computational expense, while still maintaining the accuracy of the predictions. Published 2013 American Institute of Chemical Engineers AIChE J 60: 473–484, 2014     

Monte Carlo modeling of fluidized bed coating and layering processes

A stochastic modeling approach based on a Monte Carlo method for fluidized bed layering and coating is presented. In this method, the process is described by droplet deposition on the particle surface, droplet drying and the formation of a solid layer due to drying. The model is able to provide information about the coating coverage (fraction of the particle surface covered with coating), the particle‐size distribution, and the layer thickness distribution of single particles. Analytical solutions for simplified test cases are used to validate the model theoretically. The simulation results are compared with experimental data on particle‐size distributions and layer thickness distributions of single particles coated in a lab‐scale fluidized bed. Good agreement between the simulation results and the measured data is observed. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2670–2680, 2016     

Charge neutralization of submicron aerosols using surface-discharge microplasma

In this study we investigated the charging characteristics of a novel aerosol neutralizer (Surface-discharge Microplasma Aerosol Charger; SMAC) based on the dielectric barrier discharging. The surface discharge was induced by supplying positive and negative DC pulses with a pair of micro-structured electrodes. We confirmed the occurrence of the surface discharge by measuring the microdischarge current, and evaluated the charging performance of the SMAC as a particle neutralizer by measuring the penetration efficiency, neutralizing probability, and charge distribution for particles in the size range of 10–200 nm. The SMAC was found to obtain a particle penetration exceeding 90% for the whole particle size range. The neutral fraction obtained by the SMAC showed good agreement with a bipolar diffusion charging theory and the fraction obtained by an ²⁴¹Am radioactive source when the SMAC was optimized for aerosol neutralization with the offset voltage control. The charge distributions of negatively and positively charged particles by the SMAC and the ²⁴¹Am neutralizer were in good agreement also. The charge balance of positive and negative particles obtained by the SMAC was effectively controlled by adjusting the offset voltage on each electrode. This is the first study to demonstrate the successful use of dielectric barrier surface discharge to bring particles of 10–200 nm to an equilibrium charging state in a controllable manner.     

Density segregation of dry and wet granular mixtures in gas fluidized beds

The Discrete Element Method combined with Computational Fluid Dynamics was coupled to a capillary liquid bridge force model for computational studies of mixing and segregation behaviors in gas fluidized beds containing dry or wet mixtures of granular materials with different densities. The tendency for density segregation decreased with increasing fluidizing velocity, coefficient of restitution, and amount of liquid present. Due to the presence of strong capillary forces between wet particles, there was a high tendency for particles to form agglomerates during the fluidization process, resulting in lower segregation efficiency in comparison with fluidization of dry particles. Particle‐particle collision forces were on average stronger than both fluid drag forces and capillary forces. The magnitudes of drag forces and particle‐particle collision forces increased with increasing fluidizing velocity and this led to higher mixing or segregation efficiencies observed in dry particles as well as in wet particles at higher fluidizing velocities. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4069–4086, 2015     

Charge distributions of aerosol dioctyl sebacate particles charged in a dielectric barrier discharger

The collection efficiencies of submicron aerosol particles using a two-stage, dielectric barrier discharge (DBD) type electrostatic precipitator have been reported previously [Byeon et al. (2006). Collection of submicron particles by an electrostatic precipitator using a dielectric barrier discharge. Journal of Aerosol Science, 37, 1618–1628]. In this paper, the charge distributions of aerosol dioctyl sebacate (DOS) particles, which had a mobility equivalent diameter of 118, 175, and 241 nm and were charged in a DBD charger, were examined using a tandem differential mobility analyzer (TDMA) system at applied voltages of 9–11 kV and frequencies of 60–120 Hz. The mean number of elementary charges for positively or negatively charged particles increased slightly with increasing applied voltage or frequency. However, the number of elementary charges increased significantly with increasing particle size. At any applied voltage and frequency, the charge distributions of these particles of these sizes indicated asymmetric bipolar charging. The positive-to-negative charge ratios were 10.4, 4.7, and 3.0 for particle sizes of 118, 175, and 241 nm, respectively, at a DBD voltage and frequency was 9 kV and 60 Hz, respectively. Fluorometric analysis showed that average positive-to-negative charge ratios were 11.5, 4.9, and 3.7 for particle sizes of 118, 175, and 241 nm, which agrees well with the TDMA results. Further fluorometric analyses with larger particles (514 and 710 nm) and higher frequencies (1 and 2 kHz) showed that the positive-to-negative charge ratio reached almost unity with increasing particle size or frequency.     

Absolute Mass and Size Measurement of Monodisperse Particles Using a Modified Millikan's Method: Part I—Theoretical Framework of the Electro-Gravitational Aerosol Balance

A new method for accurate mass and size measurement of monodisperse particles is proposed. In this method, charged aerosol particles are introduced into parallel plate electrodes similar to the Millikan cell, and the number of particles left suspended after a certainty holding time has elapsed is measured. The particle survival rate as a function of the voltage applied to the electrodes is used to determine the particle mass. The particle size is deduced by using the particle density which is determined in a separate experiment. The expression of the particle survival function, which is defined as the survival rate as a function of the mass, for particles with and without Brownian diffusion is derived. The sensitivity of this method to the number average diameter, as well as other size distribution parameters, is analyzed on the basis of the survival function.     

Modelling the 3D microstructure and performance of solid oxide fuel cell electrodes: Computational parameters

In this paper, the computational parameters for a 3D model for solid oxide fuel cell (SOFC) electrodes developed to link the microstructure of the electrode to its performance are investigated. The 3D microstructure model, which is based on Monte Carlo packing of spherical particles of different types, can be used to handle different particle sizes and generate a heterogeneous network of the composite materials. Once formed, the synthetic electrodes are discretized into voxels (small cubes) of equal sizes from which a range of microstructural properties can be calculated, including phase volume fraction, percolation and three-phase boundary (TPB) length. Transport phenomena and electrochemical reactions taking place within the electrode are modelled so that the performance of the synthetic electrode can be predicted. The degree of microstructure discretization required to obtain reliable microstructural analysis is found to be related to the particle sizes used for generating the structure; the particle diameter should be at least 20–40 times greater than the edge length of a voxel. The structure should also contain at least 25³ discrete volumes which are called volume-of-fluid (VOF) units for the purpose of transport and electrochemical modelling. To adequately represent the electrode microstructure, the characterized volume of the electrode should be equivalent to a cube having a minimum length of 7.5 times the particle diameter. Using the modelling approach, the impacts of microstructural parameters on the electrochemical performance of the electrodes are illustrated on synthetic electrodes.     

Bubble dynamics in a 3‐D gas–solid fluidized bed using ultrafast electron beam X‐ray tomography and two‐fluid model

Bubble characteristics in a three‐dimension gas‐fluidized bed (FB) have been measured using noninvasive ultrafast electron beam X‐ray tomography. The measurements are compared with predictions by a two‐fluid model (TFM) based on kinetic theory of granular flow. The effect of bed material (glass, alumina, and low linear density polyethylene (LLDPE), d_p ～1 mm), inlet gas velocity, and initial particle bed height on the bubble behavior is investigated in a cylindrical column of 0.1‐m diameter. The bubble rise velocity is determined by cross correlation of images from dual horizontal planes. The bubble characteristics depend highly upon the particle collisional properties. The bubble sizes obtained from experiments and simulations show good agreement. The LLDPE particles show high gas hold‐up and higher bubble rise velocity than predicted on basis of literature correlations. The bed expansion is relatively high for LLDPE particles. The X‐ray tomography and TFM results provide in‐depth understanding of bubble behavior in FBs containing different granular material types. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1632–1644, 2014     

The effect of particle rotation on the motion and rejection of capsular particles in slit pores

The results from a two‐dimensional computational model describing the motion of capsule‐shaped particles in a slit pore under small Re conditions are reported. Average particle velocities and particle rejection coefficients were determined for capsules with aspect ratios of 2 and 4. Two different approaches were used to characterize particle rotation and hydrodynamic particle‐pore wall interactions. In one approach, all sterically allowed particle orientation angles had equal probability, i.e., infinite rotational diffusion was assumed. In the second approach, particles were allowed to freely rotate in the pore; particle orientations were dictated by hydrodynamic forces acting on the particle surface and rotational particle diffusion was neglected. Minimal lateral migration across the pore was observed for the freely rotating particles. Although particle alignment was observed for the freely rotating particles, rejections predicted from the two approaches were found to be in close agreement. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2828–2836, 2018     

The importance of gravity in droplet evaporation: A comparison of pendant and sessile drop evaporation with particles

As a droplet with particles evaporates, the particles deposit on the substrate surface. In this work, we show the extent of gravitational effects on the particle deposition profile and propose a new model for particle tracing in an evaporating droplet which accounts for gravitational effects. Experimentally, we compare pendant and sessile water droplets with 1 and 3 μm polystyrene particles. Numerically, the finite element method was used to create a transport model of the evaporating droplet system and particle deposition. The numerical and experimental results have excellent agreement and show that a pendant water droplet with 1 and 3 μm polystyrene spheres has significant separation of the two particle sizes. Finally, a phase diagaram was created to map different deposition profiles for various gravitational Péclet numbers (Pe_G) and ratios of Péclet number to Damköhler number (Pe/Da). © 2015 American Institute of Chemical Engineers AIChE J, 62: 947–955, 2016