Analysis of Particle Transport and Deposition of Micron-Sized Particles in a 90° Bend Using a Two-Fluid Eulerian–Eulerian Approach

Two-phase flows involving dispersed particle and droplet phases are common in a variety of natural and industrial processes, such as aerosols, blood flow, emulsions, and gas-catalyst systems. For sufficiently dilute particle/aerosol phases, a simplified one-way coupling is often assumed, in which the continuous primary phase is unaffected by the presence of the dispersed secondary phase and standard CFD methods can be applied. To predict the transport and deposition of the particle phase, typically a Lagrangian particle-tracking or Eulerian one-fluid/two-phase drift-flux approach is used. Here, a full two-fluid Eulerian modeling approach is presented for coarse particles (>1 μm), in which transport equations are numerically solved for both particle-phase continuity and particle-phase momentum. Simulation results were obtained for a laminar flow regime (Re 100 and 1000) in a 90° elbow, and the effects of grid topology and resolution were investigated. Additionally, gravity effects were considered for both Re cases. Results using this full two-fluid Eulerian approach were validated against experimental data and other computational studies. One key novel contribution of this work is presentation of a simple algorithm for stabilizing the Eulerian particle-phase equation. To the authors' knowledge, this is the first study documenting a full two-fluid Eulerian approach for dilute particle phases in laminar flow on unstructured (prism/tetrahedral) meshes. The results show the potential of the two-fluid approach for providing a useful alternative to the more typical Lagrangian approach for prediction of coarse-particle transport and wall deposition.

Copyright 2015 American Association for Aerosol Research     

应用Lattice Boltzmann方法数值模拟顶盖驱动流

Lattice Boltzmann方法是近十年来发展起来的基于介观层次上的新算法,是一个崭新的求解流体系统偏微分方程的行之有效且效率比较高的数值计算方法,以其为物理现象建模的手段,在很多领域得到了应用,尤其在化工领域中具有复杂边界和复杂流场的模拟中取得巨大成功,如湍流、多孔介质流、化学反应流、燃烧模拟、结晶过程、磁流体等等。采用LB方法中的D2Q9模型,采用BGK碰撞模型及BounceBack边界条件数值模拟流体在顶盖驱动中的流动现象,给出流场的流线和等压线图,计算结果表明该方法运用到顶盖驱动流动计算中,所得结果与基准解吻合良好。     

Electrophoretic deposition of carbon nanotube–ceramic nanocomposites

The purpose of this paper is to present an up-to-date comprehensive overview of current research progress in the development of carbon nanotube (CNT)–ceramic nanocomposites by electrophoretic deposition (EPD). Micron-sized and nanoscale ceramic particles have been combined with CNTs, both multiwalled and single-walled, using EPD for a variety of functional, structural and biomedical applications. Systems reviewed include SiO₂/CNT, TiO₂/CNT, MnO₂/CNT, Fe₃O₄/CNT, hydroxyapatite (HA)/CNT and bioactive glass/CNT. EPD has been shown to be a very convenient method to manipulate and arrange CNTs from well dispersed suspensions onto conductive substrates. CNT–ceramic composite layers of thickness in the range <1–50 μm have been produced. Sequential EPD of layered nanocomposites as well as electrophoretic co-deposition from diphasic suspensions have been investigated. A critical step for the success of EPD is the prior functionalization of CNTs, usually by their treatment in acid solutions, in order to create functional groups on CNT surfaces so that they can be dispersed uniformly in solvents, for example water or organic media. The preparation and characterisation of stable CNT and CNT/ceramic particle suspensions as well as relevant EPD mechanisms are discussed. Key processing stages, including functionalization of CNTs, tailoring zeta potential of CNTs and ceramic particles in suspension as well as specific EPD parameters, such as deposition voltage and time, are discussed in terms of their influence on the quality of the developed CNT/ceramic nanocomposites. The analysis of the literature confirms that EPD is the technique of choice for the development of complex CNT–ceramic nanocomposite layers and coatings of high structural homogeneity and reproducible properties. Potential and realised applications of the resulting CNT–ceramic composite coatings are highlighted, including fuel cell and supercapacitor electrodes, field emission devices, bioelectrodes, photocatalytic films, sensors as well as a wide range of functional, structural and bioactive coatings.     

Spray Deposition Methods for Improving Interfacial Strength of Copper–Epoxy Systems

A simple spray method using a plain orifice atomizer has been developed for depositing γ-aminopropyltriethoxysilane (APS) from solutions in water and in methanol onto copper surfaces. The evaporative patterns of the sprayed droplets were studied to determine the distribution of deposited APS and the percent coverage of the surface. The peel strengths between copper foil and epoxy resin were measured with and without APS deposition. It was shown that the application of APS resulted in a considerable increase in interfacial adhesion. APS applied from a 1 wt% solution in methanol resulted in a higher peel strength than when applied from a 1 wt% aqueous solution; the opposite was true with 0.2 wt% APS solutions, indicating a trade-off between deposited APS film thickness and surface coverage. In all cases, a higher concentration of APS gives a higher peel strength. APS was very effective when chemisorption occurred at the surface but much less effective when only physisorption took place. A study of the fracture surfaces showed cohesive failure inside the epoxy layer, and that the deposited APS on the copper surfaces had a long-range effect which was seen deep into the epoxy layer, well away from the copper surface.     

Fibrous Particle Deposition in a Turbulent Channel Flow—An Experimental Study

The deposition rate of glass cylinders and dust paper fibers in a turbulent duct flow was studied experimentally. The glass fibers with a minimum diameter of 5 μm and the paper fibers with a minimum diameter of 1–20 μm and aspect ratios from 4 to 20 were deposited on a flat gold plate. The particle concentration at the test section was measured with the aid of an isokinetic probe in conjunction with a digital image processing technique. An oil lubricant was used on the plate to reduce the effect of particle bounce from the surface. The experimental data show that the deposition rate increases with an increase in fiber length and size. For a fixed minimum diameter or a fixed equivalent relaxation time, the deposition rate increases rapidly with fiber aspect ratio. When the equivalent spherical particle relaxation time is used, the deposition rate of the fibers was found to increase only slightly with aspect ratio and resemble those of spherical particles. The measured deposition velocities were in good agreement with the empirical model predictions and previous data.     

Particle size control of cathode components for high-performance all-solid-state lithium–sulfur batteries

Understanding the size effect of each component on battery performance is essential for designing high-performance Li₂S/S cathode for all-solid-state Li–S batteries. However, the size effects of different components are always coupled because ball-milling, an indispensable process to synthesize reversible cathode, simultaneously and uncontrollably reduces the particle size of all the components. Here, a liquid-phase method, without ball-milling, is developed to synthesize the Li₂S composite cathode, so that the particle size of the active material Li₂S and the solid electrolyte Li₃PS₄ (LPS) can be independently controlled at nano- or microscale. This helps reveal that compositing Li₂S and the conductive agent at nanoscale is essential for enhancing the reaction kinetics, whereas the nanoscale particle size and homogenous distribution of LPS is important for accommodating the large volume change of the cathode. By reducing the particle size of Li₂S to 9.4 nm and that of LPS to 44 nm, the liquid-phase-synthesized composite cathode exhibits reversible capacity and 100% utilization of Li₂S under 0.1 C rate.     

Electrophoretic deposition of functionally-graded NiO–YSZ composite films

Functionally-graded NiO–8 mol % YSZ composite films were prepared by a controlled voltage-decay electophoretic deposition (EPD) process. The films consisted of three layers with varying NiO concentrations and porosities. Effects of different parameters including the type of the organic media, solid concentration, NiO:YSZ ratio, and iodine on the stability of EPD suspensions and deposition kinetics were studied. A stable NiO–YSZ suspension was attained in isopropanol with NiO–YSZ ratio of 60:40 and iodine concentration of 0.5 mM. The composite film contained varying NiO concentration from 46 wt.% near the substrate to 32 wt.% close to the electrolyte with 42 wt% NiO in the intermediate region. The thickness of each layer is about 10, 44 and 68 μm, respectively. The prepared anode could be promising for solid oxide full cells as it compromises good contact to the electrode with higher corrosion resistance and active reaction zone with the electrolyte.     

Particle Classification by the Tandem Differential Mobility Analyzer–Particle Mass Analyzer System

Particle mass analyzers, such as the aerosol particle mass analyzer (APM) and the Couette centrifugal particle mass analyzer (CPMA), are frequently combined with a differential mobility analyzer (DMA) to measure particle mass m_p and effective density ρ_eff distributions of particles with a specific electrical mobility diameter d_m. Combinations of these instruments, which are referred to as the DMA–APM or DMA–CPMA system, are also used to quantify the mass-mobility exponent D_m of non-spherical particles as well as to eliminate multiple charged particles. This study investigates the transfer functions of these setups, focusing especially on the DMA–APM system. The transfer function of the DMA–APM system was derived by multiplying the transfer functions of DMA and APM. The APM transfer function can be calculated using either the uniform or parabolic flow models. The uniform flow model provides an analytical function, while the parabolic flow model is more accurate. The resulting DMA–APM transfer functions were plotted on log(m_p)-log(d_p) space. A theoretical analysis of the DMA–APM transfer function demonstrated that the resolution of the setup is maintained when the rotation speed ω of APM is scanned to measure distribution. In addition, an equation was derived to numerically calculate the minimum values of the APM resolution parameter λ_c for eliminating multiple charged particles.

Copyright 2015 American Association for Aerosol Research     

Electrophoretic deposition of carbon nanotube-reinforced hydroxyapatite bioactive layers on Ti–6Al–4V alloys for biomedical applications

Ultra-fine (20 nm) hydroxyapatite powders-reinforced with multi-walled carbon nanotubes were coated on Ti–6Al–4V medical alloy using electrophoretic deposition in an attempt to increase poor mechanical properties of hydroxyapatite, in particular inter-laminar shear strength between coating layer and implant surface. It is shown that the addition of carbon nanotubes increases both hardness, elastic modulus and inter-laminar shear strength of monolithic hydroxyapatite layers. A deposit thickness of 25 μm is also found to be critical for preventing crack formation during sintering.     

Gas-to-Particle Conversion in the Particle Precipitation–Aided Chemical Vapor Deposition Process I. Synthesis of the Binary Compound Titanium Nitride

Particle precipitation-aided chemical vapor deposition (PP-CVD) is a modification of the conventional CVD process, where an aerosol is formed in the gas phase at an elevated temperature, and particles are deposited on a cooled substrate. The synthesis of titanium nitride (TiN), using titanium tetrachloride vapor (TiCl₄), nitrogen (N₂), ammonia (NH₃), and hydrogen (H₂), by the PP-CVD process is studied. TiN is formed by a heterogeneous reaction, using TiCl₄, N₂, H₂, whereas simultaneously TiCl₄ and NH₃ react to form an aerosol. The activation energy of this homogeneous reaction is on the order of 100 kJ/mol. The powder formation process is determined by the dissociation of a titanium containing intermediate species. At low temperature differences between substrate and gas phase (i.e., < 2 K), only dense columnar microstructures, with growth rates of around 20 μm/h, are observed. At these temperature differences no particle deposition is observed. The layers are formed by a molecular diffusion controlled CVD growth mechanism. Porous coherent layers are found in experiments, where intermediate temperature differences are applied (i.e., approximately 2–10 K). The observed interconnection of the particles has to originate from a heterogeneous reaction. Apparently, under these conditions the heterogeneous reaction is fast enough, with respect to the particle precipitation rate, to interconnect the precipitated particles. A further increase in temperature difference between the susceptor and the gas phase only leads to loose powder deposits. In principle, the PPCVD process is a suitable method for the synthesis of thin porous layers of ceramics. To obtain uniform coherent porous layers two separate reaction mechanisms are required under the same experimental conditions. There should be a homogeneous reaction in the gas phase as well as a heterogeneous reaction, which is controlled by surface kinetics, in order to interconnect precipitated particles to obtain a coherent porous layer. Porous ceramic layers can be formed as long as the particle precipitation rate is slow enough with respect to the heterogeneous reaction rate.     

Gas-to-Particle Conversion in the Particle Precipitation–Aided Chemical Vapor Deposition Process II. Synthesis of the Perovskite Oxide Yttrium Chromite

In the particle precipitation-aided chemical vapor deposition process, an aerosol is formed in the gas phase at elevated temperatures. The particles are deposited on a cooled substrate. Coherent layers with a controlled porosity can be obtained by a simultaneous heterogeneous reaction, which interconnects the deposited particles. The synthesis of submicrometer powder of the perovskite oxide yttrium chromite (YCrO₃) by gas to particle conversion, which is the first step of the PP-CVD process, has been investigated, and preliminary results are shown. The powders have been synthesized using yttrium trichloride vapor (YCl₃), chromium trichloride vapor (CrCl₃), and steam and oxygen as reactants. The influence of the input molar ratio of the elements on the composition and characteristics of the powders has been investigated. Phase composition has been determined by X-ray diffraction (XRD). The powders have been characterized by transmission electron microscopy (TEM) and sedimentation field flow fractionation (SF³). At a reaction temperature of 1283 K the powders consist of chromium sesquioxide (Cr₂O₃), or a mixture of Cr₂O₃ and YCrO₃. At stoichiometric input amounts of metal chlorides and steam the formation of YCrO₃ seems to be favored. Two typical particle size distributions have been observed. The primary particle size ranges from 5 to 30 nm for small particles, and from 40 to 250 nm for large particles, depending on the process conditions. The particles tend to be agglomerated. The weight of the agglomerates is independent of the primary particle diameter.     

An Extended Approach for the Development of Fluorogenic trans-Cyclooctene–Tetrazine Cycloadditions

Inverse-electron-demand Diels–Alder (iEDDA) cycloaddition between 1,2,4,5-tetrazines and strained dienophiles belongs among the most popular bioconjugation reactions. In addition to its fast kinetics, this cycloaddition can be tailored to produce fluorescent products from non-fluorescent starting materials. Here we show that even the reaction intermediates formed in iEDDA cycloaddition can lead to the formation of new types of fluorophores. The influence of various substituents on their photophysical properties and the generality of the approach with use of various trans-cyclooctene derivatives were studied. Model bioimaging experiments demonstrate the application potential of fluorogenic iEDDA cycloaddition.     

Simple Approach for Quantifying the Thermodynamic Potential of Polymer–Polymer Adhesion

The free energies of mixing a series of water-soluble polymers with cellulose were calculated using the UNIFAC (universal functional group activity coefficients) algorithm, and the results were correlated with measurements of polymer/cellulose adhesion. The more negative the minimum free energy of mixing, the greater the measured adhesion. Adhesion was quantified by single-lap shear test in which regenerated cellulose films were laminated with aqueous polymer. The results are relevant to the use of adsorbed water-borne polymers to strengthen cellulose fiber–fiber bonds in paper. The calculations did not anticipate the exceptional strength-enhancing properties of carboxymethyl cellulose, nor did they predict molecular-weight effects. Nevertheless, the approach may have utility as a general tool to relate polymer chemistry to adhesion performance.     

Protonated Nickel Bis-Glycine Chelate: Effective Precursor for Electroless Deposition of Nickel–Phosphorus Alloy

Theoretical Foundations of Chemical Engineering - The ionic equilibria in the NiSO4–H2Suc–HGly system were calculated using the Brinkley algorithm to assess the true composition of the...     

A Laboratory Comparison of Real-Time Measurement Methods for 10–100-nm Particle Size Distributions

We present information regarding the relative performance of five TSI particle sizing instruments when presented with several log-normally distributed particle populations that vary in terms of composition, concentration, and modal mean diameter (in the range of 10–100 nm) in a controlled laboratory environment. In experiments conducted with NaCl, NaNO₃, and organic aerosols, across a total particle concentration suite ranging from approximately 1 × 10⁴ cm^?3 to 1 × 10⁶ cm^?3, total number concentrations of sub-100-nm diameter particles from four SMPS systems and an FMPS all fall within ±50% of each other (and generally are within ±30%). However, larger discrepancies are evident in the particle size distribution, particularly for the NaCl particles, with an SMPS operated with a water-based CPC exhibiting large negative bias in modal peak concentrations relative to the isobutanol-based SMPS systems and the FMPS. Much closer agreement is found for NaNO₃ particles, although the SMPS systems tended to exhibit higher modal peak concentrations, and a slight shifting toward lower modal peak diameter than the FMPS.

Copyright 2014 American Association for Aerosol Research     

Electrostatic Spray Deposition of Copper–Indium Thin Films

Electrostatic spray deposition is an innovative coating technique that produces fine, uniform, self-dispersive (due to Coulombic repulsion), and highly wettable, atomized droplets. Copper–indium salts are dissolved in an alcohol-based solvent; this precursor is then electrostatically sprayed onto a moderately heated, molybdenum-coated substrate. Precursor flowrates range from 0.02 to 5 mL/h under applied voltages of 1–18 kV, yielding droplet sizes around a few hundred nanometers. Comparing scanning electron microscope images of the coated samples showed that the substrate temperature, applied voltage, and precursor flowrate were the primary parameters controlling coating quality. Also, the most stable electrostatic spray mode that reliably produced uniform and fine droplets was the cone-jet mode with a Taylor cone issuing from the nozzle.