Average Particle Height Research Articles

Comparison of sub-grid drag laws for modeling fluidized beds with the coarse grain DEM–CFD approach

Fluidized particulate systems can be well described by coupling the discrete element method (DEM) with computational fluid dynamics (CFD). However, the simulations are computationally very demanding. The computational demand is drastically reduced by applying the coarse grain (CG) approach, where several particles are summarized into larger grains. Scaling rules are applied to the dominant forces to obtain precise solutions. However, with growing grain size, an adequate representation of the interaction forces and, thus, representation of sub-grid effects such as bubble and cluster formation in the fluidized particulate system becomes challenging. As a result, particle drag can be overestimated, leading to an increase in average particle height. In this work, limitations of the system-to-grain ratio are identified but also a dependency on system width. To address this issue, sub-grid drag models are often applied to increase the accuracy of simulations. Nonetheless, the sub-grid models tend to have an ad hoc fitting, and thorough testing of the system configurations is often missing. Here, five different sub-grid drag models are compared and tested on fluidized bed systems with different Geldart group particles, fluidization velocity, and system-to-grain diameter ratios.

Vapor Deposited Zeolitic Imidazolate Framework-8 Derived from Porous ZnO Thin Films

In recent years, the vapor deposition of zeolitic imidazolate framework-8 (ZIF-8) has gained high attraction due to its good scalability, conformality, and thickness control. The present study provides new fundamental insights regarding the vapor deposition of ZIF-8 from zinc oxide (ZnO). During synthesis, ZnO thin films with different percentages of open porosity (14.5%–24%) were subjected to a 2-methylimidazole vapor for different conversion times (20 min–24 h). For the first time, the impact of the porosity of ZnO thin films onto the converted ZIF-8 is investigated. Grazing incidence X-ray diffraction reveals randomly oriented crystallites of ZIF-8, which already appear after 20 min of conversion. The thickness, roughness, and average particle height of the ZIF-8 layers increase with the conversion time, reaching values up to (172 ± 20) nm, (29 ± 3) nm, and (113 ± 8) nm, respectively, for ZIF-8 obtained from ZnO with 14.5% open porosity. At long conversion times (i.e., 24 h), the results hint at greater precursor porosities resulting in lower thicknesses of ZIF-8, as the thickness, roughness, and average particle height for ZIF-8 obtained from 24%-porous ZnO show values of (132 ± 20) nm, (25 ± 3) nm and (80 ± 8) nm, respectively. Additionally, the potential of the ZIF-8 layers as a photocatalyst for the degradation of the organic dye methylene blue was studied. The ZIF-8 enhances the degradation by approximately 8% when compared to degradation without a photocatalyst.

A study of 8 MeV e-beam on localized defect states in ZnO nanostructures and its role on photoluminescence and third harmonic generation

In this article we have explored an effect of electron beam irradiation (EBI) on physical and nonlinear optical properties ZnO thin nano films. Nanostructured ZnO thin films were grown by low cost spray pyrolysis technique. The irradiation dosage has been fixed at 5 kGy, 10kGY, 15 kGy and 20 kGy. The structural investigation by Glancing angle X-Ray Diffractometer (GAXRD) confirms a polycrystalline phase of ZnO with wurtzite structure. The variation in the surface morphology upon EBI has been demonstrated using 2D and 3D Atomic force microscopy (AFM) images. Nanoscope software analysis quantifies the variation in surface roughness and average particle height upon EBI. The defect states created in the films upon irradiation experiments were investigated using UV–visible spectrophotometer, Room temperature Photoluminescence (RTPL), Raman and X-ray photoelectron spectroscopy (XPS). The increase in urbach tail validates the creation of localized defect states in the films The Gaussian fitting on RTPL spectra shows the quenching in the luminescent centers upon irradiation arised as result of recombination of vacancy defects. Phonon confinement model fitting on Raman spectra endorses that shift in the phonon modes observed on irradiation is due to spatial confinement of phonons. The elemental composition and impurity states of the EBI ZnO thin films were studied using XPS spectra. The shift in the binding energy of Zn and O elements infers the electron beam induced changes in the films. The electron beam irradiation has resulted in the increment of third order optical susceptibility χ(3) 3.5 × 10−4 esu to 8.13 × 10−3 esu due to the enhancement of electronic transition to different defect levels formed in the films and through local heating effects arising due to continuous wave (CW) laser illumination. The enhanced THG signal investigated using Nd:YAG laser at 1064 nm and 8 ns pulse width shows the promising features of EBI ZnO films for frequency tripling applications.

Effect of drag models on CFD–DEM predictions of bubbling fluidized beds with Geldart D particles

The selection of a drag model is of critical importance for fluidized bed simulations. In this study, the effect of different drag models was investigated by conducting Computational Fluid Dynamics and Discrete Element Method (CFD–DEM) simulations of bubbling fluidized beds and comparing the results with two sets of experimental data. For the data reported by Goldschmidt et al. (2004), the Di Felice model resulted in average particle height with less than 16% discrepancy, while the other drag models resulted in significantly lower values with discrepancies between 11 and 45%. For the NETL data (Gopalan et al., 2016), all the drag models showed reasonable qualitative agreement for the radial profiles of the solid velocities; however, no single model resulted in close quantitative predictions. None of the models were found to be suitable for both data sets. The analysis suggests that the Ayeni model and Di Felice model provide better predictions than the conventionally used Gidaspow model and Syamlal–O'Brien model.

Ultrasensitive Determination of Piroxicam at Diflunisal-Derived Gold Nanoparticle-Modified Glassy Carbon Electrode

We present a simple and green approach for synthesis of gold nanoparticles (AuNps) using analgesic drug diflunisal (DF) as capping and stabilizing agent in aqueous solution. Characterization of the synthesized diflunisal-derived gold nanoparticles (DF-AuNps) was performed by ultraviolet–visible (UV–Vis) spectroscopy, revealing the surface plasmon absorption band at 520 nm under optimized experimental conditions. Fourier-transform infrared (FTIR) spectroscopy established the effective interaction of the capping agent with the AuNps. Topographical features of the synthesized DF-AuNps were assessed by atomic force microscopy (AFM), revealing average particle height of 29 nm to 32 nm. X-ray diffractometry was used to study the crystalline nature, revealing that the synthesized DF-AuNps possessed excellent crystalline properties. The synthesized DF-AuNps were employed to modify the surface of glassy carbon electrode (GCE) for selective determination of piroxicam (PX) using differential pulse voltammetry technique. The fabricated Nafion/DF-AuNps/GCE sensor exhibited high sensitivity compared with bare GCE. The current response of the fabricated sensor was found to be linear in the PX concentration range of 0.5 μM to 50 μM, with limit of detection (LOD) and limit of quantification (LOQ) of 50 nM and 150 nM, respectively. The proposed sensor was successfully utilized for sensitive and rapid determination of PX in human serum, urine, and pharmaceutical samples.

Assessment of polydisperse drag models for the size segregation in a bubbling fluidized bed using discrete particle method

Polydisperse gas-particle flow is often encountered in industry and many polydisperse drag models have been developed in literature. In this work, discrete particle method was employed to assess polydisperse drag models for the segregation and mixing of binary gas-particle flow in a bubbling fluidized bed. The degree of particle segregation and the characteristic bubble frequency using different polydisperse drag models were analyzed. It was shown that the results predicted by the model of Rong et al. (2014) are in a best agreement with experimental data with 5.3% errors on average, and two dominant bubble frequencies were found by analyzing the fluctuations of average particle height.

The surface morphology of thin Au films deposited on Si(001) substrates by sputter deposition

Thin (100nm) gold films were deposited on the native oxide of Si(001) substrates by direct current magnetron sputtering. The effects of the deposition rate, the target/substrate distance, the substrate orientation, substrate bias, and substrate temperature on the surface morphology of the gold film have been studied using atomic force microscopy. It was observed that the deposition of Au on Si(001) is characterized, in most cases, by hemi-spherical particles distributed uniformly on the surface. Decreasing the target/substrate distance caused both the average particle diameter and the height to increase. However, at a target/substrate distance of 5cm using a deposition rate of 0.1Å/s, samples with different morphologies were produced characterized by the coalescence of the surface Au particles. Increasing the relative angle from 0° to 90° between the substrate and the sputtering target caused the average particle diameter to decrease by approximately 8.7% and the average particle height to increase by approximately 52.3%. Applying a high negative voltage to the substrate during the deposition caused a small decrease of approximately 10.2% in the average particle size and a change of 26.2% to the average particle height. Lowering the substrate temperature from 12 to −11°C during the deposition process caused a decrease of 21.6% in the average grain size and an increase of 44.7% in the average grain height. By adjusting the above parameters it was possible to obtain samples with an average particle size ranging from 25.8 to 180nm with root-mean-square roughness values ranging from 0.8 to 21nm. The results of this work provide an understanding on how to produce a wide range of surface morphologies of thin Au films on Si(001+native oxide) for applications such as cantilever sensing and for producing bio-functionalized tips for atomic-force microscopy.

Simulation of a dust lifting process with rough walls

The aim of this paper is to present results of Eulerian-Lagrangian simulations of the dust lifting behind a shock wave in a two-dimensional domain with rough walls. Since interparticle and particle-wall collisions are important for the development of the process, simulating walls with a certain roughness is of interest influencing the trajectories of the near-wall particles, which then exchange momentum with particles higher up on the layer. Results of the simulations are shown as snapshots of particle positions at certain points in time. Comparisons between simulations with smooth walls and rough walls with varying initial dust layer thicknesses and number of particles are presented. Statistical data from the simulations are compared, such as average particle height and the number of particle-particle collisions, as is the mechanical energy lost in collisions. For the rough wall simulations, statistics relating the inclination of the virtual-wall with the emergent vertical velocity of particles and the energy lost in collisions are shown for different Gaussian distributions of angles. It was found that the general lifting effect is more intense in the rough wall simulations, the difference increasing with layer thickness. The statistical and energy data also showed significant differences between the smooth and rough wall simulations. The trends seen are substantiated by presenting some results of

Calculation of ac Electric Field Effects on the Average Height of a Charged Colloid: Effects of Electrophoretic and Brownian Motions

Numerical solutions are presented for the time-dependent probability density of a charged colloidal particle near a planar wall, subjected to an alternating electric field, Brownian motion, and DLVO forces. These are the first time-dependent probability distribution solutions for a driven particle in a mobility gradient. The effects of electrophoretic particle motion on the probability distribution for finding a single, 6 μm diameter, polystyrene particle at a given height above an indium−tin oxide surface were studied via numerical solution of the complete convective−diffusion equation, ignoring inertia, in one dimension. Application of an ac electric field monotonically increased the average particle height over a complete cycle of the electric field; the strongest increase was at low frequency and large electric field strengths. These results agreed with observed behavior in potassium hydroxide solutions at high voltages but did not capture the depression of the average height at low voltages. The calculations agreed with the monotonic increase of average height observed in sodium bicarbonate solutions, but the slope of the increase was far less than experimentally observed. The calculated effects are present in the experimental results but do not encompass all the observations.

AFM study of templated growth of cadmium sulfide nanoparticles using pure and mixed arachidate films

Langmuir–Blodgett (LB) multilayers of arachidic acid (AA) and octadecylamine (ODA) were used as templates in order to produce cadmium sulfide (CdS) nanoparticle arrays. Both atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were used to characterize the film. In the absence of ODA, the cadmium arachidate trilayers were highly crystalline with a lattice constant of 0.42 nm. Upon reaction with hydrogen sulfide (H 2S), an ordered array of CdS nanoparticles with a particle separation of 4.2 nm was imaged. The existence of CdS was also confirmed by XPS. No CdS nanoparticles were formed when ODA was used as the sole component. In the presence of ODA, the crystalline structure of the AA film was disturbed, resulted in randomly distributed particles. The average particle height was reduced from 4 to 1 nm when the amount of ODA was increased. It is concluded that there is a direct correlation between the ordering of the organic template and that of the nanoparticle array. There is also a correlation between the particle size and the ratio of AA and ODA. Mixed LB films are promising in synthesizing semiconducting nanoparticle arrays of limited particle sizes.