Statistical analysis of packed beds,the origin of short-range disorder,and its impact on eddy dispersion

We quantified the microstructural disorder of packed beds and correlated it with the resulting eddy dispersion. For this purpose we designed a set of bulk (unconfined) monodisperse random sphere packings with a systematic, protocol-dependent degree of microstructural heterogeneity, covering a porosity range from the random-close to the random-loose packing limit (? = 0.366–0.46). With the precise knowledge of particle positions, size, and shape we conducted a Voronoï tessellation of all packings and correlated the statistical moments of the Voronoï volume distributions (standard deviation and skewness) with the porosity and the protocol-dependent microstructural disorder. The deviation of the Voronoï volume distributions from the delta function of a crystalline packing describes the origin of short-range disorder of the investigated random packings. Eddy dispersion was simulated over a wide range of reduced velocities (0.5 ≤  ν ≤ 750) and analyzed with the comprehensive Giddings equation. Transient dispersion was found to correlate with the spatial scales of heterogeneity in the packings. The analysis of short-range disorder based on the Voronoï volume distributions revealed a strong correlation with the short-range interchannel contribution to eddy dispersion, whereas transchannel dispersion was relatively little affected. The presented approach defines a strictly scientific route to the key morphology–transport relationships of current and future chromatographic supports, including their morphological reconstruction, statistical analysis, and the correlation with relevant transport phenomena. It also guides us in our understanding, comparison, and optimization of the diverse packing algorithms and protocols used in simulations and experimental studies.     

The dynamic behavior of a stratified column bed packed with porous adsorbent particles having partially fractal structures and a nonuniform ligand density distribution

The dynamic behavior of adsorption in a single column and in stratified column beds packed with porous adsorbent particles having partially fractal structures is studied when all columns have the same total length and the spatial ligand density distribution in the porous microspheres from which the porous adsorbent particles are made, is either uniform or nonuniform and such that the concentration of the immobilized ligands (active sites) increases monotonically from the center of the microspheres to their outer surface. The total number of immobilized ligands in the porous adsorbent particles has the same value whether the spatial ligand density distribution is uniform or nonuniform. The results in this study clearly show that for a given value of the superficial velocity of the flowing fluid stream in the column (for a given value of throughput) the breakthrough time is significantly increased when the radius of the microspheres is decreased, the total number of sections of the stratified column bed is increased, and the spatial ligand density distribution employed in the microspheres is nonuniform. Furthermore, when the superficial velocity of the flowing fluid stream in the column is increased (throughput is increased) the effect that (i) the reduction in the radius of the microspheres and (ii) the increase in the number of sections of the stratified column bed have on providing robust and effective dynamic adsorptive capacity and smaller reductions on the breakthrough time is substantially larger than that realized through the use of the nonuniform ligand density distribution. Similar trends are also observed in the dynamic behavior of adsorption in the systems studied here when the value of the concentration of the adsorbate in the flowing fluid stream entering the column (inlet concentration) has such a high magnitude that the value of the equilibrium concentration of the adsorbate in the adsorbed phase determined from the equilibrium Langmuir isotherm that would correspond to the inlet concentration of the adsorbate in the flowing fluid stream is, for all practical purposes, at its saturation limit.     

Adsorption in a stratified column bed packed with porous particles having partially fractal structures and a distribution of particle diameters

Stratified column bed systems whose sections are formed by packing adsorbent particles with a partially fractal structure are proposed and studied. The simulation results clearly show that the breakthrough times and the shape of the breakthrough curves obtained from stratified column beds are significantly larger and sharper than those obtained from conventional columns. The stratified column beds provide, to the designer and user of chromatographic column systems, more degrees of freedom with respect to the number of parameters and variables that could be controlled in the design, construction, and operation of efficient chromatographic adsorption systems. Furthermore, the results suggest that the stratified column beds could provide a higher dynamic adsorptive capacity than conventional columns when it is required to increase the column throughput.     

Computation of radiative image formation in isolated source and collimated irradiation problems

Due to the ray effect, it is not suitable to employ the discrete ordinates method to calculate the radiation field and the image-formation process in radiative problems with isolated radiative sources (such as point and line sources, isolated medium or boundary source). In this paper, a hybrid method, named Monte Carlo-discrete ordinates method (MCDOM) is developed. Firstly, the Monte Carlo method is used to calculate the emission process. Secondly, the discrete ordinates method is employed to calculate the scattering process, correspondingly, an alternative energy partitioning method is proposed to combine the above two conventional methods. Thirdly, the DOS+ISW algorithm (JQSRT, 2003, 78: 437-453) is used to calculate the image-formation process. Finally, the MCDOM is applied to computing the image formation of an endoscope, which was used to study the hydrodynamics of circulating fluidized beds (Powder Technology, 2001;114:71-83).     

水雾与可燃多孔介质火焰相互作用的实验研究

采用非传播扩散火焰形式,研究了固体可燃多孔介质中水雾-火焰的相互作用,探讨了床层厚度、多孔介质粒度以及燃料预燃时间对水雾灭火效果的影响。结果表明,随着预燃时间增长,水雾停止后床层内部可能发生闷烧现象,随着燃料粒度的减小,这种闷烧几率反而降低。这表明,固体火焰与水雾的相互作用有其独特之处。     

Numerical simulation of fluid–particle hydrodynamics in a rectangular spouted vessel

A three-dimensional, Eulerian simulation was developed to describe isothermal, two-phase flow of the continuous (water) and dispersed (solid particles) phases in a rectangular spouted vessel. The mass and momentum conservation equations for each phase were solved using the finite volume technique, which treats each phase separately, while coupling them through drag, turbulence, and energy dissipation due to particle fluctuations. Particle–particle interactions via friction were also included.     

Magnetized quark and strange quark matter in the spherical symmetric space–time admitting conformal motion

In this paper, we have examined magnetized quark and strange quark matter in the spherical symmetric space–time admitting one-parameter group of conformal motions. For this purpose, we have solved Einstein’s field equations for spherical symmetric space–time via conformal motions. Also, we have discussed the features of the obtained solutions.     

Flow Through a Two-Scale Porosity,Oriented Fibre Porous Medium

A model is described for the meso- and micro-flow through an array of oriented fibre tows with meso-channels between the tows. Axial Stokes's flow was considered in the meso-channels and Darcy's law was applied within the porous fibre tows, taking into account injection pressure and capillary pressures in both types of flow. Transverse flow transfer was modelled from the leading flow front to the lagging flow and a partial-slip boundary condition was applied at the permeable boundaries of meso-channels. Flow visualisation experiments and microstructural characterisation of laminates provided appropriate experimental data for model validation. In this, the predictions for the progress of the leading meso-flow were in excellent agreement with the experimental data. Parametric studies followed including the effects of injection pressure and meso-channel size.     

Agar: a natural and environmentally-friendly support composed of copper oxide nanoparticles for the green synthesis of 1,2,3–triazoles

ABSTRACT

A novel, green and cost-effective heterogeneous nanocatalyst was synthesized by supporting copper (I) oxide nanoparticles on magnetic agar (Cu₂O/Agar@Fe₃O₄). Then, it was characterized with multiple techniques, such as scanning electron microscopy and transmission electron microscopy images, energy-dispersive X-ray analysis, Fourier-transform infrared (FT–IR) spectroscopy, thermogravimetric (TG) analysis, X-ray diffraction pattern, vibrating sample magnetometer curve, and inductively coupled plasma analysis. The catalytic activity of the newly designed catalyst was investigated in a one-pot three-component reaction of alkyl halides, sodium azide, and alkynes to obtain 1,4–disubstituted 1,2,3–triazoles in high yields in water–ethanol media. The present catalyst was simply separated from the reaction media by an external magnet and reused at least five subsequent runs without significant activity loss.     

Operating range of magnetic stabilization flow regime for magnetized fluidized bed with Geldart-B magnetizable and nonmagnetizable particles

The magnetic stabilization flow regime could also be created for Geldart-B nonmagnetizable particles provided some magnetizable particles are introduced and the magnetic field is applied. This study aimed to explore the size (d_pM) and density (Ͽ_pM) effects of magnetizable particles on its operating range. The upper limit (U_mbH) could not be determined from the οP_b⿿U_g⿿ curve but could from analyzing the variation of οP_b-fluctuation with increasing U_g. Due to the variation of U_mfH (lower limit) with d_pM and Ͽ_pM, both U_mbH⿿U_mfH and (U_mbH⿿U_mfH)/U_mfH were used to quantify the operating range of magnetic stabilization. U_mbH⿿U_mfH varied hardly with d_pM but increased significantly with decreasing Ͽ_pM. (U_mbH⿿U_mfH)/U_mfH increased as d_pM or Ͽ_pM decreased. It was more difficult for the nonmagnetizable particles to escape from the network formed by the smaller/lighter magnetizable particles. For the same magnitude of change, d_pM had a stronger effect than Ͽ_pM on (U_mbH⿿U_mfH)/U_mfH. Neither U_mbH⿿U_mfH nor (U_mbH⿿U_mfH)/U_mfH varied monotonously with the minimum fluidization velocity of the magnetizable particles, indicating that no straightforward criterion for matching the magnetizable particles to the given nonmagnetizable particles could be established based on their minimum fluidization velocities to maximize the operating range of magnetic stabilization.