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.     

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.     

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).     

Polythioether Particles Armored with Modifiable Graphene Oxide Nanosheets

Facile and scalable fabrication methods are attractive to prepare materials for diverse applications. Herein, a method is presented to prepare cross‐linked polymeric nanoparticles with graphene oxide (GO) nanosheets covalently attached to the surface. Alkene‐modified GO serves as a surfactant in a miniemulsion polymerization, and the alkene functionalities of GO exposed to the oil‐phase are incorporated into the polymer particle through thiol‐ene reactions, leaving the unreacted alkene functional groups of the other face of GO available for further functionalization. The surface of GO‐armored polymer particles is then modified with a small molecule fluorophore or carboxylic acid functional groups that bind to Fe₂O₃ and TiO₂ nanoparticles. This methodology provides a facile route to preparing complex hybrid composite materials.

     

红层区城镇地下水对建筑物基础腐蚀及防治研究——以天水市为例

地下水对建筑物基础腐蚀是发育广泛、速率缓慢的地质灾害,它对红层区城市基础工程危害尤显突出。以天水市的红层区为例,利用长期积累的大量地下水化学资料,探讨了腐蚀性地下水的成因,提出了防治地下水对建筑物基础腐蚀的对策。     

Bottom bed regimes in a circulating fluidized bed boiler

This paper extends previous work on the fluidization regimes of the bottom bed of circulating flyidized bed (CFB) boilers. Pressure measurements were performed to obtain the time-average bottom bed voidage and to study the bed pressure fluctuations. The measurements were carried out in a 12 MW_th CFB boiler operated at 850°C and also under ambient conditions (40°C). Two bubbling regimes were identified: a “single bubble regime” with large single bubbles present at low fluidization velocities, and, at high fluidization velocities, an “exploding bubble regime” with bubbles often stretching all the way from the air distributor to the surface of the bottom bed. The exploding bubble regime results in a high through-flow of gas, indirectly seen from the low average voidage of the bottom bed, which is similar to that of a stationary fluidized bed boiler, despite the higher gas velocities in the CFB boiler. Methods to determine the fluidization velocity at the transition from the single to the exploding bubble regime are proposed and discussed. The transition velocity increases with an increase in particle size and bed height.     

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.     

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.     

毫米波被动探测信号的熵特征研究

针对毫米波被动探测系统中以幅度值作为判决特征时,容易将无源干扰(如平面金属、地面积水等)误识别为装甲目标的问题,提出了毫米波被动探测信号的新特征量——熵。从毫米波被动探测典型地物目标的天线温度基本组成出发,提出了熵的提取方法。对一定样本量的地物探测信号进行熵特征分析,结果表明装甲目标的熵与平面金属及地面积水有明显差异,对装甲目标识别的研究提供了新的分析思路和理论指导。