Geldart B 类颗粒气固流化床内的压力波动特性(英文)

采用多通道压力采集系统测量了Geldart B类颗粒（树脂）矩形流化床(2.000m×0.300m×0.025m)内的压力波动,探索了流化床内的压力波动特征;同时采用标准方差、自相关和互相关函数分析了表观气速和静床高度对压力波动、压力波速度和压力波主频的影响。结果表明,气泡行为（如：气泡的形成、发展、聚并和破碎）是影响流化床内压力波动的主要因素;密相和稀相界面处的压力波动幅值主要由气泡崩塌决定;压力波在流化床内进行传播,并且具有明显的周期性特征;此外,压力波动、压力波速度和压力波主频均与表观气速和静床高度密切相关。     

Fluidization in tapered vessels

Methods for the prediction of bed height and pressure drop in tapered air-fluidized beds are proposed. A comparison was made with measurements in slugging fluidized beds in the slow bubble regime over a wide range of apex angle from 0° (rectangular) to 45°. The bed height and pressure drop are well predicted by each of the proposed methods using the same constant values of bubble rise velocity and fluctuation ratio as for the rectangular fluidized bed with the same distributor geometry.     

循环流化床生物质气化炉内计算流体动力学模拟——鼓泡流化床内改进的颗粒床模型（英文）

采用改进颗粒床模型的CFD方法模拟了实验室规模冷模装置内鼓泡床的流体流动时空特性。模拟结果表明表观气速是影响气固动态特征和压力波动的主要因素之一：随表观气速的增大，气泡数目增加，气泡体积增大，压力波动增强；气速越高时均压降越大；在内循环鼓泡流化床内固体颗粒呈“单室”流型。上述与实验观察相吻合的模拟结果将有助于放大和设计商业化的内循环流化床生物质气化炉。     

多组分气固射流床流动特性 Ⅱ流型的划分

在３００×５０×２６００ｍｍ的二维射流流化床中,使用压力波动的功率谱分析方法,考察了９种单一、双组分混合物物性因素（粒径、密度）、操作因素（射流气速、喷口直径、静床高度、环隙气量）对射流流化床的三种流型：气泡串、射流、喷流相互转变的影响。结果表明,在较低静床高时,随着射流气速的增大,射流床内流型由气泡串、射流过渡到喷流;而静床高较高时,射流气速增大仅由气泡串过渡到射流。环隙气量增大、粒径增大、密度增大,喷流流型出现较困难,最后得出了流型转变图及转变的定量关系式     

Bubble cell for magnetic bead trapping in capillary electrophoresis

A bubble cell capillary classically used to extend the optical path length for UV–vis detection is employed here to trap magnetic beads. With this system, a large amount of beads can be captured without inducing a strong pressure drop, as it is the case with magnetic beads trapped in a standard capillary, thereby having less effect on the experimental conditions. Using numerical simulations and microscopic visualizations, the capture of beads inside a bubble cell was investigated with two magnet configurations. Pressure-driven and electro-osmotic flow velocities were measured for different amounts of protein-A-coated beads or C18-functionalized beads (RPC-18). Solid-phase extraction of a model antibody on protein-A beads and preconcentration of fluorescein on RPC-18 beads were performed as proof of concept experiments.     

加压流化床流化性质的实验与模拟研究

在二维射流流化床装置中,考察了压力对颗粒和气泡运动的影响规律.通过使用摄像技术详细的记录了压力下气泡的行为,并对其进行了分析,由此解决了较高压力下测量流态化性质较为困难的问题.数值研究通过CFD双欧拉模型模拟了带有V形分布器和中心射流的二维流化床内压力对气泡大小、床的膨胀率和射流深度的影响.实验和理论结果表明,在加压状态下,射流气速和分布板气速对气泡的产生、大小及形状有不同的影响.在较高的操作压力下,射流气速增加,气泡变长;分布器气速增大,气泡则变大;射流高度随着分布器气速的增加而降低.模拟结果与实验数据吻合较好,由此该模型为研究较高操作压力下射流流化床流化性质提供了有利的工具.     

About frequency coupling between riser and plenum in a gas fluidized bed

This article deals with the explanation of pressure fluctuations coupling between riser and plenum in a gas fluidized bed. It has been noticed by former experiments that the pressure fluctuations taking place in the riser due to bubbles eruptions is also observed underneath the distributor, in the plenum (also called windbow) under certain conditions. In order to explain how effective is the coupling depending on the bed and air distributor design but also on the flow characteristics, we have developped a simple model associated to an experiment presented hereunder.     

Influence of interparticle interaction effects on the rheological properties of low density polyethylene filled with glass beads

The rheological properties of Low-density polyethylene (LDPE) compounds with different fractions of glass beads have been investigated by means of high pressure capillary rheometry. The purpose of this study is to find a functional approach for describing the flow behaviour of suspensions as a function of the volumetric filler content and the applied shear stress or shear rate, respectively. The flow behaviour of suspensions is influenced by interaction effects, which are dependent on the filler particle, its volume content and particle size. While small glass beads exhibit pronounced interparticle interaction effects even at low volumetric filler concentrations, large glass beads show a plateau of negligibly interactions up to approx. 20% volumetric filler content. With introducing a generalized interaction function the flow behaviour of the tested suspensions could be described with reasonable accuracy in consideration of the transition from negligible to pronounced interactions.     

气固流化床内射流特性的研究

采用Brandani等的数学模型模拟了中心射流宽度为0.01m的二维气固流化床(高1.6m、宽0.3m)内鼓泡和射流的瞬态及时均流体动力学特性。一种典型的Geldart B颗粒――砂子(粒径为500mm、密度为2660kg/m3)作为研究的模拟物料。瞬态结果表明，床内射流产生和发展、射流崩塌后所形成气泡尺寸以及全床内的气体速度场和空隙率均存在明显的非对称性，但是由压力信号功率谱密度得到的时均压力特性则有较好的对称性。因此，对于商业化稳定运转的射流床，可以用半床模拟结果近似解释整床特性；然而，在考察射流床的瞬态特性时，半床模拟结果与整床结果存在明显偏差。     

Nanoparticle flotation collectors: mechanisms behind a new technology

This is the first report describing a new technology where hydrophobic nanoparticles adsorb onto much larger, hydrophilic mineral particle surfaces to facilitate attachment to air bubbles in flotation. The adsorption of 46 nm cationic polystyrene nanoparticles onto 43 μm diameter glass beads, a mineral model, facilitates virtually complete removal of the beads by flotation. As little as 5% coverage of the bead surfaces with nanoparticles promotes high flotation efficiencies. The maximum force required to pull a glass bead from an air bubble interface into the aqueous phase was measured by micromechanics. The pull-off force was 1.9 μN for glass beads coated with nanoparticles, compared to 0.0086 μN for clean beads. The pull-off forces were modeled using Scheludko's classical expression. We propose that the bubble/bead contact area may not be dry (completely dewetted). Instead, for hydrophobic nanoparticles sitting on a hydrophilic surface, it is possible that only the nanoparticles penetrate the air/water interface to form a three-phase contact line. We present a new model for pull-off forces for such a wet contact patch between the bead and the air bubble. Contact angle measurements of both nanoparticle coated glass and smooth films from dissolved nanoparticles were performed to support the modeling.     

Fluidized Bed Polyethylene Reactor Modeling in Condensed Mode Operation

Summary: Modeling of fluidized bed reactor for polyethylene production in the condensed mode operation is proposed in this paper. A two-phase model including the emulsion and bubble phases with the constant bubble size is employed to describe hydrodynamic behavior of the reactor. The kinetics of Ziegler-Natta polymerization is also modeled with a two active site model. The phase behavior and solubility of low molecular weight components in polyethylene are estimated with the Sanchez-Lacombe equation of state. The validation of the model is carried out with industrial data for an ethylene and 1-butene copolymerization with the isopentane as a condensable component. The simulation results are in good agreement with industrial data. The model is also used to study quantitatively the effect of the inlet stream temperature to the reactor and isopentane concentration in the reactor on the production rate. For instance, in a typical process, when the inlet stream temperature changes 10 °C, the production rate will alter about 40%. Furthermore, the change of the isopentane concentration around 1 mole percentage leads to a variation of production rate about 14%.     

射流流化床煤气化炉中气固流动和传热、传质的CFD模拟研究

通过双流体模型对射流流化床煤气化炉进行了CFD（Computational Fluid Dynamics,计算流体力学）模拟。模拟着重分析了流化床气化炉气固流动的特性和传质、传热过程。结果表明,流化床中气固两相的传热、传质过程与气体和颗粒的运动特性密切相关。     

Analytical determination of colouring elements and of their compounds in glass beads from graveyards of the Merowings time

428 Monochrome beads from mainly female graves excavated at Groß-Gerau, Pleidelsheim and Weingarten (Germany) were examined by non-destructive methods, i.e. energy-dispersive X-ray fluorescence analysis (EDXRF), wavelength-dispersive X-ray fluorescence analysis (WDXRF) with fundamental parameter evaluation, and X-ray diffraction analysis. The results obtained by EDXRF were compared with those for beads from Donaueschingen and Eichstetten, published in former papers. In most cases the results obtained by WDXRF show very high contents of the colouring compounds, corresponding to a low glass quality. The diffraction measurements show crystalline colouring compounds at the surface of the glass beads that can be characterized as Pb₂SnSbO_6.5 for the yellow beads and as Cu₂O for the ochre beads.     

Effect of depletion interactions on transport of colloidal particles in porous media

The influence of depletion interactions on the transport of micrometer-sized, negatively charged polystyrene latex particles through porous media was studied by analysis of particle breakthrough curves as a response to short-pulse particle injections to the inlet of a packed column of glass beads. The column outlet latex particle concentration profiles and the total amount of particles exiting the column were determined as a function of the concentration of small, silica nanoparticles in the solution and the bulk flow rate. Because of similar charges, the silica particles do not adsorb to either the latex particles or glass beads and thus induce an attractive depletion force between the latex particles and glass bead collectors. The total column outlet latex particle amount was calculated by integrating the measured breakthrough concentration curve and compared to the known amount of injected particles at the column inlet. It was found that the particle recovery was a decreasing function of the silica nanoparticle concentration and the carrier fluid residence time, and an increasing function of the velocity in the bed. In addition, removing the silica nanoparticles from the flowing solution caused a second outlet peak to appear, suggesting that some of the polystyrene particles were captured in secondary energy wells. The experimental data were interpreted using the predicted potential energy profile between a single particle and a glass bead, which was assumed to consist of electrostatic, van der Waals, and depletion components. The results indicate that secondary energy wells significantly affect particle transport behavior through porous media.     

Capture and release of CO2 by polyamidine

By CO₂ bubbling into an aqueous dimethyl sulfoxide solution, the polyamidine ( Poly‐Amd ) prepared from hexamethylenediamine and triethyl orthoacetate was converted to the bicarbonate salt, Poly‐Amd H·HCO₃, which formed aggregates. Conversely, the aggregates disappeared upon Ar bubbling to release the captured CO₂, reverting to Poly‐Amd completely. Polyethyleneimine ( PEI ) also reversibly captured and released CO₂ molecules in solution by bubbling CO₂ and Ar, respectively, in an alternate manner. No appreciable difference was observed between Poly‐Amd and PEI in CO₂ capture in solution. The binary system consisting of Poly‐Amd and polyethylene glycol ( PEG ) captured CO₂ efficiently at ordinary pressure and reached a stationary state within 200 h, at which 66% of the amidine groups bound CO₂ molecules, which was released upon exposure to a N₂ flow. In contrast to the binary system with Poly‐Amd, the binary system of PEI with PEG did not capture CO₂ efficiently, and only 5.7% of the amino groups bound CO₂ molecules after 600 h. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3404–3411     

Automated sample preparation method for suspension arrays using renewable surface separations with multiplexed flow cytometry fluorescence detection

In this paper, we describe a new method of automated sample preparation for multiplexed biological analysis systems that use flow cytometry fluorescence detection. In this approach, color-encoded microspheres derivatized to capture particular biomolecules are temporarily trapped in a renewable surface separation column to enable perfusion with sample and reagents prior to delivery to the detector. This method provides for separation of the biomolecules of interest from other sample matrix components as well as from labeling solutions. After sample preparation, the beads can be released from the renewable surface column and delivered to a flow cytometer for direct on-bead analysis one bead at a time. Using mixtures of color-encoded beads derivatized for various analytes yields suspension arrays for multiplexed analysis. Development of this approach required a new technique for automated capture and release of the color-encoded microspheres within a fluidic system. We developed a method for forming a renewable filter and demonstrate its use for capturing microspheres that are too small to be easily captured in previous flow cells for renewable separation columns. The renewable filter is created by first trapping larger beads in the flow cell, and then smaller beads are captured either within or on top of the bed of larger beads. Both the selective microspheres and filter bed are automatically emplaced and discarded for each sample. A renewable filter created with 19.9 μm beads was used to trap 5.6 μm optically encoded beads with trapping efficiencies of 99%. The larger beads forming the renewable filter did not interfere with the detection of color-encoded 5.6 μm beads by the flow cytometer fluorescence detector. The use of this method was demonstrated with model reactions for a variety of bioanalytical assay types including a one-step capture of a biotinylated label on Lumavidin beads, a two-step sandwich immunoassay, and a one-step DNA binding assay. A preliminary demonstration of multiplexed detection of two analytes using color-encoded beads was also demonstrated. The renewable filter for creating separation columns containing optically encoded beads provides a general platform for coupling renewable surface methods for sample preparation and analyte labeling with flow cytometry detectors for suspension array multiplexed analyses.     

Circulatory bubble dynamics: From physical to biological aspects

Bubbles can form in the body during or after decompression from pressure exposures such as those undergone by scuba divers, astronauts, caisson and tunnel workers. Bubble growth and detachment physics then becomes significant in predicting and controlling the probability of these bubbles causing mechanical problems by blocking vessels, displacing tissues, or inducing an inflammatory cascade if they persist for too long in the body before being dissolved. By contrast to decompression induced bubbles whose site of initial formation and exact composition are debated, there are other instances of bubbles in the bloodstream which are well-defined. Gas emboli unwillingly introduced during surgical procedures and ultrasound microbubbles injected for use as contrast or drug delivery agents are therefore also discussed. After presenting the different ways that bubbles can end up in the human bloodstream, the general mathematical formalism related to the physics of bubble growth and detachment from decompression is reviewed. Bubble behavior in the bloodstream is then discussed, including bubble dissolution in blood, bubble rheology and biological interactions for the different cases of bubble and blood composition considered.     

Structuring bubbles and foams in gelatine solutions within a circular microchannel device

A flow-focusing device with circular cross-section to produce monodispersed air bubbles and foams in several gelatine solutions is presented. Four flow regimes were studied by varying the gas pressure: dripping, bi-disperse bubbly, bubbly and foam flows. Bubble formation at the flow-focusing exit is discussed in detail and compared with that in rectangular microchannels. The bubble volume was shown to depend on the viscosity of the gelatine solution but not on the surface tension. For the bubbly flow, the frequency of bubble formation in this geometry was similar to that found in rectangular microchannels. For the foam flow the frequency was independent of the pressure. Study in the outlet microchannel for the bubbly and foam flows showed that the gas flow followed a power law with the applied pressure. Finally, the viscous resistance was measured and a pressure drop law was determined for each regime.     

Concentration polarization-based nonlinear electrokinetics in porous media: induced-charge electroosmosis

We have investigated induced-charge electroosmotic flow in a fixed bed of ion-permselective glass beads by quantitative confocal laser scanning microscopy. Externally applied electrical fields induce concentration polarization (CP) in the porous medium due to coupled mass and charge transport normal to the charge-selective interfaces. These data reveal the generation of a nonequilibrium electrical double layer in the depleted CP zones and the adjoining anodic hemispheres of the (cation-selective) glass beads above a critical field strength. This initiates CP-based induced-charge electroosmosis along curved interfaces of the quasi-electroneutral macropore space between glass beads. Caused by mutual interference of resulting nonlinear flow with (flow-inducing) space charge regions, an electrohydrodynamic instability can appear locally and realize turbulent flow behavior at low Reynolds numbers. It is characterized by a local destruction of the CP zones and concomitant removal of diffusion-limited mass transfer. More efficient pore-scale lateral mixing also improves macroscopic transport, which is reflected in the significantly reduced axial dispersion of a passive tracer.