On-chip free-flow magnetophoresis: continuous flow separation of magnetic particles and agglomerates

The separation of magnetic microparticles was achieved by on-chip free-flow magnetophoresis. In continuous flow, magnetic particles were deflected from the direction of laminar flow by a perpendicular magnetic field depending on their magnetic susceptibility and size and on the flow rate. Magnetic particles could thus be separated from each other and from nonmagnetic materials. Magnetic and nonmagnetic particles were introduced into a microfluidic separation chamber, and their deflection was studied under the microscope. The magnetic particles were 2.0 and 4.5 microm in diameter with magnetic susceptibilities of 1.12 x 10(-4) and 1.6 x 10(-4) m(3) kg(-1), respectively. The 4.5-microm particles with the larger susceptibility were deflected further from the direction of laminar flow than the 2.0-microm magnetic particles. Nonmagnetic 6-microm polystyrene beads, however, were not deflected at all. Furthermore, agglomerates of magnetic particles were found to be deflected to a larger extent than single magnetic particles. The applied flow rate and the strength and gradient of the applied magnetic field were the key parameters in controlling the deflection. This separation method has a wide applicability since magnetic particles are commonly used in bioanalysis as a solid support material for antigens, antibodies, DNA, and even cells. Free-flow magnetophoretic separations could be hyphenated with other microfluidic devices for reaction and analysis steps to form a micro total analysis system.     

Compaction of fine powders: from fluidized agglomerates to primary particles

In previous works it has been shown that fine powders (particle size 7 μm m) exhibit two well differentiated behaviors in the compaction regime at low consolidation stresses σ _c . At very low stresses the compaction process is governed by a critical-like dynamics of fractal agglomerates previously formed in the fluid-like regime, undergoing a transition from a random loose packed configuration at the jamming transition to a random close packed state. Then agglomerates are disrupted as further pressure is imposed and there is a cross over to a behavior which is ruled by the initial distribution of local voids within the jammed agglomerates that are filled during compaction. In this work we have extended the range of consolidation stresses up to MPa and we have observed a new transition of behavior at kPa. Our measurements indicate that at this level of consolidation agglomerates are fully disrupted. The compaction process is then determined by the rearrangement of primary particles that have lost memory of their initially agglomerated state in fluidization and behave similarly to noncohesive grains.     

Enhanced fluidization of solid particles in an oscillating acoustic field

Compared with an ordinary fluidized bed, the fluidization quality of solid particles can be effectively improved by vibration induced by appropriate acoustic fields. The effects of sound on the hydrodynamic behavior of fluidized bed have been investigated under the application of acoustic fields of different intensities (110–130 dB) and frequencies (50–500 Hz). The obtained results show that the perturbation effect of the sound field on fixed-bed pressure drop becomes more significant with increasing sound pressure level, exerting a larger pressure than present under ordinary conditions, due to the change in particle arrangement induced by the acoustic field. Except for a particular frequency, the minimum fluidization velocity in the bed decreases gradually with the increase in the ratio of bed height to bed diameter. The rising velocity of the bubble and the average overflow velocity of residual gas in collapse tests are reduced by the acoustic field.     

A Markov chain model to describe fluidization of particles with time-varying properties

A one-dimensional mathematical model of particulate solids thermal treatment in a fluidized bed based on the theory of Markov chains is proposed. A feature of the model takes into account the variation of particle properties that takes place during the fluidization. This variation occurs due to thermo-physical and chemical processes that take place during particulate solids treatment in the fluidized bed. These variations affect the particle settling velocity which is the main parameter that forms the bed expansion and local velocity of flow around the particles that strongly influences the thermo-physical and chemical processes in the bed. A generalized correlation for the drag force coefficient is proposed and tested for various materials. It was necessary to have more precise calculation of the particle settling velocity in the model. The model was developed to describe the drying process in the bed. A good correlation between computed and experimental data was achieved.     

Characteristics of external heat transfer in a fluidization bed of coarse particles

Results are shown of an experimental study concerning the heat transfer in a fluidization bed (2–13 mm) of particles, with a cylindrical thermoprobe used for measurements. A predominance of the convective component in the heat-transfer coefficient has been confirmed in the case of coarse particles. Acriterial formula is proposed for calculating the coefficient of external heat transfer in a fluidization bed with the Archimedes number Ar=1.4·10⁵–3.0·10⁸.Translated from Inzhenemo-Fizicheskii Zhurnal, Vol. 24, No. 4, pp. 589–593, April, 1973.     

Experimental study of fluidization characteristics of Geldart-D particles in pressurized bubbling fluidized bed

The pressurized bubbling fluidized bed shows great advantage in retreating municipal solid waste because it could effectively capture CO₂ and enhance the reaction rate of the process of combustion and gasification. In the present work, fluidization characteristics of Geldart-D particles at elevated pressure were experimentally investigated, such as flow pattern, pressure drop, minimum fluidization gas velocity. At the same fluidization gas velocity, as elevating operating pressure, the fluidization of Geldart-D particles became more intense, the bubbles got larger, the standard deviation and the power density of dominant frequency of the pressure drop signal increased. While, under the same fluidization number, as increasing operating pressure, the fluidization of Geldart-D particles became smoother, the bubble size decreased, both the standard deviation and the power density of dominant frequency of the pressure drop signal decreased. It seems that, under elevated pressure, the fluidization behavior of Geldart-D particles would transition to that of Geldart-B particles. Finally, the minimum fluidization velocity of the Geldart-D particles was found decreased with the increase of the operating pressure. A new correlation for the prediction of the minimum fluidization velocity of Geldart-D particles at elevated pressure was also formulated based on the present experimental results.     

Experimental study on fluidization characteristics of different-sized particles in a U-type reduction chamber

A novel fluidized bed reactor, which is an improvement of the loop seal, was applied successfully to iron ore reduction roasting. For this U-type reduction chamber, the fluid dynamic behaviors of different-sized particles were investigated via a cold experimental apparatus using the pressure measurement method in this study. The results showed that the measured U_mf of 71, 101 and 147 μm-sized particles were 0.033, 0.040 and 0.059 m/s, while the U_c were 0.167, 0.190 and 0.223 m/s, respectively, demonstrating that the decrease of particle size caused a rapid transition from both the fixed to bubbling regime, and the bubbling to turbulent flow regime. Under stable operation, the pressure drop, average solids holdup and axial nonuniformity index across the FC increased when particle size increased, along with the solids height and pressure drop gradient in the SC, though the differential pressure fluctuation decreased. These consequences indicated that larger particle size promotes the opportunity for particle mixing and contacting, accordingly increasing the preferential formation of the particle aggregation and deteriorating the reduction performance. These can provide guidelines for the regulation and control of industrial iron ore fluidized bed roasting.     

Investigating the fluidization of disk-like particles in a fluidized bed using CFD-DEM simulation

Fluidization of monodispersed disk-like particles with different aspect ratios in the fluidized bed is simulated by CFD-DEM, with disk-like particles being modeled by the super-ellipsoids. The relatively comprehensive investigations are performed in order to understand the fluidization behaviors of disk-like particles and to evaluate how the aspect ratio influences the fluidization. The results obtained demonstrate that disk-like particles with a larger aspect ratio possess stronger particle movement and more apparent fluidization. Comparisons between spherical particles and disk-like particles elucidate their differences in the fluidization behavior. Particle orientation is also investigated in this paper due to its important influence on the fluidization. Particles possess different preferred orientations in the static bed and in the fluidization state, and a reduced aspect ratio can drive particles to be in the preferred orientation. The existence of the walls will prompt particles to align their cross sections to be parallel to the plane of the walls.     

Electron beam initiated oxidation and coalescence of metal particles embedded in a plasma-polymer thin film matrix

Microstructural changes in plasma-polymer thin films with embedded indium or silver nanoparticles were initiated by electron beam irradiation. Oxidation of indium particles was realized by electron beam irradiation in situ with the electron microscope. By means of selected area electron diffraction it was demonstrated, that indium particles oxidize to smaller In₂O₃ crystallites. On the other hand, thermal annealing of the films results only in a formation of an indium oxide shell. At plasma-polymer films with embedded silver particles, the electron beam irradiation with a microfocus electron source results in an increase of the size of the embedded silver particles with a simultaneous decrease of the particle number (coalescence).     

Experimental study of boiling on heating surfaces during the thermal fluidization of a bed of particles

The results of an experimental investigation into the boiling of distilled water, aqueous solutions of NaCl, and sea-water brine on heating surfaces situated in a bed of mutuallydisconnected particles at atmospheric and reduced pressures are presented.     

Immobilized particle arrays: coalescence of planar- and suspension-array technologies

Combining positive attributes of planar arrays and suspension arrays, immobilized particle arrays offer a new format in which immobilized submicrometer particles are arrayed on hydrogel-coated slides, providing 100+ assay replicates within each spot. This research describes how to prepare immobilized protein arrays and how to assay the binding of labeled target molecules to the arrayed capture probes. The assay system exhibits an intrinsic dynamic range of two to three decades, with coefficients of variation from 5 to 10%. For antibody-antigen binding, target capture appears to be reaction rate limited. For labeled antibody binding to antigen on the immobilized particles, the detection limit is approximately 0.5 ng/mL. When antibodies on the immobilized particles exhibit multivalent binding of target molecules, the detection limit is approximately 0.01 ng/mL. For protein arrays, potential advantages of this format are improved coating of the capture reagent, an increased number of options for protein presentation, reduced mass transport effects, and higher density multiplexing.     

Bending strength of black and composite agglomerates of cork

The bending strength of black and composite agglomerates of cork is investigated. In the preparation of the agglomerates, the raw material used was black regranulate (BR) of cork. Specimens of black agglomerate (BA) with a different thickness were obtained. In the case of the composite agglomerate (CA), both the particle size of BR and the resin dosage were varied. The bending strength increased with the increase in the specimen thickness for BA and in the particle size and the resin dosage for CA. This later parameter, in particular, greatly influenced such a mechanical property of this agglomeration product of cork.     

Hydrodynamic studies on fluidization of Red mud: CFD simulation

Hydrodynamic studies are carried out for the fluidization process using fine i.e. Geldart-A particles. Effects of superficial velocity on bed pressure drop and bed expansion is studied in the present work. Commercial CFD software package, Fluent 13.0 is used for simulations. Red mud obtained as waste material from Aluminum industry having average particle size of 77 microns is used as the bed material. Eulerian–Eulerian model coupled with kinetic theory of granular flow is used for simulating unsteady gas–solid fluidization process. Momentum exchange coefficients are calculated using the Gidaspow drag functions. Standard k–ε model has been used to describe the turbulent pattern. Bed pressure drop and bed expansion studies are simulated by CFD which are explained with the help of contour and vector plots. CFD simulation results are compared with the experimental findings. The comparison shows that CFD modeling is capable of predicting the hydrodynamic behaviors of gas–solid fluidized bed for fine particles with reasonable accuracy.     

3D printing of tuneable agglomerates: Strain distribution and effect of internal flaws

The current study presents a novel and reliable method for producing 3D printed agglomerates with different colour distributions and material properties with 2-fold aims: providing feasible and accurate control on compression of agglomerates under different compression angles, and better tracking of individual particle position after agglomerate breakage. Multi-coloured agglomerates in cubic tetrahedral and random sphere shapes were printed with both rigid and soft bonds. The printed agglomerates were analysed thoroughly of their surface and structural properties including surface roughness and printing accuracy. The agglomerate breakage behaviours under static compression were analysed as a function of bond strength, loading rate and loading directions, with strain distribution plotted over the random sphere agglomerate structure. In addition, agglomerate structures with designed internal macro-voids in different positions and sizes were also created for breakage study, in an effort to better understand parameters governing the mechanical properties of agglomerates with cavities and voids which is inevitable in particle industry but poorly understood at present.     

Capillary instability and breakup of a viscous thread

Papageorgiou derived a similarity solution that describes the asymptotic behavior of a thinning viscous thread suspended in vacuum, near the critical time and around the location of breakup. The motion is driven by surface tension, and the fluid inertia is neglected throughout the evolution. To assess the physical relevance of the similarity solution, the evolution of an infinite thread immersed in an ambient fluid with arbitrary viscosity, subject to periodic axisymmetrtic perturbations is simulated through solution of the equations of Stokes flow by a boundary integral method. The results show that when the thread is suspended in vacuum, the similarity solution accurately describes the process of thinning over an extended length of the thread between the developing bulges, and captures the late stages of breakup for a broad range of initial conditions. But a small amount of ambient fluid viscosity, as small as 0.05 times the viscosity of the thread fluid, drastically alters the nature of the motion by shifting the location of the breakup points toward the bases of developing bulges, and causing the thread to develop locally asymmetric shapes.