Bed Of Beads Research Articles

Heat transfer in packed beds: experimental evaluation of one-phase water flow

Experimental heat transfer studies were carried out in 50.8 mm diameter packed beds of glass beads percolated by water and heated from the wall. The tube-to-particle diameter ratio (D/dp) ranged from 1.72 to 13.7 and the water flow rate from 1.1 to 9.9 l/min. Bed heights ranged from 100 mm to 700 mm. The radial temperature was measured above the bed surface by five aligned sheathed thermocouples. Variations in angular temperature were observed, independent of both radial position and particle diameter. Results of repeated tests with the same packing and with repacking did not differ statistically. The radial temperature profile at the bed entrance, measured by a ring-shaped sensor, was uniform except very close to the tube wall.

Drying of Porous Materials in Fluidized Bed of Silica Gel Beads

Drying of Porous Materials in Fluidized Bed of Silica Gel Beads

径の異なるガラス粒子からなる充填層の有効熱伝導率の検討(OS5-1 エネルギの有効利用I)

径の異なるガラス粒子からなる充填層の有効熱伝導率の検討(OS5-1 エネルギの有効利用I)

Immunomagnetic T cell capture from blood for PCR analysis using microfluidic systems

A one-step immunomagnetic separation technique was performed on a microfluidic platform for the isolation of specific cells from blood samples. The cell isolation and purification studies targeted T cells, as a model for low abundance cells (about 1:10,000 cells), with more dilute cells as the ultimate goal. T cells were successfully separated on-chip from human blood and from reconstituted blood samples. Quantitative polymerase chain reaction analysis of the captured cells was used to characterize the efficiency of T cell capture in a variety of flow path designs. Employing many (4-8), 50 microm deep narrow channels, with the same overall cross section as a single, 3 mm wide channel, was much more effective in structuring dense enough magnetic bead beds to trap cells in a flowing stream. The use of 8-multiple bifurcated flow paths increased capture efficiencies from approximately 20 up to 37%, when compared to a straight 8-way split design, indicating the value of ensuring uniform flow distribution into each channel in a flow manifold for effective cell capture. Sample flow rates of up to 3 microL min(-1) were evaluated in these capture beds.

Effect of liquid addition on heat transfer in gas-fluidized beds of large light particles

When liquid is added to large-particle gas-fluidized beds where the liquid density is similar to the particle density, the liquid addition can cause a dramatic increase in the velocity range and intensity of fluidization. In this paper it is shown that this also leads to strong enhancement of the heat transfer between the bed and an immersed tube. Experiments were carried out using a heated tube of outer diameter 25 mm in air-fluidized beds of polystyrene particles or glass beads to which small quantities of water (typically equivalent to 10 per cent of the bed volume) were added. The results from the heat transfer experiments are explained with the aid of observations of the tube surface using an industrial endoscope located inside the tube. The key factors underlying the enhancement of heat transfer are identified to be heat conduction to liquid-solid aggregates, convection to the liquid phase, convection to the gas phase and vaporization.

Experimental Validation of a Two‐Phase Flow Model for Pressure Drop and Liquid Hold‐up in Downflow Packed Bed Bubble Reactors

AbstractA new model has been developed in order to predict pressure drop and gas fraction of industrial fixed bed reactor operated in downward bubbly flow. The mechanistic approach proposed by Attou and Ferschneider (1999) has been followed. In this approach, mass and momentum balances are solved for gas‐liquid mixture. To solve the system equation, closure laws are needed for the interfacial force between liquid and solid FLS and for the gas fraction expression. These closure laws have been determined by measuring both pressure drop and gas fraction with downward air‐water bubbly flows through a 40 cm diameter fixed bed of glass beads. The averaged gas fraction is measured by using a gamma scanning system that perform attenuation measurements along 64 chords across a section. Finally, a new bubble flow model is proposed to interpret the results.

Quantitative Study of Electrokinetic Transport in Porous Media by Confocal Laser Scanning Microscopy

Refractive index matching of liquid and solid phases in a bed of porous spherical glass beads allowed the use of confocal laser scanning microscopy for a quantitative study of intraparticle electrokinetic transport phenomena. By recording transient profiles of fluorescent, charged, and uncharged tracers, a significantly faster mass transfer was demonstrated for the electrokinetically enhanced transport as compared to a diffusion-limited process. Intraparticle electroosmotic and electrophoretic migration velocities were found to produce nonsymmetric distributions of tracer inside a sphere, contrasting with the symmetric profiles observed for diffusive transport.

Mixing and segregation of binary mixtures of particles in liquid–solid fluidized beds

The effects of size, shape, and density of tracer particles on mixing and segregation in liquid–solid fluidized beds were studied. A collision technique was used to define a new mixing index. Collisions between tracer particles and probes were found at 16 locations inside the fluidized bed simultaneously. The collision frequency of particles on probes was considered to be proportional to their local concentration inside the fluidized bed. Glass beads (3 and 5 mm in diameter) were used to study the effect of size on mixing. Graphite beads and cylindrical aluminum beads were introduced into a bed of spherical glass beads to investigate the density and shape effects, respectively. Smaller bed heights enhanced the mixing of particles lighter than the bed particles. Particle density had a greater effect on segregation than size and shape.

Separation of proteins in a multicompartment electrolyzer with chambers defined by a bed of gel beads.

Multicompartment electrolyzers (MEs) with isoelectric membranes were introduced in 1989 for purifying proteins in an electric field. At the basis of ME technology there are membranes consisting of cross-linked copolymers of acrylamide and acrylamido monomers bearing protolytic groups. The technology employed for casting the membranes is an extension of the isoelectric focusing in immobilized pH gradient technique for which specific acrylamido monomers, known with the trade name of Immobiline, have been developed. However, the use of continuous membranes presents several disadvantages. Due to the mechanical characteristics of polyacrylamide, the gel must physically adhere onto a rigid support, which prevents it from collapsing. The support must have a highly porous structure in order to be permeable to proteins. The mechanical fragility of the membranes is one of the main problems that hinders the industrial scale application of ME separators. In order to overcome this problem, we propose to substitute the continuous membranes with a bed of gel beads of identical comonomer composition, obtained by an inverse emulsion polymerization process.

Experimental Study on Microwave Vacuum Drying of Two-Porosity Level Media

Microwave vacuum drying experiments were performed on a laboratory scale dryer with a two-level porosity material: a packed bed of porous alumina beads. The incident microwave power and the vacuum pressure level were fixed, the main varying parameters being the beads diameter and porosity, and the mean pore diameter. The drying kinetics and the evolution of the product temperature are presented. The drying kinetics can be divided into two main periods. The first one corresponds to the drying from the bed voids according to evaporation mechanism that we describe with a stagnant film law. The second one corresponds to the drying from the particle pores and we divide it into two parts: we suggest that the former is dominated by capillarity driven moisture transport, and the latter is limited by the desorption kinetics of the few water layers left.

G222 CO_2 地中隔離における多孔質内二相流の MRI 計測

This paper describes experimental research on two-phase flow of supercritical CO_2 and water in a porous medium. We used a magnetic resonance imaging (MRI) technique to directly visualize the distribution of supercritical CO_2 injected into a packed bed of glass beads containing water. After the CO_2 displaced much of the water, about 20% of water remained in the porous medium under the condition at the depth of 1000m. Supercritical CO_2 moves upward swiftly due to buoyancy.

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.

Oil mobility in a saturated water-wetted bed of glass beads

The mobilization of an oil bank in a packed bed of glass beads saturated with an aqueous phase has been studied both theoretically and experimentally. The size of the glass beads was varied in the range between 0.5 and 5 mm. Two oils (hexadecane and hexane) with viscosities different for an order of magnitude and densities smaller than that of water have been used. A few more runs have been carried out using perchloroethylene (PCE), with density greater than that of water. The interfacial tension in the aqueous phase was varied in a quite large range (0.38–39.1 dyn/cm) by adding surfactants to the water. The glass assembly made it possible to follow the evolution of the dyed oily phase by the use of a digital camera. A very simple stochastic model for describing the porous structure of the packed bed made it possible to set a criterion for determining the probability of mobilization of ganglia which are produced by the fragmentation of the oil bank. The same model permits also to estimate the probability function of the velocity of a ganglion of an assigned size.

Near real-time biosensor-based detection of 2,4-dinitrophenol

A fluorescent biosensor assay has been developed for near real-time detection of 2,4-dinitrophenol (DNP). The assay was based on fluorescent detection principles that allow for the analysis of antibody/antigen interactions in solution using the KinExA™ immunoassay instrument. Our KinExA™ consisted of a capillary flow observation cell containing a microporous screen that maintains a compact capture antigen-coated bead bed. The bead bed was comprised of polymethylmethacrylate (PMMA) beads coated with dinitrophenol–human serum albumin (DNP–HSA) conjugate. Phosphate buffered saline (PBS) solutions, containing various concentrations of free DNP, were incubated for 30 min with mouse anti-DNP monoclonal antibody to equilibrium. Solutions containing the DNP–monoclonal antibody complex and possible excess free antibodies were then passed over DNP–HSA labeled beads. The free monoclonal anti-DNP antibody, if available, was then bound to the DNP–HSA fixed on the beads. The system was then flushed with excess PBS to remove unbound reactants in the bead bed. The beads were then subjected to brief contact with PBS solutions containing goat anti-mouse fluorescein isothiocyanate (FITC)-labeled secondary antibody, once again, followed by a short PBS flush. The fluorescence was recorded during the addition of the FITC labeled secondary antibody to the bead bed through the final PBS flushing with the KinExA™. The amount of DNP detected could then be determined from the fluorescent slopes that were generated or by the remaining fluorescence that was retained on the beads after final PBS flushing of the system. This assay has been able to detect a minimum of 5 ng/ml of DNP in solution and can be adapted for other analytes of interest simply by changing the capture antigen and antibody pairs.

Hydrodynamics of a uniform liquid-fluidized bed containing a binary mixture of particles

This paper examines the steady state hydrodynamics of a fluidized bed of two particle species, having different diameters and densities. Steady state mixing solutions of the volume-averaged equations of motion for the fluid and particles are sought. An expression for the fluid–particle interactive force (in the mixture) is postulated to close the continuum equations of motion using an excluded volume assumption. Solutions to the equations are found for a fluidized bed of glass beads and carbon char in water. It is shown that the solution sets not only characterize the composition and expansion behavior of the mixing states, but also provide a description of the observed phenomenon of “layer inversion”. The model identifies three possible layer inversion scenarios, one of which has been observed experimentally. Comparison with experimental data suggest that the hydrodynamic mechanism of fluid–particle interaction is not fully captured with an excluded volume assumption. Thus, we show how experimental data can be used to derive functional forms for expressing the complex hydrodynamic behavior within the framework of the model.

Reduced encephalopathy in pigs with ischemia-induced acute hepatic failure treated with a bioartificial liver containing alginate-entrapped hepatocytes.

To analyze the effects of an extracorporeal bioartificial liver containing alginate bead-entrapped hepatocytes on pigs with ischemia-induced acute hepatic failure. Prospective animal study. University and INSERM laboratory. Fifteen Large White/Pietrin female pigs weighing 20-30 kg. Acute hepatic failure was induced by end-to-side portocaval shunt and ligature of the whole porta hepatitis. The bioartificial liver was in a thermostabilized column, containing a fluidized bed of alginate beads that embedded porcine hepatocytes, connected to a plasmapheresis system. Intracranial pressure; survival; ammonia, total bilirubin, aminotransferases, alkaline phosphatase, and lactate concentrations; and clotting factors were studied. The groups were pigs with acute hepatic failure (group 1, n = 4), pigs with acute hepatic failure treated with bioartificial liver containing empty beads (group 2, n = 4), or porcine hepatocytes (group 3, n = 5). In group 1, survival of pigs averaged 10.9 +/- 1.0 hrs; intracranial pressure reached 32.3 +/- 3.8 mm Hg and was associated with coma and cerebral edema. After connection to the bioartificial liver, the survival of acute hepatic failure pigs was 12.1 +/- 1.4 hrs in group 2 and 14.8 +/- 2.5 hrs in group 3. In group 3, intracranial pressure and bilirubin concentrations were reduced significantly compared with both group 1 and group 2. Neither signs of encephalopathy nor cerebral edema was observed in any animal of group 3. In all animals, plasma ammonium, aminotransferases, alkaline phosphatase, and lactate concentrations increased and clotting factors decreased with no significant differences between the three groups. Autopsy revealed a total necrosis of the liver, which was histologically confirmed. The ischemia-induced model of acute hepatic failure in pigs is reproducible and provides measurable clinical and biological features. A bioartificial liver containing alginate bead-entrapped hepatocytes improves the signs of encephalopathy in pigs with ischemia-induced acute hepatic failure, suggesting that the bioartificial liver can clear out toxic compounds that are released from necrotic livers.

Factors influencing the nitrification efficiency of fluidized bed filter with a plastic bead medium

The performance of fluidized bed nitrification filters charged with 2×4 ABS plastic beads (specific gravity 1.06) was evaluated. Three unique bed-height to diameter ratios were established, in triplicate, using column diameters of 12.7, 15.2 and 17.8 cm. Filters received water spiked with recycled nutrients and ammonia (TAN), from one of the three 500 l feed tank system. With daily ammonia loading fixed at 8.6 g per system, TAN removal increased with column diameter at each of four tests hydraulic loading rates (6, 8, 10 and 12 Lpm). TAN in recirculated water (influent) rose from 0.5 to 1.0 mg/l as ammonia loading increased from 180 mg/m 2-day to 360 mg/m 2-day. When hydraulic loading was fixed at 12 Lpm, TAN removal (%) was maximized with ammonia loadings ranging from 225 to 270 mg/m 2-day. Biofilm thickness increased with ammonia loading, but decreased with increased hydraulic loading rates. Fluidized beds of ABS plastic beads were effective in reducing energy costs (head loss) of water treatment.

Purification of a bacterial pullulanase on a fluidized bed of calcium alginate beads

Pullulanase from Bacillus acidopullulyticus was purified on a packed bed and a fluidized bed of calcium alginate beads. The binding of enzyme activity to the medium was found to follow Langmuir isotherm pattern. The maximum binding capacity was 1476 U ml −1 matrix and the dissociation constant was 142 U ml −1. The dynamic binding capacities at 5% breakthrough in the packed and fluidized beds were 472 U ml −1 and 644 U ml −1, respectively. In the packed bed as well as the fluidized bed, an activity recovery of more than 95% with fold purification in the range of 46–59 was observed. The elution with a competitive inhibitor, viz. maltose, and high-fold purification indicate an affinity-based process. The purification process worked equally well with columns of bed volumes of 3.8 and 10 ml.

Wicking flow in irregular capillaries

Understanding capillary flow in porous media (wicking) is critical for predicting and improving the performance of absorbent structures. Capillary flow in straight circular tubes has long been known to be quite well described by the Lucas–Washburn equation. Experimental wicking results with beds of glass beads led us to investigate a minor modification of this equation to describe more complex systems. These results, as well as the mathematical treatment, are presented to describe capillary flow as a function of time in tubes irregularly shaped along their primary axis. The cross-section of the model tubes remains circular. Variations of the diameter that are periodic along the length of the tube are the focus of the study, and a sinusoidal description is argued to be sufficiently general to describe most systems. The variables used to describe the system can be divided into two groups. Fluid and surface chemistry are defined by the viscosity (η), surface tension (γ), contact angle (θ), and density (ρ). In the sinusoidal case, the capillary itself is described by Dcap, the diameter at the largest portion of the tube which determines the limiting capillary pressure, Dvis, the diameter of the throat which dominates the viscous drag, and λ, ‘wavelength’ of the fluctuations. The conclusions are: (1) as long as the wavelength of the fluctuation in diameter for the capillary is small relative to the length of travel, the actual value of this wavelength does not matter in the time derivative of the flow. This is typically the case for porous media in which the flow path dimensions fluctuate in the range of microns, and the wicking distances are measured in centimeters. (2) As a result of this simplification, a two-parameter equation can be written which yields the time t for the fluid front to reach a given distance L, analogous to the Lucas–Washburn equation:ln1−LLeq+LLeq=−C2Dcap2ρg32ηLeqtThe term Leq defines the equilibrium height and is a function of γ, θ, ρ, and Dcap. The rate is determined in addition by η and Dvis (=C×Dcap).

Effect of pseudoplastic behaviour of liquid in co-current three-phase fluidized beds on bed expansion

Gas hold-up and bed expansion measurements were carried out for a bed of glass beads fluidized in Newtonian liquids and non-Newtonian liquids with gas. The value of gas hold-up increased and decreased with increasing particle size and liquid velocity, respectively. The effect of rheological properties on gas hold-up was insignificant and therefore the gas hold-up data for both Newtonian and non-Newtonian fluids were reasonably fitted by the available correlation which had no liquid viscosity term. The bed voidage increased with increasing superficial liquid velocities and superficial gas velocities. The increase of the viscous non-Newtonian flow behaviours resulted in an increase of the bed voidage. The correlation for the bed voidage in three-phase fluidized beds was developed for gas-Newtonian or non-Newtonian liquid–solid three-phase systems by combining the generalized wake model and the correlation for liquid–solid two-phase systems proposed previously by the authors. The predictions for bed voidage were in reasonable agreement with the present experimental data for three-phase systems with Newtonian and non-Newtonian liquids in a wide range of Reynolds numbers.