Bed Of Beads Research Articles

Quantitative radial imaging of porous particles beds with varying water contents

Radial imaging protocols suitable for monitoring water transport in biopolymer and food materials during processes such as drying and rehydration are developed and tested on a well-characterized model sample. This model consisted of a randomly packed bed of Sephadex beads with varying water content. The results are interpreted with theoretical models for the dependence of the initial water magnetization, transverse relaxation, and diffusive attenuation on water content for two slice-selective radial imaging pulse sequences. It is shown that volume shrink-age and changes in packing density complicate the dependence of the initial magnetization on water content, so that the transverse relaxation rate provides the most reliable monitor of water content. Radial imaging is shown to offer many advantages over conventional two-dimensional imaging whenever the sample can be made with cylindrical symmetry.

Flow of Oil Emulsion Through Porous Media

The flow through porous media of oil emulsion is reported in this paper. Base oil, water and Triton X-100 were used to produce O/W and W/O type emulsions. Shear stress, shear rate, and yield stress were measured for the emulsions at different temperatures and oil concentrations.Results show that at low oil concentration (10% to 40%), the emulsion was oil in water type and a Newtonian behavior was observed with viscosity ranging from 1.5 to 7.7 cP. Medium oil concentration (50% to 60%) data were interpreted in terms of the power law model relationship for non-Newtonian fluid. While at high oil concentrations (70% to 90%) data were interpreted in terms of the Hershel- Bulkley model relationship for a non-Newtonian fluid with yield stress. At high oil concentration of 50 – 90% oil, the emulsion was water in oil type.Data for porous packed bed of glass beads are presented using friction factor and a general Reynolds number for the flow through porous media, which includes a fluid yield stress.

Upward solidification of a binary solution saturated porous medium

Upward solidification of a binary solution saturated porous medium was investigated experimentally and theoretically to identify the dominant physical phenomena and to document the experimental results. A solid matrix of the porous medium was a packed bed of glass beads, and the saturating liquid was an aqueous sodium chloride solution on the water-rich side of the eutectic composition. Freezing experiments were performed in a square cross-section enclosure under constant temperature conditions at the cold bottom and hot top walls. Transient temperature profiles and the liquidus and solidus positions were measured for different combinations of bead size, initial temperature and initial salt concentration. Simultaneous measurements of local concentration and temperature at selected locations were also made in a separate series of experiments. An analytical model, based on heat and species conservation principles and relations from the equilibrium phase diagram is suggested, and the predictions are compared with experimental data. The uniform distribution of the predicted average concentration suggests that species transport by diffusion is negligible, and the effect of bead size on the temperature profiles was confined to the region near the cold bottom. The behavior of dimensionless temperature under different initial temperature and concentration conditions could be explained by the relation between the local freezing rate and nonequilibrium undercooling. Also, the ‘over-enriching’ was observed in the mushy region away from the liquidus, but a quantitative analysis was not performed. The importance of incorporating models, which account for the effects of nonequilibrium undercooling and density differences between phases, and the need for experimental diagnostics, which do not disturb the physical phenomena occurring during the solidification of the mixture, are emphasized.

Freezing of a water-saturated inclined packed bed of beads

An experimental investigation is reported for the problem of transient freezing of an inclined water-saturated bed of beads. The effect of the inclination angle on the temperature field, the shape of the ice-water interface, the initiation time of ice nucleation, and the volume of the frozen region are obtained for two types of beds of beads with significantly different thermal conductivities (glass and steel). The dependence of the volume of the frozen region on the inclination angle and on time is summarized in engineering correlations for both the bed of glass beads and the bed of steel beads.

An experimental study of the transport and capture of colloids in porous media by a chromatographic technique

We present an experimental investigation of the transport and capture of model colloids in a well-defined porous medium. The experiments were performed using standard liquid chromatography equipment and involve detecting the passage of small impulses of monodisperse latex particles passing through a bed of monosize glass beads. Experiments were performed with three samples of monodisperse latex particles of diameters 226, 550 and 790 nm in carrier solutions with ionic strengths ranging from pure water up to 0.1 M at a pH of either 5.2 or 8 at flow velocities varying from 0.01 to 0.1 cm s −1. The results are presented as capture efficiency as a function of the various parameters and also in the form of Sherwood number vs Reynolds number for comparison with existing correlations of mass transfer. It is shown that capture is strongly influenced by hydrodynamics and the repulsive potential energy barrier.

NUMERICAL MODEL FOR COMBINED CONDUCTIVE AND RADIATIVE HEAT TRANSFER IN ANNULAR PACKED BEDS

A numerical model is developed for quantitatively analyzing combined conductive and radiative heat transfer in concentric annular packed beds, A packed bed is considered to be a continuous medium for heat transfer, but the porosity distribution within a packed bed is taken into account, lb examine the validity of the proposed model, combined conductive and radiative heat transfer through annular packed beds of cordierite or porcelain beads is analyzed numerically using finite differences under conditions corresponding to heat transfer experiments of these packed beds. The resultant temperature profiles and heat transfer characteristics are compared with the experimental results.

Influence of ammonium ion and glucose on mAb production in suspension and fixed bed hybridoma cultures

Previous work indicated that mAb production by a mouse-mouse hybridoma, grown in a fixed bed of macroporous glass beads with a variable feed glutamine concentration, was correlated only to Qv O2 . The work reported in this study further investigated the metabolic parameters modulating mAb production using metabolic data from a continuous stirred tank reactor (CSTR) to interpret the behaviour of cells grown in a fixed bed bioreactor (FBR). For a FBR culture grown with a feed glutamine concentration of 3 mmol l −1, Qv mAb was correlated to Qv O2 and Qv Gln . However, if the feed glutamine concentration was switched between 1 and 3 mmol l −1, the above relationship did not hold, probably because Qv O2 was at or near its maximum value. For both the FBR and CSTR, switches in the feed glutamine concentration suggested that maximum Qv mAb values were associated with glucose concentrations above 12.8 mmol l −1 and an ammonium concentration of 2.0–2.5 mmol l −1.

Culturing of primary hepatocytes as entrapped aggregates in a packed bed bioreactor: A potential bioartificial liver

Conventional culture systems for hepatocytes generally involve cells cultured as flat, monolayer cells, with limited cell-cell contact, in a static pool of medium, unlike the liver in vivo where the parenchymal cells are cuboidal, with extensive cell-cell contact, and are continuously perfused with blood. We report here a novel bioreactor system for the culturing of primary hepatocytes with cuboidal cell shape, extensive cell-cell contact, and perfusing medium. The hepatocytes were inoculated into the bioreactor and allowed to recirculate at a rate optimal for them to collide and form aggregates. These newly-formed aggregates were subsequently entrapped in a packed bed of glass beads. The bioreactor was perfused with oxygenated nutrient medium, with controlled oxygen tension, pH, and medium perfusion rate. The hepatocytes were viable for up to the longest time point studied of 15 days in culture based on urea synthesis, albumin synthesis and cell morphology. Light microscopy studies of hepatocytes cultured for 15 days in the bioreactor showed interconnecting three-dimensional structures resembling the hepatic cell plate in the liver organ. Electron microscopy studies on the same cells revealed ultrastructure similar to the hepatocytes in vivo, including the presence of plentiful mitochondria, rough and smooth endoplasmic reticulum, glycogen granules, peroxisomes, and desmosomes. We believe that our hepatocyte bioreactor is a major improvement over conventional culture systems, with important industrial applications including toxicology, drug metabolism, and protein/peptide synthesis. The hepatocyte bioreactor concept may also be used as the basis for the development of a bioartificial liver to provide extracorporeal hepatic support to patients with hepatic failure.

Multiple Spouts in a Two-dimensional Bed with a Perforated-plate Distributor.

The behavior of multiple spouts above a perforated plate in a 400 mm×15 mm two-dimensional bed of glass beads with mean diameters from 214 to 1095 μm was investigated. The operation of the perforated-plate distributor was taken into account while phase diagrams for the 2-D bed of glass beads were mapped. Two types of incoherent spouting were observed. The stability of multiple spouts was affected by bed height, superficial gas velocity, particle size and distributor design

SIMULTANEOUS VAPOR AND LIQUID DIFFUSION IN PARTIALLY WETTED POROUS MEDIA

ABSTRACT In porous materials with pores containing both a gas and a liquid phase each a mixture of several components mass transfer by diffusion may occur simultaneously in both phases. An effective diffusivity is required in order to describe these effects when a homogeneous model is used. Unsteady-state diffusion experiments were performed such that a bed of glass beads partially saturated with glycerol was either loaded by passing wet air or dried by removing water or 2-propanol initially mixed to the glycerol. The effective diffusivity was obtained by applying the equation of unsteady-state diffusion to the observed change of mass. Superposition of the limiting cases of single-phase vapor and liquid diffusion in partially saturated systems yields a simple equation that describes the effective diffusivity as a function of pore saturation and correlates well with the measured values.

Measurements of wall shear stress in particle beds when vibrations are imposed vertically along the direction of shear

Measurements were made of the wall shear stress in vibrating particle beds when vibrations were imposed vertically along the direction of shear. This work deals with five kinds of particles, and examines the dependency of the wall shear stress on vessel size, vibration frequency in the range 20-80 Hz and the ratio of vibratory to gravitational acceleration in the range 2-8. In order to examine the effect of the wall shear stress on vibrating particle beds, a comparison was made between experimentally measured air pressures at the bottom of the bed and theoretically calculated ones. When the wall shear stress was incorporated in model calculations the agreement between model predictions and measurements improved significantly in beds of large glass beads; however, the agreement deteriorated progressively with decreasing particle size.

Electrostatic behaviour in binary dielectric/conductor fluidized beds

The degree of electrification in a fluidized bed of glass beads and mixtures of glass/steel particles has been studied. The basic equipment used for me

Condensation in a Porous Region Bounded by a Cold Vertical Surface

The problem of condensation in a porous medium near a cold vertical surface is investigated numerically and experimentally. Numerical solutions to the mathematical model, which assumes that a distinct two-phase zone exists between the liquid and the vapor phases, compare favorably with the experimental results. Experiments were performed for steam condensing in packed beds of glass beads of three different sizes. In the numerical model, the effect of the vapor flow in the two-phase zone is included. The interfacial velocity was determined through the matching of shear stress and a total mass balance. The predicted interfacial velocities are around one to two orders of magnitude smaller than the Darcy velocity. The calculated liquid film thicknesses are on the order of the diameter of the glass beads. The results, presented in dimensionless format, are applicable to transport processes in geothermal reservoirs, steam-driven enhanced petroleum recovery, and a number of industrial applications.

Wood pulp washing 2. Displacement washing of aqueous lignin from model beds with cationic polymer solutions

Cationic poly(diallyldimethylammonium chloride), polyDADMAC, increased the efficiency of the displacement of aqueous kraft lignin from a bed of glass beads. The bed consisted of a cylindrical bed, 5 cm in diameter, of fine (97 μm) glass beads surrounding a center channel, 1.5 cm in diameter, filled with coarse (1200 μm) glass beads. The bed was designed to model the displacement washing characteristics of pulp fiber pads on kraft brownstock washers. The effects of polyDADMAC molecular weight and concentration on lignin displacement were investigated. The maximum washing efficiency corresponded to the polymer concentration giving the maximum yield of lignin/polyDADMAC precipitate. Low molecular weight polyDADMAC was not as effective as high molecular weight polymer whereas improved washing with polyamine was not dependent upon molecular weight. It was postulated that improved washing arose from the deposition of lignin/polyDADMAC complex in the center channel. This mechanism is called “clotting”.

A Rhuddanian (Silurian: Lower Llandovery) echinoderm fauna from Haverfordwest, Southwest Wales

Llandovery (Lower Silurian) echinoderm faunas are uncommon, an observation which has important implications for our understanding of the patterns of evolution and extinction over the Ordovician/Silurian boundary interval. For example, only two crinoid faunas of Rhuddanian or Rhuddanian+Aeronian age have so far been described, both from North America (Cataract Group, Ontario; Brassfield Formation, Ohio). A third echinoderm fauna of Rhuddanian age is now recognized from the Gasworks Mudstones (=upper Haverford Mudstone Formation) and, less certainly, the Gasworks Sandstone Formation of Haverfordwest, Dyfed, southwest Wales. Recent fieldwork has failed to relocate the precise horizon that produced this fauna and the taxa discussed herein are all based on specimens in the Turnbull Collection of the Sedgwick Museum, Cambridge. There is no published analysis of this fauna, but Ramsbottom, in his Ph.D. thesis, identified Pisocrinus sp., Macrostylocrinus sp. and Dimerocrinites sp. from this horizon.A disarticulated thecal plate has been identified as the rhombiferan Homocystites? sp., confirming that the cheirocrinids survived the end Ordovician extinction. This is only the second British Llandovery cystoid. All other specimens are crinoids. Crowns of calceocrinid disparids are assigned to two species of Calceocrinus (=“Pisocrinus sp.” of Ramsbottom). A dendrocrinid cladid is interpreted as a smmoth-cupped Dendrocrinus? A unique internal mould is a monobathrid, possibly Macrostylocrinus. Distinctive petaloid columnals of Floricolumnus (col.) sp. cf. F. girvanensis Donovan and Clark, possibly derived from a rhodocrinitid diplobathrid, are congeneric with ossicles from the Newlands Formation of southwest Scotland (latest Rhuddanian-earliest Aeronian) and the Brassfield Formation of Ohio (‘Bead Bed’). A new species of rhodocrinitid diplobathrid (=“Dimerocrinites sp.” of Ramsbottom) has low infrabasals just apparent in lateral view; a moderately bowl-shaped dorsal cup; prominent ray ridges; 2, 3 or 5 plates, respectively, in the first three tiers of interprimibrachials; and uniserial arms that branch isotomously once and heterotomously thereafter. Two further crinoid species are indeterminate. At the familial level, this fauna shows strong similarities with coeval, but more diverse, crinoid assemblages from North America.

Initiation of fire growth on fuel-soaked ground

The problem of initial fire spread over fuel-soaked ground was experimentally modeled in detail using a bed of glass beads saturated with n-decane as the fuel. After igniting the center of the horizontal fuel-soaked surface, the flame spreads concentrically and formed a growing centered flame pillar. The radial spread velocity of flame pillar base accelerated during the initial fire growth stage. The dominant mode of heat transfer controlling the spread of the flame pillar base was by flame radiation. The present study shows some important and fundamental characteristics of the growing flame pillar by using the direct video movie, Schlieren photography, particle trace technique, radiation flux measurement and temperature measurement. The study considers the spread velocity of the flame pillar base, behavior of the flame pillar, luminous height of the flame as a function of flame base diameter, frequency of flame height fluctuation as a function of flame base diameter, flow pattern of flame-induced convection, variation of flame radiation heat flux with elapsed time, and profile and fluctuation of local gas phase temperature on the axis of flame pillar. From the point of view of prevention of subsequent fire hazard, the present study discusses some important experimental results for the development of fire size and flame radiation during the initial stages of a growing flame pillar on the ground which has been soaked by spilled liquid fuels.

Pressure sores. Epidemiology and current management concepts.

Pressure sores remain common, with a prevalence of 5 to 9% and more than 70% occurring in patients over 70 years of age. They are often falsely ascribed to poor nursing care, but can more usefully be regarded as a potentially preventable complication of an acute immobility illness. Prevention involves identification of patients at risk, appropriate nursing care measures and the use of special equipment. Much of the special equipment is excessively complex and not validated by clinical trial work. The airwave system, polystyrene bead bed system and Vaperm mattress have been best studied and are effective. Management of the established sore involves treatment of the underlying medical condition(s), attention to hydration and nutrition, prevention of further tissue trauma and the use of special dressings and procedures which facilitate the inflammatory repair response. There is considerable doubt about the use of 'traditional' wound applications such as gauze or chlorinated lime and boric acid solution ('Eusol'). An extensive range of newer products is now available but these have not yet been subjected to controlled clinical trials. A useful starting point is to classify pressure sores into 4 clinical types depending on amount of tissue damage and depth of ulcer. The least severe sore (type 1) can be protected using polyurethane film dressings. Deeper ulcers (types 2 and 3) can be easily and quickly treated by hydrocolloid or alginate dressings which optimise the local wound environment, thus facilitating tissue repair. However, there may be no satisfactory dressing for sacral (near-anal) sores which are more difficult to treat than those at other body sites because of dressing detachment. Cavity ulcers (type 4) can be managed with silastic foam or hydrocolloid or alginate dressings. Debridement of necrotic material is best done manually by scalpel/scissors, although streptokinase/streptodornase (Varidase Topical) may also help if used correctly. Antiseptics have little part to play and ulcers are best cleaned with warm normal saline. Systemic antibiotics are indicated only when surrounding cellulitis is present, although metronidazole is useful for malodorous sores.

Albedos and asymmetry factors of the phase functions for packed-sphere systems

The albedos and the asymmetry factors of the phase functions of packed beds of stainless steel, alumina or glass beads have been determined experimentally by utilizing the emerging-intensity fitting method. The experimental results are compared with theoretical predictions based on our correlated-scattering theory. It has been found that the albedos obtained are close to the theoretical predictions, but the measured values of the asymmetry factors differ from the predicted values derived from our theory. In particular, the measured asymmetry factor of the packed bed of glass beads is greater than the predicted value, while the reverse is the case for the packed beds of alumina or stainless steel beads.

A capacitive system for three-dimensional imaging of fluidized beds

A novel capacitance imaging system (CIS) has been developed which has unique capabilities for providing real-time, three-dimensional monitoring of fluidized-bed density. While the system was developed primarily to serve as a high-speed, density-imaging tool in fluidization research and development, it could also be used in other applications, such as pipeline transfer of solids, where multiphase dielectric material density changes are to be monitored. The CIS uses 16 evenly spaced, circumferentially located electrodes at each of four levels evenly spaced along the axis of a 6-in. diam fluidized bed as the density-sensing elements. The electronic system utilizes interelectrode displacement current values to obtain bed density estimates at each of the 49 pixels defined at each of the four levels. The system provides a real-time display of each of the four density maps at a rate of 30 maps per second at each level. The system also stores displacement current data, updated 100 times per second, for post-run analysis of bed behavior. The CIS capabilities are demonstrated for a plastic bead bed material. Density maps show the progression of a low-density region upward through a fluidized bed. Experimental use of the system by others produced values of bubble dimension and velocity that are consistent with values predicted by accepted theory.

Etude du comportement de jets continus horizontaux ou inclinés introduits dans un lit fluidisé par un gaz Deuxième partie: profils de vitesse du gaz dans les jets horizontaux

The hydrodynamic behaviour of gas introduced as a horizontal jet into a two-dimensional fluidized bed of polystyrene beads has been studied by determining the gas velocity profiles. A Pitot-tube probe has been chosen to carry out the experiments. The influence of the distance from the nozzle, the gas injection velocity, the fluidization velocity and the nozzle shape on the gas velocity profiles has been examined. The asymmetry of gas velocity radial profiles has been pointed out, as well as the tendency of the jet to deviate to the top of the column, even in the linear expansion part, where gas velocity is still very high. A simple correlation is proposed, which enables to give the velocity of the gas on the jet aids as a fonction of the distance from the nozzle tip. A zone where the gas momentum on the jet axis is greater than its inlet momentum has been noticed.