Sintered Glass Beads Research Articles

Vacuum Drying of Porous Solids under Supercooling

Vacuum drying of sintered glass beads, cemented glass balloons, and baked clay was investigated under supercooling. Glass beads and glass balloons, which were made of a common glass material, were used for comparison. Concerning sintered glass beads, there was no effect of supercooling on drying rates at a pressure of 0.93 kPa. In cemented glass balloons as well as in baked clay, however, a prominent peak of drying rates emerged in drying rate curves and at the same time, a stepwise increase in the surface temperature appeared under supercooling at a pressure of 1.19 kPa; no peak of drying rates emerged in drying rate curves of sintered glass beads. The total amount of latent heat of vaporization and sensible heat generated at the peak of drying rates was 39–59% of the latent heat of solidification. A part of the latent heat of solidification evaporated the water in the sample, producing a peak of drying rates as well as a stepwise increase in the surface temperature of the sample.

Predicting macroscopic transport properties using microscopic image data

We consider eight data sets obtained from synchrotron computed microtomographic experiments performed on natural and synthetic sandstones at the GSECARS 13‐BM beam line at the Advanced Photon Source. Four data sets were collected on glass bead packs sintered to differing bulk densities; each of these data sets contains just over 225 million voxels (661 × 661 × 517), with voxel resolution of 3.34 μm. The other four data sets were collected from a single sample of natural sandstone. For the natural sandstone, three data sets were collected from different subvolumes within the sample, with these three data sets identical in size and resolution to those acquired for the sintered glass bead packs. A fourth data set was collected for one of the same subvolumes but at twice the resolution; this data set contains just over 1.6 billion voxels (1327 × 1327 × 920), with voxel resolution of 1.67 μm. Following processing to extract binary descriptions of the two‐phase (solid and pore) structure, the image data are analyzed to calculate porosity and specific surface area. The binarized image data are applied directly in massively parallel numerical simulations of single‐phase fluid flow performed using the lattice Boltzmann method; development of novel boundary conditions to facilitate efficient handling of these very large data sets is also described. The permeabilities predicted from 1 to 3 mm3 image volumes characterized at a length scale of ∼1.7–3.4 μm are compared to experimental measurements of intrinsic permeability performed at bench conditions on standard core‐sized samples (25.4 mm in diameter × 50.8 mm in length, or ∼26 cm3). The macroscopic permeability computed from the image data agree remarkably well with the experimentally measured bulk permeability over several orders of magnitude range in permeability and equate to over 4 orders of magnitude scale‐up. The results provide insight on the representative volume and length scales necessary to characterize geometrically complex porous media and predict fluid transport properties at the macroscale.

Drying Rate Curves of Porous Solids in Steam and in Air under Low-Pressure Conditions

Drying of porous solids such as sintered glass beads, baked clay, and cemented glass balloons in both steam and air streams was investigated under low-pressure conditions. There was no significant difference between the normalized observed drying rate curves in air at low pressures of 0.71–1.19 kPa and those in steam at low pressures of 0.97–0.99 kPa. However, lower critical moisture contents and higher drying rates in superheated steam at subatmospheric pressures of 8.27–8.33 kPa were observed compared to those in steam at pressures in the range of 0.97–0.99 kPa. Moreover, two models were validated for the prediction of drying rate curves of sintered glass beads at subatmospheric and low pressures. The patterns of the drying rate curves, which depend on the drying medium and its pressure, were common to these materials.

Phonons in porous media at intermediate frequencies

Using ultrasonic techniques, the phonon diffusion coefficient and density of states have been measured at intermediate frequencies in a porous solid network of sintered glass beads. A transition to a very strong scattering regime is observed, whereupon the diffusion coefficient becomes independent of frequency. Near crossover, the density of states is enhanced and exhibits a broad maximum. These data are in good overall agreement with a lattice-based percolation model, and give additional insight into the effects of strong scattering on phonon transport in disorderd media. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Simultaneous removal of atrazine and nitrate using a biological granulated activated carbon (BGAC) reactor

AbstractThe objective of this research was to characterize the performance of granulated activated carbon (GAC) as a carrier for Pseudomonas ADP in a non‐sterile continuous fluidized bed reactor for atrazine degradation under anoxic conditions. The GAC was compared with two non‐adsorbing carriers: non‐adsorbing carbon particles (‘Baker product’) having the same surface area available for biofilm growth as the GAC, and sintered glass beads. The initial atrazine degradation efficiency was higher than 90% in the reactors with the non‐adsorbing carriers, but deteriorated to 20% with time due to contamination by foreign denitrifying bacteria. In contrast, no deterioration was observed in the biological granulated activated carbon (BGAC) reactor. A maximal atrazine volumetric and specific degradation rate of 0.820 ± 0.052 g atrazine dm−3 day−1 and 1.7 ± 0.4 g atrazine g−1 protein day−1 respectively were observed in the BGAC reactor. Concurrent atrazine biodegradation and desorption from the carrier was shown and an effluent concentration of 0.002 mg dm−3 (below the EPA standard) was achieved in the BGAC reactor. The advantages of the BGAC reactor over the non‐adsorbing carrier reactors can probably be explained by the adsorption–desorption mechanism providing favorable microenvironmental conditions for atrazine–degrading bacteria. Copyright © 2004 Society of Chemical Industry

Modelling the toughness of porous sintered glass beads with various fracture mechanisms

The peak of the variation in the critical strain energy release rate G 1Ic with porosity, as previously measured on sintered glass beads, is modelled. The approach is an adaptation of an existing model, based on the description of the actual microstructure as resulting from the densification of an initial stacking of spheres. A previous model made use of a unique reference toughness K Ic0 of a hypothetical bulk material and as such was valid only if the micromechanisms of crack propagation were the same over the whole range of porosity. In the present case, the observed change in fracture micromechanisms with porosity in sintered glass beads is considered. The analysis of the microstructure and crack path morphologies enables specific toughnesses to be attributed to the mechanisms observed at the extreme values of porosity: crack pinning by pores at low porosities and rupture of the sintering necks at high porosities. The transition from one to the other is expressed by an evolution with porosity of the virtual reference toughness K Ic0 . The two-parameter model fits the experimental data and also predicts the effect of bead size on the G 1Ic peak extent. It is finally proposed that a similar approach could be used for other materials, other properties and other microstructural parameters.

The Differences in Drying Rate Curves of Sintered Glass Beads at Subatmospheric and Atmospheric Pressures and at Lower Pressures in Steam

AbstractSteam drying of sintered glass beads under vacuum was investigated. The drying rates were predicted from an evaporation zone model for the constant rate period, and from a receding evaporation front model for the falling rate period in which the data of moisture contents in the pendular state were estimated from those in air under vacuum. The predicted, as well as observed, normalized drying rate curves including the critical moisture contents in steam under vacuum were different from those in steam at subatmospheric and atmospheric pressures. However, they were similar to those in air under vacuum in the corresponding pressure range. This was because the moisture content in the pendular state under vacuum was larger than that at subatmospheric and atmospheric pressures, and heat transfer was a rate‐controlling step both in steam and in air under vacuum.

Confocal scanning laser microscopy applied to the study of pore and crack networks in rocks

Confocal scanning laser microscopy (CSLM) is a powerful tool to image the three-dimensional (3D) microstructure of objects in many different fields. The goal of this paper is to show that, in particular, confocal microscopy is a useful tool in geosciences because it provides accurate and relevant information on the 3D geometry of the pore space in rocks. Three important geological processes have been investigated: cracking in granites, cementation and diagenetic compaction in sandstones and hydrothermal alteration in granular materials. CSLM was used to characterise 3D crack networks in La Peyratte granite samples in which cracking was artificially induced either by heating samples at selected temperatures in order to induce thermal cracking, or by performing mechanical tests in order to develop stress-induced cracking at room temperature. Qualitative and quantitative results show the different mechanisms acting during natural cracking. CSLM was also used to study the natural cementation of sediments; for this purpose 3D observations of the pore system of Fontainebleau sandstone samples with different degrees of cementation and diagenesis were done. We found large differences in connectivity, pore size and shape depending on cementation. Finally, we present some results on artificial granular materials (sintered glass beads) altered by hot water (220°C): some microstructural parameters were analysed in order to quantify the effect of alteration on the microstructural properties of the granular material. We concluded from this study that the large drop in permeability (6 orders of magnitude), when comparing non-altered to altered samples, is due to a complete change of the pore structure and a strong reduction of the mean pore size.

COMBINED SUPERHEATED STEAM AND MICROWAVE DRYING OF SINTERED GLASS BEADS: DRYING RATE CURVES

A new drying method of combined superheated steam and microwave drying is being proposed. The drying rates of sintered glass beads in combined superheated steam and microwave drying are experimentally and theoretically investigated. Drying experiments have been carried out in a waveguide where a standing wave is formed to uniformly heat a small sample. Concerning drying rate curves in combined superheated steam and microwave drying, a distinct constant rate period has been observed. For the falling rate period, high drying rates have been observed. For both periods, the drying rates in combined superheated steam and microwave drying are higher than those in superheated steam alone. Also, in comparison with the results of combined nitrogen and microwave drying, the normalized drying rates in combined superheated steam and microwave drying are higher than those at less than the critical moisture content in combined nitrogen and microwave drying. Moreover, theoretical drying rates for the falling rate period (predicted by a modified receding evaporation front model) in combined superheated steam and microwave drying, are in good agreement with the observed drying rates. The combined superheated steam and microwave drying method can attain higher drying rates under mild external conditions.

Computational rock physics at the pore scale: Transport properties and diagenesis in realistic pore geometries

Transport properties, such as permeability, are important in many geophysical and petroleum applications. However, complex pore geometry often makes modeling and simulation of transport properties in porous media very difficult. Conventional methods are usually based on partial differential equations, but the implementation of these techniques becomes very complicated when the geometry is extremely complex. As a result, simplified geometry is often used; thus the implementation depends heavily on the model. Solving the same problem in a different geometry often means that many parts of the implementation have to be changed. Therefore, a more robust and simple tool, which can handle complex pore space without oversimplification or modification of the model, is needed. The Lattice-Boltzmann method (LBM), based on statistical description of microscopic phenomena, is one alternative. LBM describes fluid motion as collisions of imaginary particles, which are much bigger than the real fluid molecules. These particles have nearly nothing in common with real fluids, but they show almost the same behavior at a macroscopic scale. This simple collision rule is exactly equivalent to the Navier-Stokes equation within certain appropriate limits. Figure 1 shows a synthetic pore geometry (a random dense pack of identical spheres) and the corresponding digital 3-D structure. Uniform spheres in a random dense pack are a reasonable first approximation to real sandstones. Another advantage for this model is that changing porosity is relatively easy, and laboratory measurements can be mimicked using sintered glass beads. Figure 2 shows electric flux (current) calculated by the finite-element method (FEM) and hydraulic flux calculated by LBM. Both are normalized by each maximum value. The hydraulic flux shows much more sensitivity to the grain boundary than the electric current; the hydraulic flux decreases rapidly near the boundary. Also, the high flux regions are different in Figure 2, even though pore geometry …

Biodetoxification of coumaphos insecticide using immobilizedEscherichia coli expressing organophosphorus hydrolase enzyme on cell surface

Recently, we reported an improved technology for the degradation of organophosphate nerve agents using whole cells of genetically engineeredEscherichia coli that anchored and displayed the enzyme organophosphorus hydrolase on the cell surface. In this paper we report the immobilization of these cells on highly porous sintered glass beads and the subsequent application of the immobilized cell in a continuous-flow packed bed bioreactor for the biodetoxification of a widely used insecticide, coumaphos.

Effects of Flow Rate and Alkali-to-Acid Ratio on the Displacement of Acidic Oil by Alkaline Solutions in Radial Porous Media

Alkaline flooding is a method of enhanced oil recovery that relies on the formation of surface-active substances in situ by a chemical reaction between acidic components in the oil and an alkaline reagent. As the injected alkali advances through the porous medium, it keeps contacting fresh oil. At some moment dependent on the alkali/acid concentrations and the velocity, the alkali at the advancing front may become depleted and the flood becomes interfacially nonreactive. The present study is aimed at investigating the above-mentioned phenomena. Displacement studies were conducted in radial cells containing sintered glass beads as a porous medium. Light paraffin oil acidified with 10 mmol/L of linoleic acid served as the displaced (oil) phase while the displacing aqueous solution contained 0–25 mmol/L of sodium hydroxide. The highest oil recovery was obtained under the conditions of low flow rate and high alkali concentration. Increasing the flow rate at high NaOH concentration resulted in decreasing oil recovery up to a certain threshold flow rate. Conversely, the amount of oil recovered by waterflooding only (no alkali) initially increased with increasing flow rate up to the same threshold flow rate beyond which there was no difference between the alkaline flood and a waterflood.

A new fracturing mechanism for granular media

Borehole breakout experiments are performed on sintered glass bead bricks and a new microscale fracturing mechanism is described that results in a macroscopic fracture plane oriented perpendicular to the uniaxial compressive loading stress. Scanning Electron Microscopy (SEM) is used to inspect the fracture surfaces and it is found that fracture propagation occurs through a process of grain debonding and ejection from the sample. A two‐dimensional boundary integral simulation models the effect of grain removal on subsequent fracturing by reducing the Young's modulus of failed grains, thereby allowing the compressive loading stress to be transferred to adjoining grains and grain contacts. It is found that this stress concentration is sufficient to induce additional grain failure and macroscopic fracture growth perpendicular to the applied load.

Displacement imaging in porous media using the line scan NMR technique

Displacement imaging is a recent, powerful NMR method with which distributions of displacements can be acquired of e.g. fluids within a porous medium. Both motion parallel and perpendicular to the flow direction may be observed within a time window of a few milliseconds to several seconds. By combining displacement imaging with the line scan technique, one-dimensionally resolved measurements with a high temporal resolution ( < 1 min) of the spatial dependency of motion can be obtained. Here we present displacement images of flow through two simple model systems for soil: an unconsolidated glass bead water system and a sintered glass bead filter. It is demonstrated that the combination of displacement imaging and spatial resolution along a line is important to access both bulk displacement and local displacements in relation to the local porosity.

Tracer Dispersion in a Polymer Solution Flowing Through a Double Porosity Porous Medium

Experimental results on the dispersion of a tracer in a polymer solution flowing through a nonconsolidated packing of porous grains are reported. We use a scleroglucane solution with a shear viscosity decreasing as a power low of the shear-rate over a broad range : the characteristic exponent a is varied between 0.40 and 0.77 by changing the polymer content. Porous grains of size d g = 500 μm and internal porosity 30% are obtained by grinding sintered glass beads of initial diameter 110 μm. Dispersion measurements use a saline tracer at Peclet numbers Pe between 0.7 and 700. At a constant Pe, the dispersivity l D = K/U (K being the longitudinal dispersion coefficient) increases with α (by a factor of 6 between α = 0 and α = 0.77 around Pe = 10). At some Pe values, early arrival time effects are observed. The dispersivity also increases with Pe at all α values in the range of transition from diffusive towards convective transport in grains. These results are assumed to be due to the non-Newtonian characteristics of the solution increasing the contrast both between low and high velocity flow paths and between the inside and the outside of the grains.

Effect of Gas Sparger Type on Operational Characteristics of a Bubble Column under Mechanical Foam Control

The effects of gas sparger types on the operational characteristics of a bubble column (BC) with a rotating-disk mechanical foam-breaker (MFRD), such as foam-breaking, foaming, flow and mass transfer characteristics, were studied. The required critical disk rotational speed, N c , and liquid hold-up in the foam, Φ L , reflected the foam-breaking behaviour of the MFRD and the foaming behaviour of the BC respectively, which changed depending on the gas sparger type. The dependence of the gas sparger type on the gas hold-up, e g , was similar to that observed for the volumetric mass transfer coefficient, k L a. A comparative investigation of k L a with various gas spargers, in terms of the specific power input, also demonstrated the usefulness of the porous sintered glass bead filter as a gas sparger.

Electrical and dielectric properties of systems of porous solids and salt-containing nonpolar liquids

We have performed dielectric measurements on porous samples, made of sintered polypropylene grains, impregnated with an organic liquid (a mixture of mono- and dibenzyl toluenes) into which we had dissolved a salt (tetraisoamylammonium picrate). This is a system that has not been widely studied before. We find that the formation factor of electrical conduction has a cementation exponent similar to what has been previously reported for sintered glass beads. We also find an increase in the permittivity at very low frequencies. We attribute this to diffusion effects at the solid–liquid boundary. We show how this low-frequency relaxation changes with temperature.

The dielectric dispersion of liquid-filled porous sintered materials

We have used a differential effective-medium (DEM) theory to model the dielectric properties of sintered glass beads, impregnated with salty water, in the kHz and MHz ranges. The starting point of the theory is a lattice of touching spheres in pore liquid. The sintering is modelled by adding solid material and using the DEM method to calculate the dielectric response. Dipolar interactions in the system are treated by using effective depolarization factors, obtained from the dependence of the formation factor on porosity. The frequency dependence of the formation factor is in good agreement with experimental data. For the real part of the dielectric permittivity, discrepancies arise at low frequencies. This is probably due to percolation effects.

Transverse relaxation in random bead packs: Comparison of experimental data and numerical simulations

Inverse Laplace transform techniques are commonly used to convert nuclear magnetic resonance (NMR) relaxation data in porous media into lifetime distributions. In this connection, we present a direct comparison of T 2 measurements made on monosized packings of sintered glass beads and numerical simulations based on the grain consolidation model. Three systems, with porosities of 0.38, 0.22, and 0.14, were studied, and in each case we found that the position and width of the measured T 2 distribution was well represented by the random walk simulations. These systems are generally in the fast diffusion (weak surface relaxation) regime and have relatively narrow T 2 distributions. For this reason, we have found that inverse Laplace transform techniques are particularly sensitive to random noise in the measured and simulated decay spectra.

Biodegradtion of all three isomers of monochlorophenol in a fixed bed reactor to very low concentrations

An enriched mixed culture able to mineralize all three isomers of monochlorophenol (MCP) and a pure culture (Alcaligenes sp. A7-2) were used to inoculate a non-aerated fixed bed reactor filled with sintered glass beads. Oxygen was supplied in form of a 1% solution of H2O2. The 3 monochlorophenol isomers, added as a mixture (concentration of each compound 3.3 mgl−1), were eliminated to over 99%. When the MCP concentrations were lowered to 1 mgl−1 of each isomer, no addition of H2O2 was necessary since the oxygen concentration in the feed was sufficient for complete mineralization of the chlorophenols. Residual concentrations in the effluent of the reactor of below 0.2 μgl−1 for 2-MCP, 0.05 μgl−1 for 3-MCP and 4-MCP, respectively, were obtained. These values were also the detection limits for the three isomers. The low effluent levels were even obtained at hydraulic retention times of 0.7 h, which was reached stepwise. NO−3 did not serve as an alternative electron acceptor to O2.