Porous Plug Research Articles

Transport Characteristics of Co2+ Through an Ion Exchange Textile in a Continuous Electrodeionization (CEDI) System Under Electro‐Regeneration

The transport of cobalt ion in a continuous electrodeionization (CEDI) system was investigated in terms of electrochemical properties of ion exchange textile. The porous plug model and an extended Nernst‐Plank equation were applied to describe the transport of Co2+ through an ion exchange textile. The transport characteristics of Co2+ during CEDI operation suggested the transport mechanism was due mainly to the increased current induced by the high conductivity in the ion exchange textile, not accelerated ionic mobility. This study suggested the important parameter for the high performance of the CEDI system is the conductivity of the ion exchange media.

Detailed Modeling of Gas Flow in Liquid Steel: Bubble Size Distribution and Voidage Calculation

Although the role of gas purging in liquid steel systems is well recognized, it has yet to be adequately analyzed. One key aspect of this process is the prediction of gas voidage in the bath, which has been studied in great detail beginning with water modeling in the early days and using advanced multiphase models more recently. Still, there are significant unresolved issues with gas purging systems. When gas is introduced through a nozzle at high flow rate, a jet may form which is undesirable. The break-up of this jet into bubbles is a separate topic of research. The more common practice in the steel industry is to use porous plugs for gas injection. Gas entry through a porous plug can be characterized by the stretched bubble regime, and the laws of coalescence and fragmentation used to analyze bubble column reactors are generally applicable. Calculation of the bubble size distribution is important for two reasons. First, the voidage distribution in the bath is significantly modified by the injection system and flow rates used, primarily due to changes in flow regime and bubble dynamics (collision, break-up, coalescence). Second, the voidage distribution directly determines the buoyancy, that influences the physical mixing process, and the specific-area-density, that influences surface reactions (for example, decarburization, desulfurization and nitrogen pick-up). In this paper, a numerical study is presented that combines a bubble dynamics model with an Eulerian multiphase model. The results of the simulation are compared with the experimental data from Anagbo and Brimacombe (1990). Relevant discussion and reviews will be presented to distinguish the differences of this detailed bubble dynamics model with the uniform bubble diameter approximations reported in various recent studies.

An experimental realization of an unstrained, planar diffusion flame

A unique burner was constructed to experimentally realize a one-dimensional unstrained planar non-premixed flame, previously considered only in idealized theoretical models. One reactant, the fuel mixture in the current experiments, is supplied through a porous plug at the bottom of the combustion chamber and flows vertically up towards the horizontal flame. The crux of the design is the introduction of the oxidizer from above in such a way that its diffusion against the upward product flow is essentially one-dimensional, i.e., uniform over the burner cross-section. This feature was implemented by introducing the oxidizer into the burner chamber from the top through an array of 625 closely spaced hypodermic needles, and allowing the hot products to escape vertically up through the space between the needles. Due to the injection of oxidizer through discrete tubes, a three-dimensional “injection layer” exists below the exit plane of the oxidizer supply tubes. Experimental evidence suggests that this layer is thin and that oxidizer is supplied to the flame by 1-D counterdiffusion, producing a nearly unstrained flame. To characterize the burner, flame position measurements were conducted for different compositions and flowrates of H 2–CO 2 and O 2–CO 2 mixtures. The measured flame locations are compared to an idealized one-dimensional model in which only diffusion of oxidizer against the product flow is considered. The potential of the new burner is demonstrated by a study of cellular structures forming near the extinction limit. Consistent with previous investigations, cellular instabilities are shown to become more prevalent as the initial mixture strength and/or the Damköhler number are decreased. As the extinction limit is approached, the number of cells was observed to decrease progressively.

In situ fabrication of macroporous polymer networks within microfluidic devices by living radical photopolymerization and leaching

Novel fabrication techniques and polymer systems are being explored to enable mass production of low cost microfluidic devices. In this contribution we discuss a new fabrication scheme for making microfluidic devices containing porous polymer components in situ. Contact lithography, a living radical photopolymer (LRPP) system and salt leaching were used to fabricate multilayer microfluidic devices rapidly with various channel geometries and covalently attached porous polymer plugs made of various photopolymerizable substrates. LRPP systems offer the advantages of covalent attachment of microfluidic device layers and facile surface modification via grafting. Several applications of the porous plugs are also explored, including a static mixer, a high surface area-to-volume reactor and a rapidly responding hydrogel valve. Quantitative and qualitative data show an increase in mixing of a fluorescein and a water stream for channels containing porous plugs relative to channels with no porous plugs. Confocal laser scanning microscopy images demonstrate the ability to graft a functional material onto porous plug surfaces. A reaction was carried out on the grafted pore surfaces, which resulted in fluorescent labelling of the grafted material throughout the pores of the plug. Homogenous fluorescence throughout the depth of the porous plug and along pore surfaces indicated that the porous plugs were surface modified by grafting and that reactions can be carried out on the pore surfaces. Finally, porous hydrogel valves were fabricated which swelled in response to contact with various pH solutions. Results indicate that a porous hydrogel valve will swell and close more rapidly than other valve geometries made with the same polymer formulation. The LRPP-salt leaching method provides a means for rapidly incorporating porous polymer components into microfluidic devices, which can be utilized for a variety of pertinent applications upon appropriate selection of porous plug materials and surface treatments.

Spot turbulence, breakup, and coalescence of bubbles released from a porous plug injector into a gas-stirred ladle

Many metallurgical processes are connected with gas injection into liquid metals for refining purposes. For this reason, considerable effort has been made during the past 2 decades to investigate gas-injection operations in steelmaking ladles. Numerous physical and mathematical models are available in the literature as well as experiments (most of them performed in the air-water model). In theoretical works, usually, the bubble size is assumed constant, but this approximation is good just at low gas flow rates. When the gas flow rate increases, three different types of bubble dispersion patterns are observed in experiments. This situation cannot be predicted by means of the turbulence multiphase models normally implemented in commercial CFD codes. Their results predict a smooth (and wrong) bubble-size increase and not a sudden transition from a pattern to another, as in experiments. In this articles a new idea for approaching the bubble turbulence in the ladle, called “spot turbulence,” is presented and comparison with experimental data shown.

Streaming current, permeability, and microelectrophoresis of polystyrene latices in methanol?ethanol mixtures

The influence of the solvent (methanol–ethanol mixtures) on the electrokinetic behavior of polystyrene latices with sulfate groups was studied (methanol content was increased by 0.2 at a constant KBr concentration of 1 mM). Viscosity, density, and dielectric constant ( η , ρ , and ε ) were determined at experimental conditions. Two latices (with different surface charge densities and sizes) were used. Electrophoresis measurements were used for dilute dispersions. Streaming current and hydrodynamic permeability were measured for porous plugs. Linear trends in the electrokinetic measurements were observed in the whole molar fraction range. The experimental data obtained from different techniques allow determining the zeta potential according to a well-established classical relationship. The results obtained were analyzed on the basis of the solvent mixture properties and the electrical interface behavior. In addition, permeability data provided valuable information to interpret effects at the solid–liquid interface of the porous plug.

Preparation and characterization of immobilized ion exchange polyurethanes (IEPU) and their applications for continuous electrodeionization (CEDI)

Immobilized ion-exchange polyurethanes (IEPU) were prepared as ion conducting spacers in continuous electrodeionization (CEDI) for the treatment of a synthetic primary coolant. Ion exchange resins were immobilized by using allophanate/biuret cross-linking in preparation of polyurethane. Synthesized IEPU was characterized in terms of mechanical strength, ion exchange capacity (TEC), electrical conductivity and the porous plug model, which schematically represents the transport pattern through the IEPU. CEDI was carried out in a laboratory scale with an effective area of 20 cm2. The CEDI operation with a layered bed configuration showed the main removal mechanism of cobalt ion was dependent on the active surface area between ion conducting materials. The performance of the CEDI operation showed over 98% removal of cobalt ions, suggesting the feasibility of IEPU as ion conducting spacers in a CEDI system.

Spiral dynamics of pulsating methane-oxygen flames on a circular burner.

A premixed flame stabilized on a circular porous plug burner produces a uniform, steady luminous flame front. Throughout much of the parameter range hydrocarbon-oxygen mixtures form spiral-shaped fronts. In methane-oxygen flames at low pressure, the flame exhibits a sequence of states as a control parameter is decreased. These states include periodic rotation of a spiral front; precession of the spiral front in a direction opposite to its rotation, corresponding to doubly periodic petals-out meandering; and nonperiodic states with intermittent jumps associated with linear excursions of the tip, which occur after the spiral front has reached the boundary of the circular burner. We use Karhunen-Loeve (KL) analysis to find the coefficients of the dominant KL spatial eigenfunctions. Their phase space portraits and power spectra provide a description of the dynamics as flow rates are reduced and the system destabilizes. We discuss how these experimental results relate to previous theoretical studies that assume Euclidean symmetry for the experimental configuration.

The space infrared telescope facility (SIRTF) cryogenic telescope assembly (CTA) cryogenic and thermal system

SIRTF is the last of NASA's great observatories. The thermal function of the CTA is critical to the success of the SIRTF mission. The CTA cryogenic and thermal system will provide the low temperature environment that the telescope and science instruments require to conduct infrared observations. A key issue with the early flight data is the peak helium bath temperature, which depends upon cryostat isolation, the helium vent path, and pre-launch cryostat operations. This paper includes a general description of the CTA thermal/cryogenic system, followed by an update on the cryostat status and a discussion of the analysis and performance testing of the porous plug and helium vent path. The pre-launch cryostat preparations have been demonstrated, and those results are presented. There is also summary of performance from the observatory thermal balance test, which completes the verification of the CTA external thermal system. All of the pieces are in place for a successful SIRTF launch and mission.

Streaming current, permeability, and microelectrophoresis of polystyrene latices in methanol–ethanol mixtures

The influence of the solvent (methanol–ethanol mixtures) on the electrokinetic behavior of polystyrene latices with sulfate groups was studied (methanol content was increased by 0.2 at a constant KBr concentration of 1 mM). Viscosity, density, and dielectric constant ( η, ρ, and ε) were determined at experimental conditions. Two latices (with different surface charge densities and sizes) were used. Electrophoresis measurements were used for dilute dispersions. Streaming current and hydrodynamic permeability were measured for porous plugs. Linear trends in the electrokinetic measurements were observed in the whole molar fraction range. The experimental data obtained from different techniques allow determining the zeta potential according to a well-established classical relationship. The results obtained were analyzed on the basis of the solvent mixture properties and the electrical interface behavior. In addition, permeability data provided valuable information to interpret effects at the solid–liquid interface of the porous plug.

The effect of HS− ions in 1mol/dm3 NaOH solutions on the ion diffusion in wood calculated by combining the drift speed and the steady state ion diffusion

Diffusion tests through wood were made with different HS − concentrations in 1 mol/dm 3 NaOH solutions. The molar conductivity at infinite dilution of these mixtures was measured. The porosity of northern pine ( Pinus sylvestris ), birch ( Betula verrucosa ) and spruce ( Picea abies ) was also measured. The model used in the calculations was a combination of the drift speed and steady state diffusion and was dependent on the porosity of the porous plug. Both the theoretical and the experimental diffusion model were found to describe the diffusion of ion combinations well. This indicates that the diffusion is directly dependent on the conductivity of the electrolyte. The apparent porosity and the membrane resistance were dependent of the HS − concentration. The chemical interaction between wood and solution was shown to be measurable as deviations in apparent porosity.

A Joule‐Thomson process with condensation and evaporation

AbstractThe one‐dimensional flow of a fluid near saturation through a porous plug is considered. Upstream of the plug, the vapor is in the state of saturation. It is assumed that (i) the vapor cools down in a throttling process and (ii) it is in the unsaturated state downstream of the plug. At the upstream surface of the plug, the saturated vapor releases heat by partial or full condensation. If the permeability of the plug lies above a critical value the vapor condenses partially, otherwise full condensation occurs and a liquid film appears in front of the plug. In a small range of permeabilities above the critical value, the vapor condenses partially at the upstream surface, then it condenses fully at a front within the plug. Consuming the heat conducted downstream, the fluid evaporates fully at an evaporation front within the plug. The value of the critical permeability is a function of thermodynamic and transport properties of the fluid and of the thermal conductivity of the plug. The values of the permeabilities where the transitions between the different types of the process occur depend on the pressure difference across the porus plug.

Characterization of Regular and Plugged SBA-15 Silicas by Using Adsorption and Inverse Carbon Replication and Explanation of the Plug Formation Mechanism

A series of SBA-15 silicas was synthesized using triblock copolymer templates with the same length of poly(propylene oxide) block (POm; m = 70) and different average lengths of poly(ethylene oxide) blocks (EOn, n = 17−28). The average EOn length was varied by mixing EO20PO70EO20 copolymer with either EO5PO70EO5 or EO106PO70EO106 copolymer, whereas the tetraethyl orthosilicate (TEOS)/EO-unit molar ratio was kept constant. In addition, samples with the higher ratios were synthesized for the EO20PO70EO20 template. In all cases, 2-D hexagonally ordered SBA-15 silicas with interconnected primary pore structure (as inferred from carbon inverse replication) were obtained, but higher TEOS/EO-unit molar ratios resulted in the formation of samples with plugged pore structures, which were recently reported by others and referred to as plugged hexagonal templated silicas (PHTSs). Nitrogen adsorption data showed that n equal to about 19 was optimal from the point of view of formation of high-pore-volume, large-pore SBA-15 structure. All of the replicas exhibited structures with high specific surface area and pore volume and tended to have a similar pore diameter but more optimized SBA-15 structures tended to afford better ordered inverse carbon replicas. Regular and PHTS SBA-15 samples were additionally studied using argon adsorption at 77 K, which provided an important insight into the plugged structure. In particular, a PHTS sample that on the basis of nitrogen adsorption at 77 K appeared to be fully plugged, that is, with all primary mesopore channels closed by finely porous plugs, was found to be only partially plugged based on argon adsorption at 77 K, although there was evidence for the presence of some constrictions in all of the channels. A mechanism of the plug formation at high TEOS/copolymer molar ratios is proposed on the basis of similarity of the PHTSs with as-synthesized SBA-15 subjected to postsynthesis modification with TEOS. It is proposed herein that when the TEOS/EO-unit molar ratio is excessively high, only a part of TEOS present initially interacts with the EOn blocks of the copolymer template and thus hydrolyzes and condenses faster to form the SBA-15 structure. Subsequently or concurrently, the remaining TEOS, which hydrolyzes and condenses more slowly, solubilizes in the copolymer template in the SBA-15 pores (perhaps in the poly(propylene oxide) core of the micelles), or displaces the template, and then condenses to form the plugs.

Process metallurgical evaluation and application of very fine bubbling technology

The potential of VFB(very fine bubbling)-technology in steelmaking, developed for the production of super clean steels, was investigated. Recent RD 2] and to a level of 10 ppm under argon protective atmosphere [2]. The perspective of industrial application of the VFB technology to a 56-t ladle furnace of Helliniki Halyvourgia S.A., Greece, in order to improve steel cleanliness, requires additional R&D efforts. It is important to define the limits of VFB technology in respect of alloys dissolution, mixing time and homogenisation of steel and slag/metal reactions. In this work, a gas driven bubble aqueous reactor model simulating the bottom gas stirred ladle by means of gas injection through a SPP and a conventional porous plug was studied. Various operating conditions as well as different positions for the porous plug with and without a top oil layer were simulated. Tests concerning mixing time, solid-liquid mass transfer and critical gas flow rate, liquid/liquid mass transfer, using the SPP and a conventional porous plug have been performed. The evaluation of experimental results delivered important information for the design and operation of steel ladles, applying VFB-technology. Experimental results with SPP bubbles' agitated steel (1600 °C) in laboratory and technical scale experiments in IF and VIF are presented and discussed.

Electrokinetic Characterization of Porous Plugs from Streaming Potential Coupled with Electrical Resistance Measurements

The zeta potential of mixed nickel–iron oxide particles is evaluated by a new laboratory instrument. This latter allows the measurement of streaming potential together with the electrical resistance of porous plugs. The conductivity of electrolyte inside plug (pore conductivity) is deduced from electrical resistance measurements and is used together with streaming potential to evaluate the zeta potential by accounting for the surface conduction phenomenon. It is shown that neglecting the surface conduction phenomenon leads to a substantial underestimation of the zeta potential. The coupled measurements of streaming potential and plug electrical resistance yield zeta potential values that are in very good agreement with those obtained by electrophoresis. The densification of the porous plug with increasing pressure increments is put in evidence by the decrease in measured streaming potentials. Electrical resistance measurements make it possible to account for the increase in surface conductivity resulting from the more compacted structure of the plug. By doing so, the calculated zeta potential is found to be virtually independent of the pressure difference involved in streaming potential experiments, whereas the negligence of surface conduction phenomenon leads to a decrease in the apparent zeta potential with increasing pressure level.

Preparation and characterization of cation‐exchange media based on flexible polyurethane foams

AbstractContinuous electrodeionization (CEDI) is used to deionize a solution to a level attained by mixed bed ion exchange without chemical regeneration. However, handling of ion‐exchange beads is laborious for a large‐scale CEDI system. In this study, a new type of ion‐exchange polyurethane foam containing sulfonic acid groups was synthesized by bulk condensation polymerization for use as a cation‐exchange medium. Polyurethanes are synthesized by the reaction between a diisocyanate and a polyol. Toluene diisocyanate 2,4‐80%, 2,6‐20% (http://www.tciamerica.com/) was reacted with poly(propylene glycol) to synthesize a polyurethane prepolymer and then N,N‐bis(2‐hydroxylethyl)‐2‐aminoethanesulfonic acid (BES) was added to give a foam containing sulfonic acid groups. The functional polyurethane prepolymers were characterized by proton nuclear magnetic resonance spectroscopy (1H NMR), Fourier transform infrared spectroscopy (FT‐IR), elemental analysis (EA), and gel permeation chromatography (GPC). The ion‐exchange capacity was measured as 2.5 meq/g, and the equiconductance point of the polyurethane foams were 14, 19, 29, and 33 μ/cm for BES molar ratios of 0.5, 0.7, 1.0, and 1.5, respectively. The porous plug model shows that the current flows dominantly through the solution phase of the polyurethane foam, which indicates the polyurethane foam is a suitable medium for use in a CEDI operation. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1773–1781, 2002

Characterisation of porous ceramic plugs for use in electrochemical sensors

In electrochemical sensors like pH-, reference- or ion-selective electrodes a porous ceramic plug (or diaphragm) maintains the conducting junction with the test solution. These liquid junctions should have a resistance as low as possible meanwhile avoiding leakage through the junction. Five porous magnesium stabilised zirconium oxide plugs with different porosity's and pore size (distribution) were investigated as liquid junctions. The physical properties of these porous plugs were investigated with SEM and Mercury Intrusion Porosimetry. Important working conditions of these porous plugs are the resistance of the porous plug filled with an electrolyte and the contamination speed through these porous plugs, both for the test solution as the reference solution. The first property was measured by a 4-wire resistance measurement. The second property was measured by measuring the flow through rate of the reference electrolyte through the plug. It was shown that an optimal plug i.e., low leakage and high conductivity through the membrane, had a high porosity and relative small pores (0.25 μm). A simple mathematical model based on the Hagen-Poiseuille equation was developed to describe the porous plug characteristics. It was shown that mathematical calculation of the porous plug resistance was in good agreement with experimental results.

New experimental methods for the development and evaluation of aerosol samplers.

An understanding of the scaling laws governing aerosol sampler performance leads to new options for testing aerosol samplers at small scale in a small laboratory wind tunnel. Two methods are described in this paper. The first involves an extension of what is referred to as the "conventional" approach, in which scaled aerosol sampler systems are tested in a small wind tunnel while exposed to relatively monodisperse aerosols. Such aerosols are collected by test and reference samplers respectively and assessed gravimetrically. The new studies were carried out for a modified, low flowrate version of the IOM personal inhalable aerosol sampler. It was shown that such experiments can be carried out with a very high level of repeatability, and this supported the general validity of the aerosol sampler scaling laws. The second method involves a novel testing system and protocol for evaluating the performances of aerosol samplers. Here, scaled aerosol samplers of interest are exposed to polydisperse aerosols, again in a small wind tunnel. In this instance, the sampled particles are counted and sized using a direct-reading aerodynamic particle sizer (the APS). A prototype automated aerosol sampler testing system based on this approach was built and evaluated in preliminary experiments to determine the performance of another modified version of the IOM personal inhalable aerosol sampler. The design of the new test system accounts for the complex fluid mechanical coupling that occurs near the sampler inlet involving the transition between the external flow outside the sampler and the internal airflow inside the sampler, leading in turn to uncontrolled particle losses. The problem was overcome by the insertion of porous plastic foam plugs. where the penetration characteristics are well understood, into the entries of both the test and the reference samplers. Preliminary experiments with this new system also supported the general validity of the aerosol sampler scaling laws. In addition, they demonstrated high potential that this approach may be applied in a standardised aerosol testing method and protocol.

Analysis of helium II thermal links for instrument cooling in low gravity

The Low Temperature Microgravity Physics Facility (LTMPF) is a reusable, cryogenic facility that will accommodate a series of low temperature experiments to be conducted at the International Space Station. The facility will use a He II cryostat to cool the instruments. Some configurations of the science instruments in the cryostat will require an enhanced thermal link between the He II bath and parts of the instruments. Such an enhanced link can be made with plumbing filled with He II. This paper reports the results of analysis that was performed using the BATC proprietary helium flow software called SUPERFLO, on four different concepts for this link. The four concepts analyzed were: a simple tube with the heated end closed, a closed end tube with a porous plug at its entrance, a closed end tube filled with capillary tubes, and a porous plug driven flow loop. It was found that the concepts that used a porous plug were more robust since they were much less prone to boiling. This is due to the low gravity which causes all of the liquid in helium tank and plumbing to be very close to saturated conditions unless a porous plug is used to create a thermomechanical pressure. The effects of varying system parameters such as a acceleration, heat flux, pore size and tube size were also investigated and the results are reported.

On the isothermal binary mass transport in a single pore

For the transport in an inert pore the local species momentum balance is reconsidered. This leads to a Maxwell–Stefan type equation for a component α in which the gradient in chemical potential, the interspecies friction and the α– α shear stress form the momentum balance. From the set of equations the component axial velocity profiles can be derived, and so we call this model the velocity profile model (VPM-1), in which 1 stands for the fact that we only consider here the flow in one direction. For binary systems the set of equations is solved, and pore-integrated velocities are derived. This is done both for liquids with a no-slip boundary condition and for gases with Maxwell-slip boundary condition. The pore-averaged velocities can be expressed in the same form as the binary friction model. The use of the difference in pore-averaged velocities instead of the pore-averaged differences requires a correction function, which is derived for both fluid types. For liquids the component-wall friction factors are equal to those in the binary friction model, for gases a slightly different form is obtained. Comparison of predictions for liquid ultrafiltration and gas transport through porous plugs shows in general very small differences between the present model and the BFM, and good agreement with experimental data. The VPM-1 predicts a second flow reversal point of (near-)equal mass isobaric diffusion of gases at different pressures, and a reversal with temperature. From the model follows a new expression for the velocity difference. Velocity profiles for various situations are explored such as liquid ultrafiltration and diffusion, counterdiffusion of gases and for the Stefan-tube. In the latter we find that for a zero average flux of inert gas there is a core of inert gas moving in the direction of the water vapor, and a reverse flow in the area near the wall. The model can be extended to more-dimensional flow problems such as in adsorption and heterogeneous catalysis.