Porous Plug Research Articles

Special porous plugs for the production of super clean steels

Fine bubblers to be used as special porous plugs (SPP), have been devised for fine bubbling within steel melts for improving the cleanliness efficiently by floating the micro-inclusions and removing the dissolved gases. The development principles of the magnesia-spinel porous plugs are presented. Laboratory water simulator tests have shown that small (< 1 mm), non-coagulating bubbles, with uniform distribution are formed. The characterisation and testing of the SPP has shown that under steelmaking conditions clogging from metal infiltration is limited. Erosion, cracking or changes in microstructure were not detected in high temperature long-term endurance tests. With combined treatment in a vacuum induction furnace under a 3 kPa pressure and Ar purging of 18 min through the new SPP, the total oxygen content of the steel melt was decreased from 65 to 7.7 ppm. An application has been filed for a patent for the method for the production of fine bubblers to be used as porous plugs.

Prediction of temperature in secondary steelmaking: mathematical modelling of fluid flow and heat transfer in gas purged ladle

As a first step towards prediction of temperatures in secondary steelmaking, mathematical modelling of fluid flow and heat transfer in ladle furnace was undertaken. A two-dimensional quasi-single phase model has been developed for turbulent recirculating flow by solving Reynolds averaged Navier-Stokes equations along with a two-equation k-e model. The model was then extended to include thermal transport in a conjugate domain (i.e., molten steel + refractory shell + steel shell). The flow model was validated with water model data reported in literature by different researchers. Good agreement for velocity field and satisfactory agreement for turbulent kinetic energy field were obtained. The thermal model showed good agreement with results predicted in literature. The paper also presents findings of tests for sensitivity of flow on modelling and process parameters. By comparison with water model experiments, it has been demonstrated that the flow field in a ladle with a porous plug can be represented using a gas voidage fraction in the plume obtained from experiments with nozzles for axial gas injection from the bottom. Flow and thermal fields were insensitive to initial turbulence level at nozzle. Maximum temperature inhomogeneity in the melt was 2 °C after 1.5 min and negligible after 3 min of onset of gas purging.

Investigation and application of a model for porous foam aerosol penetration

Measurements of aerosol penetration through porous polyurethane foam plugs were carried out in order to develop a model describing the aerosol penetration behaviour. The data were found agree well with an existing semi-empirical model for porous foam aerosol penetration. This model was improved by reformulating it to use consistent units, and accurately measurable input parameters. The model was implemented as part of a design spreadsheet, to design foam modules suitable for a range of specific aerosol monitoring applications. The design spreadsheet was validated by comparing its outputs with the known characteristics of a number of pre-existing foam modules. It predicted the characteristics of these modules accurately, within the limitations due to a lack of knowledge of the precise cell diameters of the foams used to make them. The use of the design spreadsheet to explore different options for size-selective foam modules is illustrated. The results obtained highlight the importance of a reliable supply of foam, having closely specified cell diameters, in order to manufacture size-selective samplers meeting acceptable quality standards.

Characterization of Water-Filled Ag/AgCl Reference Electrode

Pressure-balanced external Ag/AgCl electrode has been extensively used for both Pressurized Water Reactor (PWR) and Boiling Water Reactor (PWR) environments. The use of KCI-based buffer solution often becomes the source of electrode potential drift due to slow leakage through its porous plug, typically made of zirconia. It is reported that results of our effort to improve the stability of electrode potential by using high purity water as the filling solution in which ion activity can be established and maintained at the solubility of AgCl even with the sustained leakage for a long period. Stability tests have been made in boron and lithium mixture solution at . The electrode potential remained stable within 10 mV over one week period. And after a thermal cycle between 288 to the potential shift of Ag/AgCl electrodes did not exceed 15 mV By using the limiting equivalent ionic conductances and Agar's hydrodynamic theory, the thermal liquid junction potential (TLJP) of the electrode has been predicted. The calculated values for the water-fiued Ag/AgCl electrode potential, in which the chlorine concentration in the filling solution was derived from the measured data at ambient temperature, had a good agreement with the experimental values.

Numerical analysis of plume characteristics and liquid circulation in gas injection through a porous plug

Two phase flows have been numerically calculated to analyze plume characteristics and liquid circulation in gas injection through a porous plug. The Eulerian approach has been used for formulation of both the continuous and dispersed phases. The turbulence in the liquid phase has been modeled using the standardk−ɛ turbulence model. The interphase friction coefficient has been calculated using correlations available in the literature. The turbulent dispersion of the phases has been modeled by the “dispersion Prandtl number”. The predicted mean flows is compared well with the experimental data. The plume region area and the axial velocities are increased with the gas flow rate and with the decrease in the inlet area. The turbulent intensity also shows the same trend. Also, the space-averaged turbulent kinetic energy for various gas flow rates and inlet areas has been obtained. The results are of interest in the design and operation of a wide variety of materials and chemical processing operations.

Minimally invasive bone harvesting tools.

The most readily available source for autologous bone graft used in spinal fusion (the gold standard) is the iliac crest. However, the open surgical approach for harvesting corticocancellous iliac bone is associated with a marked increase in morbidity. This study suggests two alternatives to the traditional open harvesting procedure. For anterior interbody fusion procedures using a cage, the autologous bone is harvested regionally from a neighboring vertebral body. Alternatively, using minimally invasive techniques, a custom bone graft harvester with a flexible tube and cutting tip allows harvesting of autologous bone from a single entry point at the iliac crest. The effect on the mechanical strength of a lumbar vertebra of removing a cylindrical regional bone graft was studied in a cadaveric model. The bone defect was filled using three different filler materials: a porous tri-calcium phosphate plug, a porous tantalum plug, and a self-setting calcium phosphate cement. After plug removal, the vertebral body's strength in flexion/compression loading was reduced significantly, but could be restored to at least intact values with any of the three filler materials. The minimally invasive bone graft harvester was tested in three cadaveric pelves. With the cutting tip being guided within the cortical boundaries of the pelvis, cancellous bone volumes of 10-20 cc could be harvested from each iliac bone. Regional bone graft harvest in anterior spine surgery is suggested to be anatomically safe and biomechanically acceptable. Any of the three filler materials can restore the vertebral body's mechanical strength, but the filler's long-term resorption/remodeling or osteointegration behavior is unknown. The minimally invasive bone graft harvester is a novel tool, which performed satisfactorily under laboratory conditions, but clinical results are still missing.

Hopf Bifurcation from Rotating Waves and Patterns in Physical Space

Hopf bifurcations from time periodic rotating waves to two frequency tori have been studied for a number of years by a variety of authors including Rand and Renardy. Rotating waves are solutions to partial differential equations where time evolution is the same as spatial rotation.Thus rotating waves can exist mathematically only in problems that have at least SO(2) symmetry. In this paper we study the effect on this Hopf bifurcation when the problem has more than SO(2) symmetry. These effects manifest themselves in physical space and not in phase space. We use as motivating examples the experiments of Gorman et al. on porous plug burner flames, of Swinney et al. on the Taylor-Couette system, and of a variety of people on meandering spiral waves in the Belousov-Zhabotinsky reaction. In our analysis we recover and complete Rand’s classification of modulated wavy vortices in the Taylor-Couette system. It is both curious and intriguing that the spatial manifestations of the two frequency motions in each of these experiments is different, and it is these differences that we seek to explain. In particular, we give a mathematical explanation of the differences between the nonuniform rotation of cellular flames in Gorman’s experiments and the meandering of spiral waves in the Belousov-Zhabotinsky reaction. Our approach is based on the center bundle construction of Krupa with compact group actions and its extension to noncompact group actions by Sandstede, Scheel, and Wulff.

Particulate penetration of porous foam used as a low flow rate respirable dust size classifier.

Porous foam has been used as a material for classification of particulate matter into various size fractions. The penetration characteristics of a nominal 90 pores per inch porous foam were studied at various flow rates, face velocities, and foam plug diameters and compared to the aerosol penetration of a 10 mm Dorr Oliver cyclone operated at 1.7 L/min. Poly-dispersed triethanolamine spheres were classified through porous foam plugs and the resulting penetration was determined using an aerodynamic particle sizer. Results showed that for a given plug diameter, as face velocity increased from 26 to 39 cm/sec, the 50 percent cut point decreased from 4.5 to 3.8 microns. Furthermore, as the diameter of the plug increased from 4 to 12 mm, the 50 percent cut points were similar to other plug diameters at equivalent face velocities. The best match to the 1.7 L/min cyclone penetration characteristics occurred at a flow rate of 250 ml/min through a 25 mm by 4 mm diameter section of 90 pore per inch foam. Because of the need to provide short-term or real-time estimates of worker respirable dust exposure, porous foam may be a viable classification media for a low flow rate, disposable respirable dust sampler for use in the coal mining industry.

Thermodynamic Inhibitors for Hydrate Plug Melting

Abstract: The hydrate melting efficiency of thermodynamic inhibitors has been shown to depend on hydrate plug properties, inhibitor properties, and the turbulence of the liquid system in question. Inefficient mixing of inhibitor and water, lack of contact between inhibitor and hydrate, and a solid or gel precipitation in the melting region have been demonstrated to give low melting efficiency. MeOH seems to be the most efficient inhibitor for melting porous plugs, but may not melt a plug with low porosity. MEG has the ability to penetrate into a compact plug and cause melting. However, when used at high concentrations, MEG may freeze out as a solid or gel, which can lead to reduced hydrate melting efficiency. At high pressures and in the presence of a hydrocarbon liquid, MEG solutions were shown to freeze out at temperatures more than 30°C higher than values given in the literature. TEG seems to easily freeze and become inefficient for melting hydrate plugs.

Low-Frequency Dielectric Responses, Static Conductivities, and Streaming Potentials of Polymer-Coated Latex Dispersions and Porous Plugs

The low-frequency permittivity and conductivity increments and the static conductivity of well-characterized latex dispersions and plugs have been measured over a wide range of ionic strengths. We have investigated the effects of adsorption of the neutral polymer polyethylene oxide on these electrodynamic phenomena. It is shown that the counterion mobility in the double layer is significantly reduced by the adsorbed polymer. A model is developed to describe the retarded motion of ions in the gel-like polymer layer, which is considered a Brinkman fluid. The required ionic and polymer distribution functions are obtained from a self-consistent field model. Furthermore, ζ-potentials were inferred from streaming potentials of close-packed latex plugs. Since a significant part of the conduction is due to ions behind the shear plane, it was necessary to make use of the plug conductivity data in obtaining the correct ζ-potentials, especially at low ionic strengths. The ζ-potentials of the polymer-coated surface a...

Calculation of Zeta Potential from Electrokinetic Measurements on Titania Plugs

The O'Brien theory developed for the electrical conductivity and electro-osmosis in porous plugs consisting of nonconducting particles has been applied for the calculation of ζ-potentials from conductivity and streaming potential measurements at two pH values, 3.3 and 6.5 or 5.8, on plugs composed of titania (undoped and doped with W6+and Li+ions) particles. The particles have been prepared both by precipitation (continuous crystallization at constant supersaturation) and by the sol-gel method. It was found that O'Brien's theory is also applicable inn-type semiconductor particles, such as titania (doped and undoped). Specifically, for the correct determination of ζ-potentials measured in solutions of relatively low ionic strength, it is necessary to take into account surface conduction behind the shear plane, for all samples measured at pH 3.3, a value considerably lower than the isoelectric point (i.e.p.) of titania. Under these conditions the surface charge of the suspended titania particles is high, and consequently the contribution of surface conductance to the conductivity of the plug is significant. The effect of surface conduction behind the shear plane on the calculation of ζ-potential is enhanced for the Li+-doped preparations due to the increase of surface conductivity caused by doping with Li+. Measurements of the streaming potential for the samples prepared with the sol-gel method were made at pH 6.5 (5.8 for the undoped titania); i.e., near the pH corresponding to the i.e.p., correct values of ζ-potential may be obtained in suspensions even at low ionic strength without taking into account the polarization of the double layer due to surface conduction, by applying the primitive Smoluchowski theory. This treatment is valid because at pH values near the i.e.p. the surface charge of the particles is very low, and consequently surface conductance is negligible compared with the conductivity of the plug.

Investigation of large dynamic range helium II liquid/vapor phase separator for SIRTF

A large dynamic range superfluid helium, helium II, liquid–vapor phase separator is required for the thermal design of the Space Infrared Telescope Facility (SIRTF). A porous plug type phase separator is adopted for SIRTF mission. A candidate porous plug was tested using two different types of experimental apparatus to obtain the exact flow characteristics. Mass flow rate, pressure and temperature differences across the porous plug were measured in this experiment. The experimental data are compared with the theoretical predictions. The fundamental feature of the flow phenomena through the tested porous plug provides valuable data for the practical design of a phase separator for SIRTF needs.

99/00569 Large-scale baseload wind power in China

Bubbles released from a porous plug into a gas-stirred ladle present different bubbly dispersion patterns that can be studied by CFD means. Recent modeling (Alexiadis et al.) has, in fact, led to numerical results in accord with experimental data. However, due to the high number of equations involved, it is not easy to understand the physical reasons of the transitions between these patterns. In the present paper, attention was focused on the role of fragmentation and coalescence and the pattern-transition modeled by means of intersection points between these functions.

A Capacitance Probe for Measurement of Bubbles in Molten Metals.

A probe has been developed for measuring bubble size, velocity and frequency in molten metals. The probe has been tested on a low melting point alloy (Belmont alloy) and on aluminum. Bubble signals are discernible in either metal. The probe measures the change in capacitance between a wire and the metal as a bubble passes. Because there is no electrical contact necessary between the wire and the metal, the wire may be sheathed with a material (e.g. alumina) that is inert to the metal. The ruggedness of this design was demonstrated by its use for three hours in aluminum. A bridge circuit which can measure the small capacitance change was devised and a deconvolution procedure has been developed whereby bubble size distributions can be obtained. Measurements have been made of the bubble size and velocity above J-shaped nozzles through which argon was injected. Similar measurements have been made of the bubble size distribution above a porous alumina plug and the bubbles were larger than those observed in water at a comparable flowrate.

Permeability of Ceramic Membranes to Gas Flow

A number of industrial processes, such as particle removal from gases by filtration and gas injection by porous plugs in steel refining, makes use of rigid and porous ceramic products through which fluid flow at high temperature takes place. The correct design and proper structure of such a membrane can save an appreciable amount of energy in the process, as the pressure drop due to fluid flow and membrane clogging are minimized. However, the number of experimental works found in the literature on this subject is still scarce, particularly in the applications concerning gas filtration at high temperatures. In this work, the formation and characterization of rigid refractory membranes with foam-like structure is carried out. These ceramic bodies were formed by impregnating an uniform polyurethane foam with a suspension of refractory raw materials, followed by drying and calcination. The membranes structural characteristics are correlated to its permeability to air flow, with gas superficial velocity varying from 2 to 12 cm/s, which are typical values for gas filtration. The results indicate a very high dependence of porosity to the permeability of rigid ceramic membrane for gas flow.

Streaming potentials and conductivities of porous silica plugs

Streaming potentials and conductivities of close-packed plugs of spherical Stöber-silica particles were measured. Stöber silica is highly porous; more than 98% of the countercharge may be situated inside the particle. Only the countercharge in the double layer region outside the porous particle contributes to the plug conductivity and the streaming potential. The countercharge obtained from plug conductivities is less than the double layer charge obtained from titrations. The countercharge obtained from streaming potentials is less than obtained from plug conductivities, which indicates the occurrence of conduction behind the shear plane. It is essential to take this conduction into proper account in order to arrive at more realistic ζ-potentials.

Electro-kinetic measurements on plugs of doped titania

The z-potential and the surface conductivity of pure anatase and anatase doped with Li +, Nb 5+ and W 6+ prepared with both the precipitation (continuous crystallization at constant supersaturation) and the sol–gel method have been determined at two pH values (3.3. and 6.0 or 6.5). This was carried out by measuring the streaming potential and electrical conductivity of a porous plug containing the anatase particles. The sol–gel preparations exhibited a higher density than those obtained by precipitation. Plots of the plug conductivity as a function of the conductivity of the solution are essentially linear, allowing for the establishment of the surface conductivity, K σ. The main contribution to K σ stemmed from the counter charge behind the slip plane. At pH 3.3, i.e. much lower than the i.e.p., doping with Nb 5+ and Li + caused a considerable increase of the surface conductivity in both preparations, whereas at a pH 6.0 or 6.5, i.e. near the i.e.p., doping led to a slight decrease of the relatively high surface conductivity of the sample prepared by precipitation. At pH 6.5 sol–gel preparations showed negligible surface conductivity, independent of the doping, with the exception of the preparation with a high concentration of W 6+. Moreover, doping with W 6+ did not considerably change the surface conductivity. There is some indirect correlation between the surface and the bulk conductivity of the various samples. Tangential mobilities of Cl − ions in the stagnant layers are of the same order of magnitude as those in the bulk solution.

Hydrate dissociation rates in pipelines

Recent laboratory and field data suggest that hydrates form very porous pipeline plugs which transmit pressure freely, while hydrates act as significant flow obstructions. The blocked flow causes an ocean pipeline to rapidly equilibrate to the ocean temperature at 4°C. When the hydrate plug is dissociated through total depressurization of the pipeline, the hydrate plug will be converted to an ice plug which significantly dissociates longer than the hydrate. This work formulates the first dissociation model in rectilinear coordinates. It indicates that there may be an optimum pipeline pressure for the most rapid dissociation of all solid phases resulting from hydrate pipeline blockages. Surprisingly, the high ice thermal diffusivity provides the highest heat flux when some ice is present.

Vapor–Liquid Phase separation of He II

A theory is proposed which uses both the permeability and bubble point diameter of the porous plug to characterize the full range operation of the Vapor Liquid Phase Separation (VLPS) of liquid helium. A computer model has been written based on the theory presented in this paper, which gives good correlation with VLPS data in the literature. The predicted performance of the SIRTF flight plug is also presented.

Streaming Potentials and Conductivities of Latex Plugs in Indifferent Electrolytes

Streaming potential and conductivity measurements were performed on porous plugs in a number of indifferent electrolytes. The plugs were made of monodisperse spherical polystyrene sulfate latex with fixed surface charge density. The observed surface conductivity could be interpreted with the classical Bikerman expression extended with the contribution from conduction behind the shear plane. It was shown that electroosmosis contributes positively, while the depletion of co-ions in the double layer contributes negatively to the surface conductivity. It was further demonstrated that a significant part of the conduction is located behind the slip plane. The ion mobility of the indifferent counterions behind, as well as beyond, the shear plane is close to the bulk mobility. In the correct determination of ζ-potentials in the low electrolyte concentration range, it is necessary to take surface conduction behind the plane of shear into account. When this is done, the maximum in the curve of the ζ-potential versus electrolyte concentration disappears.