Porous Plug Research Articles

Network model of cryogenic phase separators

We have studied a simple network model for porous plug phase separators bycomparing the flow of helium through a straight capillary to that of a capillary which branches into two capillaries of different diameters. For helium flow above a critical value, the straight capillary model has shown that in order to maintain phase equilibrium the liquid-vapor interface retreats into the capillary. This result is consistent with previous single capillary models. Branch points (nodes) were added to the straight capillary in two ways. The first configuration connects five capillaries to form an H (two nodes). The H-shape configuration proved to be intractable. The second configuration consists of three capillaries connected to form a Y (single node). In this case, we have been able to find solutions which satisfy conditions of steady-state equilibrium.

Studies on helium flow in experimental loops with different impedances operated with fountain effect pumps

An experimental flow loop with He II flow driven by fountain effect pumps (FEPs) is studied with respect to operation at different flow impedances and with thermal loads applied at different positions. The measured values of temperature, flow rate and pressure drop are compared with calculations resulting from a simplified model which assumes ideal performance of the porous plug and of the heat exchangers and which does not take into account Gorter-Mellink (GM) conduction. The main features of the loop are shown to be well described by this model. Refined calculations with a more complex model, including GM conduction of the He II, are only required for predicting the temperature distribution in some discrete regions of the loop.

Deterministic Chaos in Laminar Premixed Flames: Experimental Classification of Chaotic Dynamics

Abstract Our previous experiments on the dynamics of laminar premixed flames on a circular porous plug burner have revealed periodic modes with different spatial and temporal characteristics. In this paper representative examples of nonperiodic modes will be presented, and it will be argued that these modes fall into two distinct classes. The method of data analysis used to make this identification will be explained and the experimental conditions that are conducive to observing the flame as a dynamical system will be described in detail. Our results suggest that the techniques of nonlinear dynamics are useful in classifying the periodic and chaotic modes of pulsating and cellular premixed flames but are probably not relevant to diffusion flames.

Accretion growth on single-pipe tuyeres: Part II. Model results and discussion

A mathematical model of accretion growth on single-pipe injectors has been used to analyze the process of accretion growth during copper converting and inert gas stirring of steel. A sen-sitivity analysis of the model developed in Part I of this article revealed that the critical unknown factor controlling the growth process is the local bath velocity. It is likely that the asymmetric forms seen in accretions are due primarily to nonuniformity in bath flow around the accretion. The important factors controlling the size of accretions in copper converting are bath superheat, gas flow rate, and oxygen content. Blockage of the tuyeres in the converter is a function of wall and bath superheat and likely is a result of the freezing of matte in the pipe. The effect of gas-flow rate on accretion size is clearly shown in the case of inert gas injection into steel. The transition between the different accretion types found on single-pipe tuyeres, pipes, porous pipes, and hemispheres, depends on events at the tuyere-pipe tip. Conditions of high back-attack frequency, low superheat, and small tuyere diameters tend to lead to accretions forming over the tip. If this takes place at high injection pressures and with a relatively ductile material, a “porous plug” will form, on which a hemisphere will grow. Under other conditions, it may result in a blockage. The presence of accretions at a tuyere has a strong influence on the thermal profile in the surrounding refractory and tuyere pipe. Steep thermal gradients near the tip in both regions will likely lead to refractory deterioration and pipe distortion.

Accretion growth on single-pipe tuyeres: Part I. Model development and preliminary analysis

A mathematical model of the growth of accretions on submerged single pipes has been developed based on the heat transfer in the vicinity of the injection point. The model is able to predict the formation of either pipe or hemispherical accretions based only on the input con-ditions. It is assumed that a hemispherical accretion is formed only when a porous plug is formed within the tuyere tip by the freezing of bath material during regular penetration episodes. Gas flow within the bath is calculated from physical modeling results, and allowances are made for the possibility of a gas/bath reaction. A preliminary analysis of the model predictions for copper converter and steel ladle stirring applications has been carried out. The model predicts that, under normal operating conditions, the accretions formed in copper converters are very small but can become appreciable under low superheat conditions. The time required to reach steady state depends upon the final accretion length but can be as much as 5 minutes. In ladle stirring applications, the model predicts that the accretion formed will be approximately 4.5-cm high with a slightly larger basal radius. This accretion requires approximately 10 minutes to reach steady state. The final shape and size of an accretion are dependent upon the balance of heat flows around it, with steady state occurring when heat inputs to the accretion exactly equal heat outputs.

Effect of Ethyl Xanthogenate on Sorption of an Acid Dye on Polyester Fibers

An investigation of the streaming potential, sorption, and electrical conductance of a porous plug of polyester fibers treated with ethyl xanthogenate and afterwards dyed with the acid dye Sirius red 4B at varying temperatures is described. The zeta potential of the polyester/potassium ethyl xanthogenate system is negative in the whole range of concentrations studied (10-6 to 10 -2 mole/liter), and the absolute value of this parameter increases when the temperature of the system is increased. Uptake of ethyl xanthogenate on the polyester in the temperature interval tested is improved by the increased temperature. These results reveal that uptake occurs with the establishment of strong chemical bonds. The zeta potential of the fiber/dye solution system is negative in the range of concentrations studied, and the absolute value of the system's zeta potential decreases markedly when the temperature increases. Dye adsorption on polyester decreases when the adsorption temperature increases, sug gesting that dye adsorption on polyester in the temperature interval tested takes place without the establishment of strong chemical bonds. The absolute value of the system's negative zeta potential decreases markedly when the amount of ethyl xanthogenate previously taken up by the fiber increases at constant temperature. Dye uptake by the pretreated polyester improves with increasing amounts of ethyl xanthogenate taken up by the fiber and with increased sorption temperature, suggesting that dye uptake with this system takes place with the establishment of strong chemical bonds. On the basis of the molecular structure of these compounds, dye uptake probably takes place by means of a nucleophilic attack of the -S- group of the ethyl xanthogenate on the carbonyl group of Sirius red 4B. The electrical conductance of the system increases with both increasing dye concentration in solution and increased sorption temperature which agrees with the hypothesis of strong chemical bonds involved in this process.

Application results of Al2O3 porous plug containing TiO2, Al2O3 and MgO as matrixes on an actual operation

Al2O3 porous plugs containing TiO2, Al2O3 and MgO in the matrix were applied for 200‐t ladle (improved porous plug). Although cracks occurred in longitudinal and transverse direction in the conventional porous plugs, no cracks were observed in the improved porous plug. Therefore, the latter was superior to the conventional one in thermal shock resistance. Wear rate was 9.0 mm/heat for improved plug and 9.8 mm/heat for the conventional one in average. The improved plug showed higher corrosion resistance than the conventional one. With the improved porous plug O2 cleaning was only necessary after every two heats. This was due to the high penetration resistance.

Electroviscous Effect in Porous Polystyrene Plugs

The disagreement between the experimental determined hydrodynamic coefficients of the polystyrene/methanol-water (50% v/v) mixture for different electrolyte concentrations, and those predicted by the classical treatment of Overbeek is explained on the basis of an electroviscous effet

Modeling flows and mixing in steelmaking ladles designed for single- and dual-plug bubbling operations

Through solutions of appropriate forms of the Navier-Stokes equation, the intermixing of fluid within gas-stirred ladles, with asymmetric single and multiporous plugs, can be modeled quite satisfactorily. In this study, mixing behavior and mixing mechanisms are analyzed as a function of porous plug location, tracer injection point, and ladle monitoring point. It is shown that off-centered bubbling gives the most consistent results in terms of minimizing mixing times, since angular momentum intermixes fluid across the width of a ladle. Comparisons between mathematical and experimental data are presented.

Measurement of the relaxation time in Darcy flow

The inertia of a liquid flowing through a porous medium is normally ignored, but if the acceleration is great, it may be important. The relaxation time, defined so that it alone accounts for the inertia, has been determined experimentally with a simple oscillator. A U-Tube is provided with a porous plug and filled with a liquid. During pendulation of the liquid, the frequency and the damping define the relaxation time. The measured value of the relaxation time is about 10 times the theoretical estimate derived from Navier-Stokes equation.

Electro-kinetic transport coefficients of aqueous binary mixtures through titanium oxide porous plug

Hydrodynamic and electro-osmotic permeabilities of different mole fractions of water in ethylene glycol (EG) and diethylene glycol (DEG) across a titanium oxide porous plug have been investigated. The dependence of hydrodynamic and electro-osmotic permeabilities on X w in accordance with Spiegler's model has not been found. The linear phenomenological relationships describing the phenomenon of electro-osmosis hold up to 100, 220 and 260 V for water, EG and DEG respectively. The higher order coefficients introduced owing to the non-validity of linear phenomenological relationships have been estimated from the data of electro-osmosis and electro-osmotic pressure difference. The data of second order coefficients have been analysed in terms of the Rastogi and Shabd theory of the electrical double layer.

A novel batch electrode design for use in stripping potentiometry facilitating medium exchange

AbstractMedium exchange between electrolysis and stripping steps affords numerous advantages in both voltammetric and potentiometric stripping techniques. A new electrode design for batch mode stripping analysis that allows simple medium exchange under potentiostatic control is described. This is achieved by adherence of a drop of sample to a glass tube containing a glassy‐carbon disc working electrode and a porous ceramic plug, which is in liquid contact with the inner solution in which the reference and counter electrodes are situated. The electrode can be used both for manual operation and for an automated system with a sample changer. Its use is demonstrated in the constant‐current stripping potentiometry determination of the dimethylglyoxime complexes of nickel(II) and cobalt(II) after medium exchange with stripping in 5 M CaCl2, thus avoiding interferences from dissolved oxygen and excessive amounts of zinc(II).

Cooling options for ASTROMAG

A comparison of the various cooling options for the ASTROMAG particle physics experiment is presented. The baseline design for the cryogenic system involves using a natural circulation fountain-effect driven flow loop (Hofmann type). The present paper considers two alternative options for cooling. The first design involves a thermal strap made of a high-conductivity metal, e.g., high-purity aluminium or copper, which connects the coil to the helium reservoir. Venting helium vapour can also be used to minimize the temperature of the magnet and recover from a quench. The second design is based on a He II heat pipe concept where steady state heat transport is by counterflow. Cavitation is prevented by use of a porous plug. Forced flow He II is also available but only during extraordinary operating conditions.

Anomalous on-orbit behaviour of the NASA Cosmic Background Explorer (COBE) Dewar

The cryogenic operation of NASA's Cosmic Background Explorer (COBE) ended on September 21, 1990, with the depletion of the liquid helium cryogen, after COBE had completed more than 10 months of successful Dewar and instrument operation. In this report we provide a brief summary of the nominal cryogenic performance of the Dewar (for more detail consult Reference 1). We present in detail several aspects of the helium and spacecraft dynamical behaviour. We discuss the occurrence of temperature and pressure oscillations in the Dewar porous plug. We review the impact of internal instrument malfunctions and of external radiation sources on the performance of the Dewar and of the instruments. From measurements of the COBE spacecraft spin rate we are able to monitor the spin coupling of the liquid helium to the walls of the Dewar. We analyse the spin measurements and present a model for the coupling. Finally, we review a number of helium Dewar ‘lessons learned’ from the COBE mission, and remark on the applicability of these lessons to future missions involving cryogenic payloads.

Automating the Arealometer: Examination of the Kozeny Equation

Samples of eleven cottons with a wide range of fineness and immaturity properties, as measured by the Arealometer, were studied for airflow behavior on an experimental computerized system. Specific surface areas as calculated from the Kozeny relationship were obtained for void fractions ranging between 0.60 to 0.90. The observed variation in fiber fineness with void fraction was unexpected as originally applied to the Areal ometer. Nevertheless, both the specific surface areas A and AH at low and high specimen compressions, respectively, correlated favorably with results of the Arealometer. These correlations were best when the values obtained on the newly automated system were at fixed void fractions rather than fixed porous plug resistances to airflow as built into the Arealometer.

Tissue reaction to intraperitoneally implanted catheter materials

The limiting factor that introduces long-term complications of intraperitoneal (i.p.) catheters used, for example, with the Programable Implantable Medication System (PIMS) is the encapsulation of the catheter tip with tissues due to tissue reaction. The objective is the development of new catheters for PIMS or other systems for i.p. insulin delivery that allow continued insulin flow. The study is based on two hypotheses: (1) vascularized tissue will grow into a porous end plug mounted at the catheter tip (100–300 μm pore diameter), with sufficient blood supply to carry the insulin to the circulation; (2) use of a narrow pore diameter (25 μm or less) end plug will prevent tissue ingrowth yet allow insulin flow. The biological response to the following materials, all designed for use in catheters, were studied: polyurethane, segmented polyether-urethane, alumina coated on Teflon (proplast regular and micro-pore), pyrolytic carbon, high density polyethylene, ultra high molecular weight polyethylene, hydroxyapatite, bioglass, and expanded Teflon. Some of these materials also are used for several other applications: vascular grafts, in the cardiovascular system, and for dental, orthopaedic, and other purposes. The shape and size of the end plugs made from each of the materials were as similar as possible to minimize size effects. The test materials were implanted i.p. in 12 dogs for a period of 12 weeks. The cylindrical plugs were typically 1.5–2.5 cm long, with an inside diameter of 0.3 cm, and an outside diameter of 0.6 cm. When the explants were retrieved, thin capsules were observed, of varying thickness and blood supply, surrounding the end of the catheters. Pathological evaluation revealed the best large pore material to be proplast regular and the best small pore materials to be carbon and polyurethane.

Porous plug made of tungsten wires and its conductance

A porous plug suitable for uhv systems was fabricated and its conductance was measured under various working conditions. The porous plug was made by inserting tungsten wires into a small hole. The porous plug with four wires inserted into a small hole of 138 microm radius and 0.15 cm long was shown to have a conductance of the order of 10 −4 l s −1 for nitrogen, argon and helium, and to be stable for repeated bakeouts up to a temperature as high as 400°C. The relative conductance for a number of gases, nitrogen, argon and helium, was inversely proportional to the square root of the gas molecular weight. The conductance value of the porous plug can easily be varied by changing the number of tungsten wires and dimensions of the hole.

Control of turbulent separation in diffuser by periodic disturbance.

The effects of periodic disturbance on a turbulent separating air flow in a two-dimensional diffuser have been investigated at the Reynolds number of 42000. The disturbance was generated by the external speaker and introduced from the walls of the asymmetric diffuser through a porous plug. With varying disturbance amplitude and frequency, the percent downstream flow, the pressure recovery coefficient, as well as the streamwise- and the normal velocity components, were measured. The results indicated the significant suppression of separation and the improvement of pressure recovery. This was mainly due to the periodic suction and injection from the wall but due to neither the change of the turbulence structure upstream of the incipient detachment point nor the excitation of instability in the separated shear layer.

Plume characteristics and liquid circulation in gas injection through a porous plug

Various forms of plumes have been identified following the injection of air at different rates through a porous plug into water contained in a ladle-shaped vessel. Discrete bubbles form at the plug and rise uniformly through the column of liquid at gas flow rates up to 14 cm3/s cm2 of plug surface; at higher flow rates, groups of bubbles increasingly coalesce into larger gas pockets, and beyond about 40 cm3/s cm2, the gas globes are large enough to cover the entire plug surface before detachment and gradual disintegration as they rise through the body of liquid. The gas fraction, as well as bubble frequency, bubble velocity, and bubble size, have been measured in the various dispersion regimes by means of an electroresistivity probe. The radial distributions of gas fraction and bubble frequency are approximately bell-shaped about the axis of flow, and the reduced values are close to Gaussian functions of the reduced radial distance from the axis. The gas fraction along the axis has been correlated to the reduced height of the plume; it increases with decreasing distance above the plug and with increasing gas flow rate. The axial bubble frequency shows a decrease in the vicinity of the plug with the onset of bubble coalescence, but the values of the frequencies at all gas injection rates converge to about 12 s−1 toward the surface of the bath. The mean bubble velocity increases with increasing flow rate but drops once coalescence is fully established. Conversely, there is a sudden increase in the mean bubble diameter with the onset of coalescence. The axial and radial components of the velocity of the liquid surrounding the plume have been measured by means of a Laser-Doppler Velocimeter (LDV), and the results show that the circulation patterns are identical, irrespective of the dispersion regime. The axial flow which is upward in the vicinity of the plume decreases in magnitude with increasing radial distance, ultimately reversing to an in-creasing downward flow beyond a certain distance from the plug axis. Similarly, the radial flow which is outward from the plume near the liquid surface decreases steadily with depth and eventually reverses to an inward flow at a depth independent of the gas injection rate. The profiles of the axial velocities are almost sigmoidal, except in the coalescence regime, where the effect of turbulence is profound at the upper liquid layers. The radial liquid velocities are generally small relative to the axial components, only about one-fifth as large, considering the maximum average values.

Covalent immobilization of proteins and peptides for solid-phase sequencing using prepacked capillary columns

The use of prepacked capillary columns for immobilizing proteins and peptides for solid-phase Edman degradation is described. Capillary tubes with an internal volume of about 30 μl are filled with glass beads bearing isothiocyanato groups (DITC-glass), aminophenyl groups (AP-glass), or aminoethylaminopropyl groups (AEAP-glass) and are sealed with porous plugs. Proteins or peptides in appropriate buffers are introduced into the columns by capillary action and are covalently coupled to the glass beads, either by reaction of lysine side-chain amino groups with DITC-glass, by carbodiimide-mediated reaction of carboxyl groups with AP-glass, or by reaction of homoserine lactone groups with AEAP-glass. Optimization of attachment conditions is described. The capillary columns are loaded into the sequencer and, when sequencing has been completed, are discarded. This technique greatly simplifies polypeptide immobilization and is suitable for microsequencing (<50–1000 pmol) or macrosequencing (1–50 nmol).