Vacuum Permeation Research Articles

Parametric Study of the Vacuum Permeator for the Tritium Extraction eXperiment

Tritium breeding is a critical component of any self-sustaining future fusion reactor. The liquid-metal eutectic PbLi is of particular interest as a tritium breeder material due to its favorable thermophysical and neutronic properties. One of the several remaining challenges facing PbLi breeder blankets is the need to design and validate a highly efficient tritium extraction system. The vacuum permeator is a promising extraction concept that utilizes tritium permeation through a highly permeable metal membrane. The Tritium Extraction eXperiment (TEX) is a forced-convection PbLi loop constructed to investigate tritium extraction from PbLi with vacuum permeators. Accurate thermal-hydraulic and tritium transport models are required to establish appropriate test matrices, predict experiment outcomes, and analyze data. However, the hydrogen transport properties of PbLi and permeator materials have large uncertainties. A database is collected and a parametric analysis is conducted on the effect of hydrogen transport material properties, including diffusivity of H in PbLi and the permeator, solubility of H in PbLi and the permeator, and the permeator surface recombination constant, on the expected tritium extraction efficiency for a vacuum permeator installed in TEX. Herein, we observe that the solubility of H in PbLi and the permeator and the recombination constant of the permeator have the largest effect on extraction efficiency.

Low-temperature vacuum permeation of sodium tripolyphosphate and trehalose suppresses the denaturation of myofibrillar proteins in peeled shrimp (Litopenaeus vannamei) during frozen storage.

Phosphates and trehalose are widely accepted additives in animal muscle products. In this study, the effects of pre-soaking with sodium tripolyphosphate (STPP) and trehalose under vacuum permeation (VP) conditions on the physicochemical properties of shrimp muscle were evaluated over 120 d of frozen storage. The results indicate the STPP/trehalose-VP treatments significantly reduced the thawing loss and prevented changes in the texture, myofibrillar protein (MP) content, and Ca2+-ATPase activity of shrimp muscle during frozen storage compared with results of control and individual STPP or trehalose soaking treatments. The histological structure analysis revealed the permeated STPP/trehalose distinctly inhibited the dissociation of muscle fibers and reduced physical damage to connective tissues during storage. Furthermore, analysis of the thermal properties indicated STPP/trehalose treatment increased the values of shrimp muscle tissues, likely by restricting the mobility of water molecules in muscle tissues and embedding proteins in the glassy matrix. Thus, the physical destruction caused by ice crystal growth was greatly reduced, due to the absence of water molecules around muscle proteins during frozen storage. Accordingly, the combined STPP/trehalose-VP treatment significantly enhanced the stability of frozen shrimp, and the results support the application of traditional cryoprotective additives. The treated shrimp can be stored at comparatively higher temperatures with limited physicochemical reactions during frozen storage.

The Source Permeator System and Tritium Transport in the TEX PbLi Loop

Permeation is investigated for the introduction of hydrogen isotopes into lead lithium (PbLi) for the Tritium Extraction eXperiment (TEX). TEX is a forced-convection PbLi loop under construction at Idaho National Laboratory that will test the vacuum permeator (VP) method of tritium extraction from PbLi. The source permeator (SP) delivers atomic hydrogen (H, D, and T) from a gas-phase reservoir into the PbLi via a permeable dense metal membrane. A modular system and a fixed SP system are presented. In the modular design, PbLi flows through the inside of a tubular membrane, and gas-phase hydrogen is introduced on the outside of the membrane. Atomic hydrogen permeates radially inward through the membrane into the PbLi. In the fixed design, PbLi flows into an expansion chamber with closed-ended tubular membranes inserted. Gas-phase hydrogen is introduced on the inside of the closed-ended membranes, and atomic hydrogen permeates radially outward into the flowing PbLi. Hydrogen transport models based on steady-state mass transport through PbLi and permeation through the metal membrane were developed to assess the operation of the SP relative to experimental variables and to allow understanding of uncertain parameter effects, such as PbLi hydrogen transport properties and the effective hydrogen permeability of the VP. This modeling effort considers iron as the SP material and vanadium as the VP material.

Conceptual Design for a Blanket Tritium Extraction Test Stand

Future fusion reactors must be able to breed the tritium they will consume. Several breeding and tritium extraction technologies are under investigation internationally. PbLi is of particular interest as a breeder material. A new forced convection PbLi loop, the Tritium Extraction eXperiment (TEX), is being designed and constructed to investigate tritium extraction from PbLi. Specifically, TEX will serve to investigate the extraction efficiency of various vacuum permeator membranes and configurations. The major components of the loop include a moving magnet pump, reverse permeator, furnace test section, analysis chamber, supply tank, and plenum. As significant hazards are present in such experiments, safety is an integral focus of the experimental design.

Numerical simulation of tritium extraction from LiPb by vacuum permeator

It is conceived that tritium can be extracted from breeding liquid metals by using vacuum permeator. The properties of hydrogen isotopes under various operating conditions in the permeation system are basic condition of the optimal design of Permeator Against Vacuum (PAV). The capabilities of two different numerical models that can be used for predicting the permeation process of hydrogen isotope controlled by solid state bonding and convective diffusion, are described in this work. One model is tritium transport numerical computation, normally can be achieved by using Matlab and it can reveal whether radial transport is limited by the LiPb eutectic or by the solid membrane. Another model is based on Computational Fluid Dynamics (CFD) by using COMSOL Multiphysics. The geometry is simplified as a permeator tube with an α-Fe membrane. The simulation results show that by decreasing the flow rate and the tube diameter, and increasing the tube length, the permeator extraction efficiency can be improved to the greatest extent. In addition, the differences between the two models show that the permeator’s efficiency can be influenced by the fluid field in the permeator tube.

Investigations of the Deuterium Permeability of As-Deposited and Oxidized Ti2AlN Coatings.

Aluminum containing Mn+1AXn (MAX) phase materials have attracted increasing attention due to their corrosion resistance, a pronounced self-healing effect and promising diffusion barrier properties for hydrogen. We synthesized Ti2AlN coatings on ferritic steel substrates by physical vapor deposition of alternating Ti- and AlN-layers followed by thermal annealing. The microstructure developed a {0001}-texture with platelet-like shaped grains. To investigate the oxidation behavior, the samples were exposed to a temperature of 700 °C in a muffle furnace. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) depth profiles revealed the formation of oxide scales, which consisted mainly of dense and stable α-Al2O3. The oxide layer thickness increased with a time dependency of ~t1/4. Electron probe micro analysis (EPMA) scans revealed a diffusion of Al from the coating into the substrate. Steel membranes with as-deposited Ti2AlN and partially oxidized Ti2AlN coatings were used for permeation tests. The permeation of deuterium from the gas phase was measured in an ultra-high vacuum (UHV) permeation cell by mass spectrometry at temperatures of 30–400 °C. We obtained a permeation reduction factor (PRF) of 45 for a pure Ti2AlN coating and a PRF of ~3700 for the oxidized sample. Thus, protective coatings, which prevent hydrogen-induced corrosion, can be achieved by the proper design of Ti2AlN coatings with suitable oxide scale thicknesses.

Studies on Tasar Cocoon Cooking Using Permeation Method

Cocoon cooking is an important process before reeling of tasar silk yarn. Cooking ensures loosening of the filaments in the tasar cocoons thereby easing the process of yarn withdrawal during reeling process. Tasar cocoons have very hard shell and hence these cocoons need chemical cooking process to loosen the silk filaments. Attempt has been made in this article to study the effect of using vacuum permeation chamber for tasar cocoon cooking in order to reduce the cooking time and improve the quality of tasar silk yarn. Vacuum assisted permeation cooking method has been studied in this article on tasar daba cocoons for cooking efficiency, deflossing and reelability. Its efficiency has been evaluated with respect to different cooking methods viz, traditional and open pan cooking methods. The tasar silk produced after reeling process has been tested for fineness, strength and cohesion properties. Results indicate that permeation method of tasar cooking ensures uniform cooking with higher efficiency along with better reeling performance and improved yarn properties.

Vacuum Permeator Analysis for Extraction of Tritium from DCLL Blankets

It is envisioned that tritium will be extracted from DCLL blankets using a vacuum permeator. We derive here an analytical solution for the extraction efficiency of a permeator tube, which is a function of only two dimensionless numbers: one that indicates whether radial transport is limited by the PbLi or by the solid membrane, and another that is the ratio of axial and radial transport times in the PbLi. The permeator efficiency is maximized by decreasing the velocity and tube diameter, and increasing the tube length. This is true regardless of the mass transport correlation used; we review several and find that they differ little, and the choice of correlation is not a source of significant uncertainty here. The PbLi solubility, on the other hand, is a large source of uncertainty, and we identify upper and lower bounds from the literature data. Under the most optimistic assumptions, we find that a ferritic steel permeator operating at 470 °C will need to be about twenty times larger in volume than previous conceptual designs using niobium and operating at higher temperatures.

Technological parameters optimization by orthogonal array designs for steeping silk slices on small reels

A new steeping method is put forward in this paper, in which steeping assistant is added into the solution during the vacuum permeation for the treatment of silk slices on small reels. With this new method, the traditional process of steeping raw silk and drying can be omitted. Orthogonal array L16 (43) is used to study the new method. The result shows that the optimal technological parameters are 2 h, 1.25% and five times for balance drying time, assistant concentration and vacuum number, respectively. The test indicates that the properties of silk slices show no significant difference between steeping on small reels and conventional steeping, and the new process of steeping silk slices on small reels can mostly meet the technological requirements of steeping. It is also found that the properties of knitted fabric produced by the new steeping method and conventional steeping method are quite similar to each other. However, some special properties of the former, such as abrasion resistance, bursting strength and draping, are better than the latter. Compared with the conventional steeping of raw silk, the new steeping method has lower cost and higher efficiency.

Separation of VOC vapor from air by a surface-soaked liquid membrane module using triethylene glycol

A novel surface-soaked liquid membrane with triethylene glycol (TEG) and its flat membrane modules were used for the separation of VOC vapor from air. The liquid membrane setup with a vacuum pump had a 0.39 m 2 membrane area and 21 μm liquid membrane thickness, which operated in a vacuum permeation mode with sweep air. The performance of the membrane process was tested for the separation of VOC vapors, such as benzene, toluene, etc., at a 1000 ppm concentration from air in a 1 m 3 chamber. The TEG liquid membrane process showed a VOC removal rate comparable to a ventilation and adsorption process with active carbon. The TEG liquid membrane process proved to be useful for the VOC separation from room air. A model based on the permeability through the TEG liquid membrane predicted the separation performance of the liquid membrane process.

Influence of Oxygen on Permeation of Hydrogen Isotopes Through Group 5 Metals

Group 5 metals (V, Nb and Ta) are potential candidates of tube material in vacuum permeator for tritium recovery from Pb-17Li liquid blanket system. From this viewpoint, the influence of oxygen on the surface reaction rates of hydrogen on V and Ta were examined in an ultra-high vacuum apparatuses at elevated temperatures, and the results were compared with the data on Nb acquired in a previous study. The surface reaction rates of hydrogen on V and Ta, and consequently permeation rates, decreased with increasing oxygen concentration in the bulk as previously observed for Nb. These observations were ascribed to the increase in surface oxygen coverage with increasing bulk oxygen concentration. The weakest influence of oxygen on hydrogen permeation rate was observed for V. The expected permeation rate through V under typical blanket conditions, however, was not necessarily high due to high oxygen solubility in V. The evaluation indicated that the highest permeation rate should be obtained with Nb under typical blanket conditions.

Recent research and development for the dual-coolant blanket concept in the US

The dual-coolant lead-lithium, or DCLL, blanket concept is of strong interest in the US fusion technology program. In the DCLL blanket, the flow channel insert (FCI) is a critical component. FCIs must have low electrical and thermal conductivity and be compatible with lead–lithium eutectic alloy (Pb–17Li) at elevated temperatures. FCIs must retain structural integrity and desirable properties even under irradiation and large temperature gradients during operation. FCIs must not fail in such a way that Pb–17Li enters the FCI and changes its electrical or thermal conductivity significantly. Another important issue for the DCLL is the development of a suitable tritium extraction from the Pb–17Li to achieve low tritium partial pressure, thus facilitating decisive tritium control. In this paper, the state of DCLL development in the US is presented including recent design modifications and results from recent R&D efforts. Such R&D includes the progress on development and property quantification of SiC/SiC composites and SiC foams as candidate FCI materials; Pb–17Li material capability and infiltration studies; simulations of MHD Pb–17Li flow characteristics and of resultant temperature distributions; and the analysis of FCI stress states based on these thermal loads. In addition, tritium extraction from Pb–17Li based on a vacuum permeator concept is shown to have the potential to achieve the desired tritium control. A discussion of DCLL optimization and unresolved DCLL issues and future R&D needs is also presented.

Correlation between Hydrogen Isotope Permeation through Niobium and Bulk Oxygen Concentration: Possible Influence of Oxygen on Tritium Recovery from Pb-Li by Vacuum Permeator

Niobium is a potential candidate of tube material in vacuum permeator for tritium recovery from Pb-17Li liquid blanket system. From this viewpoint, the permeation of hydrogen through a Nb membrane was investigated with an ultra-high vacuum apparatus under the conditions relevant to the blanket system where no oxide films could be retained on the membrane surfaces. It was, however, found that the permeation rate sharply decreased with increasing oxygen concentration in the bulk of membrane; at upstream H2 pressure of 1 Pa and membrane temperature of 700°C, for example, the permeation rate at oxygen concentration corresponding to oxygen potential in Pb-17Li (0.054 at%) was evaluated to be 1/5 of the value expected from hydrogen solubility and diffusivity in Nb. Such small permeation rate was ascribed to the presence of oxygen monolayer formed by surface segregation from the bulk. Surface modification by Pd coating was found to give only limited improvement due to degradation in coating effect induced by interdiffusion between Pd and Nb. Methods to improve the high temperature stability of Pd coating was discussed.

Impedance spectroscopy characterization of functionalized alumina membranes

Anodic alumina membranes have been impregnated with a protonic conductor either by immersion or by vacuum permeation of a saturated aqueous solution of CsHSO 4 for different times. Synthetized salt, obtained through the reaction of cesium carbonate with sulphuric acid (in excess), contained a small quantity of Cs 2SO 4. Unmodified membranes consist of amorphous Al 2O 3 with a regular distribution of pores (average diameter: 200 nm) and are stable up to 850 °C. Long impregnation times caused partial dissolution of alumina, with formation of Al(HSO 4) 3 on the front surfaces as well as into pore walls. From the frequency dispersion of the impedance, the “macroscopic conductivity” of membranes after different treatments was derived as a function of temperature, and compared with those relative to both unmodified membranes and the pure protonic conductor. The latter shows a sudden increase in conductivity at T > 140 °C, where a superprotonic transition occurs according to DTA analysis.

Precise static and dynamic permeation measurements using a continuous-flow vacuum cell

A new vacuum permeation cell is described whose development was motivated by the desire to measure permeation transients directly, rapidly and precisely. The new cell also allows direct, rapid and precise measurement to be made of the response time of the measurement system itself, enabling measurement corrections to be easily assessed and applied. The transient measurements allow diffusion coefficient, flux, permeant concentration in the membrane and solubility coefficient to be rapidly determined. The cell behaviour is illustrated using the rapid diffusion of water through poly (dimethylsiloxane), a stringent performance indicator. Significant differences between these measurements and measurements previously published are briefly mentioned.

Barrier-layer formation and its control during hydrogen permeation through Ti-24AI-11Nb alloy

Hydrogen transport through Ti-24Al-11Nb (at. pct) alloy has been measured using ultrahigh vacuum permeation techniques over the temperature range of 500 °C to 900 °C and a hydrogen pressure range of 20 to 1333 Pa. The hydrogen uptake behavior of the alloy is influenced by even very small amounts of contaminants in the hydrogen gas. It is shown that contaminants such as CO and H2O are released from the walls of the vacuum system by the incoming hydrogen gas due to collision-induced desorption and that these species form a barrier layer. In the presence of the barrier layer, the hydrogen-permeation behavior of the alloy has two apparent temperature regimes: a high-temperature regime where the barrier layer has minimal effect, and a low-temperature regime where the barrier layer inhibits the hydrogen uptake. A physical model to explain this behavior is presented. It is further shown that the effect of the barrier layer can be minimized by maintaining dynamic flow conditions in the upstream chamber. Under these conditions, the transport process is diffusion-limited: the permeability has a weak temperature dependence, but the diffusivity has a strong temperature dependence.

Study of the oxygen transport through Ag (110), Ag (poly), and Ag 2.0 Zr

The transport of oxygen through high-purity membranes of Ag (110), Ag (poly), Ag (nano), and Ag 2.0 Zr has been studied by an ultrahigh vacuum permeation method over the temperature range of 400–800 °C. The data show that there are substantial deviations from ordinary diffusion-controlled transport. A surface limitation has been confirmed by glow-discharge studies where the upstream O2 supply has been partially converted to atoms, which, for the same temperature and pressure, gave rise to over an order of magnitude increase in transport flux. Further, the addition of 2.0 wt % Zr to the Ag has provided increased dissociative adsorption rates, which, in turn, increased the transport flux by a factor of 2. It was also observed that below a temperature of 630 °C, the diffusivity exhibits an increase in activation energy of over 4 kcal/mol, which has been attributed to trapping of the atomic oxygen and/or kinetic barriers at the surface and subsurface of the vacuum interface. Above 630 °C, the activation barrier decreases to the accepted value of ∼11 kcal/mol for Ag (poly), consistent with zero concentration at the vacuum interface.

Separation of liquid mixtures by using polymer membranes. III. Grafted poly(vinyl alcohol) membranes in vacuum permeation and dialysis

AbstractA series of poly(vinyl alcohol) membranes were modifed by radiation‐induced graft copolymerization with acrylic acid and methacrylic acid monomers. These grafted poly(vinyl alcohol) membranes were then tested for their separation and permeability characteristics in vacuum permeation and dialysis experiments. The permselectivity of the membranes toward methanol and water was studied on a vacuum permeation apparatus at 30, 40, and 50°C. The permeation process was found to be a temperature‐activated process. The logarithm of the permeation rate varied linearly with the reciprocal of the absolute temperature. The permeability of the grafted membranes was found to increase with the degree of grafting, with no appreciable selectivity toward water in binary mixtures. The acrylic acid‐grafted membranes generally showed greater improvement in permeability than the methacylic‐grafted membranes. The permeability of the grafted membranes toward methanol, sodium chloride, urea, creatinine, and uric acid was studied in a dialyzer. In all cases, the grafted membranes showed an improved permeability toward these solutes over the commercial poly(vinyl alcohol) membranes. The dialysis results were then compared with those obtained for dialysis‐grade cellophane membranes. For the case of sodium chloride, urea, and methanol, the permeability of the grafted membranes was comparable to that of cellophane. A comparison of commercial and grafted poly(vinyl alcohol) membranes in their permeability toward ionic solutes exhibited somewhat anomalous behavior in that the permeability of the commercial membranes was higher than that of the grafted membranes. This related to the ionic nature of the modified membrane. The permeability coefficients determined in the dialysis experiments were found to be directly related to the degree of hydration of the grafted membrane. This behavior was attributed to changes in the size and shape of voids within the membrane structure.