Results 1 - 10 of 1541
Results 1 - 10 of 1541. Search took: 0.025 seconds
|Sort by: date | relevance|
[en] In this work the performance of a Pd/Au disk membrane for the selective separation of hydrogen from a low pressure gas mixture was analyzed. The membrane consists of a thin film of Pd/Au of 10 μm thick deposited on a porous stainless steel disk of 12.7 mm (diameter) x 3.17 mm (thickness), with an interface of ZrO2. The dependence of the membrane permeate flow with feeding pressure was evaluated under feeding flows of pure hydrogen and of a gas mixture containing H2: N2 + H2O in an approximate ratio 49:1. Measurements were performed by fixing different feeding flows at temperatures between 300°C and 500°C and waiting up to observe equilibrium conditions. The feed streams ranged from 0.21 sccm to 15 sccm and the pressure differences between both sides of the membrane ranged from 10 kPa to 600 kPa. The withheld flow was maintained constant at 1 sccm. On the other hand, measurements we performed by filling a reservoir with the gas mixture up to 200 kPa and allowing the separation to proceed until the pressure of the system was reduced to 40 kPa. These measurements were performed at temperatures between 300°C and 500°C. According to the experimental setup, the permeated hydrogen was evacuated from the system by a vacuum pump while the retained gases (hydrogen + impurities) were returned continuously to the reservoir. Separation times were determined and compared with the case of separation from pure hydrogen. The main objective of the characterization is to estimate the potential of these membranes in the separation of hydrogen from the gas mixture that is generated during one of the stages of radioisotope production. (author)
[es]En este trabajo se analizó el desempeño de una membrana de disco de aleación Pd/Au para la separación selectiva de hidrógeno a partir de una mezcla gaseosa de baja presión. La membrana consiste en una delgada película de Pd/Au de 10 μm de espesor depositada sobre un disco de acero inoxidable poroso de dimensiones 12,7 mm (diámetro) x 3,17 mm (espesor), con una interfase de ZrO2. Se analizó la dependencia del flujo de hidrógeno permeado en función de la presión del lado del retenido para flujos de alimentación de hidrógeno puro y de una mezcla gaseosa compuesta por H2:H2O+N2 en relación 49:1. Las mediciones se realizaron estableciendo diferentes flujos de alimentación a temperaturas entre 300°C y 500°C y aguardando hasta que el sistema alcanzara el equilibrio. Los flujos de alimentación variaron desde 0,21 sccm hasta 15 sccm y las diferencias de presión entre ambos lados de la membrana tomaron valores desde 10 kPa hasta 600 kPa. El flujo retenido se mantuvo constante en 1 sccm. Posteriormente se realizaron pruebas en las que se cargó un recipiente con la mezcla gaseosa a 200 kPa y se dejó avanzar la separación hasta que la presión del sistema se reducía a 40 kPa. Estas mediciones se efectuaron a temperaturas entre 300°C y 500°C. De acuerdo al arreglo experimental usado, el hidrógeno permeado era evacuado del sistema mediante una bomba de vacío, mientras que los gases retenidos (hidrógeno + impurezas) se hacían retornar al recipiente donde se encontraban originalmente. Se determinaron los tiempos de separación y se compararon con el caso de separaciones a partir de hidrógeno puro. El objetivo de la caracterización es estimar el potencial uso de las membranas estudiadas en la separación de hidrógeno a partir de la mezcla gaseosa que es generada durante una de las etapas de la producción de radioisótopos. (author)
[en] This paper considers the case where an electronegative gas is diluted by an electropositive one, as is typical in plasma processing applications, and examines the way in which the relevant parameters vary. The impact of dilution is examined over a wide range of pressures (3 mTorr cm-300 Torr cm) and a wide range of degrees of ionization (10-6-10-2), for dilutions of 0%, 90% and 99%. In order to be specific, the case of argon diluting chlorine is studied in detail. But comparison with experiment awaits such data, so only general conclusions can be reached
[en] Thermoacoustic engines convert thermal energy into acoustic work with the distinct merits of simple configuration, potentially high efficiency, no moving parts and no harm to the environment. In order to take full use of low grade thermal energy, it may be an effective approach to decrease further the onset temperature of thermoacoustic engines. This paper proposes a new method to decrease the onset temperature of thermoacoustic systems by introducing a pressure disturbance. The feasibility has been experimentally verified on a self made hybrid thermoacoustic engine. Experimental results show that the pressure disturbance can significantly decrease the onset temperature of the engine. For example, with nitrogen of 0.91 MPa filled in the engine, the onset temperature of 219 deg. C without the pressure disturbance decreases to 193 deg. C with the disturbance. Furthermore, the influence of the pressure disturbance on the dynamic onset and damping processes has also been investigated and compared with conventional ones. The results will be helpful for further understanding of the onset mechanism of thermoacoustic engines and to commercialize the engine by using low grade thermal energy
[en] Isobaric (vapour + liquid) equilibrium of (1,3-dioxolane or 1,4-dioxane + 2-methyl-1-propanol or 2-methyl-2-propanol) at 40.0 kPa and 101.3 kPa has been studied with a dynamic recirculating still. The experimental VLE data are thermodynamically consistent. From these data, activity coefficients were calculated and correlated with the Margules, van Laar, Wilson, NRTL and UNIQUAC equations. The VLE results have been compared with the predictions by the UNIFAC and ASOG methods
[en] The aim of the Karlsruhe Tritium Neutrino (KATRIN) experiment is the model-independent measurement of the anti-neutrino mass. KATRIN measures the endpoint region of the electron energy spectrum of tritium beta decay where a non-vanishing neutrino mass has an influence on the shape of the spectrum. The beta electrons are produced in a windowless gaseous tritium source. In order to reach the design sensitivity of 200 meV/c2 (90% C.L.) the tritium concentration of the inlet gas is continuously monitored by a laser Raman system with 0.1% statistical uncertainty. The system uses an optical measurement cell which is located in-line in the tritium loop of KATRIN. Tritium resistant optical coatings on all windows surfaces of the measurement cell are necessary to maintain a reliable and almost maintenance-free nonstop operation of the Raman system over 5 years of KATRIN measurements. However the up to now employed electron-beam deposited coatings were damaged after about 3 months of contact with a high purity tritium gas atmosphere (∝200 mbar, >90% purity). Therefore commercially available coating types are currently being tested in a dedicated COAting Test EXperiment (COATEX) by repeated exposures to tritium gas and subsequent measurements of their optical properties. In this talk an overview of COATEX is given, and results from the first series of exposures are presented.
[en] Conventional nanoimprint lithography with expensive rigid molds is used to pattern ferroelectric polymer nanostructures on hard substrate for use in, e.g., organic electronics. The main innovation here is the use of inexpensive soft polycarbonate molds derived from recordable DVDs and reverse nanoimprint lithography at low pressure, which is compatible with flexible substrates. This approach was implemented to produce regular stripe arrays with a spacing of 700 nm from vinylidene fluoride co trifluoroethylene ferroelectric copolymer on flexible polyethylene terephthalate substrates. The nanostructures have very stable and switchable piezoelectric response and good crystallinity, and are highly promising for use in organic electronics enhanced or complemented by the unique properties of the ferroelectric polymer, such as bistable polarization, piezoelectric response, pyroelectric response, or electrocaloric function. The soft-mold reverse nanoimprint lithography also leaves little or no residual layer, affording good isolation of the nanostructures. This approach reduces the cost and facilitates large-area, high-throughput production of isolated functional polymer nanostructures on flexible substrates for the increasing application of ferroelectric polymers in flexible electronics. (paper)
[en] The possibility of lasing on the third continuum in argon was studied theoretically. This possibility is considered from the point of view of two hypotheses on the nature of the third continua, which have survived through the mid-1990s. The gain was calculated under conditions when the oscillation is most probable, namely, in the pressure range between 1 and 30 bar for specific pump power in the range 10-3-10 MW cm-3 bar-1. The gain is shown to be negative under the above conditions and, hence, lasing cannot be achieved. (active media)
[en] Currently, High Pressure Time Projection Chambers (HP-TPC) are intensely discussed in the neutrino detector community as active targets. Increased pressure results in likewise increased probability for gas interactions, but retains a low momentum detection threshold, compared to e.g. liquid gas detectors, for final state particles. The CERN Neutrino Platform has formed a working group to investigate new technologies needed for the operation of HP-TPCs. One of the adressed aspects for long term operation at high pressures is the monitoring of gas properties. This can be done by building a gas monitioring chamber capable of measuring drift and gain properties up to 10 bar.
[en] A low-vacuum standard, which is based on the static expansion method and can generate vacuum in the wide range of 1 Pa–100 kPa, has been developed. The largest chamber of this system, in which the known pressures are generated, has an orifice-flow pressure generator for gauge calibration. This dual function for the largest chamber permits a more efficient routine calibration of gauges than a traditional chamber as follows: reference gauges attached to the largest chamber are calibrated by the static expansion method which generates known pressures; these gauges are then left in place in the calibration chamber; other gauges to be calibrated can be attached to the large chamber and calibrated against the reference gauges by the comparison method. The reference gauges only need to be recalibrated infrequently