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Gas Temperature (gas + temperature)

Distribution by Scientific Domains

Physics and Astronomy	36%
Engineering	30%
Chemistry	20%

Selected Abstracts

Rotational and Vibrational Temperature Measurements in a High-Pressure Cylindrical Dielectric Barrier Discharge (C-DBD)

CONTRIBUTIONS TO PLASMA PHYSICS, Issue 1 2005
N. Masoud
Abstract The rotational (TR) and vibrational (Tv) temperatures of N2 molecules were measured in a high-pressure cylindrical dielectric barrier discharge (C-DBD) source in Ne with trace amounts (0.02 %) of N2 and dry air excited by radio-frequency (rf) power. Both TR and Tv of the N2 molecules in the C 3,u state were determined from an emission spectroscopic analysis the 2nd positive system (C 3,u , B3,g). Gas temperatures were inferred from the measured rotational temperatures. As a function of pressure, the rotational temperature is essentially constant at about 360 K in the range from 200 Torr to 600 Torr (at 30W rf power) and increases slightly with increasing rf power at constant pressure. As one would expect, vibrational temperature measurements revealed significantly higher temperatures. The vibrational temperature decreases with pressure from 3030 K at 200 Torr to 2270 K at 600 Torr (at 30 W rf power). As a function of rf power, the vibrational temperature increases from 2520 K at 20 W to 2940 K at 60 W (at 400 Torr). Both TR and Tv also show a dependence on the excitation frequency at the two frequencies that we studied, 400 kHz and 13.56 MHz. Adding trace amounts of air instead of N2 to the Ne in the discharge resulted in higher TR and Tv values and in a different pressure dependence of the rotational and vibrational temperatures. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Simulation of Direct-Current Microdischarges for Application in Electro-Thermal Class of Small Satellite Propulsion Devices

CONTRIBUTIONS TO PLASMA PHYSICS, Issue 1-2 2007
P. S. Kothnur
Abstract Microdischarges are miniature non-equilibrium plasma discharges with characteristic dimensions of ,10's,100's ,m and relatively high operating pressures of ,10's,100's Torr. Microdischarges possess several unique properties that have been exploited in a number of new applications. We have recently proposed amicrodischargebased electro-thermal class of microthrusters for small satellite propulsion. These devices utilize intense gas heating in microdischarges to preheat a propellant gas stream before it is expanded in a micronozzle to produce thrust; thereby improving specific impulse of the device over a conventional cold gas microthruster. This paper addresses direct-current microdischarge phenomena in a flowing gas stream. A two-dimensional, selfconsistent, fluid model of a helium microdischarge in a bulk gas flow is developed. For relatively high current/power levels considered in this study, the microdischarge operates in an abnormal glow mode with positive differential resistivity. Increasing discharge pressures for fixed power and bulk flow rates results in a decrease in charged species densities and the electron and gas temperatures. Also the discharge becomes increasingly constricted with increasing pressures, resulting in a more normal glow mode-like operation. Increasing bulk flow rates results in exactly the same trends as increasing pressures. For given input power and pressure, there exists an optimum flow rate for which the average outlet gas temperature from the discharge is a maximum. An increase in input electrical power results in an almost linear increase in the gas temperatures; this property of microdischarges is the key feature that is exploited in our microdischarge-based thruster concept. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Transient response of closed-loop MHD experimental facility

ELECTRICAL ENGINEERING IN JAPAN, Issue 1 2007
Hidemasa Takana
Abstract Transient responses of a closed-loop MHD experimental facility from nonpower generation to power generation have been investigated by means of time-dependent quasi-one-dimensional numerical simulations. For the long-time continuous power generation experiment, the time required to obtain the steady state for the power generation is estimated to be approximately 20 hours. By increasing the electrical input power to the heater as an exponential function of time, the temperature increment of ceramics can be moderated. When the duration of the experiment is around 10 minutes, argon gas temperature at the exit of the heater hardly changes because of the large heat capacity of structure materials. It is found that the fluid disturbances are induced at the instant of the power generation and they propagate as they repeatedly reflect at the sudden change of duct shape. Since all of the induced disturbances attenuate approximately 0.4 second after the power generation, the time scale that the disturbances exist in the facility is estimated to be 1 second at most. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 158(1): 46,52, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20237 [source]

Ammonium perfluorooctanoate as a volatile surfactant for the analysis of N -methylcarbamates by MEKC-ESI-MS

ELECTROPHORESIS, Issue 22 2006
Geert Van Biesen
Abstract Ammonium perfluorooctanoate (APFOA) was investigated as an MS-friendly surfactant for the analysis of a mixture of ten N -methylcarbamates with MEKC-ESI-MS. Because of the relatively low boiling point of perfluorooctanoic acid (,190°C), APFOA can be introduced into a mass spectrometer without the adverse effects of less volatile surfactants such as SDS. With a BGE consisting of 50,mM APFOA/isopropanol (IPA) 98:2 and with 30,kV applied, a very fast separation (,6,min) was possible with only one pair of analytes comigrating. Using an experimental design with four factors (voltage, nebulizer pressure, concentration of APFOA, and concentration of IPA) we were able to resolve all analytes in just over 11,min. Sheath liquid composition and flow rate, drying gas temperature and flow rate, and fragmentor voltage were then optimized for maximum signal intensity and S/N. It was found that the faster method gave better S/N because of narrower peak widths, and detection limits in SIM mode were between 0.01 (aldicarb) and 0.08,mg/L (methomyl). Calibration curves were prepared with standards of 0.50, 1.00, and 2.00,mg/L for the analysis of samples obtained after SPE of tap water spiked with the ten N -methylcarbamates at a level of 10,µg/L. All analytes showed very good recoveries (>86%), except for the most polar analyte aldicarb sulfone (recovery of 73%), testifying for the potential use of APFOA for this kind of analyses. [source]

Application of polymeric surfactants in micellar electrokinetic chromatography-electrospray ionization mass spectrometry of benzodiazepines and benzoxazocine chiral drugs

ELECTROPHORESIS, Issue 5-6 2006
Jingguo Hou
Abstract Chiral micellar EKC (CMEKC) coupled to ESI-MS using polymeric surfactants as pseudostationary phases is investigated for simultaneous enantioseparation of two benzodiazepines, (±)-oxazepam ((±)-OXA) and (±)-lorazepam ((±)-LOR), and one benzoxazocine, (±)-nefopam ((±)-NEF). First, enantioselectivity and electrospray sensitivity of six chiral polymeric surfactants for all three chiral compounds are compared. Second, using poly(sodium N -undecenoyl- L -leucinate) as pseudostationary phase, the organic modifiers (methanol (MeOH), isopropanol, and ACN) are added into the running buffer to further improve chiral resolution (RS). Next, a CMEKC-ESI-MS method for the simultaneous enantioseparation of two benzodiazepines is further developed by using a dipeptide polymeric surfactant, poly(sodium N -undecenoxy carbonyl- L,L -leucyl-valinate) (poly- L,L -SUCLV). The CMEKC conditions including nebulizer pressure, capillary length, ammonium acetate concentration, pH, poly- L,L -SUCLV concentration, and capillary temperature were optimized to achieve maximum chiral RS and highest sensitivity of MS detection. The spray chamber parameters (drying gas temperature and drying gas flow rate) as well as sheath liquid conditions (MeOH content, pH, flow rate, and ionic strength) were found to significantly influence MS S/N of both (±)-OXA and (±)-LOR. Finally, a comparative study between simultaneous UV and MS detection showed high plate numbers, better chiral RS, and enhanced detectability with CMEKC-MS. However, speed of analysis was faster using CMEKC-UV. [source]

Development of capillary zone electrophoresis-electrospray ionization-mass spectrometry for the determination of lamotrigine in human plasma

ELECTROPHORESIS, Issue 13 2004
Jack Zheng
Abstract A method of coupling capillary zone electrophoresis (CZE) with electrospray ionization-mass spectrometry (ESI-MS) detection has been developed for monitoring an antiepileptic drug, lamotrigine (LTG) in human plasma. The CZE-MS was developed in three stages: (i) CZE separation and ESI-MS detection of LTG and tyramine (TRM, internal standard) were simultaneously optimized by studying the influence of CZE background electrolyte (BGE) pH, BGE ionic strength, and nebulizer pressure of the MS sprayer; (ii) sheath liquid parameters, such as pH, ionic strength, organic modifier content, and flow rate of the sheath liquid, were systematically varied under optimum CZE-MS conditions developed in the first stage; (iii) MS sprayer chamber parameters (drying gas temperature and drying gas flow rate) were varied for the best MS detection of LTG. The developed assay was finally applied for the determination of LTG in plasma samples. The linear range of LTG in plasma sample assay was between 0.1,5.0 ,g/mL with a limit of detection as low as 0.05 ,g/mL and run time less than 6 min. Finally, the concentration-time profile of LTG in human plasma sample was found to correlate well when CZE-ESI-MS was compared to a more established method of high-performance liquid chromatography with ultraviolet detection. [source]

Effective thermal actions and thermal properties of timber members in natural fires

FIRE AND MATERIALS, Issue 1 2006
Jürgen KönigArticle first published online: 28 JUL 200
Abstract For the thermal analysis of structural or non-structural timber members, using conventional simplified heat transfer models, thermal conductivity values of timber are normally calibrated to test results such that they implicitly take into account influences such as mass transport that are not included in the model. Various researchers and designers have used such effective thermal conductivity values, originally determined for standard fire exposure, to evaluate other fire scenarios such as natural fires. This paper discusses in qualitative terms some parameters that govern the burning of wood and their influence on effective conductivity values. Reviewing fire tests of timber slabs under natural fire conditions, the study explains why effective conductivity values, giving correct results for the ISO 834 standard fire scenario, should not be used in other fire scenarios. For this reason, the thermal properties of timber given in EN 1995-1-2 are limited to standard fire exposure. As shown by heat transfer calculations, the effective thermal conductivity of the char layer is strongly dependent on the charring rate and therefore varies during a natural fire scenario. It has also been shown that char oxidation during the decay phase in a natural fire has a significant influence on the temperature development in the timber member, since char surface temperatures exceed the gas temperature in the compartment or furnace. Using increased effective gas temperature as thermal action during the decay phase, and varying conductivity values for the char layer, fairly good agreement could be obtained regarding the temperature development in the timber member and the char depth. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Examples of fire engineering design for steel members, using a standard curve versus a new parametric curve

FIRE AND MATERIALS, Issue 2-4 2004
C. R. Barnett
Abstract This paper presents examples of the differences that can occur when a standard time-temperature curve and a parametric time-temperature curve are used to determine temperatures likely to be reached by uninsulated and insulated steel members during a fire. For low and moderate structural fire severity situations, determination of the adequacy of a steel member by comparing the temperature reached in a ,design fire' with the limiting temperature based on the member heat sink characteristics, extent of insulation and utilization factor is becoming increasingly common fire engineering design practice. For this it is important to have an accurate and widely applicable parametric fire model as is practicable. The standard time-temperature curve used in the examples is the ISO 834 curve. The two parametric time-temperature curves used in the paper are the Eurocode parametric curve and a recently developed one termed the ,BFD curve'. The latter has been found to fit the results of a wide range of actual fire tests more closely than do existing parametric curves and is mathematically simpler in form. The shape of the BFD curve and the parameters used to define it bear a strong relationship to both the pyrolysis coefficient (R/Avhv0.5) and the opening factor, F02. The curve also models the development of fire without the need for time shifts. It uses a single and relatively simple equation to generate the temperature of both the growth and decay phases of a fire in a building and only three factors are required to derive the curve. These factors are (i) the maximum gas temperature, (ii) the time at which this maximum temperature occurs, and (iii) a shape constant for the curve. If desired, the shape constant can be different on the growth and the decay sides to model a very wide range of natural fire conditions and test results. This paper presents an overview of the background to the BFD curve. It then illustrates its use in a simple fire engineering design application, where the adequacy of a steel beam is checked using the Eurocode parametric curve and the BFD curve to represent the fire. Copyright © 2004 John Wiley & Sons, Ltd. [source]

An investigation on thermal-recycling of recycled plastic resin (spherically symmetric analysis of abrupt heating processes of a micro plastic-resin particle)

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 4 2006
Ryuji Yamakita
Abstract A fundamental understanding of the physical properties of a micro plastic-resin particle subjected suddenly to hot combustion gas, such as the temperature history in the micro particle and its lifetime, is necessary for effectively realizing thermal recycling of recycled plastic resin. However, micro plastic particles have such small diameters, ranging from 100 µm to 200 µm, that the measurement of temperature histories within them is extremely difficult. In this paper, therefore, a spherically symmetric one-dimensional analysis is applied to the abrupt heating process of a micro plastic resin particle in a high temperature inert atmosphere. Variations of the temperature history and the lifetime with the ambient gas temperature and the initial particle diameter are numerically analyzed, by dividing the entire heating process into four independent periods; the solid heating period, the melting period, the liquid heating period, and the vaporization period. Effects of the Nusselt number on the particle lifetime are also discussed. It is found that, by suitably taking account of the influences of heat transfer properties, the proposed simplified analysis is useful for estimating the fundamental and overall temperature characteristics of a micro plastic resin particle under abrupt heating. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(4): 279,293, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20113 [source]

A simple reactive gasdynamic model for the computation of gas temperature and species concentrations behind reflected shock waves,

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 4 2008
H. Li
A simple gasdynamic model, called CHEMSHOCK, has been developed to predict the temporal evolution of combustion gas temperature and species concentrations behind reflected shock waves with significant energy release. CHEMSHOCK provides a convenient simulation method to study various sized combustion mechanisms over a wide range of conditions. The model consists of two successive suboperations that are performed on a control mass during each infinitesimal time step: (1) first the gas mixture is allowed to combust at constant internal energy and volume; (2) then the gas is isentropically expanded (or compressed) at frozen composition to the measured pressure. The CHEMSHOCK model is first validated against results from a one-dimensional reacting computational fluid dynamics (CFD) code for a representative case of heptane/O2/Ar mixture using a reduced mechanism. CHEMSHOCK is found to accurately reproduce the results of the CFD calculation with significantly reduced computational time. The CHEMSHOCK simulation results are then compared to experimental results, for gas temperature and water vapor concentration, obtained using a novel laser sensor based on fixed-wavelength absorption of two H2O rovibrational transitions near 1.4 ,m. Excellent agreement is found between CHEMSHOCK simulations and measurements in a progression of shock wave tests: (1) in H2O/Ar, with no energy release; (2) in H2/O2/Ar, with relatively small energy release; and (3) in heptane/O2/Ar, with large energy release. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 189,198, 2008 [source]

Probabilistic aspects in the technical and economic analysis of the industrial waste heat recovery system generating useful heat and refrigeration

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 6 2005
J. Kozio
Abstract The technical and economic analysis of the industrial waste heat recovery system, considering probabilistic distribution of the input data is presented. A prospect and rationality of the application of the waste heat boiler and absorption refrigerator has been examined as an example, in view of covering integrated heat and refrigeration demands. The influence of changing ambient conditions as well as the exhaust gas temperature and its flow rate on the overall system performance has been simulated and assessed. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Moisture Migration in Solid Food Matrices

JOURNAL OF FOOD SCIENCE, Issue 8 2003
Y.-C. Fu
ABSTRACT: The goals of this study were to measure moisture migration in a porous solid matrix simulating a real food (flour dough) and to accomplish heating of the solid matrix. An off-line technique and a microwave temperature controller system were developed for measuring moisture concentration under isothermal heating condition. A temperature profile of a cylindrical dough sample was achieved by accurate control of microwave energy input and preheated carrier gas temperature. Results showed a simplified 1st order kinetic model adequately predicted moisture loss in dough samples. Effect of temperature on the rate constant was adequately modeled by the Arrhenius relationship. The rate constant was found to be affected by porosity of the dough sample. [source]

Mapping low- and high-density clouds in astrophysical nebulae by imaging forbidden line emission,

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2009
J. E. Steiner
ABSTRACT Emission line ratios have been essential for determining physical parameters such as gas temperature and density in astrophysical gaseous nebulae. With the advent of panoramic spectroscopic devices, images of regions with emission lines related to these physical parameters can, in principle, also be produced. We show that, with observations from modern instruments, it is possible to transform images taken from density-sensitive forbidden lines into images of emission from high- and low-density clouds by applying a transformation matrix. In order to achieve this, images of the pairs of density-sensitive lines as well as the adjacent continuum have to be observed and combined. We have computed the critical densities for a series of pairs of lines in the infrared, optical, ultraviolet and X-rays bands, and calculated the pair line intensity ratios in the high- and low-density limit using a four- and five-level atom approximation. In order to illustrate the method, we applied it to Gemini Multi-Object Spectrograph (GMOS) Integral Field Unit (GMOS-IFU) data of two galactic nuclei. We conclude that this method provides new information of astrophysical interest, especially for mapping low- and high-density clouds; for this reason, we call it ,the ld/hd imaging method'. [source]

Numerical simulations of type III planetary migration , I. Disc model and convergence tests

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008
A. Pepli
ABSTRACT We investigate the fast (type III) migration regime of high-mass protoplanets orbiting in protoplanetary discs. This type of migration is dominated by corotational torques. We study the details of flow structure in the planet's vicinity, the dependence of migration rate on the adopted disc model and the numerical convergence of models (independence of certain numerical parameters such as gravitational softening). We use two-dimensional hydrodynamical simulations with adaptive mesh refinement, based on the flash code with improved time-stepping scheme. We perform global disc simulations with sufficient resolution close to the planet, which is allowed to freely move throughout the grid. We employ a new type of equation of state in which the gas temperature depends on both the distance to the star and planet, and a simplified correction for self-gravity of the circumplanetary gas. We find that the migration rate in the type III migration regime depends strongly on the gas dynamics inside the Hill sphere (Roche lobe of the planet) which, in turn, is sensitive to the aspect ratio of the circumplanetary disc. Furthermore, corrections due to the gas self-gravity are necessary to reduce numerical artefacts that act against rapid planet migration. Reliable numerical studies of type III migration thus require consideration of both the thermal and the self-gravity corrections, as well as a sufficient spatial resolution and the calculation of disc,planet attraction both inside and outside the Hill sphere. With this proviso, we find type III migration to be a robust mode of migration, astrophysically promising because of a speed much faster than in the previously studied modes of migration. [source]

The impact of dark matter decays and annihilations on the formation of the first structures

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007
E. Ripamonti
ABSTRACT We derive the effects of dark matter (DM) decays and annihilations on structure formation. We consider moderately massive DM particles (sterile neutrinos and light DM), as they are expected to give the maximum contribution to heating and reionization. The energy injection from DM decays and annihilations produces both an enhancement in the abundance of coolants (H2 and HD) and an increase of gas temperature. We find that for all the considered DM models the critical halo mass for collapse, mcrit, is generally higher than in the unperturbed case. However, the variation of mcrit is small. In the most extreme cases, that is, considering light DM annihilations (decays) and haloes virializing at redshift zvir > 30 (zvir, 10), mcrit increases by a factor of ,4 (,2). In the case of annihilations the variations of mcrit are also sensitive to the assumed profile of the DM halo. Furthermore, we note that the fraction of gas which is retained inside the halo can be substantially reduced (to ,40 per cent of the cosmic value), especially in the smallest haloes, as a consequence of the energy injection by DM decays and annihilations. [source]

, -model and cooling flows in X-ray clusters of galaxies

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2000
Stefano Ettori
The spatial emission from the core of cooling-flow clusters of galaxies is inadequately described by a , -model. Spectrally, the central region of these clusters is well approximated with a two-temperature model, where the inner temperature represents the multiphase status of the core and the outer temperature is a measure of the ambient gas temperature. Following this observational evidence, I extend the use of the , -model to a two-phase gas emission, where the two components coexist within a boundary radius rcool and the ambient gas alone fills the volume shell at a radius above rcool. This simple model still provides an analytic expression for the total surface brightness profile (Note in the first term the different sign with respect to the standard , -model.) Based upon a physically meaningful model for the X-ray emission, this formula can be used (i) to improve significantly the modelling of the surface brightness profile of cooling flow clusters of galaxies when compared to the standard , -model results, (ii) to constrain properly the physical characteristics of the intracluster plasma in the outskirts, like, e.g., the ambient gas temperature. [source]

H2 reformation in post-shock regions

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2010
H. M. Cuppen
ABSTRACT H2 formation is an important process in post-shock regions, since H2 is an active participant in the cooling and shielding of the environment. The onset of H2 formation therefore has a strong effect on the temperature and chemical evolution in the post-shock regions. We recently developed a model for H2 formation on a graphite surface in warm conditions. The graphite surface acts as a model system for grains containing large areas of polycyclic aromatic hydrocarbon structures. Here, this model is used to obtain a new description of the H2 formation rate as a function of gas temperature that can be implemented in molecular shock models. The H2 formation rate is substantially higher at high gas temperatures as compared to the original implementation of this rate in shock models, because of the introduction of H atoms which are chemically bonded to the grain (chemisorption). Since H2 plays such a key role in the cooling, the increased rate is found to have a substantial effect on the predicted line fluxes of an important coolant in dissociative shocks [O i] at 63.2 and 145.5 ,m. With the new model, a better agreement between the model and observations is obtained. Since one of the goals of Herschel/PACS will be to observe these lines with higher spatial resolution and sensitivity than the former observations by Infrared Space Observatory -LWS, this more accurate model is very timely to help with the interpretation of these future results. [source]

Utility of nonaqueous capillary electrophoresis for the determination of lidocaine and its metabolites in human plasma: a comparison of ultraviolet and mass spectrometric detection

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 22 2004
Magnus S. Anderson
A nonaqueous capillary electrophoresis/electrospray mass spectrometry method for the separation of lidocaine (LID) and two of its metabolites, monoethylglycinexylidide (MEGX) and glycinexylidide (GX), has been developed. The separation medium was: 70,mM ammonium formate and 2.0,M formic acid in acetonitrile/methanol (60:40 v/v). With a sheath liquid of methanol/water (80:20 v/v) containing 2% formic acid and positive ion detection, reproducible determinations (8,11% relative standard deviation (RSD)) of lidocaine and its metabolites were performed in spiked human plasma. The limits of detection (LODs) were between 69.1 and 337,nM. The influences of sheath liquid composition, nebulizing gas pressure and drying gas temperature on the separation were examined. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Hydrogen Production from a Fluidized-bed Coal Gasifier with In Situ Fixation of CO2,Part I: Numerical Model

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 2 2008
J. Lu
Abstract In order to attempt to eliminate global warming effects, it is highly desirable that new technologies with lower or zero emission of CO2 to the environment are developed. In this work, a high-pressure fluidized-bed coal gasifier for H2 production with in situ fixation of CO2 is simulated by a comprehensive two-dimensional model. The Eddy Dissipation Concept (EDC) model is first adopted in the pulverized coal gasification model to simultaneously describe the turbulent mixing and detailed chemical kinetics. The developed model is verified with experimental results. The simulated concentrations for the gas product agree well with the experimental data. The simulated distributions for gas temperature and velocity correlate well with the reaction mechanism and experimental phenomena. [source]

Spectroscopic Diagnostics of Pulsed arc Plasmas for Particle Generation

CONTRIBUTIONS TO PLASMA PHYSICS, Issue 8 2008
K. Behringer
Abstract Pulsed arc plasmas were diagnosed by means of emission spectroscopy. A capacitor was discharged through argon and hydrogen leading to a few cycles of damped current oscillation with ,120 ,s period and 5-12 kA maximum current. Spectroscopic measurements in the visible range were carried out in order to characterise the electron temperature and density in the arc channel as well as electron and gas temperatures in the afterglow plasmas. Spectra were integrated over 10 ,s time windows and shifted in time from pulse to pulse. The plasmas also contained substantial fractions of electrode material (brass), namely copper and zinc. The electron density was measured in the conventional way from the broadening of H, or from the Ar I Stark width. In the arc channel, it ranged from about 3 · 1022 to 2 · 1023 m,3. The broadening of Zn II lines could also be used. Ratios of Ar I to Ar II and of Zn I to Zn II line intensities were analysed for the electron temperature. Line pairs were found which lay conveniently close in one frame of the spectrometer allowing automatic on-line analysis without relying on reproducibility. Atomic physics models including opacity were developed for Ar II and Zn II in order to check the existence of a Boltzmann distribution of their excited states. These calculations showed that the observed levels were in fact close to thermodynamic equilibrium, in particular, if the resonance lines were optically thick. Electron temperature measurements yielded values between 14000 K and 21000 K. The gas temperature in the afterglow, where particles should have formed, was derived from the rotational and vibrational temperatures of C2 molecular bands. Ratios between Cu I line intensities yielded the electron temperatures. Both were found to be a few 1000 K. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Simulation of Direct-Current Microdischarges for Application in Electro-Thermal Class of Small Satellite Propulsion Devices

Temperature effects on the mass flow rate in the SBI and similar heat-release rate test equipment

FIRE AND MATERIALS, Issue 1 2007
Bart J. G. Sette
Abstract In various medium-to-large-scale fire test equipments like the ISO room corner test (RC), and more recently, the single burning item test (SBI) the mass flow rate measurement of the combustion gases plays a key role in the determination of the heat-release rate and smoke-production rate. With the knowledge of the velocity profile and the temperature of the flow, the mass flow rate is obtained by measuring the velocity on the axis of the duct. This is done by means of a bi-directional probe based on the pitot principle. However, due to the variation of the mean temperature and the temperature gradient in any cross section of the duct, introduced by ever changing combustion gas temperatures, the velocity nor the density profile are constant in time. This paper examines the resulting uncertainty on the mass flow rate. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Evaluation of Noble Gas Recharge Temperatures in a Shallow Unconfined Aquifer

GROUND WATER, Issue 5 2009
Bradley D. Cey
Water table temperatures inferred from dissolved noble gas concentrations (noble gas temperatures, NGT) are useful as a quantitative proxy for air temperature change since the last glacial maximum. Despite their importance in paleoclimate research, few studies have investigated the relationship between NGT and actual recharge temperatures in field settings. This study presents dissolved noble gas data from a shallow unconfined aquifer heavily impacted by agriculture. Considering samples unaffected by degassing, NGT calculated from common physically based interpretive gas dissolution models that correct measured noble gas concentrations for "excess air" agreed with measured water table temperatures (WTT). The ability to fit data to multiple interpretive models indicates that model goodness-of-fit does not necessarily mean that the model reflects actual gas dissolution processes. Although NGT are useful in that they reflect WTT, caution is recommended when using these interpretive models. There was no measurable difference in excess air characteristics (amount and degree of fractionation) between two recharge regimes studied (higher flux recharge primarily during spring and summer vs. continuous, low flux recharge). Approximately 20% of samples had dissolved gas concentrations below equilibrium concentration with respect to atmospheric pressure, indicating degassing. Geochemical and dissolved gas data indicate that saturated zone denitrification caused degassing by gas stripping. Modeling indicates that minor degassing (<10% ,Ne) may cause underestimation of ground water recharge temperature by up to 2°C. Such errors are problematic because degassing may not be apparent and degassed samples may be fit by a model with a high degree of certainty. [source]

Performance analysis of gas liquefaction cycles

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 1 2008
Mehmet Kanoglu
Abstract Relations are developed for first- and second-law analyses of the simple Linde,Hampson cycle used in gas liquefaction systems. An expression for the minimum work requirement, which is applicable to any gas liquefaction system, is developed with the help of a Carnot refrigerator. It is shown that the minimum work depends only on the properties of the incoming and outgoing gas streams and the environment temperature. Numerical calculations are performed to obtain the performance parameters of different gases while parametric studies are done to investigate the effects of liquefaction and inlet gas temperatures on various first- and second-law performance parameters. As the liquefaction temperature increases and the inlet gas temperature decreases, the liquefied mass fraction, the coefficient of performance (COP) and the exergy efficiency increase while actual and reversible work consumptions decrease. The exergy efficiency values appear to be low, indicating significant potential exists for improving efficiency and thus decreasing the required work consumption for a specified amount of liquefaction. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Transportation of nanosecond laser pulses by hollow core photonic crystal fiber for laser ignition

LASER PHYSICS LETTERS, Issue 11 2005
A. H. Al-Janabi
Abstract Laser ignition via hollow core photonic crystal fiber (PCF) as a delivery medium has been demonstrated in the present work. Minimum pulse energy from a Q-switched Nd:YAG laser of only 150 µJ was achieved to ignite rich fuel mixtures of methane-air. Aspheric lens of high numerical aperture has been used to focus the laser beam. Different air/fuel ratios have been examined with different gas temperatures. The results indicate the feasibility of using hollow core PCF for high power beam transmission for laser ignition applications. (© 2005 by Astro, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source]

A new austenitic alumina forming alloy: an aluminium-coated FeNi32Cr20

MATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 6 2008
H. Hattendorf
Abstract The FeCrAl alloys owe their low oxidation rate to the formation of a slow growing , -aluminium oxide scale. Therefore they are used, for example, as a substrate material in metal-supported automotive catalytic converters. Increasing exhaust gas temperatures mean that, in addition to the oxidation properties, high temperature mechanical properties should also be improved. Compared to the ferritic FeCrAl alloys, austenitic alloys possess the required high mechanical strength at higher temperatures. However for most commercially available materials the oxidation resistance is not sufficient due to a low aluminium content. High aluminium contents are avoided in austenitic alloys, since they cause severe workability problems, even at aluminium contents, which are below the necessary amount to get a pure alumina scale. The newly developed material Nicrofer 3220 PAl (coated FeNiCrAl) consists of an austenitic FeNi32Cr20 alloy coated with aluminium on both sides. It combines the outstanding oxidation resistance of an alumina forming FeCrAl alloy with the advantage of the high temperature strength of an austenitic alloy. Additionally the oxidation is even lower than the oxidation of the commercial grade Aluchrom YHf (FeCr20Al6),conventional homogenous FeCrAl. Aluminium coated FeNiCrAl can easily be formed into its final shape. Prior to service, an in situ heat treatment is recommended in order to optimize the properties. [source]