Showing papers on "Total pressure published in 1998"

Residual stress in low pressure chemical vapor deposition SiNx films deposited from silane and ammonia

Abstract: Varied SiNx films have been deposited by low pressure chemical vapor deposition from silane SiH4 and ammonia NH3 and the influences of the deposition parameters (temperature, total pressure and NH3/SiH4 gaseous ratio) on the film deposition rate, refractive index (assessed at a 830 nm wavelength), stoichiometry and thermomechanical stress are investigated and correlated. Low stress (≈600 MPa) Si3N4 films are obtained for the highest deposition temperature and the lowest total pressure but the gaseous ratio is shown to be the dominant parameter. According to the SiNx stoichiometry, silicon-rich silicon nitride and nitrogen-doped silicon (called NIDOS) depositions are obtained and compressive to tensile stresses are reported. A maximum in compressive stress is put into evidence for N/Si ratio roughly equal to 0.7 and is related to the cumulated effects of silicon nitridation and crystallization, characterizing the transition between nitrogen-doped silicon and silicon-rich silicon nitride. Finally, by consid...

Earthquakes, volcanoes, and rectified diffusion

Abstract: Rectified diffusion is a mechanism by which a strain wave can rapidly pump volatiles into a bubble and therefore increase the pressure in a closed system. The dynamic strain of either distant regional tectonic earthquakes or local volcanic tremor can be translated to static strain inside a magma chamber via this process. We formulate a theory appropriate to the conditions of a magma chamber and calculate the increased pressure using realistic physical parameters. For a basaltic system initially at 130 MPa pressure, the excess pressure from rectified diffusion is between 0.4 and 4 MPa for a regional M≥8 earthquake. The pressure from rectified diffusion is often significantly above the static stress caused by deformation for documented cases of triggered eruptions and thus presents a more viable mechanism for triggering. Prolonged tremor can have a similar effect since the total pressure added increases linearly with the duration of the excitation.

Microgravity n-Heptane Droplet Combustion in Oxygen-Helium Mixtures at Atmospheric Pressure

Abstract: Results are presented from experiments on the combustion of freely floated n-heptane droplets in helium-oxygen environments conducted in Spacelab onboard the Space Shuttle Columbia during the first launch (STS-83) of the Microgravity Science Laboratory mission in April 1997. During this shortened flight, a total of eight droplets were burned successfully in nominally 300 K oxygen-helium atmospheres having oxygen mole fractions of 25, 30, and 35% at a total pressure of 1 atm. Initial droplet sizes ranged from about 2 to 4 mm. The results demonstrated both radiative and diffusive flame extinction during burning, whereas droplet surface regression followed the d-square law. The full range of possible droplet-burning behaviors was thus observed. The results provide information for testing future theoretical and computational predictions of burning rates, soot and flame characteristics, and extinction conditions.

Properties of a new a-Si:H-like material: hydrogenated polymorphous silicon

Abstract: A new a-Si:H-like material has been obtained in a radio frequency-powered plasma-enhanced chemical vapor deposition system (RF-PECVD). This material prepared with dilution of silane into He or H2, under high total pressure (≈132 Pa) and high RF power exhibits enhanced electronic transport properties. The room temperature electronic mobility-lifetime product is increased by a factor up to 200 compared to hydrogenated amorphous silicon (a-Si:H) prepared under standard deposition conditions (lower pressure, lower RF power). The density of states measured by modulated photocurrent and the deep defect density measured by the constant photocurrent method are both less than that of standard a-Si:H. These transport properties are linked to the structure of this new material deposited under conditions close to those for powder formation. This structure seems to result in a decrease of the deep defect density and capture cross sections.

Modeling Mitigation Effects of Watershield on Shock Waves

Abstract: The object of this analysis is to investigate mitigation effects of watershield on air blast waves. To examine the water mitigation concept, features of the free-field detonation process are studied from a series of one-dimensional simulations using a multimaterial Eulerian finite element technique. Five different shock Hugoniots for water are compared, and the most accurate data are suggested. To verify the numerical procedure, results are compared with available experimental data for UNDEX problem and analytical predictions for air shocks. For the case of contact watershield, the magnitude of peak pressure generally decreases and the shock arrival time increases with increasing thickness of watershield. The total pressure impulse is reduced significantly at near field. Non-contact watershield was also examined, and was found to provide a better design criterion based on the further decay of peak pressure.

Effects of Inlet Distortion on the Flow Field in a Transonic Compressor Rotor

Abstract: The effects of circumferential distortions in inlet total pressure on the flow field in a low-aspect-ratio, high-speed, high-pressure-ratio, transonic compressor rotor are investigated in this paper. The flow field was studied experimentally and numerically with and without inlet total pressure distortion. Total pressure distortion was created by screens mounted upstream from the rotor inlet. Circumferential distortions of eight periods per revolution were investigated at two different rotor speeds. The unsteady blade surface pressures were measured with miniature pressure transducers mounted in the blade. The flow fields with and without inlet total pressure distortion were analyzed numerically by solving steady and unsteady forms of the Reynolds-averaged Navier-Stokes equations. Steady three-dimensional viscous flow calculations were performed for the flow without inlet distortion while unsteady three-dimensional viscous flow calculations were used for the flow with inlet distortion. For the time-accurate calculation, circumferential and radial variations of the inlet total pressure were used as a time-dependent inflow boundary condition. A second-order implicit scheme was used for the time integration. The experimental measurements and the numerical analysis are highly complementary for this study because of the extreme complexity of the flow field. The current investigation shows that inlet flow distortions travel through the rotor blademore » passage and are convected into the following stator. At a high rotor speed where the flow is transonic, the passage shock was found to oscillate by as much as 20% of the blade chord, and very strong interactions between the unsteady passage shock and the blade boundary layer were observed. This interaction increases the effective blockage of the passage, resulting in an increased aerodynamic loss and a reduced stall margin.« less

Miniature quadrupole residual gas analyzer for process monitoring at milliTorr pressures

Abstract: Monitoring of gas composition for processes in the mTorr range is not possible with a conventional residual gas analyzer (RGA) unless a pressure reduction pumping system is used. A miniature sensor, having dimensions compatible with the mean-free path of gas molecules can operate directly at mTorr pressures while being less expensive and more compact than a conventional apparatus. This article describes a quadrupole RGA which is scaled down by a factor of 7 to operate at pressures up to 10 mTorr. This sensor requires different construction methods and drive electronics than a traditional RGA. A unique ion source with high output has been developed. The small sensor has resolution characteristics very similar to standard size models but sensitivity is reduced in proportion to the ratio of cross-sectional area for each quadrupole r0. Response is linear to the mTorr range and a correction method for gas scattering, based on pressure measured by a total pressure gauge included in the ion source design, extend...

A Family of Designs for Aspirated Compressors

Abstract: The performance of compressors can be enhanced by the judicious removal of the viscous boundary layer fluid from the flow path. Removal of the boundary layer fluid just prior to or in a region of rapid pressure rise, either at shock impingement or more generally at the point of rapid pressure rise on the suction surface of the blade, can give significant increases in the diffusion and therefore increase the work done per stage for a given blade speed. It also provides a thermodynamic benefit by removing the high-entropy fluid from the flow path. Design studies have been done using quasi 3-D viscous and 3-D Euler computational tools on a family of fan stages of varying tip speed that lake advantage of such viscous fluid removal. One stage in this family is a low tip speed fan stage designed to produce a pressure ratio of 1.5 at a tip speed of 700 ft/sec. Fan noise reductions resulting from the decrease in tangential Mach number, without sacrificing total pressure ratio, could make this design attractive for the fan of medium-bypass ratio engines. Another stage in the family would produce a total pressure ratio of 2.0 at a tip speed of 1000 ft/sec and could be very attractive as a fan stage on a lower bypass ratio engine or as a first stage of a low speed core compressor. The final stage in the family would achieve a pressure ratio of more than 3.0 at a tip speed of 1500 ft/sec and could be very attractive as a first stage of a core compressor, or as a fan for a military engine. A design for the suction passages to deal with the fluid removal has been completed for an experimental version of the 1.5 pressure ratio design. A tip shroud allows bleeding of the tip surface boundary layer from the rotor, and carries the fluid removed from the blade surfaces through the tip. One of these stages will be tested in the MIT Blowdown Compressor, serving a dual purpose: as a validation of the computational design process and as a test of the concept of aspirated compressors.Copyright © 1998 by ASME

Gas amplification and ionization coefficients in isobutane and argon–isobutane mixtures at low gas pressures

Abstract: Measurements of the mean gas amplification factor in isobutane and in argon–isobutane mixtures are performed at total gas pressures of 10, 20, 30, 60 and 90 kPa over a range of reduced electric field strength 5 × 104 α/P=A ∗ exp (−B ∗ /S a ) was derived The fitting parameters A* and B* increase when: (i) the pure isobutane pressure decreases, (ii) the isobutane concentration in the mixtures increases at constant total pressure, and when (iii) the total pressure decreases at constant isobutane concentration The α/P for isobutane is compared with other experimental and calculated values which are all obtained for equilibrium conditions An interesting behavior of the ionization coefficient curves for argon–isobutane mixtures is found: at low Sa the α/P increases when the isobutane concentration decreases, while at higher Sa the opposite behavior is observed Both the reduced electric field strength and the ionization coefficient where the multiplication starts (M=2) increase with the decrease of the total pressure, as well as with the increase of isobutane concentration in the mixture at constant total pressure

Calculation of Pressure in Ocean Simulations

Abstract: Many state-of-the-art numerical ocean models calculate pressure using the hydrostatic balance, or an equation derived from it. The proper form of this deceptively simple-looking equation, ∂p/∂z = −gρ(S, T, p) (where notation is standard), is nonlinear in the pressure p. In contrast, most numerical models solve the linear equation ∂p/∂z = −gρ(S, T, z). This modification essentially replaces the total pressure, which includes a time-dependent signal, with an approximate time-independent pressure associated with the depth of a model grid point. In this paper, the authors argue that the inclusion of the total pressure when solving the hydrostatic equation can generate a depth-dependent baroclinic pressure gradient equivalent to a geostrophic velocity of several centimeters per second. Further, this effective velocity can increase with depth and is largest in dynamically important areas like western boundary currents. These points suggest that the full feedback of pressure on density should be include...

Bi(Pb)-2223 phase formation in Ag-sheathed tapes : the role of oxygen partial pressure during sintering

Abstract: phase formation has been studied in Ag-sheathed multifilamentary tapes processed in different oxygen partial pressures during sintering. In the furnace the total pressure was always kept at and the volume fraction of was varied. The samples prepared for the series were characterized by the critical current density , ac susceptibility and x-ray diffraction. Detailed investigations of the microstructure were carried out by SEM and TEM for samples sintered at 8 and 10% oxygen. The formation of the Bi(Pb)-2223 phase occurs at initial stages of the heat treatment, in which , alkaline earth cuprates and Pb compounds act as the precursor phases. The phase formation rate depends sensitively on the established oxygen partial pressure with an optimum partial pressure being approximately 10 vol.% oxygen. The critical current density varies more sensitively with the applied oxygen partial pressure and temperature than the Bi(Pb)-2223 phase fraction as determined by x-ray diffraction. Optimum values can only be obtained in a fairly small temperature/oxygen partial pressure window. One explanation for the strong decrease in is the poor crystalline quality of the grains. By TEM columnar defects were observed with diameters of typically 50 nm extending parallel to the c-axis of the grains. The individual grains contain a high density of these defects yielding still strong x-ray diffraction peaks but obviously poor superconducting properties. The formation rate and defect density depends sensitively on both the temperature and the oxygen partial pressure during sintering. The phase composition at initial stages of the heat treatment, particularly the phase fraction of the lead oxide compounds, can be controlled by the applied oxygen partial pressure. The reason for this is that Pb changes its oxidation state from 4+ to 2+. A stability line was determined for lead oxide compounds with lead being , e.g. .

Influence of Vane-Blade Spacing on Transonic Turbine Stage Aerodynamics: Part II — Time-Resolved Data and Analysis

Abstract: This paper presents results of a combined experimental/computational investigation into the effects of vane-blade spacing on the unsteady aerodynamics of a transonic turbine stage. Time-resolved data were taken in a shock-tunnel facility in which the flow was generated with a short-duration source of heated and pressurized air. This data is compared with the results obtained from four unsteady Navier-Stokes solvers.The time-resolved flow for three axial spacings is examined. For each vane-blade spacing, the inlet conditions were nearly identical and the vane exit flow was transonic. Surface-mounted high-response pressure transducers at midspan were used to obtain the pressure measurements.The computed two-dimensional unsteady airfoil surface pressure predictions are compared with the Kulite pressure transducer measurements. The unsteady and axial spacing effects on loading and performance are examined.In general the numerical solutions compared very favorably with each other and with the experimental data. The overall predicted stage losses and efficiencies did not vary much with vane/blade axial spacing. The computations indicated that any increases in the blade relative total pressure loss were offset by a decrease in vane loss as the axial spacing was decreased. The decrease in predicted vane total pressure loss with decreased axial spacing was primarily due to a reduction in the wake mixing losses. The increase in predicted blade relative total pressure loss with a decrease in axial spacing was found to be mainly due to increased vane wake/blade interaction.Copyright © 1998 by ASME

Preparation of 10 kg Ingot of Ultra-Pure Iron

Abstract: A new induction melting furnace with a cold-copper crucible has been designed and constructed using ultra-high vacuum technology. The main chamber can be evacuated to 6.7 × 10—8 Pa as the base pressure. The furnace can melt high-purity iron of 10 kg, at most, within 300 s. The total pressure becomes less than 4 × 10—6 Pa during melting of iron under the best condition. As starting materials for melting, high-purity electrolytic iron containing impurities of 25.2 massppm which is determined after the analysis of 18 elements was prepared. The content of gaseous impurities such as carbon, nitrogen, oxygen, sulfur and hydrogen is 19.6 massppm in total. It is concluded that ultra-high vacuum melting of iron is quite useful to increase the purity of iron. The total content of impurities in iron is reduced from 25.2 to 12.6 massppm by melting under the atmosphere of 7.5 × 10—6 Pa. The amount of gaseous impurities can be reduced from 19.6 to 10.1 massppm in total. Especially, the amount of oxygen is reduced from 14.1 to 7.5 massppm. These amounts of gaseous impurities are almost the limit of detection by conventional methods of analysis.

Formation of C3H6 from the Reaction C3H7 + O2 between 450 and 550 K

Abstract: The generation of C3H6 from the reaction C3H7 + O2 (1) has been investigated as a function both of temperature (450−550 K) at constant density (5.5 × 1018 molecules/cm3) and of pressure (55−550 Torr) at 490 K. The experiments were carried out by UV irradiation of mixtures of C3H8, Cl2, and O2 to generate propyl radicals. C3H8, C3H6, and C3H7Cl were monitored by gas chromatographic analysis. The propylene yield is 0.7% at 450 K. Based on these measurements and previous data at 298 K, the propylene yield has an apparent activation energy which is less than 2.5 kcal mol-1 below 450 K. Beginning near 450 K, the yield increases rapidly with an apparent activation energy of ∼32 kcal mol-1, similar to previous observations on the generation of C2H4 from the reaction C2H5 + O2. At 490 K, the propylene yield from reaction 1 depends inversely on total pressure (YC3H6 ∝ P-0.6) between 55 and 550 Torr, while the overall value of k1 has a much smaller pressure dependence (P0.18). These observations show that above 450...

An Experimental Examination of Cantilevered and Shrouded Stators in a Multistage Axial Compressor

Abstract: This paper presents experimental investigations on a large-scale low-speed compressor facility with four repeating stages equipped with CDA-profiles (Controlled Diffusion Airfoils). Two different builds were investigated. Both builds used identical rotors, but had stators configured either in cantilevered or in shrouded form.Traverse measurements of total pressure and flow angle at six axial locations (IGV, two rotor and three stator exit planes) were performed between 1% and 99% annulus height and across two blade pitches. Circumferentially mass-averaged radial profiles were used in a through-flow code for reconstruction analysis of the measurements. In addition to the traverse measurements surface static pressures on stage 3 rotor and stator were measured. The effect of the “free-end” configuration on an embedded stage of this multistage compressor is described and compared to the shrouded configuration. The objective of this study was to investigate the differences of these two configurations and especially the effects caused by the hub clearance vortex in the cantilevered case.The entire set of measurements and through-flow analysis was performed at two operating points of the compressor i.e. at peak efficiency and near stall condition. Thus also the effects of the hub clearance vortex which influences the stall margin of the compressor are described. The analysis of the results shows slightly higher pressure rise coefficients for shrouded stators, but slightly higher stall margin in the cantilevered case. This is due to a stabilizing effect of the hub clearance vortex (cleans up separation on hub) in the cantilevered configuration because its direction is opposite to the secondary flow in the passage.Copyright © 1998 by ASME

A unified theory for the interpretation of total pressure and temperature in two-phase flows at subsonic and supersonic speeds

Abstract: This paper presents a unified theory on the interpretation of total pressure and total temperature in multiphase flows The present approach applies to both vapour-droplet mixtures and solid-particle laden gases, and at subsonic as well as supersonic velocities It is shown here that the non-equilibrium processes occurring in the vicinity of a stagnation point are important These processes may be responsible for the generation of entropy and affect the pressure and temperature at the stagnation point They should be properly considered while inferring, say, flow velocity or entropy generation from Pitot measurements By proper non-dimensionalization of the relevant parameters, it is possible to find a single (theoretically obtained) calibration curve for the total pressure as a function of the particle size, which is almost independent of the constituents of the multiphase mixture and of the flow conditions The calibration curve is a plot of a pressure recovery factor versus Stokes number and specifies the total pressure under different non-equilibrium conditions The total pressure, predicted by the present theory, varies monotonically between the two limiting values: the frozen total pressure (when there is no interphase mass, momentum and energy transfer in the decelerating flow towards the stagnation point) and the equilibrium total pressure (when the dispersed phase, either the liquid droplets or the solid particles, is always at inertial and thermodynamic equilibrium with the continuous vapour phase) The equilibrium total pressure is always higher than the frozen total pressure It is shown that the equilibrium total temperature, on the other hand, may be higher or lower than the frozen total temperature In addition, unlike the case of total pressure, the calibration curve for total temperature is not so universal, and the total temperature under non-equilibrium conditions is not necessarily bounded between the frozen and equilibrium values It is further shown that the entropy of a multiphase mixture has to be carefully interpreted and is not unequivocally related to the total pressure even in steady adiabatic flow

The spatial profiles of charged particles in a multipolar magnetically confined Ar- plasma

Abstract: The spatial profiles of charged particles in multipolar magnetically confined Ar- plasmas produced by dc discharges are investigated by varying the total pressure from 2 to 10 mTorr, the discharge current from 10 to 90 mA and the oxygen content from 4 to 20%. The measured spatial negative ion and electron density profiles, which are approximated as a parabolic distribution and a uniform one except in the vicinity of the chamber wall, respectively, allow us to divide the entire discharge into three regions: (i) an electronegative region, (ii) an electropositive region and (iii) the sheath. The ratio of the negative ion density to the electron density measured at the centre increases with increasing oxygen content and pressure, but decreases with increasing discharge current. Oxygen content- and discharge current-dependences of the electronegative region's length are similar to those of the ratio, although the length does not strongly depend on the pressure. A global model, in which the flux balance equations for charged particles and a power balance equation for electrons are taken into account, to estimate plasma parameters such as the individual charged particle density and electron temperature is proposed, and then compared with the experimental results.

Optical emission spectroscopy on pulsed-DC plasmas used for TiN depositions

Abstract: The plasma-assisted chemical vapour deposition process in a large-scale industrial plant for coating of TiN on tool steels was investigated by optical emission spectroscopy Several atomic lines and molecular bands were identified A parametric study of the dependence of bias voltage, total pressure and gas flows, H 2 , N 2 , Ar and TiCl 4 , on the plasma characteristics was performed to gain understanding of the influence of the parameters on the deposition process With the change of process parameters, large variations in the emitted light, corresponding to changes in plasma conditions, were observed In the parameter range studied, the deposition rate depends linearly on the N + 2 signal when varying the pressure and the N 2 flow, whereas no clear correlation between the OES signal and the deposition rate could be found for variations of the other parameters

Mean global surface pressure series evaluated from ECMWF reanalysis data

Abstract: Time series (1979–93) of the global mean surface pressure are determined using data provided by the ECMWF ReAnalysis (ERA) project. Total pressure, water vapour pressure and dry-air pressure are evaluated. It is shown that a trend of only 0.01 hPa per decade exists for the total surface pressure whereas that of the water vapour surface pressure is 0.05 hPa per decade. This underlines the homogeneous character of the time series of ERA data, at least for the integral quantities surface pressure and water vapour surface pressure.