Showing papers on "Total pressure published in 1993"

Shock/boundary-layer interaction control with vortex generators and passive cavity

Abstract: This paper describes an experimental comparison of two passive approaches for controlling the shock interaction with a turbulent boundary layer: low-profile vortex generators and a passive cavity (porous wall with a shallow cavity underneath). This investigation is the first known direct comparison of the two methods wherein the advantages and disadvantages of both are revealed. The experiments were conducted with a normal shock wave in an axisymmetric wind tunnel. The shock strength (M = 1.56-1.65) was of sufficient magnitude to induce a large separation bubble, thus causing substantial boundary-layer losses. The low-profile vortex generators were found to significantly suppress the shock-induced separation and improve the boundary-layer characteristics downstream of the shock. However, the suppression of the separation bubble decreased the extent of the low total pressure loss region associated with the lambda foot shock system which results in a lower mass-averaged total pressure downstream of the shock. The passive cavity substantially reduced the total pressure loss through the shock system (and thus wave drag) by causing a more isentropic compression over a larger lateral extent. However, the boundary-layer losses downstream of the shock were significantly increased.

Mass transfer at the air/water interface: Mass accommodation coefficients of SO2, HNO3, NO2 and NH3

Abstract: We present here experimental determinations of mass accommodation coefficients β using a low pressure tube reactor in which monodispersed droplets, generated by a vibrating orifice, are brought into contact with known amounts of trace gases. The uptake of the gases and the accommodation coefficient are determined by chemical analysis of the aqueous phase. We report in this article measurements of βexp=(6.0±0.8)×10−2 at 298 K and with a total pressure of 38 Torr for SO2, (5.0±1.0)×10−2 at 297 K and total pressure of 52 Torr for HNO3, (1.5±0.6)×10−3 at 298 K and total pressure of 50 Torr for NO2, (2.4±1.0)×10−2 at 290 K and total pressure of 70 Torr for NH3. These values are corrected for mass transport limitations in the gas phase leading to β=(1.3±0.1)×10−1 (298 K) for SO2, (1.1±0.1)×10−1 (298 K) for HNO3, (9.7±0.9)×10−2 (290 K) for NH3, (1.5±0.8)×10−3 (298 K) for NO2 but this last value should not be considered as the true value of β for NO2 because of possible chemical interferences. Results are discussed in terms of experimental conditions which determine the presence of limitations on the mass transport rates of gaseous species into an aqueous phase, which permits the correction of the experimental values.

Superposed epoch analysis of pressure and magnetic field configuration changes in the plasma sheet

Abstract: Using data from 41 substorm events in the near-Earth magnetotail, we have combined plasma, energetic ion, and magnetic field data from the AMPTE/IRM spacecraft to perform a superposed epoch analysis of changes in the total pressure and in the magnetic field configuration as a function of time relative to substorm onset. Unloading is evident in the total pressure profile; the pressure decreases by about 20 percent. Pressure changes during the growth phase are not as uniform for the different substorms as the pressure changes during the expansion phase. To study changes in the magnetic field configuration, we have determined the development of the plasma pressure profiles in z for an average of data from 15 to 19 R(E). At substorm onset, the field line dipolarization begins on the innermost field lines and then progresses to the outer field lines. The field lines map the closest to the Earth about 45 min after substorm onset, and then begin to stretch out again during the recovery phase of the substorm.

High rate deposition of alumina films by reactive gas flow sputtering

Abstract: A new sputter which enables higher deposition rates than standard magnetron sputtering, especially for oxide films, has been developed. The deposition process typically works at several tenths of a millibar and requires no high vacuum environment. It is based on a hollow cathode discharge in combination with a suitable directed gas flow. The particular route of the gas flow also strongly decreases the residual gas influence on the target and substrate. For practical applications a linear sputter source of length 10 cm and width 2 cm which allows the coating of an area of approximately 50 cm2 has been tested. Up to now deposition rates of 10 μm h-1 at 1.4 kW d.c. power have been realized. The total pressure and gas flow were in the region of 0.4 mbar and 800 sccm (standard cm3 min-1) respectively. In spite of the rather high working pressure and the intense argon gas flow towards the substrate, the argon content of the films is very low (0.01 wt.% or less). The concept of the linear hollow cathode with two parallel rectangular targets was found to be simple in construction and operation and can be easily extended in two dimensions for the coating of large areas.

Correlations between the fluctuations of pressure, density, temperature and magnetic field in the solar wind

Abstract: Compressive fluctuations and the pressure balance in the solar wind are investigated with Helios data obtained in 1975-1976 from measurements in the inner heliosphere between 03 and 10 AU Broad-band (6×10 −3 Hz-6×10 −6 Hz) correlation spectra and hourly correlation coefficients for any pair of solar wind parameters like speed, density, temperature, magnetic field magnitude, thermal and magnetic pressure, and the total pressure of the plasma are calcultated and analysed We find that the nature and intensity of the compressive fluctuations strongly depend on the flow speed and systematically vary with the stream structure

An experimental investigation of S-duct flow control using arrays of low-profile vortex generators

Abstract: An experimental investigation was undertaken to measure the effect of various configurations of low-profile vortex generator arrays on the flow in a diffusing S-duct. Three parameters that characterize the vortex generator array were systematically varied to determine their effect: (1) the vortex generator height; (2) the streamwise location of the vortex generator array; and (3) the vortex generator spacing. Detailed measurements of total pressure at the duct exit, surface static pressure, and surface flow visualization were gathered for each vortex generator configuration. These results are reported here along with total pressure recovery and distortion coefficients determined from the experimental data. Each array of vortex generators tested improved total pressure recovery. The configuration employing the largest vortex generators was the most effective in reducing total pressure recovery. No configuration of vortex generators completely eliminated the flow separation that naturally occurs in the S-duct, however the extent of the separated flow region was reduced.

Gas turbine engine control based on inlet pressure distortion

Abstract: Circumferential and radial inlet pressure distortion on an aircraft gas turbine engine are detected by a plurality of static pressure sensors and a signal processor, which computes the total pressure for each sensor to determine a pressure distortion pattern which the processor correlates with stored data for the engine and inlet to determine if the airflow geometry should be altered during flight. Time varying changes in the pressure from one or more of the pressure sensors is used to determine a stall condition, causing a change in engine airflow geometry to increase stall margin.

Studies on the Reactions of CH(v=0 and 1) with NO and O2.

Abstract: Rate constants for the reactions of CH(X2Π : v = 0,1) with NO and O2 are measured under pseudo-first-order conditions at 297 ± 5 K. CH(X2Π : v = 0,1) radicals are generated by excimer laser photolysis of CHBr3 and (CH3)2 CO at 193 nm, and detected by the laser-induced fluorescence (LIF) technique. The overall rate constants obtained at the total pressure of 20 Torr Ar are: kNO(v = 0) = (1.6 ± 0.2) × 10−10, kNO(v = 1) = (1.3 ± 0.6) × 10−10, kO2(v = 0) = (3.5 ± 0.3) × 10−11, and kO2(v = 1) = (3.4 ± 0.8) × 10−11 (cm3 molecule−1 s−1). No apparent pressure dependence is indicated for the rate constants over the pressure range of 5—50 Torr Ar for CH + NO, and 5—30 Torr Ar for CH + O2 reactions, respectively. The reaction mechanisms are discussed based on the quantum mechanical calculations of the potential energy surfaces of CH + NO and CH + O2 systems.

Chemistry of SiO2 Plasma Deposition

Abstract: The chemistry of deposition from undiluted and He‐diluted mixtures was studied by line‐of‐sight mass spectrometry of plasma species coupled with analysis of film IR absorption and dielectric properties. It was found that if RF power is sufficient to generate an O atom supply well in excess of that needed to convert all of the to , then clean IR spectra and high dielectric strength are obtained independent of dilution. Under these plasma conditions, many gas‐phase products of the form were detected. Their concentration increased steeply with the partial pressure of the reactants , and they are the likely source of the downstream particles and deposition rate loss which were seen at 130 Pa of reactant pressure. Reduction of reactant partial pressure to 13 Pa either by He dilution or by undiluted total pressure reduction eliminated these problems. No other effects of He dilution could be detected either in the plasma chemistry or in the film properties. Both concentration and electron trapping rate in the films were much higher than in thermal oxide and were unaffected by He dilution. There is some evidence that He plasma treatment does improve Si interface quality.

Regularities of pyrolytic boron nitride coating formation on a graphite matrix

Abstract: The kinetics and structure of chemical vapour-phase deposition of boron nitride ceramics on a graphite matrix from the mixture BCl3/NH3/N2 have been investigated for a wide range of conditions (temperature 1300–2100°C, pressure 130–2600 Pa, at varying partial pressures of the components). The growth-rate was found to vary non-linearly with the consumption rates of the reagents. The content of hexagonal components in the BN-ceramics rose, while the turbostrate microphase content diminished with temperature. The dependences of the concentrations of hexagonal, turbostratic and amorphous fractions in BN-ceramics on the reaction mixture composition and total pressure have been determined.

Low hydrogen content silicon nitride films from electron cyclotron resonance plasmas

Abstract: The material and electrical properties of SiNx:H films deposited using a 2% SiH4/N2 mixture with additional N2 in an electron cyclotron resonance reactor have been evaluated. Deposition rate, refractive index, and stoichiometry have been determined using ellipsometry, Rutherford backscattering spectrometry, and infrared spectroscopy. Current‐voltage and dielectric breakdown characteristics have been measured on metal‐insulator‐silicon structures. Stoichiometric material with a hydrogen content of 1.5 at. % is created using a ratio of SiH4/N2=0.003, P=2 mTorr, T=250 °C, and power=650 W. Hydrogen levels are reduced by using lower ratios of SiH4/N2, lower total pressure, or higher microwave power. Higher total pressure results in significantly enhanced deposition rates, but with greatly increased H and O content. The low‐field resistivity of these films is largely independent of the process parameters over the range investigated. The dielectric breakdown strength is significantly greater in films deposited a...

The Formation Mechanism and Step Coverage Quality of Tetraethylorthosilicate ‐ SiO2 Films Studied by the Micro/Macrocavity Method

Abstract: The formation mechanism and step-coverage quality of SiO 2 films formed by the pyrolysis of tetraethylorthosilicate (TEOS) were studied, using a novel experimental technique called the «multi-layered micro/macrocavity method.» The growth rate profiles at millimeter (macrocavity) and submicron (microtrench) sales deposited under a total pressure ranging from 2 to 760 Torr were simultaneously analyzed. The step coverage approaches conformal deposition either with decreasing volume-to-surface ratio (V/S) of the macrocavity reaction zone or with increasing total pressure. Combining these results with the growth-rate profiles of the macrocavity shows that two kinds of intermediate species participate in deposition. One is a high-activity species with a surface sticking probability near 1, and the other is a low-activity

Kinetics of the trichloromethyl association reaction with molecular oxygen at 298 and 333 K and from 1 to 760 Torr of total pressure

Abstract: The reaction CCl 3 + O 2 + M → CCl 3 O 2 + M (eq 1) was studied at 298 and 333 K as a function of pressure, from 1 to 760 Torr, using two experimental techniques. Low-pressure experiments (1-12 Torr) were carried out with the laser photolysis/photoionization mass spectrometry technique. The experiments conducted in helium at low pressure yielded rate constants that were about a factor of 2 smaller than in N 2 , confirming that two previous studies are in good agreement once the third body collisional efficiency of the bath gas is taken into account

Refinement of the evaluation of the role of CO 2 in modifying estimates of the pressure of epithermal mineralization

Abstract: Pressure is the most important of the intensive parameters for relating epithermal mineralization to the geologic setting. This paper describes the limitations on pressure (and therefore depth) of mineralization that may reasonably be derived from simple observations of the behavior of fluid inclusions (i.e., the existence of ice or CO 2 clathrate on the liquidus, the amount of expansion or contraction of the bubble as the host inclusion is crushed in oil on the microscope stage, and the freezing and homogenization temperatures for the inclusion). It is based on the reasonable model that mineralization occurs from a hydrostatically pressured NaCl-CO 2 -H 2 O fluid, consistent with the probability that H 2 O and CO 2 are the only gases contributing significantly to the total pressure. The pressure of CO 2 is, of course, a function of CO 2 content, but, from 100 degrees to 300 degrees C, it is a surprisingly minor function of either temperature or salinity. The presence of the clathrate in freezing studies of fluid inclusions indicates pressures of CO 2 that add at least 1 km to the probable depth of inclusion trapping compared to that estimated from CO 2 -free water. Thus undetected (i.e., no clathrates on cooling) CO 2 in fluid inclusions can nonetheless contribute very significantly to the possible depth of epithermal mineralization. On the other hand, the observation that fluid inclusions crushed in oil have bubbles that do not expand (i.e., 2 ) at 25 degrees C), demonstrates CO 2 contents that could add at most a few tens of meters to the depth of mineralization.

Relative Flow and Turbulence Measurements Downstream of a Backward Centrifugal Impeller

Abstract: The paper presents the results of an experimental investigation on the three-dimensional relative flow at the exit of the backward bladed centrifugal impeller of the high-pressure stage of a two-stage biregulating pump-turbine model, operating at the pump nominal point. Mean velocity, Reynolds stress tensor, and total pressure of the relative flow have been measured with stationary hot-wire probes and fast response miniature pressure transducers, by means of a phase-locked ensemble-average technique. The results, shown in terms of secondary vector plots and contours of mean flow characteristics and Reynolds stress components, give a detailed picture of the flow kinematic structure and of the complex relative total pressure loss and turbulence distributions

The Si-C-O system

Abstract: Accurate data allow one to draw a precise pressure — P CO/P SiO ratio — temperature (PRT) diagram taking into account the mass balance of the independent components in the Si-C-O system. The existence of a congruent point for the mixture 2SiO2+1SiC is shown, when the total pressure is lower than 36 700 Pa. From the PRT diagram it is possible to construct the phase diagrams at all temperatures and pressures.

Creep closure of channels in deforming subglacial till

Abstract: We examine theoretically the creep closure of subglacial tunnels cut into basal till, generalizing Nye’s classical analysis of tunnel closure in glacier ice to rheologies in which the creep rate depends on effective pressure (the difference between total pressure and pore-water pressure). The solutions depend critically on a dimensionless permeability parameter. For the appealingly simple Boulton–Hindmarsh rheology in which strain rate depends on powers of applied stress and effective pressure, solutions to the closure problem may not exist; this is related to the existence of a ‘failed’ zone next to the channel, where piping occurs, and also to a non-physical degeneracy of the assumed rheology, whereby the viscosity is indeterminate at zero effective pressure. Consideration of the failed zone allows solutions to be obtained and shows that the closure characteristics of high permeability tills and low permeability tills are very different.

Pressure and temperature dependence of the rate of reaction between CN radicals and NO over the range 99 ⩽T/K ⩽ 450

Abstract: Pulsed laser photolysis, laser-induced fluorescence experiments have been performed on the kinetics of reaction between CN radicals and NO. The measurements cover a range of temperature (99 ⩽T/K ⩽ 450) and total pressure {at 296 K, 5–400 Torr [1 Torr =(101 325/760) Pa]; at other temperatures, a smaller range}. Two methods were employed to extract rate constants in the limit of low and high pressure and their temperature dependences from the experimental results. Comparison of the values of the low-pressure rate constants derived from experiment with calculated values suggests that levels derived, in zeroth order, from the excited S1 and T1 electronic states mix with those in the ground S0 state thereby contributing to the density of NCNO states in the region of the CN + NO dissociation limit and hence to the rate of association in the limit of low pressure.

Model for entropy production and pressure variation in confined turbulent mixing

Abstract: A quasi-one-dimensional model for the planar, confined shear layer is constructed with the purpose of obtaining estimates of entropy production and pressure variation due to turbulent mixing. The turbulent Prandtl and Lewis numbers are assumed to be unity. It is found that entropy production is strongly coupled to the intrinsic compressibility, with total pressure losses becoming significant as the convective Mach number increases

Miniature, fast-response five-hole conical probe for supersonic flowfield measurements

Abstract: Five-hole probes have been used successfully for several decades to measure Mach number, total pressure, and flow angularity of complex, three-dimensional supersonic flowfields. However, the time response of conventional five-hole probes is typically on the order of seconds. A new probe design incorporating internally mounted miniature piezoelectric transducers has improved the time response by more than two orders of magnitude from 5 s to 20 ms, while maintaining better than 1-mm spatial resolution. This probe has been calibrated over the range Mach 2-4, and uncertainties in derived flowfield quantities have been shown to be small. Sample measurements of a supersonic vortex have been made to demonstrate the capabilities of the probe

Influence of nitrogen on the oxygen dissociation in a DC discharge

Abstract: The effect of the addition of molecular nitrogen on the oxygen dissociation is investigated in a low pressure gas discharge. The dissociation efficiency is measured as a function of N2 concentration, for a total pressure ranging from 0.4 to 3 Torr in discharge tubes with diameter between 6 and 21 mm. The concentration of O atoms is obtained by the NO+O chemiluminescent reaction. The authors show that for a few percent of nitrogen the oxygen dissociation degree varies by a factor of 1.5-10 depending on the nitrogen concentration, tube diameter and total pressure. The ratio of the dissociation degree for pure oxygen and mixtures of oxygen and nitrogen is calculated, and the authors show that their results imply that, as the tube diameter tends to infinity, the dissociation efficiency tends to one. The authors conclude that the most important reason for the increase in the dissociation of oxygen in the presence of nitrogen is the reduction of wall diffusion losses.

Plasma etch process

Abstract: An improved SiOx etch which employs CHF3, N2 and a light mass cooling gas in total pressure on the order of 3000 mT in a confined plasma reactor. High aspect ratios at least 10:1 are obtainable.

Distributions and thermalization of protons and alpha particles at collisionless quasi-parallel shocks.

Abstract: The dissipation processes of protons and a minor ion component, alpha particles, at quasi-parallel supercritical collisionless shocks are investigated by one-dimensional hybrid simulations. For both ion components the dissipation at these shocks is due to two different mechanisms: Heating is either caused by the nonadiabatic transition of the ions through the shock ramp where ions move through the region of the sharp jump in the magnetic field magnitude and direction, or by a mechanism which involves the occurrence of specularly reflected ions and subsequent shock reformation. In the latter case, reflected ions form a counterstreaming beam and lead to re-formation of the shock at the leading edge of the reflected ion beam. The region between the re-formed and the old shock, where the initial solar wind and the reflected beam have not completely merged, exhibits a sharp increase of the total pressure, which is caused by the difference in the bulk velocities of the two components. At low plasma beta (thermal to magnetic pressure) shocks, the downstream total pressure is mainly determined by the pressure of the directly transmitted ions and the pressure of the specular reflected ions provides only a minor contribution. With increasing plasma beta the reflected component more and more dominates the downstream pressure. We have also investigated the dependence of the downstream alpha particle to proton temperature ratio r T (ds)=(T α /T p ) ds as a function of the upstream density ratio n α /n p , the plasma beta and the Alfven Mach number M A of the shock. Quasiparallel collisionless shock heating of alpha particles is more efficient than heating of protons. The downstream temperature ratio r T (ds) is higher than the upstream solar wind temperature ratio and can be for low Mach Number shocks as high as ∼7. The downstream temperature ratio enhancement decreases with increasing upstream density n α /n p , plasma beta and/or the shock Mach number

Polymerization of olefins through heterogeneous catalysis. XIV. The influence of temperature in the solution copolymerization of ethylene

Abstract: The high-temperature solution homopolymerization of ethylene and copolymerization with 1-hexane using highly active TiCl[sub 4]/MgCl[sub 2]-supported catalyst was studied. Experiments with pressure variations in the range 100--400 Psig were carried out at 185 C and for 10 min polymerization time. Both peak initial rate of polymerization and the catalyst productivity in homo- and copolymerization were found to increase steadily with increasing reactor pressure. Higher polymerization rates arose in copolymerization compared to homopolymerization, especially above 200 Psig total pressure. In both cases, the reaction order with respect to ethylene concentration was close to two. The number-average molecular weight was found to be almost independent of pressure, whereas in copolymerization, the weight-average molecular weight was observed to decrease from about 200,000 to 120,000 over the range of pressure studied. The polydispersity index in copolymerization was found to decrease steadily from 8 to about 4 with increasing pressure.

Measurement and analysis of a small nozzle plume in vacuum

Abstract: Measurements of Pitot pressure and flow angle were made in the plume of a nozzle flowing nitrogen and exhausting to a vacuum. The measurements were compared to results from a numerical simulation of the flow that was based on kinetic theory and used the direct-simulation Monte Carlo (DSMC) method. Numerical results were compared with measurements made in the plume at various axial and radial stations. Total pressure measurements were made with Pitot tubes sized for specific regions of the plume. Flow angle measurements were made with a conical probe. The measurement area for flow angle extended to 160 mm (5 exit diameters) downstream of the nozzle exit plane and radially to 60 mm (1.9 exit diameters) from the plume axis. The total pressure measurements extended 480 mm (16 exit diameters) downstream and radially to 60 mm. Comparisons of computed results from the DSMC method with measurements of flow angle displayed improved agreement with increasing distance from the exit plane. Pitot pressures computed from the DSMC method were in reasonably good agreement with experimental results over the entire measurement area.

Reactive magnetron sputtering of zirconium carbide films using Ar-CH4 gas mixtures

Abstract: Zirconium carbide coatings have been produced by reactive r.f. sputtering on cold-rolled steel samples. The films were deposited in an argon-methane atmosphere. The influence of total pressure, methane partial pressure, substrate temperature and bias voltage on the structure and properties was investigated. The coatings were mainly characterized by X-ray diffraction (XRD), scanning electron microscopy and hardness measurements. Energy dispersive X-ray spectroscopy analysis was used to detect impurities such as argon. It could be shown that an increasing methane partial pressure results in an increasing lattice parameter. The films have a BlNaCl structure with a (111) preferred orientation. With increasing bias voltage the structure becomes more dense and the deposition rate decreases. A very thin intermediate iron carbide layer was observed by XRD analysis of ZrC films about 100 nm thick.

Method of growing a compound semiconductor film

Abstract: A method of fabricating a semiconductor device comprises the steps of growing a first layer of a group III-V compound semiconductor material on a substrate by a vapor phase deposition process by setting the temperature at a first temperature, raising the temperature from the first temperature to a second, higher temperature, growing a second layer of a group III-V compound semiconductor material on the first layer, wherein the step of raising the temperature is conducted while supplying a source gas for the group V element under a condition, determined in terms of a total pressure and a partial pressure of the source gas, such that the condition falls within a region defined by a first condition wherein the total pressure is set to 76 Torr and the partial pressure is set to 0.35 Torr, a second condition wherein the total pressure is set to 760 Torr and the partial pressure is set to 0.6 Torr, a third condition wherein the total pressure is set to 760 Torr and the partial pressure is set to 5.7 Torr, and a fourth condition wherein the total pressure is set to 76 Torr and the partial pressure is set to 1.3 Torr.

Extraction of Kinetic Parameters for the Chemical Vapor Deposition of Polycrystalline Silicon at Medium and Low Pressures

Abstract: The deposition of silicon (Si) from silane (SiH4) was studied in the silane pressure range from 0.5 to 100 Pa (0.005 to1 mbar) and total pressure range from 10 to 1000 Pa using N2 or He as carrier gases. The two reaction paths, namely,heterogeneous and homogeneous decomposition could be separated by varying the amount of wafer area per unit volume(wafer-distance variation) and the SiH4 partial pressure as well as the total pressure. Rate constants were derived by fittingthe experimental results. The heterogeneous reaction path could be described by only the adsorption rate constants ofreactive species and the desorption rate constant of hydrogen using a Langmuir-Hinshelwood mechanism. Hydrogen andphosphine were found to suppress the deposition rate at low silane pressures. At high silane pressures or high totalpressures the unimolecular decomposition of silane dominates. The unimolecular rate constant was found to be one to twoorders larger than literature values based on RRKM analyses of high pressure rate data. The relative efficiency of SiH4-N2and SiH4-He collisions compared with SiH4-SiH4 collisions in the unimolecular gas-phase decomposition of SiH4 has beeninvestigated. Helium was found to be a weak collider compared to silane and nitrogen.