Showing papers on "Total pressure published in 1992"

The Physical Basis of Ultrahigh Vacuum

Abstract: Contents: Molecule-Molecule and Molecule-Interactions. Collision Processes in Gases. Interaction of Charged Particles with Surfaces. Interaction of Radiation with Surfaces. Mechanical Properties of Materials at Very Low Pressures. General Considerations of Pressure Measurement. Total Pressure Gauges. Partial Pressure Gauges. Processing Techniques for Ultrahigh Vacuum. Pumps for Ultrahigh Vacuum. Examples of Ultrahigh Vacuum Systems.

Pressure changes in the plasma sheet during substorm injections

Abstract: Data from the CHEM instrument on AMPTE CCE, data from the 3D plasma instrument and the SULEICA instrument on AMPTE IRM, and magnetometer data from both spacecraft are used to determine the particle pressure and total pressure as a function of radial distance in the plasma sheet for periods before and after the onset of substorm-associated ion enhancements over the range 7-19 RE. Events were chosen that occurred during times of increasing magnetospheric activity, as determined by an increasing AE index, in which a sudden increase, or 'injection', of energetic particle flux is observed. It is shown that the simultaneous appearance of energetic particles and changes in the magnetic field results naturally from pressure balance and does not necessarily indicate that the local changing field is accelerating the particles.

The role of oxygen excitation and loss in plasma‐enhanced deposition of silicon dioxide from tetraethylorthosilicate

Abstract: The deposition rate of silicon dioxide from tetraethylorthosilicate/O2 capacitively coupled plasmas increases with increasing applied rf power, increasing total pressure and decreasing wafer temperature. These measured deposition rate dependences can be explained by a simple plasma deposition model in which deposition occurs through both an ion‐assisted and an oxygen atom initiated pathway. The relative contributions of these pathways were roughly isolated using limiting step coverage measurements on low aspect ratio trenches. Limiting step coverages decreased, and hence directionality increased, with increasing rf power density, decreasing total pressure, and increasing wafer temperature. A simple bulk plasma chemistry model combined with an analytical sheath model was developed to qualitatively explain our experimental findings. The model suggests that the ion‐enhanced deposition rate is directly proportional to oxygen ion flux, with a reactive sticking coefficient approaching unity. Using literature va...

Production of magnetic recording medium

Abstract: PURPOSE:To control magnetic characteristics such as coercive force, squareness ratio, coercive force squareness ratio, etc., with good reproducibility by forming a magnetic thin film containing Co in a noble gas atmosphere containing oxygen by a specified proportion to the nitrogen partial pressure. CONSTITUTION:The atmosphere for forming the magnetic thin film containing Co is specified to such a noble gas atmosphere containing 0.1 - 10% oxygen to the nitrogen partial pressure. The nitrogen partial pressure is not limited and preferably about 1 - 100% of the total pressure. By controlling the partial pressure ratio of oxygen to nitrogen, magnetic characteristics of the medium, especially, coercive force Hc, squareness ratio S and coercive force squareness ratio S* are controlled with good reproducibility.

Hydrodynamics of Two-Phase Flow Across Horizontal In-line and Staggered Rod Bundles

Abstract: This paper reports on void fraction and friction pressure drop measurements made for vertical two-phase flow of air-water across staggered and in-line rod bundles with different pitch-to-diameter ratios. All void fraction data showed a strong mass velocity effect and were significantly less than the values predicted by a homogeneous flow model, but were well correlated using the dimensionless gas velocity, j[sup [asterisk]][sub g]. The two-phase friction multiplier data could be well correlated with the Martinelli parameter for G [gt] 200 kg/m[sup 2]s. The correlations developed for void fraction and two-phase friction multiplier were successfully tested in predicting the total pressure drop in boiling R-113 experiments.

Impingement Cooling of Electronics

Abstract: Experiments were conducted to determine the performance of a system of low-velocity air jets used to cool a simulated electronics package. The test model consisted of a uniform array of rectangular elements mounted to a circuit board. Each element was cooled by a cluster of four jets, and the spent fluid was vented at one end of the channel formed between the circuit board and the plate from which the jets were discharged. Reported are measurements of system pressure drop and convective heat transfer coefficients for elements at various sites within the array. Results indicate that (for the geometry tested) the largest portion of the total pressure drop occurs across the jet orifices. Further, the crossflow of spent air appears to enhance heat transfer for those elements near the exit end of the channel.

A concentration probe for the study of mixing in supersonic shear flows

Abstract: An aspirating hot-film probe is developed to measure local mean gas composition in supersonic flows. The probe consists of a constant temperature hot-film sensor operating in a channel with a choked exit. Thus, the flow over the hot film is influenced only by total temperature, total pressure, and gas concentration. The use of the probe requires a separate measurement of the total temperature in the gas flow. The probe has a spatial resolution of 0.011 in. and shows acceptable sensitivity to flow angularity. The probe is used in the study of an unheated supersonic air/helium mixing layer in a 23 cm × 23 cm supersonic wind tunnel. Data are presented in raw form and after reduction to concentration and mean flow quantities.

Separation of carbon dioxide by asymmetric hollow fiber membrane of cellulose triacetate

Abstract: Permeation behavior of pure CO2, O2, and N2 and separation characteristics of CO2–air mixtures were examined using hollow fiber modules of asymmetric cellulose triacetate membrane at 30°C. The ideal separation factor for CO2 relative to N2 ranged from 21 to 24. Permeation behavior for pure CO2 was interpreted in terms of the total immobilization model, i.e., a limiting case of the dual-mode mobility model for glassy polymer, where the diffusion coefficient for Henry's law mode is not assumed to be constant and depends on gas pressure via a modified free-volume model. Based on pure gas permeabilities to CO2, O2, and N2, simulation for the separation of CO2–air mixtures was made using a counter-current plug flow model, and the result fitted the corresponding experimental data fairly well. Membrane plasticization induced by CO2 had negligible effect on permeation to mixture of CO2 and air in the range of CO2 composition up to 50% and upstream total pressure up to 1.5 MPa.

Uncoupling crystal growth and nucleation in the deposition of diamond from the gas phase

Abstract: Diamond deposits of well-separated particles have been obtained by the hot filament CVD technique on Si(100) wafers. Particle counting in SEM images and determination of their linear dimensions require a separate study of growth rates and of nucleation densities as a function of time, substrate temperature (500 °C–950 °C), gas phase composition (0.5–2% CH4 in H2), and total pressure (15–76 Torr). It is shown that recent models proposed for the growth process can successfully be applied if proper consideration is given to the high catalytic activity of the growing diamond surface for the heterogeneous recombination of gaseous H-atoms. This fast reaction controls the H-atom concentration at the surface and couples growth rates and nucleation densities via the gas phase.

A Computational Procedure for Diffuser-Combustor Flow Interaction Analysis

Abstract: This paper describes a diffuser-combustor flow interaction analysis procedure for gas turbine combustion systems. The method is based on the solution of the Navier-Stokes equations in a generalized non-orthogonal coordinate system. The turbulence effects are modeled via the standard two-equation (k-e) model. The method has been applied to a practical gas turbine combustor-diffuser system that includes support struts and fuel nozzles. Results have been presented for a three-dimensional simulation, as well as for a simplified axisymmetric simulation. The flow exhibits significant three-dimensional behavior. The axisymmetric simulation is shown to predict the static pressure recovery and the total pressure losses reasonably well.Copyright © 1990 by ASME

Reduced-pressure MOCVD of highly crystalline BaTiO3 thin films

Abstract: Epitaxial BaTi3 films have been grown on NdGaO3 [100] substrates by reduced pressure MOCVD for the first time. The substrate temperature was 1000 °C and the total pressure was 4 Torr. Electron and x-ray diffraction measurements indicate highly textured, single phase films on the NdGaO3 substrate which are predominantly [100], with [110] also present. TEM and selected area electron diffraction (SAED) indicate two specific orientational relationships between the [110] and the [001] diffraction patterns.

Experimental Results on a Rotatable Low Solidity Vaned Diffuser

Abstract: This paper reviews test results from a rotatable low solidity vaned diffuser (RLSD). The device was installed in a single stage test vehicle consisting of a pseudo-return channel inlet, a subsonic centrifugal impeller (approx. 2:1 pressure ratio), the rotatable diffuser, a return channel and a dump collector. Static taps, total pressure probes, and thermocouples were located in critical areas throughout the stage. Manual traverse probes measured the pressure and angle profiles at RLSD leading and trailing edges. Results for various stagger angles, leading edge radius ratios, etc. are presented in terms of pressure recovery (Cp) and loss coefficient (LC). Comments are made regarding the applicability of the RLSD in production units.Copyright © 1992 by ASME

Investigation into Development of Liquid Layer and Formation of Surface Plasma During CO2 Laser Cutting Process

Abstract: Interaction studies between the liquid metal and gas jet during laser cutting were made and relationships between the various parameters influencing the cutting action were identified theoretically. In the theoretical analysis, the effect of the jet on the process, due to jet momentum and the interface (gas-liquid) shear stress, were considered. On the experimental side, the work was carried out in two parts. In the first part, cutting of mild steel at the different thickness levels was carried out using an argon/oxygen gas mixture at 5/1 pressure ratio and 138 kPa total pressure. The depth of resolidification around the keyhole resulted from the cutting process and was examined microscopically. In the second part, the motion of plasma generated during the laser cutting process was monitored using a CCD (icharge coupled device) camera, fibre-optic probe and microlens camera. In this case oxygen was used as the assisting gas.

Three-dimensional compressible turbulent computations for a nondiffusing S-duct

Abstract: The PARC3D code was used to compute the compressible turbulent flow within a three dimensional, nondiffusing S-duct. A frame of reference is provided for future computational fluid dynamics studies of internal flows with strong secondary flows and provides an understanding of the performance characteristics of a typical S-duct with attached flow. The predicted results, obtained with both H- and O-grids, are compared with the experimental wall pressure, static and total pressure fields, and velocity vectors. Additionally, computed boundary layer thickness, velocity profiles in wall coordinates, and skin friction values are presented.

Pressure and temperature dependence of the kinetics of the reaction aluminum + carbon dioxide

Abstract: We measured the pressure and temperature dependence of the rate constants of the reaction of Al+CO 2 between 10 and 600 Torr total pressure and 298 and 1215 K in our high-temperature reactor. The Al atoms were generated by the 248-nm photolysis of Al(CH 3 ) 3 and probed by laser-induced fluorescence. Below 700 K, the rate constants show a strong pressure dependence suggesting that the reaction is proceeding through a complex formation mechanism with some decomposition of the complex to the products AlO and CO.

Reactions within quartz-carbon mixtures in a nitrogen atmosphere

Abstract: A number of carbon-quartz mixtures have been heat-treated in nitrogen at different pressures. The experiments were performed in a gas autoclave (pressure = 0·1–6 MPa, temperature = 1400–1680°C) allowing nitrogen to flow through the sample holder at a controlled rate, with continuous measurement of carbon monoxide in the exhaust gas. The samples were characterised by electron microscopy and elemental analyses, X-ray diffraction techniques and differential scanning calorimetry. The degree of conversion to Si 3 N 4 in mixtures of different types was determined and compared with the amount of quartz consumed. It was found that by rapid heating (20°C/min) to high temperatures (1550, 1680°C) even a fairly coarse-grained SiO 2 -reagent (1 m 2 /g) is rapidly transformed to amorphous SiO 2 , with just a minor part converted to Si 3 N 4 . The nitridation process during this initial stage, and the subsequent continuous heating, is governed by temperature, total pressure, nitrogen flow rate and SiO 2 and C surface areas. The relative importance of these parameters for the Si 3 N 4 yield is discussed. Nitridation was virtually complete after 1 h annealing of a mixture with a SiO 2 surface area of 1 m 2 /g at a high nitrogen flow ⋍ 20 litres/min. The SiO evaporation was found to be rate controlling under these conditions.

Total pressure measurements for pentane + methanol + ethanol at 303.15 K

Abstract: In this paper total pressure is reported as a function of liquid-phase composition for pentane + methanol + ethanol at 303.15 K. The data were reduced using Barker's method. The excess Gibbs energy of the liquid phase is represented by a rational function obtained by making an empirical modification to the nonrandom two-liquid (NRTL) equation. The resulting fit to the data is superior to that obtained using a previous representation based on a modified Margules equation.

Process Study of Silicon Carbide Coatings Deposited on Steel by Plasma-Assisted Chemical Vapor Deposition from Tetramethylsilane-Argon Gas System

Abstract: Silicon carbide coatings were prepared in an RF plasma-assisted chemical vapor deposition (CVD) device from the tetramethylsilane-argon gas system. The present paper is devoted to investigation of the plasma process and determination of the deposition rate with the experimental parameters. By employing the general convective diffusion equation, we obtain a simple analytical expression of the deposition rate. Calculated results are compared with experimental data. The agreement between calculated and measured results as functions of total pressure, total flow rate, reactant composition, and plasma geometry is fairly good. The kinetic parameters selected are found to have a reasonable order of magnitude in comparison to those of other studies.

Rotating disc gauge for absolute total pressure measurement in high vacuum

Abstract: An absolute vacuum gauge exploiting molecular drag between coaxial discs, a configuration suggested by Langmuir, is being further investigated. The device operates in a range similar to that of the spinning rotor gauge. It consists of a silicon disc 92 mm in diameter suspended on a calibrated torsion fiber a few mm above a metal disc of the same size which rotates at speeds up to 50 000 rpm. Molecules leaving this rotor communicate a torque to the suspended disc by molecular drag. The angular deflection thus produced is sensed optically and is about 2° at 10−6 mbar. The critical factors relevant to absolute measurement, such as tangential momentum accommodation, geometry, and edge effects have been investigated and experimental comparisons with a spinning rotor gauge demonstrate that absolute pressure measurements with uncertainty better than ±5% are possible at pressures ∼ 10−6 mbar. Measurements of similar uncertainty will be possible at 10−7 mbar.

The Thermodynamic Behavior of the Si‐H System and Its Role in Si‐CVD from SiH4

Abstract: Thermodynamic calculations of the Si-H system were performed at typical chemical vapor deposition conditions of total pressure, partial pressure of SiH 4 , ambient, and temperature. Effects of the conditions on the equilibria of the system were examined, and homogeneous reaction mechanisms in the system were qualitatively discussed. The main conclusions include that Si deposition at low temperatures is due to SiH 4 alone and high-temperature film deposition is dominated by gaseous silane intermediates produced through homogeneous reactions of SiH 4

Elementary Model to Predict the Pressure Loss across a Spacer Grid Without a Mixing Vane

Abstract: A simple rational-based model is developed to predict the pressure loss of a pressurized water reactor-type nonmixing vaned spacer grid. The total pressure loss is obtained by adding the form and friction losses. Elementary fluid-mechanical correlations are used to model each loss. The model reasonably predicts the available spacer grid loss data.