Showing papers on "Total pressure published in 2007"

Self-healing mechanisms of a SiC fiber reinforced multi-layered ceramic matrix composite in high pressure steam environments

Abstract: Non-oxide ceramic matrix composites are potential candidates to replace the current nickel-based alloys for a variety of high temperature applications in the aerospace field. The durability of a SiC ( f ) /PyC ( i ) /[Si,C,B] ( m ) composite with a sequenced self-sealing matrix and Hi-Nicalon fibers was investigated at 600 °C for exposure durations up to 600 h. The specimens are aged in a variety of slow-flowing air/steam gas mixtures and total pressures, ranging from atmospheric pressure with a 10–50% water vapor content to 1 MPa with 10–20% water vapor content. The degradation of the composite was determined from the measurement of residual strength and strain to failure on post-exposure specimens and correlated with microstructural observations, weight changes and characterizations of the generated oxides. All of the post-exposure characterizations demonstrate the ability of the sequenced [Si,C,B] matrix to protect the PyC interphase from environmental attacks. Two different oxidation modes of the matrix, depending on the total pressure are discussed in terms of the reactivity of the boron-containing layers, and their relative positions in the sequenced matrix. In high pressure environments, a strong localized dissolving of a small amount of SiC fibers in the boria-containing oxide is evidenced at 600 °C.

Method and apparatus for detecting conditions conducive to ice formation

Abstract: A method for detecting ambient conditions conducive to ice formation. The method includes the steps of measuring at least one parameter selected from a group of parameters consisting of a static pressure, a total pressure, a total temperature, a dew point temperature, and a liquid water content, and determining whether ambient conditions are conducive to ice formation based on the measured parameter.

Neutral gas density depletion due to neutral gas heating and pressure balance in an inductively coupled plasma

Abstract: The spatial distribution of neutral gas temperature and total pressure have been measured for pure N2, He/5%N2 and Ar/5%N2 in an inductively coupled plasma (ICP) reactor, and a significant rise in the neutral gas temperature has been observed. When thermal transpiration is used to correct total pressure measurements, the total pressure remains constant regardless of the plasma condition. Neutral pressure is depleted due to the pressure balance when the plasma pressure (mainly electron pressure) becomes comparable to the neutral pressure in high density plasma. Since the neutral gas follows the ideal gas law, the neutral gas density profile was obtained from the neutral gas temperature and the corrected neutral pressure measurements. The results show that the neutral gas density at the centre of the plasma chamber (factor of 2–4 ×) decreases significantly in the presence of a plasma discharge. Significant spatial variation in neutral gas uniformity occurs in such plasmas due to neutral gas heating and pressure balance.

Ordered growth of tilted ZnO nanowires: morphological, structural and optical characterization

Abstract: Tilted ZnO nanowires have been grown by high-pressure pulsed laser deposition (PLD) on m-plane sapphire without employing any catalyst species. The nanowires are inclined 30° with respect to the substrate normal and show well-defined epitaxial relationships with the m-plane sapphire substrate, the projection of the nanowires' axis being parallel to the in-plane sapphire direction. Two sets of nanowires, differing in diameter and length, coexist within the initial growth stages, but only the narrowest and longest nanowires are found to keep on growing as deposition proceeds. A systematic study of the effects of growth conditions, including number of pulses, temperature, total pressure and oxygen partial pressure, has been carried out to determine those conditions under which a completely ordered array of tilted nanowires, with a minimum angular distribution, is obtained. Among the growth conditions, temperature and oxygen partial pressure are seen to mainly affect the nanowires' axial and lateral growth rates, respectively, while the total chamber pressure allows monitoring of the evolution from thin film growth, at low pressure, to a mixture of nanowire/nanobelt growth, at high pressure. Finally, cathodoluminescence (CL) shows that low growth temperatures and high oxygen partial pressures improve the overall optical quality of the ZnO nanowire arrays.

Growth kinetics of enstatite reaction rims studied on nano-scale, Part I: Methodology, microscopic observations and the role of water

Abstract: The kinetics of (Mg, Fe)SiO3 pyroxene layer growth within silicate thin films with total thickness <1 μm was studied experimentally at 0.1 MPa total pressure, controlled fO2 and temperatures from 1,000 to 1,300°C. The starting samples were produced by pulsed laser deposition. Layer thickness before and after the experiments and layer composition as well as microstructures, grain size and shape of the interfaces were determined by Rutherford back scattering and transmission electron microscopy assisted by focused ion beam milling. Due to the miniaturization of the starting samples and the use of high resolution analytical methods the experimentally accessible temperature range for rim growth experiments was extended by about 300°C towards lower temperatures. The thickness of the layers at a given temperature increases proprotional to the square root of time, indicating a diffusion-controlled growth mechanism. The temperature dependence of rim growth yields an apparent activation energy of 426 ± 34 kJ/mol. The small grain size in the orthopyroxene rims implies a significant contribution of grain boundary diffusion to the bulk diffusion properties of the polycrystalline rims. Based on microstructural observations diffusion scenarios are discussed for which the SiO2 component behaves immobile relative to the MgO component. Volume diffusion data for Mg in orthopyroxene from the literature indicate that the measured diffusivity is probably controlled by the mobility of oxygen. The observed reaction rates are consistent with earlier results from dry high-temperature experiments on orthopyroxene rim growth. Compared to high pressure experiments at 1,000°C and low water fugacities, reaction rates are 3–4 orders of magnitude smaller. This observation is taken as direct evidence for a strong effect of small amounts of water on diffusion in silicate polycrystals. In particular SiO2 changes from an immobile component at dry conditions to an extremely mobile component even at very low water fugacities.

Migration of Combustor Exit Profiles Through High Pressure Turbine Vanes

Abstract: The high pressure turbine stage within gas turbine engines is exposed to combustor exit flows that are nonuniform in both stagnation pressure and temperature These highly turbulent flows typically enter the first stage vanes with significant spatial gradients near the inner and outer diameter endwalls These gradients can result in secondary flow development within the vane passage that is different than what classical secondary flow models predict The heat transfer between the working fluid and the turbine vane surface and endwalls is directly related to the secondary flows The goal of the current study was to examine the migration of different inlet radial temperature and pressure profiles through the high turbine vane of a modern turbine engine The tests were performed using an inlet profile generator located in the Turbine Research Facility at the Air Force Research Laboratory Comparisons of area-averaged radial exit profiles are reported as well as profiles at three vane pitch locations to document the circumferential variation in the profiles The results show that the shape of the total pressure profile near the endwalls at the inlet of the vane can alter the redistribution of stagnation enthalpy through the airfoil passage significantly Total pressure loss and exit flow angle variations are also examined for the different inlet profiles

Experimental Research on Aerodynamic Performance and Exit Flow Field of Low Pressure Axial Flow Fan with Circumferential Skewed Blades

Abstract: In this article, the low pressure axial flow fan with circumferential skewed rotor blade, including the radial blade, the forward-skewed blade and the backward-skewed blade, was studied with experimental methods. The aerodynamic performance of the rotors was measured. At the design condition at outlet of the rotors, detailed flow measurements were performed with a five-hole probe and a Hot-Wire Anemometer (HWA). The results show that compared to the radial rotor, the forward-skewed rotor demonstrates a wider Stable Operating Range (SOR), is able to reduce the total pressure loss in the hub region and make main loading of blade accumulating in the mid-span region. There is a wider wake in the upper mid-span region of the forward-skewed rotor. Compared to the radial rotor, in the backward-skewed rotor there is higher total pressure loss near the hub and shroud regions and lower loss in the mid-span region. In addition, the velocity deficit in the wake is lower at mid-span of the backward-skewed rotor than the forward-skewed rotor.

RF Magnetron Sputtering Growth of Epitaxial SrRuO3 Films with High Conductivity

Abstract: SrRuO3 films were grown on (001)SrTiO3 single crystal substrates by rf magnetron sputtering under various total pressures, and their crystal structure, room temperature resistivity, and temperature dependency of resistivity were investigated High-resolution X-ray diffraction (XRD) analysis revealed that the unit cell volume of these films decreased with increasing total pressure from 13 to 27 Pa and was almost constant above 27 Pa corresponding to that of bulk SrRuO3 SrRuO3 films deposited under a total pressure of 27 Pa showed the lowest room temperature resistivity, ie, 250 µΩcm, almost the same as the reported one of the SrRuO3 single crystal This film also showed a positive temperature dependency of resistivity with a temperature dependency change at about 150 K, which was also in good agreement with the reported one of the SrRuO3 single crystal

Effect of acetic acid on co2 corrosion of carbon steel in vapor-water two-phase horizontal flow

Abstract: The effect of acetic acid on the corrosion behavior of X 65 and C 1018 carbon steel in vapor-water two-phase stratified flow (Vsg: 2 m/s; Vsl: 0.1 m/s) at 2 bars total pressure, 1.54 bars CO2 partial pressure, pH 5.5, and 80°C was studied in a low pressure-high temperature multiphase flow horizontal loop using electrochemical and mass loss techniques. The liquid phase is composed of 1% NaCl aqueous solution containing different concentrations of acetic acid (500 to 5000 ppm total acetic acid), and the gas phase is composed of CO2-acetic acid-water vapor mixture. The corrosion rates, on both the top and bottom of the line, increase with increase in acetic acid concentration, which was attributed to the contribution of hydrogen ions by the free acetic acid to the cathodic reaction. Partial coverage of the metal surface by FeCO3 on both the top and bottom of the line is reported to be responsible for the observed localized corrosion. Surface analysis investigated with SEM and XRD is reported. A vapor-liquid ...

Hydroformylation of Cyclohexene with Carbon Dioxide and Hydrogen Using Ruthenium Carbonyl Catalyst: Influence of Pressures of Gaseous Components

Abstract: Hydroformylation of cyclohexene was studied with a catalyst system of Ru3(CO)12 and LiCl using H2 and CO2 instead of CO in NMP. The influence of H2 and CO2 pressures on the total conversion and the product distribution was examined. It was shown that increasing total pressure of H2 and CO2 promoted the reverse water gas shift reaction and increased the yield of cyclohexanecarboxaldehyde. Its hydrogenation to cyclohexanemethanol was promoted with increasing H2 pressure but suppressed with increasing CO2 pressure. Cyclohexane was also formed along with those products and this direct hydrogenation was suppressed with increasing CO2 pressure. The roles of CO2 as a promoter as well as a reactant were further examined by phase behavior observations and high pressure FTIR measurements.

Modeling the solubility of ternary mixtures of ethylene, iso-pentane, n-hexane in semicrystalline polyethylene

Abstract: The coabsorptions of ethylene and iso-pentane, and ethylene and n-hexane were measured by the use of a pressure decay method. The solubility data of ethylene-iso-pentane and ethylene-n-hexane in semicrystalline polyethylene (PE) of crystallinity of 48.6% were obtained at temperatures 70, 80, and 90 °C, and the total pressure 2 MPa, iso-pentane partial pressure 80–190 KPa, n-hexane partial pressure 20–90 KPa. The presence of iso-pentane or n-hexane in the corresponding ternary system leads to increase the solubility of ethylene, while the solubility of iso-pentane or n-hexane remains unchanged with an increase of the ethylene partial pressure, even slightly decreases. Assumed that the presence of iso-pentane or n-hexane decreases the crystallinity of the polymer sample, a coabsorption model was built to model the solubility of each gas in the ternary systems. The relative root mean square errors of the coabsorption model for ethylene-iso-pentane-PE system and ethylene-n-hexane-PE system are 5.13% and 4.64%, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3654–3662, 2007

Optimization Design and Experimental Study of Low-Pressure Axial Fan with Forward-Skewed Blades

Abstract: This paper presents an experimental study of the optimization of blade skew in low pressure axial fan. Using back propagation (BP) neural network and genetic algorithm (GA), the optimization was performed for a radial blade. An optimized blade is obtained through blade forward skew. Measurement of the two blades was carried out in aerodynamic and aeroacoustic performance. Compared to the radial blade, the optimized blade demonstrated improvements in efficiency, total pressure ratio, stable operating range, and aerodynamic noise. Detailed flow measurement was performed in outlet flow field for investigating the responsible flow mechanisms. The optimized blade can cause a spanwise redistribution of flow toward the blade midspan and reduce tip loading. This results in reduced significantly total pressure loss near hub and shroud endwall region, despite the slight increase of total pressure loss at midspan. In addition, the measured spectrums show that the broadband noise of the impeller is dominant.

A Coupling Model of Water Flows and Gas Flows in Exhausted Gas Bubble on Missile Launched Underwater

Abstract: The gas and water flows during an underwater missile launch are numerically studied. For the gas flow, the explicit difference scheme of Non-oscillation and Non-free-parameter Dissipation (NND) is utilized to solve the Euler equations for compressible fluids in the body-fitted coordinates. For the water flow, the Hess-Smith method is employed to solve the Laplace equation for the velocity potential of irrotational water flows based on the potential theory and the boundary element method. The hybrid Eulerian-Lagrangian formulation for the free boundary conditions is used to compute the changes of the free surface of the exhausted gas bubble in time stepping. On the free surface of the exhausted gas bubble, the matched conditions of both the normal velocities and pressures are satisfied. From the numerical simulation, it is found that the exhausted gas bubble grows more rapidly in the axial direction than in the radial direction and the bubble will shrink at its “neck” finally. Numerical results of the movement of the shock wave and the distribution of the Mach number and the gas pressure within the bubble were presented, which reveals that at some time, the gas flow in the Laval nozzle is subsonic and the gas pressure in the nozzle is very high. Influences of various initial missile velocities and chamber total pressures and water depths on both the time interval when the gas flow in the nozzle is subsonic and the peak of the gas pressure at the nozzle end were discussed. It was suggested that a reasonable adjustment of the chamber total pressure can improve the performance of the engine during the underwater launch of missiles.

Method and device for measuring the gas permeability through films and walls of containers

Abstract: A device for measuring permeability to a gas sample through a thin film, or a wall (2), arranged at membrane between a first and a second chamber (3 and 4) of a measurement cell (1) comprises, upstream from each inlet to the measurement cell (1), a respective regulator of pressure (β and 9) associated with a respective pressure sensor (5 and 8), and can comprise an humifier. The device comprises, furthermore, valves (11 and 12) adapted to switch the flows of gas between a starting wash and a measurement step. Each gas flow is, moreover, adjusted at the exit means of a respective flow regulator (15 and 16). A control unit (23), operates the pressure regulators (6 and 9) and flow regulators (15 and 18) in order to keep at predetermined values the total pressure in the first and in the second chamber (3 and 4), said values being always equal to each other.

Formation Mechanism of Porous Alumina With Oriented Cylindrical Pores Fabricated by Unidirectional Solidification

Abstract: Porous alumina whose pores were aligned in one direction was fabricated by the unidirectional solidification method under a pressurized hydrogen atmosphere. The porous structure is formed at the solid–liquid interface during solidification due to a hydrogen solubility gap at the melting point. The hydrogen gas is dissolved into molten alumina according to Sieverts' law and insoluble gas that corresponds to the amount of solubility gap evolves from the solid phase at the solid–liquid interface during the unidirectional solidification to form the pores. The porosity and pore size of the solidified samples decreased with increasing total pressure where the environmental gas consisted of pure hydrogen or hydrogen–argon mixed gases. There is a reverse proportion relation between the pore diameter and the total pressure according to Boyle's law.

Fluid-dynamic optimality in the generation-averaged length-to-diameter ratio of the human bronchial tree.

Abstract: It is shown in this paper that the nearly constant length-to-diameter ratio observed with conducting airways of human bronchial tree can be explained based on the fluid dynamic optimality principle. In any branched tube there are two pressure loss mechanisms, one for wall friction in the tube section and the other for flow division in the branching section, and there exists an optimal length-to-diameter ratio which minimizes the total pressure loss for a branched tube in laminar flow condition. The optimal length-to-diameter ratio predicted by the pressure loss minimization shows an excellent agreement with the length-to-diameter ratios found in the human conducting airways.

Measurement and Analysis of Aerodynamic and Thermodynamic Losses in Pre-Swirl System Arrangements

Abstract: In order to separately describe the dominating loss mechanisms in pre-swirled cooling air delivery systems, discharge, temperature and velocity measurements were performed for numerous designs. Whereas pre-swirl nozzles, as first component, were characterized by their discharge coefficients, total pressure losses occurring at the inlet of the receiver holes were correlated depending on the incident angle of the cooling flow. To quantify losses generated inside the rotor-stator gap, flow velocity data, acquired by means of 3D PIV, were compared to total temperature measurements. In addition the influence of wall friction and mixing losses due to the strong velocity gradients inside the preswirl chamber was discussed by means of a simple loss model. Finally, dimensionless loss coefficients, discharge behaviour and expected cooling temperature can be predicted for a family of realistic pre-swirl systems. Moreover, this detailed description of the losses provides a methodology to quantify the impact of individual loss sources on the global efficiency of the pre-swirl system, thus allowing improved designs.Copyright © 2007 by ASME

OMC-1: A Cool Arching Filament in a Hot Gaseous Cavity: Geometry, Kinematics, Magnetic Vectors, and Pressure Balance

Abstract: We have assembled data on large (Galactic shell), middle (filament), and small (protostar) scales. OMC-1 is embedded in a hot cavity. Here we have made multiconstituent (gas/dust/field) homogeneous maps of the central part of the OMC-1 filament, covering an area of 2' ? 2'. We find here that the vertical filament has a turbulent pressure about equal to the magnetic pressure; its total pressure roughly equals that in the surrounding medium. The magnetic field crosses the filament with an estimated strength of 300-350 ?G in the sky plane. It could be an externally wrapped U-shaped magnetic field going around the filament (due to a large shock front traveling in the cavity), or else an internally generated helical field (of unknown origin). Near the OMC-1 map center, we map the low-velocity outflow near IRc2-source I, with a pattern of blue south-southwest gas and red north-northeast gas. Our James Clerk Maxwell Telescope data yield a plane-of-sky field of 2.4-2.6 mG across the outflow; this strength nearly equals the published Zeeman line-of-sight data. Farther out, the Zeeman data show a negative magnetic field, possibly suggesting a pole-on dipolar field.

Gasification kinetics of five coal chars with CO2 at elevated pressure

Abstract: For five coals, the reactivity of char-CO2 gasification was investigated with a pressurized thermogravimetric analyzer (PTGA) in the temperature range 850-1,000 C and the total pressure range 0.5-2.0 MPa. The effect of coal rank, initial char characteristics and pressure on the reaction rate were evaluated for five coal chars. The reactivity of low lank coal char was better than that of high rank coal char. It was found that Meso/macro-pores of char markedly affect char reactivity by way of providing channels for diffusion of reactant gas into the reactive surface area. Over the range of tested pressure, the reaction rate is proportional to CO2 partial pressure and the reaction order ranges from about 0.4 to 0.7 for five chars. Kinetic parameters, based on the shrinking particle model, were obtained for five chars.