Showing papers on "Total pressure published in 1997"

Adsorption of CH4−CF4 Mixtures in Silicalite: Simulation, Experiment, and Theory

Abstract: Grand canonical Monte Carlo (GCMC) simulations of binary Lennard-Jones mixtures in the zeolite silicalite have been used to predict the adsorption of CH4 and CF4 mixtures as a function of gas phase composition, total pressure, and temperature. For single components and mixtures, predictions of adsorption isotherms and isosteric heats are in good agreement with experiment at room temperature. Within the experimental pressure range of 0 to 17 bar, the mixtures are well described by the ideal adsorbed solution (IAS) theory. For very high loading, deviations from IAS theory appear. The configurations generated in the simulation were used to calculate sorbate−zeolite interaction energy distributions for different types of siting locations within the zeolite pores. These distributions display a pore shape related energetic heterogeneity in different regions of silicalite. Near saturation at a total loading of 12 molecules per unit cell, the shape of the observed energy distribution is relatively independent of ...

Analysis of the Synchrotron Emission from the M87 Jet

Abstract: We propose that the intensity changes and spectral evolution along the M87 jet can be explained by adiabatic changes to the particle momentum distribution function and the magnetic field. This is supported by the lack of any significant variation in the radio-to-optical spectral index along the jet and by the moderate changes in radio brightness. Assuming a simple scaling law between magnetic field and density, we use the deprojection of a 2 cm VLA intensity map by Sparks, Biretta, & Macchetto to predict the spectral evolution along the jet. We derive limits for the magnetic field and the total pressure by comparing our results with the spatially resolved fit to the spectral data by Neumann, Meisenheimer, & Roser of a model spectrum that cuts off at ≈ 1015 Hz. To explain the weakness of synchrotron cooling along the jet, the magnetic field strength must lie below the equipartition value. Although the inferred pressure in the limit of nonrelativistic bulk flow lies far above the estimated pressure of the interstellar matter in the center of M87, bulk Lorentz factors Γjet in the range of 3-5 and inclination angles θLOS 25° lead to pressure estimates close to the interstellar medium pressure. The average best-fit magnetic fields we derive fall in the range of 20-40 μG, departing from equipartition by a factor ≈ 1.5-5. This model is consistent with the proposal by Bicknell & Begelman that the knots in the M87 jet are weak, oblique shocks. First-order Fermi acceleration will then have a minimal effect on the slope of the radio-to-optical spectrum while possibly accounting for the X-ray spectrum.

Semidilute and Concentrated Polymer Solutions near Attractive Walls: Dynamic Monte Carlo Simulation of Density and Pressure Profiles of a Coarse-Grained Model

Abstract: Using a bead−spring model of flexible polymer chains, we study polymer adsorption from solutions onto attractive planar walls, varying both the strength of the adsorption potential e and the concentration of the solution over a wide range. Treating the case of good solvents, the profiles of density and pressure are computed and it is shown that thermal equilibrium between the adsorbed layer and the bulk solution is obtained. The case of a wall with purely repulsive potential under otherwise identical conditions is treated for comparison. It is shown that for the strongly adsorbing wall there is a pronounced layering, while a layered structure at the repulsive wall occurs only for high concentrations, and this layering is also much weaker. These features carry over to the profile of the total pressure as well. From the difference in the pressure components in the parallel and perpendicular directions we compute also the interfacial energy between the polymer film and the repulsive wall as a function of the...

Preparation and Characterization of Iridium Oxide Thin Films Grown by DC Reactive Sputtering

Abstract: Iridium oxide ( IrO2) thin films were successfully grown by a DC magnetron reactive sputtering method. It was found that the crystalline nature and morphology of IrO2 films were strongly dependent on the oxygen partial pressure, total pressure and growth temperature. The growth of IrO2 is well explained by the generic curve for the total pressure as a function of O2 content. The films showed good barrier performance between Pt and poly-Si up to 750° C. A 40-nm-thick Ba0.5Sr0.5TiO3 film was grown by RF magnetron sputtering on the Pt/IrO2/poly-Si electrode. The leakage current density and dielectric constant of a Pt/Ba0.5Sr0.5TiO3/Pt capacitor on the IrO2/poly-Si electrode were comparable to those of the capacitor on a SiO2/Si substrate. However, an additional ohmic layer was required to prevent the formation of a SiO2 layer between the IrO2 and poly-Si.

A pulse-expansion wave tube for nucleation studies at high pressures

Abstract: The design and performance of a new pulse-expansion wave tube for nucleation studies at high pressures are described. The pulse-expansion wave tube is a special shock tube in which a nucleation pulse is formed at the endwall of the high pressure section. The nucleation pulse is due to reflections of the initial shock wave at a local widening situated in the low pressure section at a short distance from the diaphragm. The nucleation pulse has a duration of the order of 200 μs, while nucleation pressures that can be achieved range from 1 to 50 bar total pressure. Droplet size and droplet number density can accurately be determined by a 90°-Mie light scattering method and a light extinction method. The range of nucleation rates that can be measured is 108 cm-3 s-1

Production of , , , , and in and (50 - 50) - mixtures exposed to negative coronas

Abstract: This study concerns the production of , , , , and when is subjected to negative polarity corona discharges of varying durations (with transported charges of 1.5, 4 and 6 C) performed with a point-to-plane set-up using a stainless steel or aluminium plane electrode. During the experiments, the parameters varied were the way the measurement cell was prepared (clean and very clean), the pressure (50 to 400 kPa), the concentration of additives such as (0 to 50%) for total gas pressures of 200 kPa and 300 kPa, water (0 to 0.2%) and oxygen (0 to 1%) for a total pressure of 300 kPa. Analyses were carried out using gas phase chromatography. The mode of preparation of the cell proved to be representative of the action of impurities such as water and oxygen on each of the compounds studied. This effect was all the stronger when the pressure was low. In the very clean conditions (effect of and reduced to a minimum) we observed a decrease of the quantities of the main products formed as the pressure or the percentage of was increased. Concerning the effect of the small quantities of added water and oxygen studied in both pure and in the 50 - 50 - mixture, the results showed that, overall, the oxygen and the water enhance the production of all the sulphur oxyfluorides from the fragments (except for which is inhibited by oxygen to the benefit of ) and inhibit the production of . The presence of 50% , a fluorine source, inhibited the production of all the compounds studied independently of the transported charge, the metal used for the plane electrode and the percentages of impurities (, ) added.

Structures and Dynamics Committee Best Paper of 1996 Award: Inlet Distortion Generated Forced Response of a Low-Aspect-Ratio Transonic Fan

Abstract: This paper describes a portion of an experimental and computational program (ADLARF), which incorporates, for the first time, measurements of all aspects of the forced response of an airfoil row, i.e., the flow defect, the unsteady pressure loadings, and the vibratory response. The purpose of this portion was to extend the knowledge of the unsteady aerodynamics associated with a low-aspect-ratio transonic fan where the flow defects were generated by inlet distortions. Measurements of screen distortion patterns were obtained with total pressure rakes and casing static pressures. The unsteady pressure loadings on the blade were determined from high response pressure transducers. The resulting blade vibrations were measured with strain gages. The steady flow was analyzed using a three-dimensional Navier-Stokes solver while the unsteady flow was determined with a quasi-three-dimensional linearized Euler solver. Experimental results showed that the distortions had strong vortical, moderate entropic, and weak acoustic parts. The three-dimensional Navier-Stokes analyses showed that the steady flow is predominantly two-dimensional, with radially outward flow existing only in the blade surface boundary layers downstream of shocks and in the aft part of the suction surface. At near resonance conditions, the strain gage data showed blade-to-blade motion variations and thus, linearized unsteady Euler solutionsmore » showed poorer agreement with the unsteady loading data than comparisons at off-resonance speeds. Data analysis showed that entropic waves generated unsteady loadings comparable to vortical waves in the blade regions where shocks existed.« less

Hydroisomerization of n-hexane on Pt/SO42--ZrO2: effect of total and hydrogen partial pressure

Abstract: The effect of both total pressure and hydrogen partial pressure during the n-hexane isomerization on Pt/SO4 2™-ZrO2 at 200°C and 4 h™1 weight hourly space velocity was studied. Total pressure was varied between 1.0 and 10.0 kg cm-2; different hydrogen partial pressures were obtained by dilution with nitrogen keeping the total pressure at 6 kg cm-2. The n-hexane isomerization activity increases when increasing either total pressure or hydrogen partial pressure. Methylpentanes are the C6 isomers formed in major proportion and the 2-methylpentane/3-methylpentane ratio practically reaches the equilibrium value in most of cases. Isomerization is always accompanied by hydrocracking. Hydrogenolysis products were not observed, the main cracking products being propane, isobutane and isopentane; then, the cracking product distribution cannot be interpreted by considering an intramolecular rearrangement of carbocation intermediates. A slight deactivation takes place with time-on- stream. The lifetime of surface intermediates is longer in the absence of hydrogen or at a low hydrogen partial pressure; it allows oligomerization and cracking to prevail at short times and polymerization and coke formation at long times.

Prediction Equations for Gases in Flexible Modified-Atmosphere Packages of Respiring Produce are Different Than Those for Rigid Packages

Abstract: Total pressure generally decreases in a sealed rigid package containing respiring produce, whereas total pressure is essentially constant and free volume decreases in a flexible package. We found that predicted O 2 , CO 2 , and N 2 partial pressures were different for similarly designed (same surface area, thickness, film permeabilities and produce mass) flexible and rigid packages at quasi steady state and steady state, respectively. Predicted O 2 and CO 2 partial pressures were slightly higher in a flexible package than in a rigid package and were a function of the film permeability ratio of N 2 to O 2 and of CO 2 to O 2 . They also related to the ratio of product CO 2 production rate to O 2 uptake rate, target steady-state O 2 partial pressure, and respiration characteristics. Differences were slight for films such as low-density polyethylene.

Adsorption of nitrogen, methane, carbon monoxide, and their binary mixtures on aluminophosphate molecular sieves

Abstract: Experimental isotherms describing the adsorption of pure N2, CH4 and CO in AlPO4-11, AlPO4-17, and AlPO4-18 were determined using the volumetric method at 40°C and at 23°C (AlPO4-11 only) over a pressure range up to 123 kPa, and subsequently fitted with the Langmuir or Freundlich equations, as well as the Flory-Huggins Vacancy Solution Theory equation. The capacities for the adsorbates investigated were found to depend on the geometry of the sieve pore size, as well as the molecular dimensions and the polority of the adsorbate involved. At 40°C and over the investigated pressure range, AlPO4-11 and AlPO4-17 adsorbed pure CH4 in the highest amounts, while AlPO4-18 had a slightly higher capacity for pure CO. The model parameters obtained by fitting the experimental pure-component isotherms permitted the prediction of binary adsorption information for the CO−N2, CH4−CO, and CH4−N2 gas mixtures at 101.3 kPa total pressure, using the Extended Langmuir Model, the Ideal Adsorbed Solution Theory, and/or the Flory-Huggins Vacancy Solution Theory for mixtures. An explanation of the behaviour predicted by each model for each adsorption system is attempted.

Magnetoacoustic wave propagation in current sheets

Abstract: Magnetoacoustic waves in a Harris neutral current sheet are investigated. The magnetic eld strength, Alfven speed,soundspeedandplasmadensityvarycontinuouslyacross the structure. The sheet supports body, surface and hybrid modes. Two surface modes exist (a kink and a sausage). In ad- dition, fundamental and harmonic body waves are found when their phase speeds approach the maximum Alfven speed in the sheet.Asthephasespeedsofthemodesdecrease,thewaveshave properties of both body and surface mode s{ah ybrid wave. In the long wavelength limit the phase speed of the fundamental kink body mode and sausage surface mode approach the maxi- mumAlfvenandtubespeedsrespectively.Atshortwavelengths, the phase speeds tend to constant values, each pair of kink and sausage modes merging after passing through the maximum value of the sound speed, c max . For all modes, in the inner part of the current sheet, the gas pressure is out of phase with the magnetic pressure, with the gas pressure dominating (a prop- erty of a slow mode). In the outer part of the sheet the magnetic pressure is in phase with the total pressure (a fast mode charac- teristic).Nopurelyfastorslowmodeexists.Foruniformdensity a minimum in the group velocity occurs only for the fundamen- tal kink mode. For the Epstein density prole, minima in the group velocity are found for the other modes also. Impulsively generated waves are expected to show temporal variations that are similar to observations of oscillations of radio and X-ray emission of the solar corona and neutral sheet oscillations in the Earth's magnetotail. Calculated periods of oscillation are in good agreement with observations.

Numerical and experimental study of a homogenizer impinging jet

Abstract: High-pressure homogenization is a key unit operation used to disrupt cells containing intracellular bioproducts. Modeling and optimization of this unit are restrained by a lack of information on the flow conditions within a homogenizer value. A numerical investigation of the impinging radial jet within a homogenizer value is presented. Results for a laminar and turbulent (k-epsilon turbulent model) jet are obtained using the PHOENICS finite-volume code. Experimental measurement of the stagnation region width and correlation of the cell disruption efficiency with jet stagnation pressure both indicate that the impinging jet in the homogenizer system examined is likely to be laminar under normal operating conditions. Correlation of disruption data with laminar stagnation pressure provides a better description of experimental variability than existing correlations using total pressure drop or the grouping 1/Y(2)h(2).

Temperature, pressure, and perturber dependencies of line-mixing effects in CO2 infrared spectra. I. Σ←Π Q branches

Abstract: Experimental and theoretical results on the influence of line mixing on the shape of infrared CO2 Q branches of importance for atmospheric applications are presented. Two Q branches of Σ←Π symmetry, which lie near 618 and 720 cm−1 and belong to the 1000II←0110I and 1000I←0110I bands, have been studied for many conditions of temperature (200–300 K), total pressure (0.5–10 atm), and mixture (with He, Ar, O2, and N2). The theoretical approach used is based on the Energy Corrected Sudden approximation; its parameters have been deduced from both line-broadening data and measured absorption by the Q branches. Comparisons between experimental and computed spectra demonstrate the quality of the model, regardless of the conditions. Detailed analysis of the influences of the Q-lines spectral spacing, temperature, total pressure, and collision partner are presented. They show that significantly larger line-mixing effects are obtained when CO2–He is considered with respect to CO2–(Ar,O2,N2). This is analyzed in terms...

Two-dimensional transport and wall effects in the thermal diffusion cloud chamber. I. Analysis and operations criteria

Abstract: In this paper we present results of a two-dimensional (z,r) treatment of the mass and energy transfer processes that occur during the operation of a thermal diffusion cloud chamber. The location of the wall is considered in solving the mass and energy transport equations, in addition to the vertical distance, z, between the upper and lower plate surfaces. We examine the effect of aspect (diameter to height) ratio on chamber operation; the effects of operation with either a dry or a wet interior chamber wall on temperature, supersaturation, nucleation rate, and total density profiles in the chamber; the effect of overheating the interior of the chamber wall on these conditions within the cloud chamber; and the effects associated with using different density background gases on the operation of the chamber. In a second paper, immediately following, we apply the formalism and the solutions developed in this paper to address the important problem of buoyancy-driven convection that can accompany (seemingly normal) operation of thermal diffusion cloud chambers in nearly all ranges of total pressure and temperature.

Experimental and Numerical Investigation of Boundary-Layer and Wake Development in a Transonic Turbine Cascade

Abstract: The flow in a transonic turbine rotor cascade is investigated by both experimental and numerical methods. Measurements include pressure profiles on the blade, total pressure profiles in the blade vane, boundary-layer and wake profiles. Computations are performed by two different solvers with different turbulence models and three different transition models. Results indicate that the introduction of transition models is necessary to have a realistic description of the flow field. Transition is shown to affect also the blade pressure distribution and shock strength mostly on the pressure side boundary layer. Experiments indicate the presence of trailing edge vortex shedding which is not captured by the steady computations. The transition models seem adequate for predicting the shock-boundary layer interaction which induces a small flow separation on the suction side.Copyright © 1997 by ASME

Mass and energy analyses of substrate-incident ions in TiO2deposition by RF magnetron sputtering

Abstract: Mass-resolved measurements of substrate-incident ion (SII) current and ion kinetic energy distributions (IEDs) were carried out for TiO2 deposition by rf (13.56 MHz) magnetron sputtering. Substrate-incident ion current was mainly composed of Ar+, O2+ and O+. Several minor ions, such as Ti+,TiO+, ArO+ and Ar2+ were also detected. The dominant species of substrate-incident ion was O2+ at a total pressure higher than 20 mTorr, while Ar+ was dominant one at a total pressure of 2 mTorr with which rutile TiO2 grew on a non-heated substrate. Variations in IEDs for Ar+ and O2+ against total gas pressure, oxygen flow rate and applied rf power were presented. The energy with peak intensity in IED and the mean ion energy increased with both decreasing pressure and increasing rf power. Strong correlation between IEDs and the growth of crystallized TiO2 were observed. Finally we discussed the growth condition of rutile TiO2 films based on the results including the dc self-bias voltage.

The Influence of Downstream Passage on the Flow Within an Annular S-Shaped Duct

Abstract: Experimental and numerical investigations were carried out to gain a better understanding of the flow characteristics within an annular S-shaped duct, including the influence of the shape of the downstream passage located at the exit of the duct on the flow. A duct with six struts and the same geometry as that used to connect the compressor spools on the new experimental small two-spool turbofan engine was investigated. Two types of downstream passage were used. One type had a straight annular passage and the other a curved annular passage with a meridional flow path geometry similar to that of the centrifugal compressor. Results showed that the total pressure loss near the hub is large due to instability of the flow, as compared with that near the casing. Also, a vortex related to the horseshoe vortex was observed near the casing. In the case of the curved annular passage, the total pressure loss near the hub was greatly increased compared with the case of the straight annular passage, and the spatial position of this vortex depends on the passage core pressure gradient. Furthermore, results of calculation using an in-house-developed three-dimensional Navier-Stokes code with a low-Reynolds-number {kappa}-{epsilon} turbulence model were in goodmore » qualitative agreement with experimental results. According to the simulation results, a region of very high pressure loss is observed near the hub at the duct exit with the increase of inlet boundary layer thickness. Such regions of high pressure loss may act on the downstream compressor as a large inlet distortion, and strongly affect downstream compressor performance.« less

Unsteady Total Pressure Field Downstream of an Embedded Stator in a Multistage Axial Flow Compressor

Abstract: The results from measurements of the unsteady total pressure field downstream of an embedded stage of three stage axial flow compressor are presented in this paper The measurements include area traverses of a high response kulite total pressure probe and a pneumatic five hole probe downstream of stator 2 at the peak efficiency operating point for the compressor These data indicate that both the shaft-resolved and unresolved fluctuations contribute to the unsteadiness of the total pressure field in multistage compressors Specifically, regions associated with high levels of unsteadiness and, consequently, high levels of mixing including both the hub and casing endwalls and the airfoil wakes have significant levels of shaft resolved and unresolved unsteadiness Temporal variations of stator exit flow are influenced by both shaft resolved and unresolved unsteadiness distributions The limitations of state-of-the-art instrumentation for making measurements in moderate and high speed turbomachinery and the decomposition used to analyze these data are also discussed

Depletion kinetics of low‐lying states of tungsten in the presence of NO, N2O, and SO2

Abstract: The gas-phase reactivities of W(a5DJ, a7S3) with N2O, SO2, and NO in the temperature range of 295–573 K are reported. Tungsten atoms produced by the photodissociation of W(CO)6. The tungsten atoms were detected by a laser-induced fluorescence technique. The removal rate constants for the 6s25d4 a5Dl states were found to be pressure dependent for all of the reactants. Removal rate constants for the 6s15d5 a7S3 state were found to be fast compared to the a5DJ states and often approached the gas kinetic rate constant. The reaction rates for all the states were found to be pressure independent with respect to the total pressure. Results are discussed in terms of the different electronic configurations of the states of tungsten © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 367–375 1997

Numerical Flow Analysis in a Subsonic Vaned Radial Diffuser With Leading Edge Redesign

Abstract: The flow field in a subsonic vaned radial diffuser of a single-stage centrifugal compressor is numerically investigated using a three-dimensional Navier-Stokes solver (TASCflow) and a two-dimensional analysis and inverse-design software package (MISES). The vane geometry is modified in the leading edge area (two-dimensional blade shaping) using MISES, without changing the diffuser throughflow characteristics. An analysis of the two-dimensional and three-dimensional effects of two redesigns on the flow in each of the diffuser subcomponents is performed in terms of static pressure recovery, total pressure loss production, and secondary flow reduction. The computed characteristic lines are compared with measurements, which confirm the improvement obtained by the leading edge redesign in terms of increased pressure rise and operating range.

Effect of the total activation pressure on the structural and catalytic performance of the SiC supported MoO3-carbon-modified catalyst for the n-heptane isomerization

Abstract: The formation of a molybdenum oxycarbide active for catalytic isomerization of alkanes is strongly dependent on the total pressure of reactants. High pressures of the hydrogen/hydrocarbon mixture (up to 40 bar) increase the rate of reduction of MoO 3 and the rate of diffusion of carbon into the bulk, this favors the formation of the oxycarbide at the expense of MoO 2 .

The passive control of shock-wave/boundary-layer interactions

Abstract: The passive control of a shock wave-boundary-layer interaction involves placing a porous surface beneath the interaction, allowing high pressure air from the flow downstream of the shock wave to recirculate through a plenum chamber into the low pressure flow upstream of the wave. The simple case of a normal shock wave at a Mach number of 1·4 interacting with the turbulent boundary layer on a flat wall is investigated both experimentally and numerically. The experimental investigation made use of holographic interferometry, while the computational section of the investigation made use of a Navier-Stokes code to derive pressure gradients, boundary-layer properties and total pressure losses in the interaction region. It is found that the structure of shock wave-boundary-layer interactions with passive control consists of a leading, oblique shock wave followed by a lambda foot. The oblique wave originates from the upstream end of the porous region, and its strength is determined by the magnitude of the local blowing velocities. The shape of the lambda foot depends on the position of the main shock relative to the control region, resembling an uncontrolled foot when the main shock wave is towards the downstream end of the porosity, but becoming increasingly large as the shock moves upstream and eventually merging with the leading, oblique shock to form a single, large, lambda structure. Improved forms of passive control are suggested based on the findings of this investigation, including the use of passive control systems which incorporate streamwise variations in the level of porosity.

Flow Through a Rectangular-to-Semiannular Diffusing Transition Duct

Abstract: Rectangular-to-semiannular diffusing transition ducts are critical inlet components on supersonic airplanes having bifucated engine inlets. This paper documents measured details of the flow through a rectangular-to-semiannular transition duct having an expansion area ratio of 1.53. Three-dimensional velocity vectors and total pressures at the exit plane of the diffuser are presented. Surface oil-flow visualization and surface static pressure data are shown. The tests were conducted with an inlet Mach number of 0.786 and a Reynolds number based on the inlet centerline velocity and exit diameter of 3.2 × 106. The measured data are compared with previously published computational results. The ability of vortex generators to reduce circumferential total pressure distortion is demonstrated. c_ = Ceo = C D = H = h = n p = Po = R =

Activity Coefficients of Chlorophenols in Water at Infinite Dilution

Abstract: The total pressure of aqueous solutions of chlorophenols was determined by a ebulliometric total pressure method for the aqueous solutions of phenol, 2-chlorophenol, 3-chlorophenol, 4-chlorophenol, and 2,4-dichlorophenol in the temperature range from 40 to 90 °C. The activity coefficients at infinite dilution and the Henry constants were derived.