Showing papers on "Total pressure published in 2002"

Effect of total and oxygen partial pressures on structure of photocatalytic TiO2 films sputtered on unheated substrate

Abstract: Crystalline titanium dioxide, TiO2, photocatalytic films were deposited by reactive r.f. magnetron sputtering on glass substrates without additional external heating. A pure metallic titanium target was sputtered in a mixture of argon and oxygen. The effect of the total pressure and the oxygen partial pressure on the deposition rate, the phase composition, the crystallinity, the surface morphology and the resulting photocatalytic properties was investigated. The films were characterized by X-ray diffraction, scanning electron microscopy and scanning probe microscopy. The photocatalytic activity was evaluated by the measurement of the decomposition of methylene blue under UV irradiation. The results showed that the crystalline anatase, anatase/rutile or rutile films can be successfully deposited on unheated substrate and their formation is dependent on the total pressure and the oxygen partial pressure. A schematic phase diagram was constructed. The surface morphology is strongly influenced by the total pressure and the anatase TiO2 films with a more open surface, a higher surface roughness and a larger surface area are formed at higher total pressures. The anatase films with such surface morphology deposited in the reactive sputtering mode exhibit the best photocatalytic activity.

High-resolution Fourier transform measurement of the NO2 visible and near-infrared absorption cross sections: Temperature and pressure effects

Abstract: [1] High-resolution NO2 absorption cross sections have been obtained in the near-IR (NIR) and visible regions using a Fourier transform spectrometer coupled to a multiple reflection cell. Spectra were recorded at 0.05 cm−1 in the NIR region (10,800–15,100 cm−1) and at 0.1 cm−1 in the visible region (13,800–26,000 cm−1), under various pressure conditions (pure NO2 and NO2/air mixtures) and at three temperatures (220, 240, and 294 K). The effects of the temperature and the pressure on the NO2 cross sections have been investigated. As expected, an increase of temperature results in a decrease of the absorption at the maxima of the absorption bands and an increase at the minima. From the measurements performed with pure NO2 at different temperatures a linear regression of the cross section with temperature has been carried out. This enabled the cross sections to be reproduced within 2% at room temperature and 7% at the lower temperatures. The variation of the cross sections with the total pressure of NO2/air mixtures has also been investigated at high resolution.

Theoretical Study of the MoS2 (100) Surface: A Chemical Potential Analysis of Sulfur and Hydrogen Coverage. 2. Effect of the Total Pressure on Surface Stability

Abstract: We investigate theoretically, by quantum DFT calculations, the adsorption of H2 molecules on the [100] MoS2 surfaces, considering various edge sulfur stoichiometries. Depending on the nature of the...

Correlation between structure, stress and deposition parameters in direct current sputtered zinc oxide films

Abstract: Thin ZnO and ZnO:Al films have been prepared by reactive dc magnetron sputtering, using both metallic and ceramic targets. The influence of oxygen flow and total pressure on film stress, structure, texture, and surface roughness has been examined. The properties of the films strongly depend on the deposition conditions, in particular the total pressure. Increasing the pressure from 0.5 to 2 Pa resulted in rougher, and less strained films. Increasing the oxygen flow at a constant total pressure led to a slight increase in stress, but had no visible effect on the surface roughness. Structural investigations by x-ray diffraction (XRD) showed that polycrystalline films with pronounced preferential orientation were formed. Most XRD-spectra showed a coexistence of strained and unstrained ZnO in wurtzite structure. The relative abundance of the relaxed phase is a function of the intrinsic stress only, and does not directly depend on deposition parameters. However, the deposition parameters determine the stress w...

Scaling parameters for underexpanded supersonic jets

Abstract: An analysis and experiments were carried out to study the spreading and centerline property decay rates of underexpanded supersonic jets. The main purpose was to determine a suitable set of normalization parameters that would account for the initial expansion process and allow for a comparison of the asymptotic mixing rates of jets within a large range of exit-to-ambient pressure ratios. A set of expressions were developed for after-expansion equivalent jet exit diameter, velocity, temperature, and density to allow for a better collapse of jet spreading and centerline decay rates. Measurements were made for five different underexpanded sonic jets with jet exit-to-ambient pressure ratios of p e /p a =1, 2.5, 7.5, 15.5, and 20.3, corresponding to (isentropically) fully expanded jet Mach numbers of M j =1, 1.68, 2.38, 2.85, and 3.03, respectively. For each jet, both centerline and profile measurements were made using special probes that simultaneously measured local total pressure, static pressure, total temperature in the jet, as well as ambient conditions. These measurements were made in the subsonic flow regime, in some cases, extending as far as 270 nozzle diameters from the exit plane. The experimental results were analyzed and the asymptotic jet properties were determined using the new renormalization parameters.

The kinetics of CO oxidation on RuO2(110): Bridging the pressure gap

Abstract: The steady-state rate rCO2 of CO2 formation from CO + O2 on an epitaxially grown RuO2(110) single-crystal surface was recorded as a function of the partial pressures in the 10-7−10-6 mbar range. The RuO2(110) surface exposes singly coordinatively unsaturated “Ru-cus” sites and 2-fold coordinatively unsaturated “Ru-bridge” sites. Normally, the Ru-bridge sites are saturated by oxygen (O-bridge) which can be replaced by CO. The stage of the surface was controlled by vibrational spectroscopy (HREELS), and analysis of the kinetic data was based on previous information about the structural and adsorptive properties of this surface. Measurements of the rate as a function of temperature up to ≈350 K in a 1:1 mixture of CO and O2, each with 10-7 mbar partial pressure, revealed most remarkable agreement with data reported by Zang and Kisch13 with small supported RuO2 particles prepared from aqueous solution for 1 bar total pressure. Under these conditions of temperature and ratio of partial pressures the reaction w...

JET quasistationary internal-transport-barrier operation with active control of the pressure profile.

Abstract: Quasistationary operation has been achieved on the Joint European Torus tokamak in internal-transport-barrier (ITB) scenarios, with the discharge time limited only by plant constraints. Full current drive was obtained over all the high performance phase by using lower hybrid current drive. For the first time feedback control on the total pressure and on the electron temperature profile was implemented by using, respectively, the neutral beams and the ion-cyclotron waves. Although impurity accumulation could be a problem in steady state ITBs, these experiments bring some elements to answer to it.

Fabrication of Porous Iron by Unidirectional Solidification in Nitrogen Atmosphere

Abstract: Porous iron whose long cylindrical pores are aligned in one direction has been fabricated by unidirectional solidification of the melt in a pressurized mixture gas of nitrogen and argon. Nitrogen dissolved in the molten iron is rejected at the solid-liquid interface during the solidification due to the solubility difference of nitrogen between the liquid and solid. The gas pores are evolved from the nitrogen insoluble in the solid iron, which grow unidirectionally. The porosity is controlled by the partial pressures of nitrogen and argon during melting and solidification. The porosity decreases with increase of the partial pressure of argon at a given nitrogen pressure according to the Boyle’s law. At a constant total pressure of the mixture gas, the porosity increases with increasing partial pressure of nitrogen and no pores are formed during solidification below a critical partial pressure of nitrogen. The nitrogen concentration in the solid iron increases with increasing partial pressu re of nitrogen. The solid-solution hardening has been observed in as-cast porous iron, while more significant hardening has also been found in the porous iron quenched from a high temperature 1273 K, which is due to the martensitic transformation.

A Numerical Investigation of the Influence of Casing Treatments on the Tip Leakage Flow in a HPC Front Stage

Abstract: This paper describes the influence of casing treatments on the tip leakage flow and its resulting vortex. The presented results and conclusions are based on steady state numerical simulations of a high pressure compressor stage. Without casing treatments a significant change of behavior of the tip leakage flow can be observed near surge. This change is termed as vortex breakdown and occurs after passing the shock in the blade passage. The simulations indicate the losses in total pressure inside the vortex core as the main reason for the vortex breakdown. These losses mainly depend on the blade loading. Running the compressor stage at high pressure ratios these losses can reach such a high level that the total pressure inside the vortex measured in the rotating system of the rotor falls below the static pressure after the shock. This pressure difference works as a physical barrier for the low energy vortex core and prevents it from reaching the high pressure rotor outlet. Consequently, this blockage must lead to the onset of recirculation zones — the so called vortex breakdown. Different casing treatments have been tested on their ability to delay vortex breakdown and to move the surge line to lower mass flows. Numerical simulations show that configurations with axial slots as well as circumferential grooves weaken or even destroy the characteristic tip leakage vortex and reduce its resulting losses in total pressure. This reduction in losses delays or prevents the onset of vortex breakdown compared to the untreated case explaining the effectiveness of casing treatments. Observations indicate that casing treatments do not interfere with the vortex directly. The key mechanism seems to lay mainly in the interaction with the tip leakage alone. Taking advantage of existing pressure differences in the rotor blade row casing treatments remove tip leakage flow in zones of high pressure and interrupt temporarily the feeding of the vortex. The separated tip leakage reenters the main flow in zones of low pressure again. The way how this tip leakage bypass is realized defines the influence of casing treatments on efficiency and surge line.Copyright © 2002 by ASME

Application of Boundary Layer Fences and Vortex Generators in Improving Performance of S-Duct Diffusers

Abstract: An experimental investigation was undertaken to study the effect of various fences and vortex generator configurations in reducing the exit flow distortion and improving total pressure recovery in two-dimensional S-duct diffusers of different radius ratios. Detailed measurements including total pressure and velocity distribution, surface static pressure, skin friction, and boundary layer measurements were taken in a uniform inlet flow at a Reynolds number of 7.8×10 5 . These measurements are presented here along with static pressure rise, distortion coefficient, and the transverse velocity vectors at the duct exit determined from the measured data

Fluid Dynamics of a Pre-Swirl Rotor-Stator System

Abstract: In a “direct-transfer” pre-swirl supply system, cooling air flows axially across the wheel-space from stationary pre-swirl nozzles to receiver holes located at a similar radius in the rotating turbine disc. This paper describes a combined computational and experimental study of the fluid dynamics of such a system. Measurements of total and static pressures have been made using a purpose-built rotor-stator rig, with 24 pre-swirl nozzles on the stator and 60 receiver holes in the rotor. The number of pre-swirl nozzles could be reduced, and it was possible to calculate CD , the discharge coefficient of the receiver holes. Information on the flowfield was also obtained from three-dimensional, incompressible steady turbulent flow computations. The measurements showed that there was a significant loss of total pressure between the outlet from the pre-swirl nozzles and the rotating core of fluid in the wheel-space. This loss increased as the pre-swirl flow-rate and inlet swirl ratio increased, and as the number of nozzles decreased. CD increased as the swirl ratio at the receiver hole radius approached unity; for the experiments, CD varied in the range 0.2 to 0.45. Computed pressures and tangential velocities were in mainly good agreement with the measurements. The computations help to explain the reasons for the significant losses in total pressure and for the relatively low values of CD in this pre-swirl system.© 2002 ASME

Measurements of the kinetics of the OH‐initiated oxidation of isoprene

Abstract: [1] The mechanism of the OH-initiated oxidation of isoprene has been studied at 300 K and 100 and 150 Torr total pressure using a turbulent flow technique coupled with laser-induced fluorescence detection of the OH radical. The rate constant for the reaction of OH with isoprene was measured to be (10.8 ± 0.5) × 10−11 cm3 molecule−1 s−1 at 150 Torr total pressure and independent of pressure between 100 and 150 Torr, in excellent agreement with most previous absolute measurements. In the presence of O2 and NO, propagation of OH radicals and loss of OH through radical termination resulting from the formation of organic nitrates were measured at 150 Torr total pressure and compared to simulations of the kinetics of this reaction system. The results of these experiments are consistent with an overall rate constant of (1.1 ± 0.8) × 10−11 cm3 molecule−1 s−1 for the reaction of NO with isoprene-based hydroxyalkyl peroxy radicals, with branching ratios of 0.85 ± 0.10 for the bimolecular channel (oxidation of NO to NO2) and 0.15 ± 0.10 for the termolecular channel (formation of organic nitrates). Although the organic nitrate yield reported here is the result of indirect measurements, it suggests that isoprene may be a more significant sink of NOx than previously estimated.

Flow and Heat Transfer Predictions for a Flat-Tip Turbine Blade

Abstract: Numerical calculations are performed to simulate the tip leakage flow and heat transfer on the GE-E3 High-Pressure-Turbine (HPT) rotor blade. The calculations are performed for a single blade with periodic conditions imposed along the two boundaries in the circumferential-pitch direction. Cases considered are a flat blade tip at three different tip gap clearances of 1%, 1.5% and 2.5% of the blade span. The numerical results are obtained for two different pressure ratios (ratio of inlet total pressure to exit static pressure) of 1.2 and 1.32 and an inlet turbulence level of 6.1%. To explore the effect of turbulence models on the heat transfer results, three different models of increasing complexity and computational effort (standard high Re k-e model, RNG k-e and Reynolds Stress Model) are investigated. The predicted tip heat transfer results are compared with the experimental data of Azad [1], and show satisfactory agreement with the data. Hear transfer predictions for all three turbulence models are comparable, and no significant improvements are obtained with the Reynolds-stress model.Copyright © 2002 by ASME

Catalyst Shape as a Design Parameter—Optimum Shape for Methane-Steam Reforming Catalyst

Abstract: High catalyst activity plays an important role in the safe and efficient operation of methane-steam reforming reactors. Since transport resistance limits the effectiveness factor in the reactor to values much less than unity, increasing the catalyst surface area increases its activity. Using a mathematical model of a terrace wall reactor, the effect of catalyst shape on performance of the reactor has been studied. Considering different parameters of catalyst effectiveness factor, reaction gas temperature, reactor pressure drop and mechanical strength, it has been shown that a multichannel cylinder is a good choice among different alternative catalyst pellet shapes. Compared to a standard spherical shape, a multichannel cylinder gives 10% less total pressure drop and its effectiveness factor is almost three times higher.

Experimental Investigation on Flameholding Mechanism and Combustion Performance in Hydrogen-Fueled Supersonic Combustors

Abstract: Supersonic H-2/air combustion experiments of a fixed entry Mach number 2.5 were conducted using eight different model combustors, at various stagnation conditions and global equivalence ratios. Specifically, stagnation temperature varied from 1200 to 2000 K, stagnation pressure ranged from 1 to 1.4 MPa, and the global equivalence ratio covered the range from lean to rich. In addition, the static pressure distribution in the axial direction and total pressure at the combustor exit were measured. Effects of wall injection, strut injection, and cavity flameholder were systematically investigated and compared. A one-dimensional model was further applied for data reduction and analysis. The calculated results were found to be fairly consistent with the experimental measurements. Performances of various model combustors, as well as the factors affecting combustion efficiency and total pressure recovery, were discussed.

How to determine the pressure of a methane-containing gas mixture by means of two weak Raman bands, v(3) and 2v(2)

Abstract: Raman spectra of a pure CH4 sample, two CH4C2 H6 mixtures and a CH4N2 mixture were obtained as a function of pressure at pressures up to 39.6 MPaA (MPa absolute). These spectra are presented in the region 3120–2980 cm−1. A clear pressure dependence of the area ratio between two weak methane bands, ν3 (asymmetric CH stretching) and 2ν2 (overtone of the asymmetric CH bending), is observed; the methane ν3 band intensity is lowered relative to the methane 2ν2 as the pressure is raised. The intensity ratios between these two bands, I(ν3)/I(2ν2), were determined and plotted as a function of pressure. Surprisingly it is observed that the ratio at a fixed pressure is independent of the composition and thereby of the surroundings in which the methane molecule is vibrating. A model function to predict the pressure is given. From a practical point of view, the present results could be useful for determining directly the total pressure in methane mixtures the composition of which is not known. Copyright © 2002 John Wiley & Sons, Ltd.

Fabrication of lotus-type porous stainless steel by unidirectional solidification under hydrogen atmosphere

Abstract: Lotus-type porous stainless steel SUS304L has been fabricated by unidirectional solidification under mixed gases of hydrogen and argon. The atmospheric pressure dependence of porosity and pore diameter has been investigated. The porosity is lower if the partial pressure of argon is higher under a constant partial pressure of hydrogen and is higher if the partial pressure of hydrogen is higher under a constant total pressure of atmosphere composing of hydrogen and argon. Average pore diameter increases with increasing distance from the bottom chill plane. From tensile tests, the ultimate tensile strength of the porous stainless steel with porosity about 50% has been found to be about 7 times lower than nonporous alloy in the direction perpendicular to pore growth direction.

Effects of Riblets on the Loss Behavior of a Highly Loaded Compressor Cascade

Abstract: An experimental investigation of the influence of riblet surface structures on the loss behavior of a highly loaded compressor cascade V103-180 featuring a large chord length for high spatial resolution of the flow phenomena was performed. The cascade experiments were carried out at the High Speed Cascade Wind Tunnel of the University of the Armed Forces Munich in order to simulate realistic Mach and Reynolds numbers. The riblets used for the first investigation are of symmetric v-groove type with heights of 0.0762, 0.1143 and 0.1524 mm, respectively [1]. With two total pressure probes simultaneously traversed over one pitch behind the center airfoil, the local total pressure difference between the structured and the smooth blade is determined. From these measurements, the total pressure loss coefficient can be evaluated. For a better understanding of the flow phenomena, the profile pressure distribution is measured for the smooth and the structured blade. Boundary layer calculations were performed in order to optimise the riblet size for the design conditions of the compressor cascade. Resulting from the measurements an optimised riblet configuration (size and shape) has been manufactured and transferred to the cascade. Further flow measurements have been performed in order to evaluate the total pressure loss coefficient. Additional insight into the flow phenomena of the boundary layer has been achieved by laser-two-focus measurements. The experimental results indicate that the riblets mainly influence the suction side boundary layer behaviour. The ideal dimensionless groove height is obtained h+ = 9 leading to a reduction of the loss coefficient of 6–8%. Values of h+ > 20 cause an increase of the loss coefficient due to the development of a turbulent boundary layer separation.Copyright © 2002 by ASME

Pressure Effect on the Density of Water

Abstract: A simple two-state structural model has been shown capable of quantitatively unifying oxygen-related properties of liquid water. The key variables, which remain invariant among all properties studied, are the pressure-/temperature-dependent densities and fractional compositions of the two contributing structures. In this paper, the pressure dependence of these variables for different temperatures is evaluated from density measurements of water for pressures up to 8 kbar. Data derived earlier from isothermal compressibilities provided only the leading term in the steep pressure dependence of these quantities. This leading term is found here to provide a good representation of the density of water in the pressure range from 1 to 1026 bar for 0 ≤ t ≤ 40 °C. A correctly curved pressure dependence is introduced for the accurate description of pressure-dependent properties such as the refractive index of water and the pressure denaturation of proteins, where the experimental pressure range usually exceeds 1 kbar.

Time-resolved gas-phase kinetic study of the germylene addition reaction, GeH2 + C2D4, as a function of temperature and pressure: isotope effects and mechanistic complexities

Abstract: Time-resolved studies of germylene, GeH2, generated by laser flash photolysis of 3,4-dimethyl-1-germacyclopent-3-ene, have been carried out to obtain rate constants for its bimolecular reaction with C2D4. The reaction was studied in the gas phase, mainly at a total pressure of 10 Torr (in SF6 bath gas) at five temperatures in the range 295–554 K. The second-order rate constants gave the Arrhenius equation: log(k∞/cm3 molecule−1 s−1) = (−10.76 ± 0.06) + (5.79 ± 0.46 kJ mol−1)/RT ln10Pressure variation measurements over the range 1–100 Torr (SF6) at 295, 406 and 554 K showed the rate constants to be pressure independent within experimental error. Comparison with the reaction of GeH2 + C2H4 studied earlier, which was pressure dependent, gave large inverse isotope effects which increased with increasing temperature and decreasing pressure. The data supports a mechanism, involving the reversible isomerisation of initially formed germirane-d4 to ethylgermylene-d4 and is consistent with previously carried out thermochemical and ab initio calculations of the energy surface.

Static pitot transducer

Abstract: A differential and absolute transducer are secured to a Pyrex glass header by means of a glass metal frit or other suitable interface. One of the sensors measures absolute pressure and the sensor is a sealed cavity, while the other sensor is designed to measure differential pressure and the sensor is an aperture which permits the pressure media to reach both sides of the sensor. The header itself has a through hole connected to a tube over which the differential sensor is affixed. The Pyrex glass is chosen to match the coefficient expansion of the sensors. The header in turn is attached to an adapter that enables static pressure to be applied to both sensors simultaneously and total pressure applied to the differential sensor, thus permitting the measurement of the difference between the total pressure and the static pressure. Each of the sensors is fabricated by the same processing techniques and is of the same thickness, but have different deflecting areas such that the differential sensor will have a greater stress through the same pressure. By obtaining both the differential and the static pressure, one can now determine air speed by the solution of Bernoulli's theorem for a total pressure in a compressible flow, such as through air or any other fluid.

Nonequilibrium magnetohydrodynamic control of scramjet inlets

Abstract: The paper is devoted to theoretical analysis of magnetohydrod ynamic (MHD) control of forebody flow compression and air mass capture in scramjet inlets for vehicles that would fly at Mach 6-10. Due to the low static temperature, nonequilibrium air ionization and electrical conductivity are created by electron beams injected into the gas along magnetic field lines. Two -dimensional inviscid steady-state flow equations are solved jointly with equations describing electron beam-induced ionization profiles, plasma kinetics, and MHD equations. Several scenarios are considered. At flight Mach numbers 8 and 10, with forebody and inlet geometry designed for Mach 6, the shocks that would enter the inlet can be moved back on the cowl lip by placing an MHD generator at the first compression ramp. In addition to controlling the shocks, the MHD device would generate electric power; however, Joule heating would result in losses of total pressure. Another scenario is an on-ramp MHD accelerator that should increase mass capture at Mach 6 or 8 for a vehicle designed for Mach 10. Calculations show that this scenario has only disadvantages, as the MHD device consumes high power, reduces total pressure, and actually decreases mass capture due to Joule heating and thermal expansion of the gas. A modest increase in mass capture can be in principle accomplished in an MHD generator mode, if the magnetic field has components both parallel and orthogonal to the flow. However, this scenario requires unrealistically large volumes of strong magnetic fields, and the mass capture increase is due mostly to a nonuniform gas heating. The paper proposes a new concept of a virtual inlet, where a localized off-body energy addition is used to increase mass capture, while not reducing (and even increasing) total pressure at the inlet.

Influence of temperature transients and centrifugal force on fast-response pressure transducers

Abstract: This contribution focuses on the use of fast-response semi-conductor pressure transducers to measure accurately the mean and fluctuating total pressure or static pressure in a wind tunnel environment. The problem of angular sensitivity is briefly addressed when measuring total pressure. Then, the influence of temperature is described when testing under steady or transient temperature conditions. The influence of the rotational speed is analyzed when measuring with rotating transducers. The transfer function of a sensor-cavity system is also considered. Correction methods are proposed for both the effects of the temperature and the rotational speed. Several applications are presented covering turbulence measurement with a quasi-steady probe, static and total pressure measurements in the absolute frame and the relative frame.