Showing papers on "Total pressure published in 2005"

Mass Spectrometric Identification of Si–O–H(g) Species from the Reaction of Silica with Water Vapor at Atmospheric Pressure

Abstract: A high-pressure sampling mass spectrometer was used to detect the volatile species formed from SiO2 at temperatures between 1200C and 1400C in a flowing water vapor/oxygen gas mixture at 1 bar total pressure. The primary vapor species identified was Si(OH)4. The fragment ion Si(OH)3+,' was observed in quantities 3 to 5 times larger than the parent ion Si(OH)4+. The Si(OH)3+ intensity was found to have a small temperature dependence and to increase with the water vapor partial pressure as expected. In addition, SiO(OH)+ believed to be a fragment of SiO(OH)2, was observed. These mass spectral results were compared to the behavior of silicon halides.

Controlling gas partial pressures for process optimization

Abstract: Apparatus for establishing and controlling a low pressure gas mixture in a vacuum enclosure (8) comprises at least one secondary pump (9) of the molecular, turbomolecular, or hybrid type, followed by at least one primary pump (10), with first control and adjustment means (22) such as a regulation valve (24) for controlling and adjusting the total gas pressure of the mixture of gases in the vacuum enclosure (8) as a function of a total pressure setpoint (27) The apparatus further comprises second control and adjustment means (28) such as a second regulation valve (29 a) downstream from the secondary pump (9) The second regulation valve (29 a) is controlled as a function of a delivery pressure setpoint (32) to modify the delivery pressure of the secondary pump (9) and thus to adapt its pumping capacity in selective manner This makes it possible to adjust the proportions of the gases in the mixture of gases in the vacuum enclosure, independently of the total pressure which is controlled by the first regulation valve (24)

Fabrication of lotus-type porous stainless steel by continuous zone melting technique and mechanical property

Abstract: Lotus-type porous stainless steel (SUS304L) rods were fabricated by the continuous zone melting technique under a pressurized mixed gas of hydrogen and inert gas such as argon or helium. Pores with cylindrical shape, whose growth direction is parallel to the solidification direction, are observed in the rods. The dependence of the porosity and averaged pore diameter on the partial pressure of hydrogen or the total pressure and on the transference velocity of rods was investigated. It was found that the porosity increases with increasing partial pressure of hydrogen under a constant total pressure and the pore diameter decreases with increasing transference velocity. The maximum porosity was about 60 pct under the experimental conditions in the present work. The observation of the microstructure and the measurement of the tensile strength were also carried out.

The Pressure Distribution in Thermally Bistable Turbulent Flows

Abstract: We present a systematic numerical study of the effect of turbulent velocity fluctuations on the thermal pressure distribution in thermally bistable flows. The turbulent fluctuations are characterized by their rms Mach number M (with respect to the warm medium) and the energy injection (forcing) wavenumber kfor = 1/l, where l is the injection size scale in units of the box size L = 100 pc. The numerical simulations employ random turbulent driving generated in Fourier space rather than starlike heating, in order to allow for precise control of the parameters. Our range of parameters is 0.5 ≤ M ≤ 1.25 and 2 ≤ kfor ≤ 16. Our results are consistent with the picture that as either of these parameters is increased, the local ratio of turbulent crossing time to cooling time decreases, causing transient structures in which the effective behavior is intermediate between the thermal-equilibrium and adiabatic regimes. As a result, the effective polytropic exponent γe of the simulations ranges between ~0.2 and ~1.1, and the mean pressure of the diffuse gas is generally reduced below the thermal equilibrium pressure Peq, while that of the dense gas is increased with respect to Peq. The fraction of high-density zones (n > 7.1 cm-3) with P > 104 cm-3 K increases from roughly 0.1% at kfor = 2 and M = 0.5 to roughly 70% for kfor = 16 and M = 1.25. A preliminary comparison with the recent pressure measurements of Jenkins in C I favors our case with M = 0.5 and kfor = 2. In all cases, the dynamic range of the pressure in any given density interval is larger than one order of magnitude, and the total dynamic range, summed over the entire density range, typically spans 3-4 orders of magnitude. The total pressure histogram widens as the Mach number is increased, and moreover develops near-power-law tails at high (low) pressures when γe 0.5 (γe 1), which occurs at kfor = 2 (kfor = 16) in our simulations. The opposite side of the pressure histogram decays rapidly, in an approximately lognormal form. This behavior resembles that of the corresponding density histograms, in spite of the large scatter of the pressure in any given density interval. Our results show that turbulent advection alone can generate large pressure scatters, with power-law high-P tails for large-scale driving, and provide validation for approaches attempting to derive the shape of the pressure histogram through a change of variable from the known form of the density histogram, such as that performed by Mac Low et al.

Continuous Spin Detonation in Annular Combustors

Abstract: An acetylene-oxygen mixture is burned in two annular chambers 100 mm in diameter in the spin detonation regime with supercritical and subcritical differences of oxygen pressure in the annular slot. By varying the flow rates of components of the mixture, width of the slot for oxidizer injection, point of fuel injection, and initial ambient pressure, the regions of existence and the structure of transverse detonation waves are studied, and the limits of existence of continuous detonation in terms of pressure in the chamber are determined. The losses of the total pressure in the flow in oxygen-injection slots and in fuel-injector orifices are estimated.

Toluene LIF at elevated temperatures: implications for fuel-air ratio measurements

Abstract: Toluene laser-induced fluorescence (LIF) was investigated for 266- and 248-nm excitation in the temp. range of 300-650 K in a nitrogen/oxygen bath gas of 1 bar total pressure with oxygen partial pressure in the range 0-400 mbar. Contrary to a popular assumption, the toluene LIF signal is not directly proportional to the fuel-air ratio (termed the FAR-LIF assumption) for many conditions relevant to reciprocating IC engines. With increasing temp., a higher oxygen partial pressure is required to justify the FAR-LIF assumption. The required oxygen pressure becomes unrealistic (>5 bar) for T>670 K at 266-nm excitation and for T>625 K at 248-nm excitation.

Determination of mass and heat transfer parameters during freeze-drying cycles of pharmaceutical products.

Abstract: The principal aim of this study was to evaluate the water vapour mass transfer resistance of the dried layer and the vial heat transfer coefficient values of a pharmaceutical product during the primary drying period. First, overall vial heat transfer coefficient values, Kv, were determined by a gravimetric method based on pure ice sublimation experiments. Thus, it was possible to set up a map of the total heat flux received by each vial throughout the plate surface of our pilot scale freeze-dryer. Important heterogeneities were observed for the vials placed at the plate edges and for the vials placed at the center of the plate. As well, the same gravimetric method was also used to precisely determine the influence of main lyophilization operating parameters (shelf temperature and gas total pressure) or the vial types and sizes on these overall heat transfer coefficient values. A semi-empirical relationship as a function of total gas pressure was proposed. The transient method by pressure rise analysis (PRA method) after interrupting the water vapour flow between the sublimation chamber and the condenser, previously set up and validated in our laboratory, was then extensively used with an amorphous BSA-based formulation to identify the dried layer mass transfer resistance values, Rp, the ice front temperature, and the total heat transfer coefficient values, Kv, with or without annealing treatment. It was proved that this method gave accurate and coherent data only during the first half of the sublimation period when the totality of the vials of the set was still sublimating. Thus, this rapid method allowed estimation of, on line and in situ, the sublimation front temperature and the characterization of the morphology and structure of the freeze-dried layer, all along the first part of the sublimation period. The estimated sublimation temperatures shown by the PRA model were about 2 degrees C lower than the experimental values obtained using thermocouples inserted inside the vial, in accordance with previous data given by this method for similar freeze-drying conditions. As well, by using this method we could confirm the homogenization of the dried layer porous structure by annealing treatment after the freezing step. Furthermore, frozen matrix structure analysis (mean pore diameter) using optical microscopy and mass transfer modelling of water vapour by molecular diffusion (Knudsen regime) allowed, in some cases, to predict the experimental values of this overall mass transfer resistance directly related to the freeze-dried cake permeability.

High pressure regime of plasma enhanced deposition of microcrystalline silicon

Abstract: An investigation of the effect of the total gas pressure on the deposition of microcrystalline thin films form highly diluted silane in hydrogen discharges was carried out at two different frequencies. The study was performed in conditions of constant power dissipation and constant silane partial pressure in the discharge while using a series of plasma diagnostics as electrical, optical, mass spectrometric, and in situ deposition rate measurements together with a simulator of the gas phase and the surface chemistry of SiH4∕H2 discharges. The results show that both the electron density and energy are affected by the change of the total pressure and the frequency. This in turn influences the rate of high energy electron–SiH4 dissociative processes and the total SiH4 consumption, which are favored by the frequency increase for most of the pressures. Furthermore, frequency was found to have the weakest effect on the deposition rate that was enhanced at 27.12MHz only for the lowest pressure of 1Torr. On the ot...

Preliminary Design of a 2D Supersonic Inlet to Maximize Total Pressure Recovery

Abstract: *† This paper provides a method of preliminary design for a two-dimensional, mixed compression, two-ramp supersonic inlet to maximize total pressure recovery and match the mass flow demand of the engine. For an on-design condition, the total pressure recovery is maximized according to the optimization criterion, and the dimensions of the inlet in terms of ratios to the engine face diameter are calculated. The optimization criterion is defined such that in a system of (n-1) oblique shocks and one normal shock in two dimensions, the maximum shock pressure recovery is obtained when the shocks are of equal strength. This paper also provides a method to estimate the total pressure recovery for an off-design condition for the specified inlet configuration. For an off-design condition, conservative estimation of the total pressure recovery is given so that performance of the engine at the off-design condition can be estimated. To match the mass flow demand of the engine, the second ramp angle is adjusted and the open/close schedule of a bypass door is determined. The effects of boundary layer are not considered for the supersonic part of the inlet, however friction and expansion losses are considered for the subsonic diffuser. Nomenclature α = Angle of attack j β = The installation angle of the j th ramp γ = The ratio of specific heats j δ = The flow deflection angle of the j th shock (j th ramp half angle) d θ = The half expansion angle of the subsonic diffuser j θ = The shock wave angle of the j th shock * A = The cross section area of flow tube at throat where the flow is sonic j A = The cross section area of flow at j th station point 54 AR = The ratio of inlet cross section areas at station points 5 and 4 5 d = The engine diameter at station point 5 (engine face) 6 d = The engine diameter at station point 6 (fan face) H = Flight altitude c h , 0 h = The captured freestream flow tube height i h = The height of inlet at the entry, measured perpendicular to the flight direction j h = The height of j

Dynamic calibration of fast-response probes in low-pressure shock tubes

Abstract: Shock tube flows resulting from the incomplete burst of the diaphragm are investigated in connection with the dynamic calibration of fast-response pressure probes. As a result of the partial opening of the diaphragm, pressure disturbances are observed past the shock wave and the measured total pressure profile deviates from the envisaged step signal required by the calibration process. Pressure oscillations are generated as the initially normal shock wave diffracts from the diaphragm's orifice and reflects on the shock tube walls, with the lowest local frequency roughly equal to the ratio of the sound speed in the perturbed region to the shock tube diameter. The energy integral of the perturbations decreases with increasing distance from the diaphragm, as the diffracted leading shock and downwind reflections coalesce into a single normal shock. A procedure is proposed to calibrate fast-response pressure probes downwind of a partially opened shock tube diaphragm.

Aerodynamic experiment on an ejector-jet

Abstract: Characteristics of an ejector-jet were investigated experimentally. Evaluation of a new, one-dimensional model of suction performance under the aerodynamic choking condition and observation of mixing conditions through the pseudo-shock were primary subjects of study. Supersonic primary rocket exhaust was simulated by air, and secondary airflow was simulated by nitrogen. Parameters were the ratio of the total pressure of the secondary flow to that of the primary flow, the ratio of the entrance area of the secondary flow to that of the primary flow, and the Mach number of the primary flow. A throttling valve downstream of the mixing region simulated subsonic combustion and subsequent choking, and the throttling created a pseudo-shock ahead of the valve. The suction performance increased with increased total pressure of the secondary flow, the increase of the Mach number of the primary flow, or the increase of the area of the secondary flow. The calculated results on the suction performance agreed well with these measured values. When the gases became subsonic due to throttling, the primary and secondary fluids mixed well through the pseudo-shock and became almost uniform ahead of the downstream choking position. The mixing progressed quickly in the pseudo-shock. Nomenclature A = cross section H = height M = Mach number ˙ m = mass flow rate P = pressure Pt = total pressure r = ratio of the mass flow rate of the secondary flow to that of the primary flow T = temperature Tt = total temperature u =v elocity x = streamwise coordinate from the entrance of the test section y =v ertical coordinate from the primary-flow sidewall z = spanwise coordinate from the center plane of the test section γ = ratio of specific heats ρ = density ω = mass fraction of the secondary flow

High sensitivity gas permeability measurement system for thin plastic films

Abstract: We have developed a system to quantitatively measure the permeation of gases through thin flexible substrates with high sensitivity. The system consists of two chambers, a high pressure side and an ultrahigh vacuum (UHV) side, separated by the flexible sample to be analyzed. The system is calibrated using a combination of a National Institute of Standards and Technology traceable calibrated He leak and a variable aperture calibrated orifice. The base total pressure for the UHV side is 1–3×10−10Torr. The partial pressure of individual gases that we are studying is <10−10Torr. The sample to be measured is secured between the two chambers using two 2.75 conflat flanges, two copper gaskets, and two indium “O” rings. The key factors that impact sensitivity and quantification are (1) reducing the residual partial pressure of the gas of interest to as low a value as possible on the UHV side of the system, (2) sealing the plastic sample between the two chambers with no detectable gas leakage around the sample or from the outside, (3) supporting the plastic substrate so that it can withstand 700Torr pressure on the high pressure side, and (4) developing a calibration procedure that closely mimics the actual permeability measurement. The system allows us to measure permeation rates as low as 1×10−6g∕m2-day for He, 1×10−6g∕m2-day for O2, and 5×10−7g∕m2-day for Ar.

Heat Transfer and Pressure Investigation of Dimple Impingement

Abstract: Heat transfer and pressure results of an inline array of round jets impinging on a staggered array of dimples are reported with the consideration of various geometric and parametric effects; results are normalized against flat plate data. The heat transfer was measured by using transient wideband liquid crystal method. The geometrical configurations considered were crossflow (or spent-air exit) scheme, dimple geometries and impinging positions. Three crossflow schemes were tested such as one-way, two-way and free exits. These led to the idea of the coupling effects of impingement and channel flow depending on which one dominated. Hemispherical and cusped elliptical dimple shapes with the same wetted area were considered, and found that both dimples showed the similarity in heat transfer results. Impinging positions on dimples and on flat portions adjacent to dimples were examined. Throughout the study, the pitch of the nozzle holes was kept constant at 4 jet diameters. The investigated parameters were Reynolds number (ReDj ) ranged from 5000 to 11 500, jet-to-plate spacing (H/Dj ) varied from 1 to 12 jet diameters, dimple depths (d/Dd ) of 0.15, 0.25 and 0.29, and dimple curvature (Dj /Dd ) of 0.25, 0.50 and 1.15. The shallow dimples (d/Dd = 0.15) improved heat transfer significantly by 70% at H/Dj = 2 compared to that of the flat surface, while this value was 30% for the deep ones (d/Dd = 0.25). The improvement also occurred to the moderate and high Dj /Dd . The total pressure was a function of ReDj and H/Dj when H/Dj < 2, but it was independent of the target plate geometry. The levels of the total pressure loss of the dimpled plates were not different from those of the flat surface under the same set-up conditions. Wall static pressure was measured by using static taps located across each plate. ReDj and H/Dj affected the level of the static pressure while the dimple depth influenced the stagnation peaks, and the crossflow scheme affected the shape of the peaks.Copyright © 2005 by ASME

Time resolved imaging studies of the plasma produced by laser ablation of silicon in O2/Ar atmosphere

Abstract: The dynamics of the expansion plasma produced by excimer laser ablation of a silicon target into oxygen and mixed O20Ar atmosphere were studied by means of time-resolved imaging of the expanding plume. Experiments were performed in pure oxygen, ranging between 0.13 and 13.33 Pa, and at different O20Ar ratios at a fixed total pressure of 13.33 Pa. The occurrence of a shock wave ~SW! generated by the supersonic expansion of the plasma was observed at high pressure values. The presence of the SW had a strong influence on the structure of SiOx thin films. In fact, silicon dioxidethinfilmswerealwaysobtainedinpresenceoftheSW,irrespectiveoftheoxygencontentinthegaseousmixture. On the contrary, suboxide thin films were obtained when the expansion occurred at lower pressure values ~no SW presence!. The temperature rise following the developing of the SW, is supposed to enhance the oxygen molecules dissociation by increasing the efficiency of the silicon oxidation reaction.

Pressure dependence for the CO quantum yield in the photolysis of acetone at 248 nm: a combined experimental and theoretical study.

Abstract: The quantum yield of CO in the laser pulse photolysis of acetone at 248 nm and at 298 K in the pressure range 20–900 mbar (N2) has been measured directly using quantitative infrared diode laser absorption of CO. It is found that the quantum yield of CO shows a significant dependence on total pressure with ΦCO decreasing with pressure from around 0.45 at 20 mbar to approximately 0.25 at 900 mbar. From a combination of ab initio quantum chemical calculations on the molecular properties of the acetyl (CH3CO) radical and its unimolecular fragmentation as well as the application of statistical (RRKM) and dynamical calculations we show that CO production results from prompt secondary fragmentation (via (2a)) of the internally excited primary CH3CO* photolysis product with an excess energy of approximately 62.8 kJ mol−1. Hence, our findings are consistent with a consecutive photochemically induced decomposition model, viz. step (1): CH3COCH3 + hv → CH3CO* + CH3, step (2a): CH3CO* → CH3 + CO or step (2b) CH3CO* –(+M)→ CH3CO. Formation of CO via a direct and/or concerted channel CH3COCH3 + hv → 2CH3 + CO (1′) is considered to be unimportant.

Gas heating in plasma-assisted sputter deposition

Abstract: We present a theoretical framework to deal with an important source of nonhomogeneity in plasma-assisted sputter deposition. The gas heating due to the interaction between the background gas and the flow of energetic sputtered particles seems to be of significance under realistic deposition conditions. The results illustrate that the decrease of the gas density due to this heating has to be taken into account for a proper description of the deposition process, even when the total pressure in the system remains constant. The Keller–Simmons equation, that describes the deposition rate in a parallel plate reactor, has been studied in the case of such a nonhomogeneous plasma. We determine the conditions for its applicability and find a direct relation between the throw distance, the temperature of the growing film and the cross section of elastic scattering of a sputtered atom on a gas particle.

Experimental investigations of rotating flow instabilities in the last stage of a low-pressure model steam turbine during windage

Abstract: Experimental investigations on two different three-stage low-pressure (LP) model turbines operated on steam during windage are presented. At very low flows, strain gauges identified that the two turbines exhibit different dynamic stress characteristics of the last-stage rotor blades. The first turbine experienced the highest vibrations from aerodynamic excitations at the resonant frequency of the second mode in a narrow operating range around 13 per cent of the design flow, whereas the second turbine experienced no resonance up to the fourth mode and has the highest dynamic loading at zero flow. Specially developed high-response total pressure probes have been used to determine the cause of the aerodynamic excitation from traverses of the unsteady pressure field at three planes in the last stage. The experimental data for both turbines show that unsteady pressure disturbances steadily grow when the flow is reduced below 25 per cent of design flow and that the excitations are strongest in the axial gap between the guide vane and the rotor of the last stage near the outer casing. Detailed analysis shows that high-amplitude disturbances occur at distinct frequencies and that these rotate in the circumferential direction at a fraction of the rotor speed. Comparison of the pressure signals measured at two circumferential locations on the casing of the second turbine confirmed the characteristic frequency pattern to be a so called 'rotating instability'. This unsteady phenomenon arising from the tip leakage flow has previously been observed in axial flow fans and compressors and is demonstrated for the first time here in a turbine operating at very low flow rates.