Showing papers on "Total pressure published in 1996"

Determination of the active-to-passive transition in the oxidation of silicon carbide in standard and microwave-excited air

Abstract: The active-to-passive transition is determined on sintered silicon carbide for two atmospheres: standard air and air excited by microwaves, as a function of oxygen partial pressure and temperature. The experiments were done at low total pressure ranging from 103 to 25 × 103 Pa and at high temperature from 1385 to 1765 °C at a constant air flow rate. The results are compared with literature data and we try to explain why they are so many differences between all the experimental and theoretical results.

Permeability of dense (homogeneous) cellulose acetate membranes to methane, carbon dioxide, and their mixtures at elevated pressures

Abstract: Mean permeability coefficients for CH 4 and CO 2 (P CH4 and P CO2 ) in cellulose acetate (CA, DS = 2.45) were determined at 35°C (95°F) and at pressures up to about 54 atm (800 psia). The measurements were made with pure CH 4 and CO 2 as well as with CH 4 /CO 2 mixtures containing 9.7, 24.0, and 46.1 mol % CO 2 . In the measurements with the pure gases, P CH4 was found to decrease with increasing pressure, as expected from the dual-mode sorption model. By contrast, P CO2 passes through a minimum and then increases with increasing pressure, probably due to the plasticization (swelling) of CA by CO 2 . The values of P CH4 and P CO2 determined with the mixtures containing 9.7 and 24.0 mol % CO 2 decrease with increasing total pressure ; this behavior is adequately described by the extended dual-mode sorption model for mixtures. By contrast, the values of P CH4 and P CO2 obtained with the mixture containing 46.1 mol % CO 2 pass through a minimum and then increase as the total pressure is raised, probably also due to the plasticization of CA by CO 2 . The CO 2 /CH 4 selectivity (=P CO2 /P CH4 ) of the CA membranes decreases with increasing total pressure and, at constant pressure, decreases with increasing CO 2 concentration in the feed mixture. The effects of exposing the CA membranes to high-pressure CO 2 prior to the permeability measurements (conditioning effects) on P CH4 and P CO2 have also been studied.

Determining Fluid Properties from Pressure, Volume and Temperature Measurements Made by Electric Wireline Formation Testing Tools

Abstract: A method of determining an amount of dissolved gas in a fluid sample is disclosed. The method includes hydraulically confining and expanding the sample while measuring pressure and volume. A first volume and pressure are determined at which the rate of change in pressure with respect to volume deviates from a linear relationship. A second volume and pressure at which continued expansion of the fluid causes substantially no change in pressure is determined The first pressure and volume are extrapolated by the linear relationship to intersect an extrapolation from the second volume and pressure at no change in pressure, thereby determining a bubble point comprising a bubble point pressure and a bubble point volume. A third pressure corresponding to measured pressure of the fluid sample at the bubble point volume is determined. An extrapolated sample volume is determined at the third pressure byextrapolating the linear relationship from the bubble point to a sample volume along the linear relationship corresponding to the third pressure. A volume of gas dissolved in the fluid sample is determined by linearly scaling a difference between the bubble point volume and the extrapolated sample volume with respect to a difference between the second volume and the bubble point volume.In a preferred embodiment of the invention, the sample is withdrawn into a sample chamber in an electric wireline formation test tool having a means for measuring pressure and volume of the sample chamber.

Improving curved subsonic diffuser performance with vortex generators

Abstract: The objective of this research was to use vortex generators to reduce total pressure distortion (ie, total pressure nonuniformity) and improve total pressure recovery within a curved subsonic diffuser In this study more than 20 configurations of both co- and counter-rotating arrays of vortex generators were tested in a diffusing S duct Surface static pressure, surface flow visualization, and exit plane total pressure and transverse velocity data were acquired The aerodynamic performance of each configuration was assessed by calculating total pressure recovery and spatial distortion elements The best configuration tested reduced distortion by more than 50% while improving total pressure recovery by 05% The results indicate that the mechanism responsible for improved aerodynamic performance is not boundary-layer re-energization from shed axial vortices but rather the suppression of detrimental secondary flows by redirecting the flow

Generation of dynamic pressure pulses downstream of the bow shock by variations in the interplanetary magnetic field orientation

Abstract: One-dimensional resistive MHD and hybrid simulations are carried out to study the manner by which variations of the interplanetary magnetic field (IMF) direction generate dynamic pressure pulses in the magnetosheath. The reaction of the magnetosheath to the temporal IMF variation is modeled as the interaction between the bow shock (BS) and an interplanetary rotational discontinuity (RD), an Alfven wave pulse (AW), or an Alfven wave train. The resistive MHD simulation indicates that the arrival of an RD produces two time-dependent intermediate shocks (TDISs) and two slow shocks downstream of the bow shock, which propagate through the magnetosheath toward the Earth's magnetopause. An enhancement of plasma density is present throughout the TDISs and slow shocks. A plasma dynamic pressure pulse is formed in this region. In the hybrid simulation, the two TDISs are replaced by rotational discontinuities. For a bow shock with a shock normal angle θBn > 45°, the pulse in the dynamic pressure ρV2 causes the total pressure (P + B2/2μ0 + ρV2) in the magnetosheath to increases by about 0–100% of the background value. The strength of the pressure pulse increases with the field rotation angle across the incident rotational discontinuity, while it decreases with the Mach number or upstream plasma beta of the bow shock. The pressure pulse propagates toward the magnetopause with nearly a constant amplitude. On the other hand, the BS/AW interaction leads to the generation of Alfven waves downstream of the bow shock, and large-amplitude dynamic pressure pulses are generated in the downstream Alfven wave. Pressure pulses impinging on the magnetopause may produce magnetic impulse events (MIEs) observed in the high-latitude ionosphere.

Flow measurement compensation technique for use with an averaging pitot tube type primary element

Abstract: A transmitter in a process control system for measuring flow rate measures total pressure (P TOT ) and differential pressure (h) of process fluid flowing through a process pipe. The static pressure (P STAT ) is determined based upon the total pressure (P TOT ). The calculated static pressure is used to determine the fluid density (ρ) and the gas expansion factor (Y 1 ) of the process fluid flowing in the pipe. This information is used to calculate flow rate (Q) of the process fluid.

Soot formation in a shock tube under elevated pressure conditions

Abstract: High pressure soot formation from methane, ethylene, acetylene, propane and n-heptane was studied at rich burning conditions applying the shock tube technique. Pressure behind reflected shock was varied between 15 and 100 bar. Time resolved measurements of soot particle diameter and number density were carried out using an extinction-scattering technique at 488 nm. It could be shown that soot formation at high pressures is characterized by particle diameters below 30 nm that decrease with pressure. The corresponding high particle number densities in the range of N≈1012 — 10131/cm3 turned out to be considerably higher than at atmospheric conditions. This behavior has to be attributed to reduced coagulation coefficients in the transition regime between free molecular and continuum flow. It was found that an increase in carbon concentration has a strong promoting influence on soot volume fraction. Total pressure, however, does significantly enhance soot yield at pressures up to 30 bar and loses its ...

Two-Phase Crossflow and Boiling Heat Transfer in Horizontal Tube Bundles

Abstract: An experimental study has been conducted to determine the void fraction, frictional pressure drop, and heat transfer coefficient for vertical two-phase crossflow of refrigerant R-113 in horizontal tube bundles under saturated flow boiling conditions. The tube bundle contained 5 X 20 tubes in a square in-line array with pitch-to-diameter ratio of 1.3. R-113 mass velocity ranged from 50 to 970 kg/m 2 s and test pressure from 103 to 155 kPa. The void fraction data exhibited strong mass velocity effects and were significantly less than the homogeneous and in-tube flow model predictions. They were found to be well correlated in terms of the dimensionless gas velocity, j 8 * . The two-phase friction multiplier data could be correlated well in terms of the Lockhart-Martinelli parameter. The validity of these correlations was successfully tested by predicting the total pressure drop from independent R-113 boiling experiments. The two-phase heat transfer coefficient data were found to agree well with existing pool boiling correlations, implying that nucleate boiling was the dominant heat transfer mode in the heat flux range tested.

Effect of potassium on the high pressure kinetics of ammonia synthesis over fused iron catalyst

Abstract: Measurements were performed of reaction rate in the process of ammonia synthesis (T=370–470°C) on doubly promoted (DP) (Al2O3, CaO) and triply promoted (TP) (K2O, Al2O3, CaO) iron catalysts. The latter were obtained by impregnation of the reduced and subsequently passivated DP precursors with alcoholic solution of KOH. The studies were carried out under high total pressure (10 MPa) in a wide range of ammonia partial pressure in the gas phase: from 0.25 to about 7 bar. The results are shown to be authoritative for the so-called kinetic regime. The effect of the presence of K+ cations in the catalyst was the stronger, as the temperature of the reaction was the lower and, in particular, the ammonia pressure in the gas phase the higher. The obtained results are in good accordance with the results of Somorjai's studies on activity of iron single crystal surfaces both clean and covered with (K+O) adlayer.

Investigation of the flow field downstream of a turbine trailing edge cooled nozzle guide vane

Abstract: A trailing edge cooled low aspect ratio transonic turbine guide vane is investigated in the VKI Compression Tube Cascade Facility at an outlet Mach number {bar M}{sub 2,is} = 1.05 and a coolant flow rate {dot m}c/{dot m}g = 3 percent. The outlet flow field is surveyed by combined total-directional pressure probes and temperature probes. Special emphasis is put on the development of low blockage probes. Additional information is provided by oil flow visualizations and numerical flow visualizations with a three-dimensional Navier-Stokes code. The test results describe the strong differences in the axial evolution of the hub and tip endwall and secondary flows and demonstrate the self-similarity of the midspan wake profiles. According to the total pressure and temperature profiles, the wake mixing appears to be very fast in the near-wake but very slow in the far-wake region. The total pressure wake profile appears to be little affected by the coolant flow ejection.

Unsteady numerical simulations of radial temperature profile redistribution in a single-stage turbine

Abstract: Experimental data taken from gas turbine combustors indicate that the flow exiting the combustor can contain both circumferential and radial temperature gradients. A significant amount of research recently has been devoted to studying turbine flows with inlet temperature gradients, but no total pressure gradients. Less attention has been given to flows containing both temperature and total pressure gradients at the inlet. The significance of the total pressure gradients is that the secondary flows and the temperature redistribution process in the vane blade row can be significantly altered. Experimental data previously obtained in a single-stage turbine with inlet total temperature and total pressure gradients indicated a redistribution of the warmer fluid to the pressure surface of the airfoils, and a severe underturning of the flow at the exit of the stage. In a concurrent numerical simulation, a steady, inviscid, three-dimensional flow analysis was able to capture the redistribution process, but not the exit flow angle distribution. In the current research program, a series of unsteady two- and three-dimensional Navier-Stokes simulations have been performed to study the redistribution of the radial temperature profile in the turbine stage. The three-dimensional analysis predicts both the temperature redistribution and the flow underturning observed in the more » experiments. « less

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 3D Navier–Stokes solver while the unsteady flow was determined with a quasi–3D linearized Euler solver.Experimental results showed that the distortions had strong vortical, moderate entropic and weak acoustic parts. The 3D 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 solutions 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.Copyright © 1996 by ASME

High temperature gas flow sensing element

Abstract: A high temperature gas flow sensing element is disclosed having a housing with similar internal dimensions as the fluid conduit, whether round or rectangular. An interior flow conditioner is affixed at the inlet of the flow element. A total pressure sensing pitot tube array is affixed traversing the interior cross sectional area of flow element for sensing the total pressure of fluid flowing into the flow element, and a static pressure sensing pitot tube array is also affixed traversing the interior cross sectional area of the flow element for sensing the average static pressure within the flow element. The pitot tubes and pressure sensing tubes are affixed at four places, two shell penetrations and two places at the manifolds, regardless of manifold design or the element shape. To prevent material stress and fatigue and leakage that can result from the different expansion rates of differing materials under high gradient temperature cycling, a high temperature packing, such as a ribbon packing or packing ring made of pliable material resistant to high temperatures, is used in place of the ferrule portion of a compression nut and fitting arrangement. Exterior first and second instrument taps are provide for connection of each array respectively to a differential pressure instrument for indicating flow rate and/or transmitting a flow rate signal. Further, exterior array access ports are provided to permit cleaning of each pitot arrays should they become plugged with particulates.

In Situ Optical Analysis of the Gas Phase during the Deposition of Silicon Carbide from Methyltrichlorosilane

Abstract: Coherent anti-Stokes Raman spectroscopy (CARS) was used for analysis of the gas phase during chemical vapor deposition (CVD) of silicon carbide (SiC) from a methyltrichlorosilane (MTS; CH{sub 3}SiCl{sub 3})-hydrogen (H{sub 2}) precursor mixture. CARS experiments were carried out in a low-pressure hot-wall reactor under the selected conditions: temperature T = 1,000 to 1,300 K, total pressure P{sub tot} = 2 to 5 kPa, H{sub 2} to MTS flow rate ratio {alpha} = 3 to 20, and total gas flow rate Q = 50 to 400 sccm. A systematic search for the radical and stable species present in the hot zone of the reactor was first conducted. Then partial pressures of MTS and CH{sub 4} were measured at the hot-zone outlet as a function of temperature, initial partial pressures of MTS and H{sub 2}, and residence time. Partial pressure of HCl was also measured vs. initial pressure of MTS. A reaction mechanism was tentatively drawn up to describe the decomposition of MTS in the gas phase. Then the experimental results were compared to those of a computer model which calculated concentrations of the gaseous species at the output of the hot zone by numerical integration of reaction rates.

A First Analysis of Flow Field Hysteresis in a Pump Impeller

Abstract: The measured pump pressure discharge characteristic for a high specific speed radial pump (ω s = 1.7) reveals distinct discontinuities in part load operation. These pressure discontinuities occur at different threshold volume fluxes when increasing or decreasing the pump discharge and make up a hysteresis loop. The pump impeller characteristic was evaluated experimentally and numerically by taking the difference between the integrated impeller outlet and impeller inlet total pressure. The experimental and numerical characteristics agree well including the volume flux location and magnitude of the pressure discontinuities in the hysteresis loop. For volume fluxes within the hysteresis loop two stable well converged flows were calculated numerically. The numerical calculations were made on coarse and fine grids using commercially available software with and without the impeller clearance leakage flow. Further experimental and numerical comparisons are made at the impeller inlet/outlet with emphasis on the changing flow field in the hysteresis loop flow regime and its coupling to the onset of reverse flow zones. This combined application of numerical and experimental tools provides insight for the hysteresis flow field of a pump impeller characteristic.

Injection control system

Abstract: A method of injection molding for use with an injection molding machine (10) includes: (a) generating pressurized gas and pressurized moisture within molten plastic as plastic pellets are plasticized in the injection molding machine (10), the pressurized gas and the pressurized moisture having a total pressure defining an internal counterpressure within the molten plastic; (b) pressuring air within a cavity (30) of a mold (22) in the injection molding machine (10) to an air pressure level which is substantially equal to the internal counterpressure in order to counterbalance the internal counterpressure as the molten plastic is injected into the cavity (30), thus providing a substantially pressure balanced molding environment for the plastic; and (c) maintaining the air pressure level in the cavity (30) substantially constant as the molten plastic is injected into the cavity (30). A control system is provided for maintaining desired differences between the air pressure in the cavity and the melt pressure in order to maintain a static pressure in the melt during injection to improve part quality and reduce manufacturing costs.

Influence of pressure on the gas/liquid interfacial area a and the coefficient kLa in a counter-current packed column

Abstract: The effects of pressure on the volumetric coefficient kLa and the interfacial area a in a counter-current packed column were studied in the pressure range 105 to 12 × 105 Pa. The method of gas/liquid absorption with chemical reaction was applied. The influence of the gas/liquid system on the interfacial area was also studied using three different chemical systems. It is shown that a and kLa decrease when the total pressure is increased. The authors have attempted to explain the differences between the values of a obtained under atmospheric pressure when the chemical system is changed.

Germination and Growth of Spinach under Hypobaric Conditions

Abstract: In a plant production facility designed for human life support in vacuum space, lowering total air pressures within the facilities is expected to have the engineering advantage of reducing the construction cost. In this study, low total pressure treatments were applied to spinach over the entire production period from seeding to harvest. An environment control system was constructed to grow plants under low total pressure for long durations. Spinach seeds were directly sowed on a hydroponic plant bed placed in a reduced-pressure growth chamber. The total and O2 partial pressures within the growth chamber were set at 101 and 21 kPa, 25 and 21 kPa, and 25 and 10 kPa, respectively. The CO2 partial pressure was constant at 40 Pa. At 21 kPa of O2 partial pressure, there were no significant differences in fresh and dry weights, leaf area, and shoot length of spinach at harvest between 101 and 25 kPa of total air pressure. At 10 kPa of O2 partial pressure and 25 kPa of total pressure, the dry weight was not affected, but the leaf area and shoot length at harvest were smaller than those at 21 kPa of O2. According to these results, it was evident that the entire cultivation of spinach from seeding to harvest could be carried out at one-fourth atmospheric pressure when the O2 and CO2 partial pressures are at atmospheric levels.

A parametric study of the deposition of the TiN thin films by laser reactive ablation of titanium targets in nitrogen: the roles of the total gas pressure and the contaminations with oxides

Abstract: The multipulse excimer laser-reactive ablation of a titanium target in nitrogen has been found to result in a total pressure of the ambient gas in the range 7–70 μbar, in the deposition on to a silicon collector surface of high-purity f c c TiN thin films. These films were hard and adherent to substrate. The deposition rate was 0.03–0.05 nm per pulse for an incident laser fluence of ≥5 J cm−2. For a lower gas pressure of a few microbars the deposits were amorphized with an excess of titanium. For a nitrogen pressure larger than 100 μbar, the layers were contaminated with oxides. The oxides became more abundant with further increase in the gas pressure, and the deposited layer consisted of oxides only when the pressure reached several millibars.

Experimental and numerical study of entry flow of low-density polyethylene melts

Abstract: The present work deals with experimental and numerical features of entry flows of two polyethylene melts, namely a linear low-density polyethylene (LLDPE) and a low-density polyethylene (LDPE) in an axisymmetric converging geometry. The study also involves rheological characterization of the polymers and determination of flow parameters, at 160°C. For both fluids, the data are fed into a viscoelastic integral Wagner constitutive equation. The numerical flow simulations are performed by using a stream-tube mapping analysis. Consideration of a sub-domain of the total flow domain, the “peripheral stream tube”, close to the wall of the converging duct permits to relate the results of the numerical simulation to experimental flow characteristics as total and entrance pressure drops. The agreement is good for the total pressure losses, but, concerning LDPE, a lack of consistency remains for the entrance pressure drop.

Kinetics of directed oxidation of Al-Mg alloys in the initial and final stages of synthesis of Al2O3/Al composites

Abstract: In the directed oxidation of Al-Mg alloys, MgO forms in the initial stage. The mechanism of formation of MgO from the Al-Mg alloy in the initial stage of oxidation was studied. The variables studied were the total pressure in the reaction chamber and partial pressure of oxygen. The oxidation rate in the initial stage was proportional to both the oxygen partial pressure and oxygen diffusivity. These results suggest that MgO forms by reaction-enhanced vaporization of Mg from the alloy followed by oxidation of the Mg vapour in the gas phase. The end of the initial stage corresponds to the arrival of the oxygen front close to the melt surface, when spinel formation occurs. The kinetics of formation of Al2O3 in the growth stage of directed oxidation of the Al-5wt.% Mg alloy was also investigated as a function of time, temperature and oxygen partial pressure. The growth rate decreased as a function of time, was practically independent of oxygen pressure and exhibited an activation energy of 361 kJ mol−1. In the growth stage, the kinetics of oxidation is controlled by the rate of transport of oxygen through the alloy layer near the surface to the alumina-alloy interface.

Ionization yield formation in argon-isobutane mixtures as measured by a proportional-counter method

Abstract: By using the proportional-counter method, mean ionization yields produced by 5.9 keV photons in argon-isobutane mixtures were measured as a function of the mixture composition, total gas pressure, and gas gains between about 10 3 and 2 × 10 4 . It was found that the yield for a given mixture is gain dependent: an initial increase of the yield at low gas gains is followed by almost constant yield values for gains between about 2 × 10 3 and 8 × 10 3 ; at still higher gains the yield decreases. Moreover it was observed that the ionization yield at constant gas gain depends on the total pressure of the gas mixture. This dependence leads to a rather clear correlation between yields and isobutane partial pressure. To explain the measurements a simple model of the mean energy W per ion-pair formed in Penning gas mixtures is also given. A direct comparison of calculated W values and measured data showed that the results of our proportional-counter experiments performed at high gas gains were strongly influenced by secondary effects induced during the formation of avalanches in the counter when using low isobutane partial pressures. Therefore, Penning mixtures with incomplete quenching should not be used as a counting gas in proportional counters if both high gas gain and good energy resolution are required, as for instance, in high-resolution low-energy (sub-keV) X-ray spectroscopy.

Effects of Inlet Distortion on the Flow Field in a Transonic Compressor Rotor

Abstract: The effects of circumferential distortions in inlet total pressure on the flow field in a low-aspect-ratio, high-speed, high-pressure-ratio, transonic compressor rotor are investigated in this paper. The flow field was studied experimentally and numerically with and without inlet total pressure distortion. Total pressure distortion was created by screens mounted upstream from the rotor inlet. Circumferential distortions of eight periods per revolution were investigated at two different rotor speeds. The unsteady blade surface pressures were measured with miniature pressure transducers mounted in the blade. The flow fields with and without inlet total pressure distortion were analyzed numerically by solving steady and unsteady forms of the Reynolds-averaged Navier-Stokes equations. Steady three-dimensional viscous flow calculations were performed for the flow without inlet distortion while unsteady three-dimensional viscous flow calculations were used for the flow with inlet distortion. For the time-accurate calculation, circumferential and radial variations of the inlet total pressure were used as a time-dependent inflow boundary condition. A second-order implicit scheme was used for the time integration. The experimental measurements and the numerical analysis are highly complementary for this study because of the extreme complexity of the flow field. The current investigation shows that inlet flow distortions travel through the rotor blademore » passage and are convected into the following stator. At a high rotor speed where the flow is transonic, the passage shock was found to oscillate by as much as 20% of the blade chord, and very strong interactions between the unsteady passage shock and the blade boundary layer were observed. This interaction increases the effective blockage of the passage, resulting in an increased aerodynamic loss and a reduced stall margin.« less