Showing papers on "Total pressure published in 1999"

Alkali Element Chemistry in Cool Dwarf Atmospheres

Abstract: The equilibrium thermochemistry of the alkali elements in cool dwarf atmospheres is investigated as part of a comprehensive set of chemical equilibrium calculations. The abundances of all important gases and the condensation temperatures of all initial condensates for Li, Na, K, Rb, and Cs are calculated as a function of pressure and temperature. Also discussed is the chemistry of refractory elements such as Al, Ca, Cr, Fe, Mg, Si, Ti, and V. The calculation of the alkali element and refractory element chemistry can help to constrain pressure and temperature conditions in dwarf atmospheres. A relative temperature scale is developed and compared to recent observations of the alkali elements in late-type dwarfs and brown dwarfs, such as the DENIS objects and Gliese 229B. The calculations show (1) Atomic Li gas abundances are expected to be lower than the bulk Li abundance because LiOH gas (at high total pressure) or LiCl gas (at low total pressure) form in very cool objects. Observations of only monatomic Li are therefore not a good test for the substellar nature of very cool objects. (2) The observations of atomic Cs in Gliese 229B can be understood by considering the distribution of Cs between atomic Cs and CsCl gases. (3) Liquid condensates, which may form solutions with complex compositions, form at higher pressures, and need to be considered in further atmospheric structure and opacity modeling.

Thermal stability of Peroxynitrates

Abstract: PAN [CH3C(O)O2NO2] has been measured ubiquitously in the troposphere, and in the stratosphere HO2NO2 has also been analysed. The thermal lives of both compounds as a function of pressure and temperature have been established reasonably well by laboratory studies, in particular for PAN. Other peroxynitrates including the halogenated derivatives are less important as NOx carriers or temporary RO2 reservoirs in the atmosphere at least at ambient temperature. Other loss processes of peroxynitrates, besides thermal decomposition, are the reaction with OH radicals and photolysis. A few experimental results also seem to support heterogeneous decomposition of RO2NO2 on surfaces. The relative importance of thermal decomposition rate, photolysis rate and rate of the OH reaction depends on temperature, pressure, spectral distribution of solar light intensity and the OH concentration. In principle, lower temperature and lower pressure at higher altitudes increase the importance of photolysis and OH reactions as sinks of RO2NO2, because thermal decomposition rates become much slower. The RO2NO2 are produced by the addition of NO2 to RO2 radicals. The RO2-NO2 bond energy is relatively weak and lies in the range of 85–120 kJ/mol according to recent measurements. Because these bond energies determine the thermal lifetimes, it can be estimated that at 1 bar total pressure and room temperature, the lifetime ranges from 10−1 to 104 s. In the present work, the thermal lifetimes of a variety of RO2NO2 species were studied as a function of temperature and pressure. The observed pressure dependencies of the thermal decomposition rates were fitted by calculations based on the Troe-treatment of unimolecular reactions. The data obtained within the present work allow predictions about the thermal decomposition rates of RO2NO2 species not yet studied.

Nonlinear indicial response of complex nonstationary oscillations as pulmonary hypertension responding to step hypoxia (degree of nonlinearityyFourier spectrumyHilbert spectrumynonlinear relationships)

Abstract: This paper is devoted to the quantization of the degree of nonlinearity of the relationship between two biological variables when one of the variables is a complex nonstationary oscillatory signal. An example of the situation is the indicial responses of pulmonary blood pressure (P) to step changes of oxygen tension (DpO2) in the breathing gas. For a step change of DpO2 beginning at time t1, the pulmonary blood pressure is a nonlinear function of time and DpO2, which can be written as P(t-t1 z DpO2). An effective method does not exist to examine the nonlinear function P(t-t1 z DpO2). A systematic approach is proposed here. The definitions of mean trends and oscillations about the means are the keys. With these keys a practical method of calculation is devised. We fit the mean trends of blood pressure with analytic functions of time, whose nonlinearity with respect to the oxygen level is clarified here. The associated oscillations about the mean can be transformed into Hilbert spectrum. An integration of the square of the Hilbert spectrum over frequency yields a measure of oscillatory energy, which is also a function of time, whose mean trends can be expressed by analytic functions. The degree of nonlinearity of the oscillatory energy with respect to the oxygen level also is clarified here. Theoretical extension of the experimental nonlinear indicial functions to arbitrary his- tory of hypoxia is proposed. Application of the results to tissue remodeling and tissue engineering of blood vessels is discussed. In biomedical science, we often have to deal with variables that are stochastic, oscillatory, and nonstationary and the relationship of these variables to other chemical, mechanical, physical, and pharmacological variables. In the cardiovascular system blood pressure is such a variable. This paper illustrates the mathematical approach to deal with the question of linearity or nonlinearity of the dependence of blood pressure on other variables. As a specific illustration, we consider the changes that occur in the lung when a sea-level dwelling animal is flown to a ski resort at a higher altitude where the partial pressure of oxygen in the gas that the animal breathes is lower. What happens is that the pulmonary arterial blood pressure becomes higher (1-3), the arterial blood vessel wall becomes thicker (3-5), the different layers of the arteries thicken with different rates and different courses of time (2-6), the mechanical properties of the blood vessel wall change with specific historical courses (7-9), cells in the wall modify, grow, proliferate, or move (5, 6, 10-13), intercellular matrix and interstitial space change (14, 15), the stress and strain distribution in the vessel wall change with time in a specific way (16), and because of cellular and extracellular changes the zero-stress state of the blood vessel wall changes with time (7-9). The crucial fact is the blood pressure change, because the blood pressure imposes load on the blood vessel wall, causing stress and strain, and the subsequent tissue and mechanical properties remodeling are believed to be the results of these stress and strain changes. Therefore, the exact behavior of blood pressure when the oxygen tension changes is of paramount importance. But blood pressure is stochastic (see Fig. 1). To get a meaningful and precise description of the blood pressure history is the first step. We used a catheter that was implanted in the pulmonary arterial trunk of a rat to get the instantaneous reading of blood pressure continuously over many days in a simulated laboratory chamber. The oxygen tension in the breathing gas was controlled as a constant or varied as a step decrease in time or a step increase in time. Typical blood pressure records are shown in Fig. 1. Previous reports (17) have demonstrated various features of pulmonary hypertension caused by hypoxia, but no mathematical analysis of the blood pressure-oxygen relationship was shown. The present paper shows a systematic use of the method pre- sented in refs. 18 and 19 to the study of the nonlinearity of the pulmonary blood pressure-oxygen tension relationship. METHODS Sixteen male Sprague-Dawley rats (Harlan, San Diego, CA), 358.9 6 4.9 g body weight, were used in the study. The protocol and experimental methods are presented in refs. 19 and 20. Briefly, each rat was implanted with an indwelling catheter in the pulmonary arterial trunk when breathing a gaseous anesthetic of isoflurane. After the implantation of the catheter, the rat could move freely in a standard-sized cage in a quiet room that was illuminated from 0600 to 1800 h. The catheter tubing had 0.305 mm i.d. and 0.635 mm o.d. and floated in the pulmonary arterial trunk facing downstream. The other end of the tubing was connected to a Statham pressure transducer (P23ID, Hato Rey, PR). The pressure recorded therefore was the stagnation or total pressure. The pressure was recorded continuously by a computer at a sampling rate of 100 pointsysec over a 36-h period with a time lag of 2 sec in every 60 sec for computer processing. The analog-to-digital conversion was accomplished by a data trans- lation board (DT31-EZ, Data Translation, Marlboro, MA). After 6 h in normal sea-level air with 20.9% oxygen, the rats were exposed to a hypoxic gas containing nitrogen and 17.2% O2, 13.6% O2 ,o r 10% O 2 for 24 h followed by returning to breathing normal sea-level air for 6 h. The changeover from one level of oxygen tension to the next was accomplished in 1.5 6 0.5 min each time. Hence, in the perspective of 1 day we say approximately that the oxygen level was changed as a step function of time. Four rats were used at each hypoxic level; four served as control without hypoxia. For mathematical analysis of the pressure signal, we begin by considering the time between successive extrema as the local time scale and define an intrinsic mode function (IMF) as a function that satisfies two conditions: (i) in the whole data set,

Probe measurements and global model of inductively coupled Ar/CF4 discharges

Abstract: The electron energy distribution function (EEDF) is measured with a Langmuir probe in an inductively-coupled radio frequency (RF, 13.56 MHz) Ar/CF4 discharge over a pressure range 3-30 mTorr by changing the CF4 content from 0 to 20%, while keeping the power injected into the plasma at about 50 W. EEDFs measured at a pressure lower than 10 mTorr are bi-Maxwellian distributions over the measured CF4 content, while those at a pressure of 30 mTorr are Druyvesteyn ones in the presence of a small amount of CF4. The average electron energy slightly increases with CF4 content, while the electron density decreases. The decrease in the electron density with addition of CF4 is more prominent as the total pressure increases. Dependences of the electron density and the averaged electron energy on CF4 content are predicted in the global model.

Mechanics of the squeeze flow of planar fibre suspensions

Abstract: This paper discusses the axisymmetric squeeze flow of concentrated transversely isotropic fibre suspensions in a power-law matrix and relates to the processing of composite materials such as sheet moulding compounds (SMCs) and glass mat thermoplastics (GMTs). A solution to the squeeze flow problem for a transversely isotropic power-law fluid is presented first, followed by a more detailed micromechanical analysis. In the first part of the paper a variational approach is applied to the interpretation of squeeze flow behaviour. This gives a simple expression for the total pressure, which enables the contributions due to extension and shear to be separated. Applying the procedure to GMT data suggests that the dissipation is predominantly extensional, except at very low plate separations. In the second part, a non-local constitutive equation is derived based on a simple drag law for hydrodynamic interactions. This is then used to model the pressure distribution when the effective length of the fibres is comparable to or determined by the dimensions of the squeeze flow plates. The model is shown to describe the observed squeeze flow stresses in both long and short fibre systems and to relate behaviour to the underlying resin flow properties.

Multi--Pressure Polytropes as Models for the Structure and Stability of Molecular Clouds. I. Theory

Abstract: Molecular clouds are supported by thermal pressure, magnetic pressure, and turbulent pressure. Each of these can be modeled with a polytropic equation of state, so that overall the total pressure is the sum of the individual components. We model the turbulent pressure as being due to a superposition of Alfven waves. The theory of polytropes is generalized to allow for the flow of entropy in response to a perturbation, as expected for the entropy associated with wave pressure. The equation of state of molecular clouds is "soft", so that the properties of the clouds are generally governed by the conditions at the surface. In general, the polytropes are not isentropic, and this permits large density and pressure drops to occur between the center and the edge of the polytropes, as is observed.

Unsteady heat transfer in stator-rotor interaction by two-equation turbulence model

Abstract: A transonic turbine stage is computed by means of an unsteady Navier-Stokes solver. A two-equation turbulence model is coupled to a transition model based on integral parameters and an extra transport equation. The transonic stage is modeled in two dimensions with a variable span height for the rotor row. The analysis of the transonic turbine stage with stator trailing edge coolant ejection is carried out to compute the unsteady pressure and heat transfer distribution on the rotor blade under variable operating conditions. The stator coolant ejection allows the total pressure losses to be reduced, although no significant effects on the rotor heat transfer are found both in the computer simulation and the measurements. The results compare favorable with experiments in terms of both pressure distribution and heat transfer around the rotor blade.

Optimization of Two-Dimensional Scramjet Inlets

Abstract: The classical optimization of two-dimension al supersonic inlets for maximum total pressure recovery is extended to two-dimensional scramjet inlets. The result that optimal supersonic inlets have shock waves of equal strength is often applied to scramjets. However the typical flow turning constraint required for scramjets, along with the lack of a terminating normal shock, lead to a more involved optimization problem. Despite this, optimization by the method of Lagrange multipliers indicates that scramjet inlets with maximum total pressure recovery have external shocks with almost equal strength. The optimal total pressure recovery and turning angles for some typical scramjet inlet configurations with up to five shocks are presented.

Influence of Vane-Blade Spacing on Transonic Turbine Stage Aerodynamics: Part II—Time-Resolved Data and Analysis

Abstract: This paper presents results of a combined experimental/computational investigation into the effects of vane-blade spacing on the unsteady aerodynamics of a transonic turbine stage. Time-resolved data were taken in a shock-tunnel facility in which the flow was generated with a short-duration source of heated and pressurized air. This data is compared with the results obtained from four unsteady Navier-Stokes solvers. The time-resolved flow for three axial spacings is examined. For each vane-blade spacing, the inlet conditions were nearly identical and the vane exit flow was transonic. Surface-mounted high-response pressure transducers at midspan were used to obtain the pressure measurements. The computed two-dimensional unsteady airfoil surface pressure predictions are compared with the Kulite pressure transducer measurements. The unsteady and axial spacing effects on loading and performance are examined, In general the numerical solutions compared very favorably with each other and with the experimental data. The overall predicted stage losses and efficiencies did not vary much with vane/blade axial spacing. The computations indicated that any increases in the blade relative total pressure loss were offset by a decrease in vane loss as the axial spacing was decreased. The decrease in predicted vane total pressure loss with decreased axial spacing was primarily due to a reduction in the wake mixing losses. The increase in predicted blade relative total pressure loss with a decrease in axial spacing was found to be mainly due to increased vane wake/blade interaction.

Fast Deposition of Microcrystalline Silicon Using High-Density SiH4 Microwave Plasma.

Abstract: A novel microwave discharge utilizing a spokewise antenna was applied for the fast deposition of hydrogenated microcrystalline silicon (µc-Si:H) film from SiH4 and Ar without the H2 dilution method. Systematic deposition studies were employed with total pressure, H2 dilution ratio and flow rate of SiH4, Fr[SiH4], as variables, combined with optical emission spectroscopy (OES) and Langmuir probe characterizations. It was found that the deposition rate exhibits a maximum at 40–50 mTorr at the axial distance of 10 cm from the quartz glass plate and the film crystallinity strongly depend on the total pressure. Correlation among OES signal intensity, SiH, the intensity ratio, IHα /ISi* , deposition rate and film crystallinity were demonstrated. By combining the SiH4 depletion and lower pressure conditions, a high deposition rate of 40 A/s was achieved in µc-Si:H growth with high crystallinity and photosensitivity from SiH4 and Ar plasma.

Comparison of temperature programmed char combustion in CO2 - O2 and Ar - O2 mixtures at elevated pressure

Abstract: A pressurized thermobalance (TGA) system was built. The role of CO2 was studied in the controlled temperature combustion under pressurized conditions. Particular care was taken to employ low sample masses in thin layers, to avoid self-heating phenomena and ensure kinetic control. It was found that a CO2 partial pressure of 0.57MPa at a 0.6 MPa total pressure had no effect on the overall reaction rate of a temperature programmed combustion. KEYWORDS: High pressure thermogravimetry, char, combustion, effect of carbon dioxide

Low-Flow Onset of Flow Instability in Heated Microchannels

Abstract: Onset offlow instability (OFI) in uniformly heated microchannels cooled with subcooled water at very low flow rates was experimentally investigated. Four different microchannels, all of which were 22 cm long with a 16-cm-long heated section, were used. Two were circular with 1.17- and 1.45-mm diameters. The other two represented flow channels in a microrod bundle with triangular array and had a hydraulic diameter of 1.13 mm; one was uniformly heated over its entire surface, and the other heated only over the surfaces of the surrounding rods. The test parameter ranges were as follows: 220 to 790 kg/m 2 .s mass flux, 240- to 933-kPa channel exit pressure, 30 to 74°C inlet temperature, and 0.1 to 0.5 MW/m 2 heat flux. In addition, the effect of dissolved noncondensables on OFI was examined by performing similar experiments with degassed water and water saturated with air with respect to the test section inlet temperature and exit pressure. Conditions leading to OFI were different from those reported for larger channels and for microchannels subject to higher coolant mass flow rates. In all the experiments, OFI occurred when equilibrium quality at channel exit was close to zero or positive, indicating the possibility of insignificant subcooled voidage in the channel and indicating that the widely used models and correlations that are based on the OFI phenomenology representing larger channels may not apply to microchannels at low-flow rates. The channel total pressure drops were significantly greater in tests with air-saturated water as compared with similar tests with degassed water. The impact of the dissolved noncondensable on the conditions leading to OFI was relatively small, however. With all parameters including heat flux unchanged, the presence of dissolved air changed the mass fluxes that led to OFI typically by only a few percent.

Effects of Film Stress on the Chemical Mechanical Polishing Process

Abstract: The general effects of film stress upon removal rate and WIWNU are discussed. Model Construction Curvature-induced wafer-scale pressure distribution .—There are many sources that can lead to wafer bow and deflection during integrated circuit (IC) manufacturing. In the current study, we consider only the defection due to the existence of intrinsic and thermal film stresses. These stresses may be tensile (negative bow) or compressive (positive bow), depending on the deposition process and thermal history. First, the wafer is considered as a thin circular plate while the pad is regarded as a half space. The wafer/pad contact area is approximated as a bowl with radius a defined in Fig. 1. The applied down force exerts an axially symmetric uniform pressure profile onto the wafer. In order to simplify the case, the effect of slurry flow is neglected and the interaction between wafer and pad is assumed frictionless. In other words, this is the contact problem that obeys the conditions required by Hertizan contact theory. Since the wafer is axially symmetric, all variables are constructed in the radial coordinate. In this case, the total pressure on the wafer surface can be expressed as the sum of separate pressure components P sum 5 P uniform 1 DP(P contact ) [1]

Study of a Supersonic Combustor Employing an Aerodynamic Ramp Pilot Injector

Abstract: Calculations of the fuel-air mixing characteristics of a scramjet combustor concept employing an aerodynamic ramp fuel injector coupled with a cavity flameholder have been performed. The calculations of the nonreacting flow through the combustor represent a first step in a collab- orative computational and experimental effort to investi- gate the performance of this scramjet combustor concept. The nonreacting flow through the combustor yielded a high total pressure recovery. Entrainment of fuel within the cavity produced a large volume of the cavity that had a local fuel-air equivalence ratio between 0.5 and 2.5, which did not vary appreciably as the overall fuel- air equivalence ratio increased from 0.13 to 0.72. How- ever, the stronger shock and expansion waves generated at the higher overall fuel-air equivalence ratios caused the fuel distribution within the cavity to become more three- dimensional. A shock train upstream of the fuel injectors was generated by imposing a back pressure at the exit plane of the domain. The shock train separated the side wall boundary layer and led to a dramatic increase in the fuel-air mixing. The mixing was characterized by en- hanced asymmetric spreading toward the side wall and was accompanied by an increased loss in total pressure through the combustor.

Brake signal transmitter with integrated addition redundancy

Abstract: A brake signal transmitter for an electronic braking system produces an electrical braking requirement signal as well as a mechanically produced pneumatic braking pressure. The electronic braking requirement signal is evaluated, together with other measured magnitudes which define the travel state, in an electronic vehicle control system, and a braking pressure is produced as a function of this evaluation by a braking pressure modulator. Following the principle of addition redundancy, the pressure produced mechanically by the brake signal transmitter is added to the pressure produced electrically by the brake modulator and the total pressure represents the braking pressure acting on the brake cylinders. In the event of failure of the electronic system, the mechanically produced pressure automatically becomes active as the braking pressure, and functions as the redundancy pressure. An addition device is provided within the brake signal transmitter itself, in which the pressure produced mechanically by the brake signal transmitter and the pressure produced electrically by the brake signal transmitter are added together. The electric braking pressure modulator may be part of the brake signal transmitter or, can be located outside the brake signal transmitter, and the pressure supplied thereby can be transmitted to the brake signal transmitter.

Pitot-static tube with static orifices on an upstream plate

Abstract: A Pitot-Static tube including three groups of orifices for determining the total pressure, static pressure and angle of attack, an axially symmetric body and a strut for fastening to pneumatic paths arranged between them and to electric heating elements. In order to reduce the aerodynamic drag of the Pitot-Static tube and the power required for heating the anti-icing system, the orifices for measuring the static pressure are arranged on a plate upstream of the strut.

An experimental study of vortex generators in boundary layer ingesting diffusers with a centerline offset

Abstract: A fundamental experimental investigation was conducted on the flow characteristics and performance of a diffuser ingesting a thick boundary layer of a high shape factor. The duct is characterized by a S-shaped offset and a cross-sectional area change going from a semi-circle at the entrance to a full circle at the exit. The performance of the diffuser was quantified by the two parameters of primary concern in jet engine applications: Total pressure recovery and total pressure distortion at the fan face (i.e. the exit) calculated from the total pressure data measured inside the duct. Flat plate vortex generators (vg’s) were deployed in an attempt to alter the flow structure inside the diffuser and eliminate separation in order to realize improvements in the diffuser performance descriptors. It was readily observed that the presence of the offset had a very strong effect on the behavior of the flow, causing separation and strong secondary flows in the Sduct accompanied by total pressure recovery of approximately 90% and total pressure distortion at the fan face of 77% (normalized to dynamic pressure) for the base case without flow control. Installation of vg’s in the Sduct helped to decrease the distortion to about 11% in some cases and prevented flow separation. However, in all cases, it was not possible to improve the pressure recovery in the S-duct much beyond the 90% range for the base flow with no vg’s.

Fine-particle classification apparatus and functional material production apparatus

Abstract: In the fine-particle classification apparatus of the present invention, a carrier gas velocity in a take-in section to introduce the aerosol to the fine-particle classification apparatus from the aerosol generation apparatus is increased so as to decrease the static pressure in the take-in section. It is thereby possible to decrease the static pressure in the take-in section than the total pressure in the aerosol generation apparatus. As a result, it is possible to introduce the aerosol inside the fine-particle classification apparatus with a total pressure equal to or higher than that in the aerosol generation apparatus from a fine particle generating area, i.e. aerosol generation apparatus with a pressure equal to or lower than that in the fine-particle classification apparatus.

Pitot-static tube

Abstract: The invention relates to a Pitot-Static tube including three groups of orifices (2, 5, 6, 10) for determining the total pressure, static pressure and angle of attack, an axially symmetric body (1) and a strut (4) for fastening to pneumatic paths arranged between them and to electric heating elements. In order to reduce the aerodynamic drag of the Pitot-Static tube and the power required for heating the anti-icing system, the orifices (10) for measuring the static pressure are arranged on a plate (8) upstream of the strut (4). Said arrangement will additionally simplify the design and lower the design weight.

Five-Hole Flow Angle Probe Calibration for the NASA Glenn Icing Research Tunnel

Abstract: A spring 1997 test section calibration program is scheduled for the NASA Glenn Research Center Icing Research Tunnel following the installation of new water injecting spray bars. A set of new five-hole flow angle pressure probes was fabricated to properly calibrate the test section for total pressure, static pressure, and flow angle. The probes have nine pressure ports: five total pressure ports on a hemispherical head and four static pressure ports located 14.7 diameters downstream of the head. The probes were calibrated in the NASA Glenn 3.5-in.-diameter free-jet calibration facility. After completing calibration data acquisition for two probes, two data prediction models were evaluated. Prediction errors from a linear discrete model proved to be no worse than those from a full third-order multiple regression model. The linear discrete model only required calibration data acquisition according to an abridged test matrix, thus saving considerable time and financial resources over the multiple regression model that required calibration data acquisition according to a more extensive test matrix. Uncertainties in calibration coefficients and predicted values of flow angle, total pressure, static pressure. Mach number. and velocity were examined. These uncertainties consider the instrumentation that will be available in the Icing Research Tunnel for future test section calibration testing.