Showing papers on "Atmospheric pressure published in 1979"

Field induced ion evaporation from liquid surfaces at atmospheric pressure

Abstract: A mass spectrometer system which is capable of sampling ions directly from an atmospheric pressure source has been constructed and used to investigate ions which are evaporated from the surface of highly charged water droplets. Solutions of electrolytes are sprayed into the air, and a large charge imparted to the droplets by induction; an electric field applied across the plume of evaporating spray extracts small ions, probably already clustered with solvent molecules, which are drawn through a 25 μm orifice into the vacuum chamber. Differential pumping is applied and the ions are focused into a quadrupole mass filter. Approximately 30 univalent anions and cations of various sizes and structures have been tested, and almost all have been observed to evaporate; significant exceptions are Ag+, Tl+, and Cu+. Furthermore, certain molecules such as urea and acetanilide, when present as neutrals in the sprayed water, are observed to remain attached to the ions when these evaporate. The experimental results are ...

Theoretical Modeling of Rapid Surface Vaporization with Back Pressure

Abstract: In this paper, a theoretical model is developed for rapid surface vaporization into a surrounding ambient atmosphere. The primary emphasis is on metallic surfaces. Power input levels are taken to be low enough so that thermodynamic equilibrium can be assumed before phase change to gas. At high evaporation rates there will be a narrow Knudsen layer region in the gaseous flow just outside the phase interface in which translational nonequilibrium prevails. The modeling treats this layer as a gasdynamic discontinuity and approximate jump conditions are derived. The flow Mach number just outside the Knudsen layer is dictated by the state well away from the surface. Its determination is discussed both for a simple model of transient flow induced by a laser pulse and for the general case of time-varying power input. Examples assume the metallic surface is aluminum and the surrounding air pressure ranges from 1 atm to hard vacuum.

Viking radio occultation measurements of the atmosphere and topography of Mars: Data acquired during 1 Martian year of tracking

Abstract: The results of one Martian year of radio occultation measurements of the atmosphere and topography of Mars obtained using the Viking Orbiters are briefly summarized. Determinations of the vertical distribution of tropospheric gas refractivity and ionospheric electron density obtained from atmospheric Doppler frequency perturbations of the S and X band radio tracking frequencies indicate large meteorological variations, with near-surface temperatures ranging from 150 to 250 K, 5-km atmospheric pressure ranging from 3.5 to 4.8 mbar, inversion layers over the polar caps and dust storms, and seasonal pressure variations. Double- and single-layered upper atmospheric electron density profiles were observed on the sunlit and dark sides of the planet, respectively. A topographic map of the Martian surface, obtained from the limb diffraction effects observed at ingress and egress, is found to agree well with the elevation contours of US Geological survey map M 25M 3 RMC, with the exception of the south polar and Alba Patera regions.

Thermal expansion of .GAMMA.-Mg2SiO4.

Abstract: Thermal expansion of γ-Mg2SiO4 was measured with X-ray powder diffraction method up to 750°C at atmospheric pressure. The data are analyzed in terms of Gruneisen's theory of thermal expansion and Gruneisen's parameter is obtained to be 1.27. Volume thermal expansion coefficient is 19 at 20°C and 27 at 500°C in unit of 10-6/K. These values are compared with those of γ-Fe2SiO4, MgAl2O4 and other spinel type compounds, and it is suggested that the anharmonic properties of γ-(Mg, Fe)2SiO4 may be very close to those of MgAl2O4.

Thermal tides and Martian dust storms: Direct evidence for coupling

Abstract: Evidence for the coupling of diurnal and semidiurnal thermal tides, observed as surface pressure oscillations at the Viking Lander 1 and 2 landing sites, to Martian global dust storms is presented and the implications for models of dust storm generation are discussed. Local atmospheric opacity increases and jumps in atmospheric pressure ranges were found to be essentially simultaneous, and diurnal and semidiurnal components of the pressure and wind oscillations were observed to increase markedly after the onset of a dust storm. The semidiurnal wind component can be related to the observed surface pressure variations by means of a model of a semidiurnally forced Ekman boundary layer. However, a classical atmospheric tidal model shows that the preferential enhancement of the semidiurnal surface pressure oscillation observed at the Lander 1 site can be produced by a tidal heating distribution in which most of the heating is done at an altitude above 10 km. Observations suggest that various mechanisms are important for the generation and decay of global Martian dust storms.

Barometric fluctuations in wells tapping deep unconfined aquifers

Abstract: Water levels in wells screened only below the water table in unconfined aquifers fluctuate in response to atmospheric pressure changes. These fluctuations occur because the materials composing the unsaturated zone resist air movement and have capacity to store air with a change in pressure. Consequently, the translation of any pressure change at land surface is slowed as it moves through the unsaturated zone to the water table, but it reaches the water surface in the well instantaneously. Thus a pressure imbalance is created that results in a water level fluctuation. Barometric effects on water levels in unconfined aquifers can be computed by solution of the differential equation governing the flow of gas in the unsaturated zone subject to the appropriate boundary conditions. Solutions to this equation for two sets of boundary conditions were applied to compute water level response in a well tapping the Ogallala Formation near Lubbock, Texas from simultaneous microbarograph records. One set of computations, based on the step function unit response solution and convolution, resulted in a very good match between computed and measured water levels. A second set of computations, based on analysis of the amplitude ratios of simultaneous cyclic microbarograph and water level fluctuations, gave inconsistent results in terms of the unsaturated zone pneumatic properties but provided useful insights on the nature of unconfined-aquifer water level fluctuations.

The seasonal variation of atmospheric pressure on Mars as affected by the south polar cap

Abstract: The daily mean pressures at two locations on Mars, observed over 57% of a Martian year, reveal a semiannual oscillation with a peak-to-peak difference that is 26% of the mean pressure. This intrinsically Martian phenomenon is caused by exchange of CO2 between the atmosphere and the winter polar caps. Evidence is presented that the difference in pressure at the two landers varies with season and that the seasonal variation is not completely removed by hydrostatic correction for the difference in elevation. The mass CO2 sublimed from the south polar cap is estimated to be greater than or equal to 7.9 x 10 to the 12th metric tons, corresponding to a mean thickness of solid CO2 over the maximum extent of that cap of greater than or equal to 23 cm. Estimates are formed of the meridonal wind speed conveying gas out of the dissipating cap and the associated zonal geostrophic wind, both averaged over longitude. The results are approximately 2.3 m/sec and 14 m/sec, respectively.

Experiment and theory for CO2 laser‐induced CF2HCl decomposition rate dependence on pressure and intensity

Abstract: A laser‐excited fluorescence method has been used to determine the rates at which CF2HCl molecules dissociate into CF2+HCl fragments during CO2 laser pulses of uniform fluence and known intensity. A study has been made of the dependence of the rate on CO2 laser intensity and pressure of Ar buffer gas from the collision‐free regime to atmospheric pressure. The effect of increasing Ar pressure is initially to increase the CF2HCl dissociation rate; above a moderate pressure (∼50 Torr), the rate is independent of Ar pressure up to atmospheric pressure. The data has been compared to a model, which adequately reproduces all the experimental data. The model treats the effect of collision between CF2HCl and the argon buffer gas in terms of rotational equilibration or ’’hole filling’’ in the discrete energy level region of CF2HCl. The discrete energy levels are interfaced to a quasicontinuum of vibrational–rotational states in a self‐consistent manner which incorporates a background of nonpumpable CF2HCl states as a finite heat bath interacting with the pump mode. The model is used to calculate the rate of formation of product CF2 molecules as a function of argon pressure and CO2 laser intensity. The quasicontinuum for CF2HCl is predicted to begin about four quanta above the ground state. The absorption cross section in the quasicontinuum is shown to decrease from 10−18 to 10−20 cm2 at V=15. The energy distribution in CF2HCl is predicted to be decidedly nonthermal both below and beyond threshold.

Detailed ion chemistry in methane-oxygen flames. Part 2. Negative ions

Abstract: The detailed negative-ion chemistry for two premixed methane-oxygen flames of fuel-lean and fuel-rich composition burning at atmospheric pressure is discussed. As in Part 1 a complete family of concentration profiles for natural, negative flame ions mass-spectrometrically below 100 amu (atomic mass units) for each flame, sampled along the axis through the flame front were measured. The ion chemistry is explained with reference to published data on neutral concentration profiles, rate constants for ion-molecule reactions, and thermochemical values.

Air ejector augmented compressed air energy storage system

Abstract: Energy is stored in slack demand periods by charging a plurality of underground reservoirs with air to the same peak storage pressure, during peak demand periods throttling the air from one storage reservoir into a gas turbine system at a constant inlet pressure until the air pressure in the reservoir falls to said constant inlet pressure, thereupon permitting air in a second reservoir to flow into said gas turbine system while drawing air from the first reservoir through a variable geometry air ejector and adjusting said variable geometry air ejector, said air flow being essentially at the constant inlet pressure of the gas turbine system.

Fundamental study of bubble formation in dissolved air pressure flotation

Abstract: This paper deals with the hydrodynamic performance of very fine gas bubbles required for dissolved air pressure flotation, which are produced by dissolving air in water under pressure and subsequent flashing to normal pressure. Experiments were carried out on generated air flow rate and bubble diameter when air was dissolved in water under 1-5 Kg/cm2 gauge and flashed to normal pressure through a nozzle. The results clarify the effects of dissolved pressure, liquid flow rate and nozzle geometry, and the empirical equations for the number of generated bubbles are obtained. Also, some theoretical considerations on the generated air flow rate and diameter of generated bubbles are discussed.

Temperature measurements of the hydroxyl radical and molecular nitrogen in premixed, laminar flames by laser techniques.

Abstract: Temperature profiles in an atmospheric pressure, premixed, laminar, methane–air flame were measured and systematically compared by two different nonperturbing, laser light scattering methods. The rotational temperature of the lowest vibrational state of the electronic ground state of OH was measured by laser-induced fluorescence. The vibrational temperature of the electronic ground state of N2 was also measured by laser Raman scattering. The first quantitative comparison of these two temperatures with a spatial resolution of less than 100 μm throughout both the reaction zone and the postflame zone is presented. The analysis of the data indicates that the N2 vibrational temperature is in equilibrium with the OH rotational temperature at all points.

Steam cracking of hydrocarbons 1. Pyrolysis of heptane

Abstract: The thermal decomposition of heptane in the presence of steam was studied in a flow reactor with large inner surface. The experiments were performed at atmospheric pressure in a temperature range of 680-760 OC for a mass ratio of steam to hydrocarbon 3:l. The reaction products were analyzed by gas chromatography. For the identification both comparison of retention indices with those of standard compounds and literature data and mass spectrometry were used. The conversion process appeared to be a first-order reaction with a frequency factor of 1.34 X 10'' s-' and an activation energy of 195.5 kJ mol-'. The composition of the mixture of reaction products was in agreement with the Rice-Kossiakoff theory, except for ethane and 1-hexene.

LPE growth of Hg0.60Cd0.40Te from Te‐rich solution

Abstract: Hg0.60Cd0.40Te has been grown at atmospheric pressure using a liquid phase epitaxy (LPE) slider system. The compositions are uniform to within ±0.01 mole fraction across the layer and with depth into the layer except for a 3‐μm‐thick interdiffusion region. The layers are p type as grown with carrier concentration of 1017 cm−3 and are annealable to n type with a carrier concentration of 4×1015 cm−3.

Theoretical and experimental studies of the deposition of Na2So4 from seeded combustion gases

Abstract: Flames in a Mach 0.3 atmospheric pressure laboratory burner rig were doped with sea salt, NaS04, and NaCl, respectively, in an effort to validate theoretical dew point predictions made by a local thermochemical equilibrium (LTCE) method of predicting condensation temperatures of sodium sulfate in flame environments. Deposits were collected on cylindrical platinum targets placed in the combustion products, and the deposition was studied as a function of collector temperature. Experimental deposition onset temperatures checked within experimental error with LTCE-predicted temperatures. A multicomponent mass transfer equation was developed to predict the rate of deposition of Na2SO4(c) via vapor transport at temperatures below the deposition onset temperature. Agreement between maximum deposition rates predicted by this chemically frozen boundary layer (CFBL) theory and those obtained in the seeded laboratory burner experiments is good.

Plasma polymerization of ethylene in an atmospheric pressure-pulsed discharge

Abstract: The polymerization of ethylene in an atmospheric pressure-pulsed discharge has been studied. Partial pressures of ethylene up to 4 kN/sq m were used with helium as a diluent. Deposition rates (on glass slides) were the same throughout the discharge volume over a wide range of operating conditions. These rates were in the 1-2 A/sec range. The films were clear, soft, and showed good adhesion to the glass substrates. Oligomers large enough to visibly scatter 637.8-nm light were observed in the gas phase under all conditions in which film deposition occurred. The experimental results suggest that Brownian diffusion of these oligomers was the rate-limiting step in the film deposition process.

Elastohydrodynamic lubrication at high pressures II. Non-Newtonian behaviour

Abstract: An experimental study has been made of the elastohydrodynamic behaviour of a range of fluids, including some of widely different pressure coefficient of viscosity. It is shown that the complex pattern of elasto-hydrodynamic behaviour observed at high pressure is due predominantly to the interplay between two non-Newtonian effects. The first is viscoelasticity. This has the effect that, at small degrees of shear, all the fluids behave as viscous liquids at low pressure and as elastic solids at high. The transition occurs when the viscosity attains 10 5 Pa s. The second is the non-linearity at high degrees of shear between the shear stress and the rate of shear. The consequence of this is that at sufficiently high rates of shear the fluid loses any elastic character and behaves as a non-Newtonian liquid. It is shown that the behaviour of the real system resembles that of a Maxwell viscoelastic model into which Eyring’s elementary expression for viscosity is incorporated to describe the non-Newtonian character of the liquid component. At high shear stresses the value of the traction coefficient {T/W ) is given by the expression T/W = α ¯ T 0 - T 0 /T 0 / p ln ( T 0 /2 n 0 s), where α ¯ is the pressure coefficient of viscosity, T 0 a characteristicshearstress, p the pressure, n 0 the viscosity at atmospheric pressure and s the rate of shear. The values of α ¯ which are appropriate relate to the actual pressures applied. These pressures are considerably in excess of those obtainable in conventional high pressure viscometry but it is shown that the appropriate value of α ¯ can be derived satisfactorily from the elastohydrodynamic experiments themselves. The fluid giving the highest value of the traction coefficient proved to be one whose pressure coefficient of viscosity was considerably greater at high pressure than at low. The results suggest that with high polymers the structural unit responsible for flow is considerably smaller than the polymer molecule itself. In contrast, certain types of molecules having branch chains appear to become entangled making the unit for flow appreciably larger than the individual molecule.

Method and apparatus for the adiabatic expansion of liquid anhydrous ammonia

Abstract: Cold anhydrous ammonia, preferably cold liquid anhydrous ammonia at substantially ambient or atmospheric pressure is applied to feed grains, forages and anaerobically fermentable plant material to supply thereto and provide therein non-protein nitrogen (NPN). The cold anhydrous ammonia is obtained by supplying a stream of ambient temperature, pressurized anhydrous liquid ammonia to an expansion chamber for expansion therein to provide the cold anhydrous ammonia. Cold anhydrous ammonia, preferably substantially only cold liquid anhydrous ammonia, is recovered from the expansion chamber operated under substantially adiabatic conditions, at a temperature in the range -30° F. to about -17° F. and at substantially ambient or atmospheric pressure, such as at a pressure in the range 1 pound per square inch below atmospheric pressure up to about 5 pounds per square inch atmospheric pressure.

Production and Applications of Microwave Surface Wave Plasma at Atmospheric Pressure

Abstract: Surface wave microwave excitation structures can be used to produce relatively long plasma columns at atmospheric pressure. Characteristics of this new versatile plasma are given. Applications such as trace gas analysis by optical emission spectroscopy, production of flames of various compositions, welding, and spectral lamps are presented.

New Series Exhibiting Pure Enantiotropic Nematic Reentrant Compounds at Atmospheric Pressure

Abstract: Some derivatives of an homologous series of 4-aIkoxy-benzoyloxy-4′-cyanotolanes are synthesized. Two of them exhibit a stable nematic reentrant phase at atmospheric pressure.

Simultaneous TG-DTA mass-spectrometry to 1550‡

Abstract: Newly developed coupling systems are introduced and discussed for the combination of a simultaneous TG-DTA apparatus with a quadrupole mass-spectrometer. In the study of decomposition processes under atmospheric pressure, two-stage pressure reduction systems allow an exact gas analysis by the simultaneous operation of a mass-spectrometer up to 1550‡. For measurements under high vacuum, the pressure reduction systems are removed, and by direct viewing between test body and ion source a high sensitivity is achieved. The function of these combined units is demonstrated by means of applications in inorganic and organic chemistry.

Temporal changes of particle densities and temperatures in a decaying arc discharge

Abstract: This study deals with a decaying argon plasma at atmospheric pressure. It is shown that cylindrical symmetry is maintained, which enables us to measure experimentally the plasma composition at any moment after the switch-off. The changes in the particle density and the kinetic temperature have been deduced. For an electron density lower than 3x1016cm-3, equilibration of the electrons towards the gas temperature is observed. Partial LTE between electrons and excited atoms is discussed.