Changes In Gas Density Research Articles

SUBFEMTOSECOND HIGH-INTENSITY UNIPOLAR ELECTROMAGNETIC SOLITONS AND SHOCK WAVES

We show that atomic gasses can support solitary pulses of unipolar, non-oscillating EM-field ("EM-bubbles") of up to the atomic amplitude, with their length ranging from ~10−9 s to ~10−16 s , which propagate without dispersion and are stable and insensitive to the change of gas density. We found the condition on the atomic potential necessary for formation of EM-bubble. Atomic gasses can also support an EM shock which is a precursor of a cw ionizing field.

Electromagnetic "bubbles" and shock waves: Unipolar, nonoscillating EM solitons.

We show that atomic gases can support solitary pulses of a unipolar electromagnetic field (``EM bubbles'') with amplitude up to the atomic field ( $\ensuremath{\sim}$1${0}^{9}$ V/cm) and duration down to $\ensuremath{\sim}$ ${10}^{\ensuremath{-}16}$ s. EM bubbles propagate without dispersion, are stable, and are insensitive to the change of gas density. Atomic gasses can also support an EM shock wave forming a precursor of a dc ionizing field.

Effects of axial temperature gradient on momentum and heat transfer with oscillating pressure and flow

Effects of axial temperature gradient on heat transfer, momentum transfer and energy conversion mechanisms within a closed cylinder-piston apparatus are analyzed. Assuming that the gas density change is small, the first-order and steady second-order solutions of continuity, momentum and energy equations are obtained. The solutions show that there exists a steady circulating flow and the magnitude of the steady axial velocity increases as the axial temperature gradient increases. There exists not only an oscillating component of heat flux between the gas and the wall, but also a steady component whose direction depends on axial temperature gradient. It is shown that heat is pumped from the wall near the piston to the wall near closed-end for negative axial temperature gradient. Heat transfer relation for both oscillating pressure and oscillating flow conditions is proposed.

Evaluation of a symmetrically disposed Pitot tube flowmeter for measuring gas flow during exercise

We evaluated the effect of airflow and gas composition on the linearity of measurement of airflow by a new disposable flowmeter. The flowmeter is based on the principle of differential pressure measurement across two symmetrically disposed Pitot tubes. Nonlinearities arising from the pressure-to-airflow relationship and sensitivity to changes in gas density were linearized with appropriate software and monitoring of the gas composition. With room air used as the respired gas, the measured tidal volume from a piston pump assembly was consistently within 1-2% of the target tidal volume for each of five flowmeters tested across physiological ranges of flow. Changing gas densities by varying concentrations of O2, CO2, and N2 led to errors in tidal volume measurement that ranged up to 6-8%. However, because the errors were predictable, they were corrected by software to within 0.6% of the target volume. Measurement of minute ventilation during exercise was within 1-2% of that determined from bag collections. We conclude that this type of flowmeter can accurately measure exercise minute ventilation and has advantages over some other flowmeters because of its ruggedness, reproducibility, and ease of sterilization or replacement compared with other flowmeters.

A quantitative laser schlieren method for measurement of neutral gas density in high-pressure gas switches

A quantitative laser schlieren technique has been developed to measure the changes in neutral gas density inside a spark gap switch after breakdown. The measurement system incorporates an array of narrow laser beams which are used to probe the inter-electrode gas volume at discrete distances from the spark axis. Changes in the refractive index gradient within the switch, caused by variations in neutral gas density, result in beam deflection, which is measured using a neutral density wedge/photodiode combination. The resulting schlieren profiles yield both spatially and temporally resolved refractive index data, which enable calculation of the gas density. The use of four averaged trials to obtain the final neutral gas density profiles minimizes errors caused by the turbulent nature of the cooling gas. A typical set of results is presented for SF6 at a pressure of 0.5 bar.

Signal averaging with a stabilized dual beam Mach Zehnder interferometer: Monitoring changes in gas density

A traditional Mach Zehnder interferometer has been fitted with a feedback loop that maintains a constant and known phase difference between the two optical beams. This stabilization is necessary so that signal averaging will not distort the signal. To increase sensitivity for small phase shifts and determine absolute phase shifts when large phase shifts are involved a dual beam technique, which uses circularly polarized monochromatic light, is implemented. In one arm of the interferometer a phase shift of 90° between the two polarization orientations is introduced via a quarter wave plate. Two photodiodes independently detect the polarized light beams that maintain a 90° phase difference. One of these signals provides the input for the stabilization while the other (with enhanced sensitivity) is used to monitor the density. Unambiguous phase shifts are calculated from the information contained in both signals. The interferometer is being used to monitor gas density changes resulting from vibrational to translational energy transfer.

Heat Transfer in Thin, Compact Heat Exchangers With Circular, Rectangular, or Pin-Fin Flow Passages

We have measured heat transfer and pressure drop of three thin, compact heat exchangers in helium gas at 3.5 MPa and higher, with Reynolds numbers of 450 to 36,000. The flow geometries for the three heat exchanger specimens were: circular tube, rectangular channel, and staggered pin fin with tapered pins. The specimens were heated radiatively at heat fluxes up to 77 W/cm2. Correlations were developed for the isothermal friction factor as a function of Reynolds number, and for the Nusselt number as a function of Reynolds number and the ratio of wall temperature to fluid temperature. The specimen with the pin fin internal geometry had significantly better heat transfer than the other specimens, but it also had higher pressure drop. For certain conditions of helium flow and heating, the temperature more than doubled from the inlet to the outlet of the specimens, producing large changes in gas velocity, density, viscosity, and thermal conductivity. These changes in properties did not affect the correlations for friction factor and Nusselt number in turbulent flow.

Airways impedance during single breaths of foreign gases

The changes in airways resistance (Raw) and inertance (Iaw) during single inspirations of pure methane, helium, neon, and ethane at a flow of 0.1 l/s were measured in six healthy subjects by use of a forced-oscillation technique. Raw and Iaw were computed from respiratory transfer impedance obtained at a frequency of 20 Hz by applying pressure oscillations at the chest and measuring flow at the mouth with a bag-in-box system. Compared with the air data, the changes of Iaw after inhalation of 500 ml of gas averaged -41.1% with methane, -82.8% with helium, -25.8% with neon, and +4.8% with ethane. These changes were slightly less than the changes in gas density (-45%, -86%, -31%, and +5%, respectively). The inhaled volumes at which 50% of the changes had occurred (V50) did not differ significantly among gases and were approximately 100 ml. For Raw the data were more noisy than for Iaw; they were discarded in two subjects because of a strong and irreproducible volume dependence in air. Consistent differences were seen between the remaining subjects, one of whom exhibited a predominant viscosity dependence of Raw, one a predominant density dependence, and two an intermediate pattern. V50s were larger for Raw than for Iaw, indicating a more peripheral distribution of Raw. For Raw, V50s were lower with helium than with methane, in agreement with the notion that density-dependent resistance is located mainly in the large airways. The results suggest that some information on the serial distribution of Raw and Iaw may be derived from impedance measurements with foreign gases.

Local particle velocity, size, and concentration measurements in an industrial-scale pulverized coal-fired boiler

Parametric, in situ, particle velocity, size, and number density measurements have been made in a full-scale, coal-burning power plant using an optical diagnostic technique. Available ports in the boiler allowed measurement at three locations above the burner level. Variable test parameters included furnace load, excess air, and burner tilt, using a medium volatile bituminous coal. Higher particle velocities were observed when the boiler was operated at maximum capacity due to increased air and coal flows. Port-to-port velocity variations were attributed to the rotational nature of the mean flow, changes in gas density with changing gas temperature, and the interaction of the flow with the boiler nose. Measured particle number density profiles were characterized by high values in the small particle size class (< μm), decreasing exponentially with increasing particle size. The measured number density profiles indicated that the combustion process is largely complete at locations 7 m above the burners and that the particles measured consisted primarily of ash, a conclusion which is also supported by the percent carbon-in-ash data. The mass-mean and number-mean particle sizes for all tests varied between 10 and 45, and 0.5 and 0.85 μm, respectively. The characteristic similarity between the particle size distribution of the ash and that of the parent char, previously documented in laboratory scale investigations, was also observed in the present study. Cumulative mass distribution profiles indicated that a significant centrifugal effect is exerted on the condensed phase by the rotating flow. An increase in small particle number density (∼ 0.5 μm) was also apparent at lower boiler loads due to changes in the combustion process occurring at these operating conditions, which affect the various modes of ash particle formation.

Molecular and atomic hydrogen line emission from star-forming galaxies

view Abstract Citations (99) References (49) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Molecular and Atomic Hydrogen Line Emission from Star-forming Galaxies Puxley, P. J. ; Hawarden, T. G. ; Mountain, C. M. Abstract Models of the generation of molecular and atomic hydrogen line emission from star-forming regions are discussed. These take into account the variations in the efficiency with which fluorescent H_2_ emission is produced as the ratio of the incident soft UV to the gas density changes (the lower this ratio, the higher the efficiency). The models deal with hot stars embedded within molecular clouds, large compact clusters of young stars generating intense UV fields, and emission from clouds bathed in a relatively diffuse UV field. The results from the models are compared with the ratio of the observed intensities of the H_2_ v = 1-0 S(1) and Brγ lines from the nuclear regions for a sample of 29 galaxies whose optical spectra are dominated by H II regions. Unlike previous investigators, we find that the scatter in the ratio of the two lines is quite small, suggesting a common mechanism for the H_2_ excitation. The line ratios are found to be consistent with H_2_ emission from photodissociation zones and in most of the sample can be understood in terms of ensembles of hot stars intimately mixed with molecular clouds, and perhaps forming blisters at their surface, although a few galaxies require much higher ratios of the UV intensity to the gas density, conditions which imply the presence of large numbers of massive stars in compact clusters. Publication: The Astrophysical Journal Pub Date: November 1990 DOI: 10.1086/169386 Bibcode: 1990ApJ...364...77P Keywords: Atomic Spectra; Emission Spectra; Hydrogen; Molecular Spectra; Star Formation; Starburst Galaxies; Astronomical Models; Star Clusters; Stellar Mass; Ultraviolet Radiation; Astrophysics; GALAXIES: INTERSTELLAR MATTER; INTERSTELLAR: MOLECULES; RADIATION MECHANISMS; STARS: FORMATION full text sources ADS | data products NED (29) SIMBAD (28) Related Materials (1) Erratum: 1991ApJ...372..733P

Density effects on ion mobilities in electron attaching fluids: CS2, SF6, and C6F6

Ion mobilities μ were measured at densities n ranging from those of the low density gas (n &lt; 0.01 nc, where nc = critical fluid density) through the dense gas and low-density liquid transition region (~0.5nc to 2nc) to the normal liquid (~3nc). The mobility at a given density was constant over a 10-fold variation of electric field strength, typically in the range 0.1 &lt; E(MV/m) &lt; 5. In the gas phase changes in mobility were dominated by changes in gas density. Comparison with neutral molecule transport in SF6 was used to illustrate the change in the effect of the ion on its local environment from that of molecular cluster formation to that of liquid electrostriction as density was increased. In the liquid, changes in ion mobility are dominated by changes in free volume. Mobilities in the present liquids could be described without reference to the activation energies suggested by the Arrhenius model. Keywords: ion, mobility, fluid, density, electron attaching.

The effect of density variations on elemental abundance ratios in gaseous nebulae

Using numerical analysis it is demonstrated that when there are changes in gas density within a nebulae various empirical methods for determining the electron density can give different results. Eleven different species are considered which have line pair ratios that are well-known electron density (Ne) diagnostic tools. In the presence of varying density, there is a progression in inferred values of Ne from N+ (122/204 microns) at the lowest to C(2+) (1906/1909 A) at the highest. For many of the 11 species there is a fixed order in the inferred density, while for others the order can change somewhat for different mixes of densities. When there are nonconstant density conditions, it is shown that systematic biases may occur in the empirical determination of chemical abundance ratios. Tabular material is presented that delineates the maximum bias that can occur in the determination of a particular abundance ratio in a two-component model.

Effect of Density Variations on Elemental Abundance Determinations in Gaseous Nebulae

When there are changes in gas density within a nebula, various methods of determining the electron density Ne can give different results. Irrespective of differences in ionization structure, there will be deviations in derived values of Ne due to the physics of populating the energy levels. To focus on Ne variations, the electron temperature is held constant. For two cases presented, the values of Ne inferred range over a factor of ten from nine species (line pairs); in order of increasing Ne, they are N+(122/204 μm), O++(52/88 μm), S+(6716/6731 A), S++(18.7/33.5 μm), 0+(3726/3729 A), Ne++(15/36 μm), Ar+3 (4711/4740 A), Ar++(8.99/21.8 μm), and C++(1906/1909 A). This is basically a progression from lower to higher critical densities, Nc, for the lines involved, although other factors are involved. The above order can change somewhat for different mixes of densities.

Pressure, flow, and density relationships in airway models during constant-flow ventilation.

Adequate CO2 elimination and normal arterial PCO2 levels can be maintained in dogs during apnea by delivering a continuous flow of inspired gas at high flow rate (1-3 l.min-1.kg-1) through tubes placed in the main-stem bronchi. However, during constant-flow ventilation (CFV) the mean alveolar pressure is increased, causing increased lung volume despite low pressures in the trachea. We hypothesized that the increased dynamic alveolar pressures during CFV were due to momentum transfer from the high-velocity jet stream to resident gas in the lung. To test this, we simulated CFV in straight tubes and in a branched airway model to determine whether changes in gas flow rate (V), gas density (rho), and tube diameter (D) altered the pressure difference (delta P) between alveoli and airway opening in a manner consistent with that predicted by conservation of momentum. Momentum analysis predicts that delta P should vary with V2, whereas measurements yielded a dependence of V1.69 in branched tubes and V1.9 in straight tubes. Substitution of heliox (80% He-20% O2) for air significantly reduced lung hyperinflation during CFV. As predicted by momentum transfer, delta P varied with rho 1.0. Momentum analysis also predicts that delta P should vary with D-2.0, whereas measurements indicated a dependence on D-2.02. The influence of V and rho on depth of penetration of the jet down the airway was explored in a straight tube model by varying the flow rate and gas used. The influence of geometry on penetration was measured by changing the ratio of jet-to-airway tube diameters.(ABSTRACT TRUNCATED AT 250 WORDS)

The Minimum in the Mobility-Density Curve for Electrons Injected into Insulating Dense Gases

Abstract Average force and force-force correlation formulae both point to the same result that the mobility μ of electrons injected into dense gases like Ar, Xe, CH4 and C2H6 ought to exhibit at least gross regularities with respect to changes in gas density n. This is the motivation for focussing here on the mobility minimum characterized by dμ/dn = 0. At this minimum, a formula for μmin is obtained from which the scattering length a has been eliminated in favour of its density derivative (da/dn). This density derivative, it is argued, must have the form a gasωt, where ωt, is a ‘characteristic volume for transport’ while a gas is the scattering length in the dilute gas limit. The Onsager continuum model, plus the Bottcher-Onsager formula for the dielectric constant, can be used as a first estimate of ωt, which is shown to be proportional to the cube of the ‘cavity radius’ in this model. The formula for μmin is finally brought into direct contact with experiment.

A quantitative laser-interferometric measurement of gas density in a gas-particle mixture

A description is given of an interferometric method to determine the gas density in a gas-droplet mixture. The method uses a laser Mach-Zehnder interferometer in the phase quadrature mode. It is shown that a direct, quantitative and unambiguous determination of gas density changes is possible in a medium that contains light scattering particles. Examples are given of the application of the interferometer to expanding flows with condensation and to shock wave propagation in a fog, illustrating the potential of the method for large and fast density variations.

Rotameter Corrections for Gas Density

Changes in gas density significantly affect the airflow measurements by rotometers. Using an air sampling device with rotameter at an altitude different than that for which it was calibrated can yield serious error. The correction of the rotameter for altitude is relatively straightforward but can be confusing. Prior publications in the air sampling literature dealt primarily with portable sampling pump behavior rather than that of the rotameter. The paper derives the correction equations and illustrates and tabulates their proper use for various situations.

Influence of airway geometry on expiratory flow limitation and density dependence

In a study of individuals of the same sex and similar age and size, between subject variability was noted in lung recoil, lung size, density dependence of maximum expiratory flow, tracheal cross-sectional area, and anatomic dead space. No significance was observed in the relationships to one another of lung size or either estimate of airway size, nor did the magnitude of the change in flow with change in gas density show a consistent relationship to any of the size variables. The results indicate that there is a dissociation between tracheal dimensions and anatomic dead space as well as between airway size and lung size, suggesting that dysanapsis is a general phenomenon. This introduces additional sources of interindividual variability of maximum expiratory flow and measurements of density dependence of flow.

Beam-quality-determining processes in high-energy atomic iodine amplifiers

The disturbance of the optical homogeneity of high-energy, 1.315 μm atomic iodine amplifier systems by gas density changes, produced by gas-dynamic effects following nonuniform photolysis, has been analyzed for a wide range of line-broadening buffer gases. Mechanisms of photolysis gas heating and the relative merit of different buffer gases for minimizing density changes are discussed. An experimental study of the buffer gas dependence has shown good agreement with the gas-dynamic analysis. The model has been used to determine conditions for diffraction-limited amplification for varying pump times and buffer gas composition for typical large amplifier pumping profiles, showing the possibility for significantly increasing pump pulse duration.

Infant endotracheal tube resistance

Endotracheal tube resistance may increase upper airway resistance and the work of breathing beyond the normal range in adults of children who are chronically intubated and receiving intermittent mandatory ventilation. The purpose of this study was to measure the resistance of infant endotracheal tubes (IETTs) over the range of normal infant respiratory flows while systematically changing length, diameter, and carrier gas density. Resistance was measured in IETTs of 2.5, 3.0, and 3.5 mm inner diameter at flows increasing from 10--150 ml/sec, using both air and 80% helium- 20% oxygen (He-O2) as the carrier gases. Tube length was progressively shortened from full length to 4.8 cm in 2-cm increments, and resistance to both air and He-O2 was measured at all lengths. Reynolds' number calculations and the relationship of resistance to flow showed the flow regime in IETTs to be transitional in nature. Increasing tube diameter, decreasing length, or decreasing gas density led to large decreases in IETT flow resistance. Over the range of normal infant flows, IETT resistance is equal to or higher than that of the normal upper aiaway. IETT resistance might increase the work of breathing in some infants to the point of respiratory failure, and such resistance may be lowered by systematic changes in IETT diameter, length, or carrier gas density.