Effect Of Gas Density Research Articles

The effect of gas density on glottal vibration and exit jet particle velocity

Although theoretical studies include a term for gas density in their mathematical descriptions of glottal aerodynamics, no studies have measured the effect of gas density on glottal vibration and particle velocity. This study used a constant temperature anemometer in the in vivo canine model of phonation to evaluate the effect of gas density on subglottic pressure, particle velocity, and glottal vibration by comparing phonation with air and helium. With gas flow and laryngeal nerve stimulation held constant, peak subglottic pressure was significantly greater during helium phonation (70 cm Hg) than during air phonation (62 cm Hg). In addition, peak particle velocity during helium phonation (45 m/s) was significantly greater than phonation with air (34 m/s). However, the increase in particle velocity with helium compared to air was less than predicted by the Bernoulli relationship. This loss in velocity likely represents turbulent and frictional forces at the glottal outlet.

Air pressure regulation during speech productiona)

Vocal tract pressures during speech tend to be maintained in the face of airway leaks that might be encountered by individuals with repaired palatal clefts. This study tested the hypothesis that such constant pressures can be explained as a consequence of constant pressure source characteristics of the respiratory system during speech production. This conceptualization differs from pressure regulation theories [e.g., D. Warren, Cleft Palate J. 23, 251-260 (1986)] which posit that active reflexive compensatory responses occur to regulate air pressure during speech. Four experiments were conducted to (a) confirm the distinction between constant flow versus constant pressure sources using a plastic vocal tract model, (b) compare air pressure and flow patterns associated with airway leaks in normal speakers to model data, (c) study the effects of gas density in the vocal tract model on air pressure and air flow patterns predicted by a nonreflexive constant pressure source hypothesis, and (d) compare air pressure and air flow patterns associated with airway leaks obtained from normal speakers using different gas densities to model data. Overall, observed flow and pressure patterns suggest the possible influence of constant pressure source characteristics of the respiratory system during speech on maintenance of intraoral air pressure.

Hydrogen dissociation in a microwave discharge for diamond deposition

A mathematical model was developed to predict the degree of gas dissociation in an H 2 microwave discharge sustained in a tubular reactor. Reaction rate coefficients for electron-particle reactions were determined by solving the Boltzmann equation for the electron energy distribution function (EEDF). These coefficients were parameterized and used in a plasma model to calculate the self-sustaining electric field, atomic hydrogen density and electron density in the plasma. The effects of total gas density (pressure), power, flow rate, and wall recombination probability were investigated. In the parameter range studied, gas dissociation was enhanced by lowering the total gas density and/or increasing power. Wall recombination did not affect the atom density for values of the recombination probability lower than 2 × 10 −4. Addition of 1% CH 4 to the hydrogen discharge had only a minor effect on the EEDF. Therefore, results reported here can also be used to calculate the electron-particle reaction rate coefficients in the H 2 CH 4 discharge. The model provides guidelines for controlling H 2 dissociation in plasma chemical vapor deposition reactors used for diamond growth.

Dispersed-phase structure of pressure-atomized sprays at various gas densities

The dispersed-phase structure of the dense-spray region of pressure-atom ized sprays was studied for atomization breakup conditions, considering large-scale (9.5 mm initial diameter) water jets in still-air at ambient pressures of 1, 2, and 4 atm, with both fully developed turbulent pipe flow and nonturbulent slug flow at the jet exit. Drop sizes and velocities and liquid-volume fractions and fluxes were measured using holography. Measurements were compared with predictions based on the locally homogeneous flow (LHF) approximation as well as recent correlations of drop sizes after primary breakup of turbulent and nonturbulent liquids. The dispersed-flow region beyond the liquid surface was relatively dilute (liquid-volume fractions less than 0.1%), with significant separated-flow effects throughout, and evidence of near-limit secondary breakup and drop deformation near the liquid surface. Turbulent primary breakup predictions were satisfactory at atmospheric pressure, where the correlation was developed, but failed to predict observed trends of decreasing drop sizes with increasing gas density due to aerodynamic effects; in contrast, the laminar primary breakup predictions successfully treated the relatively small effects of gas density for this breakup mechanism. Effects of liquid turbulence at the jet exit were qualitatively similar to single-phase flows, yielding faster mixing rates with increased turbulence levels even though drop sizes tended to increase as well. LHF predictions within the dispersed-flow region were only qualitatively correct due to significant separated-flow effects, but tended to improve as the ambient pressure and the distance from the jet exit increased.

Effects of gas density on the structure of liquid jets in still gases

A theoretical and experimental study of the near jet-exit region of nonevaporatin g round liquid jets in still gases is described, emphasizing effects of ambient gas density in the atomization breakup regime where liquid breakup begins right at the jet exit. Mean liquid volume fraction distributions were measured for 9.5-mm-diam water jets in still air at pressures of 1-8 atm. Mixing was strongly affected by the gas/liquid density ratio and the degree of flow development at the jet exit, with the largest gas/liquid density ratio and fully developed turbulent pipe flow yielding the fastest mixing rates. Flow properties were predicted using the locally homogeneous flow approximation, where relative velocities between the phases are assumed to be small in comparison to mean flow velocities. Predictions were in good agreement with measurements, including representation of effects of gas/liquid density ratio and flow development at the jet exit, but only at relatively high mixture fractions. In contrast, separated flow effects caused predictions to overestimate rates of flow development at low mixture fractions.

Effect of gas density on power consumption in aerated vessel agitated by a Rushton turbine.

We investigate the effect of gas density- and, by implication, pressure- on the power drawn under gassed conditions

Bubble size distributions in impeller region in a gas-sparged vessel agitated by a Rushton turbine.

Sauter mean bubble sizes and size distributions on a number basis were determined photographically in the neighbourhood of a Rushton turbine impeller. To determine the effect of gas density, four gases of molecular weights from 4 to 131 were used and deionized water (coalescing) and water saturated with carbon dioxide (repressed coalescence) were used as the liquids. Very low gassing rates with impeller speeds just above the flooding-loading transition were used to allow an unobstructed light path for photography of a flat-bottomed vessel of 0.61 m diameter.All the bubble size distributions show positive skewness with most bubbles less than 0.2 mm in diameter. The Sauter mean is in the range of 0.35 to 0.7 mm. These sizes are smaller than have usually been reported because of the point of measurement. The Sauter mean diameters decrease with increasing impeller speed, but not as rapidly as implied by Kolmogoroffs theory of isotropic turbulence. The size also increases slightly with increasing gassing rate or molecular weight of gas.

Gas mixing in lung model ventilated by high frequency oscillation: Effect of tidal volume, frequency and molecular diffusivity

The efficiency of gas mixing during sinusoidal oscillatory flow in a model of human lung cast was assessed by using a multibreath carbon dioxide washout manoeuvre. The experiments were performed at high frequencies (5, 10, 15 and 20 Hz) and low tidal volumes (50, 90 and 120 cm3). A particular effort was made to analyse the influence of flow oscillation conditions (f and VT) as well as the effect of resident alveolar gas density (molecular diffusion) on the effective diffusion coefficient (Deff). This longitudinal mixing parameter was found to be strongly dependent on the tidal volume (approximately proportional to VT1.4) and weakly dependent on the frequency (approximately proportional to f0.5). However, molecular diffusion was not, in general, a limiting factor in the gas transport process during high-frequency oscillation (HFO).

The effect of gas density on glottal vibration and exit jet particle velocity

Although theoretical studies include a term for gas density in their mathematical descriptions of glottal aerodynamics, there are no studies that have measured the effect of gas density on glottal vibration. This study used an in vivo canine model to evaluate the effect of gas density on glottal vibration by comparing phonation with air and helium. Phonation with helium at a constant flow rate resulted in an increased exit jet particle velocity, and an increased open phase, compared to phonation with air. Phonation with helium also resulted in a decrease in maximum glottal width, glottal area per period, frequency, and subglottic pressure when compared to phonation with air. These results were compared to those obtained with air and helium in a four‐mass computer model of phonation.

Effects of Gas Density and Viscosity on Response of Aerodynamic Particle Sizer

The performance of the aerodynamic particle sizer (APS) in an atmosphere that differs from standard calibration conditions was studied. The response of the APS for monodisperse polystyrene latex and dioctylphthalate particles ranging from 2.4 to 15.1 μm in diameter was measured in air, argon, and nitrous oxide atmospheres. The measurements indicated that particles in argon and in nitrous oxide accelerate faster than those in air. In order to postulate the mechanisms and interpret the observed results, the effects of both gas viscosity and gas density on instrument performance were considered. The particle density correction factor previously given by Wang and John (1987) (Aerosol Science and Technology. 6:191–198) was extended to include gas property effects. Good agreement was obtained between the new factor and the experimental data. Existing data obtained at a low pressure in air were also compared successfully with the developed model. Expected applications of the work are the use of the APS in an arb...

Pressure and gas density effects on bubble break-up and gas hold-up in bubble columns

The influence of both pressure and gas molecular weight on bubble size and gas hold-up in a bubble column was studied. It was determined that gas hold-up increases whereas the bubble size decreases with increasing gas density at a constant superficial gas velocity. It was also determined that these findings cannot be explained by the influence of gas density on bubble formation as is assumed in the literature. A new explanation for the results is presented, based on experimentally obtained evidence that gas density influences bubble break-up.

The effect of gas properties on drops in annular flow

The effect of gas density on the mean drop size and fraction of entrainment in annular two-phase flow has been studied. The data was obtained for a vertical tube of 10.26 mm dia held at a pressure of 1.5 b and ambient temperature. Drop sizes were measured using a laser diffraction technique. Reductions in the gas density show decreases in the entrained liquid fraction whilst the effect on drop size is less certain. This may be obscured by the different entrainment mechanisms, predominating in each fluid system: bag breakup in the helium/water experiments and ligament breakup in the air/water tests. A decrease in the gas density causes the deposition coefficient to increase. The results show that preferential deposition of drops, subsequent to film removal, takes place. At low gas velocities larger drops deposit first by a direct impaction mechanism, whilst at higher velocities small drops deposit out preferentially by diffusion.

Preferential axial flow during high-frequency oscillations: effects of gas density

Allen et al. (J. Clin. Invest. 76: 620-629, 1985) reported that regional phasic lung distension during high-frequency oscillations (HFO) is substantially and systemically heterogeneous when both frequency (f) and tidal volume (VT) are large. They hypothesized that this phenomenon was attributable to central airway geometry and preferential axial flow induced therein by the momentum flux of the inspiratory gas stream. According to that hypothesis, the observed distribution of phasic lung distension would depend on the ratio VT/VD* (where VD* is an index of anatomic dead space), independent of gas density (rho), when f is scaled in proportion to lung resonant frequency, fo. To test this hypothesis, we used the methods of Allen et al. (ibid.) to study six excised dog lungs during HFO (f = 2-32 Hz; VT = 5-80 ml) using gases of different densities. Alveolar pressure excursions (PA) were measured as rho spanned a 12-fold range using He, air, and SF6. The apex-to-base and right-to-left ratios of PA were used as indexes of regional heterogeneity of phasic lung distension. For each gas at low f, distension of the lung base was favored slightly independent of VT, but at higher f distension of the lung apex was favored when VT was small, whereas distension of the lung base was favored when VT was large. In addition, we observed substantial right-to-left differences in apical lobes during oscillation at high f not seen before.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of humidity and gas density on switching impulse breakdown of short airgaps

The dual purpose of the present work was first to examine the effect of humidity and gas density on the breakdown characteristics of short airgaps and secondly to investigate whether charge injection data could provide additional information concerning the probability of breakdown at low probability levels. Impulse tests were, therefore, performed in a sealed test vessel using laboratory air for pressures in the range 0.7–1.4 bar and absolute humidity levels from ∼ 2 to 15 g/m3. Both pressure and humidity could be closely controlled and measured. The impulse shape was + 100/2500 μs and the test gap consisted of a 5 cm-diameter sphere at 20 cm above an earthed plane. Statistical flashover tests and measurements of apparent charge injection at the sphere were made and both sets of data were analysed using the method of maximum likelihood. The breakdown probabilities were found to satisfy a normal distribution and the charge measurements provided significant additional information at low probability levels. The measured values of V50 were found to depend linearly upon absolute humidity with a slope of 1.5 kV/g/m3 at all pressures. The withstand voltages, on the other hand, were only weakly dependent upon absolute humidity. The humidity correction factors found in the present work agree well with the IEC standard at 1.2 and 1.4 bar, but depart appreciably at lower pressures.

On flow characteristics of a rectangular De Laval nozzle with a low density gas.

Effects of inlet gas density and pressure ratios on a discharge coefficient through a rectangular De Laval nozzle were studied. In the region of Reynolds number less than 2.0 and Knudsen number greater than 1.0, the discharge coefficient appeared to be nearly constant. The flow conductance of the nozzle was compared with free molecular flow theory. Flow characteristics with air or argon through the nozzle were measured and Mach number distributions on horizontal and vertical planes at the nozzle exit revealed. Furthermore, detached shock waves in front of a circular cylinder in a supersonic gas stream were visualized by a glow discharge technique. In this paper, shock detachment distances and pressure rises of the shock waves are compared with conventional data and theory.

HYDRODYNAMICS OF SPOUTED BEDS AT ELEVATED TEMPERATURES

A review of the literature reveals little information on the hydrodynamics of spouted beds at high temperature. Most existing correlations are based upon experiments done at ambient conditions; they have not usually been tested with data at higher temperatures. The present study focussed on obtaining data over a temperature range of 20-420°C. Spouting of three sizes of Ottawa sand with preheated air was couducted in a 156 mm diameter stainless steel semi-cylindrical column with a 60° included angle half-conical base. A transparent wire-glass panel on the flat face allowed measurement of parameters which are otherwise difficult to obtain in a full stainless steel column. In addition to air, helium and methane at room conditions were used as spouting gases. With these two additional gases, it became possible to investigate the effect of changing gas density at constant viscosity and the effect of changing gas viscosity at constant gas density. In general, it was found that the range of stable spouting decreased with decreasing gas density and increasing gas viscosity, hence with increasing air temperature. Existing equations for various spouted bed parameters were tested and, where necessary, empirically modified to fit the new data obtained. @KEYWORDS Spouted bed hydrodynamics, High temperature gas spouting, Temperature effect on spoutability

Effect of resident gas density on CO 2 elimination during high-frequency oscillation: A model study

In order to throw more light on the mechanisms governing the efficiency of intrapulmonary gas mixing during high-frequency oscillatory ventilation, an experimental, and theoretical, study was carried out on a model casting of the airways of a human lung that closely resembled the respiratory tract. The experiments were carried out under various conditions during high-frequency oscillation (HFO), by using alveolor resident gas mixtures of different densities. The efficiency of gas mixing was assessed by measuring the time constants of the CO 2 alveolar washout which were compared to those obtained from simulations on a theoretical model based on a turbulent diffusional resistance concept. Our results showed that the decay in CO 2 concentration was highly dependent on both frequency (ƒ) and tidal volume ( V T ). Tidal volume was found to have a greater effect on efficiency of gas mixing than frequency. Moreover, even though there were statistically significant differences in the time courses of CO 2 washout between N 2 and He, N 2 and SF 6 or between He and SF 6, this could not imply that gas mixing was limited by diffusion. Agreement between the experimental time constants of CO 2 elimination during HFO and the predicted mixing time constants was satisfactory. It is concluded that turbulent augmented diffusion is the main factor responsible for effective gas transport during high-frequency oscillatory ventilation.

Study of fuel distribution in diesel spray. Effects of nozzle diameter, injection pressure and ambient gas density.

The fuel distribution in a diesel spray seriously affects the performance of diesel engines. Nozzle diameter, injection pressure and ambient gas density are important factors, which affect the atomization, penetration and fuel distribution. Therefore, effects of those factors on fuel distribution in a diesel spray were investigated in the cold and quiescent atmosphere. Fuel concentration was deter-mined by the image analysis of shadow photographs of spray. As a result, the following was revealed. In the case of a smaller nozzle diameter and higher injection pressure, the mixing rate of fuel and ambient gas is greater. In similarly designed diesel engines with various power ranges, by normalizing the dimension of engines by nozzle diameter, it is supposed that the shape and fuel distribution of sprays will be similar at same crank angle.

Site of Airflow Obstruction during Early and Late Phase Asthmatic Responses to Allergen Bronchoprovocation

Chronic asthma and late asthmatic responses (LAR) are associated with local inflammation which might be expected to produce airflow obstruction in small airways and to increase nonspecific airway reactivity. In contrast, early asthmatic responses (EAR) are primarily bronchospastic and probably involve more central airways. We challenged 17 nonsmoking, mildly asthmatic atopic subjects with allergen bronchoprovocation and measured changes in spirometry (FEV1) over the next 24 hours. Each subject also performed a helium-oxygen (He-O2) flow-volume loop before challenge (baseline), during the EAR, and six hours and 24 hours after challenge to measure the effect of gas density on flow rates at midvital capacity. Twelve subjects had both an EAR and a LAR; five subjects had only a LAR. Of these 17 subjects, 15 were initially density dependent, while only two were density independent. During the EAR, 13 percent of the density dependent population had significant decreases in delta Vmax 50 percent; 47 percent had significant decreases during LAR. The He-O2 flow data analyzed at specified time points after challenge revealed significant decreases in the mean delta Vmax 50 percent at six hours in those who had only a LAR (p less than 0.01). In those who had a dual airway response, density dependence increased during the EAR, but decreased at six and significantly at 24 hours (p less than 0.05) postchallenge. There was a strong trend for the severity of the LAR (measured by changes in FEV1) to be directly related to the total decrease in delta Vmax 50 percent during the LAR. We conclude that late asthmatic responses occur frequently after a single antigenic bronchial challenge and can be associated with persistent symptoms. The LAR were often associated with a decrease in density dependence of maximal expiratory airflow, and therefore, may involve small airways.

Gas exchange in tidally ventilated and non-steadily perfused lung model

We studied the effect of cyclic lung perfusion — fast cycle in synchrony with heart beats and slow cycle in synchrony with ventilation — on gas exchange in a lung model. There was almost no effect in the fast cycle. In a homogeneous single-lung unit, arterial P O 2 increased, and the (A - a)D O 2 decreased (by approximately 0.5 Torr), as the amplitude of the slow cyclic lung perfusion (TIP) increased. The calculated (A - a)D O 2 and (a - A)D CO 2 were negative. Maximal Pa O 2 was found when peak lung perfusion was delayed with respect to ventilation by 0.2 of a cycle. In a non-homogeneous nine-unit lung, cyclic lung perfusion caused an increase in Pa O 2 and a decrease in (A - a)D O 2 by 2 Torr as compared to steady perfusion. No apparent negative (A - a)D O 2 was found, but apparent negative (a - A)D CO 2 was calculated at no pulmonary shunt and also with 5% shunt. The correlation of cyclic lung perfusion to the reduced (A - a)D O 2 in dense-gas breathing — where large swings of pleural pressure are expected — and its effect on the diffusion capacity of the lung are discussed. Non-steady perfusion of the lung as caused by ventilatory movements expanded our understanding of gas exchange and shed some light on a few controversial experimental findings, such as the negative (a - A)D CO 2 , the decreased (A - a)D O 2 while breathing dense gas, and the effects of gas density on diffusion capacity of the lung.