Variation Of Ambient Pressure Research Articles

The Effects of Ambient Pressure Upon Global Shape and Hydrodynamic Behavior of Buoyant Laminar Jet Diffusion Flames

Abstract The action of ambient pressure variation upon buoyant laminar jet diffusion flames is studied experimentally and theoretically at low Reynolds number. For the first time, the flame height and the surface area are measured as a function of ambient pressure at different flow rates and for different burner diameters. Two distinct regimes have been found: one in which the flame flickers and the other in which it does not. For steady flames, the flame surface area increases significantly with reduction of the ambient pressure, while the height increases slightly or remains nearly constant. For flickering flames, the flame height decreases with reduction of pressure, which finally results in a decrease in the surface area of the flame. A simple theoretical model based on a cylindrical flame geometry which considers both the radial diffusion of species and the buoyancy effects, is proposed to predict the trend of surface area variation for steady flames. For steady flames, both reductions of gravity lev...

The effect of systematic change in middle ear pressure on transitorily evoked otoacoustic emissions--a pressure chamber study

Otoacoustic emission power spectrum and amplitude are influenced by the middle ear transmission mechanism. In this study, the influence of progressive increase in atmospheric pressure on the frequency and amplitude of transiently evoked otoacoustic emissions (TEOAEs) was determined in normally hearing humans. For testing, subjects were seated in a pressure chamber. Transiently evoked otoacoustic emissions were tested in 20 ears of 20 subjects using of 80 microseconds unfiltered click and tone bursts duration at 0.5, 1, 2, 3, and 4 kHz presented at 40 dBnHL. Ambient air pressure was increased from 0 kPa up to 8 kPa in 2-kPa steps. In spite of large interindividual differences, the results demonstrate that the changes that occur in TEOAEs with variations in ambient air pressure are frequency specific. Amplitude and reproducibility of high-frequency TEOAEs are less influenced by middle ear pressure changes than are the amplitude and reproducibility of low- and middle-frequency TEOAEs. Results have implications for clinical and research applications of TEOAE measurements in that middle-ear and inner-ear effects on OAEs can be differentiated.

Collapse of a bubble in the cavitation zone near a rigid boundary

This paper discusses the cavitation erosion problem and one of its difficult aspects, i.e., cumulative flow development in vapor-gas bubbles and evaluation of parameters of high-speed microjets as main sources of impulse influence on a nearby rigid wall (boundary). The axisymmetric potential problem of cavity collapse in a nonviscous and incompressible liquid with variable ambient pressure is considered. The Laplace’s equation is solved numerically by use of boundary-integral methods. The influence of a rigid wall is modeled by the reflection method. Ambient pressure is calculated by use of a two-phase liquid model describing cavitation cluster dynamics. The dynamics of a bubble situated near a rigid boundary is investigated and the results are obtained for cumulative jet formation in the bubble.

Measurement of alveolar gas volume by ambient pressure changes in isolated lungs.

Alveolar gas volume (AGV) may be measured in humans (Peslin et al., J. Appl. Physiol. 62: 359-363, 1987) by applying very slow sinusoidal variations of ambient pressure (delta Pam) around the body and studying the relationship between delta Pam and the resulting gas displacement at the mouth (delta Vaw): AGVapc = (PB.delta Vaw)/(delta Pam.cos phi), where AGVapc is AGV measured by ambient pressure changes, PB is barometric minus alveolar water vapor pressure, and phi is the phase angle between Pam and Vaw. The applicability of this method to excised lungs at various transpulmonary pressures was assessed in six rabbit lungs and three dog lobes by reference to AGV measurements by He dilution (AGVdil) and by a volumetric method (AGVvol). Except in one instance, AGVapc did not change significantly when the frequency of delta Pam was varied from 0.02 to 0.2 Hz. AGVapc was highly correlated (P less than 0.001) to both AGVdil and AGVvol. It did not differ significantly from AGVdil (81.4 +/- 50.6 vs. 80.2 +/- 44.2 ml) and was only marginally higher than AGVvol (64.6 +/- 26.9 vs. 62.4 +/- 24.4 ml, P less than 0.05). We conclude that the method usually provides accurate results in excised lung preparations. Its main advantages are that it does not require manipulating the lung or changing its volume and that the measurement takes less than 1 min.

Response of Nautilus to Variation in Ambient Pressure

ABSTRACT Juvenile Nautilus, tested in a high-pressure animal maintenance apparatus, are sensitive to increases in ambient hydrostatic pressure as small as l × 105Nm−2 (= 1 atm = 100kPa). They respond to such pressure increases in a characteristic ‘depth alarm’ behaviour pattern, which consists primarily of rapid upward swimming. These activity bursts may serve to restore them to their original depth. The animals apparently continue this behaviour until fatigued. Pressure decrease elicits no obvious response. The pressure-sensing mechanism may be located within the statocyst, or possibly in the posterior mantle or siphuncle. The operation of. the latter two mechanisms involves tensional strain induced by the hydrostatic load in the outermost septum and wall of the siphuncular tube.

The active space of red-winged blackbird song

Active space, that distance from the source over which signal amplitude remains above the detection threshold of potential receivers, was determined for Red-winged Blackbird (Agelaius phoeniceus) song in an upland pasture near Ithaca, New York. Song amplitude, the rate of signal attenuation, the amplitude of ambient noise, and the sensitivity of redwings to song masked by noise determine active space and were measured in the field: 1. Maximum root-mean-square song amplitude at 1 m from a singing bird ranged from 88.5–93.5 dB SPL (\(\bar X\)± SE = 90.8±0.21 dB SPL). 2. Close to the source, song attenuates at a rate which closely matches that predicted by spherical spreading (6 dB/doubling of distance) alone. At distances beyond about 30 m, however, excess attenuation becomes important (Fig. 4). The rate of attenuation varies with relative wind direction (Table 1). 3. Ambient noise level is relatively low in early morning, rises in late morning and afternoon as air turbulence increases, and then drops again in the evening as turbulence decreases (Table 2 and Appendix). Measured on a 4 kHz octave filter scale (center frequency = 4 kHz, octave pass-band = 2.83– 5.66 kHz), noise during one day ranges from 15 dB SPL (at 06∶00 h) to 36 dB SPL (at 11∶00 h), more than a 10-fold variation in ambient sound pressure. 4. A 3 dB signal to noise ratio is sufficient for detection of song masked by noise in the field (Figs. 5 and 6). Also, redwings are able to detect differences in this ratio as small as 3 dB. 5. In the absence of wind, the maximum active space of redwing song is about 189 m for a signal SPL of 93.5 dB at 1 m. This distance varies with changes in ambient noise level during the day, and with relative wind direction.

Heat Flow Transducer Responses to Hyperbaric Environments

The responses of heat flow transducers, used in the evaluation of convective body heat losses, have been investigated at hyperbaric environments. Environmental temperatures, pressures, and gas composition were varied while transducer responses to constant heat fluxes were observed. Ambient temperatures were varied between 3° and 40° C. Ambient pressures were varied between simulated depths of 0 and 1000 feet of seawater (445 psi). Transducer responses to heat fluxes varying between 0 and 250 watts/m2 are reported in the above temperature and pressure ranges within atmospheres of helium, nitrogen, and air. Ambient pressure variations were found to have little effect on the response of the heat flow transudcers to a constant heat source once appropriate temperature corrections were made. However, transducer response variations of up to 14 percent were observed when environmental gas compositions were varied at hyperbaric conditions.

Gas phase ion–molecule reactions of dimethylsulphoxide

The gas phase ion-chemistry of dimethylsulphoxide (DMSO) and deuterated dimethylsulphoxide (DMSO-d6) has been examined using a quadrupole ion store (QUISTOR) as an ion–molecule reaction chamber. The QUISTOR results are compared with those obtained by ion trapping and high pressure mass spectrometry as reported by other workers. The performance of the QUISTOR demonstrates the versatility of the technique for ion–molecule reaction studies with variation of ambient pressure and duration of ion storage.

Gas Flow Control Employing Temperature and Pressure Compensation

Two passive gas flow controllers are presented which provide compensation for variations in ambient temperature and supply pressure. One technique, which provides first-order error compensation, utilizes a choked orifice having its area linearily varied in proportion to a diaphragm deflection. Compensation is achieved by applying upstream pressure to one side of the diaphragm, and by applying a trapped gas pressure proportional to absolute temperature on the other side of the diaphragm. General design relationships are presented, and a prototype unit constructed to control a minute flow rate of high-pressure oxygen is described. A second flow control technique is presented which provides the required nonlinear temperature compensation for flow supplied through a constant-area choked orifice. This is achieved by utilizing a compliant volume of trapped gas to generate a pressure proportional to the square root of absolute temperature. This pressure is used to control the pressure upstream of the choked orifice, thus providing constant flow.

Coupler Calibration of Microphones at Abnormal Ambient Pressure

Microphones, to be used at altitude or in the increased pressures of underwater diving, pose the need for calibration at abnormal ambient pressures. Free-field measurements are usually not feasible, since variable ambient pressure anechoic chambers are not normally available. Pressure calibration in a coupler can be performed conveniently in a small inexpensive variable-pressure tank. This paper describes such a system, utilizing a commercially available coupler with minor modifications. Various corrections, occasioned by the abnormal static pressures, are discussed.

Tidal motions in the high atmosphere

Previously published data on the semidiurnal variation of ambient pressure and wind speed obtained in the altitude interval from 15 to 130 km with such various sensors as rawinsondes, falling balloons, meteor trail drifts, and chemiluminous gas trails are examined in the contexts of a general model of isallobaric potential flow in the atmosphere and a model of tidal motion. The tidal model determines the variation of the amplitude and phase of the pressure oscillation with height, and, on the assumption that the pressure varies sinusoidally, the isallobaric potential flow model defines explicit relationships between the amplitudes and phases of the pressure and zonal wind oscillations and between the phases of the zonal and meridional wind oscillations. The observed values are compared with those predicted by the model, and it is concluded that the observed wind and pressure data fit an isallobaric pattern with a period of 12 hours and agree for the most part with the specific requirements of a semidiurnal atmospheric tide. In particular, however, the time of maximum of the semidiurnal pressure variation does not correspond to that predicted by present tidal theory.

Effect of Gas Pressure on the Radio Frequency Noises Generation in Fluorescent Lamps

Fluorescent lamps generate various kinds of noises with radio frequency bands.As the first step of the study on the noise generation mechanism, experimental investigations were carried out at varied ambient temperature and Argon Gas pressure.Since noise signals with various kinds of generation mechanism are mixed in a radio frequency band, it has been difficult to single out the contribution of one kind from among them. But our study demonstrated that the variations of ambient temperature and argon gas pressure are effective to analyze noise components.Because the anode noise signal is hardly changed by temperature depression, the variation in spectral distribution of total noise should be attributed to that of the reignition noise. In other words, in the case of temperature depression, the reignition noise level drops and the peak point of its distribution curve is moved into a higher frequency region.On the other hand, in the case of increasing argon gas pressure, the extinction noise level was found to drop and scarcely be affected by room temperature.The twin noise was also investigated about the effect of ambient temperature on its characteristics and the discharging condition for the noise generation was studied.In addition, the relationship between the electron beam density and the oscillation frequency was examined to analyze the noise generation mechanism.

ARC Melting of Tungsten

The direct-current, straight-polarity tungsten arc is examined in a highvacuum, open-arc system. Purity of the ingot product and the effects of ambient pressure variations on the melt rate and arc behavior are described.

Design and Operation of Airborne Refrigeration Equipment

This paper presents some of the problems associated with the design and operation of airborne vapour cycle refrigeration equipment, created by the extreme environmental conditions, and indicates where applicable the manner in which the difficulties can be overcome. The design philosophy behind a small high‐speed oil‐free reciprocating compressor is described, by certain fundamental requirements which the designer of airborne cooling equipment must consider. The particular difficulties, associated with effects due to rapid variation of ambient air temperature and pressure, which are peculiar to design and operation of such equipment are then explained. Rapid changes in heat load necessitate careful selection of the type of compressor drive and capacity control, and since extremes of temperature occur during a comparatively short operating cycle, particular attention must be paid to control of condensing pressure, and to prevention of migration of the refrigerant liquid into the low side of the system. The effects of vibration and of high acceleration make it necessary to design the components in such a manner that they can withstand these extreme effects, both while operating and during off‐cycle periods. In conclusion, the author contends that a new field of application for refrigeration equipment is emerging as a result of the more stringent aircraft and missile requirements; considerable theoretical and experimental effort is being devoted to the many problems, and the hope is expressed that continued co‐operation between the Refrigeration and Aircraft Industries may contribute to the more conventional as well as to the more specialized applications of refrigeration.

Studies in the Static Electrification of Filaments

An apparatus has been constructed to rub filaments together under controlled mechanical and ambient conditions and to measure the charge remaining after separa tion. The apparatus is similar to that of Hersh and Montgomery, with refinements to ohtain better control of mechanical variables and to allow variation of ambient pressure. A photomultiplier has been added near the filaments to detect the incidence of electrical breakdown of the atmosphere. Many of Hersh's findings for 45°-45° rubs have been confirmed, specifically those on reproducibility and triboelectric series. On the other hand, some findings have not been substantiated when the range of vari ahles is extended. For nylon rubbed on polyethylene. the charge q shows a square-root dependence on the normal force F, in place of the linear dependence found by Hersh; the charge shows an inverse proportionality with diameter d, in contrast with the inde pendence noted by Hersh. For tantalum rubbed on nylon. the charge is found to depend on a combination of velocity v. conductivity σ, and presumably dielectric con stant . together with a characteristic distance l to be determined empirically. If the charge dependence on length of rub L is taken to he the proportionality found by Hersh. the combined relation is suggested, where the sign and the magnitude of c are in principle determined by the details of the band structure, but in practice are fixed experimentally. No detailed theoretical picture has been obtained to justify the rest of the expression, and it must be considered at present as an empirical relation whose generality and basis remain to be established.