Effects Of Ambient Air Pressure Research Articles

Thermal and fire risk analysis of low pressure on building energy conservation material flexible polyurethane with various inclined facade constructions

This study investigated the factors affecting the fire safety analysis of the common construction material flexible polyurethane foam, based on combustion at various inclination angles and the ambient pressures at the altitudes of the cities of Hefei (99.8 kPa) and Lhasa (66.5 kPa). The effects of ambient air pressure, specimen width and inclination angle on the burning rate (as determined by mass loss), average flame spreading velocity, flame temperature and flame length were examined. The combustion rate was lower at 66.5 kPa and the wider specimens exhibited gradual spreading of the flame front in conjunction with melting and dripping. The burning rates at various inclinations were found to correlate with the pressure according to the expression ṁ∝pn,0.67<n<1.36, and this result can be explained based on pool fire theory. The average flame spreading velocity was found to correlate with pressure at various inclinations according to the relationship Va∝pn,2/3<n<1. The flame temperature was also observed to increase somewhat at the lower pressure, leading to an increase in the flame puffing frequency. Finally, a power law was used to describe the relationship between flame height and pressure, while a linear relationship was obtained between the index and the angle of inclination.

不同气压环境对飞秒激光在铬膜表面诱导周期性条纹结构的影响

不同气压环境对飞秒激光在铬膜表面诱导周期性条纹结构的影响

Effects of ambient air pressure on surface structures produced by ultrashort laser pulse irradiation.

We report an experimental analysis addressing striking effects of residual air ambient pressure, from atmospheric conditions (103 mbar) to high vacuum (10-4 mbar), on the surface structures induced on a silicon target by direct femtosecond laser irradiation. We observe an interesting direct impact of the ambient pressure on the period and depth of the generated ripples as well as on the formation of microgrooves. Moreover, a significant correlation is observed between the ripples' period and depth. The change of pressure is accompanied by a variation of the degree of nanoparticle coverage, which is eventually recognized as an important factor for the development of the final surface structures. These results shed light on the intriguing mechanisms underlying the formation of the various surface textures, also evidencing that the ambient pressure can act as an effective parameter to tailor some characteristic features of the processed surface.

The Effect of Ambient Pressure on Blast Reflected Impulse and Overpressure

Reflected blast pressure and impulse for bare 226.8 g spherical C-4 charges under various atmospheric pressure conditions were studied both experimentally and numerically. Blast pressure measurements were conducted using an array of high resonant frequency tourmaline-based piezoelectric pressure transducers to record normally reflected blast pressure histories at a 61 cm standoff. The explosive detonation and pressure measurements were conducted inside a pressure vessel which allowed the ambient pressure surrounding the C-4 charge to be varied. The recorded pressure histories were analyzed for blast wave arrival time, peak reflected overpressure, and positive phase impulse. The numerical analysis of blast pressures under varying ambient conditions was conducted using an axi-symmetric Arbitrary Lagrangian Eulerian (ALE) finite element technique with LS-DYNA. Numerical predictions were carried out for a 61 cm standoff that allowed direct comparison to the measured data. Additionally, the ALE simulations considered the effects of ambient pressure on blast impulse for varying standoff distances in the range of 12.7 to 61 cm. At a 61 cm standoff, measured peak reflected pressures showed no significant effect of varying ambient pressure while normally reflected impulses increased with increasing ambient pressure. Predictions by LS-DYNA for standoffs less than 61 cm showed a decreasing effect of ambient pressure on the normally reflected impulse as the standoff distance decreased. For small standoff distances it was predicted that the effects of ambient air pressure on normally reflected impulse were not significant. As the standoff distance between the explosive charge and the reflecting structure increases, higher ambient air pressures did cause a significant increase in reflected impulse.

Experimental Investigation of Droplet Impact on Metal Surfaces in Reduced Ambient Pressure

Impacting water droplets are capable of eroding steam turbine blades, high speed aircraft and even serve as a machining operation. In this latter process, high velocity (∼100m/s) water droplets impact a solid surface under conditions in which the ambient air pressure is sub-atmospheric. The physics of this erosion mechanism is not completely understood. To begin to unravel these physics, we present results pertaining to the effects of ambient air pressure on the impact force of low velocity (1m/s) droplets. It is well known that droplet splash is suppressed when the ambient air pressure is reduced. The effects on the associated impact force are, however, unknown. In this article we examine the impact force of 3.5mm diameter, low velocity droplets in a reduced pressure environment. A 38x38x50cm vacuum chamber fitted with a unidirectional piezoelectric force sensor to measure the transient force of impacting droplets. Preliminary results in atmospheric air pressure reveal that the impulse of the droplets depends linearly on impact velocity while the average impact force depends quadratically on impact velocity. The results under reduced pressures are compared and discussed relative to the underlying physics.

Numerical Study on the Effects of Ambient Air Pressure on Water Mist Characteristics

Abstract The effects of ambient air pressure on water mist characteristics were investigated with CFD code FDS6.0. The cases with ambient air pressures of 0.2, 0.4, 0.6, 0.8, 1.0, 1.5, 2.0, 2.5 and 3.0 atm, and water mist operating pressure of 1.5 MPa were considered in the numerical simulation, while the validation experiments were conducted with a single orifice nozzle at normal ambient pressure by using a LaVision Particle-Master Shadow system. The results show that the Sauter mean diameter (D32) of water mist decreased and the droplet velocity increased with the decrease of the ambient air pressure in the same location within the spray. Spray contraction phenomenon occurred where the contraction locations were different under different ambient pressures. Some of the results should be helpful for optimising the water mist fire suppression system.

Effect of ambient air pressure on synthesis of copper and copper oxide nanoparticles by wire explosion process

Nanoparticles of copper and copper oxide were synthesized by wire explosion technique in the environment of different ambient air pressure. Copper wire with a diameter of 125 μm and 6.1 cm in length has been exploded in air at 1 bar, 500 mbar, 100 mbar and 50 mbar. Current density in the order of 10 6 A cm −2 has been applied to disintegrate the wire by discharging a 1.85 μF capacitor at 10 kV. It is found that the particle size distribution for nano-sized particles follows the log-normal distribution and the median diameter is found to decrease from 31.3 nm to 23.6 nm as the pressure is decreased from 1 bar to 50 mbar.

Drop Impact upon Micro- and Nanostructured Superhydrophobic Surfaces

We experimentally investigate drop impact dynamics onto different superhydrophobic surfaces, consisting of regular polymeric micropatterns and rough carbon nanofibers, with similar static contact angles. The main control parameters are the Weber number We and the roughness of the surface. At small We, i.e., small impact velocity, the impact evolutions are similar for both types of substrates, exhibiting Fakir state, complete bouncing, partial rebouncing, trapping of an air bubble, jetting, and sticky vibrating water balls. At large We, splashing impacts emerge forming several satellite droplets, which are more pronounced for the multiscale rough carbon nanofiber jungles. The results imply that the multiscale surface roughness at nanoscale plays a minor role in the impact events for small We less than or approximately equal 120 but an important one for large We greater than or approximately equal 120. Finally, we find the effect of ambient air pressure to be negligible in the explored parameter regime We less than or approximately equal 150.

Effect of ambient air pressure on the oxidation kinetics of Fe–6 at.% Si alloy

Surface oxidation of Fe–6 at.% Si alloy was investigated during annealing in ambient air of various pressures with simultaneous isothermal resistivity registrations. Measurements have been done in the temperature range 500–540 °C. Chemical and phase compositions of the samples were analyzed using X-ray photoelectron spectroscopy, conversion electron Mössbauer spectroscopy (CEMS), transmission Mössbauer spectroscopy (TMS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Phase analysis showed that during isothermal resistivity measurement in a low pressure air 100 mbar a protective film of hematite α-Fe 2O 3 was formed on the surface of FeSi substrate. By decreasing pressure to 10 −2 mbar the time dependence of the resistivity exhibits an increase due to the transformation of hematite to magnetite Fe 3O 4. The activation energy for this transformation is 115 ± 5 kJ/mol. By regressive increasing the pressure back from 10 −2 to 100 mbar a non-protective oxide scale of hematite + magnetite was formed. The results were interpreted in the light of the iron-oxygen phase diagram.

Effects of mass difference on pressure-dependent emission characteristics in laser-induced plasma spectroscopy

A comprehensive experimental study was performed to demonstrate the effects of ambient air pressure on the emission characteristics of analyte elements in a variety of host materials in laser-induced plasma spectroscopy in low ambient air pressures. It was shown that the pressure-dependent characteristics of the emission lines are generally influenced by host elements when significant mass difference exists between the analyte and the host elements. Further investigation on the time profiles of the spatially integrated emission intensities reveal the important interplay among the dynamical factors associated with the mass-difference effect, which effectively influence the shock wave excitation process and hence the related emission intensities. The result of this study also indicates the need of proper control of time delay for the detection of maximum emission intensity in the cases considered.

Effect of ambient air pressure on debris redeposition during laser ablation of glass

The effect of ambient air pressure on the redeposition of debris, ablated from the zinc borosilicate glass target using 6ns, 266nm laser pulses, has been studied for incident fluences of 3–18J∕cm2. Measurements were carried out in air at pressures ranging from 10–750Torr. Scanning electron microscopy and optical microscope observations of the target surface were made to analyze the morphology of the redeposited debris. It was found that for higher values of the laser fluence and ambient pressure, the target surface is extremely rough, with large pieces of molten glass and debris fragments deposited near and around the ablation site. The profile of the redeposited debris also shows signs of a strong shock-wave-cleaning effect and possibly a Rayleigh-Taylor instability at higher pressures. Contrary to this, under low-pressure environment the surface of the redeposited debris is cleaner and smoother, with minimal damage around the ablated crater. The measured radius of the debris field was found to be proportional to the inverse cube root of the ambient pressure, consistent with the stagnation distance of the expansion plume when energy balance with the displaced air is considered. In addition to this, the mass of the redeposited debris was estimated from the measured optical thickness of the film and compared to the ablated mass. In the range below 100Torr, both the mass of the redeposited debris and the percentage of the ablated mass which was redeposited were found to increase with the increasing fluence and the ambient air pressure.

Balloon borne optical particle counter for stratospheric observation

This article presents the ambient air pressure effects on a balloon borne optical particle counter (an aerosol sonde: AS) equipped with a laser as the light source, and the relevant measures to overcome these effects. To investigate the effects of ambient air pressure varying from 1013 to 10 hPa (from ground level to an altitude of about 30 km) and estimate the general performance of the AS, a novel versatile pressure-variable test chamber was constructed equipped with a built-in nebulizer system. To overcome the direct effect of ambient air pressure on the sensing zone occurring when an open cavity laser (an external mirror-type laser) is used, a flat parallel window was adopted in place of the Brewster window, and in addition, only the laser tube was sealed in an aluminum tube under normal atmospheric pressure. Consequently, the laser power change was suppressed to within ±0.5% for the pressure variation range. To overcome the large dependence in the aerosol sampling flow rate on the ambient air pressure, a new flow rate ratio (flow rate at low pressure divided by that at 1013 hPa) was defined to fall within the ±0.5% variation, as measured using a newly developed technique for measuring the flow rate ratio, owing to an incorporated gear pump system devised to be speed controlled through a pressure sensor. The nonlinear increase of the noise component with decreasing ambient air pressure is discussed, and shown to be overcome electrically, confirming the presumption that this increase is ascribable to the corona discharge caused by high voltage. Thus, for polystyrene latex spheres 0.1 μm in diameter, the developed AS maintained signal-to-noise ratio larger than 2–3 for the pressure variation, as revealed from analysis of the histograms obtained with a multichannel analyzer. Finally, actual field measurements were performed at Bandong, Indonesia, and the results were subjected to a cross-check with those obtained almost simultaneously at the same location using an established conventional sonde, confirming the satisfactory accuracy and reliability of the developed AS.

The effects of ambient air pressure on oxygen consumption of resting and hovering honeybees

1. The rate of oxygen consumption for honeybees hovering at normal air pressure was 94.3 ml O2 g−1 h−1. The rate of oxygen consumption declined for honeybees hovering at higher air pressures, and declined for bees hovering at pressures less than 600 Torr. 2. The rate of oxygen consumption by resting honeybees was slightly, but significantly, affected by air pressure. Mean resting rate of oxygen consumption at normal air pressure was 12.3 ml O2 g−1 h−1. 3. The rate of oxygen consumption for honeybees during a 30 min peroid after hovering was 3.0 ml O2 g−1 h−1 at normal pressure, and increased slightly but significantly, at lower pressures. 4. Thoracic temperature was maintained relatively constant at 31–33°C during hovering, and was slightly, but significantly, elevated at lower air pressures. 5. The decline in rate of oxygen consumption for honeybees hovering at high pressure is attributed to decreased power requirements for flight, whereas the decline in rate of oxygen consumption at low pressures is attributed to the limitation of low\(P_{O_2 } \) to oxygen transport capacity. 6. The rate of change in oxygen consumption at low air pressures suggests that the inertial power requirement for hovering flight is about 60 ml O2 g−1 h−1 whereas the aerodynamic power requirement is about 33 ml O2 g−1 h−1.

うず巻噴射弁の噴霧特性に及ぼす周囲空気圧力の影響

うず巻噴射弁の噴霧特性に及ぼす周囲空気圧力の影響

Minimal utilizable oxygen and the oxygen dissociation curve of blood of rodents.

Minimal utilizable oxygen and the oxygen dissociation curve of blood of rodents.