Influence Of Air Pressure Research Articles

The preparation of nano size nickel oxide powder by spray pyrolysis process

This study involves using nickel chloride solution as a raw material to produce nano-sized nickel oxide powder with average particle size below 50 nm by the spray pyrolysis reaction. The influences of reaction parameters on the properties of the produced powder are examined. These parameters include concentration of raw material solution and atmospheric air pressure. When the nickel concentration of the raw material solution is 30 g/l, the average particle size of the powder is below 20 nm and the particle size distribution appears to be relatively regular. When the nickel concentration increases to 100 g/l, particles of sizes ranging from 20 nm to 50 nm coexist. When the nickel concentration increases to 150 g/l, the average particle size reduces to about 20 nm. When the nickel concentration increases to 220 g/l, the particles of sizes ranging from 20–30 nm to 80–100 nm coexist and show a very uneven particle size distribution. As the air pressure increases from 0.1 kg/cm 2 to 3 kg/cm 2 , the average particle size of the powder decreases while the particle size distribution gradually becomes more even. When the air pressure is at 0.1 kg/cm 2 , the particle size distribution appears to be 20–80 nm. When the air pressure increases to 0.5 kg/cm 2 and 1 kg/cm 2 , the particle size distribution becomes 20–50 nm and 20–40 nm respectively. When the air pressure increases to 3 kg/cm 2 , the average particle size becomes about 25 nm. To produce the nanosize nickel oxide powder, a spray pyrolysis system is specially designed. The raw material solution is fed into an inlet of the nozzle, while the compressed air is fed into the other inlet of the nozzle. And, the produced powder can be collected by bag filter in reaction furnace. ► A fabrication of powder with average particle size below 50 nm ► A spray pyrolysis system is specially designed and built for this study. ► The influence of concentration of solution on the properties of the powder ► The influence of air pressure on the properties of the powder

Influence of annealing conditions on the formation of regular lattices of voids and Ge quantum dots in an amorphous alumina matrix

In this work, the influence of air pressure during the annealing of Ge quantum dot (QD) lattices embedded in an amorphous Al2O3 matrix on the structural, morphological and compositional properties of the film is studied. The formation of a regularly ordered void lattice after performing a thermal annealing process is explored. Our results show that both the Ge desorption from the film and the regular ordering of the QDs are very sensitive to the annealing parameters. The conditions for the formation of a void lattice, a crystalline Ge QD lattice and a disordered QD lattice are presented. The observed effects are explained in terms of oxygen interaction with the Ge present in the film.

Comparison between AC and DC flashover performance and discharge process of ice-covered insulators under the conditions of low air pressure and pollution

This study, based on AC and DC flashover tests of porcelain, glass and composite insulators under the conditions of low air pressure and pollution, discusses the differences between AC and DC flashover performance and discharge process of ice-covered insulators. Results of the study indicate that the influence of air pressure on ice-covered insulator string's AC flashover voltage is greater than that on DC flashover voltage, whereas the influence of pollution on both AC and DC flashover voltage is almost the same. Good agreement is achieved between experimental results and the equivalent electrical circuit model proposed previously. Moreover, n (characteristic index of the influence of air pressure on ice-covered insulators’ flashover voltage) differs slightly when calculated with the icing-water-conductivity method and solid-layer method, respectively, and the duration from the occurrence of local arc to flashover is longer under the condition of AC than DC. Although arc floats are more seriously under the condition of DC.

Features of focused propagation of intense femtosecond laser pulses in air under low pressure

The results of theoretical and experimental investigations of the influence of air pressure on the dimensional and power parameters of preliminary focused GW femtosecond laser radiation are presented. A nonlinear region of the focus of a laser beam is examined. It is established that in rarefied air the achievement of higher values of laser radiation intensity in the focal waist is possible due to a decrease in the plasma blocking action.

Suction of splash after impact on dry quick sand

It is well known that a splash occurs when an object impacts at high velocity on a liquid's surface. If the impact is fast enough, surface tension and air pressure gradi- ents pull the crown-shape splash all the way towards the axis of symmetry, making it to collapse and seal the surface. In this paper we show that splash and surface sealing are also observed in impacts on soft, dry sand. We observe influence of air pressure and grains size on the shape of the splash. By tracking individual grains using high-speed imaging we calculate their acceleration, which results from gravity and drag forces. Assuming friction drag parallel, and pressure drag perpendicular to the direction of motion of grains we estimate the friction and pressure drag contributions to the drag force. Our results support the idea that pressure drag from Bernoulli effect is at the origin of the surface seal.

Study for Spray Experiment and Simulation of Nozzle on Icing Wind Tunnel

In this paper, Malvern laser particle size analyzer is used to study the spray characteristic experiment of air atomizing nozzle designed by ourselves. We measured the MVD(medium volume droplet diameter) under different conditions. From the test result, the influences of air pressure, water pressure and ALR(air liquid rate) to MVD and uniformity are analyzed. Furthermore, the variation of the MVD from the distance increase is discussed. The three-dimensional flow field model is built to make numerical simulation by software FLUENT. The simulation results are very consistent with experiment results, which indicate the spray effect of atomizing nozzle is well, and the nozzle designed by ourselves can be well used for the spray system of ice wind tunnel.

Experimental investigation of heat transfer between hot air nozzle flow and cylinder

A variety of experimental measurements were performed to clarify the influence of air pressure and distance from a nozzle outlet on the heat transfer intensity between a cylinder's surface and the hot air flowing around the cylinder,which is placed in a rectangular air channel. The surface temperatures of five different surface pointsand air temperatures are recorded during each experiment. The heat transfer coefficient is calculated from the following recorded parameters: air temperature, calculated surface temperature, and heat flux. The surface temperature and the heat flux are obtained from finite element analyses using ANSYS. The boundary conditions for these analyses are taken from the temperature history records. Three different values of air pressures and distances are tested. The distribution of the heat transfer coefficient around the cylindrical surface is determined for these testing conditions.Results are presented in the form of graphs.

Effects of Air Pressure on the Fabrication of Nano-Sized Tin Oxide Powder by Spray Pyrolysis Process

In this study, nano-sized tin oxide powder with an average particle size of below 50 nm is prepared by the spray pyrolysis process. The influence of air pressure on the properties of the generated powder is examined. Along with the rise of air pressure from <TEX>$0.1kg/cm^2$</TEX> to <TEX>$3kg/cm^2$</TEX>, the average size of the droplet-shaped particles decreases, while the particle size distribution becomes more regular. When the air pressure increases from <TEX>$0.1kg/cm^2$</TEX> to <TEX>$1kg/cm^2$</TEX>, the average size of the dropletshaped particles, which is around 30-50 nm, shows hardly any change. When the air pressure increases up to <TEX>$3kg/cm^2$</TEX>, the average size of the droplet-shaped particles decreases to 30 nm. For the independent generated particles, when the air pressure is at <TEX>$0.1kg/cm^2$</TEX>, the average particle size is approximately 100 nm; when the air pressure increases up to <TEX>$0.5kg/m^2$</TEX>, the average particle size becomes more than 100 nm, and the surface structure becomes more compact; when the air pressure increases up to <TEX>$1kg/cm^2$</TEX>, the surface structure is almost the same as in the case of <TEX>$0.5kg/cm^2$</TEX>, and the average particle size is around 80- 100 nm; when the air pressure increases up to <TEX>$3kg/cm^2$</TEX>, the surface structure becomes incompact compared to the cases of other air pressures, and the average particle size is around 80-100 nm. Along with the rise of air pressure from <TEX>$0.1kg/cm^2$</TEX> to <TEX>$0.5kg/cm^2$</TEX>, the XRD peak intensity slightly decreases, and the specific surface area increases. When the air pressure increases up to <TEX>$1kg/cm^2$</TEX> and <TEX>$3kg/cm^2$</TEX>, the XRD peak intensity increases, while the specific surface area also increases.

Influence of air pressure, humidity, solar radiation, temperature, and wind speed on ambulatory visits due to chronic obstructive pulmonary disease in Bavaria, Germany

Chronic obstructive pulmonary disease (COPD) is one of the most important causes of morbidity and mortality in the world. The disease is often aggravated by periods of increased symptoms requiring medical attention. Among the possible triggers for these exacerbations, meteorological factors are under consideration. The objective of this study was to assess the influence of various meteorological factors on the health status of patients with COPD. For this purpose, the daily number of ambulatory care visits due to COPD was analysed in Bavaria, Germany, for the years 2006 and 2007. The meteorological factors were provided by the model at the European Centre for Medium Range Weather Forecast (ECMWF). For the multivariate analysis, a generalised linear model was used. In Bavaria, an increase of 1% of daily consultations (about 103 visits per day) was found to be associated with a change of 0.72 K temperature, 209.55 of log air surface pressure in Pa, and a decrease of 1% of daily consultations with 1,453,763 Ws m(2) of solar radiation. There also seem to be regional differences between north and south Bavaria; for instance, the effect of wind speed and specific humidity with a lag of 1 day were only significant in the north. This study could contribute to a tool for the prevention of exacerbations. It also serves as a model for the further evaluation of the impact of meteorological factors on health, and could easily be applied to other diseases or other regions.

AC pollution flashover circuit model for composite insulator based on multiple arcs series

AbstractWith the increasing application of composite insulator in the power system, pollution flashover often occurs. However, no model can exactly predict pollution flashover voltage of composite insulator at present. Based on high‐speed photography of AC pollution flashover process, a model, which is in view of pollution severity, air pressure, shed configuration, and hydrophobicity level and which is suitable for composite insulator with any shed configuration, is proposed. Influences of pollution severity and hydrophobicity on flashover voltage and pressure characteristic exponent are analyzed, from which derives a calculative formula of flashover voltage. Calculated results from the model, validated by experiments, demonstrate that there is a power function relationship between flashover voltage and hydrophobicity level β, and characteristic exponent of hydrophobicity level β is the same as that of pollution severity. Meanwhile, the exponent characterizing the influence of air pressure increases with the fall of pollution severity and the rise of hydrophobicity. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Influence of air pressure on soliton formation in hollow-core photonic bandgap fibers

Soliton formation during dispersive compression of chirped few-picosecond pulses at the microjoule level in a hollow-core photonic bandgap (HC-PBG) fiber is studied by numerical simulations. Long-pass filtering of the emerging frequency-shifted solitons is investigated with the objective of obtaining pedestal-free output pulses. Particular emphasis is placed on the influence of the air pressure in the HC-PBG fiber. It is found that a reduction in air pressure enables an increase in the fraction of power going into the most redshifted soliton and also improves the quality of the filtered pulse at high powers. This allows a scaling of the output pulse energy toward the microjoule level.

Study of AC Pollution Flashover Performance of Porcelain Insulators at High Altitude Sites of 2800 $\sim$ 4500 m

The external insulation of electric equipments will be affected by the atmospheric conditions in the high altitude regions. However, a few investigations at the high altitude sites of 3000 m and above have been conducted. This paper reports on the laboratory tests of artificially polluted cap-and-pin porcelain insulators performed at the high altitudes of 2800 m to 4500 m. The test results and analysis show that the pollution flashover voltages in high altitude regions are affected not only by the pollution grades but also by the atmospheric parameters. The exponent characterizing the influence of equivalent salt deposit density is 0.26 to 0.29 and the one characterizing the influence of nonsoluble deposit density is 0.09 to 0.15. The ac pollution flashover voltage <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">U</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> will decrease with the decrease of air pressure <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> and increase with the decrease of ambient temperature <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> . <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">U</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> is a power function of the ration of air pressure <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> / <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> and also is a power function of the ambient temperature coefficient (1 + 0.02( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> - 20)). The average exponent characterizing the influence of air pressure is about 0.56 and the exponent characterizing the influence of ambient temperature is about 0.21 for the three types of insulators in the paper.

A poly( l-lactic acid) nanofibre mesh scaffold for endothelial cells on vascular prostheses

The absence of neoendothelium covering the intimal surface of small-diameter PET vascular prostheses is known to be one cause of failure following implantation in humans. Protein coatings currently used to seal porous textile structures have not shown evidence of in vivo neoendothelium formation. In this study, we covered the inner wall of textile prostheses with a biodegradable synthetic scaffold made of poly( l-lactic) acid (PLLA) nanofibres obtained by an air-spinning process we developed that produces nanofibres by stretching a solution of polymer with a high-speed compressed air jet. The air spinning was designed to process a scaffold that would support good endothelial cell proliferation. Our innovative process enabled us to very rapidly cover textile samples with PLLA nanofibres to determine the influence of air pressure, polymer solution flow rate and polymer concentration on fibre quality. High air pressure was shown to induce a significant number of ruptures. High polymer flow rate stimulated the formation of polymer droplets, and the fibre diameter mean increased for the 4% and 7% polymer concentrations. The adherence and proliferation of bovine aortic endothelial cells was assessed to compare prosthesis samples with or without the PLLA nanofibre scaffold and PET film. The PLLA nanofibres displayed a significantly better proliferation rate, and enabled endothelial cells to proliferate in the monolayer. Our novel approach therefore opens the door to the development of partially degradable textile prostheses with a blood/textile interface that supports endothelial cell proliferation.

Study on AC pollution flashover performance of composite insulators at high altitude sites of 2800-4500 m

The newly constructed Qinghai-Tibet Railway connecting Golumd and Lhasa is the highest railway in the world, which is located on the hinterland of Qinghai- Tibet Plateau with the average altitude of above 4000 m. Therefore, the external insulation of electric equipments will be affected by the atmospheric conditions in the high altitude regions. In contrast to many test investigations in the artificial climate chamber, there are few ones at the high altitude sites of 3000 m and above. In the paper, the AC artificial pollution tests of four types of composite insulators are carried out at three high altitude sites of 2820 m, 3575 m and 4484 m along the Qinghai-Tibet Railway. The test results show that the AC pollution flashover voltages in high altitude regions are affected not only by the pollution grades but also by the atmospheric parameters. The pollution flashover voltages will decrease with the increase of air pressure but increase with the decreases of ambient temperature. The exponent characterizing the influence of equivalent salt deposit density is 0.26 to 0.32 and the exponent characterizing the influence of non-soluble deposit density is 0.12 to 0.16, the influence of non-soluble deposit density cannot be neglected. The exponent characterizing the influence of air pressure is 0.507 to 0.587. The exponent characterizing the influence of ambient temperature is about 0.20. Considering the combined influence of the air pressure and ambient temperature, the AC flashover voltage of the polluted composite insulators will decrease by 4.0% to 6.4% for the altitude increased per 1000 m.

Low pressure acoustic pyrometer signal generator

An acoustic pyrometer measures the average gas temperature across a space of known distance, especially turbulent, high temperature gas loaded with caustic particulates. It includes an acoustic signal generator that generates a high amplitude acoustic signal with a short rise time The acoustic signal generator includes an outer tank closed at top and bottom ends by top and bottom end walls and enclosing an outer chamber. A cylinder is supported within the tank and has top and bottom opposed ends. A mid-plate extends across the cylinder and defines the bottom end, and an axial opening in the mid-plate receives a shaft of a piston assembly having an upper piston and a lower piston at ends of the shaft. A throat is attached to the bottom end, and receives the lower piston. The lower piston seals the throat when received in the throat. The upper piston is slidable in the cylinder under influence of air pressure. A pneumatic operating system for charging said cylinder and said outer chamber with gas at a moderate pressure includes a coupling for connection to a source of gas pressure and a remotely operated vent to allow pressurized gas in the cylinder to escape, thereby allowing the piston assembly to open said throat and allow pressurized gas to escape and produce a shock wave for use by the acoustic pyrometer.

Switching impulse flashover performance of different types of insulators at high altitude sites of above 2800 m

This paper explores the influence of air pressure, temperature and humidity on the switching impulse (SI) flashover performance of different types of clean and dry insulators at different high altitude sites of 2820 m to 5050 m along the Qinghai-Tibet Railway, the highest elevation railway in the world. Seven types of insulators are used in the flashover tests: one is a composite insulator, two are glass insulators and four are porcelain insulators. At the test sites, the ambient temperature varies between 6.7 degC to 28.5 degC and the absolute humidity is between 4.11 g/m3 to 9.69 g/m3. The test results show that the 50% switching impulse flashover voltage of different types of insulators at high altitude sites is independent of the materials and sheds of insulators but has a multi-factor non-linear relation with the shortest arc distance, the dry air pressure, the absolute humidity and the ambient temperature. The relative flashover voltage decreased with the ambient temperature is dependent on the voltage polarity, with 0.152% to 0.165% /degC for negative SI and 0.099% to 0.108% /degC for positive SI at the ambient temperature of from 6.7 degC to 28.5 degC. The relative flashover voltage increased with the absolute humidity and is dependent on the air pressure. The higher the altitude is, the more the influence is of the absolute humidity on the flashover voltage of insulators.

Butt Joining of Magnesium Alloy Sheet by Shot Peening

Magnesium and its alloys are very attractive for light weight applications. However, their use is complicated by the fact that dissimilar metals are joined by fusion welding. In the present study, the ability of shot peening to enhance butt joining of a magnesium alloy sheet with dissimilar material sheets was investigated. Shot peening improves the performance of the engineering components. In this process the substrate undergoes a large plastic deformation near its surface when hit by many shots. The substrate material close to the surface flows during shot peening. This plastic flow is characterized by a shear droop at the edge of the substrate, namely, the peened material overflows at the edge. When the dissimilar metal sheets with notched edges are connected without a level difference and then the connection is shot-peened, the sheets can be joined by the plastic flow generated by the large plastic deformation during shot peening. In this experiment, an air shot peening machine was used. The influences of air pressure and peening time on the joinability were examined. The joint strength increased with peening time, i.e., the amount of plastic flow. It was found that the present method can be used to enhance the butt joining of a magnesium alloy sheet with a dissimilar material sheet.

The influence of low atmospheric pressure on carbon monoxide of n-heptane pool fires

Qualitative theoretical analysis about air pressure influence upon the gas concentration of a fire plume was given, different scale n-heptane pool fires were conducted in a small and a standard compartment room in Lhasa and Hefei, respectively. The experimental results show that, in Lhasa, the average mass burning rates in the small room and the standard room both decrease, burning time increases at about 53% in small room and 45% in standard room more than in Hefei. Whereas for maximum changes of CO concentration, in the small room, in Lhasa, CO concentrations reach about twice bigger peak values at larger increase rates than in Hefei. While in the standard room, in Lhasa and Hefei, there are no significant changes for CO concentration, which agrees well with the theoretical analysis results.

Study on Pollution Flashover Performance of Short Samples of Composite Insulators Intended for /spl plusmn/800 kV UHV DC

Based on the artificial pollution tests, the effects of pollution and high altitude on the flashover performance of short samples of five kinds of UHV/EHV dc composite long rod insulators are analyzed. The exponent characterizing the influence of salt deposit density on the flashover voltage is related with the profile and the material of the insulator shed. The values of the samples' exponents vary between 0.24 and 0.30, which are smaller than those of porcelain or glass cap-and-pin insulators, namely, the influence of the pollution on the composite long rod insulators is less, relatively. Thus, the composite insulators have certain advantages in severe pollution regions. The best ratio of the leakage distance to the arcing distance is about 3.35. The exponent characterizing the influence of air pressure on the flashover voltage is related with the profile and the material of the insulator shed and the pollution severity, the values of the samples' exponents vary between 0.6 and 0.8, which are larger than those of porcelain or glass cap-and-pin insulators. Therefore, the dc composite insulator used in high altitude regions should have enough arcing distance. Based on the test results, if insulator sample Type E is selected for the plusmn800 kV UHV dc transmission lines, the basic arcing distance should be no less than 8.16 m and the basic leakage distance no less than 30.2 m.

Influence of air pressure on mechanical effect of laser plasma shock wave

The influence of air pressure on mechanical effect of laser plasma shock wave in a vacuum chamber produced by a Nd:YAG laser has been studied. The laser pulses with pulse width of 10ns and pulse energy of about 320mJ at 1.06μm wavelength is focused on the aluminium target mounted on a ballistic pendulum, and the air pressure in the chamber changes from 2.8 × 103 to 1.01 × 105Pa. The experimental results show that the impulse coupling coefficient changes as the air pressure and the distance of the target from focus change. The mechanical effects of the plasma shock wave on the target are analysed at different distances from focus and the air pressure.