Decrease In Ambient Pressure Research Articles

Effect of EMC and air in wood on the new in-process moisture content monitoring concept under radiofrequency/vacuum (RF/V) drying

To improve the accuracy of the new in-process moisture content (MC) monitoring concept under radiofrequency/vacuum (RF/V) drying, equilibrium moisture content (EMC) tests were carried out under various ambient pressures, and pressure curves in wood were analyzed during chamber evacuation and heating phases. The results showed that EMC increased with a decrease in ambient pressure regardless of temperature, relative humidity (RH), and species. The accuracy of MC estimation for Hinoki under RF/V drying was improved from 1.5% maximum absolute errors to 0.6% after EMC modification. The pressure curves for Hinoki and Sugi under RF/V drying showed similar tendencies to an idealized process. Russian larch showed different curves, indicating that the pressure in the wood did not reach the ambient pressure because of its low permeability. Therefore, MC could not be estimated using this monitoring concept because of the presence of much air in the wood of Russian larch.

Typical off-design analytical performances of internal combustion engine cogeneration

Based on experimental data, typical off-design characteristic curves with corresponding formulas of internal combustion engine (ICE) are summarized and investigated. In combination with analytical solution of single-pressure heat recovery steam generator (HRSG) and influence of ambient pressure on combined heat and power (CHP) system, off-design operation regularities of ICE cogeneration are analyzed. The approach temperature difference ΔTa, relative steam production and superheated steam temperature decrease with the decrease in engine load. The total energy efficiency, equivalent exergy efficiency and economic exergy efficiency first increase and then decrease. Therefore, there exists an optimum value, corresponding to ICE best efficiency operating condition. It is worth emphasizing that ΔTa is likely to be negative in low load condition with high design steam parameter and low ICE design exhaust gas temperature. Compared with single shaft gas turbine cogeneration, ΔTa in ICE cogeneration is more likely to be negative. The main reason for this is that the gas turbine has an increased exhaust gas flow with the decrease in load; while ICE is on the contrary. Moreover, ICE power output and efficiency decrease with the decrease in ambient pressure. Hence, approach temperature difference, relative steam production and superheated steam temperature decrease rapidly while the cogeneration efficiencies decrease slightly. It is necessary to consider the influence of ambient conditions, especially the optimization of ICE performances at different places, on cogeneration performances.

229 溶射粒子偏平挙動に対する雰囲気圧力の影響(コーティング・溶射・薄膜プロセス)

In this paper, the effect of ambient pressure on the flattening behavior of thermal sprayed particle was investigated. As adsorbate/condensate may be strongly affected by ambient pressure, amount of adsorbate/condensate on SUS304 substrate surface was measured Based on the measurement results, relation between flattening behavior of the thermal sprayed particle onto substrate surface and amount of adsorbate/condensate was investigated. Consequently, it was indicated that splashing may be suppressed with decrease of ambient pressure by improving wettability of the substrate and a molten droplet.

Intrapulmonary Bronchogenic Cyst and Cerebral Gas Embolism in an Aircraft Flight Passenger

Although it is estimated that > 1 billion passengers travel by air worldwide each year, the incidence of in-flight emergencies is low. However, due to nonstandardized reporting requirements for in-flight medical emergencies, the true incidence of pulmonary barotrauma in airplane passengers is unknown. We describe the case of a passenger with an asymptomatic intrapulmonary cyst in whom a severe case of cerebral gas embolism developed during an aircraft flight. The decrease in ambient pressure during the aircraft climb resulted in expansion of the cyst volume based on Boyle's law (pressure x volume = constant). Due to the cyst expansion, we believe tears in the wall led to the leakage of air into the surrounding vessels followed by brain gas emboli. Adult patients with intrapulmonary cysts should be strongly considered for cyst resection or should at least be advised to abstain from activities leading to considerable changes in ambient pressure.

Effects of atmospheric pressure on dc resistance to tracking of polymer insulating materials

Polymer insulating materials are required for use in high altitude regions. For the use of polymer insulating materials in such regions, it must be confirmed whether the resistance to tracking at high altitudes is different from that at altitudes near the sea level. In this paper, an artificial atmospheric chamber was set up to investigate the resistance to tracking on a polymer insulating surface at DC voltage application under a reduced pressure. The tests were carried out in accordance with IEC 60112. The test results showed that the dependences of the resistance to tracking for polymer insulating materials upon the decrease in ambient pressure could be classified into three types. One type is for paper-based phenolic laminate and polycarbonate, where the resistance increases with the decreasing ambient pressure; the second is for polybutylene terephthalate where the resistance decreases with the decreasing ambient pressure; the last type is for epoxy resin where the resistance is almost independent of the decrease in the pressure. A Gaussian wavelet analysis was applied to discharge currents to discuss correlations among the resistance to tracking, the discharge energy level and the ambient pressure. It was found that the data of resistance to tracking with some of the materials obtained at altitudes near sea level are inadequate for use in a high-altitude environment. Problems may occur with respect to the safety and reliability of polymer insulating materials when the DC resistance to tracking decreases under low-pressure conditions.

Influence of air intake pipe on engine exhaust emission

The exhaust emissions of a four-cylinder four-stroke petrol engine have been measured. Tests have been conducted at engine speeds ranges from 1000 to 4000 rpm and at air intake pipe diameters of 20, 25, 30, 35, 40 and 63 mm. The results demonstrate that the concentrations of the hydrocarbon (HC) and that of the carbon monoxide (CO) are relatively high at small air intake pipe diameter of 20 mm and at low engine speed of about 1000 rpm. Both pollutants have a minimum at large air intake pipe diameter of about 63 mm and at high engine speed of about 4000 rpm. The exhaust emissions HC and CO increase also as the ambient pressure decreases and as the altitude of the engine increases. The values of carbon dioxide (CO2) and the oxygen (O2) remain relatively constant at a wide range of different operating conditions. Therefore the knowledge about the effect of the above parameters could lead to improve the emission control technology as well as the engine performance on engine development and design.

Energy transfer from a laser pulse to a blast wave in reduced-pressure air atmospheres

Focusing a transversely excited atmospheric CO2 laser beam in air atmospheres induced a blast wave. The kinetic energy of a laser-induced blast wave was determined from shadowgraph images of shock wave expansion. Results showed that the fraction of input laser energy that is converted into the blast wave energy decreased from 0.45 to 0.2 concomitant with the decrease in ambient pressure from 100 to 10 kPa. Also, it was insensitive to input laser energy from 4 to 13 J.

Theoretical study of the ambient-pressure dependence of sonochemical reactions

Computer simulations of bubble oscillations are performed for various ambient pressures in order to study the mechanism of the ambient-pressure dependence of sonochemical reactions: sonochemiluminescence of aqueous luminol solutions [T. Tuziuti et al., J. Chem. Phys. 116, 6221 (2002)] and the oxidation of iodide [A. Henglein et al., J. Phys. Chem. 97, 158 (1993)]. It is shown that for air bubbles there exists an optimal bubble temperature for the production of the oxidants such as O, OH, H2O2, and O3 inside bubbles regardless of the ambient pressure because at higher bubble temperature the oxidants are consumed inside bubbles by oxidizing nitrogen. Correspondingly there exists an optimal acoustic amplitude for each ambient pressure, which shifts toward a lower value as the ambient pressure decreases because bubbles expand more. It results in the higher rate of sonochemical reactions for lower ambient pressure at relatively low acoustic amplitude. For oxygen bubbles, the amount of the oxidants created inside bubbles is larger for higher bubble temperature because in this case the oxidants are not consumed inside bubbles due to the absence of nitrogen. Regardless of the species of the gas inside bubbles, the decrease of the ambient pressure works as if the acoustic amplitude increases because bubbles expand more.

Parametric Characterization of High-Pressure Diesel Fuel Injection Systems

The focus of the study described herein is the characterization of the high-pressure hydraulic electronic unit injector (HEUI) and of the electronic unit injector (EUI) diesel injection systems. The characterization items include injection pressure, injection rate, injector response time, needle lift, start up injection transient, and dynamic discharge coefficient of the nozzles. Macroscopic and microscopic spray visualizations were also performed. The effects of injection conditions and nozzle configurations on injection characteristics were reviewed. Nozzle sac pressure was measured to correlate with the up-stream injection pressure. A LabVIEW data acquisition and controls system was implemented to operate the injection systems and to acquire and analyze data. For an HEUI system, based on the results of the study, it can be concluded that common-rail pressure and length of the injection rate-shaping pipe determine the injection pressure, while the pressure rising rate and injection duration determine the peak injection pressure; it was also found that the nozzle flow area, common-rail pressure, and the length of the rate-shaping pipe are the dominating parameters that control the injection rate, and the rate shape is affected mainly by common-rail pressure, especially the pressure rising rate and length of the rate-shaping pipe. Both injection pressure and ambient pressure affected the spray tip penetration significantly. The penetration increased corresponding to the increase of injection pressure or decrease of ambient pressure. The variation of spray penetration depends on the type of injection system, nozzle configuration, and ambient pressure. The large penetration variation observed on the HEUI sprays could be caused by eccentricity of the VCO (valve-covered-orifices) nozzle. The variation of the mini-sac nozzle was 50% less than that of the VCO nozzle. The near-field spray behavior was shown to be highly transient and strongly depended on injector design, nozzle configuration, needle lift and oscillation, and injection pressure.

Effect of atmospheric altitude on engine performance

The air capacity and the fuel consumption of a four-cylinder four-stroke petrol engine have been measured. Tests have been conducted at engine speeds from 1000 to 4000 rpm and at atmospheric altitude from 600 to 850 m above the sea-level as well as at ambient pressure from 0.9 to 0.95 bar. The performance of the engine at low speeds is different from that at high speeds. At low engine speeds up to 2500 rpm the air capacity, the fuel consumption and the volumetric efficiency decreases with increases of engine altitude by which the ambient pressure decreases. However at higher speeds engine than 3000 rpm the engine performances decreases with decreases of engine altitude and so with increases of atmosphere pressure. A 200 m change on the altitude of the engine, corresponding to a change in atmosphere pressure of about 3000 Pa, may lead to change fuel consumption and volumetric efficiency up to 40%. It is shown that to obtain maximum engine efficiency and minimum fuel consumption, fuel mixture should be varied with respect to the altitude of engine. The knowledge about the altitude effect could therefore lead to improve the performances on engine development and design.

Circulatory oxygen transport in the water flea Daphnia magna.

To determine the contribution of circulatory convection to tissue oxygen supply in animals of Daphnia magna, heart rate ( f(H)), in-vivo Hb oxygen-saturation ( S(Hb)) and NADH fluorescence intensity ( I(NADH)) as a measure of the tissue oxygenation state were simultaneously measured using digital motion analysis, microabsorption spectroscopy and fluorescence microscopy. In addition, the relationship between stroke volume and body size was established. Groups of differently sized animals (small: 1.4-1.6 mm, medium: 2.7-2.9 mm, large: 3.3 mm) with either low (Hb-poor) or high Hb concentration (Hb-rich) in the hemolymph were exposed to a gradual decrease in ambient oxygen partial pressure ( P(O2amb)) between normoxia and anoxia. In all groups, f(H) increased in response to progressive hypoxia. The hypoxic maximum in f(H) was highest in medium-sized Hb-poor animals, whereas perfusion rate increased continuously with increasing body size in Hb-poor and Hb-rich animals. The P(O2amb) at which Hb in the heart region was half-saturated (in-vivo P(50)) was higher in medium-sized (Hb-poor: 3.2 kPa, Hb-rich: 2.0 kPa) than in small (Hb-poor: 2.1 kPa, Hb-rich: 1.5 kPa) and large animals (Hb-poor: 1.9 kPa). The in-vivo P(50) was always lower in Hb-rich than in Hb-poor animals. The I(NADH) indicated an impairment of tissue oxygenation starting at higher critical P(O2amb) with increasing body size and with lower Hb concentration. Model calculations suggest that at the respective critical P(O2amb), circulatory convection delivers less than half of the oxygen demand in Hb-poor animals. In contrast, in Hb-rich animals, the contribution of circulatory convection to tissue oxygen supply at respective critical P(O2amb) was much greater due to the higher concentration of Hb.

Benefits of haemoglobin in the cladoceran crustacean Daphnia magna.

To determine the contribution of haemoglobin (Hb) to the hypoxia-tolerance of Daphnia magna, we exposed Hb-poor and Hb-rich individuals (2.4-2.8 mm long) to a stepwise decrease in ambient oxygen partial pressure (P(O(2)amb)) over a period of 51 min from normoxia (20.56 kPa) to anoxia (<0.27 kPa) and looked for differences in their physiological performance. The haem-based concentrations of Hb in the haemolymph were 49 micromol l(-1) in Hb-poor and 337 micromol l(-1) in Hb-rich animals, respectively. The experimental apparatus made simultaneous measurement of appendage beating rate (fA), NADH fluorescence intensity (I(NADH)) of the appendage muscles, heart rate (fH) and in vivo Hb oxygen-saturation possible. In response to progressive, moderate hypoxia, both groups showed pronounced tachycardia and a slight decrease in fA. The fA and fH of Hb-rich animals were generally 4-6 % lower than those of Hb-poor animals. In addition, Hb-rich animals showed a significant decrease in the P(O(2)amb) at which the Hb in the heart region was half-saturated and a striking reduction in the critical P(O(2)amb) of appendage-related variables. In Hb-poor animals, the I(NADH) signal indicated that the oxygen supply to the limb muscle tissue started to become impeded at a critical P(O(2)amb) of 4.75 kPa, although the high level of fA was largely maintained until 1.77 kPa. The obvious discrepancy between these two critical P(O(2)amb) values suggested an anaerobic supplementation of energy provision in the range 4.75-1.77 kPa. The fact that I(NADH) of Hb-rich animals did not rise until P(O(2)amb) fell below 1.32 kPa strongly suggests that the extra Hb available to Hb-rich animals ensured an adequate oxygen supply to the limb muscle tissue in the P(O(2)amb) range 4.75-1.32 kPa. This finding illustrates the physiological benefit of Hb in enabling the animal to sustain its aerobic metabolism as the energetically most efficient mode of fuel utilization under conditions of reduced oxygen availability.

Response of microscopic bubbles to sudden decrease of ambient pressure in viscous compressible liquid

A shock tube is used to investigate the bubble dynamics under sudden decrease of ambient pressure. Both the oscillating and monotonously growing bubbles were simultaneously observed. Theoretical approach is based on the Rayleigh-Plesset and Herring’s equations for incompressible and compressible liquids, respectively. Considering the linear approximation of these equations for the quasiequilibrium state, two critical Weber numbers are defined. They enable one to predict the following modes of the bubble expansion: (i) unbounded growth, (ii) asymptotic growth to limited volume and (iii) attenuated oscillations, depending on the pressure force, viscosity and compressibility of the liquid.

Ambient Pressure Effect on Single-Bubble Sonoluminescence

We report the first results on the influence of ambient pressure on single bubble sonoluminescence. The equilibrium radius as well as the maximum radius of the bubble increased as the ambient pressure over the liquid head was decreased. The number of photons emitted during a sonoluminescence pulse increased linearly with a decrease of ambient pressure. These results are in good agreement with the theory of the ambient pressure effect [L. Kondic et al., Phys. Rev. E 57, R32 (1998)] and with the recent dissociation hypothesis.

Experimental observations of the effect of ambient pressure on single-bubble sonoluminescence

The experimental observations of the influence of ambient pressure on single-bubble sonoluminescence will be presented. In the SBSL regime as the ambient pressure was decreased only about 10%, the SL intensity increased significantly as predicted [L. Kondic, C. Yuan, and C. K. Chan, Phys. Rev. E 57(1), R32–R35 (1998)]. There was an increase of about five times in SL intensity as the ambient pressure was decreased by about 10%–12%, at constant driving acoustic pressure. This increment continued until a certain value of the ambient pressure, below which the bubble became unstable and vanished. The equilibrium radius and the maximum radius of the SBSL bubble both incerased with decrease of ambient pressure. This observation provides valuable insight into the mass flow mechanism between the bubble and the liquid, and gives the first direct confirmation of ‘‘argon bubble hypothesis.’’ [Work supported by NSERC and Concordia Seagram Fund for Innovative Research.]

Thermal disequilibrium at the top of volcanic clouds and its effect on estimates of the column height

SATELLITE images of large volcanic explosions reveal that the tops of volcanic eruption columns are much colder than the surrounding atmosphere1. We propose that this effect occurs whenever a mixture of hot volcanic ash and entrained air ascends sufficiently high into a stably stratified atmosphere. Although the mixture is initially very hot, it expands and cools as the ambient pressure decreases. We show that cloud-top undercoolings in excess of 20°C may develop in clouds that penetrate the stratosphere; this is consistent with observations of the 4 April 1982 eruption of El Chichon1 and the 18 May 1980 eruption of Mount St Helens2. Furthermore, from our model results, we predict that for a given cloud-top temperature, variations in the initial temperature of 100–200°C may correspond to variations in the column height of 5–10 km. We deduce that the present practice of converting satellite-based measurements of the temperature at the top of volcanic eruption columns to estimates of the column height will produce rather inaccurate results and should therefore be discontinued.

Assessing the effects of positive buoyancy on rainbow trout (Oncorhynchus mykiss) held in gas supersaturated water

We examined the effects of swim bladder overinflation associated with dissolved gas supersaturation on rainbow trout (Oncorhynchus mykiss). The change in swim bladder volume with increased swim bladder pressure was measured in fish subjected to a decrease in ambient pressure. An expansion of swim bladder volume occurs that is related to the excess swim bladder pressure. The volume change results in a decrease in density and positive buoyancy in the fish. Small fish are adversely affected when exposed to gas supersaturated water because of the high swim bladder pressure required to force gas out the pneumatic duct. Changes in behaviour and depth distribution of fish held in gas supersaturated water were measured in a 2 m deep observation column. A large change in density caused small fish to increase depth and compensate for the swim bladder expansion. Although swim bladder inflation occurs for all sizes of trout held in gas supersaturated water, the impact is greatest for small fish and they must compensate by seeking depth. However, adequate depth to compensate for positive buoyancy may not always exist. In such a case, fish must swim continuously in a head down position to overcome excess buoyancy. The power necessary for a fish to swim with an overinflated swim bladder is greatest for small fish that show the largest change in density.

Effect of atmospheric pressure on friction and wear of 0.45% C steel in fretting

Oxidative wear is significant in fretting wear when sufficient oxygen is supplied. In vacuum, however, oxide does not form readily. In this paper friction and wear behaviours were studied at various atmospheric pressures in order to clarify the effect of ambient pressure on them. Experiments were conducted with 0.45% C steel at ambient pressures from 1.0 × 10 5 to 1.3 × 10 −3 Pa. The load was 14 N, the peak-to-peak slip amplitudes were 35 and 110 μm and the frequency was usually 8.3 Hz. Friction behaviours are characterized into three types according to the ambient pressure: 1.0 × 10 5 − 10 Pa, 10 − 10 −1 Pa and below 10 −1 Pa. The coefficient of friction increases with a decrease in ambient pressure below 1 Pa. The critical pressure in fretting is found to be 10 Pa, above which the oxidation rate is independent of the ambient pressure and α-Fe 2O 3 is formed. Wear decreases with ambient pressure below the critical pressure where Fe 3O 4 is formed. Adhesive transfer of metallic debris occurs below 10 −1 Pa. The relationship between the coefficient of friction and oxide thickness is obtained analytically, and the effect of frequency on the oxidation rate is considered.

Air Transportation After Eye Surgery-Reply

In Reply.— Dr Roper is correct in noting that the danger of air travel after recent eye surgery is expansion of gas bubbles remaining within the eye as the ambient pressure decreases. All such patients should be examined and cleared by an ophthalmologist before attempting to travel aboard pressurized or nonpressurized aircraft. Incidentally, this caution also applies to transportation by air ambulance services. The Commission on Emergency Medical Services' somewhat sweeping statement was made to ensure an ophthalmologist's clearance on every patient.

Error in Dasibi flight measurements of atmospheric ozone due to instrument wall‐loss

Theory suggests that in laminar flow the percent loss of a trace constituent to the walls of a measuring instrument varies as P−2/3, where P is the total gas pressure. Preliminary laboratory ozone wall‐loss measurements confirm this P−2/3 dependence. Accurate assessment of wall‐loss is thus of particular importance for those balloon‐borne instruments utilizing laminar flow at ambient pressure, since the ambient pressure decreases by a factor of 350 during ascent to 40 km. Measurements and extrapolations made for a Dasibi ozone monitor modified for balloon flight indicate that the wall‐loss error at 40 km was between 6 and 30 percent and that the wall‐loss error in the derived total ozone column‐content for the region from the surface to 40 km altitude was between 2 and 10 percent. At 1000 mb, turbulence caused an order of magnitude increase in the Dasibi wall‐loss.