Influence Of Low Pressure Research Articles

Investigation of the electret properties of PDLA/PEC porous composite films

In the present paper the influence of both time and low pressure on the surface potential decay of porous composite films of poly(D-lactic acid) and poly(ε-caprolactone) was investigated. The samples were charged in a corona discharge by means of a corona triode system under room conditions. Positive or negative voltage was applied to the corona electrode and voltage of the same polarity as that of the corona electrode was applied to the grid. After charging, the initial surface potential was measured using the method of the vibrating electrode with compensation. Two groups of tests were performed. In the first group, after charging, the electrets were placed into a vacuum chamber where the pressure was reduced step by step in the range from 1000 mbar to 0.1 mbar. At each step the samples were stored for 1 minute. After that the electrets were removed from the vacuum chamber, their surface potential was measured again and the normalized surface potential was calculated. The influence of low pressure was analyzed by the equation that describes processes of desorption from the electret’s surface. In the second group, after charging, the electret surface potential was measured by the time of storage. The possible surface potential decay mechanisms responsible for the electret’s behavior were discussed. It was established that the surface potential decay depends on both corona polarity and type of films. It was shown that the samples charged in a positive corona are more stable than those charged in a negative corona.

Low pressure influence on a direct fuel cell battery hybrid system for aviation

Fuel-cell-based, hydrogen-driven aircraft can significantly reduce the climate impact of aviation but the low ambient pressures at high altitude negatively affect the performance of fuel cells. The influence of low pressures on the behavior of a direct hybrid-system that connects a fuel cell and a battery without a DC/DC converter, is examined and compared to a fuel-cell-only system. Low ambient pressure leads to a reduced fuel cell voltage and power output. The voltage change between maximum voltage and the voltage level at the operational power increases with a decreasing air pressure for both the hybrid-system and the fuel-cell-only system. However, in a direct hybrid, the battery stabilizes the system voltage level and the voltage decrease is significantly smaller for the hybrid-system than for the fuel-cell-only system. At an ambient pressure of 300 mbar, the voltage variation of a 4 kW system is 96% lower for a hybrid-system compared to a fuel-cell-only system. The lower pressure also reduces the power output of the fuel cell. In the direct hybrid the battery contributes a demand related share of power and the contribution from the fuel cell decreases with air pressure as the contribution of the battery rises.

Impacts of low atmospheric pressure on distribution of indoor hot air jet in plateau area

The existing design parameters of hot-air heating for local buildings do not consider the distinctive low-pressure that can be experienced in the plateau regions, resulting in significant inefficiency. In this study, a numerical model based on the Reynolds time-averaged method coupled with the RNG k–ε turbulence model was established by considering the air thermal properties influenced by pressure. Four atmospheric conditions of 101.325 kPa, 84.547 kPa, 70.093 kPa and 57.708 kPa were selected to simulate the velocity and temperature fields of the horizontal and vertical hot-air jets. The influence of low pressure on the flow characteristics of hot-air jets was analyzed subsequently. The results suggest the jet flow patterns are essentially similar under various pressures. The horizontal hot-air jets bent upward more significantly and the diffusion range of the vertical jets was reduced under low pressure. The jet velocity decayed faster at low pressure, and the axial velocity of a vertical jet at 57.708 kPa was 0.26 m/s lower than that at 101.325 kPa. The temperature gradient of the room with a hot-air jet was increased with decreasing pressure, which was 5.0 K/m at 57.708 kPa. This study should be helpful to the detailed design and efficient operation of hot-air heating in buildings in the plateau regions.

Levitation Performance of YBCO Bulks in Supercooling Condition Under a Low-Pressure Environment

Taking the influence of low pressure on levitation performance of high temperature superconducting (HTS) maglev into account, we established a simple super-cooling platform based on pumping method to study the levitation performance of YBCO bulks above the Halbach permanent magnet guideway (PMG) under different pressure conditions. Through measuring the temperature of liquid nitrogen (LN2) during the decreasing process of pressure, it is known that the LN 2 would turn into a super-cooling state as the pressure reduction. Measurements of the levitation force versus vertical motion and the force relaxation were performed both in case of zero-field-cooling (ZFC) and field-cooling (FC). The experimental result showing that the decreasing pressure is beneficial to improve the levitation performance of HTS bulks, and the maximum force increase up to 23.5% and 22.1% were realized in ZFC and FC compared with the atmospheric pressure, respectively. Moreover, the low pressure could also reduce the hysteresis loop area and restrain the relaxation decay of levitation force. These results imply that, the low pressure environment in evacuated tube will be beneficial to the levitation performance of HTS maglev system.

Low pressure influence on the electrets stability of gamma irradiated PP and PET films

The influence of low pressure on the surface potential decay of gamma irradiated polymer films of polypropylene (PP) and poly(ethylene terephtalate) (PET) were studied. Polymer film samples were subjected to integral irradiation doses (Ey = 1.25 MeV, 60Co source) of 5 kGy and 25 kGy accumulated in air at a dose rate of 0.26 Mrad/h. After irradiation, the samples were charged in a corona discharge by means of a corona triode system for 1 minute under room conditions. Positive or negative 5 kV voltages were applied to the corona electrode. Four different voltages of the same polarity as that of the corona electrode were applied to the grid. The electret surface potential V0 was measured by the method of the vibrating electrode with compensation. After charging the electrets were placed into a vacuum chamber as the pressure was reduced step by step in the range of 1000 mbar to 0.1 mbar. At each step the samples were stored for 1 minute and the surface potential V was measured again. Then values of the normalized surface potential V/V0 were calculated. Low pressure dependences of the normalized surface potential for positively and negatively charged PP and PET films were presented. It was established that the low pressure led to the surface potential decay of the electrets. The influence of low pressure was analyzed by the equation that describes processes of desorption from the electret surface accompanied with surface diffusion. The experimental results obtained show a significant change in the electret behaviour of the polimer films after gamma irradiation and storage at different low pressure. It was established that the surface potential decay depends on the corona polarity, gamma irradiation and the values of low pressure.

Influence of low pressure on mercury removal from coals via mild pyrolysis

Anthropogenic Hg emission control has drawn worldwide attention along with enactments of strict legislation. In response to the need for mercury emission control from flue gases in coal combustion, studies have focused on mild pyrolysis as a promising technology for mercury removal before combustion. However, reaction pressure has not yet been studied, which might affect mercury removal in mild pyrolysis. In this paper, three types of powdery bituminous coal, Coals A-C, from the western plateau area of China, were studied. The core aim was to explore the effect of low reaction pressure on the efficiency of Hg removal. Data of the three coals under different pyrolysis pressures showed that reducing the pressure would improve the mercury removal rate and removal efficiency and that the effect was distinguished by coal type. The role of pyrolysis pressure in Hg removal was limited. When the residence time was long enough, the eventual Hg removal was dependent on the thermal decomposition temperature. These findings might be of some guidance for designing pyrolysis reactors. Furthermore, this article aims to provide some explanation about the mechanism and offer guidance for optimizing the technological parameters of Hg removal by mild pyrolysis.

A Nanosecond Surface Dielectric Barrier Discharge Operating Under Altitude Conditions for Aeronautics Applications

The objective of this paper is to investigate the influence of environmental conditions on a nanosecond pulsed dielectric barrier discharge (NP-DBD). A test chamber where pressure and temperature can be changed to match with realistic altitude conditions has been used. Electrical and optical characterizations of the NP-DBD are proposed for pressure and temperature changes in range related to flow control applications. In particular, the influence of low pressure is investigated. The results indicate that a reduction in pressure leads to a more diffuse plasma layer to a more diffuse plasma layer and an enhanced propagation. The energy dissipated by the discharge increases with a reducing pressure. Regardless of the pressure level, the heat released by the NP-DBD leads to the formation of a pressure wave propagating at sound speed. A good correlation was found between the extension of the plasma layer and the planar part of the produced pressure wave. Similar electrical characterization has been conducted when the temperature is reduced, while the pressure is maintained at an atmospheric level. It was shown that temperature has the minor effect on the discharge characteristics, but lower is the temperature and lower is the deposited energy. In a final part, the influence of the altitude is investigated by studying the combined effects of pressure and temperature. It results that the pressure variation dominates the temperature influence. As a result, higher energy deposition is reported when the altitude is increased. The effect of changes in the pressure and temperature is interpreted as an effect of changes in the gas density. It is concluded that the gas density, $N$ , is an important parameter for studying DBD under the altitude conditions. Indeed, quantities such as the plasma extent and the deposited energy scale with $N^{-0.5}$ . However, the gas density does not consider changes in the dielectric permittivity, which restricts the use of the gas density matching method to altitudes with moderate ambient temperature.

Experiment investigation on the influence of low pressure on ceiling temperature profile in aircraft cargo compartment fires

The objective of the present study is to evaluate the low pressure effects on ceiling temperature profile in aircraft cargo compartment fires, which will affect the activation of fire detectors. A Series of fire tests were carried out in a full scale simulated aircraft cargo compartment at four atmospheric pressures (100 kPa, 90 kPa, 80 kPa and 70 kPa) corresponding to the pressure within an actual aircraft cargo compartment from the sea level to the cruising altitude (about 10,000 m). Results show that the maximum ceiling temperature increases and the ceiling temperature decays faster as ambient pressure reduces. The air entrainment ratio Cα is proposed in the correlation to predict the maximum ceiling temperature based on previous plume theory, considering the low pressure effect and entrainment coefficient. Meanwhile, modified by the air entrainment ratio Cα, the previous classic correlations established by Alpert, Heskestad and Delichatsios for the ceiling temperature decay profile are further extended to low pressure conditions. The results based on Heskestad and Delichatsios method are more accurate than that of Alpert method in the experiments. All these findings would provide theoretical basis for the design of fire detection system in the aircraft cargo compartment.

Low pressure and time storage influences on the electrets stability of HDPE composite films

The influence of both low pressure and time storage on the surface potential decay of high density polyethylene (HDPE) composite films with different weight concentrations of the zeolite particles - 0 wt.%, 2 wt.% and 6 wt.% were studied. The samples were charged in a corona discharge by means of a corona triode system for ' minute under room conditions. Positive or negative 5kV voltage was applied to the corona electrode and 1 kV voltage of the same polarity as that of the corona electrode was applied to the grid. After charging, the electret surface potential was measured by the method of the vibrating electrode with compensation. Two groups of tests were performed. In the first group after charging, the electrets were placed into a vacuum chamber where the pressure was reduced step by step in the range from 1000 mbar to 0.1 mbar. At each step the samples were stored for 1 minute. Then the electrets were removed from the vacuum chamber, the surface potential was measured again and the normalized surface potential was calculated. It was established that the low pressure had led to the surface potential decay of the electrets. The influence of the low pressure was analyzed by the equation that describes processes of desorption from the electret surface accompanied with surface diffusion. In the second group after charging, the electret surface potential was measured with the time of storage for two months. The experimental results obtained show a significant change in the electret behaviour of the composite films after the incorporation of zeolite particles with different concentration into the HDPE matrix. It was established that the surface potential decay depends on the corona polarity and the particle concentration.

The effect of pressure variations on the formation of gas inclusions in the rotational molding process

Abstract The major disadvantage of rotational molding is the cycle time, which is very long compared to other plastic processing methods. A major percentage of the cycle time besides heating and cooling results from the time necessary to remove gas inclusions from the polymer melt, which are trapped while sintering the polymer powder. In this work the formation of gas inclusions is investigated by conducting a cycle time variation on a uniaxial rotational molding machine. The influence of low pressure during melting on the formation of inclusions is investigated by examining sintering experiments with a pressure variation during the melting of the polymer. Sintering experiments are conducted with different melt residence times to investigate the mechanisms of gas inclusion removal. By comparing the time to reach a pore-free polymeric melt, the cycle time reduction potential under low-pressure application while melting the polymeric powder is estimated.

Lower Flammability Limits of Hydrogen and Light Hydrocarbons at Subatmospheric Pressures

The knowledge of flammability limits is essential in the prevention of fire/explosion when handling combustible gases and vapors. In this study, the lower flammability limits (LFLs) of hydrogen–air, methane–air, ethane–air, n-butane–air, and ethylene–air were measured in a closed cylindrical vessel (inner diameter 10.22 cm, length 100 cm) with upward flame propagation, at room temperature (20 °C) and initial pressure of 1.0, 0.7, 0.5, 0.3, and 0.1 atm. The LFL of hydrogen initially decreased with pressure from 1.0 to 0.3 atm, and then the LFL increased with the further decrease of pressure. In contrast, the LFLs of the hydrocarbons increased when the pressure decreased from 1.0 to 0.1 atm, except for methane for which the LFL did not change with pressure. The adiabatic flame temperatures (AFTs) at the obtained LFL concentrations of hydrogen and the hydrocarbons were also calculated at subatmospheric pressure conditions. The behaviors of the AFTs of hydrogen and the hydrocarbons were similar to those of the LFLs under the influence of low pressures. On average, at initial pressures from 1.0 to 0.1 atm and LFL concentration, the AFT of hydrogen was 730 K, of the alkanes was 1900 K, and of ethylene was 1800 K. On the basis of the LFLs and AFTs, the risk/hazard associated with fire/explosion of hydrogen and the hydrocarbons at subatmospheric pressures was also discussed.

Influence of low pressure on laser inducing leaky Lamb wave and Scholte wave at air–solid interface

A setup with Q-switched Nd:YAG laser inducing acoustic wave at air–solid interface and air-coupled optical deflection sensor was developed to research the influences of low air pressure on laser inducing leaky Lamb and Scholte waves at air–solid interface. The solid plate is settled in an airtight vessel abounded with standard air and its pressure can be adjusted by a vacuum pump. By experiments, the waveforms of laser induced interface acoustic waves, leaky Lamb and Scholte waves, under air pressures from 0.02 to 0.08 MPa with 0.01 MPa interval were first measured comprehensively. From the waveforms, we find that with increasing air pressure, the leaky energy of Lamb waves increase linearly and the amplitude of Scholte waves increase exponentially, but the velocity of Scholte waves decreases obviously.

Low pressure and humidity influences on the electret surface potential decay

In the present paper the influence of both relative humidity and low pressure on the surface potential decay of charged 20 μm polypropylene films was investigated. Sample charging was performed in a three-electrode corona discharge system. After charging the initial surface potential was measured using the method of the vibrating electrode with compensation. Two groups of tests were performed. In the first group, after charging the electrets were placed into a vacuum chamber under various low pressures (from 0.1 mbar to 1000 mbar) for 30 minutes. After that the electrets were removed from the vacuum chamber. The surface potential was measured again and the normalized surface potential was calculated. The influence of low pressure was analyzed by the equation that describes processes of desorption from the electret surface. In the second group after charging the electrets were put in desiccators at 0% and 100% relative humidity for 220 days at room temperature. After that the surface potential was measured periodically out of the desiccators. The results obtained were analyzed with the percolation 2D model. It was established that the higher values of the relative humidity led to a faster decay of the surface potential. We assume the presence of surface discharge processes.

Influence of low pressure on electrets behaviour at various air gaps

Polypropylene samples, 20 μm thick, charged in a negative corona were studied. Each sample was placed on a metal pad. The samples were charged to different initial surface potentials, by means of a conventional corona triode system. The negative corona voltage was 5 kV and the grid voltages of the same polarity were 350 V, 500 V, 650 V, 800 V and 950 V. After measuring the surface potential, the samples, together with their metal pads, were placed for 30 min between two short circuited plate electrodes in a vacuum chamber under various low pressures from 10 Pa to 1 × 10 5 Pa. The air gap thicknesses between the charged surface of electrets and the upper electrode were 0.28 mm, 0.84 mm, 1.69 mm and 3.00 mm, respectively. The results obtained show that there is a pressure range within which the surface potential sharply decays. The sharp surface potential decay depends on the pressure-to-initial surface potential ratio and it is different for different air gap thicknesses and for different initial surface potentials. A spark breakdown in the air gap according to the Paschen’s law and processes of desorption from the electret surface are assumed to occur.

Light Oil Recovery From Cyclic CO2 Injection: Influence of Low Pressures, Impure CO2, and Reservoir Gas

Summary This paper is a laboratory and field investigation of the CO2 huff ‘n’ puff process for the enhanced recovery of light crude oil. Cyclic CO2 displacement results with live and dead oils in watered-out Berea cores are presented. Sixty-five single-well cyclic CO2 field tests conducted in a pressure-depleted reservoir are evaluated.