Fluid-chemical modeling of the near-cathode sheath formation process in a high current broken in DC air circuit breaker

When the contacts of a medium-voltage DC air circuit breaker(DCCB) are separated, the energy distribution of the arc is determined by the formation process of the near-electrode sheath. Therefore, the voltage drop through the near-electrode sheath is an important means to build up the arc voltage, which directly determines the current-limiting performance of the DCCB. A numerical model to describe the near-electrode sheath formation process can provide insight into the physical mechanism of the arc formation, and thus provide a method for arc energy regulation. In this work, we establish a two-dimensional axisymmetric time-varying model of a medium-voltage DCCB arc when interrupted by high current based on a fluid-chemical model involving 16 kinds of species and 46 collision reactions. The transient distributions of electron number density, positive and negative ion number density, net space charge density, axial electric field, axial potential between electrodes, and near-cathode sheath are obtained from the numerical model. The computational results show that the electron density in the arc column increases, then decreases, and then stabilizes during the near-cathode sheath formation process, and the arc column's diameter gradually becomes wider. The 11.14 V–12.33 V drops along the17 μm space charge layer away from the cathode(65.5 k V/m–72.5 k V/m) when the current varies from 20 k A–80 k A.The homogeneous external magnetic field has little effect on the distribution of particles in the near-cathode sheath core,but the electron number density at the near-cathode sheath periphery can increase as the magnetic field increases and the homogeneous external magnetic field will lead to arc diffusion. The validity of the numerical model can be proven by comparison with the experiment.

Air pressure law of a reservoir constructed in karst sinkholes

Karst sinkholes with natural negative landform provide favorable conditions for the pumped storage reservoir construction for less excavation work.However,the construction of the reservoir would plug the natural karst channels for water and air,which would cause remarkable air pressure in karst channels when the groundwater level fluctuates.A large laboratory simulation test was carried out to study the air pressure variation of a reservoir built on the karst sinkhole.The air pressure in the karst channel and inside the model was monitored during the groundwater rising and falling process.Result showed that the variation of air pressure in the karst channel and the surrounding rock exhibited a high degree of similarity.The air pressure increased rapidly at the initial stage of water level rising,followed by a slight decrease,then the air pressure increased sharply when the water level approached the top of the karst cave.The initial peak of air pressure and the final peak of air pressure were defined,and both air pressure peaks were linearly increasing with the water level rising rate.The negative air pressure was also analyzed during the drainage process,which was linearly correlated with the water level falling rate.The causes of air pressure variation in karst channels of a pumped storage reservoir built on the karst sinkhole were discussed.The initial rapid increase,then slight decrease and final sudden increase of air pressure were controlled by the combined effects of air compression in karst channel and air seepage into the surrounding rock.For the drainage process,the instant negative air pressure and gradual recovering of air pressure were controlled by the combined effects of negative air pressure induced by water level falling and air supply from surrounding rock.This work could provide valuable reference for the reservoir construction in karst area.

The Influence of Atmospheric Pressure on Air Content and Pore Structure of Air-entrained Concrete

To study the effect of atmospheric pressure on the properties of fresh and hardened airentrained concrete, three kinds of air entraining agents were used for preparing air-entrained concrete in the plateaus(Lhasa, 61 kPa) and the plains(Beijing, 101 kPa). Air content, slump, compressive strength and pore structure of the three air-entrained concretes were tested in these two places. It is found that the air content of concrete under low atmospheric pressure(LAP) is 4%-36% lower than that of concrete under normal atmospheric pressure(NAP), which explaines the decrease of slump for air-entrained concrete under LAP. Pore number of hardened concrete under LAP is reduced by 48%-69%. While, the proportion of big pores(pore diameter >1 200 μm) and air void spacing factor are increased by 1.5%-7.3% and 51%-92%, respectively. The deterioration of pore structure results in a 3%-9% reduction in the compressive strength of concrete. From the results we have obtained, it can be concluded that the increase of critical nucleation energy of air bubbles and the decrease of volumetric compressibility coefficient of air in the concrete are responsible for the variation of air content and pore structure of concrete under LAP.

Impacts of air pressure on the evolution of nanosecond pulse discharge products

Based on the nonequilibrium plasma dynamics of air discharge, a dynamic model of zero-dimensional plasma is established by combining the component density equation, the Boltzmann equation, and the energy transfer equation. The evolution properties of nanosecond pulse discharge （NPD） plasma under different air pressures are calculated. The results show that the air pressure has significant impacts on the NPD products and the peak values of particle number density for particles such as O atoms, 03 molecules, N2（A3） molecules in excited states, and NO molecules. It increases at first and then decreases with the increase of air pressure. On the other hand, the peak values of particle number density for N2（B3） and N2（C3） molecules in excited states are only slightly affected by the air pressure.

Cold atmospheric-pressure air plasma treatment of C6 glioma cells:effects of reactive oxygen species in the medium produced by the plasma on cell death

An atmospheric-pressure air plasma is employed to treat C6 glioma cells in vitro. To elucidate on the mechanism causing cell death and role of reactive species （RS） in the medium produced by the plasma, the concentration of the long-lived RS such as hydrogen peroxide, nitrate, and ozone in the plasma-treated liquid （phosphate-buffered saline solution） is measured. When vitamin C is added to the medium as a ROS quencher, the viability of C6 glioma cells after the plasma treatment is different from that without vitamin C. The results demonstrate that reactive oxygen species （ROS） such as H2O2, and O3 constitute the main factors for inactivation of C6 glioma cells and the reactive nitrogen species （RNS） may only play an auxiliary role in cell death.

Influence of air pressure on the performance of plasma synthetic jet actuator

Plasma synthetic jet actuator（PSJA） has a wide application prospect in the high-speed flow control field for its high jet velocity.In this paper,the influence of the air pressure on the performance of a two-electrode PSJA is investigated by the schlieren method in a large range from 7 k Pa to 100 k Pa.The energy consumed by the PSJA is roughly the same for all the pressure levels.Traces of the precursor shock wave velocity and the jet front velocity vary a lot for different pressures.The precursor shock wave velocity first decreases gradually and then remains at 345 m/s as the air pressure increases.The peak jet front velocity always appears at the first appearance of a jet,and it decreases gradually with the increase of the air pressure.A maximum precursor shock wave velocity of 520 m/s and a maximum jet front velocity of 440 m/s are observed at the pressure of 7 k Pa.The averaged jet velocity in one period ranges from 44 m/s to 54 m/s for all air pressures,and it drops with the rising of the air pressure.High velocities of the precursor shock wave and the jet front indicate that this type of PSJA can still be used to influence the high-speed flow field at 7 k Pa.

Design, Development and Testing of an Air Damper to Control the Resonant Response of a SDOF Quarter-Car Suspension System

An air damper possesses the advantages that there are no long term changes in the damping properties, there is no dependence on working temperature and additionally, it has less manufacturing and maintenance costs. As such, an air damper has been designed and developed based on the Maxwell type model concept in the approach of Nishihara and Asami [1]. The cylinder-piston and air-tank type damper characteristics such as air damping ratio and air spring rate have been studied by changing the length and diameter of the capillary pipe between the air cylinder and the air tank, operating air pressure and the air tank volume. A SDOF quarter-car vehicle suspension system using the developed air enclosed cylinder-piston and air-tank type damper has been analyzed for its motion transmissibility characteristics. Optimal values of the air damping ratio at various values of air spring rate have been determined for minimum motion transmissibility of the sprung mass. An experimental setup has been developed for SDOF quarter-car suspension system model using the developed air enclosed cylinder-piston and air-tank type damper to determine the motion transmissibility characteristics of the sprung mass. An attendant air pressure control system has been designed to vary air damping in the developed air damper. The results of the theoretical analysis have been compared with the experimental analysis.

The Analysis of the Line Pattern of Nonlinear Winding Filament on FRP Composite Air Vessel Resisting High Pressure

The FW process is a prefect method of manufacturing FRP composite air vessel resisting high pressure and aerial press vessel.In this paper FW pattern of FRP composite air vessel resisting high pressure was analyzed in a nutshell.The stability of FW patterns on end head is very sensitive to changing of pattern parameter.Consequently,its FW pattern was based on geodesic track.The FW angles and on equators depend on the dimension of end part and the condition of geodesic FW.Generally speaking, the polar holes of rocket engine shell are disproportional.Therefore,the FW angles of the shell column are changeable.The feasi- bility of nongeodesic FW of the shell column was discussed in this paper.Furthermore,it expounded the indispensable condition be- tween the length of shell column and the FW friction coefficient.At the same time,the general mathematic models of the movement control of nongeodesic FW were deduced.

Calculation of the Choked Back Pressure for Steam Turbines with Air Cooled Condensers

The choked back pressure characteristic of the steam turbine unit with air cooled condenser is very different with the unit with wet cooling technology, and the understanding of the choked back pressure performance change with operation load is important to guide the economic operation of the unit. One simplified Variable Operation Condition Analysis Method was put forward for calculation of the unit output-turbine back pressure characteristics. Based on this method, the choked back pressure for each operation load can be determined. An example was given for a super-critical, regenerative single-shaft, 2-casing with 2-exhaust steam turbine generation unit with air cooled condenser. The calculation result was provided and compared with the result of the unit with wet cooling technology.

A Novel Low Air Pressure-Assisted Approach for the Construction of Cells-Decellularized Tendon Scaffold Complex

Objective The goal of this study was to develop a decellularized tendon scaffold(DTS)and repopulate it with adipose-derived stem cells(ADSCs)assisted by low air pressure(LP).Methods The porcine superficial flexor tendons were processed into the DTSs using a combination of physical,chemical,and enzymatic treatments.The effectiveness of decellularization was verified by histological analysis and DNA quantification.The properties of the DTSs were evaluated by quantitative analysis of biochemical characterization,porosimetry,in vitro biocompatibility assessment,and biomechanical testing.Subsequently,the ADSCs-DTS complexes were constructed via cell injection assisted by LP or under atmospheric pressure.The differences in cell distribution,biomechanical properties,and the total DNA content were compared by histological analysis,biomechanical testing,and DNA quantification,respectively.Results Histological analysis confirmed that no cells or condensed nuclear materials were retained within the DTSs with widened interfibrillar space.The decellularization treatment resulted in a significant decrease in the content of DNA and glycosaminoglycans,and a significant increase in the porosity.The DTSs were cytocompatible in vitro and did not show reduced collagen content and inferior biomechanical properties compared with the fresh-frozen tendons.The assistance of LP promoted the broader distribution of cells into the adjacent interfibrillar space and cell proliferation in DTSs.The biomechanical properties of the scaffolds were not significantly affected by the recellularization treatments.Conclusion A novel LP-assisted approach for the construction of cells-DTS complex was established,which could be a methodological foundation for further bioreactor and in vitro studies.

Study on the Relationship of Spray Rate to Air Pressure and Gravity Drop of Siphonic Nozzle

In order to further clarify the spraying performance of siphonic nozzle, the spray rate of siponic cone nozzle with aperture of 1.0 mm was determined at 15 different air pressure levels and 12 gravity drop levels, and DPS and SPSS were used to make the difference analysis and modeling, which clarified the relationship between the spray rate of the siphonic cone nozzle with aperture of 1.0 mm and air pressure and gravity drop, getting the regression equation of Y=406.854P＋ 1.904G＋77.524. The study could provide a theoretical basis for the optimization and improvement of plant protection spraying equipment.

About the Change in Air Pressure in the Pipeline during the Pneumatic Transportation of Cotton

The article is devoted to the study of the issues of determining the patterns of changes in air pressure along the length of a pneumatic transmission pipeline for raw cotton at different flow parameters and different pipeline diameters. Theoretical studies have proved the reduction of static and total pressure along the line of pneumatic cotton transportation. The dependence of the pressure change on the diameter of the transport line and the aerodynamic drag of the pipeline is obtained. The results obtained are recommended for use in the design of raw cotton pneumatic transport systems.

Pre-placement of adhesive tape around wound sites can prevent air leakage in negative pressure wound therapy procedures

The introduction of negative pressure wound therapy has revolutionized the management of complicated wounds.However,the maintenance of an effective negative pressure environment is difficult in some instances,such as wounds in close proximity to an intestinal stoma or wounds surrounded by external fixations.We found that adhesive tape adheres more easily to itself than to wet skin or uneven surfaces.Therefore,we placed adhesive tape around surgical wounds prior to covering them with foam and sealing them with more tape.As a result of the strong adhesive force between pieces of tape,this method could provide a better environmental seal,even in situations where space is limited.Pre-placed adhesive tape around the wound site prior to foam placement could provide sufficient adhesion to maintain a continuous negative pressure environment during treatment.

A Method of Using a Carbon Fiber Spiral-Contact Electrode to Achieve Atmospheric Pressure Glow Discharge in Air

During discharge, appropriately changing the development paths of electron avalanches and increasing the number of initial electrons can effectively inhibit the formation of filamentary discharge. Based on the aforementioned phenomenon, we propose a method of using microdischarge electrodes to produce a macroscopic discharge phenomenon. In the form of an asymmetric structure composed of a carbon fiber electrode, an electrode structure of carbon fiber spiral-contact type is designed to achieve an atmospheric pressure glow discharge in air, which is characterized by low discharge voltage, low energy consumption, good diffusion and less ozone generation.

Pressure drop of the film-enlarged tube bundles in air-water two-phase cross flow in evaporative air cooler

An experiment was carried out to investigate the relation of the maximum velocity of air passing through narrowest passage, mass flux of spray water in one square meter in one hour and the pressure drop of tube bundles. Twelve equations were obtained for the relation. The results show that the pressure drop of the tube bundles increases with increase of the maximum velocity of air and the mass flux of spray water. Comparing the pressure drop of the bare tube bundles with that of the film-enhanced tube bundles, it is found that the pressure drop of the film-enhanced tube bundles is lower about 11% and the surface roughness of the film-enhanced plates is a main factor that influences the pressure drop. The data and method obtained in the paper can be used to compute the pressure drop of the film-enhanced tube bundles and is helpful for selection of fan.

Effects of total pressures and equivalence ratios on kerosene/air rotating detonation engines using a paralleling CE/SE method

In this paper,the kerosene/air rotating detonation engines(RDE)are numerically investigated,and the emphasis is laid on the effects of total pressures and equivalence ratios on the operation characteristics of RDE including the initiation,instabilities,and propulsive performance.A hybrid MPI t OpenMP parallel computing model is applied and it is proved to be able to obtain a more effective parallel performance on high performance computing(HPC)systems.A series of cases with the total pressure of 1 MPa,1.5 MPa,2 MPa,and the equivalence ratio of 0.9,1,1.4 are simulated.On one hand,the total pressure shows a significant impact on the instabilities of rotating detonation waves.The instability phenomenon is observed in cases with low total pressure(1 MPa)and weakened with the increase of the total pressure.The total pressure has a small impact on the detonation wave velocity and the specific impulse.On the other hand,the equivalence ratio shows a negligible influence on the instabilities,while it affects the ignition process and accounts for the detonation velocity deficit.It is more difficult to initiate rotating detonation waves directly in the lean fuel operation condition.Little difference was observed in the thrust with different equivalence ratios of 0.9,1,and 1.4.The highest specific impulse was obtained in the lean fuel cases,which is around 2700 s.The findings could provide insights into the understanding of the operation characteristics of kerosene/air RDE.

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 × 10^ 3 to 1.01 × 10^5pa. 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.

Interannual and Interdecadal Variability of East Asian Acas and Their Impact on Temperature of China in Winter Season for the Last Century

The interannual and interdecadal varinbility of the Siberian High (SH) and the Aleutian Low (AL) from aspects of strength and location for the past one hundred years as well as their possible relations with temperature changes over China's Mainland are investigated. The data sets used are the historical sea level pressure for 1871-1995 and surface air temperature (SAT) over China in the last 100 years. The results show that the SAT in different regions over China, central strength of the SH and the AL, the south-reaching latitude of the 1030 hPa contour of the SH and the pressure gradient between the SH and the AL experienced two obvious changes during this period. One occurred in the 1920s, with a more prominent one in the 1980s. These variations are closely linked with the change of winter temperature over China in the interdecadal timescale. In the last 50 years, there is a remarkable interannual correlation between the strength of Active Centers of Atmosphere (Acas) and the winter temperature of northern and eastern regions in China. The abrupt change of Acas in the 1980s is consistent with the rising of the SAT in China. Since the late 1980s, the atmospheric circulation is experiencing a remarkable modulation, which may cause the interdecadal transition of warming trend.

Effect of Air Pressure on Hardened Layer of U75V 60 kg/m Heavy Rail after Heat Treatment

The samples cut from U75V 60 kg/m heavy rail are heated to 900 ℃ in resistance furnace and then put into air spraying channel to be cooled for 80 s, and change air pressure from 0.16 MPa to 0.33 MPa, and observe the effect of air pressure on hardened layer. The thickness and hardness of hardened layer increases with the increase of air pressure, and the thickness is more than 24 mm at the center and top fillets of rail head, and more than 15 mm at the blow fillets of rail head when air pressure is more than 0.26 MPa. During the tempering after heat treatment, tempering temperature of rail head is more than 570 ℃ when air pressure is separately 0.16 MPa, 0.20 MPa and 0.23 MPa, which is higher than finishing temperature of pearlite transformation at the cooling rate of 3 ℃/s according to CCT curve of U75V steel. When air pressure is separately 0.26, 0.30 and 0.33 MPa, the tempering temperature is 529 ℃ lower than finishing temperature of pearlite transformation at the cooling rate of 3 ℃/s. Under this condition, pearlite transformation is finished totally, so in order to reduce air consumption and control the cost, proper air pressure for U75V 60 kg/m heavy rail heat treating should be 0.26 MPa; the cooling rate increases with the increase of air pressure, and the average cooling rate on the surface of rail head is more than 3.21 ℃/s when air pressure is more than 0.26 MPa, and the largest cooling rate occurs at the top fillets of rail head.

Laboratory testing of a shuttle car canopy air curtain for respirable coal mine dust control

Canopy air curtain （CAC） technology has been developed by the National Institute for Occupational Safety and Health （NIOSH） for use on continuous miners and subsequently roof bolting machines in underground coal mines to protect operators of these machines from overexposure to respirable coal mine dust. The next logical progression is to develop a CAC for shuttle cars to protect operators from the same overexposures. NIOSH awarded a contract to Marshall University and J.H. Fletcher to develop the shuttle car CAC. NIOSH conducted laboratory testing to determine the dust control efficiency of the shuttle car CAC. Testing was conducted on two different cab configurations： a center drive similar to that on a Joy 10SC32AA cab model and an end drive similar to that on a Joy 10SC32AB cab model. Three different ventilation velocities were tested-0.61, 2.0, 4.3 rrds （120, 400, and 850 fpm）. The lowest, 0.61 m/s （120 fpm）, represented the ventilation velocity encountered during loading by the continuous miner, while the 4.3 m/s （850 fpm） velocity represented ventilation velocity airflow over the shuttle car while tramming against ventilation airflow. Test results showed an average of the dust control efficiencies ranging from 74 to 83% for 0.61 m/s （120 fpm）, 39%-43% for 2.0 m/s （400 fpm）, and 6%-16% for 4.3 m/s （850 fpm）. Incorporating an airflow spoiler to the shuttle car CAC design and placing the CAC so that it is located 22.86 cm （9 in.） forward of the operator improved the dust control efficiency to 51%-55% for 4.3 m/s （850 fpm） with minimal impact on dust control efficiencies for lower ventilation velocities. These laboratory tests demonstrate that the newly developed shuttle car CAC has the potential to successfully protect shuttle car operators from coal mine respirable dust overexposures.