Total pressure

About: Total pressure is a research topic. Over the lifetime, 5199 publications have been published within this topic receiving 66658 citations.

Evaluation of Interruption Capability on Various Gases

Abstract: SF6 gas is widely used as interrupting medium for disconnecting switch and circuit breaker in power system whose voltage is above 72kV or medium voltage. Global warming effect of SF6, however, is well known and emission of this gas is strictly limited by regulation. As for research to find out substitute for SF6 gas, many works have worked out. Gleitzes [1] compared with SF6 and N2 and found out characteristic of dv/dt that SF6 was about three times larger than that of N2 Mr. Grant [2] examined dv/dt to the mixture ratio of N2-SF6 at the total pressure 5bar, 6bar, and 7bar of di/dt=9 A/ μ s for SLF interruption performance. It was shown that interruptible dv/dt became N2-SF6 gas mixture of 65% to 90% had higher than pure SF6 gas, and this will be explained by synergistic effect. Also for He-SF6 gas mixture its rate varied from 25%,50% to 75% and interruptible dv/dt characteristic were observed higher for gas mixture compared with pure SF6. Leel[3] also carried out experiment and showed that the higher the mixture ratio of SF6 with N2 and He higher the interruptible current and that of He mixture was always inferior to that of N2 Mr. Nakagawa [4] measured di/dt, which could interrupt the mixed gas when increasing the pressure of N2 with a constant SF6 pressure of 3 bars. As a result, if the pressure of SF6 was the same, it was shown that increasing of total pressure became higher, interruption performance would be smaller. As mentioned before interruption and insulation abilities with various gas and their mixture have been studied by many researchers, but research especially for interruption was not done sufficiently.

Oxygen mass transfer at liquid-metal-vapour interfaces under a low total pressure

Abstract: The problem of oxygen exchange at the interface between a gas and a liquid metal is treated for systems under a “vacuum” (Knudsen regime, pressures lower than 1 Pa), where, due to the large mean free path of gas molecules in a vacuum, transport processes in the gas phase have no influence on the total interphase mass exchange, which is controlled by interface phenomena and by oxygen partition equilibrium inside the liquid. Owing to the double contribution of molecular O2 and volatile oxides to the oxygen flux from the surface, non-equilibrium steady-state conditions can be established, in which no variations in the composition of the two phases occur with time, as the result of opposite oxygen exchanges. The total oxygen and metal evaporation rates are evaluated as a function of the overall thermodynamic driving forces, and an account of the transport kinetics is given by using appropriate coefficients. A steady-state saturation degree s r, is defined which relates the oxygen activity in the liquid metal to the O2 pressure imposed and to the vapour pressures of volatile oxides. When metals able to form volatile oxides are considered, pressures of molecular O2 higher than those defined under equilibrium conditions have to be imposed in the experimental set-up in order to obtain a certain saturation degree, as a consequence of the condensation of the oxide vapours on the reactor walls. Effective oxidation parameters are determined, which define the conditions leading the liquid to a definite steady-state composition under a “vacuum” when it is out of equilibrium. The effective value of the oxygen pressure which corresponds to the complete oxygen saturation of the metal, $$P_{O_{2,} s}^E $$ , is evaluated at different temperatures for the systems Si-O and Al-O. The results are represented as curves of $$P_{O_{2,} s}^E $$ against T, which separate different oxidation regimes; these results agree well with the experimental data found in the literature.

Magnetoacoustic wave propagation in current sheets

Abstract: Magnetoacoustic waves in a Harris neutral current sheet are investigated. The magnetic eld strength, Alfven speed,soundspeedandplasmadensityvarycontinuouslyacross the structure. The sheet supports body, surface and hybrid modes. Two surface modes exist (a kink and a sausage). In ad- dition, fundamental and harmonic body waves are found when their phase speeds approach the maximum Alfven speed in the sheet.Asthephasespeedsofthemodesdecrease,thewaveshave properties of both body and surface mode s{ah ybrid wave. In the long wavelength limit the phase speed of the fundamental kink body mode and sausage surface mode approach the maxi- mumAlfvenandtubespeedsrespectively.Atshortwavelengths, the phase speeds tend to constant values, each pair of kink and sausage modes merging after passing through the maximum value of the sound speed, c max . For all modes, in the inner part of the current sheet, the gas pressure is out of phase with the magnetic pressure, with the gas pressure dominating (a prop- erty of a slow mode). In the outer part of the sheet the magnetic pressure is in phase with the total pressure (a fast mode charac- teristic).Nopurelyfastorslowmodeexists.Foruniformdensity a minimum in the group velocity occurs only for the fundamen- tal kink mode. For the Epstein density prole, minima in the group velocity are found for the other modes also. Impulsively generated waves are expected to show temporal variations that are similar to observations of oscillations of radio and X-ray emission of the solar corona and neutral sheet oscillations in the Earth's magnetotail. Calculated periods of oscillation are in good agreement with observations.

The Electrical Properties of Zinc Selenide Heat-Treated in Controlled Partial Pressures of Constituent Elements

Abstract: ZnSe single crystals, some of which had been previously heat-treated in molten Zn or doped with Cu, were heat-treated in Zn or Se vapor The Hall effect and the electrical conductivity were measured and examined as a function of the vapor pressure Conduction after heat treatment in Se vapor is considered to be dominated by Zn vacancies, Se interstitials, or associated defects containing one of these, while the high n-type conductivity observed after heat treatment in Zn vapor is dominated by Se vacancies or Zn interstitials With decrease of the acceptor impurity concentration, the transition vapor pressure from low to high conductivity shifts from a high Zn vapor pressure to a low one corresponding to the total pressure minimum

Study of a Supersonic Combustor Employing an Aerodynamic Ramp Pilot Injector

Abstract: Calculations of the fuel-air mixing characteristics of a scramjet combustor concept employing an aerodynamic ramp fuel injector coupled with a cavity flameholder have been performed. The calculations of the nonreacting flow through the combustor represent a first step in a collab- orative computational and experimental effort to investi- gate the performance of this scramjet combustor concept. The nonreacting flow through the combustor yielded a high total pressure recovery. Entrainment of fuel within the cavity produced a large volume of the cavity that had a local fuel-air equivalence ratio between 0.5 and 2.5, which did not vary appreciably as the overall fuel- air equivalence ratio increased from 0.13 to 0.72. How- ever, the stronger shock and expansion waves generated at the higher overall fuel-air equivalence ratios caused the fuel distribution within the cavity to become more three- dimensional. A shock train upstream of the fuel injectors was generated by imposing a back pressure at the exit plane of the domain. The shock train separated the side wall boundary layer and led to a dramatic increase in the fuel-air mixing. The mixing was characterized by en- hanced asymmetric spreading toward the side wall and was accompanied by an increased loss in total pressure through the combustor.