Radial Profiles Of Gas Temperature Research Articles

The Borg Cube Simulation: Cosmological Hydrodynamics with CRK-SPH

Abstract A challenging requirement posed by next-generation observations is a firm theoretical grasp of the impact of baryons on structure formation. Cosmological hydrodynamic simulations modeling gas physics are vital in this regard. A high degree of modeling flexibility exists in this space, making it important to explore a range of methods in order to gauge the accuracy of simulation predictions. We present results from the first cosmological simulation using Conservative Reproducing Kernel Smoothed Particle Hydrodynamics (CRK-SPH). We employ two simulations: one evolved purely under gravity, and the other with nonradiative hydrodynamics. Each contains 2 × 23043 cold dark matter plus baryon particles in an box. We compare statistics to previous nonradiative simulations including power spectra, mass functions, baryon fractions, and concentration. We find self-similar radial profiles of gas temperature, entropy, and pressure and show that a simple analytic model recovers these results to better than 40% over two orders of magnitude in mass. We quantify the level of nonthermal pressure support in halos and demonstrate that hydrostatic mass estimates are biased low by 24% (10%) for halos of mass . We compute angular power spectra for the thermal and kinematic Sunyaev–Zel’dovich effects and find good agreement with the low-ℓ Planck measurements. Finally, artificial scattering between particles of unequal mass is shown to have a large impact on the gravity-only run, and we highlight the importance of better understanding this issue in hydrodynamic applications. This is the first in a simulation campaign using CRK-SPH, with future work including subresolution gas treatments.

Suzakustudy of gas properties along filaments of A2744

Context: We present the results of Suzaku observations of a massive galaxy cluster A2744, which is an active merger at $z=0.308$. Aims: By using long X-ray observations of A2744, we aim to understand the growth of the cluster and the gas heating process through mass accretion along the surrounding filaments. Methods: We analyzed data from two-pointed Suzaku observations of A2744 to derive the temperature distribution out to the virial radius in three different directions. We also performed a deprojection analysis to study radial profiles of gas temperature, density, and entropy and compared the X-ray results with multi-wavelength data to investigate correlations with the surface density of galaxies and with radio relics. Results: The gas temperature was measured out to the virial radius $r_{200}$ in the north-east region and to about $1.5r_{200}$ in the north-west and south regions. The radial profile of the gas temperature is rather flat and the temperature is very high (even near $r_{200}$); it is comparable to the mean temperature of this cluster ($kT=9$ keV). These characteristics have not been reported in any other cluster. We find a hint of temperature jump in the northeast region whose location coincides with a large radio relic, indicating that the cluster experienced gas heating because of merger or mass accretion onto the main cluster. The temperature distribution is anisotropic and shows no clear positive correlation with the galaxy density, which suggests an inhomogeneous mass structure and a complex merger history in A2744.

Suzakuobservations of the low surface brightness cluster A76

Context: We present results of Suzaku observations of a nearby galaxy cluster A76 at z=0.0395. This cluster is characterized by extremely low X-ray surface brightness and is hereafter referred to as the LSB cluster. Aims: To understand the nature and thermodynamic evolution of the LSB cluster by studying the physical properties of the hot intracluster medium in A76. Methods: We conducted two-pointed Suzaku observations of A76 and examined the global gas properties of the cluster by XIS spectral analysis. We also performed deprojection analysis of annular spectra and derived radial profiles of gas temperature, density and entropy out to approximately 850 kpc (~ 0.6 r_200) and 560 kpc (~0.4 r_200) in A76 East and A76 West, respectively. Results: The measured global temperature and metal abundance are approximately 3.3 keV and 0.24 solar, respectively. From the deprojection analysis, the entropy profile is found to be flat with respect to radius. The entropy within the central region (r < 0.2r_200) is exceptionally high (~400 keV cm^2). This phenomenon is not readily explained by either gravitational heating or preheating. The X-ray morphology is clumped and irregular, and the electron density is extremely low (1e-4 -- 1e-3 cm^-3) for the observed high temperature, suggesting that A76 is in the early phase of cluster formation and the gas compression due to gravitational potential confinement is lagging behind the gas heating.

Reconstruction of Gas Temperature and Density Profiles of the Galaxy Cluster RX J1347.5–1145

We use observations of Sunyaev-Zel'dovich effect and X-ray surface brightness to reconstruct the radial profiles of gas temperature and density under the assumption of a spherically symmetric distribution of the gas. The method of reconstruction, first raised by Silk & White, depends directly on the observations of the Sunyaev-Zel'dovich effect and the X-ray surface brightness, without involving additional assumptions such as the equation of state of the gas or the conditions of hydrostatic equilibrium. We applied this method to the cluster RX J1347.5-1145, which has both the Sunyaev-Zel'dovich effect and X-ray observations with relative high precision. It is shown that it will be an effective method to obtain the gas distribution in galaxy clusters. Statistical errors of the derived temperature and density profiles of gas were estimated according to the observational uncertainties.

Spectroscopic determination of oxygen DC glow-discharge temperature: Radial profile of gas temperature

Rotational temperature in the oxygen DC glow discharge is determined from atmospheric A-band of molecular oxygen. Two methods of estimation of this parameter taking into account the quality of the detected spectra are analysed and compared. Radial profile of the rotational temperature is measured. No radial variations of rotational temperature have been observed in the positive column under our experimental conditions.

Shock wave propagation and dispersion in glow discharge plasmas

Spark-generated shock waves were studied in glow discharges in argon and argon–nitrogen mixtures. Ultraviolet filtered Rayleigh scattering was used to measure radial profiles of gas temperature, and the laser schlieren method was used to measure shock arrival times and axial density gradients. Time accurate, inviscid, axisymmetric fluid dynamics computations were run and results compared with the experiments. Our simulation show that changes in shock structure and velocity in weakly ionized gases are explained by classical gas dynamics, with the critical role of thermal and multi-dimensional effects (transverse gradients, shock curvature, etc.). A direct proof of the thermal mechanism was obtained by pulsing the discharge. With a sub-millisecond delay between starting the discharge and shock launch, plasma parameters reach their steady-state values, but the temperature is still low, laser schlieren signals are virtually identical to those without the discharge, differing dramatically from the signals in discharges with fully established temperature profiles.

The Effect of Nitrogen Dilution on Nonfuel Hydrocarbons in Laminar Nonpremixed Flames

Centerline and radial profiles of gas temperature and C3 to CI2 hydrocarbon concentrations were measured in nitrogen-diluted methane and ethylene coflowing nonpremixed flames. The methane or ethylene volumetric flowrates were kept constant while the nitrogen flowrate in the fuel mixture was systematically varied. In both series of flames, the lemperatures in the pyrolysis zone were shifted to higher heights in the flame by increases in the overall flame length, and were reduced both by the decrease in the adiabatic flame temperature and by a mechanism that likely involves decreased heat transfer from the flame front to the centerline. The maximum centerline concentrations of every measured non-fuel hydrocarbon monotonically decreased and shifted to higher heights in the flame as dilution was increased. The maximum mole fractions of most linear hydrocarbons were roughly proportional to the hydrocarbon mole fraction in the un reacted fuel mixture, while the maximum mole fractions of aromatic hydrocarbons varied roughly as the square of that quantity. The decrease in the initial methane or ethylene concentration in the fuel appears to be the primary cause of the reductions in the maximum nonfuel hydrocarbon concentrations. For all hydrocarbons the shape of the centerline mole fraction profiles, including the location of the maximum concentration and of the species'disappearance, correlate well with temperature.

Modeling of Gas Turbine Fuel Nozzle Spray

Satisfactory performance of the gas turbine combustor relies on the careful design of various components, particularly the fuel injector. It is, therefore, essential to establish a fundamental basis for fuel injection modeling that involves various atomization processes. A two-dimensional fuel injection model has been formulated to simulate the airflow within and downstream of the atomizer and address the formation and breakup of the liquid sheet formed at the atomizer exit. The sheet breakup under the effects of airblast, fuel pressure, or the combined atomization mode of the airassist type is considered in the calculation. The model accounts for secondary breakup of drops and the stochastic Lagrangian treatment of spray. The calculation of spray evaporation addresses both droplet heat-up and steady-state mechanisms, and fuel vapor concentration is based on the partial pressure concept. An enhanced evaporation model has been developed that accounts for multicomponent, finite mass diffusivity and conductivity effects, and addresses near-critical evaporation. The presents investigation involved predictions of flow and spray characteristics of two distinctively different fuel atomizers under both nonreacting and reacting conditions. The predictions of the continuous phase velocity components and the spray mean drop sizes agree well with the detailed measurements obtained for the two atomizers, which indicates the model accounts for key aspects of atomization. The model also provides insight into ligament formation and breakup at the atomizer exit and the initial drop sizes formed in the atomizer near field region where measurements are difficult to obtain. The calculations of the reacting spray show the fuel-rich region occupied most of the spray volume with two-peak radial gas temperature profiles. The results also provided local concentrations of unburned hydrocarbon (UHC) and carbon monoxide (CO) in atomizer flowfield, information that could support the effort to reduce emission levels of gas turbine combustors.

Transient effects in burst-mode operation of pulsed barium vapor lasers

An externally heated barium laser has been operated in burst mode in order to investigate the approach of the medium to steady-state operation in a continuously pulsed self-heated mode. Studies of the temporal evolution of discharge-current and cathode-voltage waveforms and laser output throughout a burst of pulses reveal short-term (first few pulses) and long-term (tens of pulses) transient effects. The former are attributed to changing prepulse conditions early in the burst, and the latter to the build up of radial thermal gradients in the laser medium due to gas heating. Simple models enabling the calculation of time-averaged radial gas temperature profiles in the steady-state limit and temporal evolution of spatially averaged gas temperatures are presented to elucidate the effects of gas heating. >

Direct evidence of departure from local thermodynamic equilibrium in a free-burning arc-discharge plasma.

Radial profiles of gas temperature, electron temperature, and electron density were measured in a free-burning atmospheric-pressure argon arc-discharge plasma using line-shape analysis of scattered laser light. This method yields gas temperature, electron temperature, and electron density directly, with no reliance on the assumption of local thermodynamic equilibrium (LTE). Our results show a significant departure from LTE in the center of the discharge, contrary to expectations.

Measurements of gas temperature in an argon positive column using acoustic wave propagation

Experiments on acoustic wave propagation and gas temperature measurement in an argon discharge are presented. Ultrasonic waves of pulsed or CW (40 kHz) mode were transmitted across the positive column of diameter 4.6 cm, pressure 2-5 Torr and discharge current approximately 200 mA. Line-of-sight average (LSA) values of the gas temperature were obtained from the acoustic speed measurement. A thermocouple was also used to measure gas temperatures in the plasma. It is shown that the LSA gas temperatures are in good agreement with those derived from radial profile measurements by the thermocouple. The measured radial profiles of gas temperature are consistent with the calculated profiles from a model which balances the heat input from the electrons with the loss by thermal conduction in the gas.

Diffuse and constricted glow discharges in SF6

SF6 glow discharges have been investigated for currents up to 20 mA, in the pressure range 0.1 to 10 Torr. As the pressure is increased, the discharge changes from an abnormal glow with a diffuse positive column to a normal glow with a constricted, positive column. The diffuse discharges have positive voltage-current characteristics, while the characteristics of the constricted discharges are negative. From measurements of axial potential distribution and radial profiles of gas temperature in the positive column, radial profiles of E/N (electric field/gas number density) were determined. E/N falls off from the axis to the wall, and the profiles show that the radial limit of the positive column for both diffuse and constricted discharges corresponds closely to the position where E/N=(E/N)c, the value (362 Td) where the rates of ionisation and attachment in SF6 are the same. The E/N measurements have been used, together with established electron and ion transport data for SF6 and a set of continuity equations for the electrons and ions, to determine radial density profiles for electrons, positive ions and negative ions in several SF6 diffuse and constricted positive columns.

Untersuchungen der kontrahierten Edelgassäule bei mittleren Drücken. I Verfahren zur Ermittlung der Plasmaparameter und ihrer Radialverteilungen

AbstractPresented is a method to determine iteratively electron density, electron temperature, and gas temperature in medium pressure rare gas discharges. This method bases on the linear relationship between emission coefficient of continuum radiation and electron density according to electron‐atom‐bremsstrahlung. The radial profile of gas temperature is determined by solving the energy balance equation. The electron temperature is calculated from the reduced electric field strength and the degree of ionization. The received profiles and the values at axis permit to examine present theoretical conceptions and to estimate the influence of various elementary processes on discharge mechanism.

Gas Heating Effects in the Constriction of a High-Pressure Glow Discharge Column

Numerical calculations have been made to examine effects of rapid gas heating and subsequent gas density changes on the current density distribution in a high-pressure positive column. Radial profiles of gas temperature, radial expansion velocity, density, and pressure and of electron current density are calculated as functions of time for a simplified model of a glow discharge column. Initially, the glow is diffuse and the background gas is uniform. Considered specifically is a hydrogen discharge with an initial pressure of 500 Torr, an initial current of 6.0 A, a constant axial electric field of 10 kV/cm, and a radius of ∼0.75 mm. The gas dynamics are described by conservation equations for mass, momentum, and energy in a viscous, thermally conductive, compressible fluid and by the equation of state for a perfect gas. The dependence of the ionization rate on the electric field to gas density ratio makes the electron current density a sensitive function of the gas density. At 60 nsec the gas temperature near the axis is sufficiently high for the onset of rapid thermal dissociation in an axial core, and effects of gas transport are significant. The axial gas density is decreased ∼10%; the axial current density is twice its initial value; and the column is partially constricted. Calculated results are consistent with properties of a similar discharge studied experimentally by Cavenor and Meyer, particularly at the time of the formation of a filamentary channel, observed experimentally after the first stage of the glow-to-arc transition.