Showing papers on "Total pressure published in 2006"

Controllable growth of vertically aligned zinc oxide nanowires using vapour deposition

Abstract: The controllable growth of vertically aligned ZnO nanowires using a simple vapour deposition method system is reported. The growth properties are studied as a function of the thickness of the Au catalyst layer, total pressure, deposition temperature and oxygen partial pressure. The experiments indicate the existence of five main zones of growth. The zone in which the aligned wires grow varies according to the pressure, temperature and oxygen partial pressure. A specific level of low supersaturation of Zn and oxygen vapour are both necessary to ensure the correct rate of growth, which then leads to having thin and densely aligned wires. The growth kinetics are discussed in terms of the interdependent variables. It was found that the diameter and density of the nanowires is controlled mostly by the growth temperature and pressure. The zone with the most aligned nanowires with the highest aspect ratio was found to be at 5?mbar in a temperature range of 860?800??C with a flow of 27?sccm of a N2/O2 mixture.

Corrosion of selected ceramic materials in hot gas environment

Abstract: The temperature dependence of the hot gas corrosion behaviour of various ceramic materials (Al 2 O 3 , ZrO 2 (Y-TZP), mullite, ZrSiO 4 and YAG) was investigated. The tests were performed in a high temperature burner rig at temperatures between 1200 °C and 1500 °C, a total pressure of 1 atm with a water vapour partial pressure of 0.24 atm, a gas flow velocity of 100 m/s and test times of about 130–300 h. ZrO 2 (Y-TZP) showed absolutely no corrosion, however, a very high susceptibility to thermal shock and phase transformation was observed. The other materials suffered degradation above 1300 °C. This was the consequence of the formation and evaporation of volatile hydroxides (e.g. Si(OH) 4 and Al(OH) 3 ). YAG showed a low corrosion rate and the formation of a protective surface layer. The corrosion susceptibility of these materials was found to be higher with increasing temperature. Thermochemical calculations of the partial pressure of volatile species formed in reaction with water vapour, affirm the observed differences in corrosion behaviour.

Two-dimensional radiation-hydrodynamic model for limit-cycle oscillations of luminous accretion disks

Abstract: We investigate the time evolution of luminous accretion disks around black holes by conducting two-dimensional radiation-hydrodynamic simulations. We adopt the α prescription for the viscosity. The radial-azimuthal component of the viscous stress tensor is assumed to be proportional to the total pressure in the optically thick region and the gas pressure in the optically thin regime. The viscosity parameter, α, is taken to be 0.1. We find the limit-cycle variation in luminosity between high and low states. When we set the mass input rate from the outer disk boundary to be 100LE/c2, the luminosity suddenly rises from 0.3LE to 2LE, where LE is the Eddington luminosity. It decays after retaining the high value for about 40 s. Our numerical results can explain the variability amplitude and duration of the recurrent outbursts observed in microquasar GRS 1915+105. We show that multidimensional effects play an important role in the high-luminosity state. In this state, the outflow is driven by the strong radiation force, and some part of the radiation energy dissipated inside the disk is swallowed by the black hole due to the photon-trapping effects. This trapped luminosity is comparable to the disk luminosity. We also calculate two more cases: one with a much larger accretion rate than the critical value for the instability and the other with the viscous stress tensor being proportional to the gas pressure only, even when the radiation pressure is dominant. We find no quasi-periodic light variations in these cases. This confirms that the limit-cycle behavior found in the simulations is caused by the disk instability.

Study of a Modified Amine-Based Regeneration Unit

Abstract: A computational model for the regeneration unit of a monoethanolamine-based (MEA-based) absorption plant for CO2 removal has been developed. The model is developed based on the desire to operate the desorber at higher pressures than normal (>2 bar). The reason for this was to investigate whether it was possible to operate at pressures where the compressor for CO2 recompression to storage pressures of 100−140 bar could be avoided altogether, or at least where the recompression energy requirement would be significantly reduced. The idea was that adding an inert immiscible component to the desorber would give an independent addition to the pressure and thereby the total pressure could be increased. The model simulates this three-phase process in order to investigate the effects of adding an immiscible organic component to the unit to control reboiler temperature. MEA was used as an example absorbent. The results show that the desorption process using MEA is very sensitive to the reboiler temperature. The reb...

Modeling the warm absorber in active galactic nuclei

Abstract: We present a wide grid of models for the structure and transmission properties of warm absorbers in active galactic nuclei (AGN). Contrary to commonly used constant density models, our absorbing cloud is assumed to be under constant total (gas plus radiation) pressure . This assumption implies the coexistence of material at different temperatures and ionization states, which is a natural consequence of pressure and thermal equilibrium. Our photoionization code allows us to compute the profiles of the density, the temperature, the gas pressure, the radiation pressure and the ionization state across the cloud, and to calculate the radiative transfer of continuum and lines including Compton scattering. Therefore, equivalent widths of both saturated and unsaturated lines are properly modeled. For each pair of the incident spectrum slope and the ionization parameter at the cloud surface there is a natural upper limit to the total column densities of the cloud due to thermal instabilities. These maximum values are comparable to the observational constraints on the column density of warm absorbers which may give support to constant total pressure models. In all models we note considerable absorption around 6.4 keV which modifies the intrinsic relativistically broadened iron line profile originating in an accretion disk illuminated atmosphere. Our models can be applied to fitting the spectroscopic data from the XMM-Newton and Chandra satellites.

Ablation study in the capillary discharge of an electrothermal gun

Abstract: In this paper, we study the ablation phenomena associated with the operation of a capillary discharge for an electrothermal gun. Electrothermal-chemical (ETC) guns are used for enhancement of ignition and combustion of an energetic propellant. One of the major components of the ETC system is a plasma source based on a capillary discharge. In this paper, a model of the capillary discharge is developed. In this model, primary attention is paid to the ablation phenomenon. Different characteristic subregions near the ablated surface, namely, a space-charge sheath, a Knudsen layer, and a hydrodynamic layer, are considered. In this formulation, the ablation rate is determined by the parameters at the edge of the Knudsen layer. The kinetic approach is used to determine the parameters at the interface between the kinetic Knudsen layer and the hydrodynamic layer. Coupling the solution of the nonequilibrium Knudsen layer with the hydrodynamic layer provides a self-consistent solution for the ablation rate. According to the model predictions, the peak electron temperature is about 1.4 eV, the polyethylene surface temperature is about 700 K, and the pressure is about 10 MPa. It is found that the ablation rate increases with the capillary length. The ablated mass and the predicted total pressure agree with previous experimental observations.

Research on low cavitation in water hydraulic two-stage throttle poppet valve:

Abstract: Cavitation has important effects on the performances and lifespan of water hydraulic control valve, such as degrading efficiency, intense noise, and severe vibration. Two-stage throttle valve is a practicable configuration to mitigate cavitation, which is extensively used in water hydraulic pressure relief valves and throttle valves. The pressure distribution inside a medium chamber located between two throttles of a two-stage throttle valve is investigated through numerical simulations. The effects of the passage area ratio of the two throttles and the inlet and outlet pressures on the pressure inside the medium chamber are examined. The simulation results indicate that (a) the pressure inside the medium chamber is not constant, (b) the locations of maximum and minimum pressures inside the medium chamber are both fixed, which will not vary with the passage area ratio or the inlet and outlet pressures, and (c) the ratio of the pressure drop across the front throttle to the total pressure drop acro...

Aerodynamic and Heat Flux Measurements in a Single-Stage Fully Cooled Turbine—Part II: Experimental Results

Abstract: This paper presents measurements and the companion CFD predictions for a fully cooled, high-work single stage HP turbine operating in a short-duration blowdown rig. Part I of this paper presented the experimental approach, and Part II focuses on the results of the measurements and demonstrates how these results compare to predictions made using the Numeca FINE/Turbo CFD package. The measurements are presented in both time-averaged and time-accurate formats. The results include the heat transfer at multiple spans on the vane, blade, and rotor shroud as well as flow path measurements of total temperature and total pressure. Surface pressure measurements are available on the vane at midspan, and on the blade at 50% and 90% spans as well as the rotor shroud. In addition, temperature and pressure measurements obtained inside the coolant cavities of both the vanes and blades are presented. Time-averaged values for the surface pressure on the vane and blade are compared to steady CFD predictions. Additional comparisons will be made between the heat transfer on cooled blades and uncooled blades with identical surface geometry. This, along with measurements of adiabatic wall temperature, will provide a basis for analyzing the effectiveness of the film-cooling scheme at a number of locations.Copyright © 2006 by ASME

Combining a difference-frequency source with an off-axis high-finesse cavity for trace-gas monitoring around 3 μm

Abstract: High-sensitivity spectroscopy of methane around 3 microm was carried out by means of a 5.5-mW cw difference-frequency generator in conjunction with a high finesse cavity in off-axis alignment. By cavity-output integration a minimum detectable absorption coefficient of 5.7*10-9 cm-1Hz-1/2 was achieved, which compares well with results already reported in the literature. Detection of methane in natural abundance was also performed in ambient air, for different values of total pressure, allowing direct concentration measurements via evaluation of the integrated absorbance of the spectra. In particular, at atmospheric pressure, a minimum detectable concentration of 850 parts per trillion by volume (pptv)*Hz-1/2 was demonstrated.

Pressure drop for the flow of high concentration solid-liquid mixture across 90º horizontal conventional circular pipe bend

Abstract: Pressure drop across a 90° horizontal bend for fly ash slurry at high concentrations is reported in the present study. The pressure drop across the bend has been measured at five concentrations in the range of 50-65% (by weight) and the data has been analyzed to obtain the relative pressure drop, bend loss coefficient and permanent pressure loss. Measurements show that the relative pressure drop across the pipe bends increases with increase in concentration at low velocity. However, at any given concentration relative pressure drop is independent of velocity over the range tested. The bend loss coefficient at any velocity increases with increase in concentration. The permanent pressure loss increases marginally with concentration and velocity. The contribution of disturbed flow conditions downstream of the bend to the total pressure loss is much less in the case of highly concentrated slurries as compared to that in water.

A new model for the Warm Absorber in NGC 3783: a single medium in total pressure equilibrium

Abstract: Context. Many active galactic nuclei exhibit X-ray features typical of the highly ionized gas called “Warm Absorber” (WA). Such a material appears to be stratified, displaying zones of di fferent density, temperature, and ionization. In this paper, we investigate the possibility of modelling the WA gas in NGC 3783 as a single medium in total pressure equilibrium. Aims. Our goal is to demonstrate that the WA can be well modelled assuming constant total pressure, in contrast to the current de scriptions that are based on the presence of multiple regions, each in constant density. The assumption of total pressure equilibrium yields a more physical description of the WA, resulting in the natural stratificati on of the ionized gas, and providing an explanation for the presence of lines from different ionization states, as observed in WA spectra. Methods. We have used the photoionization code TITAN, developed by our team, to compute a grid of constant total pressure models with the purpose of fitting the WA in NGC 3783. We have compared our models to the 900 ks Chandra spectrum of NGC 3783 and to previous studies where the WA was described by multiple zones of constant density. Results. In the case of NGC 3783, the WA features can be well reproduced by a clumpy, ionized gas with cosmic abondances, ionization parameter� = 2500 erg cm s −1 , column density NH = 4 10 22 cm −2 , and constant total pressure. Conclusions. We have shown that the WA in NGC 3783 can be modelled by a single medium in total pressure equilibrium; this is probably the case for other WAs currently described by multi-zone, constant density models. In addition, our work demonstrates that the TITAN code is well adapted to the study of the WA in active galactic nuclei, opening new prospects for the use of TITAN by a larger community.

Computations of Turbulent Flow and Heat Transfer Through a Three-Dimensional Non-Axisymmetric Blade Passage

Abstract: The design of a three-dimensional non-axisymmetric end-wall is carried out using three-dimensional numerical simulations. The computations have been conducted both for the flat and contoured end-walls. The performance of the end-wall is evaluated by comparing the heat transfer and total pressure loss reduction. The contouring is done in such a way to have convex curvature in the pressure side and concave surface in the suction side. The convex surface increases the velocity by reducing the local static pressure while concave surface decreases the velocity by increasing the local pressure. The profiling of the end-wall is done by combining two curves, one that varies in the streamwise direction while the other varies in the pitchwise direction. Several contoured end-walls are created by varying the streamwise variation keeping the pitchwise curve constant. The flow near the contoured end-wall is seen to be significantly different than that of flat end-wall. The contoured end-wall is found to reduce the secondary flow by decreasing radial pressure gradient. The total pressure loss is also lower and the average heat transfer reduces by about 8% compared to the flat end-wall. Local reductions in heat transfer are significant (factor of 3). This study demonstrates the potential of three-dimensional end-wall contouring for reducing the thermal loading on the end wall.Copyright © 2006 by ASME

Effect of inlet swirl on the performance of annular diffusers having the same equivalent cone angle

Abstract: Annular diffusers are an integral component of the gas turbine engines of high-speed aircraft. These facilitate effective operation of the combustor by reducing the total pressure loss. The performance characteristics of these diffusers depend on their geometry and the inlet conditions. The present investigation attempts to select the range of the inlet swirl intensity for the best performance of annular diffusers with different geometries but having the same equivalent cone angle. This is analysed on the basis of the static pressure recovery and total pressure loss coefficients. The results show that the parallel diverging hub and casing annular diffuser produces the best performance at high-swirl intensities.

The carrier gas pressure effect in a laminar flow diffusion chamber, homogeneous nucleation of n-butanol in helium

Abstract: Homogeneous nucleation rate isotherms of n-butanol+helium were measured in a laminar flow diffusion chamber at total pressures ranging from 50 to 210 kPa to investigate the effect of carrier gas pressure on nucleation. Nucleation temperatures ranged from 265 to 280 K and the measured nucleation rates were between 10(2) and 10(6) cm(-3) s(-1). The measured nucleation rates decreased as a function of increasing pressure. The pressure effect was strongest at pressures below 100 kPa. This negative carrier gas effect was also temperature dependent. At nucleation temperature of 280 K and at the same saturation ratio, the maximum deviation between nucleation rates measured at 50 and 210 kPa was about three orders of magnitude. At nucleation temperature of 265 K, the effect was negligible. Qualitatively the results resemble those measured in a thermal diffusion cloud chamber. Also the slopes of the isothermal nucleation rates as a function of saturation ratio were different as a function of total pressure, 50 kPa isotherms yielded the steepest slopes, and 210 kPa isotherms the shallowest slopes. Several sources of inaccuracies were considered in the interpretation of the results: uncertainties in the transport properties, nonideal behavior of the vapor-carrier gas mixture, and shortcomings of the used mathematical model. Operation characteristics of the laminar flow diffusion chamber at both under-and over-pressure were determined to verify a correct and stable operation of the device. We conclude that a negative carrier gas pressure effect is seen in the laminar flow diffusion chamber and it cannot be totally explained with the aforementioned reasons.

Separation Control on a Trailing-Edge Flap Using Air Jet Vortex Generators

Abstract: Nomenclature A = area CD = drag coefficient CL = lift coefficient Cp = pressure coefficient CV = jet velocity ratio Cμ = blowing coefficient (jet momentum ratio) c = chord DLG = flap deflection, lap and gap f = jet orifice diameter L = lift M = Mach number n = number of jets p = static pressure p0 = total pressure q = freestream dynamic pressure S = wing reference area V = speed x/c = nondimensional distance measured in a chordwise sense α = angle of attack, or jet skew angle β = jet pitch angle γ = ratio of specific heats = flap deflection λ = jet orifice spacing ρ = density

Apparatus and method for separating carbon dioxide

Abstract: PROBLEM TO BE SOLVED: To provide an apparatus for separating carbon dioxide, in which a facilitated transport membrane for CO 2 , which can exhibit satisfactory membrane performance at high temperature of 100°C or higher and under pressure, is used. SOLUTION: The apparatus for separating carbon dioxide is constituted so that a gaseous raw material, which contains carbon dioxide and water vapor at the least in a predetermined principal component gas, is supplied to the raw material-side surface of the facilitated transport membrane 10 for CO 2 at the supply temperature of 100°C or higher and the carbon dioxide permeated through the facilitated transport membrane 10 for CO 2 is withdrawn from the permeation-side surface of the membrane 10. The facilitated transport membrane 10 for CO 2 is formed by adding 2,3-diaminopropionic acid to a gel membrane of a polyvinyl alcohol-polyacrylic acid copolymer. A pressure regulating means 15 is arranged for controlling the total pressure of the gaseous raw material to be supplied to the facilitated transport membrane for CO 2 to be equal to or higher than the pressure satisfying the lower limit degree of water vapor saturation to be set within 0.3-0.6 and be equal to or lower than the pressure satisfying the degree of water vapor saturation of 1 when the degree of water vapor saturation is defined as a ratio obtained by dividing the water vapor partial pressure in the gaseous raw material by the saturated water vapor pressure to be decided at the supply temperature. COPYRIGHT: (C)2008,JPO&INPIT

Euler flow in a supersonic mixed-compression inlet

Abstract: Numerical simulation of a two-dimensional mixed compression supersonic inlet is carried out by solving unsteady compressible Euler equations via a stabilized finite element method. The geometry of the inlet is similar to the one used by Anderson and Wong for experimental investigation for Mach 3 flow. The computations are capable of simulating the start-up problems associated with the inlet. The critical back pressure for the successful operation of the inlet is computed. The effect of inlet back pressure on the total pressure recovery and the flow distortion level is analysed. Contrary to the popular belief, it is found that in addition to the throat to inlet capture area ratio, the ramp geometry close to the throat plays an important role in the start-up dynamics. It is demonstrated via simulations that, everything else being same, the geometries of ramp upstream of the throat that are associated with a curvature higher than a certain threshold, result in unstarting the intake.

Three-body interactions and solid-liquid phase equilibria: application of a molecular dynamics algorithm.

Abstract: The effect of three-body interactions on the solid-liquid phase boundaries of argon, krypton, and xenon is investigated via a novel technique that combines both nonequilibrium and equilibrium molecular dynamics. The simulations involve the evaluation of two- and three-body forces using accurate two-body and three-body intermolecular potentials. The effect of three-body interactions is to substantially increase the coexistence pressure and to lower the densities of liquid and solid phases. Comparison with experiment indicates that three-body interactions are required to accurately determine the total pressure. In contrast to vapor-liquid phase equilibria, the relative contribution of three-body interactions to the freezing pressure exceeds the contribution of two-body interactions at all temperatures.

Aerodynamic performance of scramjet inlet models with a single strut

Abstract: A series of three-dimensional sidewall compression-type scramjet inlet models with single struts were tested in a Mach 4 wind tunnel to investigate the influence of a strut between the sidewalls. With the sidewalls having a fixed shape, five struts of the same width but different lengths and wedge angles were mounted, so that the effect of each model could be compared with the same geometrical contraction ratio. The aerodynamic performances of inlets were determined based on the total pressure efficiency and the mass capture ratio at the geometrical throat. Also, flow visualizations were carried out to examine the flow structure, especially around the strut. Some of the results were compared with previously examined nonstrut models. The additional shock waves generated by the strut created a large separation on the sidewalls and the strut wall, resulting in the reduction of the total pressure efficiency and the capture ratio. Due to this separation, the shock wave was observed to be oscillatory. Measurement of fluctuating wall pressure was also carried out, which revealed that, in some regions, the pressure signals were asynchronous on the left and right sides of the strut. It seems that a small difference of the separation bubble structure on each sidewall initiated a cascade effect of pressure imbalance around the struts.

Numerical and experimental studies of the flow field in a cyclone dryer

Abstract: The performance of a newly developed cyclone dryer is investigated using RANS-based single-phase computational fluid dynamics (CFD) and experimental model studies. The cyclone dryer is a cylindrical tower, divided by conical orifices into several chambers; recirculation of the flow within individual chambers ensures adequate retention time for drying of the transported solid material. Numerical calculations are performed using the commercial CFD code CFX5.7 for different mesh types, turbulence models, advection schemes, and mesh resolution. Results of the simulation are compared with data from experimental model studies. The RNG k- turbulence model with hexahedral mesh gives satisfactory results. A significant improvement in CFD prediction is obtained when using a second order accurate advection scheme. Useful descriptions of the axial and tangential velocity distributions are obtained, and the pressure drop across the cyclone dryer chamber is predicted with an error of approximately 10%. The optimized numerical model is used to predict the influence of orifice diameter and chamber height on total pressure drop coefficient.