Range Of Working Conditions Research Articles

A theoretical study of hydrogen chemisorption on Ni(111) and Co(0001) surfaces

To quantify the role of hydrogen in the catalytic formation of hydrocarbons, the binding energy of adsorbed hydrogen species on Ni(111) and Co(0001) surfaces was calculated using density-functional theory within the generalized gradient approximation and the full-potential linearized augmented planewave method. In order to probe a range of potential working conditions of nickel and cobalt catalysts, adsorption of hydrogen as a function of both surface coverage and adsorption site was examined. Our results were in excellent agreement with the small set of experimental values available in the literature. The most stable configurations for hydrogen were adsorption on both three-fold hollow sites on nickel and cobalt surfaces at all surface coverages. In striking contrast to our results reported earlier for the binding energy of carbon and methylidyne, the relative stabilities of hydrogen chemisorption were independent of both the transition metal surface and surface coverage, suggesting that hydrogen plays a limited role in differences in product selectivities observed for hydrocarbon growth reactions on nickel and cobalt surfaces.

The design of hydrodynamically lubricated journal bearings against yield

The stress field induced by the half-Sommerfeld pressure distribution in an infinitely elongated bearing is studied in detail. A complex potential formulation for the stress field is employed to solve the elasticity problem, with the intention to compute the required strength according to the classical von Mises criterion. Example contour plots of the yield parameter (√J2)/ pm are given and the position and magnitude of the maximum normalized von Mises parameter are determined for a range of working conditions, analytically when they are on the surface, i.e. for eccentricity ratios ε √0.6, and semi-analytically for the cases where they are located subsurface, i.e. ε > 0.6. Surprisingly simple results are obtained for eccentricity ratios lower than about 0.7, namely a maximum of the von Mises parameter proportional to the mean pressure, permitting a simple rule to be developed for the design of bearings against yielding: if the bearing works with eccentricity ratios smaller than 0.7, and the average pressure is smaller than 1.22 k, where k is the yield stress of the material in pure shear, then yielding is avoided. When bearings are used in the range of very high eccentricity ratios, a more refined calculation is needed, taking into account the actual value of the maximum von Mises parameter and the paper provides design charts for this purpose.

Superplastic Forming of Zr<sub>65</sub>Al<sub>10</sub>Ni<sub>10</sub>Cu<sub>15</sub> Metallic Glass

We have investigated the powder consolidation and bulk working by using the high-strain-rate superplasticity of a Zr 65 Al 10 Ni 10 Cu 15 (at.%) metallic glass that has a wide supercooled liquid region of 105 K. The superplastic powder-consolidation process for producing bulk metallic glasses with full tensile strength has been established. The metallic glass, moreover, had an excellent workability and a wide working condition range. The successful extrusion conditions of temperature, ram-speed and pressure, which enable to work the metallic glass with retaining the glassy phase, have been established. The superplasticity inherent in the supercooled liquid seems to affect greatly the future development of bulk amorphous and nanocrystalline materials with novel properties.

Mice without myoglobin.

Myoglobin, an intracellular haemoprotein expressed in the heart and oxidative skeletal myofibres of vertebrates, binds molecular oxygen and may facilitate oxygen transport from erythrocytes to mitochondria, thereby maintaining cellular respiration during periods of high physiological demand. Here we show, however, that mice without myoglobin, generated by gene-knockout technology, are fertile and exhibit normal exercise capacity and a normal ventilatory response to low oxygen levels (hypoxia). Heart and soleus muscles from these animals are depigmented, but function normally in standard assays of muscle performance in vitro across a range of work conditions and oxygen availability. These data show that myoglobin is not required to meet the metabolic requirements of pregnancy or exercise in a terrestrial mammal, and raise new questions about oxygen transport and metabolic regulation in working muscles.

Robust control of a remotely operated underwater vehicle

A control strategy for an underwater vehicle based on a scheduling of linear H ∞ controllers has been proposed, and the overall performance of the closed-loop system have been evaluated by means of nonlinear simulation in a broad range of working conditions, with particular attention to the effects of the underwater current that acts on the vehicle.

Experimental and Theoretical Study of Sprays Produced by Ultrasonic Atomisers

The atomisation of liquids by means of low‐frequency ultrasonic atomisers results from unstable surface waves generated on the free surface of a thin liquid film. These unstable waves are obtained from the tuning of the amplitude and the frequency of an imposed oscillation. The thin liquid film develops as the liquid spreads over the atomising surface of the atomiser. This paper focuses on a systematic experimental analysis of the sprays produced by low‐frequency ultrasonic atomisers. The thickness of the liquid film was measured and its effects on the drop diameter were studied together with the effects of both the liquid's physical properties and the ultrasonic atomiser's characteristics. The relationship between the mean drop diameter and the surface wave wavelength was accurately determined and introduced into a mathematical approach based on the maximum entropy formalism to predict the drop size distribution of the spray. Within the range of working conditions tested, the application of this formalism is successful and provides a procedure for the prediction of spray drop size distributions from calculations only.

N‐Type Conductivity in Gadolinia‐Doped Ceria

The ionic and n‐type conductivities of ceria‐based electrolytes doped with gadolinium (10 and 20 cation %) or gadolinium and praseodymium (2% Pr and 18% Gd) were studied by impedance spectroscopy in air, between 573 and 1273 K, and by constant frequency (10 kHz) conductivity measurements as a function of the oxygen partial pressure (pO2) between about 10−20 atm and air in the temperature range 1073 to 1273 K. Ion blocking measurements were also performed between 1073 and 1273 K with air at the reversible electrode. From data obtained with different experimental techniques it was concluded that estimates for the electronic conductivity of all compositions were consistent and that all materials behaved in a rather similar manner. Estimated n‐type conductivities suggest that Pr‐doped materials have a slightly lower electronic conductivity and a larger electrolytic (and ionic) domain, but overall differences are quite small. The model behavior used in analyzing experimental results is discussed based on the existing knowledge of the defect chemistry of ceria‐based electrolytes, and a range of working conditions is identified where the ionic conductivity can be assumed constant and the electronic conductivity proportional to .

Study of the nozzle flow in a cross-flow turbine

An investigation of the flow inside the nozzle of a Cross-Flow turbine, which is a hydraulic turbine where the rectangular water jet issuing from the nozzle crosses the rotor blades twice, is presented here. Part of the investigation consisted in the experimental measurement of the static pressure distribution on the inside walls of two different nozzle configurations, both with the nozzle mounted alone and in the presence of a rotor. The tests performed in the presence of a rotor included the measurement of efficiency and covered a wide range of working conditions around the best efficiency point. The analysis of the results obtained in this way give us an indication of the influence of the turbine non-dimensional volume flow rate on the flow inside the nozzle and the way it affects the reaction degree of the machine and its efficiency level. Although most of the tests were carried out with a 25-blade rotor, one of the analysed nozzle configurations (that with an inside vane) was also tested with a 10-blade rotor, permitting the assessment of the effect the number of blades has on the flow in the nozzle. The flow inside the nozzle with no inside vane was numerically analysed using a method based on a Schwarz-Christoffel conformal transformation of variables. The numerical results show a fair agreement with the experimental data collected when the rotor was not present. A qualitative discussion of some of the losses occurring in the nozzle is advanced based on the computer results, and its conclusions are used for explaining the poor performance of the nozzle with no inside vane.

Latest developments on valve seat-seal assembly

The Helicoflex® metallic seal initially designed for static assemblies is presently used as a valve primary seal for specific applications where the elastomeric seal commonly used in such a configuration is totally unsuitable owing to low resistance to radiation and high temperature, and incompatibility with ultrahigh vacuum conditions. The hydrogen injection quick valves of the JET fusion reactor, as well as the aluminium ultrahigh vacuum valves of the TRISTAN accelerator already operate using this technology over a rather narrow range of working conditions. In order to widen the field of applications and establish the basic principles of the sealing function applied to a valve seat-seal assembly, tests were carried out in the Sealing Techniques Laboratory of the French Atomic Energy Commission (CEA). The seat configuration and seal holding device have been reconsidered. Seals have been tested using different grades of sealing lining material, i.e. successively aluminium, silver and copper. In this respect, such an assembly configuration was found to be in full compliance with the requirements of the new types of valve, those which are being considered for applications where ultrahigh vacuum is combined with a leak rate requirement of 10 −10 Pa m 3 s −1 and a high bake-out temperature.

Organic and ammonium nitrogen and oxygen in relation to granular sludge growth in lab-scale UASB reactors

Laboratory studies of in-reactor granular-sludge yield (Ygran) were carried out to investigate the effect of substrates rich in proteins. Both lab-scale upflow anaerobic sludge blanket (UASB) and shake-flask systems were used to monitor the behaviour of the sludge. Influent based on molasses with a COD to N ratio of 100:2.5-3.0 gave good Ygran; increasing substitution of the carbohydrate COD by protein COD resulted in a deterioration of the sludge characteristics. The negative effects appear to be related to the protein rather than to the NH4+ formed. Of the various environmental parameters examined, the surface tension of the mixed liquor was the main deviating factor. At a proper range of oxygenation i.e., by means of monitoring of both the input COD to oxygen ratio (gCOD gO2−1) and the daily oxygen loading rate (mgO2 gVSS−1.d−1), the UASB reactors treating the nitrogen-rich wastewater showed enhanced Ygran with only a minor reduction in methanogenesis. A range of working conditions in which this principle can be applied to decrease fluffy growth to the advantage of granular increase is proposed.

The power supply system for Langmuir probes on RFX

A power supply system for Langmuir probes to be used on the reversed field pinch (RFP) thermonuclear fusion experiment RFX has been developed. It is based on a full-bridge converter concept, using a pulse width modulation (PWM) technique, and is characterized by a 5 A, +or-150 V rating. The power supply has been designed to ensure compatibility with the electromagnetic noise close to the machine and with the plasma, which behaves as a nonlinear rapidly varying load. The system has been optimized by numerical simulations. Tests in the laboratory and on the experiment have been performed in a wide range of working conditions and the system has been proven to suit fairly well the RFX experimental conditions.

Choice of system parameters for projection electron-beam lithography: Accelerating voltage and demagnification factor

A lithography system that uses Scattering with Angular Limitation Projection Electron Lithography (SCALPEL) allows us to vary the electron-beam accelerating voltage in a way that was not possible with systems that use absorbing stencil masks. We have discovered that the choice of operating parameters, accelerating voltage, and demagnification factor, as well as many of the subsystem designs, are dominated by the need to control thermal effects within the system. We have derived a model which allows us to find operating parameters that minimize the thermal contribution to the pattern overlay error. This information, when combined with other subsystem constraints, enables us to define a relatively narrow range of possible working conditions. The model is general to high-throughput electron beam lithography systems; we have applied the model to one example of a SCALPEL system.

Inhomogeneity of flow, force parameters and pass geometry in rotary Cone‐Roll Tube Piercing

AbstractThe relationship between redundant macroshearing and force parameters, related to a rational pass design, in a rotary 2‐cone roll seamless tube piercing process was investigated. Wax and lead billets were pierced in a range of working conditions involving decelerated, uniform and accelerated rates of flow, different plug advances, and four values of feed angles. The likely optimal piercing conditions are indicated.

Evaluation of ionic transport number of CeO 2 doped Y-TZP and PSZ ceramics with alumina additions

Different zirconia-based composite materials, one TZP (3Ce-TZP) and two PSZ (1Ce-PSZ and 2Ce-PSZ) with 10 wt% Al 2O 3 additions, were studied with respect to electrical transport properties. Ionic transport number determinations and ac conductivity results as a function of oxygen partial pressure and temperature indicated that these compositions are ionic conductors within a large range of working conditions. The TZP composition exhibited the largest ionic conductivity and pure ionic behavior in air, from 800° to 1100°C. In PSZ materials the presence of significant amounts of cubic phase and/or the presence of some monoclinic phase may be responsible for the observed low ionic transport numbers.

Solar energy: battery energy storage control

A number of applications of battery energy storage in photovoltaic installations have been analyzed. The use of lead/acid batteries enhances the efficiency and reduces the cost. Some aspects of automatic charge/discharge control have been discussed. The rate of variation of the battery voltage can be used to determine the state-of-charge. This is based upon fundamental battery characteristics related to the kinetics of the lead/acid system. Although the cost of solar cells is still quite high, photovoltaic energy systems are competitive, not only in small remote installations, but also in large industrial applications. The wide range of working conditions necessitates precise evaluations of the solar array, but no particular problems appear to exist for the battery and the peripheral equipment.

Thawning time prediction for simple shaped foods using a generalized graphical method

A graphical method is proposed for the estimation of thawing times of foods with a high water content. It has been developed from the prediction of a numerical model which solves the heat balance for a food undergoing thawing. The method is valid for foods with different shapes (slab, cylinder and sphere) and covers a wide range of working conditions for industrial thawers. It also enables the prediction to be made for any given end temperature in the thermal centre of the food. Thawing time predicted by this method have been compared with published experimental data. giving an average error in the predicted values of only 6.5%.

Extraction performance of dual-grid ion optics: Simulation and experiment

A comprehensive comparison between experimental and simulated data for the ion beam characteristics of a two-grid extraction system is presented. An existing description for dc ion sources has been generalized and extended to capacitively coupled rf ion sources. The essential parameter in dc technology—the discharge voltage—was replaced by the plasma edge potential used also by simulation, allowing direct correlation between experimental and simulated data. Experimental results show 50% higher divergence angles if a part of the ion trajectories impinges on the accelerator grid. The reasons for this discrepancy are analyzed. Simple empirical formulas are proposed which describe the performance of the beamlet formed by one hole of a multiaperture extraction optic for a wide range of working conditions. These formulas permit better modeling of the broad beam and optimization of ion optics.

Performance analysis of solar air heaters of conventional design

This article analyzes the technical performances of seven solar air heaters of conventional design. The study is generalized by means of two coefficients: air mass flow rate per unit collector area (G) and the collector geometric coefficient (K), which make collector performances invariant, under the same conditions of design, material choice and ambient values. By use of the zero-capacitance model, the air heater performances were computed for the most usual range of design and working conditions; the graphs presented can be used when dealing with planning problems of air collectors.

Broad ion beam modeling for extraction optics optimization and etching process simulation

A model for calculating the ion–current density distribution of a broad-beam ion source at the target level is proposed. Three model parameters related to a single beamlet such as the beam divergence, the maximum ion–current density in the beamlet center, and a possible misalignment between the different grids are needed to describe the overall extraction performance. These parameters were determined partially with the axcel simulation code or experimentally via etch tests. In this work the model parameters have been determined for a capacitively coupled filamentless 13.56 MHz rf source operated with argon at low power levels ranging from 20–100 W and low acceleration voltages (100–1000 V). However, the model proposed is applicable also for other types of ion sources, for different extraction grid sets with varying geometry and a wide range of working conditions. Intensity profiles predicted by the above model show good agreement with experimental results.

Freezing time predictions for regular shaped foods: a simplified graphical method

A graphical method is proposed for the estimation of freezing times of foods been developed from the predictions of a numerical model which solves the heat balance for a food undergoing freezing. The method is valid for foods with different shapes (flat plate, cylinder and sphere) and covers a wide range of working conditions for industrial freezers. It also enables the prediction to be made for any given end temperature in the thermal centre of the food. Freezing times predicted by this method have been compared with published experimental data, giving an average error in the predicted values of only 4%.