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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 1898-1908 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A two-dimensional, axisymmetric model was developed to study the response of a radio-frequency inductively coupled plasma to a sudden change in its active power. The time-dependent equations for the conservation of mass, momentum, and energy, along with Maxwell's equations were solved numerically. Results were obtained for a pressure range of 200–760 Torr, a frequency range of 1–3 MHz; torch diameters between 40 and 75 mm; and, argon/hydrogen flow rates of 40–75 slpm. Initially, the plasma was assumed to be under steady-state condition at 20 kW. The plasma power was then reduced to 10 kW for 35 ms and, the response of the plasma fields and the coil current were predicted numerically. When power was reduced, the coil current reduced significantly in 2 ms. It then increased to a maximum before smoothly decreasing to its new steady-state value. The response of the plasma depended, to different degrees, on all the parameters considered here. Depending on the position within the torch, it could vary from 2 ms to several tens of millisecond. The plasma response was fastest within the skin-depth region where power was dissipated. The response time was most strongly affected by the changes in discharge pressure; and was least affected by the induction frequency. The response time increased with pressure and/or torch diameter, and decreased with frequency and/or flow rate. We also found that, depending on the magnitude of induction frequency, an increase in plasma power may cause an oscillatory plasma behavior. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 7757-7767 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The behavior of an argon arc in a transferred arc furnace with a cold cathode and anode has been investigated using an elliptic model with emphasis on a high-current, long arc (L=100–200 mm, I=500 A). Conservation equations for the laminar arc column are written assuming local thermodynamic equilibrium. The governing equations are solved by employing an efficient finite difference method. The anode is included in the calculation domain. Numerical calculations performed for a transferred argon arc show good agreement with temperature measurements obtained by emission spectroscopy. The results also indicate that, except in regions close to the anode, the arc behavior is parabolic. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 4178-4185 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A mathematical representation is given for the turbulent fluid flow and energy transfer in an rf induction plasma. The flow and temperature fields are obtained through the solution of the two-dimensional rotationally symmetric turbulent Navier–Stokes equations along with the energy and the one-dimensional Maxwell's equations for the electric and magnetic fields. The turbulent viscosity is determined using the standard k-ε model. Results are given for an argon plasma under atmospheric conditions. Different aspects of turbulent flows and their implications in rf plasmas are discussed. The results indicate the presence of both laminar and turbulent regimes in the same flow field. The effect of swirl in the plasma gas is to increase the overall turbulence level in the torch.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Plasma chemistry and plasma processing 15 (1995), S. 607-628 
    ISSN: 1572-8986
    Keywords: Argon plasma jets ; thermal spraying ; shrouded nozzles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract A new design is proposed for dc plasma spray gas shroud attachments. It has been found experimentally that the performance of a conventional conical gas shroud is not satisfactory due to the entrainment of the cold air inside the gas shroud. Numerical simulations confirmed this finding. Parameters such as the cone angle and the main gas flow rate can significantly influence the flow pattern inside the nozzle, resulting in air entrainnient and formation of a circulation zone at the exit region. A new design is proposed which can considerably improve the performance of shrouded nozzles. The superior performance of the proposed design has been demonstrated by numerical simulation. The new design is based on a modification of the conical shape by optimizing the profile of the nozzle from a conical shape with a constant angle to a streamlined configuration. The optimized shape was obtained from an analysis of the streamlines of a fixed angle nozzle.
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  • 5
    ISSN: 1572-8986
    Keywords: Enthalpy probe ; systematic error ; stagnation pressure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Errors in stagnation-pressure measurement, due to a large temperature gradient at the face of a water-cooled enthalpy probe, were experimentally measured and numerically simulated. Two probes were used to measure the stagnation-pressure in a dc plasma jet; a standard water-cooled enthalpy probe and an uncooled ceramic (Thoria) probe. There was a maximum difference of 10% between the two measurements, with the water-cooled probe measuring lower pressures. Numerical simulations of plasma flow around the probe showed that the magnitude of the error depends on the thickness of the thermal boundary layer. The measurement error causes a maximum of 3% error in velocity measurements, using the Bernoulli equation. This error is no worse than other measurement errors associated with water-cooled enthalpy probe meaurements.
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  • 6
    ISSN: 1572-8986
    Keywords: Induction plasma ; modeling ; chemical equilibrium ; silicon nitride synthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract A mathematical model is presented for the numerical simulation of the flow, temperature, and concentration fields in an rf plasma chemical reactor. The simulation is performed assuming chemical equilibrium. The extent of validity of this assumption is discussed. The system considered is the reaction of SiCl4 and NH3 for the production of Si3N4.
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  • 7
    ISSN: 1572-8986
    Keywords: Induction plasma ; modeling ; chemical kinetics ; dissociation of silicon tetrachloride
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract A kinetic model has been developed for the prediction of the concentration gelds in an rf plasma reactor. A sample calculation for a SiCl4/H2 system is then performed. The model considers the mixing processes along with the kinetics of seven reactions involving the decomposition of these reactants. The results obtained are compared to those assuming chemical equilibrium. The predictions indicate that an equilibrium assumption will result in lower predicted temperature fields in the reactor. Furthermore, for the chemical system considered here, while differences exist between the concentration fields obtained by the two models, the differences are not substantial.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1572-8986
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract The spreading and simultaneous solidification of a liquid droplet upon its impingement onto a substrate permitting thermal contact resistance has been numerically simulated; the effect of contact resistance and the importance of solidification on droplet spreading are investigated. The numerical solution for the complete Navier-Stokes equations is based on the modified SOLA-VOF method using rectangular mesh in axisymmetric geometry. The solidification of the deforming droplet is considered by a one-dimensional heat conduction model. The predictions are in good agreement with the available experimental data and the model may be well suited for investigating droplet impact and simultaneous solidification permitting contact resistance at the substrate. We found that the final splat diameter could be extremely sensitive to the magnitude of the thermal contact resistance. The results also show that for the condition of higher Reynolds and/or higher Stefan numbers the effect of solidification on the final splat diameter is more important.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Heat and mass transfer 13 (1980), S. 3-9 
    ISSN: 1432-1181
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Description / Table of Contents: Zusammenfassung Die Energieeinsparung in Gebäuden wird besonders bei unterirdischen Bauwerken stark von den thermischen Eigenschaften des Bodenmaterials bestimmt. Es werden in der vorliegenden Arbeit experimentelle Ergebnisse aus Wärmeleitfähigkeitsmessungen an verschiedenen Bodenarten nach einem quasistationären Verfahren [1] dargestellt. Das Probenmaterial befindet sich dabei zwischen zwei konzentrischen Rohren, wobei das innere gleichmäßig beheizt und das äußere isoliert ist. Bei Untersuchungen vier verschiedener Bodenproben in einem Temperaturintervall von −5°C bis 30°C, drei verschiedenen Dichtewerten und Feuchtigkeitsgehalten von 0,5 bis annäherend 12 Gew.−% erweist sich der Feuchtigkeitsgehalt als der bestimmende Parameter. Die Wärmeleitfähigkeit nimmt etwa mit derselben Größenordnung wie die Feuchtigkeit zu. Außerdem tritt eine starke Änderung der Wärmeleitfähigeit beim Phasenübergang von ungefrorenem zu gefrorenem Boden auf.
    Notes: Abstract Energy conservation in buildings, in particular in underground constructions, is strongly affected by the thermal properties of the soil surrounding such buildings. Experimental results of thermal conductivity studies of different soils are reported based on a quasisteady method [1]. The soil sample is placed in the annular space between two concentric tubes and is heated uniformly on the inside wall keeping the outside wall insulated. Four different types of soils (Moon Valley, River Sand, In-situ, and Ridgedale), are studied over a temperature range from −5°C to 30°C for three different densities and moisture contents ranging from 0.5 to approximately 12% (by weight). The results indicate that the moisture content is by far the most important parameter. The thermal conductivity may increase by almost an order of magnitude as the moisture content increases. In addition, there may be a strong variation of the thermal conductivity in the phase transition region from unfrozen to frozen soils.
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  • 10
    ISSN: 0584-8547
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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