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• 1
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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• 2
Electronic Resource
Springer
Journal of materials science 11 (2000), S. 523-531
ISSN: 1573-4838
Source: Springer Online Journal Archives 1860-2000
Topics: Medicine , Technology
Notes: Abstract Nanometer size hydroxyapatite (HA) crystals are prepared by a wet chemical precipitation method at different synthesis temperatures and with various reactant addition rates. The resulting aqueous suspensions are studied in terms of morphology (transmission electron microscope, specific surface area), phase (X-ray diffraction, electron diffraction and infrared spectroscopy) and rheological properties. This work shows that shape, size and specific surface area of the HA nanoparticles are very sensitive to the reaction temperature and also to the reactant addition rate. The measured pH at the end of synthesis, which is strongly linked with the reactant addition rate, is a key parameter which can be used to determine the purity of the synthesized HA nanocrystal and also for the stabilization (dispersion) of the suspension. HA nanoparticles synthesized at low temperature (T 〈 6°C) are monocrystalline. A transition temperature (T=60 °C) can be defined as a limit for the synthesis of monocrystalline HA nanocrystals, above this critical temperature nanocrystals become polycrystalline. HA monocrystals adopt a needle shape and are oriented following the c-axis of the hexagonal HA structure. The as-synthesized suspension is then concentrated and the effect of a dispersing agent addition, which is needed to get a high solid/liquid ratio coupled with good flowability of the suspension, is also shown, because this suspension is used in the suspension plasma spraying process.
Type of Medium: Electronic Resource
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• 3
Electronic Resource
Hoboken, NJ : Wiley-Blackwell
AIChE Journal 29 (1983), S. 236-243
ISSN: 0001-1541
Keywords: Chemistry ; Chemical Engineering
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
Notes: Measurements were made of the two-dimensional flow and temperature field in a d.c. plasma jet under different operating conditions. The particle velocity and the in-flight particle temperature were also measured for narrow cuts of alumina powders, of mean particle diameters of 18, 23, 39 and 46 μm, injected in the jet. The results are compared with the predictions of a one-dimensional mathematical model. The measured and computed particle velocities are in good agreement. This is, however, not the case for the particle temperature where considerable differences are observed. An attempt is made to determine the parameters which are often unduly neglected in modelling work and to identify the areas where further work is needed.
Type of Medium: Electronic Resource
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• 4
Electronic Resource
Hoboken, NJ : Wiley-Blackwell
AIChE Journal 34 (1988), S. 567-573
ISSN: 0001-1541
Keywords: Chemistry ; Chemical Engineering
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
Notes: A study was carried out of the momentum and the heat transfer to fine alumina particles injected into a DC plasma jet. Measurements are reported of particle number flux distribution, particle velocity, and inflight particle surface temperature under different operating conditions. The results show that the particle trajectories and associated particle flux distribution depends to a large extent on the particle injection velocity. The maximum particle velocity and surface temperature are noted, however, to remain close to the centerline of the jet, independent of the particle injection conditions. The maximum surface temperature reached by the particles increases with increasing plasma power and the use of an Ar/H2 plasma gas (17 vol. % H2) compared to that for a pure argon plasma.The particle velocity data are in good agreement with the predictions of a two-dimensional mathermatical model used for the calculation of the particle trajectories and temperature history. The model predictions, however, agreed only in trend with the measured particle surface temperatures. Deviations between the two could still be observed at large distances from the point of injection of the powder. The computed particle number flux distributions were narrower than the measured profiles, which can be attributed to the fact that the model did not include, at this stage, turbulent particle diffusion effects.
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• 5
Electronic Resource
Hoboken, NJ : Wiley-Blackwell
AIChE Journal 27 (1981), S. 358-364
ISSN: 0001-1541
Keywords: Chemistry ; Chemical Engineering
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
Notes: Laser Doppler Anemometry (LDA) was used for the simultaneous measurement of the gas and particle velocities in a gas-solid, two-phase flow. The flow configuration consists of an air jet at ambient temperature in which a spherical glass powder of a mean particle diameter of 97.0 or 13.7 μm was injected from one side using a secondary air jet. Both principal and secondary jets were also seeded with talcum powder with a mean particle diameter of about 1 μm which served as a tracer.The probability density distribution function (PDF) of the LDA output showed two distinct peaks corresponding to the particle and gas velocities. As the particles were accelerated by the flow, the slip velocity between the gas and the particles decreased causing the gap between these two peaks to narrow. The measured mean particle velocity profiles were in agreement with the predictions of a theoretical model.The objectives of the present investigation was to obtain experimental data on the dependence of the particle trajectories and their mean velocities on the injection conditions in a free jet stream. The principal question, however, was whether such data could be obtained using Laser Doppler Anemometry (LDA). In other words, whether LDA could be effectively used in two-phase flow systems for the simultaneous measurement of the gas and particle velocities? Obviously, the answer to this last question can affect far beyond this particular study and more than justified the effort for this detailed investigation. It should be pointed out that, while LDA has been known for sometime, and the necessary equipments for an LDA system are available on a commercial bases, relatively little attention has been given to its application to other than single-phase, fluid-flow measurements.
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• 6
Electronic Resource
Springer
Plasma chemistry and plasma processing 10 (1990), S. 133-150
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
Electronic Resource
Springer
Plasma chemistry and plasma processing 10 (1990), S. 151-166
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.
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• 8
Electronic Resource
Springer
Plasma chemistry and plasma processing 15 (1995), S. 653-675
ISSN: 1572-8986
Keywords: Plasma spraying ; induction plasma ; particle diagnostics ; particle surface temperature and velocity ; two-color pyrometry ; particle time-of-flight technique ; laser Doppler anemometry
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 laser Doppler anemometer combined with a particle-emission spectrometer, are used for the study of the induction plasma spraying process. For this, the effects of chamber pressure, spray distance and torch nozzle design on the particle surface temperature and velocity as well as the fraction of hot particles included in the stream of processed material, were investigated. A comparison between the velocity measurements by laser Doppler anemometry (LDA) and by the particle time-of-flight technique is presented in order to emphasize the deference between the velocity of the hot particles, and that of the total particle population, cold and hot. The influence of the individual particle mass on particle entrainment in the plasma jet from the ambient atmosphere in the vacuum chamber is discussed.
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• 9
Electronic Resource
Springer
ISSN: 1572-8986
Keywords: Laser Doppler anemometry ; induction plasma ; particle trajectory
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 Laser Doppler anemometry is used for the measurements of the plasma and particle velocity profiles in the coil region of an inductively coupled r.f. plasma. Results are reported for a 50 mm i.d. induction plasma torch operated at atmospheric pressure with argon as the plasma gas. The oscillator frequency is 3 MHz and the plate power is varied between 4.6 and 10.5 kW. Plasma velocity measurements are obtained using a fine carbon powder as a tracer. Measurements are also given for larger silicon particles ( $$\bar d_p = {\text{ }}33{\text{ }}\mu m and \sigma = 13 \mu m$$ ) centrally injected into the discharge under different operating conditions.
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• 10
Electronic Resource
Springer
Plasma chemistry and plasma processing 19 (1999), S. 327-340
ISSN: 1572-8986
Keywords: Thermal plasmas ; induction plasma reactor ; toxic wastes ; energy distribution ; mass balance ; energy balance
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 study of the treatment of liquid wastes in a radio frequency (rf) induction plasma reactor is reported. Ethylene glycol was used as a surrogate for the waste because of safety considerations. Thermodynamic analyses demonstrated complete and safe decomposition at the conditions studied. The solution was injected axially into the center of an argon–oxygen plasma operated at a plate power of 50 kW to study blast atomization and operating conditions. A factorial analysis revealed, at a confidence level of 0.99, that both reduction of pressure and liquid flow rate increase the destruction and removal efficiency (DRE) and that a higher plate power increased DRE. The study also revealed that poor atomization was responsible for the reduction of the DRE by 10–15% (to 80–85%) and that 94% of the exothermic energy of the reaction was available for further use. The specific energy requirement (SER) of the process was estimated at 8.33 kWh/kg of solute. This value can be expected to drop significantly with scale-up of the process.
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