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  • Articles  (15)
  • heat transfer  (8)
  • Microwave plasma  (7)
  • 1985-1989  (10)
  • 1980-1984  (5)
  • 1960-1964
  • 1940-1944
  • Technology  (15)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Plasma chemistry and plasma processing 1 (1981), S. 377-395 
    ISSN: 1572-8986
    Keywords: Microwave plasma ; polymerization ; plasma diagnostics
    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 microwave plasmas of gaseous mixtures of methane-argon and propyleneargon were analyzed along the flow stream by the electrical double floating probe system, optical spectroscopy, and quadrupole mass spectrometry. The plasma variables measured and considered were current density, electric field strength, electron temperature, positive ion and electron concentrations, and concentration of pyrolyzed and polymerized species. The results indicate that an irreversible process of polymerization of the hydrocarbons takes place in the plasma. The polymerization process reaches its maximum conversion downstream beyond the microwave cavity. The extent of polymerization was correlated to the concentration of positive ions and electrons in the plasma.
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  • 2
    Electronic Resource
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    Springer
    Plasma chemistry and plasma processing 7 (1987), S. 341-348 
    ISSN: 1572-8986
    Keywords: Microwave plasma ; chemical vapor deposition ; optical fibers
    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 An atmospheric-pressure CVD method is described that uses microwave plasma for manufacturing preforms that are used in the production of optical fibers for telecommunication. The method takes advantage of the very high deposition efficiency and high deposition rates attained when using microwave plasma as well as of efficient glassing of oxide layers by means of the traditional system of burners. A simple theoretical model that allows calculations of close-to-reality plasma temperature profiles is presented.
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  • 3
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    Springer
    Plasma chemistry and plasma processing 3 (1983), S. 97-113 
    ISSN: 1572-8986
    Keywords: Knudsen effect ; heat transfer ; small particles ; thermal plasmas ; analytical studies
    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 Knudsen effect on heat transfer to a particle exposed to a thermal plasma is important for many practical situations experienced in plasma chemistry and plasma processing. This paper provides theoretical results of this effect based on the “heat conduction potential jump” approach. It is shown that a correction factor which depends on the Knudsen number must be introduced into the expressions for heat fluxes obtained previously based on the continuum approach. The Knudsen effect is stronger for smaller particles and it is also more pronounced for an Ar-H2 plasma (compared to Ar and nitrogen plasmas at the same temperature). Since the Knudsen effect depends on the surface temperature of a particle, calculation of particle heating becomes more complicated.
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  • 4
    Electronic Resource
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    Springer
    Plasma chemistry and plasma processing 8 (1988), S. 293-314 
    ISSN: 1572-8986
    Keywords: Microwave plasma ; chlorinated hydrocarbon ; global kinetic analysis
    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 reaction of trichloroethylene (C2HCl3) with water vapor or molecular hydrogen has been studied in a low-pressure [ca. 5 Torr (0.67 kPa)] microwave plasma tubular flow reactor. The experimental apparatus included feed introduction systems, a microwave plasma reactor, and full product analysis by flame ionization and thermal-conductivity gas chromatography, mass spectrometry, and specific ion or pH detection for hydrogen chloride [HCl]. Conversions of C2HCl3 in the range 50 to almost 100% are achieved. Product analyses indicate conversion to HCl, some light hydrocarbons, nonparent chlorocarbons, and soot C(s). For the H2O case, carbon monoxide and trace carbon dioxide were produced in place of some light hydrocarbons and C(s). At least 85 mole % of chlorine (Cl) from the converted parent C2HCl3 forms thermodynamically stable HCl at parent conversions of 80% or more. The remaining chlorine was present as nonparent chlorocarbons. Preliminary kinetic analyses were performed. The global reaction in the plasma was found to follow one-half-order kinetic dependence on each of C2HCl3 and H2O or H2. Elementary plasma reaction mechanisms are presented to account for C2HCl3 conversion and the observed product distribution.
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  • 5
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    Springer
    Plasma chemistry and plasma processing 8 (1988), S. 331-346 
    ISSN: 1572-8986
    Keywords: Microwave plasma ; plasma etching ; cellulose ; coating distribution ; ESCA ; neutron activation
    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 effects of plasma etching on surface structure and chemistry of several papers have been investigated. Plasma etching acts like a fine microtome, continuously removing infinitesimally thin layers at the surface. It has allowed us to observe the internal structure of fibers, and interfiber bonding. The kinetics of plasma etching and its temperature dependence are reported; the thermal activation energy determined from the latter was found to be 0.15 eV. Possible applications of plasma etching techniques to study the structural and physical properites of paper in the z-direction and the distribution of coating material across the thickness of a paper sample are discussed.
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  • 6
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    Springer
    Plasma chemistry and plasma processing 2 (1982), S. 361-386 
    ISSN: 1572-8986
    Keywords: Transferred arc ; characteristics ; heat transfer ; experimental
    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 specially designed plasma chamber was constructed to study the operating characteristics of a dc plasma-transferred arc of argon, struck between a fluid convective cathode and a water-cooled anode. The arc voltage increased markedly with arc length and with an increase in the inlet velocity of the argon flow past the cathode tip, and much less with an increase in current. Radiation from the plasma column to the chamber walls and transfer of energy to the anode were the two principal modes of transfer of the arc energy. The former was dominant in the case of long arcs and at high inlet argon velocities. At the anode, the major contribution was from electron transfer, which occurred on a very small area of the anode (∼5 mm in diameter). Convective heat transfer from the plasma was somewhat less. In all cases, the arc energy contributions to cathode cooling and to the exit gas enthalpy were small. From total heat flux and radiative heat transfer measurements, it was estimated that the plasma temperature just above the anode was in the range 10,000–12,000 K. Preliminary experiments with an anode consisting of molten copper showed that the arc root was no longer fixed but moved around continuously. The arc was othwewise quite stable, and its operating characteristics differed little from those reported for solid anodes, in spite of the greater extent of metal vaporization.
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  • 7
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    Springer
    Plasma chemistry and plasma processing 5 (1985), S. 255-261 
    ISSN: 1572-8986
    Keywords: Microwave plasma ; surface-wave discharge ; Stark broadening ; argon plasma
    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 electron density of microwave-generated surface-wave discharges in argon have been measured using Stark broadening and calculated from the measured wavelengths of the standing surface wave. Results obtained from these two techniques compare well. The electron density varies from 1013 to 1014/cm3 for pressures ranging from 50 to 800 torr.
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  • 8
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    Transport in porous media 3 (1988), S. 95-106 
    ISSN: 1573-1634
    Keywords: Free convection ; heat transfer ; Porous media ; natural convection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract An analysis is presented for the calculation of heat transfer due to free convective flow along a vertical plate embedded in a porous medium with an arbitrarily varying surface heat flux. By applying the appropriate coordinate transformations and the Merk series, the governing energy equation is expressed as a set of ordinary differential equations. Numerical solutions are presented for these equations which represent universal functions and several computational examples are provided.
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  • 9
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    Transport in porous media 3 (1988), S. 325-341 
    ISSN: 1573-1634
    Keywords: Natural convection ; heat transfer ; boundaries ; modes ; critical ; Nusselt ; power integral method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The ‘power integral method’ of calculating heat transfer across a convecting porous layer is extended to flux and porous boundaries. Convection starts at lower Rayleigh numbers for constant flux than for isothermal impervious boundaries and the flux is much greater. At higher Rayleigh numbers, as more of the higher modes contribute to the flux, the type of boundary has less influence on the heat transfer across the layer. For constant flux boundaries, simplified equations are developed to determine critical values for the second and higher modes and these values can be related simply to those for isothermal impervious boundaries.
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  • 10
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    Springer
    Transport in porous media 3 (1988), S. 437-453 
    ISSN: 1573-1634
    Keywords: Natural convection ; heat transfer ; flow ; critical ; Nusselt ; power integral method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Temperature decay in sealed rockbeds has been recorded. The rockbeds lost energy through the top surface and the results indicated that different natural convective flows occurred in beds of fixed depth and rock size but different lateral dimensions. However, the different flows had no effect on the mean power density dissipated through the top of the beds. A simple numerical conduction model based on the ‘power integral method’ was used to calculate the temperature decay. The experimental results suggested that an insulated porous lower boundary was appropriate for the model and this gave the best agreement with the experiments.
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  • 11
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    Springer
    Transport in porous media 1 (1986), S. 361-370 
    ISSN: 1573-1634
    Keywords: Vertical layers ; mathematical models ; geothermal systems ; heat transfer ; convection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Some studies already made have investigated the criterion for onset of convection and heat and mass flow distributions in a porous slab composed of horizontal layers of different materials. This paper reports a study of such criteria for the case where the slab is composed of vertically-aligned strata with different permeabilities and thermal conductivities. This has particular relevance to where blocks of different materials abut in a vertical plane, as well as the case of very narrow highly permeable vertical layers which represent vertical faults in a geological structure. Results indicate that permeability and/or thermal conductivity contrasts between layers can significantly affect the flow pattern and the spatial distribution of the surface heat flux. The concentration of flow in highly permeable ‘faults’ produces marked irregularities in the heat flow through the surface above them.
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  • 12
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    Plasma chemistry and plasma processing 8 (1988), S. 263-280 
    ISSN: 1572-8986
    Keywords: Microwave plasma ; gas-phase reactions ; mass spectrometer sampling ; discharge chemistry of SF6 with O2
    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 Processes which occur in microwave discharges of dilute mixtures of SF6 and O2 in He have been examined using a flow reactor sampled by a mass spectrometer. Two classes of experiments were performed. In the first set of experiments, mixtures containing 6×1011 cm−3 SF6, 6×1016 cm−3 He, and O2 in the range (0–3.6)×1013 cm−3 were passed through a 20-W 2450-MHz microwave discharge. The gas mixtures arriving at a sample point downstream from the discharge were examined for SF6, SF4, SOF2, SOF4, SO2F2, SO2, F, and O. In the second class of experiments, rate coefficients were measured for the reactions of SF4 with O and O2 and for the reaction of SF with O. The rate coefficient for the reaction of SF with O was found to be (4.2±1.5)×10−11 cm−3 s−1. SF4 was found to react so slowly with both oxygen atoms and oxygen molecules that only upper limits could be placed on the rate coefficients for these reactions. These values were 2×10−14 cm3 s−1 and 5×10−15 cm3 s−1 for reactions with O and O2 respectively. The observed distribution of products from the discharged mixtures is discussed in terms of the measured rate coefficients.
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  • 13
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    Plasma chemistry and plasma processing 9 (1989), S. 135S 
    ISSN: 1572-8986
    Keywords: Modeling ; thermal plasma processing ; supersonic jets ; heat transfer ; control
    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 Thermal plasma processing of materials is a rapidly growing area of research. The commercialization of these processes, however, has been limited by the lack of fundamental understanding of how the various processes work. Research has historically focused on developing models of fluid flow and heat transfer to particles injected into either DC arc or RF plasma jets. These models in the past have simplified boundary conditions to meet computational limitations. Recent advances in models have now been made, allowing evaluations of more of the plasma process variables. Supersonic flow modeling in a DC jet and modeling of the effects of particle loading (particulate feed rate) have been accomplished and are reviewed here. Materials processing using thermal plasmas has been separated into the categories of synthesis, melting, and deposition, and is discussed in view of the processing effects on the resultant material structures. Process modeling leading to process understanding is reviewed with an emphasis on process control and optimization. Commercialization of plasma processes requires controls and process transducers which result from experimentation and process models. Approaches to develop process controls from the current technical base are presented.
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  • 14
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    Plasma chemistry and plasma processing 3 (1983), S. 235-248 
    ISSN: 1572-8986
    Keywords: Microwave plasma ; plasma polymerization ; silicon tetrachloride ; experimental
    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 Mass spectrometry has been used to analyze microwave-induced plasmas of silicon tetrachloride diluted in mixtures of hydrogen and argon. The effects of process parameters such as pressure in the reactor, power input, and the composition of the gas mixture were investigated. Sampling by a quadrupole mass-spectrometer along the gas stream showed that the reactions were initiated upstream where the reactants enter the plasma. It was found that the input power had an optimal value for the decomposition rate of SiCl4; above that optimum, recombination occurred downstream. Upstream the concentrations of SiCl4 decrease with increasing pressure in the range 1–10 torr, independent of the input power. The effect of admixing argon to the reaction mixture is discussed, and the results obtained are correlated to experimental results reported in previous works concerning silicon deposition from SiCl4 on a grounded substrate.
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  • 15
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    Plasma chemistry and plasma processing 3 (1983), S. 351-366 
    ISSN: 1572-8986
    Keywords: Small particles ; heat transfer ; drag ; Knudsen effect ; convection ; thermal plasma ; computation
    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 In this paper computational results are presented which reveal the effects of the Knudsen number on heat transfer and drag of small particles in a flowing thermal argon plasma. The Knudsen number is restricted to moderate values so that “temperature jump” and “velocity slip” conditions may be employed, and for the governing equations the continuum approach remains valid. It is shown that the ratio of the heat fluxes with and without the Knudsen effect is almost identical to the ratio obtained by the authors for the case of pure heat conduction. This fact is very important for modeling of the behavior of particles injected into an actual plasma reactor when the Knudsen effect has to be taken into account.
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