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  • Articles  (29)
  • Thermal plasmas  (15)
  • porous media  (14)
  • 2010-2014
  • 1990-1994  (18)
  • 1985-1989  (11)
  • 1950-1954
  • Technology  (29)
  • 1
    Electronic Resource
    Electronic Resource
    Hydraulic radius and transport in reconstructed model three-dimensional porous media (1994)
    Springer
    Transport in porous media 17 (1994), S. 221-238 
    Details
    ISSN: 1573-1634
    Keywords: building technology ; conductivity ; critical diameter ; hydraulic radius ; permeability ; porous media ; reconstruction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Methods for reconstructing three-dimensional porous media from two-dimensional cross sections are evaluated in terms of the transport properties of the reconstructed systems. Two-dimensional slices are selected at random from model three-dimensional microstructures, based on penetrable spheres, and processed to create a reconstructed representation of the original system. Permeability, conductivity, and a critial pore diameter are computed for the original and reconstructed microstructures to assess the validity of the reconstruction technique. A surface curvature algorithm is utilized to further modify the reconstructed systems by matching the hydraulic radius of the reconstructed three-dimensional system to that of the two-dimensional slice. While having only minor effects on conductivity, this modification significantly improves the agreement between permeabilities and critical diameters of the original and reconstructed systems for porosities in the range of 25–40%. For lower porosities, critical pore diameter is unaffected by the curvature modification so that little improvement between original and reconstructed permeabilities is obtained by matching hydraulic radii.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00613583
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  • 2
    Electronic Resource
    Electronic Resource
    Flow characteristics of anisotropic structures constructed with porous layers (1994)
    Springer
    Transport in porous media 15 (1994), S. 151-173 
    Details
    ISSN: 1573-1634
    Keywords: Anisotropic ; porous media ; flow characteristic ; permeability ; Forchheimer extension ; regression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Artificial structures, serving as the solid matrix of anisotropic porous media and satisfying the requirement needed for flow visualization, were constructed with the perforated Polypropylene plates in order to improve the understanding of transport phenomena occurring in anisotropic porous media. This paper reports the regressed correlations of the experimental pressure gradient and filtration velocity data of three anisotropic and one isotropic porous media measured along two mutually orthogonal directions, which correspond to the principal axes of the permeability tensor, for the filtration velocities ranging from 0.2 to 12 mm/s with water as the fluid. To reflect the observed data, the regression equation with two types of deviations was formulated, in which the pressure gradient is represented by the sum of the linear and nonlinear terms of the filtration velocity. The physical model developed for the linear term assumes the solid matrix as repeated circular orifices when the filtration velocity approaches zero. The exponent of the filtration velocity in the nonlinear term was determined to be that of the Forchheimer extension. Also, four models for the coefficient of the nonlinear term were examined and the results were compared. The distribution of the residuals (the differences between the observed and the correlated values) validated the suggested regression procedure and the resulting correlations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00625514
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  • 3
    Electronic Resource
    Electronic Resource
    Estimation of three-phase relative permeabilities (1994)
    Springer
    Transport in porous media 16 (1994), S. 263-287 
    Details
    ISSN: 1573-1634
    Keywords: Three-phase flow ; relative permeabilities ; porous media ; residual saturation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract We have extended the Alemán-Slattery model to provide a self-consistent prediction for the residual saturation of the intermediate-wetting phase. Previous experimental studies of three-phase relative permeabilities are critiqued. Only a portion of the data of Oaket al. (J. Petrol. Tech. 42 (1990) 1054) and Oak (SPE/DOE 20183, Society of Petroleum Engineers, 1990) is regarded as suitable for comparison with available models. While the extended Alemán-Slattery model appears to give the best representation of these data, a definitive conclusion is premature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00617151
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  • 4
    Electronic Resource
    Electronic Resource
    Fluid boundary layer effects in atmospheric-pressure plasma diamond film deposition (1993)
    Springer
    Plasma chemistry and plasma processing 13 (1993), S. 169-187 
    Details
    ISSN: 1572-8986
    Keywords: Thermal plasmas ; chemical vapor deposition ; diamond film ; impinging jet ; atomic carbon
    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 Diamond films were deposited in an atmospheric-pressure radio frequency plasma reactor. Hydrogen and methane were injected coaxially into the plasma as a high-velocity jet which impinged on the molybdenum substrate. In some cases argon was added to the reactant jet to increase its momentum, thereby reducing the boundary layer thickness. In most cases argon addition substantially, improved diamond growth. A numerical model was developed, which calculated two-dimensional reactor temperature and velocity, distributions, and the chemical kinetics in the boundary layer. The calculations indicate that under the experimental conditions argon addition reduced the thickness of the hydrogen nonequilibrium boundary layer from 3.5 to 1.0 mm. In addition, the calculations suggest that monatomic carbon may be a key diamond growth species under thermal plasma conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01466040
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  • 5
    Electronic Resource
    Electronic Resource
    Capillary end effect in a water saturated porous layer (1993)
    Springer
    Transport in porous media 13 (1993), S. 261-275 
    Details
    ISSN: 1573-1634
    Keywords: Oil-water flow ; porous media ; capillary end effect ; free imbibition ; Buckley-Leverett zone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The uni-directional propagation of oil injected into water flowing through a water wetted porous slab of a finite length is investigated. The inlet and outlet edges of the slab are impermeable to the oil flux. Hence, the oil accumulates within the slab, thereby leading to a saturation build-up-capillary end effect. This phenomenon is studied analytically on the basis of a nonlinear equation describing oil-water transport in porous media. A dimensionless criterion is derived, which governs the appearance and relative strength of the capillary end effect. For weak oil-water interfacial tension (large capillary number) and long porous slabs the above effect is not observed and the temporal evolution of the oil saturation is described by the Buckley-Leverett solution. Short porous slabs are found to be almost entirely subjected to the capillary end effect. Intermediate situations are identified and quantitatively described, in which the downstream part of the slab may be divided into two zones: one-characterized by the capillary end effect, and the other being a Buckley-Leverett zone. It is shown, that the oil flux injected into the slab is limited by a maximum value which depends upon the location of the injection point. The partition of the inlet flux between the upstream and downstream directions is investigated. In the upstream side of the porous slab the oil moves under the action of free imbibition only. It is found that the upstream flux is limited by the value, which is independent of the slab's length and of the location of the injection point.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00622446
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  • 6
    Electronic Resource
    Electronic Resource
    A theory of macrodispersion for the scale-up problem (1993)
    Springer
    Transport in porous media 13 (1993), S. 97-122 
    Details
    ISSN: 1573-1634
    Keywords: Scale up ; dispersion ; porous media ; random field
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Dispersion is the result, observable on large length scales, of events which are random on small length scales. When the length scale on which the randomness operates is not small, relative to the observations, then classical dispersion theory fails. The scale up problem refers to situations in which randomness occurs on all length scales, and for which classical dispersion theory necessarily fails. The purpose of this article is to present non-Fickian, theories of dispersion, which do not assume a scale separation between the randomness and the observed consequences, and which do not assume a single length scale. Porous media flow properties are heterogeneous on all length scales. The geological variation on length scales below the observational length scale can be regarded as unknown and unknowable, and thus as a random variable. We develop a systematic theory relating scaling behavior of the geological heterogeneity to the scaling behavior of the fluid dispersivity. Three qualitatively distinct regimes (Fickian, non-Fickian and nonrenormalizable) are found. The theory gives consistent answers within several distinct analytic approximations, and with numerical simulation of the equations of porous media flow. Comparison to field data is made. The use of Kriging to generate constrained ensembles for conditional simulation is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00613272
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  • 7
    Electronic Resource
    Electronic Resource
    Spectroscopic study of a magnetically rotating arc between opper electrodes in contaminated argon (1992)
    Springer
    Plasma chemistry and plasma processing 12 (1992), S. 1-16 
    Details
    ISSN: 1572-8986
    Keywords: Thermal plasmas ; electrode erosion ; plasma spectroscopy ; metal vapor plasma ; electrode contamination
    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 N2 and CO contaminants in atmospheric-pressure argon on an arc rotating between two concentric copper electrodes has been studied using optical spectroscopy of copper lines. The axial temperature of the magnetically driven arc in Ar + %N2 was determined to be around 10,000 K for arc currents of SO to 200 A. The diffusion process of the copper vapor from the cathode was also studied. A copper density maximum 1 mm from the cathode along the arc column was found in Ar + %N2. Removal of the contaminated cathode surface layers by the arc when contaminant injection in the plasma gas was stopped was found to be a slow process with a time scale depending on the type of the gas contaminant. The presence of gas contaminant in the electrode material controls the cathode erosion mechanism and the overall arc behavior in the transition between a contaminated to a pure argon arc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01447941
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  • 8
    Electronic Resource
    Electronic Resource
    Computational fluid dynamics modeling of multicomponent thermal plasmas (1992)
    Springer
    Plasma chemistry and plasma processing 12 (1992), S. 299-325 
    Details
    ISSN: 1572-8986
    Keywords: Thermal plasmas ; plasma processing ; rnulticomponent ; chemistry ; diffusion
    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 comprehensive computational model has been developed Jbr flowing thermal plasmas in the absence of electromagnetic fields, with particular emphasis on plasma jets. The plasma is represented as a rnulticomponent chemicalh, reacting ideal gas with temperature-dependent thermodynamic and transport properties. The plasma flow is governed by the transient compressible Navier-Stokes equations in two or three space dimensions. Turbulence is represented by subgrid-scale and k-ε models. Species diffusion is calculated by an effective binary diffusion approximation, generalized to allow /or ambipolar diffusion of charged species. Ionization, dissociation, recombination, and other chemical reactions are computed by general kinetic and equilibrium chemistry algorithms. Radiation heat loss is currently modeled as a temperature-dependent energy sink. Finite-difference approximations to the governing equations are solved on a rectangular spatial mesh using explicit temporal differencing. Computational inefficiency at low Mach number is avoided br reducing the effective sound speed. The overall computational model is embodied in a new computer code called LAVA. Computational results and comparisons with experimental data are presented Jbr LAVA simulations of a steady-stare axisymmetric argon plasma jet flowing into cold argon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01447028
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  • 9
    Electronic Resource
    Electronic Resource
    Gravitational migration of fuel in porous media (1992)
    Springer
    Transport in porous media 9 (1992), S. 187-205 
    Details
    ISSN: 1573-1634
    Keywords: Two-phase flow ; buoyancy force ; porous media ; Bond number
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Fuel migration in a water flowing through a porous medium generally occurs parallel to porous strata, which may not be horizontal. In this case, gravity tends to cause vertical segregation of fluids, depending on their densities. This phenomenon can exert a strong effect on fuel migration. The gravitational force creates the buoyancy force which acts upon the fuel, and may be either parallel or anti-parallel to the water flow direction. In this study, the above effects are investigated using the one-dimensional model of Pistineret al. We go beyond the latter investigation in describing the influence of the gravitational forces upon the movement of fuel saturation fronts in a vertical porous layer against and along the water flow direction. It is found that when the directions of the buoyancy force and of the water flow are anti-parallel, fuel migrates in the direction of the buoyancy force, provided the latter is strong enough. However, in the case of a weak buoyancy force, the direction of migration of the fuel depends on its mass. Small fuel masses move mainly in the direction of the water flow. However, big fuel slugs possessing large masses will move mainly in the direction of the buoyancy force. Slugs, characterized by intermediate masses, have no preferable moving direction and are almost stagnant.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00611966
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  • 10
    Electronic Resource
    Electronic Resource
    Heat transfer from a transferred-arc plasma to a cylindrical enclosure (1991)
    Springer
    Plasma chemistry and plasma processing 11 (1991), S. 57-79 
    Details
    ISSN: 1572-8986
    Keywords: Thermal plasmas ; transferred arc ; plasma reactor ; radiated power ; heat transfer to enclosure ; voltage gradient ; electric field
    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 Hear-transfer rates from an axially enclosed transferred arc to a surrounding water-cooled cylindrical sleeve, 15 cm high, were measured. The arc (argon or nitrogen) was struck between a movable cathode within the sleeve and a bath of molten copper below the sleeve, serving as anode. The distance from the bottom of the sleeve to the surface of the molten copper (L o) was constant. Variables studied were the diameterD of the sleeve (5, 7.5. and 10 cm), the length of the arc within the sleeveL (5, 10, and 15 cm), the currentI (200, 250, and 300 A) and a tangential flow of gas or vortex within the sleeve (0, ?0, and 50 liters/min). The total power transferred to the sleeve,P s was measured caloronetrically and was the sure ofP r the effective power radiated by the arc of lengthL within the sleeve.P a, the power radiated into the sleeve from the arc of length Lo below the sleeve, andP o , the power radiated from the melt surface (a constant of small value), minusP a , the power lost by convection from the sleeve (negligible, except for a strong vortex). BothP r andP o were found to be equal to the product of the Joule heat released within their respective arc lengths, IVgL and IVg0L0 (where Vg and Vg0 are the voltage gradients), and dimenonless efliciency factors, ηr and η0. which are functions ofL/D andL 0 /D, respectively, for each gas, regardless of the geometry of the sleeve, the current, and the strength of the vortex.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01447034
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  • 11
    Electronic Resource
    Electronic Resource
    Formulation of electro-chemico-osmotic processes in soils (1991)
    Springer
    Transport in porous media 6 (1991), S. 435-444 
    Details
    ISSN: 1573-1634
    Keywords: Electrokinetics ; electrophoresis ; electro-osmosis ; chemico-osmosis ; porous media ; transport processes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Electrokinetic techniques have been used for various purposes including consolidation of soils, dewatering of sludges, and hazardous waste remediation among others. Estimating the feasibility of employing electro-osmosis in a particular operation depends on the ability to predict the outcome under a variety of conditions. Predictions of this type are frequently facilitated by the use of a mathematical model designed to represent the physical system under consideration in a rigorous fashion. First, a review of fundamental aspects of electro-chemico-osmotic flow in soils is presented. Following a brief outline of previous studies, identification and quantification of the significant processes, and the construction of mathematical representations are given. This is achieved using an approach based on the macroscopic conservation of mass equations and the principle of a continuum, in contrast to an approach based on the irreversible thermodynamics of coupled flows. Special emphasis is given to coupling effects on transport processes. A complete model and associated boundary conditions are then obtained for electrokinetic processes in a compressible porous medium. The proposed model takes into consideration the migration of a contaminant plume in a flow field generated by an applied electric potential.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00136350
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  • 12
    Electronic Resource
    Electronic Resource
    Effects of anisotropy on the free convection from a vertical plate embedded in a porous medium (1991)
    Springer
    Transport in porous media 6 (1991), S. 183-194 
    Details
    ISSN: 1573-1634
    Keywords: Free convection ; heat transfer ; porous media ; natural convection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The effects of anisotropy on the steady laminar boundary-layer free convection over a vertical impermeable surface are analysed by using the method of integral relations. If the permeability in the direction orthogonal to the plate is greater than the permeability along the plate, then there is an increase in the temperature field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00179280
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  • 13
    Electronic Resource
    Electronic Resource
    Scaling mixing during miscible displacement in heterogeneous porous media (1991)
    Springer
    Transport in porous media 6 (1991), S. 607-626 
    Details
    ISSN: 1573-1634
    Keywords: dispersion ; dispersivity ; heterogenity ; miscible ; porous media ; scaling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract This paper discusses scaling of mixing during miscible flow in heterogeneous porous media. In large field systems dispersivity appears to depend on system length due to heterogeneities. Three types of scaling are discussed to investigate the heterogeneous effects. Dimensional analysis of mixing during flow through geometerically scaled heterogeneous models is illustrated using measured dispersion. Fractal analysis of mixing in statistically scaled heterogeneous porous media is discussed. Analog scaling of pressure transients in heterogeneous porous media is suggested as an in-situ method of estimating dispersion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00137852
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  • 14
    Electronic Resource
    Electronic Resource
    Hydrodynamics and heat transfer in a plasma spouted bed reactor (1990)
    Springer
    Plasma chemistry and plasma processing 10 (1990), S. 71-85 
    Details
    ISSN: 1572-8986
    Keywords: Thermal plasmas ; spouted bed ; hydrodynamics ; heat transfer
    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 literature reveals very little intformation about plasma spouted bed hydrodynamics. Spouting of corindon particles with diameters ranging from 0.4 to 3.36 mm with argon plasma was conducted in a 90-mm-diameter column in the temperature range 300–1300°C. It was found that the maximum spoutable height (Hm) decreases with increasing particle diameter and decreasing mean bed temperature. A relation between the inlet plasma velocity and Hm is proposed. Concerning heat transport phenomena in the annulus, measurements and calculations indicate a large axial diffusivity but a poor radial mixing. Typical values of Dz and Dr are proposed on the basis of an identification procedure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01460448
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  • 15
    Electronic Resource
    Electronic Resource
    One-dimensional analysis of the wall region for a multiple-temperature argon plasma (1990)
    Springer
    Plasma chemistry and plasma processing 10 (1990), S. 189-206 
    Details
    ISSN: 1572-8986
    Keywords: Thermal plasmas ; modeling ; heat and mass transfer
    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 present analysis is restricted to the wall region for a confined gas plasma and applied specifically to an argon plasma. The wall may be either positive or negative in potential with respect to the plasma, and the electric current may flow either parallel or normal to the wall. Estimates of the Debye shielding distance and the mean free path of various components are made to obtain the range of validity of the analysis, in addition to the situation where the wall acts like a cathode, an anode, or an electrical insulation. Analysis is for a one-dimensional case with an outer boundary, where the plasma temperature is specified. The computational domain is split into a continuum region, where both equilibrium compositions for a two-temperature plasma and a chemically reacting plasma are studied, and a free-fall region. The results allow a quantitative assessment of temperature nonequilibrium and electrical potential distribution in the free-fall region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01460455
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  • 16
    Electronic Resource
    Electronic Resource
    Similarity solutions for immiscible phase migration in porous media: an analysis of free boundaries (1990)
    Springer
    Transport in porous media 5 (1990), S. 491-515 
    Details
    ISSN: 1573-1634
    Keywords: Two-phase flow ; fuel saturation ; self-similar solutions ; porous media ; convective dispersion ; capillary number
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract A fuel pollutant migrating in a water flow throughout a porous medium is distributed between the moving (continuous) and residual (discontinuous) phases. Usually, there is an equilibrium condition between these phases. In this study, the migration of a fuel slug confied within free boundaries moving in the porous medium is considered. This type of fuel migration pertains to circumstances in which convective fuel transport dominates fuel dispersion when fuel saturation approaches zero. A one-dimensional self-similar model is developed, describing the movement of fuel saturation fronts in a porous medium against and with the water flow direction. Several analytical solutions are found revealing the effects of the pore size, fuel viscosity, fuel mass, and the capillary number on the fuel migration in the porous medium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01403479
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  • 17
    Electronic Resource
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    Evolution of governing mass and momentum balances following an abrupt pressure impact in a porous medium (1990)
    Springer
    Transport in porous media 5 (1990), S. 169-185 
    Details
    ISSN: 1573-1634
    Keywords: Compressible fluid ; porous media ; abrupt pressure change ; time and spatial averaging ; mass and momentum balance equations ; nondimensional forms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract A mathematical model is developed of an abrupt pressure impact applied to a compressible fluid flowing through a porous medium domain. Nondimensional forms of the macroscopic fluid mass and momentum balance equations yield two new scalar numbers relating storage change to pressure rise. A sequence of four reduced forms of mass and momentum balance equations are shown to be associated with a sequence of four time periods following the onset of a pressure change. At the very first time period, pressure is proven to be distributed uniformly within the affected domain. During the second time interval, the momentum balance equation conforms to a wave form. The behavior during the third time period is governed by the averaged Navier-Stokes equation. After a long time, the fourth period is dominated by a momentum balance similar to Brinkman's equation which may convert to Darcy's equation when friction at the solid-fluid interface dominates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00144602
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  • 18
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    Numerical experiments on convective heat transfer in water-saturated porous media at near-critical conditions (1990)
    Springer
    Transport in porous media 5 (1990), S. 299-323 
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    ISSN: 1573-1634
    Keywords: Supercritical convection ; heat transfer ; numerical simulation ; porous media ; geothermal systems ; water ; critical point
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Fluid and heat flow at temperatures approaching or exceeding that at the critical point (374 °C for pure water, higher for saline fluids) may be encountered in deep zones of geothermal systems and above cooling intrusives. In the vicinity of the critical point the density and internal energy of fluids show very strong variations for small temperature and pressure changes. This suggests that convective heat transfer from thermal buoyancy flow would be strongly enhanced at near-critical conditions. This has been confirmed in laboratory experiments. We have developed special numerical techniques for modeling porous flow at near-critical conditions, which can handle the extreme nonlinearities in water properties near the critical point. Our numerical simulations show strong enhancements of convective heat transfer at near-critical conditions; however, the heat transfer rates obtained in the simulations are considerably smaller than data reported from laboratory experiments by Dunn and Hardee. We discuss possible reasons for this discrepancy and develop suggestions for additional laboratory experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00140018
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  • 19
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    Thermal plasma composition in the presence of easily and noneasily ionized components (1989)
    Springer
    Plasma chemistry and plasma processing 9 (1989), S. 445-463 
    Details
    ISSN: 1572-8986
    Keywords: Thermal plasmas ; equilibrium composition ; metal halide discharge ; easily and noneasily ionized components
    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 influence of easily and noneasily ionized components on equilibrium particle density ratios in thermal plasmas has been investigated. Particular emphasis is given to the modeling of metal halide discharges with iodine as a halide. The calculations were done for “standard” air with lithium or iodine, “standard” argon with aluminum, and with a mixture of aluminum and iodine. The system setup is in agreement with spectroscopic results for an open-chamber gas-stabilized d.c. arc, with a pressure of 1×105 Pa and temperatures corresponding to the radial distribution of temperature for this type of discharge. It is shown that the behavior of the plasma core is dominated by the easily ionized component (Li or Al) while the periphery is characterized by the noneasily ionized component (iodine).
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    URL: http://dx.doi.org/10.1007/BF01023913
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  • 20
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    Nonequilibrium effects in thermal plasma chemistry (1989)
    Springer
    Plasma chemistry and plasma processing 9 (1989), S. 435-443 
    Details
    ISSN: 1572-8986
    Keywords: Thermal plasmas ; nonequilibrium ; finite rates ; dissociation
    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 Numerical calculations have been performed to assess the potential significance of nonequilibrium effects on chemical reactivity in thermal plasmas The calculations consider situations in which the electron temperature and/or the electron density are elevated above their equilibrium values corresponding to the local gas temperature. Such nonequilibrium may occur in the plasma torch itself or could be purposefully imposed by a controlled hybrid discharge in a downstream reactor region so as to augment reactivity over a longer residence time. The calculations account for finite ionization/recombination rates of atomic and molecular species, electron-impact dissociation, dissociative recombination, dissociative attachment, and predissociation effects, as well as thermal reactions between neutral chemical species. As an example of the possible nonequilibrium enhancement of molecular decomposition, initial consideration has focused on the dissociation rates of diatomic species where heavy particle reaction rates and cross sections can be reasonably estimated. The results show that for O2 or H2 in argon at moderate temperatures, electron-temperature elevation can give rise to a notable enhancement of the dissociation rate, in comparison with the equilibrium case. Depending on the situation, it is found that either relatively energetic electron-impact dissociation or dissociative attachment (for O2) can dominate the enhanced dissociation rate—which can be more than a factor of 2 greater than in the absence of a discharge. Similar effects would be expected for the decomposition of more complicated molecules.
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    URL: http://dx.doi.org/10.1007/BF01023912
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  • 21
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    Some characteristics of transferred-Arc plasmas (1989)
    Springer
    Plasma chemistry and plasma processing 9 (1989), S. 65S 
    Details
    ISSN: 1572-8986
    Keywords: Thermal plasmas ; transferred arcs ; plasma radiation ; plasma heat transfer ; plasma columns ; plasma stability
    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 Although the theoretical foundations of the characteristics of transferred arcs were established more than three decades ago, the design of reator systems based on this method of plasma are generation is still in an early stage of development. Although deceptively simple in concept, attempts to use transferred arcs im practical applications at scales of arc length and power somewhat larger than those previously studied in the laboratory soon revealed that considerably more information was required on the arc's unique properties before a sound reactor design could be carried out. This was principally due to the much higher temperature levels (up to 20,000 K) with consequent much higher radiative power achieved in this type of arc, as well as the fluid mechanical effects of the high-velocity plasma gas flowing in the latter. These, in turn, had profound effects on the various modes of heat transfer occurring in the system, on the stability of the arc, on the injection of the material to be treated, and on the overall efficiency of energy utilization in the whole system. The objective of this paper is to summarize the experimental evidence concerning transforred arc characteristics which have been obtained by the author and his colleageus during recent years.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01015874
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    Electronic Resource
    Electronic Resource
    Particle behavior in thermal plasmas (1989)
    Springer
    Plasma chemistry and plasma processing 9 (1989), S. 167S 
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    ISSN: 1572-8986
    Keywords: Thermal plasmas ; heat, mass, and momentum transfer ; material processing ; overview
    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 overview, effects exerted on the motion and on heat and mass transfer of particulates injected into a thermal plasma are discussed, including an assessment of their relative importance in the context of thermal plasma processing of materials. Results of computer experiments are shown for particle sizes ranging from 5–50 μm, and for alumina and tungsten as sample materials. The results indicate that (i) the correction terms required for the viscous drag and the convective heat transfer due to strongly varying properties are the most important factors; (ii) noncontinuum effects are important for particle sizes 〈10 μm at atmospheric pressure, and these effects will be enhanced for smaller particles and/or reduced pressures; (iii) the Basset history term is negligible, unless relatively large and light particles are considered over long processing distances; (iv) thermophoresis is not crucial for the injection of particles into thermal plasmas; (v) turbulent dispersion becomes important for particle 〈10 μm in diameter; and (vi) vaporization describes a different particle heating history than that of the evaporation process which, however, is not a critical control mechanism for interphase mass transfer of particles injected into thermal plasmas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01015878
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    Electronic Resource
    Electronic Resource
    Silicon nitride synthesis in an atmospheric pressure convection—Stabilized arc (1989)
    Springer
    Plasma chemistry and plasma processing 9 (1989), S. 277-289 
    Details
    ISSN: 1572-8986
    Keywords: Thermal plasmas ; synthesis of Si3N4 ; experiments
    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 Submicron α-, β-, and amorphous-phase silicon nitride particles have been synthesized in an experimental plasma reactor, using metallic silicon and ammonia as reactants. Injection of ammonia at different locations of the reactor results in different yields. A maximum yield of 85 wt% has been achieved by injecting NH3 at both downstream and upstream locations of the reactor. The powders synthesized in this way contained approximately 60 wt% silicon nitride in crystal form with equal amounts of α and β phases. The remainder consisted of the amorphous phase. The average size of the particles ranged from 50 to 90 nm, with a standard deviation of 1.47–1.87 depending on the location of ammonia injection. Seeding with 1 and 10 wt% of preexisting silicon nitride particles for fostering heterogeneous nucleation did not improve the yield, but it changed the particle size distribution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01054286
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    Electronic Resource
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    Finite element modelling of two-phase heat and fluid flow in deforming porous media (1989)
    Springer
    Transport in porous media 4 (1989), S. 319-334 
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    ISSN: 1573-1634
    Keywords: Finite elements ; consolidation ; porous media ; two-phase flow
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract This paper details a finite element model which describes the flow of two-phase fluid and heat within a deforming porous medium. The coupled governing equations are derived in terms of displacements, pore pressures and temperatures, and details of the time-stepping algorithm and thermodynamic considerations are also presented. Two numerical examples are included for verification.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00165778
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  • 25
    Electronic Resource
    Electronic Resource
    Modelling particle formation and growth in a plasma synthesis reactor (1988)
    Springer
    Plasma chemistry and plasma processing 8 (1988), S. 145-157 
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    ISSN: 1572-8986
    Keywords: Thermal plasmas ; particle nucleation and growth ; modelling
    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 model for particle nucleation and growth in a thermal plasma reactor is discussed. A nondimensional form of the aerosol general dynamic equation is derived under a set of simplifying assumptions which are appropriate to plasma powder synthesis, and the resulting set of equations is solved numerically. The results are converted to dimensional form for the case of iron powder, for which experimental data are available, and for silicon carbide. Calculated particle sizes increase significantly with increasing reactant concentrations and with decreasing cooling rate, although the influence of cooling rate is mainly a residence time effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01016154
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    Electronic Resource
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    A coupled finite element model for the consolidation of nonisothermal elastoplastic porous media (1986)
    Springer
    Transport in porous media 1 (1986), S. 155-178 
    Details
    ISSN: 1573-1634
    Keywords: Three-field interaction problem ; temperature field ; flow field ; displacement field ; geothermal systems ; porous media ; elastoplastic analysis ; partitioned solution procedure ; fully coupled finite element models ; nonisothermal consolidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract A coupled finite element model for the analysis of the deformation of elastoplastic porous media due to fluid and heat flow is presented. A displacement-pressure temperature formulation is used for this purpose. This formulation results in an unsymmetric coefficient matrix, even in the case of associated plasticity. A partitioned solution procedure is applied to restore the symmetry of the coefficient matrix. The partitioning procedure is an algebraic one which is carried out after integration in the time domain. For this integration, a two-point recurrence scheme is used. The finite element model is applied to the investigation of nonisothermal consolidation in various situations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00714690
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    Electronic Resource
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    Particle dynamics and particle heat and mass transfer in thermal plasmas. Part I. The motion of a single particle without thermal effects (1985)
    Springer
    Plasma chemistry and plasma processing 5 (1985), S. 211-237 
    Details
    ISSN: 1572-8986
    Keywords: Thermal plasmas ; particle motion ; computer experiments ; review
    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 particle injected into a thermal plasma will experience a number of effects which are not present in an ordinary gas. In this paper effects exerted on the motion of a particle will be reviewed and analyzed in the context of thermal plasma processing of materials. The primary purpose of this paper is an assessment of the relative importance of various effects on particle motion. Computer experiments are described, simulating motion of a spherical particle in a laminar, confined plasma jet or in a turbulent, free plasma jet. Particle sizes range from 5 to 50 µm, and as sample materials alumina and tungsten are considered. The results indicate that (i) the correction term required for the viscous drag coefficient due to strongly varying properties is the most important factor; (ii) non-continuum effects are important for particle sizes 〈10 µm at atmospheric pressure and these effects will be enhanced for smaller particles and/or reduced pressures; (iii) the Basset history term is negligible, unless relatively large and light particles are considered over long processing distances; (iv) thermophoresis is not crucial for the injection of particles into thermal plasmas; (v) turbulent dispersion becomes important for particle 〈10 µm in diameter.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00615122
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    Particle dynamics and particle heat and mass transfer in thermal plasmas. Part II. Particle heat and mass transfer in thermal plasmas (1985)
    Springer
    Plasma chemistry and plasma processing 5 (1985), S. 391-414 
    Details
    ISSN: 1572-8986
    Keywords: Thermal plasmas ; heat and mass transfer ; review
    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 This paper is concerned with a review of heat and mass transfer between thermal plasmas and particulate matter. In this situation various effects which are not present in ordinary heat and mass transfer have to be considered, including unsteady conditions, modified convective heat transfer due to strongly varying plasma properties, radiation, internal conduction, particle shape, vaporization and evaporation, noncontinuum conditions, and particle charging. The results indicate that (i) convective heat transfer coefficients have to be modified due to strongly varying plasma properties; (ii) vaporization, defined as a mass transfer process corresponding to particle surface temperatures below the boiling point, describes a different particle heating history than that of the evaporation process which, however, is not a critical control mechanism for interphase mass transfer of particles injected into thermal plasmas; (iii) particle heat transfer under noncontinuum conditions is governed by individual contributions from the species in the plasma (electrons, ions, neutral species) and by particle charging effects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00566011
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    Generation and behavior of fine particles in thermal plasmas—A review (1985)
    Springer
    Plasma chemistry and plasma processing 5 (1985), S. 1-37 
    Details
    ISSN: 1572-8986
    Keywords: Thermal plasmas ; fine particles ; review
    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 generation and processing of fine powders in thermal plasmas has attracted increasing interest over the past years, precipitated by a growing awareness that conservation of materials is no longer an option but rather a necessity. Plasmaspheroidization, densification, fuming, metallurgical reduction, and the production of refractory oxides, carbides, nitrides, and borides in thermal plasmas are fast developing technologies which, in some cases, have already reached industrial production scale. In this survey, pertinent literature (198 references) will be reviewed with emphasis on basic studies in this field, reported over the past 20 years. The first part of this review covers powder handling, quenching characteristics, nucleation and growth, and modeling of plasma-particle interactions. The second part is concerned with plasma furnaces for the production of fine particles, including RF induction plasmas, DC anode furnaces, DC plasma jets, DC transferred arcs, cathode pump fed arcs, hybrid induction-DC plasmas, and three-phase AC furnaces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00567907
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