Library

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    An approximate variational method for improved thermodynamics of molecular fluids (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 3479-3483 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: For a certain class of thermodynamic perturbation theories, a generalization of the Gibbs–Bogoliubov inequality holds through second order of perturbation theory and for a subset of terms the inequality is true to infinite order. Using this approximate variational principle, a perturbation theory is chosen for which the Helmholtz free energy of the reference system is minimized under the constraint that the first order term is identically zero. We apply these ideas to the determination of effective spherical potentials that accurately reproduce the thermodynamics of nonspherical molecular potentials. For a diatomic-Lennard-Jones (DLJ) potential with l/σ=0.793, the resulting spherical reference potential is identical to the median average over angles for the repulsive part of the potential, but differs in the attractive well. The variational effective spherical potential leads to more accurate thermodynamics than the median, however, particularly in the triple point region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450233
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Numerical simulation of nonequilibrium effects in an argon plasma jet (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 3698-3708 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Departures from thermal (translational), ionization, and excitation equilibrium in an axisymmetric argon plasma jet have been studied by two-dimensional numerical simulations. Electrons, ions, and excited and ground states of neutral atoms are represented as separate chemical species in the mixture. Transitions between excited states, as well as ionization/recombination reactions due to both collisional and radiative processes, are treated as separate chemical reactions. Resonance radiation transport is represented using Holstein escape factors to simulate both the optically thin and optically thick limits. The optically thin calculation showed significant underpopulation of excited species in the upstream part of the jet core, whereas in the optically thick calculation this region remains close to local thermodynamic equilibrium, consistent with previous experimental observations. Resonance radiation absorption is therefore an important effect. The optically thick calculation results also show overpopulations (relative to equilibrium) of excited species and electron densities in the fringes and downstream part of the jet core. In these regions, however, the electrons and ions are essentially in partial local thermodynamic equilibrium with the excited state at the electron temperature, even though the ionized and excited states are no longer in equilibrium with the ground state. Departures from partial local thermodynamic equilibrium are observed in the outer fringes and far downstream part of the jet. These results are interpreted in terms of the local relative time scales for the various physical and chemical processes occurring in the plasma.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870905
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Indirect-drive noncryogenic double-shell ignition targets for the National Ignition Facility: Design and analysis : Review,Tutorial and Invited Papers from the 43rd Annual Meeting of the APS Division of Plasma Physics (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 2221-2233 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Analysis and design of indirect-drive National Ignition Facility double-shell targets with hohlraum temperatures of 200 eV and 250 eV are presented. The analysis of these targets includes the assessment of two-dimensional radiation asymmetry and nonlinear mix. Two-dimensional integrated hohlraum simulations indicate that the x-ray illumination can be adjusted to provide adequate symmetry control in hohlraums specially designed to have high laser-coupling efficiency [Suter et al., Phys. Plasmas 7, 2092 (2000)]. These simulations also reveal the need to diagnose and control localized 10–15 keV x-ray emission from the high-Z hohlraum wall because of strong absorption by the high-Z inner shell. Preliminary estimates of the degree of laser backscatter from an assortment of laser–plasma interactions suggest comparatively benign hohlraum conditions. The application of a variety of nonlinear mix models and phenomenological tools, including buoyancy-drag models, multimode simulations and fall-line optimization, indicates a possibility of achieving ignition, i.e., fusion yields greater than 1 MJ. Planned experiments on the Omega laser will test current understanding of high-energy radiation flux asymmetry and mix-induced yield degradation in double-shell targets. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1459451
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Ambipolar diffusion in two-temperature multicomponent plasmas (1993)
    Springer
    Plasma chemistry and plasma processing 13 (1993), S. 489-498 
    Details
    ISSN: 1572-8986
    Keywords: Diffusion ; ambipolar ; two-temperature plasmas
    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 recent formulation of multicomponent diffusion in multitemperature gas mixtures [J. D. Ramshaw, J. Non-equilib. Thermodyn. 18. 121 (1993)] is applied to ambipolar diffusion in two-temperature multicomponent plasmas in zero magnetic field. Simplifications chic to the small electron muss are systematically exploited. A general expression is derived for the ambipolar electric field E. In the special case where the electron and heavy-particle temperatures are equal, this expression reduces to a result previously obtained using a self-consistent effective binary diffusion (SCEBD) approximation [J. D. Ramshaw and C. H. Chang,Plasma Chem. Plasma Process.11. 395 (1991)]. When thermal diffusion due to electrons is neglected, the heavy particles are shown to diffuse precisely as they would in the same E field if the electrons were entirely removed from the system. Finally, the SCEBD approximation for ambipolar diffusion in multicomponent plasmas is generalized to the case, of unequal electron and heavy-particle temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01465878
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Ambipolar diffusion in multicomponent plasmas (1991)
    Springer
    Plasma chemistry and plasma processing 11 (1991), S. 395-402 
    Details
    ISSN: 1572-8986
    Keywords: Diffusion ; ambipolar diffusion ; multicomponent plasmas
    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 recently described self-consistent effective binary diffusion approximation is applied to ambipolar diffusion in a neutral multicomponent plasma in zero magnetic field, where forced diffusion due to the electric field E plays an essential role. The field E is determined by the constraint that the net current flow produced by the diffusion fluxes must be zero. The resulting effective binary diffusion fluxes are the sum of those that would obtain for E=0 and ambipolar correction terms proportional to E. The formulation is .self=consistent with respect to both mass and charge, the net diffusional fluxes of which are both identically zero. The results may be further simplified due to the small mass of the electrons. The effective binary diffusivity De of the electrons no longer appears in the simplified expressions. They are therefore well suited to numerical calculations, where the large value of De, might otherwise have resulted in unacceptable stability or accuracy restrictions. The well-known effective doubling of ion diffusivities due to ambipolar diffusion occurs in simple situations but is not a general feature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01458919
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Computational study of high-speed plasma flow impinging on an enthalpy probe (1996)
    Springer
    Plasma chemistry and plasma processing 16 (1996), S. 17-38 
    Details
    ISSN: 1572-8986
    Keywords: Enthalpy probe ; supersonic plasma flow ; chemical kinetics
    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 Enthalpy probe measurements in supersonic plasma flows are subject to various sources of error which are difficult to quantify experimentally v. The relative importance of several such errors has been assessed by means of detailed two-dimensional numerical simulations of high-speed plasma flow impinging on an enthalpy probe. The simulations show that moderate uncertainties in upstream pressure and composition (i.e., degree of ionization) can lead to significant errors in the velocity and temperature inferred from the measurements. These errors tend to be larger in velocity than temperature A second potential source of error is that enthalpy probe data are generally interepreted by means of simplified analytical relations which neglect the effects of finite-rate ionization, internal electronic excitation, thermal radiation, probe cooling, and probe sampling. The importance of these effects was also assessed, and the resulting errors were not ,significant under the conditions examined. We conclude that enthalpy probe measurements in supersonic plasma flows are use f d in situations where the upstream pressure and degree of ionization are known to reasonable accucary.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01465215
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    Numerical simulations of argon plasma jets flowing into cold air (1993)
    Springer
    Plasma chemistry and plasma processing 13 (1993), S. 189-209 
    Details
    ISSN: 1572-8986
    Keywords: Turbulent plasma jets ; argon-air plasmas
    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 Computational results and comparisons with experimental data are presented for simulations of axisymmetric turbulent argon plasma jets flowing into a cold air environment. The calculations were performed using the LAVA code [J. D. Rarnshaw and C. H. Chang,Plasma Chem. Plasma Process. 12, 299 (1992)], and were designed to simulate experiments performed by Brossa and Pfender (Plasma Chem. Plasma Process. 8, 75 (1988)) (BP) and by Finckeet al (private communication, 1992] (FSH). To our knowledge, these are the first such simulations in which multicomponent diffusion and interactions between dissociation and ionization of different species are consistently, accounted for. Turbulence effects were represented by a standardκ-ɛ model, both with and without an axisymmetric jet correction term and for several different choices of the turbulent Prandil and Schmidt numbers Prt and Scl. Simulations were performed for one FSH experiment and two BP experiments at different values of torch powerP and argon flow rateW. The inflow profiles in the FSH simulations were adjusted to matchP,W, and the experimental data slightly downstream of the torch exit as closely as possible. The same profile shapes were then used to matchP andW for the BP simulations, for which data near the torch exit were not available. Swirl was neglected except in one of the FSH calculations, where it was found to have negligible effect, as expected. Best results were obtained with the axisymmetric jet correction term omitted and with Prt = Scl = 0.7. Agreement with the experimental data was then lair overall, but still showed systematic deviations and cannot be regarded as fully satisfactory. Possible reasons for the discrepancies are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01466041
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    Modeling of nonequilibrium effects in a high-velocity nitrogen-hydrogen plasma jet (1995)
    Springer
    Plasma chemistry and plasma processing 16 (1995), S. S5 
    Details
    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 A numerical simulation has been performed of a high-velocity nitrogen hydrogen plasma jet in air at atmospheric pressure including finite-rate chemical kinetics. Ions, electrons, and neutral atoms and molecules are treated as separate species in the plasma mixture. The chemical reactions considered are dissociation of molecular species, ionization of atomic species, charge exchange and dissociatioe recombination of nitrogen, and hydrogen-oxygen reactions. The calculational results show that strong departures from ionization and dissociation equilibrium develop in the downstream region as the chemical reactions freeze out at lower temperatures, in spite of the assumed chemical equilibrium at the nozzle exit. The calculations also show that ionized species are over-populated throughout the flow, while dissociated species in the core of the jet are underpopulated near the nozzle exit and become over-populated farther downstream. This initial underpopulation is due to diffusive depletion of dissociated species and enrichment of molecular species in the core of the jet.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01512624
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    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
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 10
    Electronic Resource
    Electronic Resource
    Damped artificial compressibility iteration scheme for implicit calculations of unsteady incompressible flow (1995)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 21 (1995), S. 141-153 
    Details
    ISSN: 0271-2091
    Keywords: incompressible flow ; artificial compressibility ; artificial bulk viscosity ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Peyret (J. Fluid Mech., 78, 49-63 (1976)) and others have described artificial compressibility iteration schemes for solving implicit time discretizations of the unsteady incompressible Navier-Stokes equations. Such schemes solve the implicit equations by introduing derivatives with respect to a pseudo-time variable τ and marching out to a steady state in τ. The pseudo-time evolution equation for the pressure p takes the form ∂p/∂ = -a2∂∇.u, where a is an artificial compressibility parameter and u is the fluid velocity vector. We present a new scheme of this type in which convergence is accelerated by a new procedure for setting a and by introducing an artificial bulk viscosity b into the momentum equation. This scheme is used to solve the non-linear equations resulting from a fully implicit time differencing scheme for unsteady incompressible flow. We find that the best values of a and b are generally quite different from those in the analogous scheme for steady flow (J. D. Ramshaw and V. A. Mousseau, Comput. Fluids, 18, 361-367 (1990)), owing to the previously unrecognized fact that the character of the system is profoundly altered by the pressence of the physical time derivative terms. In particular, a Fourier dispersion analysis shows that a no longer has the significance of a wave speed for finite values of the physical time step δt,. Inded, if on sets a ˜ |u| as usual, the artificial sound waves cease to exist when δt is small and this adversely affects the iteration convergence rate. Approximate analytical expressions for a and b are proposed and the benefits of their use relative to the conventional values a ∼ |u| and b = 0 are illustrated in simple test calculations.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650210205
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...