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  • 1995-1999  (3)
  • 1999  (2)
  • 1996  (1)
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  • 1995-1999  (3)
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  • 1
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 8535-8544 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Nucleation rate data, obtained from expansion wave tube experiments, are reported for several vapor–gas mixtures at high pressure. Results are given for water–vapor in the presence of helium and nitrogen gas, and for n-nonane in helium and methane. For all these mixtures, carrier gas pressures of 10, 25, and 40 bar have been applied, with temperatures ranging from 230 to 250 K. An extended form of the nucleation theorem (in terms of the derivative of the nucleation rate with respect to carrier gas pressure) is derived, which appears to be very helpful in the interpretation of high pressure data. It can be used to obtain the carrier gas content of the critical nucleus directly from the pressure dependence of experimental nucleation rates. Combining this method with the theoretical considerations of part I of this paper [J. Chem. Phys. 111, 8524 (1999), preceding paper]: the nucleation behavior of water at high pressures of both helium and nitrogen can quantitatively be understood. For n-nonane in helium our "pressure perturbation approach" is also valid. For n-nonane in methane, however, this approach fails because of the high methane solubility in the liquid phase. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 8524-8534 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: A theoretical approach is presented that accounts for the influence of high pressure background gases on the vapor-to-liquid nucleation process. The key idea is to treat the carrier gas pressure as a perturbation parameter that modifies the properties of the nucleating substance. Two important mechanisms are identified in this respect: With increasing carrier gas pressure, the saturated vapor density tends to increase (enhancement effect), whereas the surface tension generally decreases. Several routes to obtain data for these pressure effects are outlined, in particular for the vapor–gas mixtures that have been studied experimentally. (The results of these expansion wave tube experiments are presented in Paper II of this paper [J. Chem. Phys. 111, 8535 (1999), following paper.]) Using classical nucleation theory, a criterion is then derived for the "pressure perturbation" approach to be valid: xgeq(very-much-less-than)(S−1)/S, where xgeq is the carrier gas solubility in the liquid phase, and S is the supersaturation ratio. For the semiphenomenological Kalikmanov–Van Dongen model, the implications of the enhancement effect and surface tension decrease are briefly discussed. We also illustrate how these two effects can be obtained from (binary) density functional theory. Results of the latter for a mixture of Lennard-Jones particles are presented, with potential parameters that are characteristic for n-hexane with several carrier gases. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 8804-8821 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Asymptotic solution of homogeneous condensation in expansion cloud chambers in different droplet growth regimes is presented. In particular an exactly solvable droplet growth model ranging between the Hertz–Knudsen and continuum droplet growth laws is introduced. The distinct condensation zones in each droplet growth regime are identified by the asymptotic solution of the condensation rate equation and the results are compared with those of direct numerical simulations using the classical nucleation theory. Excellent qualitative agreement is reached despite some minor quantitative differences in some of the condensation zones arising from the nature of the asymptotic solution in these zones. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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