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Gas-Condensed Phase Interactions

Gas-Condensed Phase Interactions. Flame-Surface Heat Exchange. John E. Adams Department of Chemistry University of Missouri-Columbia Columbia, MO 65211-7600. Context. Early deflagration models gasification + single reaction no explicit chemical mechanisms Refined models

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Gas-Condensed Phase Interactions

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  1. Gas-Condensed Phase Interactions Flame-Surface Heat Exchange John E. Adams Department of Chemistry University of Missouri-Columbia Columbia, MO 65211-7600

  2. Context • Early deflagration models • gasification + single reaction • no explicit chemical mechanisms • Refined models • inclusion of one or more condensed-phase reactions • detailed gas-phase combustion chemistry • gas-phase transport • phenomenological treatment of the dependence of burning rate on Ts

  3. Goal of Our Work • Predict the burning rate(depends on surface temperature) • Evaporation • Gas-phase combustion • Liquid surface heating by hot combustion products • Condensed-phase reactions

  4. Previous Work • Energy transfer at a solid surface • Many workers since the late 1960’s (polycrystalline surfaces, since 1930’s) • Adsorbate coverage, collision geometry and Ts dependences (Zhao and Adams, 1985 and 1986)

  5. Previous Work (continued) • Gas-liquid scattering—early work • Sinha and Fenn (1975) • Balooch, Siekhaus, and Olander (1986, 1988) • Nathanson group • Scattering of inert gases and smallmolecules (CH4, NH3, D2O, SF6) fromliquids and solutions having low vaporpressures (glycerol, squalane, conc.H2SO4, perfluorinated polyethers,metals, alloys) • TOF spectra, in-plane scattering fluxas a function of incident and observationangles

  6. General Features • Initial conditions • Solid layers • Liquid “layers” (periodic boundary conditions) • Gas-phase combustion products impinge on liquid surface, uniform distribution of incident angles • Kinetic energy analysis of scattered species

  7. Input/Output • I:Potential energy functions • Analytical forms (Brenner group) • “On-the-fly” • I:Combustion product analysis(Thompson group) • O:Energy transfer as a function of Ts(Rice; Miller and Anderson) • Angle-averaged energy loss to the surface • Identification of scattering components • Direct scattering • Trapping-desorption • Reactive scattering

  8. Initial Efforts • Method development and calibration • Simple Lennard-Jones fluidtest caseAr/In(6.4 and 92 kJ/mol,i=55°; 436 K)experiments byNathanson, et al. Atselected incidentenergies and angles

  9. Extensions • Energy transfer to a solution • Ar/Bi:Ga (0.02% Bi), 313-673 K • Segregation of the solute to the surface at low T • Simple molecular case • Self-sustained frozen O3 deflagration • Good models for the burning rate exist • Relatively simple mechanism (3 combustion reactions), reaction products • Possibility of reaction of incident species with the surface

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