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

Context n Early deflagration models –gasification + single reaction –no explicit chemical mechanisms n 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 T s

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

Previous Work n Energy transfer at a solid surface –Many workers since the late 1960’s (polycrystalline surfaces, since 1930’s) –Adsorbate coverage, collision geometry and T s dependences (Zhao and Adams, 1985 and 1986)

Previous Work (continued) n Gas-liquid scattering—early work –Sinha and Fenn (1975) –Balooch, Siekhaus, and Olander (1986, 1988) n Nathanson group –Scattering of inert gases and small molecules (CH 4, NH 3, D 2 O, SF 6 ) from liquids and solutions having low vapor pressures (glycerol, squalane, conc. H 2 SO 4, perfluorinated polyethers, metals, alloys) –TOF spectra, in-plane scattering flux as a function of incident and observation angles

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

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

Initial Efforts n Method development and calibration –Simple Lennard-Jones fluid test case Ar/In (6.4 and 92 kJ/mol,  i =55°; 436 K) experiments by Nathanson, et al. At selected incident energies and angles

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