Gas-Condensed Phase Gas-Condensed Phase InteractionsInteractions

Flame-Surface Heat ExchangeFlame-Surface Heat Exchange

John E. AdamsDepartment of Chemistry

University of Missouri-ColumbiaColumbia, MO 65211-7600

ContextContext

Early deflagration modelsEarly deflagration models– gasification + single reactiongasification + single reaction– no explicit chemical mechanismsno explicit chemical mechanisms

Refined modelsRefined models– inclusion of one or more condensed-phase inclusion of one or more condensed-phase

reactionsreactions– detailed gas-phase combustion chemistrydetailed gas-phase combustion chemistry– gas-phase transportgas-phase transport– phenomenological treatment of the phenomenological treatment of the

dependence of burning rate on dependence of burning rate on TTss

Goal of Our WorkGoal of Our Work

Predict the burning ratePredict the burning rate(depends on surface temperature)(depends on surface temperature)– EvaporationEvaporation– Gas-phase combustionGas-phase combustion– Liquid surface heating by hot combustion productsLiquid surface heating by hot combustion products– Condensed-phase reactionsCondensed-phase reactions

Previous WorkPrevious Work

Energy transfer at a solid surfaceEnergy transfer at a solid surface– Many workers since the late 1960’s (polycrystalline Many workers since the late 1960’s (polycrystalline

surfaces, since 1930’s)surfaces, since 1930’s)

– Adsorbate coverage, collision geometry and Adsorbate coverage, collision geometry and TTss dependences (Zhao and Adams, 1985 and 1986)dependences (Zhao and Adams, 1985 and 1986)

Previous Work Previous Work (continued)(continued)

Gas-liquid scattering—early workGas-liquid scattering—early work– Sinha and Fenn (1975)Sinha and Fenn (1975)– Balooch, Siekhaus, and Olander (1986, 1988)Balooch, Siekhaus, and Olander (1986, 1988)

Nathanson groupNathanson group– Scattering of inert gases and smallScattering of inert gases and small

molecules (CHmolecules (CH44, NH, NH33, D, D22O, SFO, SF66) from) fromliquids and solutions having low vaporliquids and solutions having low vaporpressures (glycerol, squalane, conc.pressures (glycerol, squalane, conc.HH22SOSO44, perfluorinated polyethers,, perfluorinated polyethers,metals, alloys)metals, alloys)

– TOF spectra, in-plane scattering fluxTOF spectra, in-plane scattering fluxas a function of incident and observationas a function of incident and observationanglesangles

General FeaturesGeneral Features

Initial conditionsInitial conditions– Solid layersSolid layers

– Liquid “layers” (periodic Liquid “layers” (periodic boundary conditions)boundary conditions)

Gas-phase combustion Gas-phase combustion products impinge on products impinge on liquid surface, uniform liquid surface, uniform distribution of incident distribution of incident anglesangles Kinetic energy analysis Kinetic energy analysis of scattered speciesof scattered species

Input/OutputInput/Output

I:I: Potential energy functionsPotential energy functions– Analytical forms Analytical forms (Brenner group)(Brenner group)

– ““On-the-fly”On-the-fly”

I:I: Combustion product analysisCombustion product analysis (Thompson group)(Thompson group)

O:O: Energy transfer as a function of Energy transfer as a function of TTss (Rice; Miller (Rice; Miller

and Anderson)and Anderson)

– Angle-averaged energy loss to the surfaceAngle-averaged energy loss to the surface

– Identification of scattering componentsIdentification of scattering components Direct scatteringDirect scattering Trapping-desorptionTrapping-desorption Reactive scatteringReactive scattering

Initial EffortsInitial Efforts

Method development and calibrationMethod development and calibration– Simple Lennard-Jones fluidSimple Lennard-Jones fluid

test casetest case

Ar/InAr/In(6.4 and 92 kJ/mol,(6.4 and 92 kJ/mol,ii=55°; 436 K)=55°; 436 K)

experiments byexperiments byNathanson, Nathanson, et al.et al. At Atselected incidentselected incidentenergies and anglesenergies and angles

ExtensionsExtensions

Energy transfer to a solutionEnergy transfer to a solution– Ar/Bi:Ga (0.02% Bi), 313-673 KAr/Bi:Ga (0.02% Bi), 313-673 K– Segregation of the solute to the surface at low TSegregation of the solute to the surface at low T

Simple molecular caseSimple molecular case– Self-sustained frozen OSelf-sustained frozen O33 deflagration deflagration

Good models for the burning rate existGood models for the burning rate exist Relatively simple mechanism (3 combustion reactions), Relatively simple mechanism (3 combustion reactions),

reaction productsreaction products Possibility of reaction of incident species with the Possibility of reaction of incident species with the

surfacesurface