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Development of a Detailed Surface Chemistry Framework in SPARTA
K. Swaminathan-Gopalan,a A. Borner,b K. A. Stephaniaa Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign,
b Science and Technology Corporation at NASA Ames Research Center
Acknowledgments
This work was performed under the Entry System Modeling Project (M. J. Wright, Project Manager) for the NASA Game Changing Development (GCD) Program and supported by NASA Grant NNX15AU92A.
DSMC Workshop 2017 Santa Fe, NM27th – 30th Aug 2017
Outline
§ Motivation
§ Overview of Surface Chemistry Framework
§ Gas-Surface (GS) Reactions
§ Pure-Surface (PS) Reactions
§ Applications
§ Parallelization strategies
§ Summary and Future Work
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Motivation
Objective:To construct a general, detailed physics-based surface chemistry framework in DSMC.
Ablative TPS
3
Adsorption and reactive surface chemistry
Somorjai andLi[1]
Imagecredit:NASA
1 Somorjai, G. A., & Li, Y. (2010). Introduction to surface chemistry and catalysis. John Wiley & Sons.
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Surface chemistry at microporous catalysts.
Flow through porous preform carbon TPS using SPARTA. Imagecredit:Sandstorm
Computational framework
• Finite-ratesurfacechemistrymodulewithadsorption.• Includesgas-surface(GS)andpure-surface(PS)reactions.• Bothcatalyticandsurfacealtering(oxidation/nitridation)reactions.• ComputationalframeworksimilartoMarschall,MacleanandDriver[2,3]forCFD.• Langmuirmodelforsurfacesites.• DiverseVDFandangulardistributionsofscatteredproducts.
takenfromMarschall andMaclean[1].
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3 Marschall, J., & MacLean, M. (2011). Finite-rate surface chemistry model, I: Formulation and reaction system examples. AIAA Paper, 3783, 2011.3 MacLean, M., Marschall, J., & Driver, D. M. (2011). Finite-rate surface chemistry model, II: coupling to viscous Navier–Stokes code. AIAA Paper, 3784, 2011.
Computational framework
• Particlesadsorbed(deleted)anddesorbed(created),surfaceelementstoresadsorbedparticleconcentration.
• Surfacereactionsbasedonconcentrationwithinsurfaceelement.• Multipletriangulatedelements(likecells)onsurfaces• Surfacetreatedasinfinitesinkandsource.
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takenfromMarschall andMaclean[1].
3 Marschall, J., & MacLean, M. (2011). Finite-rate surface chemistry model, I: Formulation and reaction system examples. AIAA Paper, 3783, 2011.3 MacLean, M., Marschall, J., & Driver, D. M. (2011). Finite-rate surface chemistry model, II: coupling to viscous Navier–Stokes code. AIAA Paper, 3784, 2011.
List of gas-surface (GS) reactions
• Reactantsincludebothgas-phaseandsurfacespecies.• Comprehensivesetofreactions– Includesreactiontypesfromthermalregimeand
hyperthermalenergyregime.
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Modeling of gas-surface (GS) reactions
• GSreactionprobabilitycomputedwhengas-phasespecieshitssurface.• Reactionprobabilityfunctionof:
o rateconstanto gas-phaseparticleproperties(energy,angle,etc.)o surfaceconditions(temperature,surfacecoverage,etc.)
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List of pure-surface (PS) reactions
• Pure-surface(PS)reactantsincludeonlysurfacespecies(adsorbedandbulk).• Comprehensivesetofreactions
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Modeling of pure-surface (PS) reactions
• Characteristictimecomputedbetweentworeactions:Timecountermethod[5].• Characteristictimefunctionof
o reactionrateconstanto surfaceconditions(temperature,surfacecoverage,etc.).
• Timecounteralgorithmsdevelopedtobeindependentofdt.
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5 Molchanova, A. N., A. V. Kashkovsky, and Ye A. Bondar. "A detailed DSMC surface chemistry model." In AIP Conference Proceedings, vol. 1628, no. 1, pp. 131-138. AIP, 2014.
Scattering models
CurrentmodelsinSPARTA• Specular• Diffuse– Maxwell’smodel
Additionalmodels• CLLmodel– Thermalregimescattering.Cancapturefullandpartialenergyand
angularaccommodation[6,7].• Thermal– Thermallydesorbingparticleswithoptionssuchasdesorption
barrier,additionalenergytransferduetolocalhot-spots,etc.• Impulsive– Structuralregimescatteringathyperthermalenergies.• Non-thermal– Transitionregimescatteringatsuperthermal energieswithout
fullaccommodation
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6 Lord, R. G. (1991). Some extensions to the Cercignani–Lampis gas–surface scattering kernel. Physics of Fluids A: Fluid Dynamics, 3(4),706-710.7 Lord, R. G. "Some further extensions of the Cercignani–Lampis gas–surface interaction model." Physics of Fluids 7, no. 5 (1995): 1159-1161.
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Application: Simulating Beam Experiments
• PerformDSMCsimulationsofthemolecularbeamexperimentsofoxygenbeamonVitreousCarbonandFiberform – Murrayetal [8].
• Usedtoconstructafiniteratesurfaceoxidationmodelforcarbon.
8 Murray, V J., et al. "Inelastic and Reactive Scattering Dynamics of Hyperthermal O and O2 on Hot Vitreous Carbon Surfaces." The Journal of Physical Chemistry C 119.26 (2015): 14780-14796.
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Vitreous carbon
FiberForm®
SPI Supplies
100µm
25mm
Murray et al [1]
O:1875K
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Application: Vitreous Carbon Oxidation Model
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CO:1875K
O:1875K
CO:1875K
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Application: Vitreous Carbon Oxidation Model
Parallelization in DSMC with surface chemistry
• Particleonthesurfaceisnotstoredanymore(onlyitsinformation).
• Parallelizationbasedonthenumberof(gas-phase)particleswillnotworkinDSMC-SC
• TwoadditionalkernelsinDSMC-SC– GSandPSreactions.
• Move• Collide• GS(Gas-Surface)reactions• PS(Pure-Surface)reactions
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DSMC
DSMC-SC
Surfaceboundary
Newpartition
Oldpartition
Flowchart for DSMC-SC
Move
Collide PS
PSGSif(surf)
if(surf)
M+GS
C+PS
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Twostrategies
1. Keeptrackofthecomputertimetakenforeachcellforalengthoftime.Usethisinformationtopartitionthedomain.• Workswellforsteadyflows
2. Doapproximatecalculationofthecomputertimebasedontheinformationandthealgorithmsused.
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Parallelization in DSMC with surface chemistry
• tmove =O(np *nsteps){moving}+O(np *nsteps){boundary/surface/cellexitcheck}
• tGS =O(nsurf-elem *nsurf-coll *nGS-rxns)
• tcollide =O!.#∗&'(
)*{assumingtemperatureandcrosssectionsareconstant}
• tPS =O(nsurf-elem *nPS-rxns-occur *nPS-rxns)nPS-rxns-occur =+,
-./0(!.#)∑ 𝜈5&67859:
• 𝜈5α Rate(k,nad,order)
tC+PS =tcollide +tPS tM+GS =tmove +tGS
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Parallelization in DSMC with surface chemistry
Summary• A general, detailed, physics-based surface chemistry framework implemented in
SPARTA.
• Includes physical models with wide range of options and parameters to captureall/several experimental details.
• Capability to model various types of surface reactions accommodating userspecified reaction rates, surface properties and parameters.
Future Work• Further develop and implement parallelization strategies.
• Extension to ionization and plasma chemistry.
• Inclusion of internal energy scattering details.
Summary and Future Work
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• This work was performed under the Entry System Modeling Project (M. J.Wright Project Manager) at the NASA Game Changing Development (GCD)Program and supported by NASA Grant NNX15AU92A.
Acknowledgements
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Backup Slides
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Adsorption modeling
• Adsorption:directandindirectpathways.• DirectadsorptioncapturedusingtheLangmuirmodel.• Kisliuk model[4]usedtocapturetheindirectadsorptionpathway.• Keq isanadditionalparameter– Keq=0givestheLangmuirmodel.
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4 Kisliuk, P. "The sticking probabilities of gases chemisorbed on the surfaces of solids." Journal of Physics and Chemistry of Solids 3, no. 1-2 (1957): 95-101.
Eley-Rideal (ER) mechanism : A(s) + B à AB + (s)
Langmuir-Hinshelwood (LH) mechanism : A(s) + B(s) à AB + 2(s)
From: UCL Center for Cosmic Chemistry and Physics
Surface Reaction Mechanisms
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The Langmuir-Hinshelwood mechanism has two steps –
Based on time scale arguments 4 types of LH mechanisms can be defined
1. tf << τ td << τ - Prompt thermal mechanism
2. tf ~ τ td << τ - LH limited by formation3. tf << τ td ~ τ - LH limited by desorption4. tf ~ τ td ~ τ - LH limited by both desorption and formation
Timescaleofinterest=τ𝑂 𝑔 + 𝐶 𝑏 → 𝐶𝑂 𝑔 (3)
𝑂 𝑔 + 𝑠 → 𝑂 𝑠
𝐶𝑂 𝑠 → 𝐶𝑂 𝑔 + 𝑠 (2) − 𝑡+
𝑂 𝑠 + 𝐶 𝑏 → 𝐶𝑂 𝑠 1 − 𝑡G
FormationDesorption
Different Types of LH Mechanisms
𝑂 𝑠 – Reactant𝐶𝑂 𝑠 – Intermediate𝐶𝑂 𝑔 – Product
2331st Aug 2017 9th Ablation Workshop 2017