Thin Liquid Film Modeling in OpenFOAM

Thin Liquid FilmModeling inOpenFOAMKarl MeredithJune 23, 2010

BackgroundFM Global◮ Commercial propertyinsurance◮ Water-based firesuppression (sprinklers)◮ Testing evaluates sprinklerprotection requirements◮ Reduce the number ofexperimental testsJune 23, 2010 Thin Liquid Film Modeling in OpenFOAM 2 / 21

Current Modeling FrameworkFireFOAM◮ http://code.google.com/p/firefoam-dev/◮ http://fmglobal.com/modeling◮ A new OpenFOAMbased solver◮ Components for firegrowth◮ Buoyancy◮ Turbulence (LES)◮ Combustion(Mixture fraction)◮ Soot/Radiation (FV)◮ Pyrolysis (1D)June 23, 2010 Thin Liquid Film Modeling in OpenFOAM 3 / 21

Missing ComponentsFire suppression modelsneed to be developed◮ Sprinkler SprayPatternation◮ Flame/Spray Interaction◮ Water Film TransportJune 23, 2010 Thin Liquid Film Modeling in OpenFOAM 4 / 21

Liquid-Film ScopeJune 23, 2010 Thin Liquid Film Modeling in OpenFOAM 5 / 21

Liquid-Film PhenomenaJune 23, 2010 Thin Liquid Film Modeling in OpenFOAM 6 / 21

Modeling Approach‘Thin-film’ assumptions1 wall-normal velocity is zero2 wall-tangential diffusion (momentum, energy) negligiblecompared to wall-normal diffusionResult: Transport equations can be integrated in wall-normal directionJune 23, 2010 Thin Liquid Film Modeling in OpenFOAM 7 / 21

Integrated Film-Transport EquationsContinuityMomentum∂ρδU∂t∂ρδ∂t + ∇ s · (ρδU) = S ρδ+ ∇ s · (ρδUU) = −δ∇ s p + S ρδUEnergy∂ρδh∂t+ ∇ s · (ρδUh) = S ρδhEquations implemented in conjuction with Andy Heather of OpenCFDJune 23, 2010 Thin Liquid Film Modeling in OpenFOAM 8 / 21

Source TermsPhase interactionsMassMomentumEnergyS ρδ = S ρδ,imp + S ρδ,splash + S ρδ,vap + S ρδ,abs + S ρδ,sepNormalTangentialp =p imp + p splash + p vap + p σ + p δ + p gS ρδU =τ g − τ w + τ mar + ρgδ + F θ+ S ρδU,imp + S ρδU,splash + S ρδU,sepS ρδh =q ′′g − q ′′ w + S ρδh,vap + S ρδh,rad+ S ρδh,imp + S ρδh,splash + S ρδh,sep + S ρδh,absJune 23, 2010 Thin Liquid Film Modeling in OpenFOAM 9 / 21

Momentum Source TermsJune 23, 2010 Thin Liquid Film Modeling in OpenFOAM 10 / 21

Solution in OpenFOAM◮ Extruded, 2.5D Mesh◮ Uses 3D FVoperations◮ Solution variablesmapped to/from gasphase mesh◮ Source terms handleinterfacial transport◮ Can be solve in’stand-alone’ modeJune 23, 2010 Thin Liquid Film Modeling in OpenFOAM 11 / 21

Implementation StatusCompletedimpingementcapillary pressurehydrostatic pressuregas-phase pressureshear stressthermocapillary stressgravity body forcecontact-angle forceconvective heat fluxPartialfilm separationconvective heat fluxPendingsplashingvaporization/boilingmass absorptionseparationratiative absorptionJune 23, 2010 Thin Liquid Film Modeling in OpenFOAM 12 / 21

VerificationComparison to Nusselt Solution( )δ= 3ν2 1/3Re (1/3 νg sin θincU=g sin θ inc 3) 1/3Re2/3 Re=δU/νJune 23, 2010 Thin Liquid Film Modeling in OpenFOAM 13 / 21

Flow over Vertical PlateJune 23, 2010 Thin Liquid Film Modeling in OpenFOAM 14 / 21

Flow over Vertical PlateAnimationJune 23, 2010 Thin Liquid Film Modeling in OpenFOAM 15 / 21

Film Transport over Boxes2x3x2 array◮ Spray injected from8x6 array of nozzles◮ Three waterapplication ratestestedJune 23, 2010 Thin Liquid Film Modeling in OpenFOAM 16 / 21

2x3x2 Array Results0.1 gpm/m 2 0.6 gpm/m 2June 23, 2010 Thin Liquid Film Modeling in OpenFOAM 17 / 21

Mass Flow Rate per TierJune 23, 2010 Thin Liquid Film Modeling in OpenFOAM 18 / 21

2x3x2 Array Animation0.1 gpm/ft 2June 23, 2010 Thin Liquid Film Modeling in OpenFOAM 19 / 21

2x3x2 Array Animation0.6 gpm/ft 2June 23, 2010 Thin Liquid Film Modeling in OpenFOAM 20 / 21

Summary◮ Fire-suppressionmodeling mustcapture filmtransport behavior◮ Thin film assumptionsimplifies tranportequations◮ Initial thin film modelimplemented inOpenFOAMJune 23, 2010 Thin Liquid Film Modeling in OpenFOAM 21 / 21