Development of 3D Heat Transfer and Pyrolysis in FDS Randall McDermott 1 , Chao Zhang 1 , Morgan Bruns 2 , Salah Benkorichi 3 1 National Institute of Standards and Technology, Gaithersburg, Maryland, USA 2 Virginia Military Institute, Lexington, Virginia, USA 3 Omega Fire Engineering Ltd., Manchester, UK Fire and Evacuation Modeling Technical Conference 2018 Oct 1-3, Gaithersburg, Maryland
Background and Motivation • Structural analysis • Lateral and downward flame spread • Smoldering combustion Choe, 2017 Ohlemiller & Shields, 2008 Huang et al., 2016 FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 2
Previous Work • Andreas Vischer, Aachen, 2009 thesis • Volker Hohm and Matthias Siemon, Building Materials, Solid Construction and Fire Protection (iBMB) at Technische Universtät Braunschweig • Gpyro, Chris Lautenberger, Reax Engineering • Thermakin, Stas Stoliarov, U. Maryland FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 3
Integration into FDS master TEMPERATURE SLICE FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 4
Governing Equations Local deformation affects heat flux FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 5
Computing Heat Flux Fourier’s law: FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 6
Input Parameters HT3D=T invokes 2-way coupling with gas phase FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 7
Heat Diffusion in Steel I-Beam Any mention of commercial products within this paper is for information only; it does not imply recommendation or endorsement by NIST. FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 8
Internal Heating in Sphere • Constant, uniform internal heat generation • Constant, ambient surface temperature FDS6.7.0-515-g7416f3a-master 60 50 C) Temperature ( ° Analytical FDS t =10 s FDS t =20 s 40 FDS t =60 s FDS t =120 s FDS t =180 s 30 20 0 0.02 0.04 0.06 0.08 0.1 Radial Distance (m) FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 9
Density Definitions 1. Material 2. Bulk 3. Total solid FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 10
Modeling Deformation • Changes in composition generally cause contraction or expansion of material • Some challenges in 3D: 1. Mechanical constitutive relation 2. Advection term in conservation equations 3. Moving boundaries • Simple solution: 1. Subgrid scale models of fluxes 2. Burn away — remove solid cells as cell density goes to zero FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 11
Heat Flux with Local Deformation • As material contracts (expands), distance between material points decreases (increases) FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 12
Local Material Deformation Two simple models: 1. Isotropic: 2. Unidirectional: FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 13
Compute new Compute solid Compute heat Compute new densities fluxes on temperatures volumes using old solid volumes using heat using new temperatures densities fluxes FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 14
PMMA Slab: Mass Loss Rate and Thickness FDS6.7.0-515-g7416f3a-master 0.04 3D Pyrolysis (pyro3d_vs_pyro1d) 0.03 MLRPUA (kg/s/m 2 ) 0.02 0.01 PYRO1D (no burn away) PYRO3D (burn away) 0 0 100 200 300 400 500 600 Time (s) FDS6.7.0-515-g7416f3a-master 0.012 3D Pyrolysis (pyro3d_vs_pyro1d) 0.01 Thickness (m) 0.008 0.006 0.004 0.002 PYRO1D (no burn away) PYRO3D (burn away) 0 FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 15 0 100 200 300 400 500 600 Time (s)
Radiative Heat Transfer • Many problems are thermally thick • Diffusion approximation is extremely efficient in 3D Material Absorption Coefficient (1/m) Thermal Thickness for 1 cm slab HDPE 1300 13 PMMA 2700 27 PA66 3920 39.2 FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 16
Radiation Verification FDS6.7.0-610-g8606b24-master 800 HT3D Internal Radiation (ht3d_radiation) 600 C) Temperature ( ° 400 Exact =100 1/m FDS =100 1/m Nx =10 FDS =100 1/m Nx =20 FDS =100 1/m Nx =40 200 Exact =2000 1/m FDS =2000 1/m Nx =10 FDS =2000 1/m Nx =20 Exact solution from Modest, FDS =2000 1/m Nx =40 0 Radiative Heat Transfer, 2 nd 0 0.02 0.04 0.06 0.08 0.1 Edition. x (m) FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 17
Pyrolysis Gas Transport ? FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 18
3D Model 1D Model Burn Away • 40 cm cubes • Low density “foam” • Compartment walls at 1100 °C FDS6.7.0-534-g33dc811-master 1.5 Pyrolyzed Mass (box_burn_away1) 1 Mass (kg) 0.5 Ideal PYRO1D (fuel) PYRO3D (fuel) PYRO3D w/ transport (fuel) 0 0 5 10 15 20 25 30 Time (s) FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 19
Solid Sub-Surface Heat Flux Model FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 20
Closing remarks • Development of an efficient 3D pyrolysis model is needed for reliable predictions of flame spread (work in progress) • Subgrid-scale models of heat and mass fluxes were used to account for local deformation • The resultant model has been verified and tested for several scenarios • Next steps: • Anisotropy • Thin obstructions (coupling with 1D model?) • Porous media flow FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 21
Acknowledgements • FDS development team • Simo Hostikka, Deepak Paudel FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 22
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