Development of 3D Heat Transfer and Pyrolysis in FDS Randall - - PowerPoint PPT Presentation

▶

Feb 18, 2023 7 likes •229 views

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,

SLIDE 1

Development of 3D Heat Transfer and Pyrolysis in FDS

Randall McDermott1, Chao Zhang1, Morgan Bruns2, Salah Benkorichi3

1National Institute of Standards and Technology, Gaithersburg, Maryland, USA 2Virginia Military Institute, Lexington, Virginia, USA 3Omega Fire Engineering Ltd., Manchester, UK

Fire and Evacuation Modeling Technical Conference 2018 Oct 1-3, Gaithersburg, Maryland

SLIDE 2

Background and Motivation

Structural analysis
Lateral and downward flame spread
Smoldering combustion

FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 2 Ohlemiller & Shields, 2008 Choe, 2017 Huang et al., 2016

SLIDE 3

Previous Work

FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 3

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

SLIDE 4

Integration into FDS master

FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 4

TEMPERATURE SLICE

SLIDE 5

Governing Equations

FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 5

Local deformation affects heat flux

SLIDE 6

Computing Heat Flux

Fourier’s law:

FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 6

SLIDE 7

Input Parameters

FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 7

HT3D=T invokes 2-way coupling with gas phase

SLIDE 8

Heat Diffusion in Steel I-Beam

FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 8 Any mention of commercial products within this paper is for information

nly; it does not imply recommendation or endorsement by NIST.

SLIDE 9

Internal Heating in Sphere

FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 9

Constant, uniform internal

heat generation

Constant, ambient surface

temperature

0.02 0.04 0.06 0.08 0.1 Radial Distance (m) 20 30 40 50 60 Temperature (° C)

FDS6.7.0-515-g7416f3a-master

Analytical FDS t=10 s FDS t=20 s FDS t=60 s FDS t=120 s FDS t=180 s

SLIDE 10

Density Definitions

1. Material
2. Bulk
3. Total solid

FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 10

SLIDE 11

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

SLIDE 12

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

SLIDE 13

Local Material Deformation

Two simple models:

1. Isotropic:
2. Unidirectional:

FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 13

SLIDE 14

Compute new densities using old temperatures Compute solid volumes using new densities Compute new temperatures using heat fluxes Compute heat fluxes on solid volumes

FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 14

SLIDE 15

PMMA Slab: Mass Loss Rate and Thickness

100 200 300 400 500 600 Time (s) 0.01 0.02 0.03 0.04 MLRPUA (kg/s/m2) 3D Pyrolysis (pyro3d_vs_pyro1d)

FDS6.7.0-515-g7416f3a-master

PYRO1D (no burn away) PYRO3D (burn away)

FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 15

100 200 300 400 500 600 Time (s) 0.002 0.004 0.006 0.008 0.01 0.012 Thickness (m) 3D Pyrolysis (pyro3d_vs_pyro1d)

FDS6.7.0-515-g7416f3a-master

PYRO1D (no burn away) PYRO3D (burn away)

SLIDE 16

Radiative Heat Transfer

Many problems are

thermally thick

Diffusion approximation

is extremely efficient in 3D

FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 16

Material Absorption Coefficient (1/m) Thermal Thickness for 1 cm slab HDPE 1300 13 PMMA 2700 27 PA66 3920 39.2

SLIDE 17

Radiation Verification

FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 17

Exact solution from Modest, Radiative Heat Transfer, 2nd Edition.

0.02 0.04 0.06 0.08 0.1

x (m)

200 400 600 800

Temperature (° C)

HT3D Internal Radiation (ht3d_radiation)

FDS6.7.0-610-g8606b24-master

Exact =100 1/m FDS =100 1/m Nx=10 FDS =100 1/m Nx=20 FDS =100 1/m Nx=40 Exact =2000 1/m FDS =2000 1/m Nx=10 FDS =2000 1/m Nx=20 FDS =2000 1/m Nx=40

SLIDE 18

Pyrolysis Gas Transport

FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 18

?

SLIDE 19

Burn Away

40 cm cubes
Low density “foam”
Compartment walls

at 1100 °C

FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 19

3D Model 1D Model

5 10 15 20 25 30

Time (s)

0.5 1 1.5

Mass (kg)

Pyrolyzed Mass (box_burn_away1)

FDS6.7.0-534-g33dc811-master

Ideal PYRO1D (fuel) PYRO3D (fuel) PYRO3D w/ transport (fuel)

SLIDE 20

Solid Sub-Surface Heat Flux Model

FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 20

SLIDE 21

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

SLIDE 22

Acknowledgements

FDS development team
Simo Hostikka, Deepak Paudel

FEMTC 2018 3D Heat Transfer and Pyrolysis in FDS 22