Materials and Surfaces¶

FDS material and surface namelists define thermal and combustion properties of boundaries.

Overview¶

Materials and surfaces in FDS control:

Heat transfer: Convection, radiation, conduction
Combustion: Pyrolysis, burning rates
Thermal properties: Conductivity, specific heat, density
Boundary conditions: Heat flux, temperature

SURF - Surface Properties¶

The SURF namelist defines boundary conditions and material properties.

Basic Thermal Properties¶

from pyfds import Surface

# Simple surface with heat release
fire = Surface(
    id='FIRE',
    hrrpua=500.0,  # Heat release rate per unit area [kW/m²]
    tmp_front=800.0  # Surface temperature [°C]
)

# Inert surface
wall = Surface(
    id='WALL',
    emissivity=0.9,
    tmp_front=20.0
)

Multi-Layer Materials¶

# Multi-layer wall
wall = Surface(
    id='INSULATED_WALL',
    matl_id=['GYPSUM', 'INSULATION', 'GYPSUM'],  # Layer materials
    thickness=[0.013, 0.089, 0.013],             # Layer thicknesses [m]
    matl_mass_fraction=[[1.0], [1.0], [1.0]]     # Mass fractions
)

Advanced Heat Transfer¶

# Surface with 3D heat conduction
thermal_surface = Surface(
    id='THERMAL_WALL',
    matl_id='CONCRETE',
    thickness=0.2,
    ht3d=True,  # Enable 3D heat conduction
    tmp_inner=20.0  # Initial interior temperature
)

# Custom convection
custom_ht = Surface(
    id='CUSTOM_CONVECTION',
    heat_transfer_coefficient=10.0,  # Fixed HTC [W/(m²·K)]
    heat_transfer_model='LOGLAW'     # Heat transfer correlation
)

Thermal Boundary Conditions¶

# Fixed temperature back surface
insulated = Surface(
    id='INSULATED',
    tmp_back=20.0,  # Fixed back temperature
    adiabatic=False
)

# Adiabatic surface (no heat transfer)
adiabatic = Surface(
    id='ADIABATIC',
    adiabatic=True
)

Time-Varying Conditions¶

# Time-varying heat flux
transient = Surface(
    id='TRANSIENT_HEAT',
    ramp_ef='HEAT_RAMP'  # External flux ramp
)

# Temperature profile
temp_profile = Surface(
    id='TEMP_PROFILE',
    ramp_t='TEMPERATURE_RAMP'
)

MATL - Material Definitions¶

The MATL namelist defines bulk material properties for pyrolysis and thermal response.

Simple Materials¶

from pyfds import Material

# Basic thermal material
steel = Material(
    id='STEEL',
    density=7850.0,        # [kg/m³]
    thermal_conductivity=45.0,  # [W/(m·K)]
    specific_heat=0.46,    # [kJ/(kg·K)]
    emissivity=0.9
)

# Insulating material
insulation = Material(
    id='INSULATION',
    density=50.0,
    thermal_conductivity=0.04,
    specific_heat=1.2,
    emissivity=0.9
)

Pyrolysis Materials¶

# Single-step pyrolysis
wood = Material(
    id='WOOD',
    density=500.0,
    thermal_conductivity=0.12,
    specific_heat=2.5,
    # Pyrolysis reaction
    a=1e10,        # Pre-exponential factor [1/s]
    e=150000.0,    # Activation energy [J/mol]
    nu_matl=1.0,   # Stoichiometric coefficient
    matl_id='CHAR' # Residue material
)

# Multi-step pyrolysis
polymer = Material(
    id='POLYMER',
    density=1200.0,
    thermal_conductivity=0.25,
    specific_heat=1.5,
    # Multiple reactions
    a=[1e12, 5e8],
    e=[180000.0, 120000.0],
    nu_matl=[0.3, 0.7],
    matl_id=['VOLATILES', 'CHAR'],
    nu_spec=[1.0, 0.5],      # Gas yields
    spec_id=['FUEL', 'CO']
)

Structured Pyrolysis API¶

pyfds provides a structured API for defining pyrolysis reactions that is cleaner and less error-prone than using parallel arrays.

PyrolysisReaction Class¶

The PyrolysisReaction class represents a single decomposition reaction with validation for kinetic parameters and product yields.

from pyfds.core.models import PyrolysisReaction, PyrolysisProduct

# Arrhenius kinetics with gas and char products
reaction = PyrolysisReaction(
    a=1e10,                    # Pre-exponential factor [1/s]
    e=100000,                  # Activation energy [kJ/kmol]
    heat_of_reaction=500,      # Endothermic [kJ/kg]
    products=[
        PyrolysisProduct(spec_id="FUEL_GAS", nu_spec=0.8),
        PyrolysisProduct(matl_id="CHAR", nu_matl=0.2),
    ]
)

# Simplified kinetics with reference temperature
reaction = PyrolysisReaction(
    reference_temperature=350,  # Peak temperature [°C]
    pyrolysis_range=80,        # Temperature width [°C]
    heat_of_reaction=1000,
    products=[
        PyrolysisProduct(spec_id="WOOD_GAS", nu_spec=0.75),
        PyrolysisProduct(matl_id="CHAR", nu_matl=0.25),
    ]
)

Using with Material Class¶

You can use PyrolysisReaction directly with the Material class:

from pyfds.core.models import PyrolysisReaction, PyrolysisProduct
from pyfds.core.namelists import Material

material = Material(
    id="WOOD",
    density=500,
    conductivity=0.13,
    specific_heat=2.5,
    reactions=[
        PyrolysisReaction(
            reference_temperature=350,
            heat_of_reaction=500,
            products=[
                PyrolysisProduct(spec_id="WOOD_GAS", nu_spec=0.75),
                PyrolysisProduct(matl_id="CHAR", nu_matl=0.25),
            ]
        )
    ]
)

Note: The reactions list provides structured pyrolysis modeling with full validation. Use PyrolysisReaction objects to define reaction kinetics and products.

Advanced Material Properties¶

# Material with oxidation
steel_oxidizing = Material(
    id='STEEL_OXIDIZING',
    density=7850.0,
    thermal_conductivity=45.0,
    specific_heat=0.46,
    # Oxidation
    surface_oxidation_model=True,
    nu_o2=1.0,      # Oxygen consumption
    nu_h2o=0.5      # Water production
)

# Temperature-dependent properties
temp_dependent = Material(
    id='TEMP_DEPENDENT',
    density=1000.0,
    # Temperature-dependent conductivity
    thermal_conductivity_ramp='K_RAMP',
    specific_heat_ramp='CP_RAMP'
)

Integration Examples¶

Complete Wall Assembly¶

from pyfds import Surface, Material

# Define materials
gypsum = Material(
    id='GYPSUM',
    density=800.0,
    thermal_conductivity=0.16,
    specific_heat=1.0
)

insulation = Material(
    id='INSULATION',
    density=50.0,
    thermal_conductivity=0.04,
    specific_heat=1.2
)

# Create surface with layers
wall = Surface(
    id='WALL_ASSEMBLY',
    matl_id=['GYPSUM', 'INSULATION', 'GYPSUM'],
    thickness=[0.013, 0.089, 0.013],
    ht3d=True  # Enable 3D conduction
)

Burning Object¶

from pyfds import Surface, Material

# Fuel material
fuel = Material(
    id='FUEL',
    density=400.0,
    thermal_conductivity=0.1,
    specific_heat=2.0,
    # Pyrolysis
    a=1e8,
    e=100000.0,
    nu_matl=1.0,
    spec_id='PROPANE',
    nu_spec=1.0
)

# Burning surface
burner = Surface(
    id='BURNER',
    matl_id='FUEL',
    thickness=0.05,
    hrrpua=300.0,
    tmp_front=400.0
)

Insulated Structure¶

# Steel structure with insulation
steel = Material(id='STEEL', density=7850, thermal_conductivity=45, specific_heat=0.46)
mineral_wool = Material(id='MINERAL_WOOL', density=130, thermal_conductivity=0.04, specific_heat=0.8)

insulated_steel = Surface(
    id='INSULATED_STEEL',
    matl_id=['STEEL', 'MINERAL_WOOL'],
    thickness=[0.005, 0.05],  # 5mm steel, 50mm insulation
    tmp_back=20.0,            # Fixed back temperature
    ht3d=True
)

Parameter Reference¶

SURF Parameters¶

Basic Properties¶

Parameter	Description	Units	Default
`id`	Surface identifier	-	Required
`rgb`	RGB color	0-255	-
`color`	Named color	-	-
`transparency`	Transparency	0-1	1.0

Heat Release¶

Parameter	Description	Units	Default
`hrrpua`	Heat release rate per unit area	kW/m²	0.0
`tmp_front`	Front surface temperature	°C	20.0
`tmp_front_initial`	Initial front temperature	°C	-

Heat Transfer¶

Parameter	Description	Units	Default
`emissivity`	Surface emissivity	-	0.9
`emissivity_back`	Back surface emissivity	-	-
`adiabatic`	Adiabatic surface	-	False
`heat_transfer_coefficient`	Fixed HTC	W/(m²·K)	-
`heat_transfer_model`	HTC model	-	-

Material Layers¶

Parameter	Description	Units	Default
`matl_id`	Material IDs	-	-
`thickness`	Layer thicknesses	m	-
`matl_mass_fraction`	Mass fractions	-	-

Advanced Thermal¶

Parameter	Description	Units	Default
`ht3d`	3D heat conduction	-	False
`tmp_inner`	Initial interior temperature	°C	-
`tmp_back`	Fixed back temperature	°C	-

MATL Parameters¶

Basic Properties¶

Parameter	Description	Units	Default
`id`	Material identifier	-	Required
`density`	Material density	kg/m³	Required
`thermal_conductivity`	Thermal conductivity	W/(m·K)	Required
`specific_heat`	Specific heat capacity	kJ/(kg·K)	Required
`emissivity`	Surface emissivity	-	0.9

Pyrolysis¶

Parameter	Description	Units	Default
`a`	Pre-exponential factor	1/s	-
`e`	Activation energy	J/mol	-
`nu_matl`	Material stoichiometric coeff	-	-
`matl_id`	Residue material	-	-
`spec_id`	Gas species	-	-
`nu_spec`	Gas stoichiometric coeff	-	-

Advanced¶

Parameter	Description	Units	Default
`surface_oxidation_model`	Enable oxidation	-	False
`thermal_conductivity_ramp`	Temperature-dependent k	-	-
`specific_heat_ramp`	Temperature-dependent Cp	-	-

Materials and Surfaces¶

Overview¶

SURF - Surface Properties¶

Basic Thermal Properties¶

Multi-Layer Materials¶

Advanced Heat Transfer¶

Thermal Boundary Conditions¶

Time-Varying Conditions¶

MATL - Material Definitions¶

Simple Materials¶

Pyrolysis Materials¶

Structured Pyrolysis API¶

PyrolysisReaction Class¶

Using with Material Class¶

Advanced Material Properties¶

Integration Examples¶

Complete Wall Assembly¶

Burning Object¶

Insulated Structure¶

Parameter Reference¶

SURF Parameters¶

Basic Properties¶

Heat Release¶

Heat Transfer¶

Material Layers¶

Advanced Thermal¶

MATL Parameters¶

Basic Properties¶

Pyrolysis¶

Advanced¶

See Also¶