Combustion of walls covered with a water film

Update: January 18, 2018
OpenFOAM 4.x

Case directory

$FOAM_TUTORIALS/combustion/fireFoam/les/flameSpreadWaterSuppressionPanel

Summary

Propane flows in from the region "inlet" (red), a part of the floor of the air-filled domain, and burns. The wall on the side of the combustion area (green) is combustible, but a film of water is poured on the surface to prevent it from burning. The other surfaces except the combustible wall and floor are assumed to be open, and calculations are made for 10 seconds after ignition.

Model geometry Model geometry

The combustible wall, water film, and empty space are calculated separately, and the whole phenomenon is calculated by mapping the solutions.

The chemical species, propane and air, in the empty space and combustion reactions are defined in the file "reactions" in the directory "constant" as follows. The properties of each chemical species are defined in the file "thermo.compressibleGas" in the same directory.

species
(
    O2
    H2O
    C3H8
    CO2
    N2
);
reactions
{
    propaneReaction
    {
        type irreversibleinfiniteReaction;
        reaction     "C3H8 + 5O2 + 18.8N2 = 3CO2 + 4H2O + 18.8N2";
    }
}

These two files, "reactions" and "thermo.compressibleGas", are imported in the file "thermophysicalProperties" in the directory "constant" to do the configuration.

Also the file "pyrolysisZones" in the directory "constant" defines combustible walls, and the file "surfaceFilmProperties" defines thin films of water.

The material of the walls and the combustion reactions are defined in the file "reactions" in the directory "constant/pyrolysisRegion" as follows. We can see that the wall material (wood) is burning and turning into charcoal (char) and gas.

species
(
    wood
    char
);
gaseousSpecies
(
    gas
);
reactions
{
    charReaction
    {
        type        irreversibleArrheniusSolidReaction;
        reaction    "wood^4.86 = char + gas";
        A           7.83e10;
        Ta          15274.57;
        Tcrit       400;
    }
}

The meshes are as follows.

Mesh Meshes
Meshes of combustible wall (thin 8 layers is combustible wall) Meshes of combustible wall (thin 8 layers is combustible wall)

The calculation result is as follows. Volume rendering is used to draw the distribution of CO2.

CO2 at 1 sec (CO2) CO2 at 1 sec (CO2)
CO2 at 2 sec (CO2) CO2 at 2 sec (CO2)
CO2 at 3 sec (CO2) CO2 at 3 sec (CO2)
CO2 at 5 sec (CO2) CO2 at 5 sec (CO2)
CO2 at 10 sec (CO2) CO2 at 10 sec (CO2)

The temperature on the combustible wall is shown below. We can see that the temperature rises upon ignition, but gradually decreases due to the thin film of water.

Temperature at 1 sec (T) Temperature at 1 sec (T)
Temperature at 2 sec (T) Temperature at 2 sec (T)
Temperature at 3 sec (T) Temperature at 3 sec (T)
Temperature at 5 sec (T) Temperature at 5 sec (T)
Temperature at 10 sec (T) Temperature at 10 sec (T)

The volume fraction of the material on the combustible wall at the final time is shown below. It can be seen that the volume fraction is decreasing in the center of the region where the combustion is intense.

Volume fraction at 10 sec (wood) Volume fraction at 10 sec (wood)

Commands

cp -r $FOAM_TUTORIALS/combustion/fireFoam/les/flameSpreadWaterSuppressionPanel flameSpreadWaterSuppressionPanel
cd flameSpreadWaterSuppressionPanel

# Make base meshes blockMesh

# Make a propane inflow region topoSet
createPatch -overwrite

# Make meshes for water film by extruding
extrudeToRegionMesh -dict system/extrudeToRegionMeshDictFilm -overwrite

# Make meshes for combustible wall by extruding
rm log.extrudeToRegionMesh
extrudeToRegionMesh -dict system/extrudeToRegionMeshDictPyr -overwrite

# Make the region from meshes for water film
changeDictionary -region filmRegion -constant
rm log.topoSet
topoSet -region filmRegion
rm log.createPatch
createPatch -region filmRegion -overwrite

cp 0/ph_rgh.orig 0/ph_rgh

fireFoam

paraFoam -touchAll

# if you want to read combustible wall and water film, use -region option
paraFoam
paraFoam -region pyrolysisRegion
paraFoam -region filmRegion

Calculation time

4 minutes 46.04 seconds *Single, Inter(R) Core(TM) i7-2600 CPU @ 3.40GHz 3.40GHz