Canola Oil Pan Fire

Samuel Lam

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Nov 9, 2021, 10:34:47 AM11/9/21

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Hello, everyone!

I am trying to raise the temperature of a steel pan containing canola oil beyond its auto-ignition temperature, thence let it burn. I will then study how well various systems can suppress the canola oil fire.

My problem is that the temperature of the canola oil did not significantly rise, and thus could not be ignited.

I learnt from a thread from a few years ago that I can define the pan with a layered material, with canola oil on top of steel (SURF: 'Canola Oil and Pot Bottom'; OBST: 'Pot Bottom').

I also learnt that I can put an INTERNAL_HEAT_SOURCE to a material (SURF: Steel), or alternatively use a heater outside the pan to raise the temperature by conduction (SURF: Electric Heater; VENT: Cooker Top). I have put both in my file, but still there was only a slight temperature rise.

For the sake of simplicity in the discussion, I have taken out all DEVC from my code before pasting it below.

Would you please kindly advise what could have gone wrong. Thank you very much.

&HEAD CHID='12pan', TITLE='12pan'/

&TIME T_END=900.0, WALL_INCREMENT=10/

&DUMP COLUMN_DUMP_LIMIT=.TRUE., DT_RESTART=300.0, DT_SL3D=0.25/

&MISC Y_O2_INFTY=0.23, BAROCLINIC=.FALSE./

&MESH ID='Mesh01', IJK=30,30,25, XB=0.0,3.0,0.0,3.0,0.0,2.5/

&REAC ID='Canola Oil',

FUEL='REAC_FUEL',

FORMULA='C18H33O2',

AUTO_IGNITION_TEMPERATURE=280.0,

SOOT_YIELD=0.03,

HEAT_OF_COMBUSTION=4.145E4/

&MATL ID='Canola Oil',

SPECIFIC_HEAT=1.913,

CONDUCTIVITY=0.1835,

DENSITY=915.0,

HEAT_OF_COMBUSTION=3.852E4,

HEAT_OF_REACTION=0.0,

BOILING_TEMPERATURE=205.0/

&MATL ID='STEEL',

SPECIFIC_HEAT=0.46,

CONDUCTIVITY=45.8,

DENSITY=7850.0,

EMISSIVITY=1.0/

&SURF ID='Canola Oil and Pot Bottom',

RGB=204,204,0,

BACKING='VOID',

MATL_ID(1,1)='Canola Oil',

MATL_ID(2,1)='STEEL',

MATL_MASS_FRACTION(1,1)=1.0,

MATL_MASS_FRACTION(2,1)=1.0,

THICKNESS(1:2)=0.015,1.0E-3/

&SURF ID='Steel',

RGB=0,204,255,

BACKING='VOID',

MATL_ID(1,1)='STEEL',

MATL_MASS_FRACTION(1,1)=1.0,

THICKNESS(1)=1.0E-3,

GEOMETRY='CARTESIAN',

LENGTH=0.0,

WIDTH=0.0,

INTERNAL_HEAT_SOURCE=3000/

&SURF ID='Electric Heater',

RGB=255,102,0,

TMP_FRONT=400.0/

&OBST ID='Cooker', XB=1.41,1.59,2.66,2.84,0.77,0.869, SURF_ID='INERT'/

&OBST ID='Pot Bottom', XB=1.411,1.589,2.661,2.839,0.869,0.885, SURF_ID='Canola Oil and Pot Bottom'/

&OBST ID='Pot Wall', XB=1.41,1.411,2.66,2.84,0.869,0.999, RGB=0,204,204, SURF_ID='Steel'/

&OBST ID='Pot Wall', XB=1.589,1.59,2.66,2.84,0.869,0.999, RGB=0,204,204, SURF_ID='Steel'/

&OBST ID='Pot Wall', XB=1.411,1.589,2.66,2.661,0.869,0.999, RGB=0,204,204, SURF_ID='Steel'/

&OBST ID='Pot Wall', XB=1.411,1.589,2.839,2.84,0.869,0.999, RGB=0,204,204, SURF_ID='Steel'/

&VENT ID='Mesh Vent: Mesh01 [YMIN]', SURF_ID='OPEN', XB=0.0,3.0,0.0,0.0,0.0,2.5/

&VENT ID='Cooker Top', SURF_ID='Electric Heater', XB=1.41,1.59,2.66,2.84,0.869,0.869/

&TAIL /

Kevin McGrattan

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Nov 9, 2021, 11:26:18 AM11/9/21

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You cannot use OBSTs to create solid layers. Each OBST will just overwrite the previous one.

Message has been deleted

Samuel Lam

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Nov 10, 2021, 12:17:04 PM11/10/21

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Thank you Kevin for pointing this out. I have amended the file so that the bottom of the pot and the oil itself are now two OBST. I even added an INTERNAL_HEAT_SOURCE to the oil SURF. The major changes to the fire are hightlighted in red.

Yet, there is still only an insignificant temperature change. Would anyone please kindly advise?

&HEAD CHID='16pan', TITLE='16pan'/

&TIME T_END=900.0, WALL_INCREMENT=10/

&DUMP COLUMN_DUMP_LIMIT=.TRUE., DT_RESTART=300.0, DT_SL3D=0.25/

&MISC Y_O2_INFTY=0.23, BAROCLINIC=.FALSE./

&MESH ID='Mesh01', IJK=30,30,25, XB=0.0,3.0,0.0,3.0,0.0,2.5/

&REAC ID='Canola Oil',

FUEL='REAC_FUEL',

FORMULA='C18H33O2',

AUTO_IGNITION_TEMPERATURE=280.0,

SOOT_YIELD=0.03,

HEAT_OF_COMBUSTION=4.145E4/

&MATL ID='STEEL',

SPECIFIC_HEAT=0.46,

CONDUCTIVITY=45.8,

DENSITY=7850.0,

EMISSIVITY=1.0/

&MATL ID='Canola Oil',

SPECIFIC_HEAT=1.913,

CONDUCTIVITY=0.1835,

DENSITY=915.0,

HEAT_OF_COMBUSTION=3.852E4,

HEAT_OF_REACTION=0.0,

BOILING_TEMPERATURE=205.0/

&SURF ID='Steel',

RGB=0,204,255,

BACKING='VOID',

MATL_ID(1,1)='STEEL',

MATL_MASS_FRACTION(1,1)=1.0,

THICKNESS(1)=1.0E-3,

GEOMETRY='CARTESIAN',

LENGTH=0.0,

WIDTH=0.0/

&SURF ID='Canola Oil',

RGB=204,204,0,

BACKING='VOID',

MATL_ID(1,1)='Canola Oil',

MATL_MASS_FRACTION(1,1)=1.0,

THICKNESS(1)=0.015,

INTERNAL_HEAT_SOURCE=30000/

&SURF ID='Electric Heater',

RGB=255,102,0,

TMP_FRONT=4000.0/

&OBST ID='Cooker', XB=1.41,1.59,2.66,2.84,0.77,0.869, SURF_ID='INERT'/

&OBST ID='Pot Bottom', XB=1.411,1.589,2.661,2.839,0.869,0.87, SURF_ID='Steel'/

&OBST ID='Oil', XB=1.411,1.589,2.661,2.839,0.9,1.0, SURF_ID='Canola Oil'/

&OBST ID='Pot Wall', XB=1.41,1.411,2.66,2.84,0.869,0.999, RGB=0,204,204, SURF_ID='Steel'/

&OBST ID='Pot Wall', XB=1.589,1.59,2.66,2.84,0.869,0.999, RGB=0,204,204, SURF_ID='Steel'/

&OBST ID='Pot Wall', XB=1.411,1.589,2.66,2.661,0.869,0.999, RGB=0,204,204, SURF_ID='Steel'/

&OBST ID='Pot Wall', XB=1.411,1.589,2.839,2.84,0.869,0.999, RGB=0,204,204, SURF_ID='Steel'/

&VENT ID='Mesh Vent: Mesh01 [YMIN]', SURF_ID='OPEN', XB=0.0,3.0,0.0,0.0,0.0,2.5/

&VENT ID='Cooker Top', SURF_ID='Electric Heater', XB=1.41,1.59,2.66,2.84,0.869,0.869, IOR=3/

&SLCF QUANTITY='TEMPERATURE', PBX=1.5/

&SLCF QUANTITY='TEMPERATURE', PBZ=0.88/

&TAIL /

o...@aquacoustics.biz

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Nov 11, 2021, 2:43:12 AM11/11/21

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You might want to read Sect 11.3.3 of the Users Manual and consider what BACK='VOID' actually implements.

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o...@aquacoustics.biz

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Nov 14, 2021, 4:17:15 PM11/14/21

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While I could simply post some code that will represent your pan fire this would be a lost learning opportunity for you.

There are a few issues with your approach and with your model. If you have read Section 11.3.3 then you should understand that, with 1D heat transfer, you need a one cell air gap between obstructions.

This feature only works if the wall OBST is less than or equal to one mesh cell thick, and if there is a non-zero volume of computational domain on the other side of the wall OBST. Obviously, if the wall is an external boundary of the domain, the heat is lost to an ambient temperature void. The same happens if the back side gas cell cannot be found (i.e. the wall OBST is greater than one cell thick).

Your obstructions do not conform to the computational grid. This can result in all manner of problems. Some (the pot walls) reduce to zero thickness, while others are expanded over multiple cells. Note that the FDS calculation is confined to the mesh.

If you want a better approximation to actual heat transfer between the cooker, pot, oil and air then you might want to be using the 3D heat transfer model. Note that the oil will behave as a solid so you’re not going to get convective mass flow in the oil.

Arguably the best model building approach in FDS is to copy someone else’s code, study it to work out what it is actually doing, and gradually refine it to suit your purposes. A Google search on ‘FDS pan fire’ will give a raft of starting models using liquid fuel (ethanol).

If you do need to build a model from scratch then start simple and gradually introduce new features.

On Monday, 15 November 2021 at 04:36:33 UTC+13 sze...@gmail.com wrote:

Thank you for pointing that out for me. I have set the backing as "exposed" and still nothing happens to the oil.

Would you guys please kindly advise me further?

Thank you soooooo much!

Samuel Lam

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Nov 17, 2021, 3:59:34 PM11/17/21

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Thank you for your suggestions. I downloaded a ethanol pan fire from GitHub. That ethanol pan worked.

Then, modifying physical properties of ethanol to those of canola oil from that file, my canola oil still doesn't burn. Would you please have a quick look on my model below?

Thank you very much.

&HEAD CHID='Oil03Web', TITLE='Oil03'/

&TIME T_END=600.0/

&DUMP DT_DEVC=2.0, DT_HRR=2.0, DT_DEVC_LINE=50.0/

&MISC SIMULATION_MODE='LES'/

&RADI C_MIN=0.5/

&COMB N_SIMPLE_CHEMISTRY_REACTIONS=2, FUEL_H_TO_H2_FRACTION=0.5, RADIATIVE_FRACTION=0.2, FUEL_C_TO_CO_FRACTION=1.0/

&MESH ID='Mesh01', IJK=60,60,50, XB=0.0,3.0,0.0,3.0,0.0,2.5/

&SPEC ID='CANOLA OIL', FORMULA='C56.8H101.3O6'/

&REAC ID='Reaction1',

FUEL='CANOLA OIL',

C=56.8,

H=101.3,

O=6.0,

AUTO_IGNITION_TEMPERATURE=0.0,

SOOT_YIELD=0.1,

HEAT_OF_COMBUSTION=3.92E4/

&MATL ID='STEEL',

SPECIFIC_HEAT=0.465,

CONDUCTIVITY=54.0,

DENSITY=7800.0,

EMISSIVITY=0.8/

&MATL ID='CANOLA OIL LIQUID',

SPECIFIC_HEAT=1.91,

CONDUCTIVITY=0.161,

DENSITY=914.0,

HEAT_OF_REACTION=209.0,

SPEC_ID(1,1)='CANOLA OIL',

NU_SPEC(1,1)=1.0,

BOILING_TEMPERATURE=311.0/

&SURF ID='PAN',

COLOR='GRAY 50',

MATL_ID(1,1)='STEEL',

MATL_MASS_FRACTION(1,1)=1.0,

THICKNESS(1)=3.0E-3/

&SURF ID='POOL',

COLOR='LIGHT BLUE',

MATL_ID(1,1)='CANOLA OIL LIQUID',

MATL_MASS_FRACTION(1,1)=1.0,

THICKNESS(1)=0.05/

&OBST ID='Oil and Pan', XB=1.4,1.6,2.6,2.8,0.85,0.9, SURF_IDS='POOL','PAN','PAN'/

&VENT ID='Mesh Vent: Mesh01 [YMIN]', SURF_ID='OPEN', XB=0.0,3.0,0.0,0.0,0.0,2.5/

&BNDF QUANTITY='BURNING RATE'/

&BNDF QUANTITY='WALL TEMPERATURE'/

&BNDF QUANTITY='GAUGE HEAT FLUX'/

&SLCF QUANTITY='VELOCITY', VECTOR=.TRUE., PBX=1.5/

&SLCF QUANTITY='TEMPERATURE', CELL_CENTERED=.TRUE., PBX=1.5/

&SLCF QUANTITY='VOLUME FRACTION', SPEC_ID='WATER VAPOR', CELL_CENTERED=.TRUE., PBX=1.5/

&TAIL /

Kevin McGrattan

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Nov 17, 2021, 4:08:27 PM11/17/21

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There is a considerable difference between ethanol and cooking oil, wouldn't you say?

o...@aquacoustics.biz

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Nov 18, 2021, 3:47:41 AM11/18/21

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Read section 11.5.7 of the Users Guide. With liquid fuels the heat of reaction is the latent heat of vaporization. But your model has no heat source. So there isn't any fuel vapor and everything just sits there at 20°C.

As noted by Kevin, canola oil (rape seed oil) will not burn like a simple short chain hydrocarbon. I could not find a definitive reference for the latent heat of vaporization for canola oil, but given that this vegetable oil has a smoke point, thereafter exhibits a colour, change , and polymerization on cooling, it may actually undergo partial pyrolysis (like wood and many other natural products) as opposed to a simple vaporization phase change prior to combustion. Interestingly, canola oil is often used for seasoning steel and cast iron frying pans.

Getting back to your original intent - studying suppression of cooking oil fires - this will be very challenging for any CFD model, particularly using water mist or spray.

Would you mind emailing me directly at o...@aquacoustics.biz (taking this discussion off the group for now) and I will see if I can assist you with your understanding of FDS 1D conduction in layered material obstructions, and getting your oil to burn.

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