diffusion flame sustainability

[Kuswan Toro]

Hi to All
first, I want to thank you for all your work on the software and on this group

I want to simulate a fire on 3 vertical flat wood with distance 50mm between, the heat source is stationery particle with temperatur 1000 C position in between the plate.
After 60s i remove the heat source by specifiyng the age of that particle. I was expecting the fire would last but it is not. I have try to prolong the source but still the flame unable to sustain. Can someone enlight me

fds code:

&HEAD CHID='tes1'/
&TIME T_END=90.0/

&MESH ID='MESH01', IJK=16,16,20, XB=0.8,1.2,0.8,1.2,0.0,0.5/

&PART ID='ignitor',
      STATIC=.TRUE.,
      SURF_ID='hot',
      AGE=60.0/
 
&REAC ID='WOOD_PINE',
      FUEL='REAC_FUEL',
      C=1.0,
      H=1.7,
      O=0.83,
      CO_YIELD=0.005/
 
&DEVC ID='temp1', QUANTITY='WALL TEMPERATURE', XYZ=0.9,1.0,0.15, IOR=-1/
&DEVC ID='temp2', QUANTITY='WALL TEMPERATURE', XYZ=0.925,1.0,0.15, IOR=1/
&DEVC ID='temp3', QUANTITY='WALL TEMPERATURE', XYZ=0.975,1.0,0.15, IOR=-1/
&DEVC ID='temp4', QUANTITY='WALL TEMPERATURE', XYZ=1.0,1.0,0.15, IOR=1/
&DEVC ID='temp5', QUANTITY='WALL TEMPERATURE', XYZ=1.05,1.0,0.15, IOR=-1/
&DEVC ID='temp6', QUANTITY='WALL TEMPERATURE', XYZ=1.075,1.0,0.15, IOR=1/
 
&MATL ID='YELLOW PINE',
      SPECIFIC_HEAT=2.85,
      CONDUCTIVITY=0.14,
      DENSITY=640.0,
      HEAT_OF_COMBUSTION=2.1E4,
      N_REACTIONS=1,
      SPEC_ID(1,1)='REAC_FUEL',
      NU_SPEC(1,1)=1.0,
      REFERENCE_TEMPERATURE=350.0/
 
&SURF ID='wood',
      RGB=146.0,202.0,166.0,
      HEAT_TRANSFER_COEFFICIENT=0.0,
      BACKING='INSULATED',
      MATL_ID(1,1)='YELLOW PINE',
      MATL_MASS_FRACTION(1,1)=1.0,
      THICKNESS(1)=0.025/
&SURF ID='hot',
      RGB=255.0,0.0,51.0,
      TMP_FRONT=1000.0,
      GEOMETRY='SPHERICAL',
      RADIUS=0.001/
 
&INIT ID='Particle Cloud', PART_ID='ignitor', N_PARTICLES=100, XYZ=0.95,0.95,0.15/
&INIT ID='Particle Cloud', PART_ID='ignitor', N_PARTICLES=100, XYZ=1.025,0.95,0.15/
&INIT ID='Particle Cloud', PART_ID='ignitor', N_PARTICLES=100, XYZ=0.95,0.95,0.05/
&INIT ID='Particle Cloud', PART_ID='ignitor', N_PARTICLES=100, XYZ=1.025,0.95,0.05/
&INIT ID='Particle Cloud', PART_ID='ignitor', N_PARTICLES=100, XYZ=0.95,1.0,0.15/
&INIT ID='Particle Cloud', PART_ID='ignitor', N_PARTICLES=100, XYZ=1.025,1.0,0.15/
&INIT ID='Particle Cloud', PART_ID='ignitor', N_PARTICLES=100, XYZ=0.95,1.0,0.05/
&INIT ID='Particle Cloud', PART_ID='ignitor', N_PARTICLES=100, XYZ=1.025,1.0,0.05/
&INIT ID='Particle Cloud', PART_ID='ignitor', N_PARTICLES=100, XYZ=0.95,1.05,0.15/
&INIT ID='Particle Cloud', PART_ID='ignitor', N_PARTICLES=100, XYZ=1.025,1.05,0.15/
&INIT ID='Particle Cloud', PART_ID='ignitor', N_PARTICLES=100, XYZ=0.95,1.05,0.05/
&INIT ID='Particle Cloud', PART_ID='ignitor', N_PARTICLES=100, XYZ=1.025,1.05,0.05/
 
&OBST ID='Obstruction', XB=0.9,0.925,0.9,1.1,0.0,0.3, SURF_ID='wood'/
&OBST ID='Obstruction', XB=0.975,1.0,0.9,1.1,0.0,0.3, SURF_ID='wood'/
&OBST ID='Obstruction', XB=1.05,1.075,0.9,1.1,0.0,0.3, SURF_ID='wood'/
 
&VENT ID='Vent09', SURF_ID='OPEN', XB=0.8,1.2,0.8,1.2,0.5,0.5/
 
&BNDF QUANTITY='ADIABATIC SURFACE TEMPERATURE'/
&BNDF QUANTITY='BACK WALL TEMPERATURE'/
&BNDF QUANTITY='BURNING RATE'/
&BNDF QUANTITY='NET HEAT FLUX'/
&BNDF QUANTITY='HEAT TRANSFER COEFFICIENT'/
&BNDF QUANTITY='RADIATIVE HEAT FLUX'/
&BNDF QUANTITY='WALL TEMPERATURE'/
 
&SLCF QUANTITY='TEMPERATURE', PBY=1.0/

&TAIL /

[Salah Benkorichi]

You need sufficient heat to sustain your pyrolysis. Once your particles are disabled, then the flame itself isn't enough to keep the burning going with the characteristics of your materials. 

Where did you get REFERENCE_TEMPERATURE from? Do you have experiment work done on the same? Why don't you look for cone/FPA data to specify E,A,n 

Also, you should specify the HEAT_OF_COMBUSTION on your REAC line for your material. 

You should consider using EXTERNAL HEAT FLUX instead of particles. 

Refining your mesh, might improve it a bit, but I don't expect you would get the burning sustained with these setup. 

--
You received this message because you are subscribed to the Google Groups "FDS and Smokeview Discussions" group.
To unsubscribe from this group and stop receiving emails from it, send an email to fds-smv+unsubscribe@googlegroups.com.
To post to this group, send email to fds...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/fds-smv/32d98f60-6759-4d9d-b082-bb797ed4ff3b%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[Kevin]

Why would you do this

HEAT_TRANSFER_COEFFICIENT=0.0

if you want this object to burn?

Why this

BACKING='INSULATED' ?

Finally, you have specified a one step reaction for "wood" that is much more like a thermoplastic. Why have you done this?


[Kuswan Toro]

I get the reference temperature from a paper about TGA wood material,
I already try using external heat flux it is the same, Ok I will try your other sugestion and will update the result here. Thanks

[Kuswan Toro]

Hi Kevin Thanks for the reply,

that HEAT_TRANSFER_COEFFICIENT=0.0 actually trial and error because I see my Q_cond was high but I had try without one and its same. 

I was specified BACKING='INSULATED' because I need it too get hot and store heat, Yes I know thats a complex reaction but I had to simplified

To unsubscribe from this group and stop receiving emails from it, send an email to fds-smv+u...@googlegroups.com.

[Kuswan Toro]

Mr. Salah I manage it however it need to specified either HoC in the order of 10^5 kJ/kg or high pyrolysis rate or heat_transfer_coefficient > 1000 kW/m2 which is unrealistic. I think one approach is by specifying low thickness on the surf (which also mean dense grid) so it need lower heat flux to achieve sustainable pyrolysis but I can't prove it since didn't have the resource at the moment.

regards

Kuswantoro

To unsubscribe from this group and stop receiving emails from it, send an email to fds-smv+u...@googlegroups.com.

[Salah Benkorichi]

Well, you're not specifying what you want to do. 

Are you trying to study a physical phenomena or an imaginary case? If the former, then I would expect you have the setup of your case --otherwise, assumptions alone aren't good enough. --Even by tweaking parameters doesn't mean you're solving for the real physics. 

Specifying low thickness means reducing your initial mass. What's the mass of your samples? 

To unsubscribe from this group and stop receiving emails from it, send an email to fds-smv+unsubscribe@googlegroups.com.

To post to this group, send email to fds...@googlegroups.com.

To view this discussion on the web visit https://groups.google.com/d/msgid/fds-smv/dd9418df-d7d9-4965-953c-4227b297614a%40googlegroups.com.

[Salah Benkorichi]

Also, as Kevin noted, your wood material, you're only turning it into, plastic, I would expect there would be char product remaining as it wont burn all. So, you need to add that as well. Wood has been studied extensively in the past years. Check good work by Di Blasi 

http://www.sciencedirect.com/science/article/pii/S0360128507000214

Usually wood pyrolysis into three reactions --Cellulose, Hemicellulose, and Lignin. 

I don't see that in your case. 

[dr_jfloyd]

Each one of your 12 groups of particles has an energy output about equal to a cigarette lighter.  If you were to hold a cigarette lighter to a solid block of wood for one minute, would you expect combustion to be sustained when you remove the lighter? 

My guess is that the in depth wood temperature is still fairly cold at 60 s.  When the particles are removed, the heat loss to the cold interior reduces the surface temperature below the reference temperature. Keep your particles present for a longer period of time and/or increase their temperature.