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Author Topic: No temperature rise behind wall  (Read 252 times)

Paul Hoondert

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No temperature rise behind wall
« on: February 03, 2023, 08:34:04 am »

Good afternoon,

My name is Paul Hoondert, and for a dissertation research in Fire Safety Engineering I am modelling facade test setups.

I have modelled a propane burner, where the temperature raises to around 1000 degrees.

The burner is placed in front of a back wall. I see on the temperature slice no temperature rise behind the wall, as shown in the figure.
The wall is modelled as a 20 mm wall of the material steel.

How is it possible that their is no temperature rise behind the wall?

I suppose I have the wrong settings for the wall. I have modelled the wall as layered.

! hope you could help me.

Kind Regards,

Paul Hoondert
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JordanBrown321

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Re: No temperature rise behind wall
« Reply #1 on: February 03, 2023, 06:09:16 pm »

Hi,
You must use the EXPOSED backing boundary condition for the layered surface. I believe it must also be 1 or 0 cells thick.
As seen in the attached figure.

Also look at this link, it will describe a little more about conduction in fds.
https://support.thunderheadeng.com/tutorials/pyrosim/heat-conduction/#:~:text=FDS%20assumes%20one%2Ddimensional%20heat,heat%20flows%20through%20the%20obstruction.

I have found there are some quirks when using conduction in FDS. I would consult the user guide for details.
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Paul Hoondert

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Re: No temperature rise behind wall
« Reply #2 on: February 06, 2023, 12:33:43 pm »

Dear Jordan,

Thanks a lot for your reply!

I have simulated the backwall as exposed, as described in the tutorial.
But this had not change the results. But I wasn't able to set the initial internal temperature the same as in the tutorial, as in the screenshot attached.

The wall is 1 cell in width (the wall is 20 mm, and my grid is 20 x 20 x 20 mm).




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JordanBrown321

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Re: No temperature rise behind wall
« Reply #3 on: February 06, 2023, 06:24:46 pm »

Strange, I was able to get it to work. I have attached an fds script you can try out and see. The two surface temperature devices show the transfer of heat.

Are both sides of the obstruction the same layered material?

untitled.fds
Generated by PyroSim - Version 2022.3.1208
6-Feb-2023 4:17:31 PM

&HEAD CHID='untitled'/
&TIME T_END=1000.0/
&DUMP DT_SL3D=0.25/

&MESH ID='Mesh01', IJK=10,10,10, XB=0.0,2.0,0.0,2.0,0.0,2.0/


&REAC ID='FDS6 PROPANE',
      FYI='FDS6 Predefined',
      FUEL='PROPANE'/

&DEVC ID='Front Surface Temp', QUANTITY='WALL TEMPERATURE', XYZ=1.0,1.0,1.0, IOR=3/
&DEVC ID='Rear Surface Temp', QUANTITY='WALL TEMPERATURE', XYZ=1.0,1.0,0.8, IOR=-3/

&MATL ID='STEEL',
      FYI='Drysdale, Intro to Fire Dynamics - ATF NIST Multi-Floor Validation',
      SPECIFIC_HEAT=0.46,
      CONDUCTIVITY=45.8,
      DENSITY=7850.0,
      EMISSIVITY=0.95/

&SURF ID='Steel',
      RGB=146,202,166,
      MATL_ID(1,1)='STEEL',
      MATL_MASS_FRACTION(1,1)=1.0,
      THICKNESS(1)=0.2/
&SURF ID='Burner',
      COLOR='RED',
      HRRPUA=1000.0,
      TMP_FRONT=300.0/

&OBST ID='Obstruction', XB=0.0,2.0,0.0,2.0,0.8,1.0, SURF_ID='Steel'/

&VENT ID='Mesh Vent: Mesh01 [XMAX]', SURF_ID='OPEN', XB=2.0,2.0,0.0,2.0,0.0,2.0/
&VENT ID='Mesh Vent: Mesh01 [XMIN]', SURF_ID='OPEN', XB=0.0,0.0,0.0,2.0,0.0,2.0/
&VENT ID='Mesh Vent: Mesh01 [YMAX]', SURF_ID='OPEN', XB=0.0,2.0,2.0,2.0,0.0,2.0/
&VENT ID='Mesh Vent: Mesh01 [YMIN]', SURF_ID='OPEN', XB=0.0,2.0,0.0,0.0,0.0,2.0/
&VENT ID='Mesh Vent: Mesh01 [ZMIN]', SURF_ID='OPEN', XB=0.0,2.0,0.0,2.0,0.0,0.0/
&VENT ID='Vent', SURF_ID='Burner', XB=0.0,2.0,0.0,2.0,2.0,2.0/

&SLCF QUANTITY='TEMPERATURE', ID='Slice', PBX=1.0/


&TAIL /
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Paul Hoondert

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Re: No temperature rise behind wall
« Reply #4 on: February 11, 2023, 06:59:46 am »

Hi Jordan,

Yes with the devices you suggested I found a (small) temperature rise. But I haven't simulated that long.
But it works now! Thanks for your help!
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