Soot Deposition

Posted: October 6th, 2015 in News

Updated Information Available

PyroSim 2018.2 now supports complex stoichiometry in the user interface. The post Complex Stoichiometry in PyroSim updates and replaces the contents of this post.

FDS can model the deposition of smoke and aerosols onto solid surfaces. Deposition cannot be defined using the Simple Chemistry model, instead, it requires the use of the Complex Stoichiometry framework. This post describes how to accomplish this using PyroSim.

As background, review the introduction to Complex Stoichiometry in Section 12.2 of the FDS User Guide. Then proceed to Section 12.4 and review the Special Topic: Aerosol Deposition. In this post, we will replicate the deposition reaction given in Section 12.4. We will base our model on the propane flame deposition model that you can download from the FDS Validation and Verification page. To do this:

  1. Go to http://firemodels.github.io/fds-smv/
  2. Click the View on GitHub button at the top of the page, and search the repository for propane_flame_deposition.
  3. Select the propane_flame_deposition.fds file, click Raw, and save the text file.

This FDS propane_flame_deposition.fds verification file is also listed below. The quantities related to the deposition reaction are highlighted in red. Our goal is to add this Complex Stoichiometry in PyroSim. We will:

  1. Create the model components not related to the reaction.
  2. Create the species that we will use in the reaction.
  3. Use the Additional Records option in PyroSim to define the deposition reaction.
Propane burner test case to check basic chemistry model and soot deposition

&HEAD CHID='propane_flame_deposition', TITLE='Verification of simple chemistry flame with soot deposition'/

&MESH IJK=10,10,20, XB=0.0,1.0,0.0,1.0,0.0,2.0 /

&TIME T_END=10.0, DT=0.01 /
&DUMP MASS_FILE=.TRUE., DT_DEVC=0.5, DT_MASS=0.5 /

&MISC SUPPRESSION=.FALSE.
      GRAVITATIONAL_DEPOSITION = .TRUE.
      THERMOPHORETIC_DEPOSITION = .TRUE.
      TURBULENT_DEPOSITION = .TRUE. /

&OBST XB = 0.3,0.7,0.3,0.7,0.0,0.10, SURF_IDS = 'BURNER','INERT','INERT' /
&SURF ID = 'BURNER', HRRPUA=625., RAMP_Q='fire'/

&RAMP ID='fire', T=0, F=0.0 /
&RAMP ID='fire', T=1, F=1.0 /
&RAMP ID='fire', T=4, F=1.0 /
&RAMP ID='fire', T=5, F=0.0 /

&SPEC ID = 'NITROGEN',        LUMPED_COMPONENT_ONLY = .TRUE. /
&SPEC ID = 'OXYGEN',          LUMPED_COMPONENT_ONLY = .TRUE. /
&SPEC ID = 'CARBON DIOXIDE',  LUMPED_COMPONENT_ONLY = .TRUE. /
&SPEC ID = 'WATER VAPOR',     LUMPED_COMPONENT_ONLY = .TRUE. /
&SPEC ID = 'PROPANE' /
&SPEC ID = 'SOOT', AEROSOL=.TRUE. /

&SPEC ID = 'AIR', SPEC_ID ='NITROGEN','OXYGEN',
      VOLUME_FRACTION = 3.7619,1.000, BACKGROUND = .TRUE. /
&SPEC ID = 'PRODUCTS', SPEC_ID ='NITROGEN','CARBON DIOXIDE','WATER VAPOR', 
      VOLUME_FRACTION = 18.10631,2.81813,3.98990/

&REAC FUEL = 'PROPANE', 
      SPEC_ID_NU = 'PROPANE','AIR','PRODUCTS','SOOT',
      NU=-1.,-4.81308,1,0.20208/

&SLCF PBY = 0.5, QUANTITY = 'TEMPERATURE' /
&SLCF PBY = 0.5, QUANTITY = 'HRRPUV' /

&BNDF QUANTITY='SURFACE DEPOSITION', SPEC_ID='SOOT' /

&DEVC XB=0,1,0,1,0,2, QUANTITY='SURFACE DEPOSITION', ID='depo', STATISTICS='SURFACE INTEGRAL', SPEC_ID='SOOT' /

&TAIL /

Our first step is to create a new model in PyroSim and define the model components not related to the reaction.

  1. Copy the first block of blue lines highlighted above and, on the Edit menu in PyroSim, click Paste. Click Yes to All to replace Simulation Parameters.
  2. Repeat and paste the two other blocks of blue lines.

Now we define the species that will be used in our reaction. We delete the species that we will not use or will redefine.

  1. On the Model menu, click Edit Species. Delete AIR, CARBON MONOXIDE, and PRODUCTS. Close the dialog.

Next, we edit the species. We will modify SOOT and add Propane, AIR, and PRODUCTS as species.

  1. On the Model menu, click Edit Species. Select SOOT and click the Advanced tab. In the Name type AEROSOL and in the Value type .TRUE. (include the starting and ending periods). Click Apply.
  2. In the Edit Species dialog, click New. Select Predefined and then select Propane. Click OK.
  3. In the Edit Species dialog, click New. Select Custom so that we can edit the composition and type the name AIR. Select Lumped and click OK. Now select by Volume and type the NITROGEN value as 3.7619 and the OXYGEN value as 1. Click the Advanced tab and in the Name type BACKGROUND and in the Value type .TRUE. (include the starting and ending periods). Click Apply. This has created a new species named AIR that consists only of nitrogen and oxygen.
  4. In the Edit Species dialog, click New. Select Custom so that we can edit the composition and type the name PRODUCTS. Select Lumped and click OK. Now select by Volume and type the CARBON DIOXIDE value as 2.81813, the NITROGEN value as 18.10631, and the WATER VAPOR value as 3.98990. Click OK to close the dialog.

At this time, you should have eight species.

Species in the model.
Species in the model.

By default, PyroSim only writes the species that are referenced by the reaction defined in PyroSim. In this case, we will write our own special reaction, so we need to force PyroSim to write the species we will reference. To do this:

  1. On the Model menu, click Edit Species.
  2. Now, select AIR, select the Advanced tab, click Always Write FDS Record, and click Apply.
  3. Repeat this for each species.
  4. Close the Edit Species dialog.

Complex Stoichiometry reactions are not supported directly in the PyroSim interface. Instead, we define the reaction in the Additional Records section of the input file. Note that we must have pre-calculated the stiochiometric coefficients of the reaction before defining the reaction.

  1. Click the Record View tab at the bottom of the display window.
  2. In the Additional Records section, paste the reaction listed below.
  3. Return to the 3D View.
&REAC FUEL = 'PROPANE', 
      SPEC_ID_NU = 'PROPANE','AIR','PRODUCTS','SOOT',
      NU=-1.,-4.81308,1,0.20208/

To finish the model:

  1. On the Output menu, click Boundary Quantities.
  2. Select [Species: SOOT] Surface Deposition and close the dialog.
  3. On the FDS menu, click Simulation Parameters.
  4. In the RECORD select MISC, in the Name type SUPPRESSION and in the Value type .FALSE. Click OK.

Now, run the model and display the results. Select Ignore in the Warning dialog, since we defined a reaction in the Additional Records section. After Smokeview starts:

  1. Right-click on the window and select Load/UnLoad->Boundary file->SOOT SURFACE DEPOSITION.
Soot deposition on surfaces.
Soot deposition on surfaces.

We have now completed this example and shown how we can define a Complex Stoichiometry reaction in PryoSim. The same approach can be used for other Complex Stoichiometry situations.

 

Edited 2016-01-04 to update to FDS 6.3.2 and PyroSim 2015.4.

Comments or Questions

This post was written by Daniel Swenson. For comments or questions, send email to support@thunderheadeng.com.