Transport of Diluted Species in Porous Media Interface
During the Generate Space-Dependent Model procedure several feature nodes were added along with the new physics interfaces. Now go through these features one by one and enter settings, and make sure that they are assigned to the proper domains and boundaries in the geometry.
1
In the Model Builder window, under Monolith Reactor Model click Transport of Diluted Species in Porous Media.
2
In the Settings window for Transport of Diluted Species in Porous Media, locate the Domain Selection section.
3
From the Selection list, choose Porous and Free Flow Domains.
The fluid will be modeled as compressible. This setting is available in the Laminar Flow interface. This means that the mass conservation equation should be of the conservative form. Choose this form from the Advanced Settings section in the mass transfer interface’s settings window.
1
Click the Show More Options button in the Model Builder toolbar.
2
In the Show More Options dialog, in the tree, select the checkbox for the node Physics > Advanced Physics Options.
3
Click OK.
4
In the Settings window for Transport of Diluted Species in Porous Media, click to expand the Advanced Settings section.
5
From the Material balance form list, choose Conservative.
Porous Medium
In the Model Builder window, expand the Transport of Diluted Species in Porous Media node.
Fluid
The mass transport model for the monolith channels assumes that there is only diffusive mass transport in the axial direction of the reactor, here along the z-axis. This can be accomplished by specifying the diffusivity only in the first element of the diagonal diffusion matrix. This may be difficult to converge though, and a more robust alternative is to set the radial diffusivity to a very low value.
1
In the Model Builder window, expand the Porous Medium 1 node, then click Fluid 1.
2
In the Settings window for Fluid, locate the Diffusion section.
3
From the Source list, choose Material.
4
From the Fluid material list, choose Gas: Nitrogen Solvent.
For each species, change from Isotropic to Diagonal, for the Fluid diffusion coefficient.
5
From the list, choose Diagonal.
6
Specify the DF,cH2O matrix as
pp1mat1.df5.D11*0.0001
0
0
pp1mat1.df5.D11
7
From the list, choose Diagonal.
8
Specify the DF,cNH3 matrix as
pp1mat1.df1.D11*0.0001
0
0
pp1mat1.df1.D11
9
From the list, choose Diagonal.
10
Specify the DF,cNO matrix as
pp1mat1.df2.D11*0.0001
0
0
pp1mat1.df2.D11
11
From the list, choose Diagonal.
12
Specify the DF,cNO2 matrix as
pp1mat1.df3.D11*0.0001
0
0
pp1mat1.df3.D11
13
From the list, choose Diagonal.
14
Specify the DF,cO2 matrix as
pp1mat1.df4.D11*0.0001
0
0
pp1mat1.df4.D11
The entered expressions were set up by the Generate Material wizard and they can be found under the Global Definitions > Materials > Gas: Nitrogen node. D11 represents the zz-component in the diffusivity matrix.
Porous Matrix 1
The porosity is by default defined by the Porous Material node.
Initial Values 1
This model is highly nonlinear due to the reaction kinetics. In this case, starting from a nonreacting system leads to a more robust simulation. To achieve this set the initial concentration to zero.
In addition to the default feature nodes, the nodes Reactions 1, Inflow 1 and Outflow 1 were also added during the Generate Space-Dependent Model procedure. The Reaction feature gets input from the first Chemistry interface in the component. The inflow and outflow features’ icons are marked with the warning sign in the Model Builder window. The warning message, seen when placing the mouse pointer on top of the icons, reveals that they are empty and need to be assigned to the proper domains and boundaries in the geometry.
Reactions SCR
1
In the Model Builder window, under Monolith Reactor Model > Transport of Diluted Species in Porous Media  click Reactions 1.
2
In the Settings window for Reactions, type Reactions SCR in the Label text field.
3
Locate the Domain Selection section. From the Selection list, choose SCR Catalyst.
Reactions ASC
1
In the Physics toolbar, click  Domains and choose Reactions.
2
In the Settings window for Reactions, type Reactions ASC in the Label text field.
3
Locate the Domain Selection section. From the Selection list, choose ASC Catalyst.
4
Locate the Reaction Rates section. From the Chemistry list, choose Chemistry: ASC (chem2).
5
Expand the Reacting Volume section and select Pore volume to specify the region where the reactions occur.
6
Drag the Reactions SCR node and place it below Reactions SCR.
Inflow 1
1
In the Model Builder window, click Inflow 1.
2
In the Settings window for Inflow, locate the Boundary Selection section.
3
From the Selection list, choose Flow Inlet.
4
Locate the Concentration section. In the c0,cH2O text field, type cH2O_in.
5
In the c0,cNH3 text field, type cNH3_in.
6
In the c0,cNO text field, type cNO_in.
7
In the c0,cNO2 text field, type cNO2_in.
8
In the c0,cO2 text field, type cO2_in.
Outflow 1
1
In the Model Builder window, click Outflow 1.
2
In the Settings window for Outflow, locate the Boundary Selection section.
3
From the Selection list, choose Flow Outlet.
Fluid 1
Next, add a Fluid feature to model the mass transfer in the free-flowing domain between the two catalysts. Use the diffusion coefficients defined by the nitrogen material.
1
In the Physics toolbar, click  Domains and choose Fluid.
2
In the Settings window for Fluid, locate the Domain Selection section.
3
From the Selection list, choose Free Flow Domain.
4
Locate the Diffusion section. From the Material list, choose Gas: Nitrogen Solvent.
5
From the DcH2O list, choose Diffusion coefficient, water in nitrogen (solvent) 5.
6
From the DcNH3 list, choose Diffusion coefficient, ammonia in nitrogen (solvent) 1.
7
From the DcNO list, choose Diffusion coefficient, nitrogen oxide in nitrogen (solvent) 2.
8
From the DcNO2 list, choose Diffusion coefficient, no2 in nitrogen (solvent) 3.
9
From the DcO2 list, choose Diffusion coefficient, oxygen in nitrogen (solvent) 4.