d.Enable Full Multicomponent Diffusion and Thermal Diffusion.

The Full Multicomponent Diffusion activates Stefan-Maxwell’s equations and computes the diffusive fluxes of all species in the mixture to all concentration gradients. The Thermal Diffusion effects cause heavy molecules to diffuse less rapidly, and light molecules to diffuse more rapidly, toward heated surfaces.

e.Click OK to close the Species Model dialog box.

f.Click OK to close the Information dialog box.

15.4.5. Defining Materials and Properties

In the following steps you will copy the gas-phase species (AsH3 , Ga(CH3)3 , CH3 , and H2 ) from the ANSYS Fluent database, specify the mixture materials, setup the reactions, and modify the material properties. You will also create the site species (Ga_s and As_s) and the solid species (Ga and As).

1.Copy arsenic-trihydride, hydrogen, methyl-radical, and trimethyl-gallium from the ANSYS Fluent material database to the list of fluid materials and modify their properties.

Setup → Materials → Fluid → air Edit...

a.Click Fluent Database... in the Create/Edit Materials dialog box to open the Fluent Database Materials dialog box.

b.In the Fluent Database Materials dialog box, select fluid from the Material Type drop-down list.

c.From the Fluent Fluid Materials selection list, select arsenic-trihydride (ash3), hydrogen (h2), methylradical (ch3), and trimethyl-gallium (game3) by clicking each species once.

Scroll down the Fluent Fluid Materials list to locate each species.

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d.Click Copy to copy the selected species to your model.

e.Click Close to close the Fluent Database Materials dialog box.

2.Create the site species (Ga_s and As_s) and the solid species (Ga and As).

a.In the Create/Edit Materials dialog box, select air from the Fluent Fluid Materials drop-down list.

b.Enter ga_s for the Name text entry field.

c.Enter ga_s for the Chemical Formula text entry field.

d.Click Change/Create to create the new material.

e.Click No in the Question dialog box when asked if you want to overwrite air.

The new material ga_s is added to your model and listed under Fluid in the Materials task page and under the Setup/Materials/Fluid tree branch.

f.Create as_s,ga, as following the same procedure as for ga_s and close the Create/Edit Materials dialog box.

Extra

To enter complex formulae such as Ga(CH3)3 in the text entry box, use ‘<’ and ‘>’ instead of ‘(’ and ‘ )’, respectively.

3. Set the mixture species.

Setup → Materials → Mixture → mixture-template Edit...

a.Enter gaas_deposition for Name.

b.Click Change/Create.

c.Click Yes in the Question dialog box to overwrite the mixture-template.

d.Set the Selected Species.

i.In Properties group box, click the Edit... button to the right of the names drop-down list for Mixture Species to open the Species dialog box.

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ii.Set the Selected Species from the Available Materials selection list as shown in Table 15.1: Selected Species (p. 512) .

Table 15.1: Selected Species

Selected Species

ash3

game3

ch3 h2

Important

•Add arsenic-trihydride (ash3), trimethyl-gallium (game3), methyl-radical (ch3), and hydrogen (h2) to the Selected Species list before removing h2o, o2, and n2.

•Ensure that h2 is at the bottom in the Selected Species selection list as shown in Table 15.1: Selected Species (p. 512). ANSYS Fluent will interpret the last species in the list as the bulk species.

Note

To add/remove the species:

•To add a particular species to the list, select the required species from the Available Materials selection list and click Add in the corresponding species selection list (Selected Species, Selected Site Species, or Selected Solid Species). The species will be added to the end of the relevant list and removed from the Available Materials list.

•To remove an unwanted species from the selection list, select the species from the selection list (Selected Species, Selected Site Species, or Selected Solid Species) and click Remove in the corresponding selection list. The species will be removed from the list and added to the Available Materials list.

iii.Click OK to close the Species dialog box.

iv.Click Change/Create and close the Creat/Edit Materials dialog box.

4.Enable chemical species transport reaction.

Physics → Models → Species...

Although you enable reactions, you still run a non-reacting flow to produce an initial solution. You will run a reacting flow in Simulating Reacting Flow (p. 530).

a.Enable Volumetric and Wall Surface in the Reactions group box.

b.Retain the selection of gaas_deposition from the Mixture Material drop-down list.

c.Disable Heat of Surface Reactions and enable Mass Deposition Source.

d.Click OK to close the Species Model dialog box.

5.Set the site and solid species and the mixture reactions in a similar manner to the mixture species.

Setup → Materials → Mixture → gaas_deposition Edit...

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a.Click the Edit... button to the right of the names drop-down list for Mixture Species in the Properties group box.

Specify the Selected Site Species and the Selected Solid Species as shown in Table 15.2: Selected Site and Solid Species (p. 514).

Table 15.2: Selected Site and Solid Species

Once you set the site and solid species, the Species dialog box should look like this:

b.Click OK to close the Species dialog box.

c.Click the Edit... button to the right of the Reaction drop-down list to open the Reactions dialog box.

d.Increase the Total Number of Reactions to 2, and define the following reactions using the parameters in Table 15.3: Reaction Parameters (p. 515) :

(15.3)

(15.4)

aSet the ID to 2 in order to set the parameters for the second reaction.

bHere, PEF = Pre-Exponential Factor, AE = Activation Energy, and TE = Temperature Exponent.

e.Click OK to save the data and close the Reactions dialog box.

f.Set the reaction mechanisms for the mixture.

i.Click the Edit... button to the right of the Mechanism drop-down list to open the Reaction Mechanisms dialog box.

ii.Retain Number of Mechanisms as 1.

iii.Enter gaas-ald for Name.

iv.Select Wall Surface in the Reaction Type group box.

v.Select gallium-dep and arsenic-dep from the Reactions selection list.

vi.Set Number of Sites to 1.

vii.Enter 1e-08 kgmol/m2 for Site Density for site-1.

viii.Click the Define... button to the right of site-1 to open the Site Parameters dialog box.

A.Set Total Number of Site Species to 2.

B.Select ga_s as the first site species and enter 0.7 for Initial Site Coverage.

C.Select as_s as the second site species and enter 0.3 for Initial Site Coverage.

D.Click Apply and close the Site Parameters dialog box.

ix.Click OK to close the Reaction Mechanisms dialog box.

g.Retain the default selection of incompressible-ideal-gas from the Density drop-down list.

h.Retain the default selection of mixing-law from the Cp (Specific Heat) drop-down list.

i.Select mass-weighted-mixing-law from the Thermal Conductivity drop-down list.

j.Select mass-weighted-mixing-law from the Viscosity drop-down list.

k.Retain the default selection of kinetic-theory from the Mass Diffusivity drop-down list.

l.Retain the default selection of kinetic-theory from the Thermal Diffusion Coefficient drop-down list.

m.Click Change/Create and close the Create/Edit Materials dialog box.

6.Specify the material properties for arsenic-trihydride, hydrogen, methyl-radical, trimethyl-gallium, site species (Ga_s and As_s), and solid species (Ga and As).

Setup → Materials → Mixture → gaas_deposition → arsenic-trihydride Edit...

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a.In the Properties group box, modify the arsenic-trihydride properties as shown in Table 15.4: Properties of Species (p. 518).

Important

Ensure Mixture is set to gaas_deposition

Tip

Scroll down in the Properties group box to see all the parameters.

b. When finished, click Change/Create to update your local copy of the species material.

Note

When you modify the properties of the material local copy, the original copy in Fluent material database stays intact.

c.In a similar way, modify the properties of trimethyl-gallium (game3), methyl-radical (ch3), and hydrogen (h2).

Note

Make sure to click Change/Create each time you modify the properties for the material to apply the changes to the local copy.

d.Select ga_s from the Fluent Fluid Materials drop-down list.

e.Enter the parameter values for the ga_s species as shown in Table 15.5: Properties of Species (p. 519).