COMSOL 6.4 - Free Molecular Flow

Free Molecular Flow

Molecular Flow 1

1

In the Model Builder expand the Component 1 > Free Molecular Flow node

, then click Molecular Flow 1

2

In the Settings window for Molecular Flow locate the Molecular Weight of Species section. In the Mn,G text field, type 0.002[kg/mol].

Set up the wafer to outgas 30 sccm of hydrogen.

1

In the Physics toolbar click Boundaries

and choose Wall

2

Select Boundary 42 only. You can do this by clicking on the outgassing wafer in the Graphics window. To click on boundaries that are behind other boundaries, you can scroll with the middle mouse wheel. Sometimes it is easier to see the boundary you want to click by enabling Wireframe Rendering

Alternatively, you can click the Paste Selection

button and type 42.

3

In the Settings window for Wall locate the Wall Type section. From the Wall type list, choose Outgassing wall.

4

Locate the Flux section.

-

From the Outgoing flux list, choose Number of SCCM units.

-

In the Qsccm,G text field, type 30.

Set up the vacuum pumps.

1

In the Physics toolbar click Boundaries

and choose Vacuum Pump

2

Select Boundary 55 only.

3

In the Settings window for Vacuum Pump locate the Vacuum Pump section. From the Specify pump flux list, choose Pump speed.

4

In the SG text field, type pumpspeedturbo.

1

In the Physics toolbar click Boundaries

and choose Vacuum Pump

2

Select Boundary 8 only.

3

In the Settings window for Vacuum Pump locate the Vacuum Pump section. From the Specify pump flux list, choose Pump speed.

4

In the SG text field, type pumpspeedcryo.

Note that each pump needs a separate boundary condition because the molecular flux is spread over the computed area of the pump feature selection.

1

Right-click Vacuum Pump 2

and choose Duplicate

2

In the Settings window for Vacuum Pump locate the Boundary Selection section. Click Clear Selection

3

Select Boundary 25 only.

1

Right-click Vacuum Pump 3

and choose Duplicate

2

In the Settings window for Vacuum Pump locate the Boundary Selection section. Click Clear Selection

3

Select Boundary 70 only.

1

Right-click Vacuum Pump 4

and choose Duplicate

2

In the Settings window for Vacuum Pump locate the Boundary Selection section. Click Clear Selection

3

Select Boundary 33 only.

Number Density Reconstruction 1

1

In the Physics toolbar click Edges

and choose Number Density Reconstruction

2

From the Selection list, choose Work Plane 1.