Global Definitions
1
In the Home toolbar click Parameters  and then select Parameters 1 . Alternatively, click the Parameters 1  node in the Model Builder.
Note: On Linux and Mac, the Home toolbar refers to the specific set of controls near the top of the Desktop.
2
In the Settings window locate the Parameters section.
3
The inserted geometry sequence uses a global parameter Ra, called the Tube radius, with a value of 3 millimeters. This parameter was automatically defined when the geometry sequence was inserted in the previous steps. The text in the Expression column, 3[mm] with square brackets, is a standard way to enter unit syntax in COMSOL models.
4
Add a second row to the table by typing u_av in the Name column, 1[cm/s] in the Expression column, and Mean velocity in the Description column. This global parameter will be used to define boundary conditions in the model.
For the parameter values entered above, and for water with an approximate density of 1000 kg/m3 and viscosity of 0.001 Pa s, the Reynolds number of the flow is approximately 60, meaning that the use of the Laminar flow physics interface is appropriate.