User routines are Fortran subroutines
(User CEL Functions, Junction Box Routines, and Particle User Routines)
that you write for the CFX-Solver. You use the User Routine details view to create objects that link your Fortran subroutines
to the CFX-Solver. To access the User Routine details view, either select Insert > Expressions, Functions and Variables > User
Routines or click Insert User Routine 
in the main toolbar.
Once your User Routines have been created and linked, they appear in the tree view under Simulation > Expressions, Functions and Variables > User Routines.
User Routine Details View
The User Routine details view creates objects that link your Fortran subroutines to the CFX-Solver.
There are four types of user routines:
For details on the fourth user-routine option,
Transient Particle Diagnostics Routine, refer to User Diagnostics Routine in the CFX-Solver Modeling Guide.