This information is part of the Modelica Standard Library maintained by the Modelica Association.

Enumeration to define the assumptions on the model for the direction of fluid flow at a port (to be selected via choices menu):

PortFlowDirection.	Meaning
Entering	Fluid flow is only entering the port from the outside
Leaving	Fluid flow is only leaving the port to the outside
Bidirectional	No restrictions on fluid flow (flow reversal possible)

The default is "PortFlowDirection.Bidirectional". If you are completely sure that the flow is only in one direction, then the other settings may make the simulation of your model faster.

Entering	Fluid flow is only entering
Leaving	Fluid flow is only leaving
Bidirectional	No restrictions on fluid flow (flow reversal possible)