WOLFRAM SYSTEM MODELER
    PortFlowDirectionEnumeration to define whether flow reversal is allowed  | 

SystemModel["Modelica.Fluid.Types.PortFlowDirection"]

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)  | 
    
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         Modelica.Fluid.Fittings.BaseClasses Base class for a splitting/joining component with three ports  | 
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         Modelica.Fluid.Sources.BaseClasses Partial component source with one fluid connector  | 
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         Modelica.Fluid.Sources.BaseClasses Partial component source with one fluid connector  |