The model is for single phase compressible flow that could become choked. Although it can be used giving the flow at one of the connectors, it is intended for the specification of the two ends pressures and calculation of the flow.
The enthalpy change is always calculated between PortA and PortB but, if the flow is chocked, the pressure variation is calculated between PortA and StateB, that becames equal to StateC. This is due to the fact that the pressure at B has been specified but is less that the choked pressure.
The model may have convergence problems when isothermal behaviour is selected, but it is possible to add heat till we arrive to isothermal situation.
In complex circuits, use this model only for the last pipe, that is the one that can become choked. For the other pipes use PipeFlow1Ph with the parameter isCompressibleFlow to true