BuildingSystems.Fluid.Interfaces.PartialTwoPortTransport

# .BuildingSystems.Fluid.Interfaces.PartialTwoPortTransport

Partial element transporting fluid between two ports without storage of mass or energy

## Information

This component transports fluid between its two ports, without storing mass or energy. Energy may be exchanged with the environment though, e.g., in the form of work. `PartialTwoPortTransport` is intended as base class for devices like orifices, valves and simple fluid machines.

Three equations need to be added by an extending class using this component:

- The momentum balance specifying the relationship between the pressure drop `dp` and the mass flow rate `m_flow`,
- `port_b.h_outflow` for flow in design direction, and
- `port_a.h_outflow` for flow in reverse direction.

Moreover appropriate values shall be assigned to the following parameters:

- `dp_start` for a guess of the pressure drop
- `m_flow_small` for regularization of zero flow.

#### Implementation

This is similar to Modelica.Fluid.Interfaces.PartialTwoPortTransport except that it does not use the `outer system` declaration. This declaration is omitted as in building energy simulation, many models use multiple media, and in practice, users have not used this global definition to assign parameters.

## Revisions

- March 30, 2021, by Michael Wetter:
  Added annotation `HideResult=true`.
  This is for IBPSA, #1459.
- September 15, 2016, by Michael Wetter:
  Removed wrong annotation, which caused an error in the pedantic model check of Dymola 2017 FD01. This is for #516.
- January 22, 2016, by Henning Francke:
  Corrected type declaration of pressure. This is for #404.
- November 19, 2015, by Michael Wetter:
  Removed assignments of parameters `port_a_exposesState` and `port_b_exposesState` in base class. This is for #351.
- August 15, 2015, by Filip Jorissen:
  Implemented more efficient computation of `port_a.Xi_outflow` and `port_a.C_outflow` when `allowFlowReversal=false`. This is for #305.
- June 6, 2015, by Michael Wetter:
  Removed protected conditional variables `state_a` and `state_b`, as they were used outside of a connect statement, which causes an error during pedantic model check in Dymola 2016. This fixes #128.
- April 1, 2015, by Michael Wetter:
  Made computation of `state_a` and `state_p` conditional on `show_T` or `show_V_flow`. This avoids computing temperature from enthalpy if temperature is a state of the medium, and the result is not used.
- October 21, 2014, by Michael Wetter:
  Revised implementation.
- October 20, 2014, by Filip Jorisson:
  First implementation.

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