Annex60.Fluid.Interfaces.PartialTwoPortInterface

# .Annex60.Fluid.Interfaces.PartialTwoPortInterface

Partial model transporting fluid between two ports without storing mass or energy

## Information

This component defines the interface for models that transports a fluid between two ports. It is similar to Modelica.Fluid.Interfaces.PartialTwoPortTransport, but it does not include the species balance

      port_b.Xi_outflow = inStream(port_a.Xi_outflow);

Thus, it can be used as a base class for a heat and mass transfer component

The model is used by other models in this package that add heat transfer, mass transfer and pressure drop equations. See for example Annex60.Fluid.Interfaces.StaticTwoPortHeatMassExchanger.

## Revisions

- November 3, 2016, by Michael Wetter:
  Renamed protected parameter `m_flow_start` to avoid a name clash with Annex60.Fluid.Movers.FlowControlled_m_flow which leads to an error as the definition were different, and also renamed protected parameter `dp_start`. This is for #552
  Moved computation of pressure drop to variable assignment so that the model won't mix graphical with textual modeling if used as a base class for a graphically implemented model.
- November 3, 2016, by Michael Wetter:
  Removed start values for mass flow rate and pressure difference to simplify the parameter window.
  This is for #552.
- January 22, 2016, by Michael Wetter:
  Corrected type declaration of pressure difference. This is for #404.
- October 3, 2014, by Michael Wetter:
  Changed assignment of nominal value to avoid in OpenModelica the warning alias set with different nominal values.
- November 12, 2013 by Michael Wetter:
  Removed `import Modelica.Constants;` statement.
- November 11, 2013 by Michael Wetter:
  Removed the parameter `homotopyInitialization` as it is no longer used in this model.
- November 10, 2013 by Michael Wetter:
  In the computation of `sta_a` and `sta_b`, removed the branch that uses the homotopy operator. The rational is that these variables are conditionally enables (because of `... if show_T`. Therefore, the Modelica Language Specification does not allow for these variables to be used in any equation. Hence, the use of the homotopy operator is not needed here.
- October 10, 2013 by Michael Wetter:
  Added `noEvent` to the computation of the states at the port. This is correct, because the states are only used for reporting, but not to compute any other variable. Use of the states to compute other variables would violate the Modelica language, as conditionally removed variables must not be used in any equation.
- October 8, 2013 by Michael Wetter:
  Removed the computation of `V_flow` and removed the parameter `show_V_flow`. The reason is that the computation of `V_flow` required the use of `sta_a` (to compute the density), but `sta_a` is also a variable that is conditionally enabled. However, this was not correct Modelica syntax as conditional variables can only be used in a `connect` statement, not in an assignment. Dymola 2014 FD01 beta3 is checking for this incorrect syntax. Hence, `V_flow` was removed as its conditional implementation would require a rather cumbersome implementation that uses a new connector that carries the state of the medium.
- April 26, 2013 by Marco Bonvini:
  Moved the definition of `dp` because it causes some problem with PyFMI.
- March 27, 2012 by Michael Wetter:
  Changed condition to remove `sta_a` to also compute the state at the inlet port if `show_V_flow=true`. The previous implementation resulted in a translation error if `show_V_flow=true`, but worked correctly otherwise because the erroneous function call is removed if `show_V_flow=false`.
- March 27, 2011 by Michael Wetter:
  Added `homotopy` operator.
- March 21, 2010 by Michael Wetter:
  Changed pressure start value from `system.p_start` to `Medium.p_default` since HVAC models may have water and air, which are typically at different pressures.
- September 19, 2008 by Michael Wetter:
  Added equations for the mass balance of extra species flow, i.e., `C` and `mC_flow`.
- March 11, 2008, by Michael Wetter:
  First implementation.

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