Heat Exchanger Connectors

[RaphaelGebhart]

Currently Open Modelica cant display cross flow heat exchangers inlets/outlets correctly (ThermofluidStream.HeatExchangers.CrossFlowNTU, ThermofluidStream.HeatExchangers.DiscretizedCrossFlowHEX, ThermofluidStream.HeatExchangers.DiscretizedCrossFlowHEX_FR), since the annotation rotation=if crossFlow then -90 for inlets/outlets seems to be ignored by Open Modelica.

Furthermore the implementation causes difficulties when connecting components to the cross flow heat exchangers (the connection lines are a mess) (At least for Dymola 2022x, it seems to work well with 2024x tho).

Therefor we might consider moving the inlets/outlets from the base classes ThermofluidStream.HeatExchangers.Internal.PartialNTU, ThermofluidStream.HeatExchangers.Internal.PartialDiscretizedHEX, ThermofluidStream.Undirected.HeatExchangers.Internal.PartialDiscretizedHEX to the inheriting models and use internal variables at the base models instead. This approach would also make it more simple to add other Heat Exchanger Configurations like Parallel Flow Heat Exchangers, because the if else crossFlow, parallelFlow, counterFlow = false, true is rather impractical i assume.

I already fixed this issue in #167, but restored the old version, since the regression test Validation fails. I assume its only a change in variable name, but still, i would rather use an independet issue for changing HEX connectors, since #167 already contains a lot of changes...

[nieweber]

This is also proposed and discussed in #230