use_dynamicFlowRegime not effective

[carlesRT]

I added comments on #1683 / #1682 but I believe this might go under if do not open a new issue.

The activation of use_dynamicFlowRegime, i.e. seting the parameter to true will not work as the variables to determine the flow regime (changes in flow direction) are based on C1_flow and C2_flow which are by definition always positive.

  // Assign the flow regime for the given heat exchanger configuration and capacity flow rates
  if use_dynamicFlowRegime then
    if (configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.ParallelFlow) then
      flowRegime = if (C1_flow*C2_flow >= 0) then Buildings.Fluid.Types.HeatExchangerFlowRegime.ParallelFlow else Buildings.Fluid.Types.HeatExchangerFlowRegime.CounterFlow;
    elseif (configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.CounterFlow) then
      flowRegime = if (C1_flow*C2_flow >= 0) then Buildings.Fluid.Types.HeatExchangerFlowRegime.CounterFlow else Buildings.Fluid.Types.HeatExchangerFlowRegime.ParallelFlow;
    elseif (configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.CrossFlowUnmixed) then
      flowRegime = Buildings.Fluid.Types.HeatExchangerFlowRegime.CrossFlowUnmixed;
    elseif (configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.CrossFlowStream1MixedStream2Unmixed) then
      flowRegime = if (C1_flow < C2_flow) then Buildings.Fluid.Types.HeatExchangerFlowRegime.CrossFlowCMinMixedCMaxUnmixed
         else Buildings.Fluid.Types.HeatExchangerFlowRegime.CrossFlowCMinUnmixedCMaxMixed;
    else
      // have ( configuration == Buildings.Fluid.Types.HeatExchangerConfiguration.CrossFlowStream1UnmixedStream2Mixed)
      flowRegime = if (C1_flow < C2_flow) then Buildings.Fluid.Types.HeatExchangerFlowRegime.CrossFlowCMinUnmixedCMaxMixed
         else Buildings.Fluid.Types.HeatExchangerFlowRegime.CrossFlowCMinMixedCMaxUnmixed;
    end if;
  else
    flowRegime = flowRegime_nominal;

Modelica.Units.SI.ThermalConductance C1_flow(
    min=0,
    nominal=m1_flow_nominal*cp1_default)=abs(m1_flow)*(if 
      allowFlowReversal1 then fra_a1*Medium1.specificHeatCapacityCp(
      state_a1_inflow) + fra_b1*Medium1.specificHeatCapacityCp(state_b1_inflow)
       else Medium1.specificHeatCapacityCp(state_a1_inflow))
    "Heat capacity flow rate medium 1";
  Modelica.Units.SI.ThermalConductance C2_flow(
    min=0,
    nominal=m2_flow_nominal*cp2_default)=abs(m2_flow)*(if 
      allowFlowReversal2 then fra_a2*Medium2.specificHeatCapacityCp(
      state_a2_inflow) + fra_b2*Medium2.specificHeatCapacityCp(state_b2_inflow)
       else Medium2.specificHeatCapacityCp(state_a2_inflow))
    "Heat capacity flow rate medium 2";

So the potential change of PartialEffectivenessNTU is open for discussion.