.BuildingSystems.Fluid.FixedResistances.Junction

Information

Model of a flow junction with an optional fixed resistance in each flow leg and an optional mixing volume at the junction.

The pressure drop is implemented using the model BuildingSystems.Fluid.FixedResistances.PressureDrop. If its nominal pressure drop is set to zero, then the pressure drop model will be removed. For example, the pressure drop declaration

  m_flow_nominal={ 0.1, 0.1,  -0.2},
  dp_nominal =   {500,    0, -6000}

would model a flow mixer that has the nominal flow rates and associated pressure drops as shown in the figure below. Note that port_3 is set to negative values. The negative values indicate that at the nominal conditions, fluid is leaving the component.

If energyDynamics <> Modelica.Fluid.Types.Dynamics.SteadyState, then at the flow junction, a fluid volume is modeled. The fluid volume is implemented using the model BuildingSystems.Fluid.Delays.DelayFirstOrder. The fluid volume has the size

  V = sum(abs(m_flow_nominal[:])/3)*tau/rho_nominal

where tau is a parameter and rho_nominal is the density of the medium in the volume at nominal condition. Setting energyDynamics=Modelica.Fluid.Types.Dynamics.FixedInitial can help reducing the size of the nonlinear system of equations.

Revisions

• April 14, 2020, by Michael Wetter:
  Changed homotopyInitialization to a constant.
  This is for IBPSA, #1341.
• February 26, 2020, by Michael Wetter:
  Changed icon to display its operating state.
  This is for #1294.
• March 26, 2018 by Filip Jorissen:
  Removed final allowFlowReversal=true from all resistances since this overrides the default simplification when the flow is not bidirectional. This change can lead to smaller algebraic loops. This is for issue 898.
• December 1, 2016, by Michael Wetter:
  Renamed model from SplitterFixedResistanceDpM to FlowJunction and removed the parameters use_dh, dh and ReC.
  This is for issue 451.
• October 14, 2016 by Michael Wetter:
  Added to Annex 60 library.
  Updated comment for parameter use_dh.
  This is for issue 451.
• Removed parameter dynamicBalance that overwrote the setting of energyDynamics and massDynamics. This is for Annex 60, issue 411.
• February 1, 2012 by Michael Wetter:
  Expanded documentation.
• August 4, 2011 by Michael Wetter:
  Added final allowFlowReversal=true to all resistances since it is impractical to avoid flow reversal in large flow networks where such a setting may be useful.
• June 11, 2008 by Michael Wetter:
  Based class on BuildingSystems.Fluid.BaseClasses.PartialThreeWayFixedResistance.
• July 20, 2007 by Michael Wetter:
  First implementation.