modelJunction

Flow splitter with fixed resistance at each port

Extends from BuildingSystems.Fluid.BaseClasses.PartialThreeWayResistance.

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.

image

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.

Parameters

TypeNameDefaultDescription
BooleanhomotopyInitializationtrue= true, use homotopy method
Nominal condition
Modelica.Units.SI.MassFlowRatem_flow_nominalMass flow rate. Set negative at outflowing ports.
Modelica.Units.SI.Pressuredp_nominalPressure drop at nominal mass flow rate, set to zero or negative number at outflowing ports.
Transition to laminar
RealdeltaM0.3Fraction of nominal mass flow rate where transition to turbulent occurs
Advanced
Booleanlinearizedfalse= true, use linear relation between m_flow and dp for any flow rate

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.