Buildings.Fluid.BaseClasses

Package with base classes for Buildings.Fluid

Information

This package contains base classes that are used to construct the models in Buildings.Fluid.

Extends from Modelica.Icons.BasesPackage (Icon for packages containing base classes).

Package Content

NameDescription
Buildings.Fluid.BaseClasses.FlowModels FlowModels Flow models for pressure drop calculations
Buildings.Fluid.BaseClasses.PartialResistance PartialResistance Partial model for a hydraulic resistance
Buildings.Fluid.BaseClasses.PartialThreeWayResistance PartialThreeWayResistance Flow splitter with partial resistance model at each port


Buildings.Fluid.BaseClasses.PartialResistance Buildings.Fluid.BaseClasses.PartialResistance

Partial model for a hydraulic resistance

Buildings.Fluid.BaseClasses.PartialResistance

Information

Partial model for a flow resistance, possible with variable flow coefficient. The pressure drop is computed by an instance of Buildings.Fluid.BaseClasses.FlowModels.BasicFlowModel, i.e., using a regularized implementation of the equation

m = sign(Δp) k √ Δp  

Extends from Buildings.Fluid.Interfaces.PartialTwoPortInterface (Partial model transporting fluid between two ports without storing mass or energy).

Parameters

TypeNameDefaultDescription
replaceable package MediumPartialMediumMedium in the component
Nominal condition
MassFlowRatem_flow_nominal Nominal mass flow rate [kg/s]
Pressuredp_nominal Pressure drop at nominal mass flow rate [Pa]
Assumptions
BooleanallowFlowReversalsystem.allowFlowReversal= true to allow flow reversal, false restricts to design direction (port_a -> port_b)
Advanced
MassFlowRatem_flow_small1E-4*abs(m_flow_nominal)Small mass flow rate for regularization of zero flow [kg/s]
BooleanhomotopyInitializationtrue= true, use homotopy method
Booleanfrom_dpfalse= true, use m_flow = f(dp) else dp = f(m_flow)
Booleanlinearizedfalse= true, use linear relation between m_flow and dp for any flow rate
Diagnostics
Booleanshow_V_flowfalse= true, if volume flow rate at inflowing port is computed
Booleanshow_Tfalse= true, if actual temperature at port is computed (may lead to events)

Connectors

TypeNameDescription
FluidPort_aport_aFluid connector a (positive design flow direction is from port_a to port_b)
FluidPort_bport_bFluid connector b (positive design flow direction is from port_a to port_b)

Modelica definition

partial model PartialResistance 
  "Partial model for a hydraulic resistance"
    extends Buildings.Fluid.Interfaces.PartialTwoPortInterface(
     show_T=false, show_V_flow=false,
     m_flow(start=0, nominal=m_flow_nominal_pos),
     dp(start=0, nominal=dp_nominal_pos));

  parameter Boolean from_dp = false 
    "= true, use m_flow = f(dp) else dp = f(m_flow)";
  parameter Modelica.SIunits.MassFlowRate m_flow_nominal 
    "Nominal mass flow rate";
  parameter Modelica.SIunits.Pressure dp_nominal(displayUnit="Pa") 
    "Pressure drop at nominal mass flow rate";
  parameter Boolean homotopyInitialization = true "= true, use homotopy method";
  parameter Boolean linearized = false 
    "= true, use linear relation between m_flow and dp for any flow rate";

  Real k(unit="") "Flow coefficient, k=m_flow/sqrt(dp), with unit=(kg.m)^(1/2)";
  Modelica.SIunits.MassFlowRate m_flow_turbulent(min=0) 
    "Turbulent flow if |m_flow| >= m_flow_turbulent, not a parameter because k can be a function of time";

protected 
  parameter Medium.ThermodynamicState sta0=
     Medium.setState_pTX(T=Medium.T_default, p=Medium.p_default, X=Medium.X_default);
  parameter Modelica.SIunits.DynamicViscosity eta_nominal=Medium.dynamicViscosity(sta0) 
    "Dynamic viscosity, used to compute transition to turbulent flow regime";
  final parameter Boolean computeFlowResistance=(dp_nominal_pos > Modelica.Constants.eps) 
    "Flag to enable/disable computation of flow resistance";
protected 
  final parameter Modelica.SIunits.MassFlowRate m_flow_nominal_pos = abs(m_flow_nominal) 
    "Absolute value of nominal flow rate";
  final parameter Modelica.SIunits.Pressure dp_nominal_pos = abs(dp_nominal) 
    "Absolute value of nominal pressure";
initial equation 
  if computeFlowResistance then
    assert(m_flow_turbulent > 0, "m_flow_turbulent must be bigger than zero.");
  end if;
equation 
  // Pressure drop calculation
  if computeFlowResistance then
    if linearized then
      m_flow*m_flow_nominal_pos = k^2*dp;
    else
      if homotopyInitialization then
        if from_dp then
          m_flow=homotopy(actual=FlowModels.basicFlowFunction_dp(dp=dp, k=k,
                                   m_flow_turbulent=m_flow_turbulent),
                                   simplified=m_flow_nominal_pos*dp/dp_nominal_pos);
        else
          dp=homotopy(actual=FlowModels.basicFlowFunction_m_flow(m_flow=m_flow, k=k,
                                   m_flow_turbulent=m_flow_turbulent),
                    simplified=dp_nominal_pos*m_flow/m_flow_nominal_pos);
         end if;  // from_dp
      else // do not use homotopy
        if from_dp then
          m_flow=FlowModels.basicFlowFunction_dp(dp=dp, k=k, m_flow_turbulent=m_flow_turbulent);
        else
          dp=FlowModels.basicFlowFunction_m_flow(m_flow=m_flow, k=k, m_flow_turbulent=m_flow_turbulent);
        end if;  // from_dp
      end if; // homotopyInitialization
    end if; // linearized
  else // do not compute flow resistance
    dp = 0;
  end if;  // computeFlowResistance

  // Isenthalpic state transformation (no storage and no loss of energy)
  port_a.h_outflow = inStream(port_b.h_outflow);
  port_b.h_outflow = inStream(port_a.h_outflow);

  // Mass balance (no storage)
  port_a.m_flow + port_b.m_flow = 0;

  // Transport of substances
  port_a.Xi_outflow = inStream(port_b.Xi_outflow);
  port_b.Xi_outflow = inStream(port_a.Xi_outflow);

  port_a.C_outflow = inStream(port_b.C_outflow);
  port_b.C_outflow = inStream(port_a.C_outflow);

end PartialResistance;

Buildings.Fluid.BaseClasses.PartialThreeWayResistance Buildings.Fluid.BaseClasses.PartialThreeWayResistance

Flow splitter with partial resistance model at each port

Buildings.Fluid.BaseClasses.PartialThreeWayResistance

Information

Partial model for flow resistances with three ports such as a flow mixer/splitter or a three way valve.

If dynamicBalance=true, then at the junction of the three flows, a mixing volume will be present. This will introduce a dynamic energy and momentum balance, which often breaks algebraic loops. The time constant of the mixing volume is determined by the parameter tau.

Extends from Buildings.Fluid.Interfaces.LumpedVolumeDeclarations (Declarations for lumped volumes).

Parameters

TypeNameDefaultDescription
replaceable package MediumPartialMediumMedium in the component
PartialTwoPortInterfaceres1redeclare Buildings.Fluid.In...Partial model, to be replaced with a fluid component
PartialTwoPortInterfaceres2redeclare Buildings.Fluid.In...Partial model, to be replaced with a fluid component
PartialTwoPortInterfaceres3redeclare Buildings.Fluid.In...Partial model, to be replaced with a fluid component
Dynamics
Equations
DynamicsenergyDynamicsModelica.Fluid.Types.Dynamic...Formulation of energy balance
DynamicsmassDynamicsenergyDynamicsFormulation of mass balance
BooleandynamicBalancetrueSet to true to use a dynamic balance, which often leads to smaller systems of equations
MassFlowRatemDyn_flow_nominal Nominal mass flow rate for dynamic momentum and energy balance [kg/s]
Nominal condition
Timetau10Time constant at nominal flow for dynamic energy and momentum balance [s]
Initialization
AbsolutePressurep_startMedium.p_defaultStart value of pressure [Pa]
TemperatureT_startMedium.T_defaultStart value of temperature [K]
MassFractionX_start[Medium.nX]Medium.X_defaultStart value of mass fractions m_i/m [kg/kg]
ExtraPropertyC_start[Medium.nC]fill(0, Medium.nC)Start value of trace substances
ExtraPropertyC_nominal[Medium.nC]fill(1E-2, Medium.nC)Nominal value of trace substances. (Set to typical order of magnitude.)
Advanced
Booleanfrom_dptrue= true, use m_flow = f(dp) else dp = f(m_flow)
BooleanhomotopyInitializationtrue= true, use homotopy method

Connectors

TypeNameDescription
FluidPort_aport_1 
FluidPort_bport_2 
FluidPort_aport_3 

Modelica definition

partial model PartialThreeWayResistance 
  "Flow splitter with partial resistance model at each port"
  extends Buildings.Fluid.Interfaces.LumpedVolumeDeclarations;
  outer Modelica.Fluid.System system "System properties";

  Modelica.Fluid.Interfaces.FluidPort_a port_1(redeclare package Medium =
        Medium, m_flow(min=if (portFlowDirection_1 == Modelica.Fluid.Types.PortFlowDirection.Entering) then 
                0.0 else -Modelica.Constants.inf, max=if (portFlowDirection_1
           == Modelica.Fluid.Types.PortFlowDirection.Leaving) then 0.0 else Modelica.Constants.inf));
  Modelica.Fluid.Interfaces.FluidPort_b port_2(redeclare package Medium =
        Medium, m_flow(min=if (portFlowDirection_2 == Modelica.Fluid.Types.PortFlowDirection.Entering) then 
                0.0 else -Modelica.Constants.inf, max=if (portFlowDirection_2
           == Modelica.Fluid.Types.PortFlowDirection.Leaving) then 0.0 else Modelica.Constants.inf));
  Modelica.Fluid.Interfaces.FluidPort_a port_3(
    redeclare package Medium=Medium,
    m_flow(min=if (portFlowDirection_3==Modelica.Fluid.Types.PortFlowDirection.Entering) then 0.0 else -Modelica.Constants.inf,
    max=if (portFlowDirection_3==Modelica.Fluid.Types.PortFlowDirection.Leaving) then 0.0 else Modelica.Constants.inf));

  parameter Boolean from_dp = true 
    "= true, use m_flow = f(dp) else dp = f(m_flow)";
  parameter Boolean homotopyInitialization = true "= true, use homotopy method";

  replaceable Buildings.Fluid.Interfaces.PartialTwoPortInterface res1(redeclare 
      package Medium = Medium, allowFlowReversal=true, homotopyInitialization=homotopyInitialization) 
    "Partial model, to be replaced with a fluid component";
  replaceable Buildings.Fluid.Interfaces.PartialTwoPortInterface res2(redeclare 
      package Medium = Medium, allowFlowReversal=true, homotopyInitialization=homotopyInitialization) 
    "Partial model, to be replaced with a fluid component";
  replaceable Buildings.Fluid.Interfaces.PartialTwoPortInterface res3(redeclare 
      package Medium = Medium, allowFlowReversal=true, homotopyInitialization=homotopyInitialization) 
    "Partial model, to be replaced with a fluid component";

protected 
  parameter Modelica.Fluid.Types.PortFlowDirection portFlowDirection_1=Modelica.Fluid.Types.PortFlowDirection.Bidirectional 
    "Flow direction for port_1";
  parameter Modelica.Fluid.Types.PortFlowDirection portFlowDirection_2=Modelica.Fluid.Types.PortFlowDirection.Bidirectional 
    "Flow direction for port_2";
  parameter Modelica.Fluid.Types.PortFlowDirection portFlowDirection_3=Modelica.Fluid.Types.PortFlowDirection.Bidirectional 
    "Flow direction for port_3";

public 
  Buildings.Fluid.Delays.DelayFirstOrder vol(
    redeclare final package Medium = Medium,
    final nPorts=3,
    final tau=tau,
    final m_flow_nominal=mDyn_flow_nominal,
    final energyDynamics=energyDynamics,
    final massDynamics=massDynamics,
    final p_start=p_start,
    final T_start=T_start,
    final X_start=X_start,
    final C_start=C_start,
    final allowFlowReversal=true,
    final prescribedHeatFlowRate=false) if 
       dynamicBalance "Fluid volume to break algebraic loop";
  parameter Boolean dynamicBalance = true 
    "Set to true to use a dynamic balance, which often leads to smaller systems of equations";

  parameter Modelica.SIunits.Time tau=10 
    "Time constant at nominal flow for dynamic energy and momentum balance";
  parameter Modelica.SIunits.MassFlowRate mDyn_flow_nominal 
    "Nominal mass flow rate for dynamic momentum and energy balance";

equation 
  connect(port_1, res1.port_a);
  connect(res2.port_a, port_2);
  connect(res3.port_a, port_3);
  connect(res1.port_b,vol. ports[1]);
  connect(res2.port_b,vol. ports[2]);
  connect(res3.port_b,vol. ports[3]);
  if not dynamicBalance then
    connect(res1.port_b, res3.port_b);
    connect(res1.port_b, res2.port_b);
  end if;
end PartialThreeWayResistance;

Automatically generated Fri Nov 4 08:28:19 2011.