Buildings.Fluid.Interfaces

Information

Extends from Modelica.Icons.InterfacesPackage (Icon for packages containing interfaces).

Package Content

Name	Description
UsersGuide	User's Guide
FourPort	Partial model with four ports
TwoPortHeatMassExchanger	Partial model transporting one fluid stream with storing mass or energy
FourPortHeatMassExchanger	Partial model transporting two fluid streams between four ports with storing mass or energy
StaticTwoPortHeatMassExchanger	Partial model transporting fluid between two ports without storing mass or energy
StaticFourPortHeatMassExchanger	Partial model transporting two fluid streams between four ports without storing mass or energy
PartialTwoPortInterface	Partial model transporting fluid between two ports without storing mass or energy
PartialFourPortInterface	Partial model transporting fluid between two ports without storing mass or energy
LumpedVolume	Lumped volume with mass and energy balance
TwoPortFlowResistanceParameters	Parameters for flow resistance for models with two ports
FourPortFlowResistanceParameters	Parameters for flow resistance for models with four ports
LumpedVolumeDeclarations	Declarations for lumped volumes
Examples	Collection of models that illustrate model use and test models

Buildings.Fluid.Interfaces.FourPort

Information

This model defines an interface for components with four ports. The parameters allowFlowReversal1 and allowFlowReversal2 may be used by models that extend this model to treat flow reversal.

This model is identical to Modelica.Fluid.Interfaces.PartialTwoPort, except that it has four ports.

Parameters

Type	Name	Default	Description
Assumptions
Boolean	allowFlowReversal1	system.allowFlowReversal	= true to allow flow reversal in medium 1, false restricts to design direction (port_a -> port_b)
Boolean	allowFlowReversal2	system.allowFlowReversal	= true to allow flow reversal in medium 2, false restricts to design direction (port_a -> port_b)
Advanced
Initialization
SpecificEnthalpy	h_outflow_a1_start	Medium1.h_default	Start value for enthalpy flowing out of port a1 [J/kg]
SpecificEnthalpy	h_outflow_b1_start	Medium1.h_default	Start value for enthalpy flowing out of port b1 [J/kg]
SpecificEnthalpy	h_outflow_a2_start	Medium2.h_default	Start value for enthalpy flowing out of port a2 [J/kg]
SpecificEnthalpy	h_outflow_b2_start	Medium2.h_default	Start value for enthalpy flowing out of port b2 [J/kg]

Connectors

Type	Name	Description
FluidPort_a	port_a1	Fluid connector a1 (positive design flow direction is from port_a1 to port_b1)
FluidPort_b	port_b1	Fluid connector b1 (positive design flow direction is from port_a1 to port_b1)
FluidPort_a	port_a2	Fluid connector a2 (positive design flow direction is from port_a2 to port_b2)
FluidPort_b	port_b2	Fluid connector b2 (positive design flow direction is from port_a2 to port_b2)

Modelica definition

model FourPort "Partial model with four ports"
  import Modelica.Constants;
  outer Modelica.Fluid.System system "System wide properties";

  replaceable package Medium1 =
      Modelica.Media.Interfaces.PartialMedium "Medium 1 in the component";
  replaceable package Medium2 =
      Modelica.Media.Interfaces.PartialMedium "Medium 2 in the component";

  parameter Boolean allowFlowReversal1 = system.allowFlowReversal 
    "= true to allow flow reversal in medium 1, false restricts to design direction (port_a -> port_b)";
  parameter Boolean allowFlowReversal2 = system.allowFlowReversal 
    "= true to allow flow reversal in medium 2, false restricts to design direction (port_a -> port_b)";

  parameter Modelica.SIunits.SpecificEnthalpy h_outflow_a1_start = Medium1.h_default 
    "Start value for enthalpy flowing out of port a1";

  parameter Modelica.SIunits.SpecificEnthalpy h_outflow_b1_start = Medium1.h_default 
    "Start value for enthalpy flowing out of port b1";

  parameter Modelica.SIunits.SpecificEnthalpy h_outflow_a2_start = Medium2.h_default 
    "Start value for enthalpy flowing out of port a2";

  parameter Modelica.SIunits.SpecificEnthalpy h_outflow_b2_start = Medium2.h_default 
    "Start value for enthalpy flowing out of port b2";

  Modelica.Fluid.Interfaces.FluidPort_a port_a1(
                                redeclare package Medium = Medium1,
                     m_flow(min=if allowFlowReversal1 then -Constants.inf else 0),
                     h_outflow(nominal=1E5, start=h_outflow_a1_start),
                     Xi_outflow(nominal=0.01)) 
    "Fluid connector a1 (positive design flow direction is from port_a1 to port_b1)";
  Modelica.Fluid.Interfaces.FluidPort_b port_b1(
                                redeclare package Medium = Medium1,
                     m_flow(max=if allowFlowReversal1 then +Constants.inf else 0),
                     h_outflow(nominal=1E5, start=h_outflow_b1_start),
                     Xi_outflow(nominal=0.01)) 
    "Fluid connector b1 (positive design flow direction is from port_a1 to port_b1)";

  Modelica.Fluid.Interfaces.FluidPort_a port_a2(
                                redeclare package Medium = Medium2,
                     m_flow(min=if allowFlowReversal2 then -Constants.inf else 0),
                     h_outflow(nominal=1E5,start=h_outflow_a2_start),
                     Xi_outflow(nominal=0.01)) 
    "Fluid connector a2 (positive design flow direction is from port_a2 to port_b2)";
  Modelica.Fluid.Interfaces.FluidPort_b port_b2(
                                redeclare package Medium = Medium2,
                     m_flow(max=if allowFlowReversal2 then +Constants.inf else 0),
                     h_outflow(nominal=1E5, start=h_outflow_b2_start),
                     Xi_outflow(nominal=0.01)) 
    "Fluid connector b2 (positive design flow direction is from port_a2 to port_b2)";

end FourPort;

Buildings.Fluid.Interfaces.TwoPortHeatMassExchanger

Information

This component transports one fluid stream. It provides the basic model for implementing dynamic and steady-state models that exchange heat and water vapor with the fluid stream. The model also computes the pressure drop due to the flow resistance. By setting the parameter dp_nominal=0, the computation of the pressure drop can be avoided. The variable vol.heatPort.T always has the value of the temperature of the medium that leaves the component. For the actual temperatures at the port, the variables sta_a.T and sta_b.T can be used. These two variables are provided by the base class Buildings.Fluid.Interfaces.PartialTwoPortInterface.

For models that extend this model, see for example

• the ideal heater or cooler Buildings.Fluid.HeatExchangers.HeaterCoolerPrescribed,
• the ideal humidifier Buildings.Fluid.HeatExchangers.HeaterCoolerPrescribed, and
• the boiler Buildings.Fluid.Boilers.BoilerPolynomial.

Implementation

The variable names follow the conventions used in Modelica.Fluid.HeatExchangers.BasicHX.

Extends from Buildings.Fluid.Interfaces.PartialTwoPortInterface (Partial model transporting fluid between two ports without storing mass or energy), Buildings.Fluid.Interfaces.TwoPortFlowResistanceParameters (Parameters for flow resistance for models with two ports).

Parameters

Type	Name	Default	Description
replaceable package Medium		PartialMedium	Medium in the component
MixingVolume	vol	redeclare Buildings.Fluid.Mi...	Volume for fluid stream
Nominal condition
MassFlowRate	m_flow_nominal		Nominal mass flow rate [kg/s]
Pressure	dp_nominal		Pressure [Pa]
Initialization
MassFlowRate	m_flow.start	0	Mass flow rate from port_a to port_b (m_flow > 0 is design flow direction) [kg/s]
Pressure	dp.start	0	Pressure difference between port_a and port_b [Pa]
Assumptions
Boolean	allowFlowReversal	system.allowFlowReversal	= true to allow flow reversal, false restricts to design direction (port_a -> port_b)
Advanced
MassFlowRate	m_flow_small	1E-4*abs(m_flow_nominal)	Small mass flow rate for regularization of zero flow [kg/s]
Boolean	homotopyInitialization	true	= true, use homotopy method
Diagnostics
Boolean	show_V_flow	false	= true, if volume flow rate at inflowing port is computed
Boolean	show_T	false	= true, if actual temperature at port is computed (may lead to events)
Flow resistance
Boolean	computeFlowResistance	true	=true, compute flow resistance. Set to false to assume no friction
Boolean	from_dp	false	= true, use m_flow = f(dp) else dp = f(m_flow)
Boolean	linearizeFlowResistance	false	= true, use linear relation between m_flow and dp for any flow rate
Real	deltaM	0.1	Fraction of nominal flow rate where flow transitions to laminar
Dynamics
Nominal condition
Time	tau	30	Time constant at nominal flow (if energyDynamics <> SteadyState) [s]
Equations
Dynamics	energyDynamics	Modelica.Fluid.Types.Dynamic...	Formulation of energy balance
Dynamics	massDynamics	energyDynamics	Formulation of mass balance
Initialization
AbsolutePressure	p_start	Medium.p_default	Start value of pressure [Pa]
Temperature	T_start	Medium.T_default	Start value of temperature [K]
MassFraction	X_start[Medium.nX]	Medium.X_default	Start value of mass fractions m_i/m [kg/kg]
ExtraProperty	C_start[Medium.nC]	fill(0, Medium.nC)	Start value of trace substances

Modelica definition

model TwoPortHeatMassExchanger 
  "Partial model transporting one fluid stream with storing mass or energy"
  extends Buildings.Fluid.Interfaces.PartialTwoPortInterface(
    port_a(h_outflow(start=h_outflow_start)),
    port_b(h_outflow(start=h_outflow_start)));
  extends Buildings.Fluid.Interfaces.TwoPortFlowResistanceParameters(
    final computeFlowResistance=true);
  import Modelica.Constants;

  replaceable Buildings.Fluid.MixingVolumes.MixingVolume vol
    constrainedby Buildings.Fluid.MixingVolumes.MixingVolume(
    redeclare final package Medium = Medium,
    nPorts = 2,
    V=m_flow_nominal*tau/rho_nominal,
    final m_flow_nominal = m_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) "Volume for fluid stream";

  parameter Modelica.SIunits.Time tau = 30 
    "Time constant at nominal flow (if energyDynamics <> SteadyState)";

  // Advanced
  parameter Boolean homotopyInitialization = true "= true, use homotopy method";

  // Dynamics
  parameter Modelica.Fluid.Types.Dynamics energyDynamics=Modelica.Fluid.Types.Dynamics.DynamicFreeInitial 
    "Formulation of energy balance";
  parameter Modelica.Fluid.Types.Dynamics massDynamics=energyDynamics 
    "Formulation of mass balance";

  // Initialization
  parameter Medium.AbsolutePressure p_start = Medium.p_default 
    "Start value of pressure";
  parameter Medium.Temperature T_start = Medium.T_default 
    "Start value of temperature";
  parameter Medium.MassFraction X_start[Medium.nX] = Medium.X_default 
    "Start value of mass fractions m_i/m";
  parameter Medium.ExtraProperty C_start[Medium.nC](
       quantity=Medium.extraPropertiesNames)=fill(0, Medium.nC) 
    "Start value of trace substances";

protected 
  parameter Medium.ThermodynamicState sta_nominal=Medium.setState_pTX(
      T=Medium.T_default, p=Medium.p_default, X=Medium.X_default);
  parameter Modelica.SIunits.Density rho_nominal=Medium.density(sta_nominal) 
    "Density, used to compute fluid volume";
  parameter Medium.ThermodynamicState sta_start=Medium.setState_pTX(
      T=T_start, p=p_start, X=X_start);
  parameter Modelica.SIunits.SpecificEnthalpy h_outflow_start = Medium.specificEnthalpy(sta_start) 
    "Start value for outflowing enthalpy";
public 
  Buildings.Fluid.FixedResistances.FixedResistanceDpM preDro(
    redeclare package Medium = Medium,
    final use_dh=false,
    final m_flow_nominal=m_flow_nominal,
    final deltaM=deltaM,
    final allowFlowReversal=allowFlowReversal,
    final m_flow_small=m_flow_small,
    final show_T=false,
    final show_V_flow=show_V_flow,
    final from_dp=from_dp,
    final linearized=linearizeFlowResistance,
    final homotopyInitialization=homotopyInitialization,
    final dp_nominal=dp_nominal) "Pressure drop model";
initial algorithm 
  assert((energyDynamics == Modelica.Fluid.Types.Dynamics.SteadyState) or 
          tau > Modelica.Constants.eps,
"The parameter tau, or the volume of the model from which tau may be derived, is unreasonably small.
 Set energyDynamics == Modelica.Fluid.Types.Dynamics.SteadyState to model steady-state.
 Received tau = " + String(tau) + "\n");
  assert((massDynamics == Modelica.Fluid.Types.Dynamics.SteadyState) or 
          tau > Modelica.Constants.eps,
"The parameter tau, or the volume of the model from which tau may be derived, is unreasonably small.          
 Set massDynamics == Modelica.Fluid.Types.Dynamics.SteadyState to model steady-state.
 Received tau = " + String(tau) + "\n");


equation 
  connect(vol.ports[2], port_b);
  connect(port_a, preDro.port_a);
  connect(preDro.port_b, vol.ports[1]);
end TwoPortHeatMassExchanger;

Buildings.Fluid.Interfaces.FourPortHeatMassExchanger

Information

This component transports two fluid streams between four ports. It provides the basic model for implementing a dynamic heat exchanger. It is used by Buildings.Fluid.HeatExchangers.BaseClasses.HexElement The variable names follow the conventions used in

Extends from Buildings.Fluid.Interfaces.PartialFourPortInterface (Partial model transporting fluid between two ports without storing mass or energy), Buildings.Fluid.Interfaces.FourPortFlowResistanceParameters (Parameters for flow resistance for models with four ports).

Parameters

Type	Name	Default	Description
replaceable package Medium1		PartialMedium	Medium 1 in the component
replaceable package Medium2		PartialMedium	Medium 2 in the component
MixingVolume	vol2	redeclare Buildings.Fluid.Mi...	Volume for fluid 2
Nominal condition
MassFlowRate	m1_flow_nominal		Nominal mass flow rate [kg/s]
MassFlowRate	m2_flow_nominal		Nominal mass flow rate [kg/s]
Pressure	dp1_nominal		Pressure [Pa]
Pressure	dp2_nominal		Pressure [Pa]
Initialization
MassFlowRate	m1_flow.start	0	Mass flow rate from port_a1 to port_b1 (m1_flow > 0 is design flow direction) [kg/s]
Pressure	dp1.start	0	Pressure difference between port_a1 and port_b1 [Pa]
MassFlowRate	m2_flow.start	0	Mass flow rate from port_a2 to port_b2 (m2_flow > 0 is design flow direction) [kg/s]
Pressure	dp2.start	0	Pressure difference between port_a2 and port_b2 [Pa]
Assumptions
Boolean	allowFlowReversal1	system.allowFlowReversal	= true to allow flow reversal in medium 1, false restricts to design direction (port_a -> port_b)
Boolean	allowFlowReversal2	system.allowFlowReversal	= true to allow flow reversal in medium 2, false restricts to design direction (port_a -> port_b)
Advanced
Initialization
SpecificEnthalpy	h_outflow_a1_start	h1_outflow_start	Start value for enthalpy flowing out of port a1 [J/kg]
SpecificEnthalpy	h_outflow_b1_start	h1_outflow_start	Start value for enthalpy flowing out of port b1 [J/kg]
SpecificEnthalpy	h_outflow_a2_start	h2_outflow_start	Start value for enthalpy flowing out of port a2 [J/kg]
SpecificEnthalpy	h_outflow_b2_start	h2_outflow_start	Start value for enthalpy flowing out of port b2 [J/kg]
MassFlowRate	m1_flow_small	1E-4*abs(m1_flow_nominal)	Small mass flow rate for regularization of zero flow [kg/s]
MassFlowRate	m2_flow_small	1E-4*abs(m2_flow_nominal)	Small mass flow rate for regularization of zero flow [kg/s]
Boolean	homotopyInitialization	true	= true, use homotopy method
Diagnostics
Boolean	show_V_flow	false	= true, if volume flow rate at inflowing port is computed
Boolean	show_T	false	= true, if actual temperature at port is computed (may lead to events)
Flow resistance
Medium 1
Boolean	computeFlowResistance1	true	=true, compute flow resistance. Set to false to assume no friction
Boolean	from_dp1	false	= true, use m_flow = f(dp) else dp = f(m_flow)
Boolean	linearizeFlowResistance1	false	= true, use linear relation between m_flow and dp for any flow rate
Real	deltaM1	0.1	Fraction of nominal flow rate where flow transitions to laminar
Medium 2
Boolean	computeFlowResistance2	true	=true, compute flow resistance. Set to false to assume no friction
Boolean	from_dp2	false	= true, use m_flow = f(dp) else dp = f(m_flow)
Boolean	linearizeFlowResistance2	false	= true, use linear relation between m_flow and dp for any flow rate
Real	deltaM2	0.1	Fraction of nominal flow rate where flow transitions to laminar
Dynamics
Nominal condition
Time	tau1	30	Time constant at nominal flow [s]
Time	tau2	30	Time constant at nominal flow [s]
Equations
Dynamics	energyDynamics	Modelica.Fluid.Types.Dynamic...	Formulation of energy balance
Dynamics	massDynamics	energyDynamics	Formulation of mass balance
Initialization
Medium 1
AbsolutePressure	p1_start	Medium1.p_default	Start value of pressure [Pa]
Temperature	T1_start	Medium1.T_default	Start value of temperature [K]
MassFraction	X1_start[Medium1.nX]	Medium1.X_default	Start value of mass fractions m_i/m [kg/kg]
ExtraProperty	C1_start[Medium1.nC]	fill(0, Medium1.nC)	Start value of trace substances
ExtraProperty	C1_nominal[Medium1.nC]	fill(1E-2, Medium1.nC)	Nominal value of trace substances. (Set to typical order of magnitude.)
Medium 2
AbsolutePressure	p2_start	Medium2.p_default	Start value of pressure [Pa]
Temperature	T2_start	Medium2.T_default	Start value of temperature [K]
MassFraction	X2_start[Medium2.nX]	Medium2.X_default	Start value of mass fractions m_i/m [kg/kg]
ExtraProperty	C2_start[Medium2.nC]	fill(0, Medium2.nC)	Start value of trace substances
ExtraProperty	C2_nominal[Medium2.nC]	fill(1E-2, Medium2.nC)	Nominal value of trace substances. (Set to typical order of magnitude.)

Connectors

Type	Name	Description
FluidPort_a	port_a1	Fluid connector a1 (positive design flow direction is from port_a1 to port_b1)
FluidPort_b	port_b1	Fluid connector b1 (positive design flow direction is from port_a1 to port_b1)
FluidPort_a	port_a2	Fluid connector a2 (positive design flow direction is from port_a2 to port_b2)
FluidPort_b	port_b2	Fluid connector b2 (positive design flow direction is from port_a2 to port_b2)

Modelica definition

model FourPortHeatMassExchanger 
  "Partial model transporting two fluid streams between four ports with storing mass or energy"
  extends Buildings.Fluid.Interfaces.PartialFourPortInterface(
    final h_outflow_a1_start = h1_outflow_start,
    final h_outflow_b1_start = h1_outflow_start,
    final h_outflow_a2_start = h2_outflow_start,
    final h_outflow_b2_start = h2_outflow_start);
  extends Buildings.Fluid.Interfaces.FourPortFlowResistanceParameters(
     final computeFlowResistance1=true, final computeFlowResistance2=true);
  import Modelica.Constants;

  Buildings.Fluid.MixingVolumes.MixingVolume vol1(
    redeclare final package Medium = Medium1,
    nPorts = 2,
    V=m1_flow_nominal*tau1/rho1_nominal,
    final m_flow_nominal=m1_flow_nominal,
    energyDynamics=if tau1 > Modelica.Constants.eps
                         then energyDynamics else 
                         Modelica.Fluid.Types.Dynamics.SteadyState,
    massDynamics=if tau1 > Modelica.Constants.eps
                         then massDynamics else 
                         Modelica.Fluid.Types.Dynamics.SteadyState,
    final p_start=p1_start,
    final T_start=T1_start,
    final X_start=X1_start,
    final C_start=C1_start,
    final C_nominal=C1_nominal) "Volume for fluid 1";

  replaceable Buildings.Fluid.MixingVolumes.MixingVolume vol2
    constrainedby Buildings.Fluid.MixingVolumes.MixingVolume(
    redeclare final package Medium = Medium2,
    nPorts = 2,
    V=m2_flow_nominal*tau2/rho2_nominal,
    final m_flow_nominal = m2_flow_nominal,
    energyDynamics=if tau2 > Modelica.Constants.eps
                         then energyDynamics else 
                         Modelica.Fluid.Types.Dynamics.SteadyState,
    massDynamics=if tau2 > Modelica.Constants.eps
                         then massDynamics else 
                         Modelica.Fluid.Types.Dynamics.SteadyState,
    final p_start=p2_start,
    final T_start=T2_start,
    final X_start=X2_start,
    final C_start=C2_start,
    final C_nominal=C2_nominal) "Volume for fluid 2";

  parameter Modelica.SIunits.Time tau1 = 30 "Time constant at nominal flow";
  parameter Modelica.SIunits.Time tau2 = 30 "Time constant at nominal flow";
  Modelica.SIunits.HeatFlowRate Q1_flow= sum(vol1.heatPort.Q_flow) 
    "Heat flow rate into medium 1";
  Modelica.SIunits.HeatFlowRate Q2_flow= sum(vol2.heatPort.Q_flow) 
    "Heat flow rate into medium 2";

  // Advanced
  parameter Boolean homotopyInitialization = true "= true, use homotopy method";

  // Assumptions
  parameter Modelica.Fluid.Types.Dynamics energyDynamics=Modelica.Fluid.Types.Dynamics.DynamicFreeInitial 
    "Formulation of energy balance";
  parameter Modelica.Fluid.Types.Dynamics massDynamics=energyDynamics 
    "Formulation of mass balance";

  // Initialization
  parameter Medium1.AbsolutePressure p1_start = Medium1.p_default 
    "Start value of pressure";
  parameter Medium1.Temperature T1_start = Medium1.T_default 
    "Start value of temperature";
  parameter Medium1.MassFraction X1_start[Medium1.nX] = Medium1.X_default 
    "Start value of mass fractions m_i/m";
  parameter Medium1.ExtraProperty C1_start[Medium1.nC](
       quantity=Medium1.extraPropertiesNames)=fill(0, Medium1.nC) 
    "Start value of trace substances";
  parameter Medium1.ExtraProperty C1_nominal[Medium1.nC](
       quantity=Medium1.extraPropertiesNames) = fill(1E-2, Medium1.nC) 
    "Nominal value of trace substances. (Set to typical order of magnitude.)";

  parameter Medium2.AbsolutePressure p2_start = Medium2.p_default 
    "Start value of pressure";
  parameter Medium2.Temperature T2_start = Medium2.T_default 
    "Start value of temperature";
  parameter Medium2.MassFraction X2_start[Medium2.nX] = Medium2.X_default 
    "Start value of mass fractions m_i/m";
  parameter Medium2.ExtraProperty C2_start[Medium2.nC](
       quantity=Medium2.extraPropertiesNames)=fill(0, Medium2.nC) 
    "Start value of trace substances";
  parameter Medium2.ExtraProperty C2_nominal[Medium2.nC](
       quantity=Medium2.extraPropertiesNames) = fill(1E-2, Medium2.nC) 
    "Nominal value of trace substances. (Set to typical order of magnitude.)";

protected 
  parameter Medium1.ThermodynamicState sta1_nominal=Medium1.setState_pTX(
      T=Medium1.T_default, p=Medium1.p_default, X=Medium1.X_default);
  parameter Modelica.SIunits.Density rho1_nominal=Medium1.density(sta1_nominal) 
    "Density, used to compute fluid volume";
  parameter Medium2.ThermodynamicState sta2_nominal=Medium2.setState_pTX(
      T=Medium2.T_default, p=Medium2.p_default, X=Medium2.X_default);
  parameter Modelica.SIunits.Density rho2_nominal=Medium2.density(sta2_nominal) 
    "Density, used to compute fluid volume";

  parameter Medium1.ThermodynamicState sta1_start=Medium1.setState_pTX(
      T=T1_start, p=p1_start, X=X1_start);
  parameter Modelica.SIunits.SpecificEnthalpy h1_outflow_start = Medium1.specificEnthalpy(sta1_start) 
    "Start value for outflowing enthalpy";
  parameter Medium2.ThermodynamicState sta2_start=Medium2.setState_pTX(
      T=T2_start, p=p2_start, X=X2_start);
  parameter Modelica.SIunits.SpecificEnthalpy h2_outflow_start = Medium2.specificEnthalpy(sta2_start) 
    "Start value for outflowing enthalpy";

public 
  FixedResistances.FixedResistanceDpM preDro1(
    redeclare package Medium = Medium1,
    final use_dh=false,
    final m_flow_nominal=m1_flow_nominal,
    final deltaM=deltaM1,
    final allowFlowReversal=allowFlowReversal1,
    final m_flow_small=m1_flow_small,
    final show_T=false,
    final show_V_flow=show_V_flow,
    final from_dp=from_dp1,
    final linearized=linearizeFlowResistance1,
    final homotopyInitialization=homotopyInitialization,
    final dp_nominal=dp1_nominal,
    final dh=1,
    final ReC=4000) "Pressure drop model for fluid 1";

  FixedResistances.FixedResistanceDpM preDro2(
    redeclare package Medium = Medium2,
    final use_dh=false,
    final m_flow_nominal=m2_flow_nominal,
    final deltaM=deltaM2,
    final allowFlowReversal=allowFlowReversal2,
    final m_flow_small=m2_flow_small,
    final show_T=false,
    final show_V_flow=show_V_flow,
    final from_dp=from_dp2,
    final linearized=linearizeFlowResistance2,
    final homotopyInitialization=homotopyInitialization,
    final dp_nominal=dp2_nominal,
    final dh=1,
    final ReC=4000) "Pressure drop model for fluid 2";

equation 
  connect(vol1.ports[2], port_b1);
  connect(vol2.ports[2], port_b2);
  connect(port_a1, preDro1.port_a);
  connect(preDro1.port_b, vol1.ports[1]);
  connect(port_a2, preDro2.port_a);
  connect(preDro2.port_b, vol2.ports[1]);
end FourPortHeatMassExchanger;

Buildings.Fluid.Interfaces.StaticTwoPortHeatMassExchanger

Information

This component transports fluid between its two ports, without storing mass or energy. It is based on Modelica.Fluid.Interfaces.PartialTwoPortTransport but it does use a different implementation for handling reverse flow because in this component, mass flow rate can be added or removed from the medium.

If dp_nominal > Modelica.Constants.eps, this component computes pressure drop due to flow friction. The pressure drop is defined by a quadratic function that goes through the point (m_flow_nominal, dp_nominal). At |m_flow| < deltaM * m_flow_nominal, the pressure drop vs. flow relation is linearized. If the parameter linearizeFlowResistance is set to true, then the whole pressure drop vs. flow resistance curve is linearized.

Implementation

This model uses inputs and constants that need to be set by models that extend or instantiate this model. The following inputs need to be assigned:

• Q_flow, which is the heat flow rate added to the medium.
• mXi_flow, which is the species mass flow rate added to the medium.

Set the constant sensibleOnly=true if the model that extends or instantiates this model sets mXi_flow = zeros(Medium.nXi).

Extends from Buildings.Fluid.Interfaces.PartialTwoPortInterface (Partial model transporting fluid between two ports without storing mass or energy), Buildings.Fluid.Interfaces.TwoPortFlowResistanceParameters (Parameters for flow resistance for models with two ports).

Parameters

Type	Name	Default	Description
replaceable package Medium		PartialMedium	Medium in the component
Boolean	sensibleOnly		Set to true if sensible exchange only
Nominal condition
MassFlowRate	m_flow_nominal		Nominal mass flow rate [kg/s]
Pressure	dp_nominal		Pressure [Pa]
Initialization
MassFlowRate	m_flow.start	0	Mass flow rate from port_a to port_b (m_flow > 0 is design flow direction) [kg/s]
Pressure	dp.start	0	Pressure difference between port_a and port_b [Pa]
Assumptions
Boolean	allowFlowReversal	system.allowFlowReversal	= true to allow flow reversal, false restricts to design direction (port_a -> port_b)
Advanced
MassFlowRate	m_flow_small	1E-4*abs(m_flow_nominal)	Small mass flow rate for regularization of zero flow [kg/s]
Boolean	homotopyInitialization	true	= true, use homotopy method
Diagnostics
Boolean	show_V_flow	false	= true, if volume flow rate at inflowing port is computed
Boolean	show_T	true	= true, if actual temperature at port is computed (may lead to events)
Flow resistance
Boolean	computeFlowResistance	(abs(dp_nominal) > Modelica....	=true, compute flow resistance. Set to false to assume no friction
Boolean	from_dp	false	= true, use m_flow = f(dp) else dp = f(m_flow)
Boolean	linearizeFlowResistance	false	= true, use linear relation between m_flow and dp for any flow rate
Real	deltaM	0.1	Fraction of nominal flow rate where flow transitions to laminar

Connectors

Type	Name	Description
FluidPort_a	port_a	Fluid connector a (positive design flow direction is from port_a to port_b)
FluidPort_b	port_b	Fluid connector b (positive design flow direction is from port_a to port_b)
output RealOutput	hOut	Leaving temperature of the component [J/kg]
output RealOutput	XiOut[Medium.nXi]	Leaving species concentration of the component [1]
output RealOutput	COut[Medium.nC]	Leaving trace substances of the component [1]

Modelica definition

model StaticTwoPortHeatMassExchanger 
  "Partial model transporting fluid between two ports without storing mass or energy"
  extends Buildings.Fluid.Interfaces.PartialTwoPortInterface(
  showDesignFlowDirection = false,
  final show_T=true);
  extends Buildings.Fluid.Interfaces.TwoPortFlowResistanceParameters(
    final computeFlowResistance=(abs(dp_nominal) > Modelica.Constants.eps));
  import Modelica.Constants;
  input Modelica.SIunits.HeatFlowRate Q_flow "Heat transfered into the medium";
  input Medium.MassFlowRate mXi_flow[Medium.nXi] 
    "Mass flow rates of independent substances added to the medium";
  constant Boolean sensibleOnly "Set to true if sensible exchange only";
  // Outputs that are needed in models that extend this model
  Modelica.Blocks.Interfaces.RealOutput hOut(unit="J/kg") 
    "Leaving temperature of the component";
  Modelica.Blocks.Interfaces.RealOutput XiOut[Medium.nXi](unit="1") 
    "Leaving species concentration of the component";
  Modelica.Blocks.Interfaces.RealOutput COut[Medium.nC](unit="1") 
    "Leaving trace substances of the component";
  constant Boolean use_safeDivision=true 
    "Set to true to improve numerical robustness";
protected 
  Real m_flowInv(unit="s/kg") "Regularization of 1/m_flow";
  final parameter Real k(unit="")=if computeFlowResistance
   then abs(m_flow_nominal)/sqrt(abs(dp_nominal)) else 0 
    "Flow coefficient, k=m_flow/sqrt(dp), with unit=(kg.m)^(1/2)";
  final parameter Real kLin(unit="") = if computeFlowResistance
   then abs(m_flow_nominal/dp_nominal) else 0;
equation 
  // Regularization of m_flow around the origin to avoid a division by zero
/*  m_flowInv = smooth(2, if (abs(port_a.m_flow) > m_flow_small/1E3) then 
      1/port_a.m_flow
      else 
      Buildings.Utilities.Math.Functions.inverseXRegularized(x=port_a.m_flow, delta=m_flow_small/1E3));
 */
 if use_safeDivision then
    m_flowInv = Buildings.Utilities.Math.Functions.inverseXRegularized(x=port_a.m_flow, delta=m_flow_small/1E3);
 else
     m_flowInv = 1/port_a.m_flow;
 end if;
 if allowFlowReversal then
/* This formulation fails to simulate in Buildings.Fluid.MixingVolumes.Examples.MixingVolumePrescribedHeatFlowRate. See also Dynasim ticket 13596
   if (port_a.m_flow >= 0) then
     hOut =  port_b.h_outflow;
     XiOut = port_b.Xi_outflow;
     COut =  port_b.C_outflow;
    else
     hOut =  port_a.h_outflow;
     XiOut = port_a.Xi_outflow;
     COut =  port_a.C_outflow;
    end if;
*/
   hOut = smooth(0, if (port_a.m_flow >= 0) then 
      port_b.h_outflow else 
      port_a.h_outflow);
   XiOut = smooth(0, if (port_a.m_flow >= 0) then 
      port_b.Xi_outflow else 
      port_a.Xi_outflow);
   COut = smooth(0, if (port_a.m_flow >= 0) then 
      port_b.C_outflow else 
      port_a.C_outflow);

 else
   hOut =  port_b.h_outflow;
   XiOut = port_b.Xi_outflow;
   COut =  port_b.C_outflow;
 end if;
  //////////////////////////////////////////////////////////////////////////////////////////
  // Energy balance and mass balance
  if sensibleOnly then
    // Mass balance
    port_a.m_flow = -port_b.m_flow;
    // Energy balance
    port_b.h_outflow = inStream(port_a.h_outflow) + Q_flow * m_flowInv;
    port_a.h_outflow = inStream(port_b.h_outflow) - Q_flow * m_flowInv;
    // Transport of species
    port_a.Xi_outflow = inStream(port_b.Xi_outflow);
    port_b.Xi_outflow = inStream(port_a.Xi_outflow);
    // Transport of trace substances
    port_a.C_outflow = inStream(port_b.C_outflow);
    port_b.C_outflow = inStream(port_a.C_outflow);
  else
    // Mass balance (no storage)
    port_a.m_flow + port_b.m_flow = -sum(mXi_flow);
    // Energy balance.
    // This equation is approximate since m_flow = port_a.m_flow is used for the mass flow rate
    // at both ports. Since mXi_flow << m_flow, the error is small.
    port_b.h_outflow = inStream(port_a.h_outflow) + Q_flow * m_flowInv;
    port_a.h_outflow = inStream(port_b.h_outflow) - Q_flow * m_flowInv;
    // Transport of species
    for i in 1:Medium.nXi loop
      port_b.Xi_outflow[i] = inStream(port_a.Xi_outflow[i]) + mXi_flow[i] * m_flowInv;
      port_a.Xi_outflow[i] = inStream(port_b.Xi_outflow[i]) - mXi_flow[i] * m_flowInv;
    end for;
    // Transport of trace substances
    for i in 1:Medium.nC loop
      port_a.m_flow*port_a.C_outflow[i] = -port_b.m_flow*inStream(port_b.C_outflow[i]);
      port_b.m_flow*port_b.C_outflow[i] = -port_a.m_flow*inStream(port_a.C_outflow[i]);
    end for;
  end if; // sensibleOnly
  //////////////////////////////////////////////////////////////////////////////////////////
  // Pressure drop calculation
  if computeFlowResistance then
    if linearizeFlowResistance then
      m_flow = kLin*dp;
    else
      if homotopyInitialization then
        if from_dp then
           m_flow = homotopy(actual=Buildings.Fluid.BaseClasses.FlowModels.basicFlowFunction_dp(
                                    dp=dp,
                                    k=k,
                                    m_flow_turbulent=deltaM * m_flow_nominal),
                                    simplified=m_flow_nominal*dp/dp_nominal);
         else
           dp = homotopy(actual=Buildings.Fluid.BaseClasses.FlowModels.basicFlowFunction_m_flow(
                                    m_flow=m_flow,
                                    k=k,
                                    m_flow_turbulent=deltaM * m_flow_nominal),
                                    simplified=dp_nominal*m_flow/m_flow_nominal);
        end if; // from_dp
      else // do not use homotopy
        if from_dp then
          m_flow = Buildings.Fluid.BaseClasses.FlowModels.basicFlowFunction_dp(
                                    dp=dp,
                                    k=k,
                                    m_flow_turbulent=deltaM * m_flow_nominal);
        else
          dp = Buildings.Fluid.BaseClasses.FlowModels.basicFlowFunction_m_flow(
                                    m_flow=m_flow,
                                    k=k,
                                    m_flow_turbulent=deltaM * m_flow_nominal);
        end if; // from_dp
      end if; // homotopyInitialization
    end if; // linearized
  else // do not compute flow resistance
    dp = 0;
  end if; // computeFlowResistance
end StaticTwoPortHeatMassExchanger;

Buildings.Fluid.Interfaces.StaticFourPortHeatMassExchanger

Information

This component transports two fluid streams between four ports, without storing mass or energy. It is similar to Buildings.Fluid.Interfaces.StaticTwoPortHeatMassExchanger, but it has four ports instead of two.

If dpN_nominal > Modelica.Constants.eps, where N denotes the fluid 1 or 2, then the model computes pressure drop due to flow friction in the respective fluid stream. The pressure drop is defined by a quadratic function that goes through the point (mN_flow_nominal, dpN_nominal). At |mN_flow| < deltaMN * mN_flow_nominal, the pressure drop vs. flow relation is linearized. If the parameter linearizeFlowResistanceN is set to true, then the whole pressure drop vs. flow resistance curve is linearized.

Implementation

This model uses inputs and constants that need to be set by models that extend or instantiate this model. The following inputs need to be assigned, where N denotes 1 or 2:

• QN_flow, which is the heat flow rate added to the medium N.
• mXiN_flow, which is the species mass flow rate added to the medium N.

Set the constant sensibleOnlyN=true if the model that extends or instantiates this model sets mXiN_flow = zeros(Medium.nXiN).

Note that the model does not implement 0 = Q1_flow + Q2_flow or 0 = mXi1_flow + mXi2_flow. If there is no heat or mass transfer with the environment, then a model that extends this model needs to provide these equations.

Extends from Buildings.Fluid.Interfaces.PartialFourPortInterface (Partial model transporting fluid between two ports without storing mass or energy), Buildings.Fluid.Interfaces.FourPortFlowResistanceParameters (Parameters for flow resistance for models with four ports).

Parameters

Type	Name	Default	Description
replaceable package Medium1		PartialMedium	Medium 1 in the component
replaceable package Medium2		PartialMedium	Medium 2 in the component
Boolean	sensibleOnly1		Set to true if sensible exchange only for medium 1
Boolean	sensibleOnly2		Set to true if sensible exchange only for medium 2
Nominal condition
MassFlowRate	m1_flow_nominal		Nominal mass flow rate [kg/s]
MassFlowRate	m2_flow_nominal		Nominal mass flow rate [kg/s]
Pressure	dp1_nominal		Pressure [Pa]
Pressure	dp2_nominal		Pressure [Pa]
Initialization
MassFlowRate	m1_flow.start	0	Mass flow rate from port_a1 to port_b1 (m1_flow > 0 is design flow direction) [kg/s]
Pressure	dp1.start	0	Pressure difference between port_a1 and port_b1 [Pa]
MassFlowRate	m2_flow.start	0	Mass flow rate from port_a2 to port_b2 (m2_flow > 0 is design flow direction) [kg/s]
Pressure	dp2.start	0	Pressure difference between port_a2 and port_b2 [Pa]
Assumptions
Boolean	allowFlowReversal1	system.allowFlowReversal	= true to allow flow reversal in medium 1, false restricts to design direction (port_a -> port_b)
Boolean	allowFlowReversal2	system.allowFlowReversal	= true to allow flow reversal in medium 2, false restricts to design direction (port_a -> port_b)
Advanced
Initialization
SpecificEnthalpy	h_outflow_a1_start	Medium1.h_default	Start value for enthalpy flowing out of port a1 [J/kg]
SpecificEnthalpy	h_outflow_b1_start	Medium1.h_default	Start value for enthalpy flowing out of port b1 [J/kg]
SpecificEnthalpy	h_outflow_a2_start	Medium2.h_default	Start value for enthalpy flowing out of port a2 [J/kg]
SpecificEnthalpy	h_outflow_b2_start	Medium2.h_default	Start value for enthalpy flowing out of port b2 [J/kg]
MassFlowRate	m1_flow_small	1E-4*abs(m1_flow_nominal)	Small mass flow rate for regularization of zero flow [kg/s]
MassFlowRate	m2_flow_small	1E-4*abs(m2_flow_nominal)	Small mass flow rate for regularization of zero flow [kg/s]
Boolean	homotopyInitialization	true	= true, use homotopy method
Diagnostics
Boolean	show_V_flow	false	= true, if volume flow rate at inflowing port is computed
Boolean	show_T	false	= true, if actual temperature at port is computed (may lead to events)
Flow resistance
Medium 1
Boolean	computeFlowResistance1	(dp1_nominal > Modelica.Cons...	=true, compute flow resistance. Set to false to assume no friction
Boolean	from_dp1	false	= true, use m_flow = f(dp) else dp = f(m_flow)
Boolean	linearizeFlowResistance1	false	= true, use linear relation between m_flow and dp for any flow rate
Real	deltaM1	0.1	Fraction of nominal flow rate where flow transitions to laminar
Medium 2
Boolean	computeFlowResistance2	(dp2_nominal > Modelica.Cons...	=true, compute flow resistance. Set to false to assume no friction
Boolean	from_dp2	false	= true, use m_flow = f(dp) else dp = f(m_flow)
Boolean	linearizeFlowResistance2	false	= true, use linear relation between m_flow and dp for any flow rate
Real	deltaM2	0.1	Fraction of nominal flow rate where flow transitions to laminar

Connectors

Type	Name	Description
FluidPort_a	port_a1	Fluid connector a1 (positive design flow direction is from port_a1 to port_b1)
FluidPort_b	port_b1	Fluid connector b1 (positive design flow direction is from port_a1 to port_b1)
FluidPort_a	port_a2	Fluid connector a2 (positive design flow direction is from port_a2 to port_b2)
FluidPort_b	port_b2	Fluid connector b2 (positive design flow direction is from port_a2 to port_b2)

Modelica definition

model StaticFourPortHeatMassExchanger 
  "Partial model transporting two fluid streams between four ports without storing mass or energy"
  extends Buildings.Fluid.Interfaces.PartialFourPortInterface;
  extends Buildings.Fluid.Interfaces.FourPortFlowResistanceParameters(
   final computeFlowResistance1=(dp1_nominal > Modelica.Constants.eps),
   final computeFlowResistance2=(dp2_nominal > Modelica.Constants.eps));
  import Modelica.Constants;
  input Modelica.SIunits.HeatFlowRate Q1_flow 
    "Heat transfered into the medium 1";
  input Medium1.MassFlowRate mXi1_flow[Medium1.nXi] 
    "Mass flow rates of independent substances added to the medium 1";
  input Modelica.SIunits.HeatFlowRate Q2_flow 
    "Heat transfered into the medium 2";
  input Medium2.MassFlowRate mXi2_flow[Medium2.nXi] 
    "Mass flow rates of independent substances added to the medium 2";
  constant Boolean sensibleOnly1 
    "Set to true if sensible exchange only for medium 1";
  constant Boolean sensibleOnly2 
    "Set to true if sensible exchange only for medium 2";
protected 
  Buildings.Fluid.Interfaces.StaticTwoPortHeatMassExchanger bal1(
    final sensibleOnly = sensibleOnly1,
    redeclare final package Medium=Medium1,
    final m_flow_nominal = m1_flow_nominal,
    final dp_nominal = dp1_nominal,
    final allowFlowReversal = allowFlowReversal1,
    final m_flow_small = m1_flow_small,
    final homotopyInitialization = homotopyInitialization,
    final show_V_flow = false,
    final from_dp = from_dp1,
    final linearizeFlowResistance = linearizeFlowResistance1,
    final deltaM = deltaM1,
    final Q_flow = Q1_flow,
    final mXi_flow = mXi1_flow) 
    "Model for heat, mass, species, trace substance and pressure balance of stream 1";
  Buildings.Fluid.Interfaces.StaticTwoPortHeatMassExchanger bal2(
    final sensibleOnly = sensibleOnly2,
    redeclare final package Medium=Medium2,
    final m_flow_nominal = m2_flow_nominal,
    final dp_nominal = dp2_nominal,
    final allowFlowReversal = allowFlowReversal2,
    final m_flow_small = m2_flow_small,
    final homotopyInitialization = homotopyInitialization,
    final show_V_flow = false,
    final from_dp = from_dp2,
    final linearizeFlowResistance = linearizeFlowResistance2,
    final deltaM = deltaM2,
    final Q_flow = Q2_flow,
    final mXi_flow = mXi2_flow) 
    "Model for heat, mass, species, trace substance and pressure balance of stream 2";
equation 
  connect(bal1.port_a, port_a1);
  connect(bal1.port_b, port_b1);
  connect(bal2.port_a, port_a2);
  connect(bal2.port_b, port_b2);
end StaticFourPortHeatMassExchanger;

Buildings.Fluid.Interfaces.PartialTwoPortInterface

Information

This component defines the interface for models that transports a fluid between two ports. It is similar to Modelica.Fluid.Interfaces.PartialTwoPortTransport, but it does not include the species balance

  port_b.Xi_outflow = inStream(port_a.Xi_outflow);

The model is used by other models in this package that add heat transfer, mass transfer and pressure drop equations. See for example Buildings.Fluid.Interfaces.StaticTwoPortHeatMassExchanger.

Extends from Modelica.Fluid.Interfaces.PartialTwoPort (Partial component with two ports).

Parameters

Type	Name	Default	Description
replaceable package Medium		PartialMedium	Medium in the component
Nominal condition
MassFlowRate	m_flow_nominal		Nominal mass flow rate [kg/s]
Assumptions
Boolean	allowFlowReversal	system.allowFlowReversal	= true to allow flow reversal, false restricts to design direction (port_a -> port_b)
Advanced
MassFlowRate	m_flow_small	1E-4*abs(m_flow_nominal)	Small mass flow rate for regularization of zero flow [kg/s]
Boolean	homotopyInitialization	true	= true, use homotopy method
Diagnostics
Boolean	show_V_flow	false	= true, if volume flow rate at inflowing port is computed
Boolean	show_T	false	= true, if actual temperature at port is computed (may lead to events)

Modelica definition

partial model PartialTwoPortInterface 
  "Partial model transporting fluid between two ports without storing mass or energy"
  import Modelica.Constants;
  extends Modelica.Fluid.Interfaces.PartialTwoPort(
    port_a(p(start=Medium.p_default,
             nominal=Medium.p_default)),
    port_b(p(start=Medium.p_default,
           nominal=Medium.p_default)));

  parameter Medium.MassFlowRate m_flow_nominal "Nominal mass flow rate";
  parameter Medium.MassFlowRate m_flow_small(min=0) = 1E-4*abs(m_flow_nominal) 
    "Small mass flow rate for regularization of zero flow";
  parameter Boolean homotopyInitialization = true "= true, use homotopy method";

  // Diagnostics
   parameter Boolean show_V_flow = false 
    "= true, if volume flow rate at inflowing port is computed";
   parameter Boolean show_T = false 
    "= true, if actual temperature at port is computed (may lead to events)";

  Modelica.SIunits.VolumeFlowRate V_flow=
      m_flow/Medium.density(sta_a) if show_V_flow 
    "Volume flow rate at inflowing port (positive when flow from port_a to port_b)";

  Medium.MassFlowRate m_flow(start=0) = port_a.m_flow 
    "Mass flow rate from port_a to port_b (m_flow > 0 is design flow direction)";
  Modelica.SIunits.Pressure dp(start=0, displayUnit="Pa") = port_a.p - port_b.p 
    "Pressure difference between port_a and port_b";

  Medium.ThermodynamicState sta_a=if homotopyInitialization then 
      Medium.setState_phX(port_a.p,
                          homotopy(actual=actualStream(port_a.h_outflow),
                                   simplified=inStream(port_a.h_outflow)),
                          homotopy(actual=actualStream(port_a.Xi_outflow),
                                   simplified=inStream(port_a.Xi_outflow)))
    else 
      Medium.setState_phX(port_a.p,
                          actualStream(port_a.h_outflow),
                          actualStream(port_a.Xi_outflow)) if 
         show_T "Medium properties in port_a";

  Medium.ThermodynamicState sta_b=if homotopyInitialization then 
      Medium.setState_phX(port_b.p,
                          homotopy(actual=actualStream(port_b.h_outflow),
                                   simplified=port_b.h_outflow),
                          homotopy(actual=actualStream(port_b.Xi_outflow),
                            simplified=port_b.Xi_outflow))
    else 
      Medium.setState_phX(port_b.p,
                          actualStream(port_b.h_outflow),
                          actualStream(port_b.Xi_outflow)) if 
          show_T "Medium properties in port_b";

end PartialTwoPortInterface;

Buildings.Fluid.Interfaces.PartialFourPortInterface

Information

This component defines the interface for models that transport two fluid streams between four ports. It is similar to Buildings.Fluid.Interfaces.PartialTwoPortInterface, but it has four ports instead of two.

The model is used by other models in this package that add heat transfer, mass transfer and pressure drop equations.

Extends from Buildings.Fluid.Interfaces.FourPort (Partial model with four ports).

Parameters

Type	Name	Default	Description
replaceable package Medium1		PartialMedium	Medium 1 in the component
replaceable package Medium2		PartialMedium	Medium 2 in the component
Nominal condition
MassFlowRate	m1_flow_nominal		Nominal mass flow rate [kg/s]
MassFlowRate	m2_flow_nominal		Nominal mass flow rate [kg/s]
Assumptions
Boolean	allowFlowReversal1	system.allowFlowReversal	= true to allow flow reversal in medium 1, false restricts to design direction (port_a -> port_b)
Boolean	allowFlowReversal2	system.allowFlowReversal	= true to allow flow reversal in medium 2, false restricts to design direction (port_a -> port_b)
Advanced
Initialization
SpecificEnthalpy	h_outflow_a1_start	Medium1.h_default	Start value for enthalpy flowing out of port a1 [J/kg]
SpecificEnthalpy	h_outflow_b1_start	Medium1.h_default	Start value for enthalpy flowing out of port b1 [J/kg]
SpecificEnthalpy	h_outflow_a2_start	Medium2.h_default	Start value for enthalpy flowing out of port a2 [J/kg]
SpecificEnthalpy	h_outflow_b2_start	Medium2.h_default	Start value for enthalpy flowing out of port b2 [J/kg]
MassFlowRate	m1_flow_small	1E-4*abs(m1_flow_nominal)	Small mass flow rate for regularization of zero flow [kg/s]
MassFlowRate	m2_flow_small	1E-4*abs(m2_flow_nominal)	Small mass flow rate for regularization of zero flow [kg/s]
Boolean	homotopyInitialization	true	= true, use homotopy method
Diagnostics
Boolean	show_V_flow	false	= true, if volume flow rate at inflowing port is computed
Boolean	show_T	false	= true, if actual temperature at port is computed (may lead to events)

Modelica definition

partial model PartialFourPortInterface 
  "Partial model transporting fluid between two ports without storing mass or energy"
  import Modelica.Constants;
  extends Buildings.Fluid.Interfaces.FourPort(
    port_a1(
      m_flow(min = if allowFlowReversal1 then -Constants.inf else 0)),
    port_b1(
      m_flow(max = if allowFlowReversal1 then +Constants.inf else 0)),
    port_a2(
      m_flow(min = if allowFlowReversal2 then -Constants.inf else 0)),
    port_b2(
      m_flow(max = if allowFlowReversal2 then +Constants.inf else 0)));
  parameter Modelica.SIunits.MassFlowRate m1_flow_nominal(min=0) 
    "Nominal mass flow rate";
  parameter Modelica.SIunits.MassFlowRate m2_flow_nominal(min=0) 
    "Nominal mass flow rate";
  parameter Medium1.MassFlowRate m1_flow_small(min=0) = 1E-4*abs(m1_flow_nominal) 
    "Small mass flow rate for regularization of zero flow";
  parameter Medium2.MassFlowRate m2_flow_small(min=0) = 1E-4*abs(m2_flow_nominal) 
    "Small mass flow rate for regularization of zero flow";
  parameter Boolean homotopyInitialization = true "= true, use homotopy method";
  // Diagnostics
  parameter Boolean show_V_flow = false 
    "= true, if volume flow rate at inflowing port is computed";
  parameter Boolean show_T = false 
    "= true, if actual temperature at port is computed (may lead to events)";
public 
  Modelica.SIunits.VolumeFlowRate V1_flow=m1_flow/Medium.density(sta_a1) if 
        show_V_flow 
    "Volume flow rate at inflowing port (positive when flow from port_a1 to port_b1)";
  Modelica.SIunits.VolumeFlowRate V2_flow=m2_flow/Medium.density(sta_a2) if 
        show_V_flow 
    "Volume flow rate at inflowing port (positive when flow from port_a2 to port_b2)";
  Medium1.MassFlowRate m1_flow(start=0) = port_a1.m_flow 
    "Mass flow rate from port_a1 to port_b1 (m1_flow > 0 is design flow direction)";
  Modelica.SIunits.Pressure dp1(start=0, displayUnit="Pa") = port_a1.p - port_b1.p 
    "Pressure difference between port_a1 and port_b1";
  Medium2.MassFlowRate m2_flow(start=0) = port_a2.m_flow 
    "Mass flow rate from port_a2 to port_b2 (m2_flow > 0 is design flow direction)";
  Modelica.SIunits.Pressure dp2(start=0, displayUnit="Pa") = port_a2.p - port_b2.p 
    "Pressure difference between port_a2 and port_b2";
  Medium1.ThermodynamicState sta_a1=if homotopyInitialization then 
      Medium1.setState_phX(port_a1.p,
         homotopy(actual=actualStream(port_a1.h_outflow),
                  simplified=inStream(port_a1.h_outflow)),
         homotopy(actual=actualStream(port_a1.Xi_outflow),
                  simplified=inStream(port_a1.Xi_outflow)))
    else 
      Medium1.setState_phX(port_a1.p,
                           actualStream(port_a1.h_outflow),
                           actualStream(port_a1.Xi_outflow)) if 
         show_T "Medium properties in port_a1";
  Medium1.ThermodynamicState sta_b1=if homotopyInitialization then 
      Medium1.setState_phX(port_b1.p,
          homotopy(actual=actualStream(port_b1.h_outflow),
                   simplified=port_b1.h_outflow),
          homotopy(actual=actualStream(port_b1.Xi_outflow),
                   simplified=port_b1.Xi_outflow))
    else 
      Medium1.setState_phX(port_b1.p,
                           actualStream(port_b1.h_outflow),
                           actualStream(port_b1.Xi_outflow)) if 
         show_T "Medium properties in port_b1";
  Medium2.ThermodynamicState sta_a2=if homotopyInitialization then 
      Medium2.setState_phX(port_b2.p,
          homotopy(actual=actualStream(port_a2.h_outflow),
                   simplified=inStream(port_a2.h_outflow)),
          homotopy(actual=actualStream(port_a2.Xi_outflow),
                   simplified=inStream(port_a2.Xi_outflow)))
    else 
      Medium2.setState_phX(port_a2.p,
                           actualStream(port_a2.h_outflow),
                           actualStream(port_a2.Xi_outflow)) if 
         show_T "Medium properties in port_a2";
  Medium2.ThermodynamicState sta_b2=if homotopyInitialization then 
      Medium2.setState_phX(port_b2.p,
          homotopy(actual=actualStream(port_b2.h_outflow),
                   simplified=port_b2.h_outflow),
          homotopy(actual=actualStream(port_b2.Xi_outflow),
                   simplified=port_b2.Xi_outflow))
    else 
      Medium2.setState_phX(port_b2.p,
                           actualStream(port_b2.h_outflow),
                           actualStream(port_b2.Xi_outflow)) if 
         show_T "Medium properties in port_b2";
protected 
  Medium1.ThermodynamicState state_a1_inflow=
    Medium1.setState_phX(port_a1.p, inStream(port_a1.h_outflow), inStream(port_a1.Xi_outflow)) 
    "state for medium inflowing through port_a1";
  Medium1.ThermodynamicState state_b1_inflow=
    Medium1.setState_phX(port_b1.p, inStream(port_b1.h_outflow), inStream(port_b1.Xi_outflow)) 
    "state for medium inflowing through port_b1";
  Medium2.ThermodynamicState state_a2_inflow=
    Medium2.setState_phX(port_a2.p, inStream(port_a2.h_outflow), inStream(port_a2.Xi_outflow)) 
    "state for medium inflowing through port_a2";
  Medium2.ThermodynamicState state_b2_inflow=
    Medium2.setState_phX(port_b2.p, inStream(port_b2.h_outflow), inStream(port_b2.Xi_outflow)) 
    "state for medium inflowing through port_b2";
end PartialFourPortInterface;

Buildings.Fluid.Interfaces.LumpedVolume

Information

Basic model for an ideally mixed fluid volume with the ability to store mass and energy.

Implementation

When extending or instantiating this model, the following inputs need to be assigned:

• fluidVolume, which is the actual volume occupied by the fluid. For most components, this can be set to a parameter. However, for components such as expansion vessels, the fluid volume can change in time.
• Q_flow, which is the sensible plus latent heat flow rate added to the medium.
• mXi_flow, which is the species mass flow rate added to the medium.

The model can be used as a dynamic model or as a steady-state model. However, for a steady-state model with exactly two fluid ports connected, the model Buildings.Fluid.Interfaces.StaticTwoPortHeatMassExchanger provides a more efficient implementation.

For models that instantiates this model, see Buildings.Fluid.MixingVolumes.MixingVolume and Buildings.Fluid.Storage.ExpansionVessel.

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

Parameters

Type	Name	Default	Description
replaceable package Medium		PartialMedium	Medium in the component
Dynamics
Equations
Dynamics	energyDynamics	Modelica.Fluid.Types.Dynamic...	Formulation of energy balance
Dynamics	massDynamics	energyDynamics	Formulation of mass balance
Initialization
AbsolutePressure	p_start	Medium.p_default	Start value of pressure [Pa]
Temperature	T_start	Medium.T_default	Start value of temperature [K]
MassFraction	X_start[Medium.nX]	Medium.X_default	Start value of mass fractions m_i/m [kg/kg]
ExtraProperty	C_start[Medium.nC]	fill(0, Medium.nC)	Start value of trace substances
ExtraProperty	C_nominal[Medium.nC]	fill(1E-2, Medium.nC)	Nominal value of trace substances. (Set to typical order of magnitude.)

Connectors

Type	Name	Description
VesselFluidPorts_b	ports[nPorts]	Fluid inlets and outlets
output RealOutput	hOut	Leaving temperature of the component [J/kg]
output RealOutput	XiOut[Medium.nXi]	Leaving species concentration of the component [1]
output RealOutput	COut[Medium.nC]	Leaving trace substances of the component [1]

Modelica definition

model LumpedVolume "Lumped volume with mass and energy balance"

//  outer Modelica.Fluid.System system "System properties";
  extends Buildings.Fluid.Interfaces.LumpedVolumeDeclarations;
  // Port definitions
  parameter Integer nPorts=0 "Number of ports";
  Modelica.Fluid.Vessels.BaseClasses.VesselFluidPorts_b ports[nPorts](
      redeclare each package Medium = Medium) "Fluid inlets and outlets";

  // Set nominal attributes where literal values can be used.
  Medium.BaseProperties medium(
    preferredMediumStates= not (energyDynamics == Modelica.Fluid.Types.Dynamics.SteadyState),
    p(start=p_start,
      nominal=Medium.p_default,
      stateSelect=if not (massDynamics == Modelica.Fluid.Types.Dynamics.SteadyState)
                     then StateSelect.prefer else StateSelect.default),
    h(start=Medium.specificEnthalpy_pTX(p_start, T_start, X_start)),
    T(start=T_start,
      nominal=Medium.T_default,
      stateSelect=if (not (energyDynamics == Modelica.Fluid.Types.Dynamics.SteadyState))
                     then StateSelect.prefer else StateSelect.default),
    Xi(start=X_start[1:Medium.nXi],
       nominal=Medium.X_default[1:Medium.nXi],
       stateSelect=if (not (substanceDynamics == Modelica.Fluid.Types.Dynamics.SteadyState))
                     then StateSelect.prefer else StateSelect.default),
    d(start=rho_nominal)) "Medium properties";

  Modelica.SIunits.Energy U "Internal energy of fluid";
  Modelica.SIunits.Mass m "Mass of fluid";
  Modelica.SIunits.Mass[Medium.nXi] mXi 
    "Masses of independent components in the fluid";
  Modelica.SIunits.Mass[Medium.nC] mC "Masses of trace substances in the fluid";
  // C need to be added here because unlike for Xi, which has medium.Xi,
  // there is no variable medium.C
  Medium.ExtraProperty C[Medium.nC](nominal=C_nominal) 
    "Trace substance mixture content";

  Modelica.SIunits.MassFlowRate mb_flow "Mass flows across boundaries";
  Modelica.SIunits.MassFlowRate[Medium.nXi] mbXi_flow 
    "Substance mass flows across boundaries";
  Medium.ExtraPropertyFlowRate[Medium.nC] mbC_flow 
    "Trace substance mass flows across boundaries";
  Modelica.SIunits.EnthalpyFlowRate Hb_flow 
    "Enthalpy flow across boundaries or energy source/sink";

  // Inputs that need to be defined by an extending class
  input Modelica.SIunits.Volume fluidVolume "Volume";
  input Modelica.SIunits.HeatFlowRate Q_flow 
    "Net heat input into component other than through the fluid ports";
  input Modelica.SIunits.MassFlowRate[Medium.nXi] mXi_flow 
    "Net substance mass flow rate into the component other than through the fluid ports";

  // Outputs that are needed in models that extend this model
  Modelica.Blocks.Interfaces.RealOutput hOut(unit="J/kg") 
    "Leaving temperature of the component";
  Modelica.Blocks.Interfaces.RealOutput XiOut[Medium.nXi](unit="1") 
    "Leaving species concentration of the component";
  Modelica.Blocks.Interfaces.RealOutput COut[Medium.nC](unit="1") 
    "Leaving trace substances of the component";
protected 
  parameter Boolean initialize_p = not Medium.singleState 
    "= true to set up initial equations for pressure";

  Medium.EnthalpyFlowRate ports_H_flow[nPorts];
  Medium.MassFlowRate ports_mXi_flow[nPorts,Medium.nXi];
  Medium.ExtraPropertyFlowRate ports_mC_flow[nPorts,Medium.nC];

  parameter Modelica.SIunits.Density rho_nominal=Medium.density(
   Medium.setState_pTX(
     T=T_start,
     p=p_start,
     X=X_start[1:Medium.nXi])) "Density, used to compute fluid mass";

equation 
  // Total quantities
  m = fluidVolume*medium.d;
  mXi = m*medium.Xi;
  U = m*medium.u;
  mC = m*C;

  hOut = medium.h;
  XiOut = medium.Xi;
  COut = C;

  for i in 1:nPorts loop
    ports_H_flow[i]     = ports[i].m_flow * actualStream(ports[i].h_outflow) 
      "Enthalpy flow";
    ports_mXi_flow[i,:] = ports[i].m_flow * actualStream(ports[i].Xi_outflow) 
      "Component mass flow";
    ports_mC_flow[i,:]  = ports[i].m_flow * actualStream(ports[i].C_outflow) 
      "Trace substance mass flow";
  end for;

  for i in 1:Medium.nXi loop
    mbXi_flow[i] = sum(ports_mXi_flow[:,i]);
  end for;

  for i in 1:Medium.nC loop
    mbC_flow[i]  = sum(ports_mC_flow[:,i]);
  end for;

  mb_flow = sum(ports.m_flow);
  Hb_flow = sum(ports_H_flow);

  // Energy and mass balances
  if energyDynamics == Modelica.Fluid.Types.Dynamics.SteadyState then
    0 = Hb_flow + Q_flow;
  else
    der(U) = Hb_flow + Q_flow;
  end if;

  if massDynamics == Modelica.Fluid.Types.Dynamics.SteadyState then
    0 = mb_flow + sum(mXi_flow);
  else
    der(m) = mb_flow + sum(mXi_flow);
  end if;

  if substanceDynamics == Modelica.Fluid.Types.Dynamics.SteadyState then
    zeros(Medium.nXi) = mbXi_flow + mXi_flow;
  else
    der(mXi) = mbXi_flow + mXi_flow;
  end if;

  if traceDynamics == Modelica.Fluid.Types.Dynamics.SteadyState then
    zeros(Medium.nC)  = mbC_flow;
  else
    der(mC)  = mbC_flow;
  end if;

  // Properties of outgoing flows
  for i in 1:nPorts loop
      ports[i].p          = medium.p;
      ports[i].h_outflow  = medium.h;
      ports[i].Xi_outflow = medium.Xi;
      ports[i].C_outflow  = C;
  end for;
initial equation 
  // Make sure that if energyDynamics is SteadyState, then
  // massDynamics is also SteadyState.
  // Otherwise, the system of ordinary differential equations may be inconsistent.
  if energyDynamics == Modelica.Fluid.Types.Dynamics.SteadyState then
    assert(massDynamics == energyDynamics, "
         If 'massDynamics == Modelica.Fluid.Types.Dynamics.SteadyState', then it is 
         required that 'energyDynamics==Modelica.Fluid.Types.Dynamics.SteadyState'.
         Otherwise, the system of equations may not be consistent.
         You need to select other parameter values.");
  end if;

  // initialization of balances
  if energyDynamics == Modelica.Fluid.Types.Dynamics.FixedInitial then
//    if use_T_start then
      medium.T = T_start;
//    else
//      medium.h = h_start;
//    end if;
  else
    if energyDynamics == Modelica.Fluid.Types.Dynamics.SteadyStateInitial then
//      if use_T_start then
        der(medium.T) = 0;
//      else
//        der(medium.h) = 0;
//      end if;
    end if;
  end if;

  if massDynamics == Modelica.Fluid.Types.Dynamics.FixedInitial then
    if initialize_p then
      medium.p = p_start;
    end if;
  else
    if massDynamics == Modelica.Fluid.Types.Dynamics.SteadyStateInitial then
      if initialize_p then
        der(medium.p) = 0;
      end if;
    end if;
  end if;

  if substanceDynamics == Modelica.Fluid.Types.Dynamics.FixedInitial then
    medium.Xi = X_start[1:Medium.nXi];
  else
    if substanceDynamics == Modelica.Fluid.Types.Dynamics.SteadyStateInitial then
      der(medium.Xi) = zeros(Medium.nXi);
    end if;
  end if;

  if traceDynamics == Modelica.Fluid.Types.Dynamics.FixedInitial then
    C = C_start[1:Medium.nC];
  else
    if traceDynamics == Modelica.Fluid.Types.Dynamics.SteadyStateInitial then
      der(C) = zeros(Medium.nC);
    end if;
  end if;

end LumpedVolume;

Buildings.Fluid.Interfaces.TwoPortFlowResistanceParameters

Information

Parameters

Type	Name	Default	Description
Nominal condition
Pressure	dp_nominal		Pressure [Pa]
Flow resistance
Boolean	computeFlowResistance	true	=true, compute flow resistance. Set to false to assume no friction
Boolean	from_dp	false	= true, use m_flow = f(dp) else dp = f(m_flow)
Boolean	linearizeFlowResistance	false	= true, use linear relation between m_flow and dp for any flow rate
Real	deltaM	0.1	Fraction of nominal flow rate where flow transitions to laminar

Modelica definition

record TwoPortFlowResistanceParameters 
  "Parameters for flow resistance for models with two ports"

  parameter Boolean computeFlowResistance = true 
    "=true, compute flow resistance. Set to false to assume no friction";

  parameter Boolean from_dp = false 
    "= true, use m_flow = f(dp) else dp = f(m_flow)";
  parameter Modelica.SIunits.Pressure dp_nominal(min=0, displayUnit="Pa") 
    "Pressure";
  parameter Boolean linearizeFlowResistance = false 
    "= true, use linear relation between m_flow and dp for any flow rate";
  parameter Real deltaM = 0.1 
    "Fraction of nominal flow rate where flow transitions to laminar";

end TwoPortFlowResistanceParameters;

Buildings.Fluid.Interfaces.FourPortFlowResistanceParameters

Information

Parameters

Type	Name	Default	Description
Nominal condition
Pressure	dp1_nominal		Pressure [Pa]
Pressure	dp2_nominal		Pressure [Pa]
Flow resistance
Medium 1
Boolean	computeFlowResistance1	true	=true, compute flow resistance. Set to false to assume no friction
Boolean	from_dp1	false	= true, use m_flow = f(dp) else dp = f(m_flow)
Boolean	linearizeFlowResistance1	false	= true, use linear relation between m_flow and dp for any flow rate
Real	deltaM1	0.1	Fraction of nominal flow rate where flow transitions to laminar
Medium 2
Boolean	computeFlowResistance2	true	=true, compute flow resistance. Set to false to assume no friction
Boolean	from_dp2	false	= true, use m_flow = f(dp) else dp = f(m_flow)
Boolean	linearizeFlowResistance2	false	= true, use linear relation between m_flow and dp for any flow rate
Real	deltaM2	0.1	Fraction of nominal flow rate where flow transitions to laminar

Modelica definition

record FourPortFlowResistanceParameters 
  "Parameters for flow resistance for models with four ports"

  parameter Boolean computeFlowResistance1 = true 
    "=true, compute flow resistance. Set to false to assume no friction";

  parameter Boolean from_dp1 = false 
    "= true, use m_flow = f(dp) else dp = f(m_flow)";
  parameter Modelica.SIunits.Pressure dp1_nominal(min=0, displayUnit="Pa") 
    "Pressure";
  parameter Boolean linearizeFlowResistance1 = false 
    "= true, use linear relation between m_flow and dp for any flow rate";
  parameter Real deltaM1 = 0.1 
    "Fraction of nominal flow rate where flow transitions to laminar";
  parameter Boolean computeFlowResistance2 = true 
    "=true, compute flow resistance. Set to false to assume no friction";

  parameter Boolean from_dp2 = false 
    "= true, use m_flow = f(dp) else dp = f(m_flow)";
  parameter Modelica.SIunits.Pressure dp2_nominal(min=0, displayUnit="Pa") 
    "Pressure";
  parameter Boolean linearizeFlowResistance2 = false 
    "= true, use linear relation between m_flow and dp for any flow rate";
  parameter Real deltaM2 = 0.1 
    "Fraction of nominal flow rate where flow transitions to laminar";
end FourPortFlowResistanceParameters;

Buildings.Fluid.Interfaces.LumpedVolumeDeclarations

Information

This class contains parameters and medium properties that are used in the lumped volume model, and in models that extend the lumped volume model.

These parameters are used by Buildings.Fluid.Interfaces.LumpedVolume, Buildings.Fluid.MixingVolumes.MixingVolume, Buildings.Rooms.MixedAir, and by Buildings.Rooms.BaseClasses.MixedAir.

Parameters

Type	Name	Default	Description
Dynamics
Equations
Dynamics	energyDynamics	Modelica.Fluid.Types.Dynamic...	Formulation of energy balance
Dynamics	massDynamics	energyDynamics	Formulation of mass balance
Initialization
AbsolutePressure	p_start	Medium.p_default	Start value of pressure [Pa]
Temperature	T_start	Medium.T_default	Start value of temperature [K]
MassFraction	X_start[Medium.nX]	Medium.X_default	Start value of mass fractions m_i/m [kg/kg]
ExtraProperty	C_start[Medium.nC]	fill(0, Medium.nC)	Start value of trace substances
ExtraProperty	C_nominal[Medium.nC]	fill(1E-2, Medium.nC)	Nominal value of trace substances. (Set to typical order of magnitude.)

Modelica definition

record LumpedVolumeDeclarations "Declarations for lumped volumes"
  replaceable package Medium =
    Modelica.Media.Interfaces.PartialMedium "Medium in the component";

  // Assumptions
  parameter Modelica.Fluid.Types.Dynamics energyDynamics=Modelica.Fluid.Types.Dynamics.DynamicFreeInitial 
    "Formulation of energy balance";
  parameter Modelica.Fluid.Types.Dynamics massDynamics=energyDynamics 
    "Formulation of mass balance";
  final parameter Modelica.Fluid.Types.Dynamics substanceDynamics=energyDynamics 
    "Formulation of substance balance";
  final parameter Modelica.Fluid.Types.Dynamics traceDynamics=energyDynamics 
    "Formulation of trace substance balance";

  // Initialization
  parameter Medium.AbsolutePressure p_start = Medium.p_default 
    "Start value of pressure";
//  parameter Boolean use_T_start = true "= true, use T_start, otherwise h_start"
 //   annotation(Dialog(tab = "Initialization"), Evaluate=true);
  parameter Medium.Temperature T_start=Medium.T_default 
    "Start value of temperature";
//  parameter Medium.SpecificEnthalpy h_start=
//    if use_T_start then Medium.specificEnthalpy_pTX(p_start, T_start, X_start) else Medium.h_default
//    "Start value of specific enthalpy"
//    annotation(Dialog(tab = "Initialization", enable = not use_T_start));
  parameter Medium.MassFraction X_start[Medium.nX] = Medium.X_default 
    "Start value of mass fractions m_i/m";
  parameter Medium.ExtraProperty C_start[Medium.nC](
       quantity=Medium.extraPropertiesNames)=fill(0, Medium.nC) 
    "Start value of trace substances";
  parameter Medium.ExtraProperty C_nominal[Medium.nC](
       quantity=Medium.extraPropertiesNames) = fill(1E-2, Medium.nC) 
    "Nominal value of trace substances. (Set to typical order of magnitude.)";

end LumpedVolumeDeclarations;