Buildings.Fluid.MixingVolumes

Package Content

Name	Description
MixingVolume	Mixing volume with inlet and outlet ports (flow reversal is allowed)
MixingVolumeDryAir	Mixing volume with heat port for latent heat exchange, to be used with dry air
MixingVolumeMoistAir	Mixing volume with heat port for latent heat exchange, to be used with media that conatin water
Examples	Collection of models that illustrate model use and test models
BaseClasses	Package with base classes for mixing volumes

Buildings.Fluid.MixingVolumes.MixingVolume

Information

Extends from Buildings.Fluid.MixingVolumes.BaseClasses.ClosedVolume (Volume of fixed size, closed to the ambient, with inlet/outlet ports).

Parameters

Type	Name	Default	Description
replaceable package Medium		PartialMedium	Medium in the component
Volume	V		Volume [m3]
Ports
Boolean	use_portsData	false	= false to neglect pressure loss and kinetic energy
VesselPortsData	portsData[nPorts]		Data of inlet/outlet ports
Assumptions
Dynamics
Dynamics	energyDynamics	system.energyDynamics	Formulation of energy balance
Dynamics	massDynamics	system.massDynamics	Formulation of mass balance
Dynamics	substanceDynamics	energyDynamics	Formulation of substance balance
Dynamics	traceDynamics	energyDynamics	Formulation of trace substance balance
Heat transfer
Boolean	use_HeatTransfer	false	= true to use the HeatTransfer model
replaceable model HeatTransfer		IdealHeatTransfer	Wall heat transfer
Initialization
AbsolutePressure	p_start	system.p_start	Start value of pressure [Pa]
Boolean	use_T_start	true	= true, use T_start, otherwise h_start
Temperature	T_start	if use_T_start then system.T...	Start value of temperature [K]
SpecificEnthalpy	h_start	if use_T_start then Medium.s...	Start value of specific enthalpy [J/kg]
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
Advanced
Port properties
MassFlowRate	m_flow_small	system.m_flow_small	Regularization range at zero mass flow rate [kg/s]

Connectors

Type	Name	Description
VesselFluidPorts_b	ports[nPorts]	Fluid inlets and outlets
HeatPort_a	heatPort

Modelica definition

model MixingVolume 
  "Mixing volume with inlet and outlet ports (flow reversal is allowed)"
  //extends Modelica.Fluid.Vessels.ClosedVolume(m(start=V*rho_nominal, fixed=false), use_portsData=false);
  extends Buildings.Fluid.MixingVolumes.BaseClasses.ClosedVolume(m(start=V*rho_nominal, fixed=false), use_portsData=false);

protected 
   parameter Medium.ThermodynamicState sta0 = Medium.setState_pTX(T=T_start,
         p=p_start, X=X_start[1:Medium.nXi]);
   parameter Modelica.SIunits.Density rho_nominal=Medium.density(sta0) 
    "Density, used to compute fluid mass";
end MixingVolume;

Buildings.Fluid.MixingVolumes.MixingVolumeDryAir

Information

This model represents the same physics as Buildings.Fluid.MixingVolumes.MixingVolume, but in addition, it allows adding (or subtracting) water in liquid phase, which causes a change in enthalpy and species concentration. The water flow rate is assumed to be added or extracted at the temperature of the input port TWat, or if this port is not connected at the medium default temperature as returned by Medium.T_default.

Note that this model can only be used with medium models that include water as a substance. In particular, the medium model need to provide the function enthalpyOfLiquid(T) and the integer variable Water that contains the index to the water substance. For medium that do not provide this functionality, use instead the model Buildings.Fluid.MixingVolumes.MixingVolumeDryAir.

Extends from BaseClasses.PartialMixingVolumeWaterPort (Partial mixing volume that allows adding or subtracting water vapor).

Parameters

Type	Name	Default	Description
replaceable package Medium		PartialMedium	Medium in the component
Volume	V		Volume [m3]
Assumptions
Dynamics
Dynamics	energyDynamics	system.energyDynamics	Formulation of energy balance
Dynamics	massDynamics	system.massDynamics	Formulation of mass balance
Heat transfer
Boolean	use_HeatTransfer	false	= true to use the HeatTransfer model
replaceable model HeatTransfer		Modelica.Fluid.Vessels.BaseC...	Wall heat transfer
Initialization
AbsolutePressure	p_start	system.p_start	Start value of pressure [Pa]
Boolean	use_T_start	true	= true, use T_start, otherwise h_start
Temperature	T_start	if use_T_start then system.T...	Start value of temperature [K]
SpecificEnthalpy	h_start	if use_T_start then Medium.s...	Start value of specific enthalpy [J/kg]
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

Connectors

Type	Name	Description
FluidPorts_b	ports[nPorts]	Fluid outlets
HeatPort_a	heatPort
input RealInput	mWat_flow	Water flow rate added into the medium [kg/s]
input RealInput	TWat	Temperature of liquid that is drained from or injected into volume [K]
output RealOutput	XWat	Species composition of medium

Modelica definition

model MixingVolumeDryAir 
  "Mixing volume with heat port for latent heat exchange, to be used with dry air"
  extends BaseClasses.PartialMixingVolumeWaterPort;

equation 
  if cardinality(mWat_flow) == 0 then
    mWat_flow = 0;
  end if;
  if cardinality(TWat) == 0 then
    TWat = Medium.T_default;
  end if;
  HWat_flow = 0;
  mXi_flow  = zeros(Medium.nXi);
// Assign output port
  XWat = 0;
end MixingVolumeDryAir;

Buildings.Fluid.MixingVolumes.MixingVolumeMoistAir

Information

This model represents the same physics as Buildings.Fluid.MixingVolumes.MixingVolume, but in addition, it allows adding (or subtracting) water in liquid phase, which causes a change in enthalpy and species concentration. The water flow rate is assumed to be added or extracted at the temperature of the input port TWat, or if this port is not connected, at the medium default temperature as defined by Medium.T_default.

Note that this model can only be used with medium models that include water as a substance. In particular, the medium model need to provide the function enthalpyOfLiquid(T) and the integer variable Water that contains the index to the water substance. For medium that do not provide this functionality, use instead the model Buildings.Fluid.MixingVolumes.MixingVolumeDryAir.

Extends from BaseClasses.PartialMixingVolumeWaterPort (Partial mixing volume that allows adding or subtracting water vapor).

Parameters

Type	Name	Default	Description
replaceable package Medium		PartialMedium	Medium in the component
Volume	V		Volume [m3]
Assumptions
Dynamics
Dynamics	energyDynamics	system.energyDynamics	Formulation of energy balance
Dynamics	massDynamics	system.massDynamics	Formulation of mass balance
Heat transfer
Boolean	use_HeatTransfer	false	= true to use the HeatTransfer model
replaceable model HeatTransfer		Modelica.Fluid.Vessels.BaseC...	Wall heat transfer
Initialization
AbsolutePressure	p_start	system.p_start	Start value of pressure [Pa]
Boolean	use_T_start	true	= true, use T_start, otherwise h_start
Temperature	T_start	if use_T_start then system.T...	Start value of temperature [K]
SpecificEnthalpy	h_start	if use_T_start then Medium.s...	Start value of specific enthalpy [J/kg]
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

Connectors

Type	Name	Description
FluidPorts_b	ports[nPorts]	Fluid outlets
HeatPort_a	heatPort
input RealInput	mWat_flow	Water flow rate added into the medium [kg/s]
input RealInput	TWat	Temperature of liquid that is drained from or injected into volume [K]
output RealOutput	XWat	Species composition of medium

Modelica definition

model MixingVolumeMoistAir 
  "Mixing volume with heat port for latent heat exchange, to be used with media that conatin water"
  extends BaseClasses.PartialMixingVolumeWaterPort;
  // redeclare Medium with a more restricting base class. This improves the error
  // message if a user selects a medium that does not contain the function
  // enthalpyOfLiquid(.)
  replaceable package Medium = Modelica.Media.Interfaces.PartialCondensingGases;

protected 
  parameter Integer iWat(min=1, fixed=false) "Index for water substance";
initial algorithm 
  iWat :=1;
  if cardinality(mWat_flow) > 0 then
    for i in 1:Medium.nXi loop
      if Modelica.Utilities.Strings.isEqual(Medium.substanceNames[i], "Water") then
        iWat :=i;
      end if;
    end for;
  end if;
equation 
  if cardinality(mWat_flow) == 0 then
    mWat_flow = 0;
    HWat_flow = 0;
    mXi_flow  = zeros(Medium.nXi);
  else
    if cardinality(TWat) == 0 then
       HWat_flow = mWat_flow * Medium.enthalpyOfLiquid(Medium.T_default);
    else
       HWat_flow = mWat_flow * Medium.enthalpyOfLiquid(TWat);
    end if;
    for i in 1:Medium.nXi loop
      mXi_flow[i] = if ( i == iWat) then mWat_flow else 0;
    end for;
  end if;
// Medium species concentration
  XWat = medium.X[iWat];
end MixingVolumeMoistAir;