Buildings.Fluids.MixingVolumes.BaseClasses

Package Content

Name	Description
PartialMixingVolume	Mixing volume with inlet and outlet ports (flow reversal is allowed)
PartialMixingVolumeWaterPort	Partial mixing volume that allows adding or subtracting water vapor

Buildings.Fluids.MixingVolumes.BaseClasses.PartialMixingVolume

Information

This model represents the same physics as Modelica_Fluid.Volumes.MixingVolume, but it allows to have more than two fluid ports. This is convenient for modeling the room volume in a building energy simulation since rooms often have more than two fluid connections, such as an HVAC inlet, outlet and a leakage flow to other rooms or the outside. If a fluid port is connected twice, the model will terminate the simulation with an error message.

Models that extend this partial model need to provide the energy, mass and species balance equations. See Buildings.Fluids.MixingVolumes.MixingVolume.

The thermal port need not be connected, but can have any number of connections.

Parameters

Type	Name	Default	Description
replaceable package Medium		PartialMedium	Medium in the component
Volume	V		Volume [m3]
Integer	nP	2	Number of ports
Boolean	steadyState	false	Set to true for steady state model
Initialization
Temp	initType	Types.Init.NoInit	Initialization option
AbsolutePressure	p_start	Medium.p_default	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 Medium.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]

Connectors

Type	Name	Description
FluidPort_a	port[nP]	Fluid port
HeatPort_a	thermalPort	Thermal port

Modelica definition

partial model PartialMixingVolume 
  "Mixing volume with inlet and outlet ports (flow reversal is allowed)" 
  extends Modelica_Fluid.Interfaces.PartialInitializationParameters;
  replaceable package Medium = Modelica.Media.Interfaces.PartialMedium 
    "Medium in the component";
  parameter Modelica.SIunits.Volume V "Volume";
  parameter Integer nP(min=1) = 2 "Number of ports";
  Modelica_Fluid.Interfaces.FluidPort_a port[nP](
     redeclare each package Medium = Medium,
     each C(nominal=1E-3)) "Fluid port";
  Medium.BaseProperties medium(
    preferredMediumStates=true,
    p(start=p_start),
    h(start=h_start),
    T(start=T_start),
    Xi(start=X_start[1:Medium.nXi]));
  Modelica.SIunits.Energy U(start=V*rho0*Medium.specificInternalEnergy(sta0)) 
    "Internal energy of fluid";
  Modelica.SIunits.Mass m(start=V*rho0) "Mass of fluid";
  Modelica.SIunits.Mass mXi[Medium.nXi] 
    "Masses of independent components in the fluid";
  Modelica.SIunits.Volume V_lumped "Volume";
  
  Medium.ExtraProperty mC[Medium.nC] 
    "Masses of auxiliary components in the fluid";
  Medium.MassFraction mc[Medium.nC](start=zeros(Medium.nC), nominal=1E-3) 
    "Mass fraction of auxiliary components in the fluid";
  
protected 
   parameter Medium.ThermodynamicState sta0 = Medium.setState_pTX(T=T_start,
         p=p_start, X=X_start[1:Medium.nXi]);
   parameter Modelica.SIunits.Density rho0=Medium.density(sta0) 
    "Density, used to compute fluid volume";
  Modelica.SIunits.HeatFlowRate Qs_flow 
    "Heat flow across boundaries or energy source/sink";
  Modelica.SIunits.Power Ws_flow=0 "Work flow across boundaries or source term";
  
public 
Modelica.Thermal.HeatTransfer.Interfaces.HeatPort_a thermalPort "Thermal port";
public 
   parameter Boolean steadyState =  false "Set to true for steady state model";
equation 
  V_lumped=V;
  thermalPort.T = medium.T;
  Qs_flow = thermalPort.Q_flow;
// boundary conditions  
  for i in 1:nP loop
    port[i].p = medium.p;
    port[i].H_flow = semiLinear(
      port[i].m_flow,
      port[i].h,
      medium.h);
    port[i].mXi_flow = semiLinear(
      port[i].m_flow,
      port[i].Xi,
      medium.Xi);
    port[i].mC_flow = semiLinear(
      port[i].m_flow,
      port[i].C,
      mc);
  end for;
// Total quantities
  m = V_lumped*medium.d;
  mXi = m*medium.Xi;
  U = m*medium.u;
  
  // The auxiliary species balances is formulated in the non-dimensional form
  // using mc instead of mC, which makes it easier to provide a nominal value
  if steadyState then
    zeros(Medium.nC) = sum(port[i].mC_flow for i in 1:nP);
  else
    der(mc) = sum(port[i].mC_flow for i in 1:nP)/m;
  end if;
  mC = mc*m;
  
// Mass and energy balance.
// To be implemented by models that extend this partial model.
//  der(m) = sum(port[i].m_flow for i in 1:nP);
//  der(mXi) = sum(port[i].mXi_flow for i in 1:nP);
//  der(U) = sum(port[i].H_flow for i in 1:nP) + Qs_flow + Ws_flow;
  
initial equation 
// Initial conditions
  for i in 1:nP loop
    assert(cardinality(port[i]) == 1, "Only one port connection allowed. To fix, increase nP and use new port.");
  end for;
  
  if initType == Modelica_Fluid.Types.Init.NoInit then
  // no initial equations
  elseif initType == Modelica_Fluid.Types.Init.InitialValues then
    if not Medium.singleState then
      medium.p = p_start;
    end if;
    if use_T_start then
      medium.T = T_start;
    else
      medium.h = h_start;
    end if;
    medium.Xi = X_start[1:Medium.nXi];
  elseif initType == Modelica_Fluid.Types.Init.SteadyState then
    if not Medium.singleState then
      der(medium.p) = 0;
    end if;
    der(medium.h) = 0;
    der(medium.Xi) = zeros(Medium.nXi);
  elseif initType == Modelica_Fluid.Types.Init.SteadyStateHydraulic then
    if not Medium.singleState then
      der(medium.p) = 0;
    end if;
    if use_T_start then
      medium.T = T_start;
    else
      medium.h = h_start;
    end if;
    medium.Xi = X_start[1:Medium.nXi];
  else
    assert(false, "Unsupported initialization option");
  end if;
end PartialMixingVolume;

Buildings.Fluids.MixingVolumes.BaseClasses.PartialMixingVolumeWaterPort

Information

This model represents the same physics as Buildings.Fluids.Components.BaseClasses.PartialMixingVolume but in addition, it allows to connect signals for the water exchanged with the volume. The model is partial in order to allow a submodel that can be used with media that contain water as a substance, and a submodel that can be used with dry air. Having separate models is required because calls to the medium property function enthalpyOfLiquid results in a linker error if a medium such as Modelica.Media.Air.SimpleAir is used that does not implement this function.

Parameters

Type	Name	Default	Description
replaceable package Medium		PartialMedium	Medium in the component
Volume	V		Volume [m3]
Integer	nP	2	Number of ports
Boolean	steadyState	false	Set to true for steady state model
Initialization
Temp	initType	Types.Init.NoInit	Initialization option
AbsolutePressure	p_start	Medium.p_default	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 Medium.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]

Connectors

Type	Name	Description
FluidPort_a	port[nP]	Fluid port
HeatPort_a	thermalPort	Thermal port
input RealInput	mWat_flow	Water flow rate added into the medium
input RealInput	TWat	Temperature of liquid that is drained from or injected into volume
output RealOutput	XWat	Species composition of medium

Modelica definition

partial model PartialMixingVolumeWaterPort 
  "Partial mixing volume that allows adding or subtracting water vapor" 
  extends PartialMixingVolume;
  Modelica.Blocks.Interfaces.RealInput mWat_flow(redeclare type SignalType = 
        Modelica.SIunits.MassFlowRate) "Water flow rate added into the medium";
  Modelica.Blocks.Interfaces.RealInput TWat(redeclare type SignalType = 
        Modelica.SIunits.Temperature) 
    "Temperature of liquid that is drained from or injected into volume";
  Modelica.Blocks.Interfaces.RealOutput XWat(redeclare type SignalType = 
        Modelica.SIunits.MassFraction) "Species composition of medium";
  Medium.MassFlowRate mXi_flow[Medium.nXi] 
    "Mass flow rates of independent substances added to the medium";
  Modelica.SIunits.HeatFlowRate HWat_flow 
    "Enthalpy flow rate of extracted water";
equation 
// Mass and energy balance
  if steadyState then
    0 = sum(port[i].m_flow for i in 1:nP) + mWat_flow;
    zeros(Medium.nXi) = sum(port[i].mXi_flow for i in 1:nP) + mXi_flow;
    0 = sum(port[i].H_flow for i in 1:nP) + Qs_flow + Ws_flow
               + HWat_flow;
  else
    der(m) = sum(port[i].m_flow for i in 1:nP) + mWat_flow;
    der(mXi) = sum(port[i].mXi_flow for i in 1:nP) + mXi_flow;
    der(U) = sum(port[i].H_flow for i in 1:nP) + Qs_flow + Ws_flow
               + HWat_flow;
  end if;
end PartialMixingVolumeWaterPort;