Buildings.Fluid.MixingVolumes.BaseClasses

Information

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

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

Package Content

Name	Description
PartialMixingVolumeWaterPort	Partial mixing volume that allows adding or subtracting water vapor

Buildings.Fluid.MixingVolumes.BaseClasses.PartialMixingVolumeWaterPort

Information

This model represents the same physics as Modelica.Fluid.Vessels.Volume 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.

Extends from Buildings.Fluid.Interfaces.PartialLumpedVolume (Lumped volume with mass and energy balance).

Parameters

Type	Name	Default	Description
replaceable package Medium		PartialMedium	Medium in the component
Volume	fluidVolume	V	Volume [m3]
Volume	V		Volume [m3]
Assumptions
Dynamics
Dynamics	energyDynamics	system.energyDynamics	Formulation of energy balance
Dynamics	massDynamics	system.massDynamics	Formulation of mass balance
Dynamics	substanceDynamics	massDynamics	Formulation of substance balance
Dynamics	traceDynamics	massDynamics	Formulation of trace substance balance
Heat transfer
Boolean	use_HeatTransfer	false	= true to use the HeatTransfer model
Initialization
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 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
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
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	X_w	Species composition of medium

Modelica definition

partial model PartialMixingVolumeWaterPort 
  "Partial mixing volume that allows adding or subtracting water vapor"
  extends Buildings.Fluid.Interfaces.PartialLumpedVolume(fluidVolume = V, m(start=V*rho_nominal, fixed=false),
      mC(nominal=V*rho_nominal*C_nominal));

// declarations similar than in PartialLumpedVolumePorts from Modelica.Fluid
  // Port definitions
  parameter Integer nPorts=0 "Number of ports";
  Modelica.Fluid.Interfaces.FluidPorts_b ports[nPorts](
      redeclare each package Medium = Medium) "Fluid outlets";

  Medium.EnthalpyFlowRate ports_H_flow[nPorts];
  Medium.MassFlowRate ports_mXi_flow[nPorts,Medium.nXi];
  Medium.MassFlowRate[Medium.nXi] sum_ports_mXi_flow 
    "Substance mass flows through ports";
  Medium.ExtraPropertyFlowRate ports_mC_flow[nPorts,Medium.nC];
  Medium.ExtraPropertyFlowRate[Medium.nC] sum_ports_mC_flow 
    "Trace substance mass flows through ports";

  // Heat transfer through boundary
  parameter Boolean use_HeatTransfer = false 
    "= true to use the HeatTransfer model";
  replaceable model HeatTransfer =
      Modelica.Fluid.Vessels.BaseClasses.HeatTransfer.IdealHeatTransfer (
       surfaceAreas={4*Modelica.Constants.pi*(3/4*V/Modelica.Constants.pi)^(2/3)})
    constrainedby 
    Modelica.Fluid.Vessels.BaseClasses.HeatTransfer.PartialVesselHeatTransfer 
    "Wall heat transfer";
  HeatTransfer heatTransfer(
    redeclare final package Medium = Medium,
    final n=1,
    final states = {medium.state},
    final use_k = use_HeatTransfer);
  Modelica.Thermal.HeatTransfer.Interfaces.HeatPort_a heatPort if use_HeatTransfer;

 // additional declarations
  Modelica.Blocks.Interfaces.RealInput mWat_flow(final quantity="MassFlowRate",
                                                 final unit = "kg/s") 
    "Water flow rate added into the medium";
  Modelica.Blocks.Interfaces.RealInput TWat(final quantity="Temperature",
                                            final unit = "K", displayUnit = "degC", min=260) 
    "Temperature of liquid that is drained from or injected into volume";
  Modelica.Blocks.Interfaces.RealOutput X_w "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";
   parameter Modelica.SIunits.Volume V "Volume";
protected 
   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 
   assert(not (energyDynamics<>Modelica.Fluid.Types.Dynamics.SteadyState and 
        massDynamics==Modelica.Fluid.Types.Dynamics.SteadyState) or Medium.singleState,
          "Bad combination of dynamics options and Medium not conserving mass if fluidVolume is fixed.");

  connect(heatPort, heatTransfer.heatPorts[1]);
//  Wb_flow = 0;

  mb_flow = sum(ports.m_flow) + mWat_flow 
    "eqn. differs from Modelica.Fluid implementation";
  mbXi_flow = sum_ports_mXi_flow + mXi_flow 
    "eqn. differs from Modelica.Fluid implementation";
  mbC_flow  = sum_ports_mC_flow;
  Hb_flow = sum(ports_H_flow) + HWat_flow 
    "eqn. differs from Modelica.Fluid implementation";
  Qb_flow = heatTransfer.Q_flows[1];

  // Only one connection allowed to a port to avoid unwanted ideal mixing
  for i in 1:nPorts loop
    assert(cardinality(ports[i]) <= 1,"
each ports[i] of volume can at most be connected to one component.
If two or more connections are present, ideal mixing takes
place with these connections, which is usually not the intention
of the modeller. Increase nPorts to add an additional port.
");
  end for;

  // Boundary conditions
  for i in 1:nPorts loop
    ports[i].p = medium.p;
  end for;
  ports.h_outflow = fill(medium.h,   nPorts);
  ports.Xi_outflow = fill(medium.Xi, nPorts);
  ports.C_outflow  = fill(C,         nPorts);

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

end PartialMixingVolumeWaterPort;

Buildings.Fluid.MixingVolumes.BaseClasses.PartialMixingVolumeWaterPort.HeatTransfer

Parameters

Type	Name	Default	Description
Area	surfaceAreas[n]	{4*Modelica.Constants.pi*(3/...	Heat transfer areas [m2]
Ambient
CoefficientOfHeatTransfer	k	0	Heat transfer coefficient to ambient [W/(m2.K)]
Temperature	T_ambient	system.T_ambient	Ambient temperature [K]
Internal Interface
replaceable package Medium		PartialMedium	Medium in the component
Integer	n	1	Number of heat transfer segments
Boolean	use_k	false	= true to use k value for thermal isolation

Connectors

Type	Name	Description
HeatPorts_a	heatPorts[n]	Heat port to component boundary

Modelica definition

replaceable model HeatTransfer =
    Modelica.Fluid.Vessels.BaseClasses.HeatTransfer.IdealHeatTransfer (
     surfaceAreas={4*Modelica.Constants.pi*(3/4*V/Modelica.Constants.pi)^(2/3)})
  constrainedby 
  Modelica.Fluid.Vessels.BaseClasses.HeatTransfer.PartialVesselHeatTransfer 
  "Wall heat transfer";