Modelica.Fluid.Vessels

Information

Extends from Modelica.Icons.VariantsPackage (Icon for package containing variants).

Package Content

Name	Description
ClosedVolume	Volume of fixed size, closed to the ambient, with inlet/outlet ports
OpenTank	Simple tank with inlet/outlet ports
BaseClasses	Base classes used in the Vessels package (only of interest to build new component models)

Modelica.Fluid.Vessels.ClosedVolume

Information

Ideally mixed volume of constant size with two fluid ports and one medium model. The flow properties are computed from the upstream quantities, pressures are equal in both nodes and the medium model if use_portsData=false. Heat transfer through a thermal port is possible, it equals zero if the port remains unconnected. A spherical shape is assumed for the heat transfer area, with V=4/3*pi*r^3, A=4*pi*r^2. Ideal heat transfer is assumed per default; the thermal port temperature is equal to the medium temperature.

If use_portsData=true, the port pressures represent the pressures just after the outlet (or just before the inlet) in the attached pipe. The hydraulic resistances portsData.zeta_in and portsData.zeta_out determine the dissipative pressure drop between volume and port depending on the direction of mass flow. See VesselPortsData and [Idelchik, Handbook of Hydraulic Resistance, 2004].

Extends from Modelica.Fluid.Vessels.BaseClasses.PartialLumpedVessel (Lumped volume with a vector of fluid ports and replaceable heat transfer model).

Parameters

Type	Name	Default	Description
replaceable package Medium		PartialMedium	Medium in the component
Volume	fluidVolume	V	Volume [m3]
Volume	V		Volume [m3]
Ports
Boolean	use_portsData	true	= 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
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 ClosedVolume 
  "Volume of fixed size, closed to the ambient, with inlet/outlet ports"
import Modelica.Constants.pi;

  // Mass and energy balance, ports
  extends Modelica.Fluid.Vessels.BaseClasses.PartialLumpedVessel(
    final fluidVolume = V,
    vesselArea = pi*(3/4*V)^(2/3),
    heatTransfer(surfaceAreas={4*pi*(3/4*V/pi)^(2/3)}));

  parameter SI.Volume V "Volume";

equation 
  Wb_flow = 0;
  for i in 1:nPorts loop
    vessel_ps_static[i] = medium.p;
  end for;

end ClosedVolume;

Modelica.Fluid.Vessels.OpenTank

Information

Model of a tank that is open to the ambient at the fixed pressure p_ambient.

The vector of connectors ports represents fluid ports at configurable heights, relative to the bottom of tank. Fluid can flow either out of or in to each port.

• The tank is filled with a single or multiple-substance medium having a density higher than the density of the ambient medium.
• The fluid has uniform density, temperature and mass fractions
• No liquid is leaving the tank through the open top; the simulation breaks with an assertion if the liquid level growths over the height.

The port pressures represent the pressures just after the outlet (or just before the inlet) in the attached pipe. The hydraulic resistances portsData.zeta_in and portsData.zeta_out determine the dissipative pressure drop between tank and port depending on the direction of mass flow. See VesselPortsData and [Idelchik, Handbook of Hydraulic Resistance, 2004].

With the setting use_portsData=false, the port pressure represents the static head at the height of the respective port. The relationship between pressure drop and mass flow rate at the port must then be provided by connected components; Heights of ports as well as kinetic and potential energy of fluid enering or leaving are not taken into account anymore.

Extends from Modelica.Fluid.Vessels.BaseClasses.PartialLumpedVessel (Lumped volume with a vector of fluid ports and replaceable heat transfer model).

Parameters

Type	Name	Default	Description
Height	height		Height of tank [m]
Area	crossArea		Area of tank [m2]
replaceable package Medium		PartialMedium	Medium in the component
Volume	fluidVolume	V	Volume [m3]
Ports
Boolean	use_portsData	true	= false to neglect pressure loss and kinetic energy
VesselPortsData	portsData[nPorts]		Data of inlet/outlet ports
Assumptions
Ambient
AbsolutePressure	p_ambient	system.p_ambient	Tank surface pressure [Pa]
Temperature	T_ambient	system.T_ambient	Tank surface Temperature [K]
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		IdealHeatTransfer	Wall heat transfer
Initialization
Height	level_start	0.5*height	Start value of tank level [m]
AbsolutePressure	p_start	p_ambient	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 OpenTank "Simple tank with inlet/outlet ports"
    import Modelica.Constants.pi;

  // Tank properties
  SI.Height level(stateSelect=StateSelect.prefer, start=max(level_start, Modelica.Constants.eps)) 
    "Level height of tank";
  SI.Volume V(stateSelect=StateSelect.never) "Actual tank volume";

  // Tank geometry
  parameter SI.Height height "Height of tank";
  parameter SI.Area crossArea "Area of tank";

  // Ambient
  parameter Medium.AbsolutePressure p_ambient=system.p_ambient 
    "Tank surface pressure";
  parameter Medium.Temperature T_ambient=system.T_ambient 
    "Tank surface Temperature";

  // Initialization
  parameter SI.Height level_start(min=0) = 0.5*height 
    "Start value of tank level";

  // Mass and energy balance, ports
  extends Modelica.Fluid.Vessels.BaseClasses.PartialLumpedVessel(
    final fluidVolume = V,
    final fluidLevel = level,
    final fluidLevel_max = height,
    final vesselArea = crossArea,
    heatTransfer(surfaceAreas={crossArea+2*sqrt(crossArea*pi)*level}),
    final initialize_p = false,
    final p_start = p_ambient);

equation 
  // Total quantities
  V = crossArea*level "Volume of fluid";
  medium.p = p_ambient;

  // Source termsEnergy balance
  if Medium.singleState or energyDynamics == Types.Dynamics.SteadyState then
    Wb_flow = 0 
      "Mechanical work is neglected, since also neglected in medium model (otherwise unphysical small temperature change, if tank level changes)";
  else
    Wb_flow = -p_ambient*der(V);
  end if;

  //Determine port properties
  for i in 1:nPorts loop
    vessel_ps_static[i] = max(0, level - portsData_height[i])*system.g*medium.d + p_ambient;
  end for;

initial equation 
  if massDynamics == Types.Dynamics.FixedInitial then
    level = level_start;
  elseif massDynamics == Types.Dynamics.SteadyStateInitial then
    der(level) = 0;
  end if;

end OpenTank;