Buildings.Fluids.Delays

Package with delay models

Package Content

NameDescription
Buildings.Fluids.Delays.DelayFirstOrder DelayFirstOrder Delay element, approximated by a first order differential equation
Buildings.Fluids.Delays.Examples Examples Collection of models that illustrate model use and test models


Buildings.Fluids.Delays.DelayFirstOrder Buildings.Fluids.Delays.DelayFirstOrder

Delay element, approximated by a first order differential equation

Buildings.Fluids.Delays.DelayFirstOrder

Information


This model approximates a transport delay using a first order differential equations.

The model consists of a mixing volume with two ports. The size of the mixing volume is such that at the nominal mass flow rate m_flow_nominal, the time constant of the volume is equal to the parameter tau.

The heat flux connector is optional, it need not be connnected.


Extends from Buildings.Fluids.MixingVolumes.MixingVolume (Mixing volume with inlet and outlet ports (flow reversal is allowed)).

Parameters

TypeNameDefaultDescription
replaceable package MediumPartialMediumMedium in the component
VolumeVV0Volume [m3]
Ports
Booleanuse_portsDatafalse= false to neglect pressure loss and kinetic energy
VesselPortsDataportsData[nPorts] Data of inlet/outlet ports
Nominal condition
Timetau60Time constant at nominal flow [s]
MassFlowRatem_flow_nominal Mass flow rate [kg/s]
Assumptions
Dynamics
DynamicsenergyDynamicssystem.energyDynamicsFormulation of energy balance
DynamicsmassDynamicssystem.massDynamicsFormulation of mass balance
Heat transfer
Booleanuse_HeatTransferfalse= true to use the HeatTransfer model
replaceable model HeatTransferIdealHeatTransferWall heat transfer
Initialization
AbsolutePressurep_startsystem.p_startStart value of pressure [Pa]
Booleanuse_T_starttrue= true, use T_start, otherwise h_start
TemperatureT_startif use_T_start then system.T...Start value of temperature [K]
SpecificEnthalpyh_startif use_T_start then Medium.s...Start value of specific enthalpy [J/kg]
MassFractionX_start[Medium.nX]Medium.X_defaultStart value of mass fractions m_i/m [kg/kg]
ExtraPropertyC_start[Medium.nC]fill(0, Medium.nC)Start value of trace substances
Advanced
Port properties
MassFlowRatem_flow_smallsystem.m_flow_smallRegularization range at zero mass flow rate [kg/s]

Connectors

TypeNameDescription
VesselFluidPorts_bports[nPorts]Fluid inlets and outlets
HeatPort_aheatPort 

Modelica definition

model DelayFirstOrder 
  "Delay element, approximated by a first order differential equation"
  extends Buildings.Fluids.MixingVolumes.MixingVolume(final V=V0, nPorts=2);

  parameter Modelica.SIunits.Time tau = 60 "Time constant at nominal flow";
  parameter Modelica.SIunits.MassFlowRate m_flow_nominal(min=0) 
    "Mass flow rate";

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 volume";
   parameter Modelica.SIunits.Volume V0 = m_flow_nominal*tau/rho_nominal 
    "Volume of delay element";
end DelayFirstOrder;

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