Extends from Modelica.Icons.VariantsPackage (Icon for package containing variants).
Name | Description |
---|---|
![]() | Pressure expansion vessel with fixed gas cushion |
![]() | Model of a stratified tank for thermal energy storage |
![]() | Stratified tank model with enhanced discretization |
![]() | Collection of models that illustrate model use and test models |
![]() | Package with base classes for Buildings.Fluid.Storage |
This is a model of a pressure expansion vessel. The vessel has a fixed total volume.
A fraction of the volume is occupied by a fixed mass of gas, and the other fraction is occupied
by the liquid that flows through the port.
The pressure p
in the vessel is
VGas0 * p_start = (VTot-VLiquid) * pwhere
VGas0
is the initial volume occupied by the gas,
p_start
is the initial pressure,
VTot
is the total volume of the vessel and
VLiquid
is the amount of liquid in the vessel.
Optionally, a heat port can be activated by setting use_HeatTransfer=true
.
This heat port connects directly to the liquid. The gas does not participate in the energy
balance.
The expansion vessel needs to be used in closed loops that contain water to set a reference pressure and, for liquids where the density is modeled as a function of temperature, to allow for the thermal expansion of the liquid.
Note that alternatively, the model Buildings.Fluid.Sources.FixedBoundary may be used to set a reference pressure. The main difference between these two models is that in this model, there is an energy and mass balance for the volume. In contrast, for Buildings.Fluid.Sources.FixedBoundary, any mass flow rate that flows out of the model will be at a user-specified temperature. Therefore, Buildings.Fluid.Sources.FixedBoundary leads to smaller systems of equations, which may result in faster simulation.
Extends from Buildings.Fluid.Interfaces.LumpedVolumeDeclarations (Declarations for lumped volumes).
Type | Name | Default | Description |
---|---|---|---|
replaceable package Medium | PartialMedium | Medium in the component | |
Volume | VTot | Total volume of vessel (water and gas side) [m3] | |
Volume | VGas0 | VTot/2 | Initial volume of gas [m3] |
Pressure | pMax | 5E5 | Maximum pressure before simulation stops with an error [Pa] |
Dynamics | |||
Equations | |||
Dynamics | energyDynamics | Modelica.Fluid.Types.Dynamic... | Formulation of energy balance |
Dynamics | massDynamics | energyDynamics | Formulation of mass balance |
Initialization | |||
AbsolutePressure | p_start | Medium.p_default | Start value of pressure [Pa] |
Temperature | T_start | Medium.T_default | Start value of temperature [K] |
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.) |
Type | Name | Description |
---|---|---|
FluidPort_a | port_a | Fluid port |
model ExpansionVessel "Pressure expansion vessel with fixed gas cushion" extends Buildings.Fluid.Interfaces.LumpedVolumeDeclarations; parameter Modelica.SIunits.Volume VTot "Total volume of vessel (water and gas side)"; parameter Modelica.SIunits.Volume VGas0 = VTot/2 "Initial volume of gas"; //////////////////////////////////////////////////////////////Modelica.Fluid.Interfaces.FluidPort_a port_a(redeclare package Medium = Medium) "Fluid port"; parameter Modelica.SIunits.Pressure pMax = 5E5 "Maximum pressure before simulation stops with an error"; Modelica.SIunits.Volume VLiq "Volume of liquid in the vessel"; // We set m(start=(VTot-VGas0)*1000, stateSelect=StateSelect.always) // since the mass accumulated in the volume should be a state. // This often leads to smaller systems of equations.protected Buildings.Fluid.Interfaces.ConservationEquation vol( redeclare final package Medium = Medium, m(start=(VTot-VGas0)*1000, stateSelect=StateSelect.always), final nPorts=1, final energyDynamics=energyDynamics, final massDynamics=massDynamics, final p_start=p_start, final T_start=T_start, final X_start=X_start, final C_start=C_start, final C_nominal=C_nominal, final fluidVolume = VLiq) "Model for mass and energy balance of water in expansion vessel"; Modelica.Blocks.Sources.Constant heaInp(final k=0) "Block to set heat input into volume"; Modelica.Blocks.Sources.Constant masExc[Medium.nXi](final k=zeros(Medium.nXi)) if Medium.nXi > 0 "Block to set mass exchange in volume"; equation assert(port_a.p < pMax, "Pressure exceeds maximum pressure.\n" + "You may need to increase VTot of the ExpansionVessel."); // Water content and pressure port_a.p * (VTot-VLiq) = p_start * VGas0;connect(heaInp.y, vol.Q_flow); connect(masExc.y, vol.mXi_flow); connect(port_a, vol.ports[1]); end ExpansionVessel;
This is a model of a stratified storage tank.
The tank uses several volumes to model the stratification.
Heat conduction is modeled between the volumes through the fluid,
and between the volumes and the ambient.
The port heaPorVol
may be used to connect a temperature sensor
that measures the fluid temperature of an individual volume. It may also
be used to add heat to individual volumes.
The tank has nSeg
fluid volumes. The top volume has the index 1
.
Thus, to add a heating element to the bottom element, connect a heat input to
heaPorVol[nSeg]
.
The heat ports outside the tank insulation can be
used to specify an ambient temperature.
Leave these ports unconnected to force adiabatic boundary conditions.
Note, however, that all heat conduction elements through the tank wall (but not the top and bottom) are connected to the
heat port heaPorSid
. Thus, not connecting
heaPorSid
means an adiabatic boundary condition in the sense
that heaPorSid.Q_flow = 0
. This, however, still allows heat to flow
through the tank walls, modelled by conWal
, from one fluid volume
to another one.
For a model with enhanced stratification, use Buildings.Fluid.Storage.StratifiedEnhanced.
Extends from Buildings.Fluid.Interfaces.PartialTwoPortInterface (Partial model transporting fluid between two ports without storing mass or energy).
Type | Name | Default | Description |
---|---|---|---|
replaceable package Medium | PartialMedium | Medium in the component | |
Volume | VTan | Tank volume [m3] | |
Length | hTan | Height of tank (without insulation) [m] | |
Length | dIns | Thickness of insulation [m] | |
ThermalConductivity | kIns | 0.04 | Specific heat conductivity of insulation [W/(m.K)] |
Integer | nSeg | 2 | Number of volume segments |
Time | tau | 1 | Time constant for mixing due to temperature inversion [s] |
Nominal condition | |||
MassFlowRate | m_flow_nominal | Nominal mass flow rate [kg/s] | |
Initialization | |||
MassFlowRate | m_flow.start | 0 | Mass flow rate from port_a to port_b (m_flow > 0 is design flow direction) [kg/s] |
Pressure | dp.start | 0 | Pressure difference between port_a and port_b [Pa] |
Assumptions | |||
Boolean | allowFlowReversal | system.allowFlowReversal | = true to allow flow reversal, false restricts to design direction (port_a -> port_b) |
Advanced | |||
MassFlowRate | m_flow_small | 1E-4*abs(m_flow_nominal) | Small mass flow rate for regularization of zero flow [kg/s] |
Boolean | homotopyInitialization | true | = true, use homotopy method |
Diagnostics | |||
Boolean | show_V_flow | false | = true, if volume flow rate at inflowing port is computed |
Boolean | show_T | false | = true, if actual temperature at port is computed (may lead to events) |
Dynamics | |||
Equations | |||
Dynamics | energyDynamics | system.energyDynamics | Formulation of energy balance |
Dynamics | massDynamics | energyDynamics | Formulation of mass balance |
Initialization | |||
AbsolutePressure | p_start | Medium.p_default | Start value of pressure [Pa] |
Temperature | T_start | Medium.T_default | Start value of temperature [K] |
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 |
Type | Name | Description |
---|---|---|
FluidPort_a | port_a | Fluid connector a (positive design flow direction is from port_a to port_b) |
FluidPort_b | port_b | Fluid connector b (positive design flow direction is from port_a to port_b) |
replaceable package Medium | ||
HeatPort_a | heaPorVol[nSeg] | Heat port of fluid volumes |
HeatPort_a | heaPorSid | Heat port tank side (outside insulation) |
HeatPort_a | heaPorTop | Heat port tank top (outside insulation) |
HeatPort_a | heaPorBot | Heat port tank bottom (outside insulation). Leave unconnected for adiabatic condition |
output RealOutput | Ql_flow | Heat loss of tank (positive if heat flows from tank to ambient) |
model Stratified "Model of a stratified tank for thermal energy storage" extends Buildings.Fluid.Interfaces.PartialTwoPortInterface( showDesignFlowDirection=false); replaceable package Medium = Modelica.Media.Interfaces.PartialSimpleMedium; import Modelica.Fluid.Types; import Modelica.Fluid.Types.Dynamics; parameter Modelica.SIunits.Volume VTan "Tank volume"; parameter Modelica.SIunits.Length hTan "Height of tank (without insulation)"; parameter Modelica.SIunits.Length dIns "Thickness of insulation"; parameter Modelica.SIunits.ThermalConductivity kIns = 0.04 "Specific heat conductivity of insulation"; parameter Integer nSeg(min=2) = 2 "Number of volume segments"; //////////////////////////////////////////////////////////////////// // Assumptions parameter Types.Dynamics energyDynamics=system.energyDynamics "Formulation of energy balance"; parameter Types.Dynamics massDynamics=energyDynamics "Formulation of mass balance"; // Initialization parameter Medium.AbsolutePressure p_start = Medium.p_default "Start value of pressure"; parameter Medium.Temperature T_start=Medium.T_default "Start value of temperature"; parameter Medium.MassFraction X_start[Medium.nX] = Medium.X_default "Start value of mass fractions m_i/m"; parameter Medium.ExtraProperty C_start[Medium.nC]( quantity=Medium.extraPropertiesNames)=fill(0, Medium.nC) "Start value of trace substances"; ////////////////////////////////////////////////////////////////////MixingVolumes.MixingVolume[nSeg] vol( redeclare each package Medium = Medium, each energyDynamics=energyDynamics, each massDynamics=massDynamics, each p_start=p_start, each T_start=T_start, each X_start=X_start, each C_start=C_start, each V=VTan/nSeg, each nPorts=nPorts, each m_flow_nominal = m_flow_nominal) "Tank segment"; Sensors.EnthalpyFlowRate hA_flow(redeclare package Medium = Medium, m_flow_nominal=m_flow_nominal) "Enthalpy flow rate at port a"; Sensors.EnthalpyFlowRate[nSeg-1] hVol_flow(redeclare package Medium = Medium, each m_flow_nominal=m_flow_nominal); Sensors.EnthalpyFlowRate hB_flow(redeclare package Medium = Medium, m_flow_nominal=m_flow_nominal) "Enthalpy flow rate at port b"; BaseClasses.Buoyancy buo( redeclare package Medium = Medium, V=VTan, nSeg=nSeg, tau=tau) "Model to prevent unstable tank stratification"; parameter Modelica.SIunits.Time tau=1 "Time constant for mixing due to temperature inversion";Modelica.Thermal.HeatTransfer.Components.ThermalConductor[ nSeg - 1] conFlu(each G= conFluSeg) "Thermal conductance in fluid between the segments"; Modelica.Thermal.HeatTransfer.Components.ThermalConductor[ nSeg] conWal( each G=2*Modelica.Constants.pi*kIns*hSeg/Modelica.Math.log((rTan+dIns)/rTan)) "Thermal conductance through tank wall"; Modelica.Thermal.HeatTransfer.Components.ThermalConductor conTop( G=conTopSeg) "Thermal conductance through tank top"; Modelica.Thermal.HeatTransfer.Components.ThermalConductor conBot( G=conTopSeg) "Thermal conductance through tank bottom"; Modelica.Thermal.HeatTransfer.Interfaces.HeatPort_a[nSeg] heaPorVol "Heat port of fluid volumes"; Modelica.Thermal.HeatTransfer.Interfaces.HeatPort_a heaPorSid "Heat port tank side (outside insulation)"; Modelica.Thermal.HeatTransfer.Sensors.HeatFlowSensor heaFloSid[ nSeg] "Heat flow at wall of tank (outside insulation)"; Modelica.Thermal.HeatTransfer.Interfaces.HeatPort_a heaPorTop "Heat port tank top (outside insulation)"; Modelica.Thermal.HeatTransfer.Sensors.HeatFlowSensor heaFloTop "Heat flow at top of tank (outside insulation)"; Modelica.Thermal.HeatTransfer.Interfaces.HeatPort_a heaPorBot "Heat port tank bottom (outside insulation). Leave unconnected for adiabatic condition"; Modelica.Thermal.HeatTransfer.Sensors.HeatFlowSensor heaFloBot "Heat flow at bottom of tank (outside insulation)"; Modelica.Blocks.Interfaces.RealOutput Ql_flow "Heat loss of tank (positive if heat flows from tank to ambient)"; protected constant Integer nPorts = 2 "Number of ports of volume"; parameter Modelica.SIunits.Length hSeg = hTan / nSeg "Height of a tank segment"; parameter Modelica.SIunits.Area ATan = VTan/hTan "Tank cross-sectional area (without insulation)"; parameter Modelica.SIunits.Length rTan = sqrt(ATan/Modelica.Constants.pi) "Tank diameter (without insulation)"; parameter Modelica.SIunits.ThermalConductance conFluSeg = ATan*Medium.lambda_const/hSeg "Thermal conductance between fluid volumes"; parameter Modelica.SIunits.ThermalConductance conTopSeg = ATan*kIns/dIns "Thermal conductance from center of top (or bottom) volume through tank insulation at top (or bottom)";protected Modelica.Blocks.Routing.Multiplex3 mul( n1=1, n2=nSeg, n3=1); Modelica.Blocks.Math.Sum sum1(nin=nSeg + 2); public Modelica.Thermal.HeatTransfer.Components.ThermalCollector theCol(m=nSeg) "Connector to assign multiple heat ports to one heat port"; equationconnect(hA_flow.port_b, vol[1].ports[1]); connect(vol[nSeg].ports[2], hB_flow.port_a); connect(hB_flow.port_b, port_b); for i in 1:(nSeg-1) loopconnect(vol[i].ports[2], hVol_flow[i].port_a); connect(hVol_flow[i].port_b, vol[i+1].ports[1]); end for;connect(port_a, hA_flow.port_a); connect(buo.heatPort, vol.heatPort); for i in 1:nSeg-1 loop // heat conduction between fluid nodesconnect(vol[i].heatPort, conFlu[i].port_a); connect(vol[i+1].heatPort, conFlu[i].port_b); end for;connect(vol[1].heatPort, conTop.port_a); connect(vol.heatPort, conWal.port_a); connect(conBot.port_a, vol[nSeg].heatPort); connect(vol.heatPort, heaPorVol); connect(conWal.port_b, heaFloSid.port_a); for i in 1:nSeg loop end for;connect(conTop.port_b, heaFloTop.port_a); connect(conBot.port_b, heaFloBot.port_a); connect(heaFloTop.port_b, heaPorTop); connect(heaFloBot.port_b, heaPorBot); connect(heaFloTop.Q_flow, mul.u1[1]); connect(heaFloSid.Q_flow, mul.u2); connect(heaFloBot.Q_flow, mul.u3[1]); connect(mul.y, sum1.u); connect(sum1.y, Ql_flow); connect(heaFloSid.port_b, theCol.port_a); connect(theCol.port_b, heaPorSid); end Stratified;
This is a model of a stratified storage tank for thermal energy storage. The model is identical to Buildings.Fluid.Storage.Stratified, except that it adds a correction that reduces the numerical dissipation. The correction uses a third order upwind scheme to compute the outlet temperatures of the segments in the tank. This model is implemented in Buildings.Fluid.Storage.BaseClasses.ThirdOrderStratifier.
The model requires at least 4 fluid segments. Hence, set nSeg
to 4 or higher.
Extends from Stratified (Model of a stratified tank for thermal energy storage).
Type | Name | Default | Description |
---|---|---|---|
replaceable package Medium | PartialMedium | Medium in the component | |
Volume | VTan | Tank volume [m3] | |
Length | hTan | Height of tank (without insulation) [m] | |
Length | dIns | Thickness of insulation [m] | |
ThermalConductivity | kIns | 0.04 | Specific heat conductivity of insulation [W/(m.K)] |
Integer | nSeg | 4 | Number of volume segments |
Time | tau | 1 | Time constant for mixing due to temperature inversion [s] |
Nominal condition | |||
MassFlowRate | m_flow_nominal | Nominal mass flow rate [kg/s] | |
Initialization | |||
MassFlowRate | m_flow.start | 0 | Mass flow rate from port_a to port_b (m_flow > 0 is design flow direction) [kg/s] |
Pressure | dp.start | 0 | Pressure difference between port_a and port_b [Pa] |
Assumptions | |||
Boolean | allowFlowReversal | system.allowFlowReversal | = true to allow flow reversal, false restricts to design direction (port_a -> port_b) |
Advanced | |||
MassFlowRate | m_flow_small | 1E-4*abs(m_flow_nominal) | Small mass flow rate for regularization of zero flow [kg/s] |
Boolean | homotopyInitialization | true | = true, use homotopy method |
Diagnostics | |||
Boolean | show_V_flow | false | = true, if volume flow rate at inflowing port is computed |
Boolean | show_T | false | = true, if actual temperature at port is computed (may lead to events) |
Dynamics | |||
Equations | |||
Dynamics | energyDynamics | system.energyDynamics | Formulation of energy balance |
Dynamics | massDynamics | energyDynamics | Formulation of mass balance |
Initialization | |||
AbsolutePressure | p_start | Medium.p_default | Start value of pressure [Pa] |
Temperature | T_start | Medium.T_default | Start value of temperature [K] |
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 |
Type | Name | Description |
---|---|---|
FluidPort_a | port_a | Fluid connector a (positive design flow direction is from port_a to port_b) |
FluidPort_b | port_b | Fluid connector b (positive design flow direction is from port_a to port_b) |
HeatPort_a | heaPorVol[nSeg] | Heat port of fluid volumes |
HeatPort_a | heaPorSid | Heat port tank side (outside insulation) |
HeatPort_a | heaPorTop | Heat port tank top (outside insulation) |
HeatPort_a | heaPorBot | Heat port tank bottom (outside insulation). Leave unconnected for adiabatic condition |
output RealOutput | Ql_flow | Heat loss of tank (positive if heat flows from tank to ambient) |
model StratifiedEnhanced "Stratified tank model with enhanced discretization" extends Stratified(nSeg=4, nPorts=3, vol(each prescribedHeatFlowRate=true));BaseClasses.ThirdOrderStratifier str( redeclare package Medium = Medium, nSeg=nSeg, m_flow_small=m_flow_small) "Model to reduce numerical dissipation"; Modelica.Blocks.Sources.RealExpression mTan_flow(y=port_a.m_flow) "Mass flow rate at port a"; equationconnect(vol[1:nSeg].ports[3], str.fluidPort[2:nSeg+1]); connect(hA_flow.H_flow, str.H_flow[1]); connect(hVol_flow[1:nSeg-1].H_flow, str.H_flow[2:nSeg]); connect(hB_flow.H_flow, str.H_flow[nSeg + 1]); connect(str.heatPort, vol.heatPort); connect(port_a, str.fluidPort[1]); connect(port_b, str.fluidPort[nSeg + 2]); connect(mTan_flow.y, str.m_flow); end StratifiedEnhanced;