Description: "Package with base classes for Buildings.Fluid"

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## Buildings.Fluid.BaseClasses

Package with base classes for Buildings.Fluid

### Information

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

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

### Package Content

Name | Description
--- | ---
IndexMassFraction | Computes the index of a substance in the mass fraction vector Xi
PartialResistance | Partial model for a hydraulic resistance
PartialThreeWayResistance | Flow splitter with partial resistance model at each port
FlowModels | Flow models for pressure drop calculations

## Buildings.Fluid.BaseClasses.IndexMassFraction

Computes the index of a substance in the mass fraction vector Xi

### Information

This block computes the index that the subtance with name `substanceName` has in the mass fraction vector `X`. If the medium model has no component called `substanceName`, then the block writes an error message and terminates the simulation.

This block is used for example to obtain the index of the subtance 'water' to obtain the water vapor concentration, or to measure any other mass fraction.

### Parameters

Type | Name | Default | Description
--- | --- | --- | ---
replaceable package Medium | Modelica.Media.Interfaces.Pa... | Medium model
String | substanceName | "" | Name of species substance

### Connectors

Type | Name | Description
--- | --- | ---
replaceable package Medium | Medium model

### Modelica definition

block IndexMassFraction "Computes the index of a substance in the mass fraction vector Xi" replaceable package Medium = Modelica.Media.Interfaces.PartialCondensingGases "Medium model"; parameter String substanceName="" "Name of species substance"; protected parameter Integer i_x(fixed=false) "Index of substance"; initial algorithm // Compute index of species vector that carries the substance name i_x :=-1; for i in 1:Medium.nXi loop if Modelica.Utilities.Strings.isEqual(string1=Medium.substanceNames[i], string2=substanceName, caseSensitive=false) then i_x :=i; end if; end for; assert(i_x > 0, "Substance '" + substanceName + "' is not present in medium '" + Medium.mediumName + "'.\n" + "Change medium model to one that has '" + substanceName + "' as a substance."); end IndexMassFraction;

## Buildings.Fluid.BaseClasses.PartialResistance

Partial model for a hydraulic resistance

### Information

Partial model for a flow resistance, possible with variable flow coefficient. Models that extend this class need to implement an equation that relates `m_flow` and `dp`, and they need to assign the parameter `m_flow_turbulent`.

See for example Buildings.Fluid.FixedResistances.FixedResistanceDpM for a model that extends this base class.

Extends from Buildings.Fluid.Interfaces.PartialTwoPortInterface (Partial model transporting fluid between two ports without storing mass or energy).

### Parameters

Type | Name | Default | Description
--- | --- | --- | ---
replaceable package Medium | PartialMedium | Medium in the component
MassFlowRate | m_flow_turbulent |  | Turbulent flow if |m_flow| >= m_flow_turbulent [kg/s]
Nominal condition
MassFlowRate | m_flow_nominal |  | Nominal mass flow rate [kg/s]
Pressure | dp_nominal |  | Pressure drop at nominal mass flow rate [Pa]
Assumptions
Boolean | allowFlowReversal | true | = 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 | from_dp | false | = true, use m_flow = f(dp) else dp = f(m_flow)
Boolean | homotopyInitialization | true | = true, use homotopy method
Boolean | linearized | false | = true, use linear relation between m_flow and dp for any flow rate
Diagnostics
Boolean | show_T | false | = true, if actual temperature at port is computed

### Connectors

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)

### Modelica definition

partial model PartialResistance "Partial model for a hydraulic resistance" extends Buildings.Fluid.Interfaces.PartialTwoPortInterface( show_T=false, dp(start=0, nominal=dp_nominal_pos), m_flow(nominal=m_flow_nominal_pos), final m_flow_small = 1E-4*abs(m_flow_nominal)); parameter Boolean from_dp = false "= true, use m_flow = f(dp) else dp = f(m_flow)"; parameter Modelica.SIunits.Pressure dp_nominal(displayUnit="Pa") "Pressure drop at nominal mass flow rate"; parameter Boolean homotopyInitialization = true "= true, use homotopy method"; parameter Boolean linearized = false "= true, use linear relation between m_flow and dp for any flow rate"; parameter Modelica.SIunits.MassFlowRate m_flow_turbulent(min=0) "Turbulent flow if |m_flow| >= m_flow_turbulent"; protected parameter Medium.ThermodynamicState sta_default= Medium.setState_pTX(T=Medium.T_default, p=Medium.p_default, X=Medium.X_default); parameter Modelica.SIunits.DynamicViscosity eta_default=Medium.dynamicViscosity(sta_default) "Dynamic viscosity, used to compute transition to turbulent flow regime"; final parameter Modelica.SIunits.MassFlowRate m_flow_nominal_pos = abs(m_flow_nominal) "Absolute value of nominal flow rate"; final parameter Modelica.SIunits.Pressure dp_nominal_pos = abs(dp_nominal) "Absolute value of nominal pressure"; equation // Isenthalpic state transformation (no storage and no loss of energy) port_a.h_outflow = inStream(port_b.h_outflow); port_b.h_outflow = inStream(port_a.h_outflow); // Mass balance (no storage) port_a.m_flow + port_b.m_flow = 0; // Transport of substances port_a.Xi_outflow = inStream(port_b.Xi_outflow); port_b.Xi_outflow = inStream(port_a.Xi_outflow); port_a.C_outflow = inStream(port_b.C_outflow); port_b.C_outflow = inStream(port_a.C_outflow); end PartialResistance;

## Buildings.Fluid.BaseClasses.PartialThreeWayResistance

Flow splitter with partial resistance model at each port

### Information

Partial model for flow resistances with three ports such as a flow mixer/splitter or a three way valve.

If `dynamicBalance=true`, then at the junction of the three flows, a mixing volume will be present. This will introduce a dynamic energy and momentum balance, which often breaks algebraic loops. The time constant of the mixing volume is determined by the parameter `tau`.

Extends from Buildings.Fluid.Interfaces.LumpedVolumeDeclarations (Declarations for lumped volumes).

### Parameters

Type | Name | Default | Description
--- | --- | --- | ---
replaceable package Medium | PartialMedium | Medium in the component
PartialTwoPortInterface | res1 | redeclare Buildings.Fluid.In... | Partial model, to be replaced with a fluid component
PartialTwoPortInterface | res2 | redeclare Buildings.Fluid.In... | Partial model, to be replaced with a fluid component
PartialTwoPortInterface | res3 | redeclare Buildings.Fluid.In... | Partial model, to be replaced with a fluid component
Dynamics
Equations
Dynamics | energyDynamics | Modelica.Fluid.Types.Dynamic... | Formulation of energy balance
Dynamics | massDynamics | energyDynamics | Formulation of mass balance
Boolean | dynamicBalance | true | Set to true to use a dynamic balance, which often leads to smaller systems of equations
MassFlowRate | mDyn_flow_nominal |  | Nominal mass flow rate for dynamic momentum and energy balance [kg/s]
Real | mSenFac | 1 | Factor for scaling the sensible thermal mass of the volume
Nominal condition
Time | tau | 10 | Time constant at nominal flow for dynamic energy and momentum balance [s]
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.)
Advanced
Boolean | from_dp | true | = true, use m_flow = f(dp) else dp = f(m_flow)
PortFlowDirection | portFlowDirection_1 | Modelica.Fluid.Types.PortFlo... | Flow direction for port_1
PortFlowDirection | portFlowDirection_2 | Modelica.Fluid.Types.PortFlo... | Flow direction for port_2
PortFlowDirection | portFlowDirection_3 | Modelica.Fluid.Types.PortFlo... | Flow direction for port_3

### Connectors

Type | Name | Description
--- | --- | ---
FluidPort_a | port_1 | First port, typically inlet
FluidPort_b | port_2 | Second port, typically outlet
FluidPort_a | port_3 | Third port, can be either inlet or outlet

### Modelica definition

partial model PartialThreeWayResistance "Flow splitter with partial resistance model at each port" extends Buildings.Fluid.Interfaces.LumpedVolumeDeclarations( final mSenFac=1); Modelica.Fluid.Interfaces.FluidPort_a port_1( redeclare package Medium = Medium, m_flow(min=if (portFlowDirection_1 == Modelica.Fluid.Types.PortFlowDirection.Entering) then 0.0 else -Modelica.Constants.inf, max=if (portFlowDirection_1== Modelica.Fluid.Types.PortFlowDirection.Leaving) then 0.0 else Modelica.Constants.inf)) "First port, typically inlet"; Modelica.Fluid.Interfaces.FluidPort_b port_2( redeclare package Medium = Medium, m_flow(min=if (portFlowDirection_2 == Modelica.Fluid.Types.PortFlowDirection.Entering) then 0.0 else -Modelica.Constants.inf, max=if (portFlowDirection_2 == Modelica.Fluid.Types.PortFlowDirection.Leaving) then 0.0 else Modelica.Constants.inf)) "Second port, typically outlet"; Modelica.Fluid.Interfaces.FluidPort_a port_3( redeclare package Medium=Medium, m_flow(min=if (portFlowDirection_3==Modelica.Fluid.Types.PortFlowDirection.Entering) then 0.0 else -Modelica.Constants.inf, max=if (portFlowDirection_3==Modelica.Fluid.Types.PortFlowDirection.Leaving) then 0.0 else Modelica.Constants.inf)) "Third port, can be either inlet or outlet"; parameter Boolean dynamicBalance = true "Set to true to use a dynamic balance, which often leads to smaller systems of equations"; parameter Modelica.SIunits.Time tau=10 "Time constant at nominal flow for dynamic energy and momentum balance"; parameter Modelica.SIunits.MassFlowRate mDyn_flow_nominal "Nominal mass flow rate for dynamic momentum and energy balance"; parameter Boolean from_dp = true "= true, use m_flow = f(dp) else dp = f(m_flow)"; parameter Modelica.Fluid.Types.PortFlowDirection portFlowDirection_1=Modelica.Fluid.Types.PortFlowDirection.Bidirectional "Flow direction for port_1"; parameter Modelica.Fluid.Types.PortFlowDirection portFlowDirection_2=Modelica.Fluid.Types.PortFlowDirection.Bidirectional "Flow direction for port_2"; parameter Modelica.Fluid.Types.PortFlowDirection portFlowDirection_3=Modelica.Fluid.Types.PortFlowDirection.Bidirectional "Flow direction for port_3"; replaceable Buildings.Fluid.Interfaces.PartialTwoPortInterface res1( redeclare package Medium = Medium, allowFlowReversal=portFlowDirection_1 == Modelica.Fluid.Types.PortFlowDirection.Bidirectional) "Partial model, to be replaced with a fluid component"; replaceable Buildings.Fluid.Interfaces.PartialTwoPortInterface res2( redeclare package Medium = Medium, allowFlowReversal=portFlowDirection_2 == Modelica.Fluid.Types.PortFlowDirection.Bidirectional) "Partial model, to be replaced with a fluid component"; replaceable Buildings.Fluid.Interfaces.PartialTwoPortInterface res3( redeclare package Medium = Medium, allowFlowReversal=portFlowDirection_3 == Modelica.Fluid.Types.PortFlowDirection.Bidirectional) "Partial model, to be replaced with a fluid component"; Buildings.Fluid.Delays.DelayFirstOrder vol( redeclare final package Medium = Medium, final nPorts=3, final tau=tau, final m_flow_nominal=mDyn_flow_nominal, 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 allowFlowReversal=true, final prescribedHeatFlowRate=false) if dynamicBalance "Fluid volume to break algebraic loop"; protected Modelica.Fluid.Interfaces.FluidPort_a port_internal( redeclare package Medium = Medium) if not dynamicBalance "Internal dummy port for easier connection of conditional connections"; equation if portFlowDirection_1==Modelica.Fluid.Types.PortFlowDirection.Leaving then if not dynamicBalance then connect(res1.port_a, port_internal); else connect(res1.port_a, vol.ports[1]); end if; connect(port_1, res1.port_b); else if not dynamicBalance then connect(res1.port_b, port_internal); else connect(res1.port_b, vol.ports[1]); end if; connect(port_1, res1.port_a); end if; if portFlowDirection_2==Modelica.Fluid.Types.PortFlowDirection.Leaving then if not dynamicBalance then connect(res2.port_a, port_internal); else connect(res2.port_a, vol.ports[2]); end if; connect(port_2, res2.port_b); else if not dynamicBalance then connect(res2.port_b, port_internal); else connect(res2.port_b, vol.ports[2]); end if; connect(port_2, res2.port_a); end if; if portFlowDirection_3==Modelica.Fluid.Types.PortFlowDirection.Leaving then if not dynamicBalance then connect(res3.port_a, port_internal); else connect(res3.port_a, vol.ports[3]); end if; connect(port_3, res3.port_b); else if not dynamicBalance then connect(res3.port_b, port_internal); else connect(res3.port_b, vol.ports[3]); end if; connect(port_3, res3.port_a); end if; end PartialThreeWayResistance;