System

System properties and default values (ambient, flow direction, initialization)

Information

This information is part of the Modelica Standard Library maintained by the Modelica Association.

A system component is needed in each fluid model to provide system-wide settings, such as ambient conditions and overall modeling assumptions. The system settings are propagated to the fluid models using the inner/outer mechanism.

A model should never directly use system parameters. Instead a local parameter should be declared, which uses the global setting as default. The only exceptions are:

the gravity system.g,
the global system.eps_m_flow, which is used to define a local m_flow_small for the local m_flow_nominal:
```
m_flow_small = system.eps_m_flow*m_flow_nominal
```

The global system.m_flow_small and system.dp_small are classic parameters. They do not distinguish between laminar flow and regularization of zero flow. Absolute small values are error prone for models with local nominal values. Moreover dp_small can generally be obtained automatically. Consider using the new system.use_eps_Re = true (see Advanced tab).

Parameters (17)

p_ambient	Value: 101325 Type: AbsolutePressure (Pa) Description: Default ambient pressure
T_ambient	Value: 293.15 Type: Temperature (K) Description: Default ambient temperature
g	Value: Modelica.Constants.g_n Type: Acceleration (m/s²) Description: Constant gravity acceleration
allowFlowReversal	Value: true Type: Boolean Description: = false to restrict to design flow direction (port_a -> port_b)
energyDynamics	Value: Modelica.Fluid.Types.Dynamics.DynamicFreeInitial Type: Dynamics Description: Default formulation of energy balances
massDynamics	Value: energyDynamics Type: Dynamics Description: Default formulation of mass balances
substanceDynamics	Value: massDynamics Type: Dynamics Description: Default formulation of substance balances
traceDynamics	Value: massDynamics Type: Dynamics Description: Default formulation of trace substance balances
momentumDynamics	Value: Modelica.Fluid.Types.Dynamics.SteadyState Type: Dynamics Description: Default formulation of momentum balances, if options available
m_flow_start	Value: 0 Type: MassFlowRate (kg/s) Description: Default start value for mass flow rates
p_start	Value: p_ambient Type: AbsolutePressure (Pa) Description: Default start value for pressures
T_start	Value: T_ambient Type: Temperature (K) Description: Default start value for temperatures
use_eps_Re	Value: false Type: Boolean Description: = true to determine turbulent region automatically using Reynolds number
m_flow_nominal	Value: if use_eps_Re then 1 else 1e2 * m_flow_small Type: MassFlowRate (kg/s) Description: Default nominal mass flow rate
eps_m_flow	Value: 1e-4 Type: Real Description: Regularization of zero flow for \|m_flow\| < eps_m_flow*m_flow_nominal
dp_small	Value: 1 Type: AbsolutePressure (Pa) Description: Default small pressure drop for regularization of laminar and zero flow
m_flow_small	Value: 1e-2 Type: MassFlowRate (kg/s) Description: Default small mass flow rate for regularization of laminar and zero flow

Used in Examples (23)

	PumpingSystem Modelica.Fluid.Examples Model of a pumping system for drinking water
	HeatingSystem Modelica.Fluid.Examples Simple model of a heating system
	DrumBoiler Modelica.Fluid.Examples.DrumBoiler Complete drum boiler model, including evaporator and supplementary components
	ThreeTanks Modelica.Fluid.Examples.Tanks Demonstrating the usage of SimpleTank
	TanksWithOverflow Modelica.Fluid.Examples.Tanks Two tanks connected with pipes at different heights
	EmptyTanks Modelica.Fluid.Examples.Tanks Show the treatment of empty tanks
	ControlledTanks Modelica.Fluid.Examples.ControlledTankSystem Demonstrating the controller of a tank filling/emptying system
	BatchPlant_StandardWater Modelica.Fluid.Examples.AST_BatchPlant Model of an experimental batch plant
	OneTank Modelica.Fluid.Examples.AST_BatchPlant.Test Tank with one time-varying top inlet mass flow rate and a bottom outlet into the ambient
	TwoTanks Modelica.Fluid.Examples.AST_BatchPlant.Test
	TankWithEmptyingPipe1 Modelica.Fluid.Examples.AST_BatchPlant.Test Demonstrates a tank with one constant top inlet mass flow rate and a bottom outlet into the ambient
	TankWithEmptyingPipe2 Modelica.Fluid.Examples.AST_BatchPlant.Test Demonstrates a tank with one constant top inlet mass flow rate and a bottom outlet into the ambient
	TanksWithEmptyingPipe1 Modelica.Fluid.Examples.AST_BatchPlant.Test Demonstrates a tank with one constant top inlet mass flow rate and a bottom outlet into the ambient
	TanksWithEmptyingPipe2 Modelica.Fluid.Examples.AST_BatchPlant.Test Demonstrates a tank with one constant top inlet mass flow rate and a bottom outlet into the ambient
	IncompressibleFluidNetwork Modelica.Fluid.Examples Multi-way connections of pipes and incompressible medium model
	BranchingDynamicPipes Modelica.Fluid.Examples Multi-way connections of pipes with dynamic momentum balance, pressure wave and flow reversal
	NonCircularPipes Modelica.Fluid.Examples Comparing a circular with a non-circular pipe
	HeatExchangerSimulation Modelica.Fluid.Examples.HeatExchanger Simulation for the heat exchanger model
	RoomCO2 Modelica.Fluid.Examples.TraceSubstances Demonstrates a room volume with CO2 accumulation
	RoomCO2WithControls Modelica.Fluid.Examples.TraceSubstances Demonstrates a room volume with CO2 controls
	InverseParameterization Modelica.Fluid.Examples Demonstrates the parameterization of a pump and a pipe for given nominal values
	MeasuringTemperature Modelica.Fluid.Examples.Explanatory Differences between using one port with and without explicit junction model and two port sensors for fluid temperature measuring
	MomentumBalanceFittings Modelica.Fluid.Examples.Explanatory Illustrating a case in which kinetic terms play a major role in the momentum balance

Used in Components (9)

	BasicHX Modelica.Fluid.Examples.HeatExchanger.BaseClasses Simple heat exchanger model
	WallConstProps Modelica.Fluid.Examples.HeatExchanger.BaseClasses Pipe wall with capacitance, assuming 1D heat conduction and constant material properties
	PumpMonitoringBase Modelica.Fluid.Machines.BaseClasses.PumpMonitoring Interface for pump monitoring
	PartialTwoPort Modelica.Fluid.Interfaces Partial component with two ports
	PartialHeatTransfer Modelica.Fluid.Interfaces Common interface for heat transfer models
	PartialLumpedVolume Modelica.Fluid.Interfaces Lumped volume with mass and energy balance
	PartialLumpedFlow Modelica.Fluid.Interfaces Base class for a lumped momentum balance
	PartialDistributedVolume Modelica.Fluid.Interfaces Base class for distributed volume models
	PartialDistributedFlow Modelica.Fluid.Interfaces Base class for a distributed momentum balance