Modelica.Fluid

Information

Library Modelica.Fluid is a free Modelica package providing components for 1-dimensional thermo-fluid flow in networks of vessels, pipes, fluid machines, valves and fittings. A unique feature is that the component equations and the media models as well as pressure loss and heat transfer correlations are decoupled from each other. All components are implemented such that they can be used for media from the Modelica.Media library. This means especially that an incompressible or compressible medium, a single or a multiple substance medium with one or more phases might be used.

In the next figure, several features of the library are demonstrated with a simple heating system with a closed flow cycle. By just changing one configuration parameter in the system object the equations are changed between steady-state and dynamic simulation with fixed or steady-state initial conditions.

With respect to previous versions, the design of the connectors has been changed in a non-backward compatible way, using the recently developed concept of stream connectors that results in much more reliable simulations (see also Stream-Connectors-Overview-Rationale.pdf). This extension was included in Modelica 3.1. As of Jan. 2009, the stream concept is supported in Dymola 7.1. It is recommended to use Dymola 7.2 (available since Feb. 2009), or a later Dymola version, since this version supports a new annotation to connect very conveniently to vectors of connectors. Other tool vendors will support the stream concept as well.

The following parts are useful, when newly starting with this library:

• Modelica.Fluid.UsersGuide.
• Modelica.Fluid.UsersGuide.ReleaseNotes summarizes the changes of the library releases.
• Modelica.Fluid.Examples contains examples that demonstrate the usage of this library.

Licensed by the Modelica Association under the Modelica License 2
Copyright © 2002-2013, ABB, DLR, Dassault Systèmes AB, Modelon, TU Braunschweig, TU Hamburg-Harburg, Politecnico di Milano.

This Modelica package is free software and the use is completely at your own risk; it can be redistributed and/or modified under the terms of the Modelica License 2. For license conditions (including the disclaimer of warranty) see Modelica.UsersGuide.ModelicaLicense2 or visit https://www.modelica.org/licenses/ModelicaLicense2.

Package Content

Name	Description
UsersGuide	User's Guide
Examples	Demonstration of the usage of the library
System	System properties and default values (ambient, flow direction, initialization)
Vessels	Devices for storing fluid
Pipes	Devices for conveying fluid
Machines	Devices for converting between energy held in a fluid and mechanical energy
Valves	Components for the regulation and control of fluid flow
Fittings	Adaptors for connections of fluid components and the regulation of fluid flow
Sources	Define fixed or prescribed boundary conditions
Sensors	Ideal sensor components to extract signals from a fluid connector
Interfaces	Interfaces for steady state and unsteady, mixed-phase, multi-substance, incompressible and compressible flow
Types	Common types for fluid models
Dissipation	Functions for convective heat transfer and pressure loss characteristics
Utilities	Utility models to construct fluid components (should not be used directly)
Icons

Modelica.Fluid.System

Information

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

Name	Description
Environment
p_ambient	Default ambient pressure [Pa]
T_ambient	Default ambient temperature [K]
g	Constant gravity acceleration [m/s2]
Assumptions
allowFlowReversal	= false to restrict to design flow direction (port_a -> port_b)
Dynamics
energyDynamics	Default formulation of energy balances
massDynamics	Default formulation of mass balances
momentumDynamics	Default formulation of momentum balances, if options available
Initialization
m_flow_start	Default start value for mass flow rates [kg/s]
p_start	Default start value for pressures [Pa]
T_start	Default start value for temperatures [K]
Advanced
use_eps_Re	= true to determine turbulent region automatically using Reynolds number
m_flow_nominal	Default nominal mass flow rate [kg/s]
eps_m_flow	Regularization of zero flow for |m_flow| < eps_m_flow*m_flow_nominal
Classic
dp_small	Default small pressure drop for regularization of laminar and zero flow [Pa]
m_flow_small	Default small mass flow rate for regularization of laminar and zero flow [kg/s]