WOLFRAM SYSTEM MODELER

# Fittings

Adaptors for connections of fluid components and the regulation of fluid flow # Package Contents Flow models for bends Flow models for orifices Flow models for generic resistances Simple generic orifice defined by pressure loss coefficient and diameter (only for flow from port_a to port_b) Pressure drop due to sharp edged orifice (for both flow directions) Pressure drop in pipe due to suddenly expanding or reducing area (for both flow directions) Multiply a port; useful if multiple connections shall be made to a port exposing a state Splitting/joining component with static balances for an infinitesimal control volume Splitting/joining component with static balances for a dynamic control volume Base classes used in the Fittings package (only of interest to build new component models)

# Information

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

This sublibrary contains models and functions providing pressure loss correlations. All models in this library have the property that no mass and no energy is stored in the component. Therefore, none of the models have a state.

All functions are continuous and have a finite, non-zero, smooth, first derivative. The functions are all guaranteed to be strict monotonically increasing. The mentioned properties guarantee that a unique inverse of every function exists. Note, the usual quadratic pressure loss correlation

• in the form m_flow = f(dp) has an infinite derivative at zero mass flow rate and is therefore problematic to use.
• in the form dp = f(m_flow) has a zero derivative at zero mass flow rate and is therefore problematic to invert, since the inverse function has then an infinite derivative at zero mass flow rate.

The two mentioned problems are solved in this package by approximating the characteristics around zero mass flow rates with appropriate polynomials. The monotonicity is guaranteed using results from:

Fritsch F.N. and Carlson R.E. (1980):
Monotone piecewise cubic interpolation. SIAM J. Numerc. Anal., Vol. 17, No. 2, April 1980, pp. 238-246

# Wolfram Language

In:= `SystemModel["Modelica.Fluid.Fittings"]`
Out:= # Revisions

• Jan. 3, 2006 by Martin Otter:
New design and implementation based on previous iterations.