Package Modelica.​Fluid.​Fittings
Adaptors for connections of fluid components and the regulation of fluid flow

Information

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

Extends from Modelica.​Icons.​VariantsPackage (Icon for package containing variants).

Package Contents

Model Modelica.​Fluid.​Fittings.​SimpleGenericOrifice
Simple generic orifice defined by pressure loss coefficient and diameter (only for flow from port_a to port_b)

Information

This pressure drop component defines a simple, generic orifice, where the loss factor ζ is provided for one flow direction (e.g., from loss table of a book):

   Δp = 0.5*ζ*ρ*v*|v|
      = 8*ζ/(π^2*D^4*ρ) * m_flow*|m_flow|

where

• Δp is the pressure drop: Δp = port_a.p - port_b.p
• D is the diameter of the orifice at the position where ζ is defined (either at port_a or port_b). If the orifice has not a circular cross section, D = 4*A/P, where A is the cross section area and P is the wetted perimeter.
• ζ is the loss factor with respect to D that depends on the geometry of the orifice. In the turbulent flow regime, it is assumed that ζ is constant.
  For small mass flow rates, the flow is laminar and is approximated by a polynomial that has a finite derivative for m_flow=0.
• v is the mean velocity.
• ρ is the upstream density.

Since the pressure loss factor zeta is provided only for a mass flow from port_a to port_b, the pressure loss is not correct when the flow is reversing. If reversing flow only occurs in a short time interval, this is most likely uncritical. If significant reversing flow can appear, this component should not be used.

Extends from Modelica.​Fluid.​Interfaces.​PartialTwoPortTransport (Partial element transporting fluid between two ports without storage of mass or energy) and Modelica.​Fluid.​Interfaces.​PartialLumpedFlow (Base class for a lumped momentum balance).

Parameters

Connectors

Model Modelica.​Fluid.​Fittings.​SharpEdgedOrifice
Pressure drop due to sharp edged orifice (for both flow directions)

Information

Extends from Modelica.​Fluid.​Fittings.​BaseClasses.​QuadraticTurbulent.​BaseModel (Generic pressure drop component with constant turbulent loss factor data and without an icon).

Parameters

Connectors

Model Modelica.​Fluid.​Fittings.​AbruptAdaptor
Pressure drop in pipe due to suddenly expanding or reducing area (for both flow directions)

Information

Extends from Modelica.​Fluid.​Fittings.​BaseClasses.​QuadraticTurbulent.​BaseModelNonconstantCrossSectionArea (Generic pressure drop component with constant turbulent loss factor data and without an icon, for non-constant cross section area).

Parameters

Connectors

Model Modelica.​Fluid.​Fittings.​MultiPort
Multiply a port; useful if multiple connections shall be made to a port exposing a state

Information

This model is useful if multiple connections shall be made to a port of a volume model exposing a state, like a pipe with ModelStructure av_vb. The mixing is shifted into the volume connected to port_a and the result is propagated back to each ports_b.

If multiple connections were directly made to the volume, then ideal mixing would take place in the connection set, outside the volume. This is normally not intended.

Parameters

Connectors

Model Modelica.​Fluid.​Fittings.​TeeJunctionIdeal
Splitting/joining component with static balances for an infinitesimal control volume

Information

This model is the simplest implementation for a splitting/joining component for three flows. Its use is not required. It just formulates the balance equations in the same way that the connect semantics would formulate them anyways. The main advantage of using this component is, that the user does not get confused when looking at the specific enthalpy at each port which might be confusing when not using a splitting/joining component. The reason for the confusion is that one examines the mixing enthalpy of the infinitesimal control volume introduced with the connect statement when looking at the specific enthalpy in the connector which might not be equal to the specific enthalpy at the port in the "real world".

Extends from Modelica.​Fluid.​Fittings.​BaseClasses.​PartialTeeJunction (Base class for a splitting/joining component with three ports).

Connectors

Model Modelica.​Fluid.​Fittings.​TeeJunctionVolume
Splitting/joining component with static balances for a dynamic control volume

Information

This model introduces a mixing volume into a junction. This might be useful to examine the non-ideal mixing taking place in a real junction.

Extends from Modelica.​Fluid.​Fittings.​BaseClasses.​PartialTeeJunction (Base class for a splitting/joining component with three ports) and Modelica.​Fluid.​Interfaces.​PartialLumpedVolume (Lumped volume with mass and energy balance).

Parameters

Connectors