Common types for fluid models

Extends from Modelica.Icons.TypesPackage (Icon for packages containing type definitions).

Name | Description |
---|---|

HydraulicConductance | Real type for hydraulic conductance |

HydraulicResistance | Real type for hydraulic resistance |

Roughness | Real type for roughness of a pipe |

Dynamics | Enumeration to define definition of balance equations |

CvTypes | Enumeration to define the choice of valve flow coefficient |

PortFlowDirection | Enumeration to define whether flow reversal is allowed |

ModelStructure | Enumeration with choices for model structure in distributed pipe model |

CheckValveHomotopyType | Enumeration with choices for check valve homotopy |

Real type for hydraulic conductance

Name | Value |
---|---|

Custom Parameters | |

quantity | "HydraulicConductance" |

unit | "kg/(s.Pa)" |

Real type for hydraulic resistance

Name | Value |
---|---|

Custom Parameters | |

quantity | "HydraulicResistance" |

unit | "Pa.s/kg" |

Real type for roughness of a pipe

This Real type defines the absolute roughness of the inner surface of a
pipe or fitting, i.e., the absolute average height of surface asperities.
It has usually to
be estimated. In *[Idelchik 1994, pp. 105-109,
Table 2-5; Miller 1990, p. 190, Table 8-1]* many examples are given.
As a short summary:

Type of pipe |
Roughness | |

Smooth pipes |
Drawn brass, copper, aluminium, glass, etc. | 0.0025 mm |

Steel pipes |
New smooth pipes | 0.025 mm |

Mortar lined, average finish | 0.1 mm | |

Heavy rust | 1 mm | |

Concrete pipes |
Steel forms, first class workmanship | 0.025 mm |

Steel forms, average workmanship | 0.1 mm | |

Block linings | 1 mm |

- Idelchik I.E. (1994):
**Handbook of Hydraulic Resistance**. 3rd edition, Begell House, ISBN 0-8493-9908-4- Miller D. S. (1990):
**Internal flow systems**. 2nd edition. Cranfield:BHRA(Information Services).

Extends from Modelica.Icons.TypeReal (Icon for Real types).

Name | Value |
---|---|

Custom Parameters | |

quantity | "Length" |

unit | "m" |

displayUnit | "mm" |

min | 0 |

Enumeration to define definition of balance equations

Enumeration to define the formulation of balance equations (to be selected via choices menu):

Dynamics. | Meaning |
---|---|

DynamicFreeInitial | Dynamic balance, Initial guess value |

FixedInitial | Dynamic balance, Initial value fixed |

SteadyStateInitial | Dynamic balance, Steady state initial with guess value |

SteadyState | Steady state balance, Initial guess value |

The enumeration "Dynamics" is used for the mass, energy and momentum balance equations respectively. The exact meaning for the three balance equations is stated in the following tables:

Mass balance | ||

Dynamics. |
Balance equation |
Initial condition |

DynamicFreeInitial | no restrictions | no initial conditions |

FixedInitial | no restrictions | if Medium.singleState thenno initial condition else p=p_start |

SteadyStateInitial | no restrictions | if Medium.singleState thenno initial condition else der(p)=0 |

SteadyState | der(m)=0 |
no initial conditions |

Energy balance | ||

Dynamics. |
Balance equation |
Initial condition |

DynamicFreeInitial | no restrictions | no initial conditions |

FixedInitial | no restrictions | T=T_start or h=h_start |

SteadyStateInitial | no restrictions | der(T)=0 or der(h)=0 |

SteadyState | der(U)=0 |
no initial conditions |

Momentum balance | ||

Dynamics. |
Balance equation |
Initial condition |

DynamicFreeInitial | no restrictions | no initial conditions |

FixedInitial | no restrictions | m_flow = m_flow_start |

SteadyStateInitial | no restrictions | der(m_flow)=0 |

SteadyState | der(m_flow)=0 |
no initial conditions |

In the tables above, the equations are given for one-substance fluids. For multiple-substance fluids and for trace substances, equivalent equations hold.

Medium.singleState is a medium property and defines whether the medium is only
described by one state (+ the mass fractions in case of a multi-substance fluid). In such
a case one initial condition less must be provided. For example, incompressible
media have Medium.singleState = **true**.

Enumeration to define the choice of valve flow coefficient

Enumeration to define the choice of valve flow coefficient (to be selected via choices menu):

CvTypes. |
Meaning |
---|---|

Av | Av (metric) flow coefficient |

Kv | Kv (metric) flow coefficient |

Cv | Cv (US) flow coefficient |

OpPoint | Av defined by operating point |

The details of the coefficients are explained in the User's Guide .

Enumeration to define whether flow reversal is allowed

Enumeration to define the assumptions on the model for the direction of fluid flow at a port (to be selected via choices menu):

PortFlowDirection. |
Meaning |
---|---|

Entering | Fluid flow is only entering the port from the outside |

Leaving | Fluid flow is only leaving the port to the outside |

Bidirectional | No restrictions on fluid flow (flow reversal possible) |

The default is "PortFlowDirection.Bidirectional". If you are completely sure that the flow is only in one direction, then the other settings may make the simulation of your model faster.

Enumeration with choices for model structure in distributed pipe model

Enumeration to define the discretization structure of distributed pipe models according to the staggered grid scheme:

ModelStructure. |
Meaning |
---|---|

av_vb | port_a - volume - flow model - volume - port_b |

a_v_b | port_a - flow model - volume - flow model - port_b |

av_b | port_a - volume - flow model - port_b |

a_vb | port_a - flow model - volume - port_b |

The default is "ModelStructure.av_vb", i.e., the distributed pipe has "volumes" at its both ends. The advantage is that connections of the pipe to flow models (like fittings) lead to the desirable structure of alternating volume and flow models, which means that no non-linear algebraic equations occur.

Direct connections of distributed pipes with this option means that two volumes are directly connected together. Due to the stream concept this means that the pressures of the two connected volumes are identical, but the temperatures are not set equal (this corresponds to volumes that are connected together with a very short distance and it needs some time until different volume temperatures are equilibrated). Since the pressures of the volumes are identical, the number of states is reduced and index reduction takes place (which means that medium equations depending on pressure are differentiated and the number of required initial conditions is reduced by one).

The default option "av_vb" cannot be used, if the dynamic pipe is connected to a model with non-differentiable pressure, like a Sources.Boundary_pT with prescribed jumping pressure. The modelStructure can be configured as appropriate in such situations, in order to place a momentum balance between a pressure state of the pipe and a non-differentiable boundary condition (e.g., if the jumping pressure component is connected to port_a, use model structure ModelStructure.a_vb).

Enumeration with choices for check valve homotopy

If it is know whether the check valve will start open or closed this can simplify the initialization.

The choice **NoHomotopy** is useful if nothing is known for the check valve.