ValveVLE_L1

Created Friday 11 January 2013

A model for for valves, throttles, orifices and similar components. The pressure loss and the opening characteristics can be user-defined using replaceable models.

1. Purpose of Model



The model can be used for introducing pressure loss effects (either due to physical or numerical motivation). Since the model neglects changes in kinetic energy it implies either small density changes or adapted flange geometry. It is possible to use the valve as a check valve, for example to avoid back flows. The numerical robustness and accuracy depend strongly on the chosen replaceable model for the pressure loss.

2. Level of Detail, Physical Effects Considered and Physical Insight


2.1 Level of Detail

Referring to Brunnemann et al. [1], this model refers to the level of detail L1 because the system is modelled under phenomenological considerations that cause the pressure to drop, i.e. the opening of the valve.

2.2 Physical Effects Considered

2.3 Level of Insight

The pressure loss can be defined by choosing and modifying the replaceable model PressureLoss in the parameter dialog. The following models are available:

all these models are based on the base class called GenericPressureLoss.

3. Limits of Validity

4. Interfaces


4.1 Physical Connectors


4.2 Inputs

4.3 Medium Models

5. Nomenclature


6. Governing Equations


6.1 System Description and General model approach

The governing equations consider mainly a isenthalpic throttling process without energy losses. The hydraulic model assumes a geometric definition as sketched below. The fluid may have inlet and outlet fittings to couple the valve to the surrounding piping. The resistance of these fittings is taken into account via a geometry correction factor.


Figure 1. Valve 2 Scheme

The state change of the valve can be displayed in a enthalpy-entropy-diagram and is considered as follows: The fluid entering at the inlet, denoted with (0) is throttled to the outlet pressure p_out. During this throttling process the fluid is accelerated due to reducing cross sections. the maximum speed is reached at the vena contracta, the smallest cross section (denoted (1)). The specific kinetic energy of the system is c²/2 is marked red in the figure below. The total enthalpy is constant since no energy losses occur.
At the vena contracta the outlet pressure is assumed to be reached. From point (1) to the outlet (2) the fluid is decelerated isobarically, thus increasing the specific enthalpy. The model assumes that inlet velocity equals outlet velocity, implying that inlet specific enthalpy equals outlet specific enthalpy. This assumption is made to increase the numerical robustness.
In reality the expansion process will differ slightly from this ideal two-stepped process, (e.g. due to friction pressure losses from (1 → 2)). However, since the states at the vena contracta (1) are not calculated this simple modelling ideas are sufficient.


6.2 Governing Model Equations


Energy Balance

For an Isenthalpic state transformation (no storage and no loss of energy, no changes of flow velocity) the enthalpies are equal, that is,

The above equation (1) implies constant kinetic energy (constant flow velocities) of the flow which must be guaranteed by constructive means, i.e. the outlet cross section must be larger than the inlet cross section to compensate the density decrease. If the medium is incompressible this assumption is fulfilled also for equal inlet and outlet cross sections.

Mass Balance

The mass balance for steady flow neglecting mass storage reads

Chemistry

No chemical reaction is taking place:

Hydraulics

The hydraulics are defined in the corresponding replaceable models and are accessed via
inlet.m_flow = pressureLoss.m_flow

Summaries

A summary is available including the following:


7. Remarks for Usage

deactivate the control signal input by setting openingInputIsActive to true
forbid reverse flow by setting checkValve to true

9. References

[1] Johannes Brunnemann and Friedrich Gottelt, Kai Wellner, Ala Renz, André Thüring, Volker Röder, Christoph Hasenbein, Christian Schulze, Gerhard Schmitz, Jörg Eiden: "Status of ClaRaCCS: Modelling and Simulation of Coal-Fired Power Plants with CO2 capture", 9th Modelica Conference, Munich, Germany, 2012.
[2] DIN EN 60534 -2.1 "Industrial-process control valves – Part 2-1: Flow capacity – Sizing equations for fluid flow under installed conditions" (German version), Beuth Verlag, Germany, 2011.
[3] Walter Wagner: "Regelarmaturen", ISBN 3-8023-15664-2, Vogel Buchverlag, Germany, 1996.

10. Authorship and Copyright Statement for original (initial) Contribution

Author:
DYNCAP/DYNSTART development team, Copyright 2011 - 2022.
Remarks:
This component was developed during DYNCAP/DYNSTART projects.
Acknowledgements:
ClaRa originated from the collaborative research projects DYNCAP and DYNSTART. Both research projects were supported by the German Federal Ministry for Economic Affairs and Energy (FKZ 03ET2009 and FKZ 03ET7060).
CLA:
The author(s) have agreed to ClaRa CLA, version 1.0. See https://claralib.com/pdf/CLA.pdf
By agreeing to ClaRa CLA, version 1.0 the author has granted the ClaRa development team a permanent right to use and modify his initial contribution as well as to publish it or its modified versions under the 3-clause BSD License.

11. Version History


Backlinks: ClaRa:A User Guide:Revisions:v1.7.0 ClaRa:Components:VolumesValvesFittings:Fittings:SprayInjectorVLE L3