HEXvle2vle L3 2ph CU ntu

Created Monday 10 June 2013

A cylindrical preheater model with non-ideal phase separation at the shell side and NTU-based heat transfer model. A commonly used geometry for low pressure preheaters, i.e. the U-type tube arrangement is assumed.

1. Purpose of Model



This model is well suited to model slow transients of commonly designed low pressure preheaters. If large-scale short-term transients occur, e.g. as can be found during start-up the model might give imprecise results since the basic assumptions of the NTU approach (applied for calculation of heat resistance) can be violated.

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 L3 because the system is modelled with the use of balance equations applied to three different zones of the component: liquid condensate at tube side, vapour and liquid volume at shell side.

2.2 Physical Effects Considered

2.3 Level of Insight


Heat Transfer


shell side

tube side:



Pressure Loss


shell side

tubes side

Phase Separation


shell side

Basics:ControlVolumes:Fundamentals:SpatialDistributionAspects:RealSeparated : non-ideal phase separation, state at ports depend on filling level and state of the distinct zones.

tube side:

Basics:ControlVolumes:Fundamentals:SpatialDistributionAspects:IdeallyStirred : ideally mixed phases


3. Limits of Validity

4. Interfaces


5. Nomenclature


6. Governing Equations


6.1 System Description and General model approach


This model is composed by instantiation of the following classes:


6.2 General Model Equations


Summary

A record summarising the most important variables is provided. Please be aware of the boolean showExpertSummary in the parameter dialog tab "Summary and Visualisation". Setting this parameter to true will give you more detailed information on the components behaviour. The summary consists of the outline:

and the summaries of the class instances named in section 6.1


7. Remarks for Usage


7.1 Naming

The naming of heat exchangers in this package follows some specific form that is defined as follows:

7.2 Heat Transfer Modelling

In most cases the heat transfer from one fluid to the other will be dominated by the heat transfer at one of fluid boundary layers. In that cases the heat transfer coefficient α at this side will be considerably smaller than on the other side. From a numerical point of view it is disadvantageous to have very high (close to infinite) heat transfer coefficients on either sides. If you want to take nearly ideal heat transfer at one of the sides into account please consider the corresponding replaceable model instead of defining arbitrary large heat transfer coefficients in the model.

7.3 Initialisation and Numerical Robustness

During first testing of NTU-based heat exchanger models it became apparent that the initialisation might be difficult. For the sake of numerical robustness of the model two PI controllers are internally used to adjust the area fraction of the different zones in the NTU wall. If you encounter problems during initialisation you might want to adjust the init conditions of these PI blocks by right clicking on the HEX and choose "show component".

8. Validation


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

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

- Defined parameter parallelTubes depending on flowOrientation, orientation and N_baffles (only affects result if Nusselt based heat transfer models were used)
- Calculation of A_front corrected for parametrisations with flowOrientation not equal to geometrical orientatio
- Temperatures at shell side for NTU-based heat transfer calculation are now calculated with inlet pressure instead of outlet pressure
- T.Hoppe, F.Gottelt, XRG Simulation
- added optional measurement conectors - Friedrich Gottelt, XRG Simulation GmbH
- bugfixed underlying NTU wall model - Annika Kuhlmann, Timm Hoppe, XRG Simulation GmbH


Backlinks: ClaRa:Components:HeatExchangers:HEXvle2vle L3 2ph CU simple ClaRa:Basics:ControlVolumes:FluidVolumes:VolumeVLE L2 ClaRa:Basics:ControlVolumes:FluidVolumes:VolumeVLE L3 TwoZonesNPort