FlatTubeFinnedHEXvle2gas L4

Created Saturday 15 January 2022

A flat tube finned HX model with Gas at fin side and VLE medium at the flat tube side. A block-geometry with flat tube loverd fins is assumed.

1. Purpose of Model

This model is well suited to model transients of commonly designed condensers/evaporators in vapour cycles.

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 L4 because the system is modelled with the use of balance equations applied to discretized vulumes on both VLE and Gas side of the HX.

2.2 Physical Effects Considered

2.3 Level of Insight


Heat Transfer


tube side

fin side

Pressure Loss


tubes side

fin side

Phase Separation


tube side:

Basics:ControlVolumes:Fundamentals:SpatialDistributionAspects:Homogeneous L4 : ideally mixed phases
Basics:ControlVolumes:Fundamentals:SpatialDistributionAspects:SimpleAnalyticalSlip L4 : slip model according to Zivi.

fin side

intrinsic ideally mixed gas flow.

Heat Exchanger Type


3. Limits of Validity

4. Interfaces


4.1 Physical Connectors

ClaRa.Basics:Interfaces:FluidPortIn In_a
ClaRa.Basics:Interfaces:FluidPortOut Out_a
ClaRa.Basics.Interfaces.GasPortIn In_b
ClaRa.Basics.Interfaces.GasPortOut Out_b

5. Nomenclature

- no model specific nomenclature -

6. Governing Equations


6.1 System Description and General model approach


The combined model consists of the following components:
Basics:ControlVolumes:FluidVolumes:VolumeVLE L4 : flat tube (flow_a) with FlatTube geo record.
Basics:ControlVolumes:GasVolumes:VolumeGas L4 : fin flow (flow_b) with FlatTubeFinned geo record.
Basics:ControlVolumes:SolidVolumes:ThinWall L4 : flat tube wall
Basics:ControlVolumes:SolidVolumes:ThinWall L4 : fin wall

Gas cell arrays are used to discretise the gas side and VLE cell arrays are used to discretise the VLE side of the HX in repective flow direction.

Summary

A summary record is available which bundles important component values.

7. Remarks for Usage

The model of HX allow different flow configuration.

7.1 Flat tube flow parallel to fin flow

Flat tube flow (flow_a) is parallel to fin flow (flow_b).

7.1.1 N_passes_a=N_passes_b

For equal number of N_passes for both flows, heat ports of each cell of the flow are connected to each other.

7.1.2 N_passes_b=1 and N_passes_a>=2

Here there were considered 3 different possible situations assumed.

7.1.2.1 N_cv_a/N_passes_a=N_cv_b

Number of flow_b cells are equal to number of flow_a cells per pass.

One of such a configuration can be seen below on picture where gas cell 1 belongs to all fluid cells 1, 6 and 7 (control volumes at the same layer, i.e. at the same position of a pass).
Below it is depicted how the heat ports of the fluid and gas cells are connected. One shall define at least 3 control volumes of flow_b (equal to number of flow_a cells per pass.).

7.1.2.2 N_cv_b/(N_cv_a/N_passes_a)>=2

Number of flow_b cells per number of flow_a cells per pass are equal or greater 2. Below is one example of such a configuration with N_cv_b=6 and N_cv_b/(N_cv_a/N_passes_a)=2. Note that N_cv_b/(N_cv_a/N_passes_a) must be a whole number.


7.1.2.3 (N_cv_a/N_passes_a)/N_cv_b>=2

Number of flow_a per pass devided by number of flow_b cells are equal or greater 2. Below is one example of such a configuration with N_cv_b=3 and (N_cv_a/N_passes_a)/N_cv_b=2. Note that (N_cv_a/N_passes_a)/N_cv_b must be a whole number.

7.2 Flat tube flow counter-current to fin flow

Flat tube flow (flow_a) is counter-current to fin flow (flow_b).

7.2.1 N_passes_a=N_passes_b

For equal number of N_passes for both flows, heat ports of each cell of the flow are connected to each other in reverse (last cell of flow_a is connected to first cell of flow_b, ...., first cell of flow_a s connected to last cell of flow_b).

7.2.2 N_passes_b=1 and N_passes_a>=2

7.2.2.1 N_cv_a/N_passes_a=N_cv_b

Assumed the same configuratioin as for the parallel flow, i.e. 7.1.2.1.

7.2.2.2 N_cv_b/(N_cv_a/N_passes_a)>=2

Assumed the same configuratioin as for the parallel flow, i.e. 7.1.2.2.

7.1.2.3 (N_cv_a/N_passes_a)/N_cv_b>=2

Assumed the same configuratioin as for the parallel flow, i.e. 7.1.2.3.

7.3 Flat tube flow cross flow to fin flow

Flat tube flow (flow_a) is cross flow to fin flow (flow_b).

7.3.1 N_passes_b=N_passes_a

For equal number of N_passes for both flows, heat ports of cells are connected according to below figure (demonstrated for N_passes_a=N_passes_b=1 and N_cv_a=N_cv_b=3). If more passes, the connections would follow this pattern. Similar it is for more N_cv and also for cases when N_cv_a is different from N_cv_b.

7.3.2 N_passes_b=1 and N_passes_a>=2

Here there were considered 3 different possible situations assumed.

7.3.2.1 N_passes_a=N_cv_b

Number of flow_b cells are equal to number of flow_a passes. Below is one example of such a configuration with N_cv_b=6 and N_passes_a=3.

7.3.2.2 N_cv_b/N_passes_a>=2

Number of flow_b cells per number of flow_a passes are equal or greater 2. Below is one example of such a configuration with N_cv_b=6 and N_passes_a=3. Note that N_cv_b/N_passes must be a whole number.


7.3.2.3 N_passes_a/N_cv_b>=2

Number of flow_a passes per number of flow_b cells are equal or greater 2. Below is one example of such a configuration with N_cv_b=3 and N_passes_a=6. Note that N_passes/N_cv_b must be a whole number.

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
[2] VDI Wärmeatlas, Verein Deutscher Ingenieure VDI-Gesellschaft Verfahrenstechnik und Chemieingenieurwesen (GVC), Springer Verlag, 10. Auflage, 2006
[3] Y.-J. CHANG and C.-C. WANG: "A generalized heat transfer correlation for louver fin geometry", In International Journal of Heat and Mass Transfer, volume 40, No. 3, pages 533-544, 1997

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

Author:
ClaRa development team, Copyright 2017 - 2022.
Remarks:
This component was developed for ClaRa library.
Acknowledgements:

CLA:

11. Version History

Date - Version - Description of changes - author/revisor
17.01.2022 - v0.1 - initial implementation of the model - Ales Vojacek, Johannes Brunnemann,XRG Simulation


Backlinks: ClaRa:A User Guide:Revisions:v1.8.0