FAQs for KFX and EXSIM

What is the difference between Phast, KFX and EXSIM?

Answer
Answer Phast is based on empirical and phenomenological models, while KFX is an advanced CFD simulator for dispersion and fires, and EXSIM is an advanced CFD simulator for gas explosion modelling. CFD simulations are typically carried out when making detailed design related decisions. Recently, we have been integrating the capabilities of our standalone CFD tools (KFX and EXSIM) into Phast to extend its capabilities and allow treatment of complex scenarios where, for example, geometry has a significant influence on the release. This work is ongoing.

Answer

Phast is based on empirical and phenomenological models, while KFX is an advanced CFD simulator for dispersion and fires, and EXSIM is an advanced CFD simulator for gas explosion modelling. CFD simulations are typically carried out when making detailed design related decisions.

Recently, we have been integrating the capabilities of our standalone CFD tools (KFX and EXSIM) into Phast to extend its capabilities and allow treatment of complex scenarios where, for example, geometry has a significant influence on the release. This work is ongoing.

What type of grid is used in KFX/EXSIM?

Answer
Answer A cartesian grid is used in KFX/EXSIM. The grid density can be modified within the calculation domain.

How many combustible fuels are included in EXSIM? If the desired gas combustible fuel is not currently built-in to EXSIM, is it possible to define the material properties of the desired combustible fuel?

Answer
Answer EXSIM can current handle the following fuels: - Methane - Ethylene - Propane - Cyclohexane - Hydrogen - Acetylene There is also a 'pseudo fuel' option that allows a molecular weight to be specified (which is helpful for modelling natural gas mixtures, for example). Moving forward, we are intending to expand the range of available fuels. It is not currently possible for users to define their own fuels, but we are happy to explore adding such a feature if it is desirable.

Answer

EXSIM can current handle the following fuels:

- Methane

- Ethylene

- Propane

- Cyclohexane

- Hydrogen

- Acetylene

There is also a 'pseudo fuel' option that allows a molecular weight to be specified (which is helpful for modelling natural gas mixtures, for example). Moving forward, we are intending to expand the range of available fuels. It is not currently possible for users to define their own fuels, but we are happy to explore adding such a feature if it is desirable.

Can a geometry model developed in SESAM be used in KFX and EXSIM for CFD analysis?

Answer
Answer The SESAM Genie model can be converted to a KFX or an EXSIM geometry model. For many analyses, a more detailed CAD model is used for the KFX simulations. The reason for this is that it is favourable to include the process equipment and secondary structures in the KFX simulation model to include the effect of these objects on the fire location and fire development.

Does KFX consider effects of passive fire protection?

Answer
Answer KFX calculates the heat loads from the fire on the nearby structures. The effect of passive fire protection can be considered when performing the structural response analysis with USFOS.

What geometry file formats can be imported into KFX/EXSIM? Do geometries need to be built in KFX/EXSIM, or can they be done using design applications?

Answer
Answer Currently, the package can directly import geometries from CAD files in the following formats: - DGN 7 - Wavefront OBJ - STL - USFOS FEM files - PDMS (RVM format) - SOSI format (for landscapes and buildings in Norway) - DEM (digital elevation format) for landscape - A subset of the IGES format - A subset of the DXF format We have also successfully performed indirect conversions using free software for IFC and DWG formats. Where possible, we recommend using the RVM format for best results.

Answer

Currently, the package can directly import geometries from CAD files in the following formats:

- DGN 7

- Wavefront OBJ

- STL

- USFOS FEM files

- PDMS (RVM format)

- SOSI format (for landscapes and buildings in Norway)

- DEM (digital elevation format) for landscape

- A subset of the IGES format

- A subset of the DXF format

We have also successfully performed indirect conversions using free software for IFC and DWG formats. Where possible, we recommend using the RVM format for best results.

How long do KFX/EXSIM calculations take to run?

Answer
Answer The run times are a strong function of the number of nodes within your computational domain, with simulations taking from a matter of minutes to several hours depending on the specifics of the case being modelled (with scenarios requiring predictions in the far-field generally taking longest).

Are the dispersion models for hydrogen releases with the influence of wind validated?

Answer
Answer KFX's dispersion modelling capabilities are well-validated for a range of conditions.

Does EXSIM model buried pipelines?

Answer
Answer EXSIM is designed to model gas explosions. For pipeline releases, EXSIM could be used to model the explosion resulting from delayed ignition of a leak from a buried pipeline.

How are key parameters in explosion modelling such as reactivity of fuel and flame acceleration utilised in EXSIM?

Answer
Answer The characteristics of the material feed directly into the quasi-laminar and turbulent combustion modelling in EXSIM.