While the main R&D focus for GexCon software development in the 1980s and 1990s was on explosion modeling, a significant effort has been devoted to dispersion modeling over the past decade. Initial efforts focussed on the generation of flammable gas clouds so that they could be integrated into explosion risk studies. More recent activities involve looking into atmospheric dispersion from gaseous jets, flashing liquids or pool evaporation.

From 1998-2001 GexCon performed numerous experiments to study combined gas dispersion and explosion. Some of these tests where part of the Phase 3B JIP in which Advantica performed similar full-scale tests. The purpose was to enhance our knowledge base on explosions in non-homogeneous gas clouds. Most of the experiments resulted in much lower overpressures (1-10%) than a worst-case stoichiometric cloud would produce, still a few of the experiments resulted in explosions of comparable strength to worst-case clouds. Shown below are two videos of these experiments.  The video on the left is an explosion of a worst-case premixed cloud and to the right an explosion of a non-homogeneous cloud from a gas release. A conclusion from this activity is that risk studies should include the dispersion process to reduce unnecessary conservatism.   

 

 


With increasing validation of the dispersion models for flammable gases, a validation study was performed to evaluate the model's capability in the area of atmospheric dispersion. Good results were seen simulating more than 100 large scale experiments from the USA (Kit Fox, Prairie Grass and MUST test series). More information about this effort can be found in: S.R. Hanna, O. R. Hansen, and S. Dharmavaram, 2004: FLACS air quality CFD model performance evaluation with Kit Fox, MUST, Prairie Grass, and EMU observations, Atm. Env., 38, 4675-4687.

From 2000-2004 GexCon performed significant research in the release and explosion of aerosols, as seen in JIPs LICOREFLA, SEBK and the EU-project FLIE. Knowledge gained in these projects has later been utilized in work for DTRA and DHS on flashing releases (particular focus on chlorine), and improved models for flashing liquid are under development.

GexCon has also been contributing to the NYC dispersion tests project simulating tracer gas releases at Manhattan. The motivation of these studies are connected to Homeland Security, and the models ability to reproduce dispersion of potential toxic vapors in a city. In connection to this project a frozen hydrodynamics concept was introduced in FLACS so that tracer gas can be dispersed in a developed wind-field faster than real-time. See our Homeland Security services section for more about this work. You may also read about this effort in the following article.

Hanna, S.R., Brown, M.J., Camelli, F.E., Chan, S., Coirier, W.J., Hansen, O.R., Huber, A.H., Kim, S., Reynolds, R.M., 2006. Detailed simulations of atmospheric flow and dispersion in urban downtown areas by Computational Fluid Dynamics (CFD) models – an application of five CFD models to Manhattan. Bull. Am. Meteorol. Soc. 87, 1713–1726.

Recent dispersion development work has been focussed on developing a flexible pool model for LNG-releases and other liquid spills.

 

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