Phast™ and Safeti™ multi component add-on
Improved modelling of mixtures
The Phast and Safeti Multi Component (MC) add-on provides improved consequence and risk results for mixtures compared with the traditional “pseudo-component” (PC) approach.
In the “pseudo-component” approach the composition, thermodynamic behaviour and properties of a mixture are calculated using simple averaging equations, whereas in the multi component approach modelling of mixtures involves more rigorous enhancements to the physical property system.
The Multi Component add-on supports the core steady-state discharge models, dispersion modelling via the unified dispersion model (UDM), and the standalone multi component pool vapourisation modelling.
More accurate modelling of phase equilibrium
For a pure component, the bubble point and the dew point are the same temperature; there is no region in which the material is two-phase across a range of temperatures.
The pseudo-component approach treats mixtures as pure components and does not model the two-phase region. On the other hand, the multi component approach models the phase equilibrium in a more rigorous manner, and both phases will be modelled when the conditions are in the two-phase region.
The composition in the liquid and in the vapour phase differ when a mixture is under two-phase conditions and, as conditions change, the equilibrium and composition in each phase will change. This behaviour is modelled in the multi component approach.
Key capabilities of the Multi Component add-on
- Integrated multi component property system with built-in chemical database and flash calculator.
- Improved source term modelling of two-phase mixtures for models including catastrophic rupture, leak, line rupture, relief valve and disc rupture.
- Calculate vapourization rates of multiple components for a mixture vapourising from a pool (using the standalone multi component pool vapourisation model).
- Supports most frequently used equations of state including Redlich-Kwong, Soave-Redlich-Kwong and Peng-Robinson.
The results using the add-on include mixture composition as release expands from storage to atmospheric conditions, as well as graphs of phase composition during dispersion.
Frequently asked questions
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The pseudo-component (PC) approach is good for pure components, non-polar, low volatility range mixtures at low pressures, while the multi-component (MC) approach is good for pure components, wide volatility range mixtures, mixtures at all pressures, non-polar or slightly polar mixtures.
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For the single aerosol method, all the aerosol droplets are assumed to have the same composition and multi-component phase equilibrium calculations are used to model the behaviour of the aerosol. For the multiple aerosol method, a range of aerosols with different compositions are modelled, where each aerosol contains all components that have the same setting for the aerosol class number, and multi-component phase equilibrium calculations are used to model the behaviour of each aerosol.
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The choice between pseudo and multi-component model will be available within the Software if you have a valid multi-component licence. It is located in the edit dialog window after double-clicking the equipment level, in the Material tab, under the heading of “Modelling of mixtures”.
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