| Popis: |
The present work describes the fundamental extension of an integral pool spreading, vaporisation and dissolution model, part of the Process Hazard Assessment Tool (Phast) software. The base model accounts for spills on land and water surfaces. For pools spreading on water, the model includes three successive regimes, gravity-resistive, viscous-resistive and viscous-surface tension. For the case of pool spreading on land, it accounts for the hold-up of liquid within the surface’s rough elements. Pool vaporisation considers two limiting cases: evaporation and boiling. The heat transfer mechanisms accounted for include conduction from the ground, convection from water and air, conduction from ice and solar incidence. The extended multi-component model tracks the transient pool inventory at each step. While the pool is boiling the liquid and vapour phases are in equilibrium. For evaporation, the model accounts for the diffusion of multiple components into air. The dissolution of water-soluble chemicals present in the mixture, a novel feature amongst existing multi-component pool models, is introduced by the present work. The application of the model to mixtures highlighted the drawbacks of approximating such systems by a single component evaporating pool. The implementation of a numerical algorithm based on Backward Differentiation Formula (BDF) showed improved numerical stability when compared to a widely used pool model (LPOOL by HGSYSTEM (Post, 1994)). The improvements were most noticeable when the model behaved as a stiff problem. The validation of the multi-component pool model against published experimental data shows good agreement for pool spreading and boiling on land and water surfaces. The pool evaporation model is in good agreement with the experimental data for low to medium volatility chemicals. Suggestions for further work include an extension to non-ideal mixtures; incorporate the modelling of chemical reactions and a stratified pool model. |
