The Pool model

The objective of the pool model used in KFX® is to have an evaporation model that is dependent on the heat fluxes generated by the fire. In addition a pool spread model is required such that a realistic pool development from a leak source is properly modelled.

The current KFX® version contains two pool models, one single component and one multi component version.

The evaporation model handles the following physical processes

  • Flashing:  Pool cells with temperature above boiling temperature will evaporate spontaneously where the evaporation energy is taken from the remaining liquid which is consequently cooled.
  • Boiling:  When the pool cells have reached boiling temperature, the evaporation is controlled by the net heat flux (convection, radiation and heat transfer from the solid surface) to the cells.
  • Heating and convective mass transfer:  If the temperature is below boiling temperature, net heat flux will heat the pool, while convective mass transfer occurs due to Lewis number =1 assumption.

 

The multi component evaporation model handles the same processes, but operates on components boiling temperature after reordering the components from lowest to highest boiling temperature.

The pool-spreading model is based on simple lubrication theory where the spread is determined by differences in pool that are used as the driving force for the spread process. When the pool reaches edges of the horizontal plane where it spreads, it will be transported down to the first cell with a solid horizontal surface, this is referred to as the “stair case” model. 

The multi component version handles this different and convirts the mass on the edge to droplets that is accumulated to pool cells on the first cell below the droplet onset with solid horizontal surface.

 

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