Three-dimensional computational fluid dynamics modelling of sodium oxide aerosol atmospheric dispersion from indoor sodium fire

In order to estimate the atmospheric impact of the release of sodium oxide aerosols from an indoor sodium fire, two chemical models describing the evolution of sodium oxide aerosols have been implemented in the atmospheric version of the computational fluid dynamic model Code_Saturne. The first chemical model is a shrinking core model. It describes the hydration and transformation of sodium oxide particles to carbonate by assuming that particles are made of layers of different compositions (sodium oxide, sodium hydroxide and carbonate). In the second model, a reactive absorption model describes more accurately the carbonate formation from sodium hydroxide. Both model implementations favorably compare to the published results produced by the model authors, as well as to experimental data resulting from experiments in laboratory. They differ in the speed of carbonate formation, and notably in the atmospheric humidity dependence of this formation. The second model may be more adapted to relative humidity larger than 50% where the core of particles is liquid. The atmospheric dispersion of sodium aerosols is modelled with Code_Saturne by assuming a release particle size distribution and by taking into account the sedimentation and deposition processes. The differences between the shrinking core model and the reactive absorption model largely influence the composition of sodium particles during their dispersion in the atmosphere. Further comparisons to experimental measurements of sodium oxide in the real atmosphere are required to evaluate the accuracy of these models at determining atmospheric sodium carbonate concentrations occurring from the transformation of sodium oxides.