An improved two-layer zone model applicable to both pre- and post-flashover fires

The present paper proposes a sub-model for two-layer zone models to describe heat and mass transfer across the interface between the upper and lower layers as a result of the temperature difference between the two layers. The sub-model is integrated into a two-layer zone fire growth and smoke movement model, which now can predict both pre- and post-flashover fires. The comparison of the numerical predictions of the improved model and experimental data shows that the improved model produces better temperature and heat release rate predictions for both pre- and post-flashover fires than the previous model. Compared with hybrid models consisting of a two-layer zone model and a single-layer zone model, the improved model has no transitional difficulties in switching from the pre- to the post-flashover state and it produces more reasonable temperature gradients for post-flashover fires.