Development of a Fire Zone Model Considering Mixing Behavior

A new zone model is proposed to compute smoke propagation and characterize smoke mixing behavior in complex enclosed spaces. A piecewise linear scalar function considering the mixing between the hot smoke and the cold air is introduced to better resolve the temperature and smoke profiles in the vertical direction. The mixing properties are approximated and characterized as turbulent transport of momentum and energy. The governing equations considering: mixing effects are derived in terms of the scalar function. Two test cases are used to evaluate the model. First, the model predictions are compared with those from the two-layer model implemented using CFAST (Consolidated Model of Fire and Smoke Transport, developed by the National Institute of Standards and Technology) and experimental data reported in the literature for a simple setting involving an interconnected set of enclosed spaces. Second, the model prediction results are compared to that from a computational fluid dynamics model, namely, FLUENT, for a two-story office building. It is shown that the newly proposed model provides more accurate predictions of temperature distributions compared to that predicted by the two-layer model and is significantly less computationally expensive when compared to a computational fluid dynamics approach. Finally, the model presented provides a new framework for zone modeling using scalar functions, in which the traditional network model and the two-layer model can be reconstructed from different distribution functions.