Influence of vertical channel on downward flame spread over extruded polystyrene foam

The influence of vertical channel with various structure factors (alpha) on downward flame spread over extruded polystyrene (XPS) foam is investigated. The flame shape, flame height (H-f), temperature in the channel (T-v) and on the curtain wall surface (T-c), flame spread rate (V-f), and induced air flow (Q) are obtained. H-f first drops and then increases as alpha rises, attributing to similar changing trends of induced airflow rate and Froude number. Concerning the temperature history, T-c > T-v at the initial stage while T-c < T-v at the middle stage. Both <(T)over bar>(c)(average value) and (T) over bar (v) drop as a rises, and (T) over bar (c) > (T) over bar (v) under most conditions. A model is established to predict the total, convective and radiative heat fluxes transferred to preheating zone. The convective heat flux is more dominant than the radiative heat feedback from the curtain wall. V-f first rises and then drops as a increases. For alpha < 1.0, the oxygen supply determines the changing trend of V-f, while the total heat transfer is dominant for 1.0 < alpha < 2.0. Predicted results using the model built in this work indicate that Q increases as alpha rises, which corresponds to experimental results.