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

The influence of vertical channel with various structure factors (α) 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 α 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 c ‾ (average value) and T v ‾ drop as α rises, and T v ‾ > T c ‾ 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 α increases. For α < 1.0, the oxygen supply determines the changing trend of V f , while the total heat transfer is dominant for 1.0< α < 2.0. Predicted results using the model built in this work indicate that Q increases as α rises, which corresponds to experimental results. • Flame height first drops and then increases as structure factor (α) rises. • Channel temperature and curtain wall surface temperature drop as α rises. • A model is built to predict heat fluxes transferred to preheating zone. • Downward flame spread rate first rises and then drops as α rises. • A model is built to predict induced air flow, which increases as α rises. [ABSTRACT FROM AUTHOR]