Flame spread over convex and inclined flat surfaces

Abstract

Convex surface is a general configuration in various building structures. Most studies for flame spread only investigated the flat surface type, while the flame spread over convex surface has not been addressed yet. A comparative study of convex and inclined flat surfaces was therefore performed by designing different curvatures (reflected by central angle φ) and flat-slope inclination angles (denoted by θ). The thermally thin PMMA sheet with a fixed horizontal projection length of 500 mm was chosen. The average path flame spread rate presents an exponential growth with increasing φ and θ. Moreover, the average horizontal flame spread rates of convex and inclined flat surfaces are close. For convex surface, radiant heat flux received by the sample rear increases with increasing φ. Also, two peaks of radiant heat flux occur at φ ≥ 45°. However, convective heat flux increases suddenly when θ ≥ 22.5°, in which convective heat transfer was the main mechanism. In addition, with increasing φ and θ, overall burnout rate increases for convex surface, but has an increasing first and then decreasing tendency for flat surface. The convection contribution on the pyrolysis zone is more obvious for inclined flat surface, in comparison to convex surface.