Fire Induced Flow Under A Sloped Ceiling

Abstract

A series of fire tests was conducted under a smooth ceiling to investigate the ceiling gas flow as affected by ceiling slope, convective heat release rate of the fire and clearance between the fuel top surface and the ceiling. Besides a horizontal ceiling reference, three ceiling slopes were investigated: lo0, 20' and 30'. Pool fires were used as f i r e sources. Two pool diameters, two different fuels (heptane and methanol) and three ceiling clearances were used. In each test, measurements were made of ceiling gas temperatures, ceiling gas velocities, and fuel mass loss. Empirical correlations for the near-maximum gas velocity and excess temperature of the ceiling flow along the steepest run were established in terms of ceiling slope, radius from the point of intersection of the ceiling with the pool centerline, and characteristics of the undeflected plume at the ceiling level. The ceiling slope had a more pronounced effect on velocity variation along the steepest run than on temperature variation. In the upward direction, the rate of velocity decrease with radius was reduced significantly as the ceiling slope increased. In the downward direction, at a certain distance from the pool centerline, the flow separated from the ceiling and turned upward. The larger the ceiling slope, the sooner the turning occurred. Furthermore, the rate a t which gas temperature approached ambient i n the downward direction increased with ceiling slope, while the temperature decrease in the upward direction was not much affected by change of ceiling slope.