An investigation of the detailed flame shape and flame length under the ceiling of a channel

This paper presents an experimental investigation on the flame shape and length under the ceiling of a channel, and altogether 48 experiments with four experimental setups were performed. The experimental setups include fires in the open space, flush with a wall without ceiling, at the longitudinal centerline of a channel and flush with the sidewall of a channel. Results showed that the flame extending under the ceiling presented a circular shape when the fire is located at the longitudinal centerline of channel, whereas for fire placed flush with sidewall, it is a half ellipse. As heat release rate (HRR) increases, the long axes of the ellipse changes from perpendicular to the sidewall plane to parallel to it, resulting from the competition between air entrainment enhancement of generated vortices and air entrainment restriction of the corner structure above fire source. Additionally, the total flame extension as a lump of the vertical flame height and horizontal flame length is quantified using dimensional analysis. The total flame extensions for fire at the longitudinal centerline are proportional to 2/5 power of dimensionless heat release rate Q̇H∗, while for fire flush with sidewall, the total flame extensions in longitudinal and transverse directions are proportional to 1/2 and 2/5 power of Q̇H∗, respectively. The critical (transient) dimensionless heat release rate can be calculated as 0.60, under which the longitudinal and transverse flame lengths are identical.