Fire Safety Science Digital Archive

Detailed experiments of smoke layer development in Atria revealed the need for refining the relationships for 1) air entrainment rates into low Froude number ( large diameter) pool fires, and 2) the convective heat transfer coefficient to the walls. Experiments were conducted in a square cross section enclosure 2 m x 2 m x 5 m high having adjustable size openings near the bottom ( for the fires air supply) and at the ceiling ( for smoke exhaust) (see Fig. 1). Steady state conditions were established prior to the measurements for methane pool fires produced by a 30 cm diameter sand box burner at two heat release rates, 10 kW and 20 kW, and various combinations of inlet and outlet vent sizes. Temperature measurements by a vertical thermocouple rack were used to determine the height of the smoke layer. Exhaust flow rates were precisely measured by using the tracer gas method, which in the present experiments included two gases: C02 and O2 (simultaneous CO measurements showed no detectable carbon monoxide levels, i.e., the combustion was complete). The pressure difference distribution and then neutral plane were determined by differential pressure transducers along the enclosure height. The redundancy and accuracy of the measurements in this project were essential for the development and estab1ishment of a new entrainment relationship for the buoyant plume of low Froude number (large diameter) pool fires the normalized entrainment rate varies proportionally to Z/D as it was proposed in a previous publication. Moreover, the convective heat transfer coefficient can be determined by using a constant Stanton number, while currently used correlations in zone models failed to reproduce the experimental results