Effects of opening aspect ratio on facade gas temperatures with and without sidewalls for underventilated conditions

Abstract

This study focuses on the gas temperature distributions in the emitted flames and the hot flow on façade walls above openings without and with sidewalls at the edges of the opening. A wide range of aspect ratios of the openings was used for the first time having width over height W/H = 0.5 to 10. These situations are important when considering fire spread on facades for high-rise buildings especially combined with measurements and correlations of heat fluxes performed in previous publications of the senior author. We have performed experiments using a small compartment with the aim of developing a predictive model for maximum gas temperatures in the vicinity of the walls above the openings. Specifically, experiments were performed using gaseous burners of varying heat release rates in the compartment having openings without and with sidewalls on the side edges, of sufficient depth to prevent entrainment from the lateral sides of the opening. The heat release rate for each opening was chosen to be equal to 1800 AH1/2 (kW) where A (m2) is the area and H (m) is the height of the opening, corresponding to actual wood crib burning at under ventilated conditions. The results are explained and well correlated based on a new theory and correlations for facade fire flows using two length scales characterize these flows. One length scale represents the lateral horizontal extent of the flow parallel to the wall and the other length scale represents the extension of the flow at the opening normal to the wall before the flow becomes vertical owing to buoyancy. For high aspect ratios (W/H≥3) no significant difference is observed between the temperature distributions in fires without or with sidewalls. By contrast, for relatively tall openings (W/H < 3) the temperature distributions are different because entrainment is not allowed from the sides when sidewalls are present.