A global non-dimensional factor characterizing side wall constraint effect on facade flame entrainment and flame height from opening of compartment fires

Abstract

This paper investigates experimentally the side wall constraint effect on facade flame behavior ejected from the opening of an under-ventilated compartment fire. Experiments are carried out in a reduced-scale experimental model of 1:8, consisting of a cubic fire compartment (including one opening) with a vertical facade wall and two side walls. The facade flame heights for different opening geometries (width, height) are recorded by a CCD camera under various side wall separation distances. It is found that as the distance of the two side walls decreases, the change of the flame height can be categorized into two regimes, due to correspondingly the two different facade flame entrainment behaviors distinguished by the dimensionless excess heat release rate Q̇ex∗, outside the opening: (a) for the “wall fire” (Q̇ex∗⩽1.3), the flame height is shown to change little with decrease of side wall distance as the dominant entrainment is from the front direction (normal to the facade wall) irrelevant to the side wall distances; (b) for the “axis-symmetrical fire” (Q̇ex∗>1.3), flame height increases prominently with decrease in side wall distance as both the entrainment from two side directions (parallel to the facade wall) and that from the front direction (normal to the facade wall) together dominate. A global non-dimensional factor K is then brought forward based on physically the side wall constraint effect on the facade flame entrainment, to characterize the side wall effect on the flame height, by including the dimensionless excess heat release rate, the characteristic length scales of the opening as well as the side wall separation distance. The experimental data are shown to be well correlated by the proposed global factor.