Similarity of energy balance in mechanically ventilated compartment fires: An insight into the conditions for reduced-scale fire experiments

Abstract

When evaluating energy balance and temperature in reduced-scale fire experiments, which are conducted as an alternative to full-scale fire experiments, it is important to consider the similarity in the scale among these experiments. In this paper, a method considering the similarity of energy balance is proposed for setting the conditions for reduced-scale experiments of mechanically ventilated compartment fires. A small-scale fire experiment consisting of various cases with different compartment geometries (aspect ratios between 0.2 and 4.7) and heights of vents and fire sources was conducted under mechanical ventilation, and the energy balance in the quasi-steady state was evaluated. The results indicate the following: (1) although the compartment geometry varies the energy balance in a mechanically ventilated compartment, the variation in the energy balance can be evaluated irrespective of the compartment size and geometry by considering scaling factor F (∝heffAwRT, where heff is the effective heat transfer coefficient, Aw is the total wall area, and RT is the ratio of the spatial mean gas temperature to the exhaust temperature); (2) the value of RT, which is a part of F, reflects the effects of the compartment geometry and corresponds to the distributions of the gas temperature and wall heat loss.