Temperature evolution and external flame height through the opening of fire compartment: Scale effect on heat/mass transfer and revisited models

This paper investigates the temperature evolution inside a compartment (i.e., room) as well as the external flame height ejected through the opening (i.e., window) of fire compartment, which is associated with complex thermal heat/mass transfer and fluid dynamics. The scale effect on this problem is revealed and quantified employing the multi-scale compartments (inner scale ranged from 0.34 to 0.76 m). The fire heat release rate (Global Equivalence Ratio, GRE), opening sizes and compartment scales were varied with 468 experimental conditions. Models for predicting the upper-part temperature evolution with heat release rate (Global Equivalence Ratio, GRE), opening dimensions and compartment scales are established base on the heat balance analysis and the derived non-dimensional quantities. The external flame height shows a considerable difference for various compartment scales, due to the change of temperature inside the compartment hence buoyancy flux of the out-flow through the opening. A general model characterizing the external flame height of various compartment scales is proposed with the newly defined dimensionless excess heat release rate accounting for opening geometry length scale and the upper-part temperature inside the compartment, which shows a good agreement with the experimental results. This study provides important and new contributions over previous knowledge and has potential practical applications generally concerning the scale effect and for the validation of numerical models.