A Prediction Formula for Critical Heat Release Rate of Flashover based on Experimental Correlations

Abstract

A prediction formula for critical heat release rate for flashover was derived and improved based on theoretical approach and experimental correlations. Based on heat balance of upper smoke layer, the minimum heat release rate for flashover was formulated as functions of opening factor and internal surface area multiplied with thermal inertia of enclosure materials. The coefficients were derived by correlations with numerical calculations of smoke layer temperature in two-layer environment. The formula was compared with datasets of flashover experiments published in literatures. By comparison, it was found that the derived formula agrees well with prototype experiments, but overestimates the values for scale model experiments. As the time to flashover affects the critical heat release rate for flashover, experimental correlation was developed and applied. The results agreed well with both prototype and scale model experiments. By adjusting the coefficients, a conservative design equation was developed to include 95%-tile of existing experimental data.