Predicting heat fluxes received by horizontal targets from two buoyant turbulent diffusion flames of propane burning in still air

Abstract

An analytical method to estimate the heat fluxes received by horizontal targets from two buoyant turbulent diffusion flames was proposed. Two identical square gas burners with side length of 15 cm were used as the fire sources with propane burning in still air. The heat release rate (HRR) and burner edge spacing were changed in experiments. Heat fluxes received by four external horizontal targets were measured. In cases with one burner or two burners with zero spacing, there is one single flame and the vertical centerline temperature distribution were divided into four zones including core zone, constant zone, intermittent flame zone and plume zone. Based on the established piecewise function for predicting the flame temperature, the cuboid flame model with hierarchical temperatures was proposed to determine the flame emissivity, the mean flame temperature of the model and the corresponding blackbody emissive power. The results showed that when the HRR of single flame ranges from 10.8 kW to 64.8 kW, the flame emissivity of 15 cm square burner ranges from 0.125 to 0.387, and the absorption coefficient ranges from 0.99 m−1 to 3.62 m−1. At a given HRR, the flame emissivities of two burners with zero spacing and infinite spacing are nearly identical, suggesting that the influence of spacing on flame emissivity is marginal. For two burners with spacing higher than zero, by assuming that the flame radiative fraction of propane is 0.3 and the flame emissivity is equal to that of the single flame, the flame radiative heat fluxes received by external targets are calculated by modeling the flame shapes as two right or tilted cuboids. The comparison validates that the calculations using the proposed cuboid models for both one and two flames agree well with the experimental results.