Abstract
Radiant power from a flame plays an important role for fire safety. Over the last decades, numerous investigations of fires on thermal radiation have been developed by various thermal radiation models, numerical simulations and measurements. However, most of thermal radiation models are not suitable for small to medium sized fires, where the effective diameter of a fire is less than 1 meter. This work investigates the radiation characteristics in simulations and experiments from the heptane liquid pool fires. These small to medium sized pool fires (14-38 cm) were originated for comparison. The computational fluid dynamics (CFD) approach was used to predict the radiative heat flux for various pool diameters, grid sizes, spectral bands and solid angles. The results show that calculated flame shapes and heights are in good agreement with the measurements, as D*/δx is over 13. In the aspect of thermal radiation, the calculated radiative fluxes located within the height of the continuous flame zone are in good agreement with the measurements, whereas the predictions beyond that level deviate markedly from the experimental results, because the simulated amount of the soot created at the side of flame surface exceeds the experimentally observed volume. Experimentally, the effect of the intermittency of a flame on thermal radiation was performed. A shield was used to shade the radiant power from a persistent flame, and the radiative flux was measured from an intermittent flame on 30 cm diameter pool fires. The results show that 36 % of the radiative flux measured is emitted from the intermittent flame when the radiometer is located at the base of the pool fire. As the radiometer is moved upwards, the radiative fluxes measured from the intermittent flame increase gradually, even to 50%. Based on the results, the thermal radiation model with oscillation frequency was developed in this work. Measurements made with small to medium-sized pool fires (14-38 cm) were compared with estimates using the model. The results indicate that the predicted radiative fluxes closely correspond to the measurements made at various locations and that the variation of radiative fraction is within 14% as the location of the radiative flux gauge is varied.