Abstract
Aim: To examine the characteristics and the accuracy of the models of thermal radiation in terms of available experimental data. Comparison of different methodologies for calculating thermal radiation.
Project and methods: Estimating the size of the external heat flux from a fire in a building to another building or another part of the same building is an important part of fire protection engineering. At the same time it is not a trivial issue, because it involves complex processes associated with a fully developed fire with dynamics controlled by air access and the presence of external flames. Calculation the range of critical heat flux leads to the establishment of the minimum required distance between buildings. Although there are many advanced numerical methods like CFD which can be used for calculating heat flux of radiation, but for practical purposes only the simplest methods for estimating the heat flux of radiation are routinely applied by fire protection engineers. Some recent experimental studies indicate that these methods may not be accurate, because they do not include radiation from external flames. Radiation from external flames is included in some of the existing computational methodologies like Eurocode or American standard NFPA 80A. The method included in Eurocode includes many input parameters like compartment geometry, characteristics of openings, fire load density and ventilation conditions, and its output parameters are the temperature of the compartment and the geometry and temperature of external flames. In this article, all the methods of calculation based on the configuration ratio, that is both the method of the radiating rectangle, and the methods including external flames, are tested using a copyright program called FireRad which allows the use of any spatial shapes as a set of radiating surfaces. The experimental data used in this paper are public literature data from Canadian and Czechoslovakian experimental programs.
Results: The results are presented as a comparison of the heat flux distributions obtained from experiments to the distributions obtained using various modeling approaches. Factors which determine the increasing convergence of experimental data and calculations were indicated.
Conclusions: The article summarized and discussed calculations using various methods; it also provided recommendations for prudent estimation of the size of the heat flux. FireRad proved to be a useful tool in calculating heat flux for complex geometries.
Keywords: thermal radiation, fire protection, external flame