Second law analysis of wildfire evolution under wind and slope effect

his paper aims at investigating possible relations between the fire main driving forces of forest fires, particularly wind speed and ground slope, and the corresponding entropy generated. Second law analysis is applied to an uncontrolled fire event in a g rassy area (grassfire). The system is first studied through a full physical numerical model, with the aim of collecting local data in the same way that would be achieve through pervasive sensors. Simulations are conducted considering separate contributions of different wind speeds and terrain slopes. Three terms that contribute to the entropy generation are separately calculated and analyzed in the parametric simulations: mass transfer term, heat transfer term (heat losses) and transient term. The first ter m is globally large, especially when large wind velocities and terrain slopes are considered. This contribution is highly variable during the fire evolution, with oscillations of about ± 120% with respect to the mean value. The second term is also large an d becomes dominant in the case of lower driving forces. Its behavior is more regular, with oscillations of the order of ± 40% with respect to the mean value. The third term, instead, gives an almost negligible contribution. Results also show that the total entropy generated during the fire propagation increases with increasing slope or wind speed, which also means with increasing fire propagation velocity. In the range of data considered in this analysis, entropy generated is well approximated by a logarithmic evolution as the function of propagation velocity, with a mean error of about 5%