Portarapillo, Maria (2021) TURBULENT FLAME PROPAGATION OF DUSTS AND DUST MIXTURES. [Tesi di dottorato]

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The present work aims at studying the explosive phenomena of dust and dust mixtures to get insights into the driving mechanisms and the explosion features affecting the flame propagation and then the course of explosion. This will be achieved by means of an extensive experimental and simulative study. The major activities that will be carried out during my PhD period are: 1. Modelling of the flame propagation of combustible dust/air and hybrids; 2. Understanding of all the issues of the standard equipment; 3. Investigation of flame propagation features and key parameters (physical, operating, chemical) controlling the flame velocity The activities are strictly related to each other. The formulation and application of a Mallard-Le Chatelier-inspired theoretical flame propagation unveils that the flame laminar burning velocity depends on several parameters that take into account the thermal behavior of the dust subjected to heating starting from the flame front to the colder layers. As a consequence, a thermal analysis of any combustible dust seems to be of crucial importance in order to fully understand the explosive behavior both in terms of intrinsic (laminar) burning velocity but also in terms of flammability/explosibility parameters. Moreover, the analysis of the thermal behavior of combustible dusts can be useful to explain a series of synergistic effects that arise in dust mixtures that can sometimes be more dangerous than pure dusts, as found by Sanchirico et al. (2018). Moreover, starting from a deep study of the fundamentals of the flame propagation of dusts and dust mixtures, the main issues related to standard test vessels will be investigated and evaluated. In particular, CFD simulations of the 20 L vessel with dust mixtures and 1 m3 sphere for the measurements of Pmax/(dP/dt)max/KSt will be developed to understand their ability dispersing a uniform dust cloud and generating a uniform turbulence field. In both the vessel, the effect of the pre-ignition turbulence level on the turbulent combustion regime and on the deflagration index was also investigated. Moreover, the overdriving phenomenon as well as the thermal effects due to the pyrotechnic ignitors explosion were assessed in both the vessel and relative to combustible dusts characterized by homogeneous or heterogeneous flame propagation. Finally, we tried to formulate a procedure to fully understand the flame propagation mechanism of the investigated dust, which standard test vessel is better to use to have conservative and reliable evaluations of explosion parameters and which issues have to be considered during testing.

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