Abstract:

This talk is about recurring questions: What is the origin and mechanism of unconfined dust explosions that give rise to the observed high combustion rates and high overpressures? We show that clustering of dust particles in the temperature stratified turbulent flow ahead of the primary flame, which results in the formation of particle clusters with particle concentrations in clusters exceeding the mean concentration of evenly dispersed particles by a few orders of magnitude, gives rise a significant increase of the absorption length of radiation. This radiative transfer clearing effect ensures that clusters of dust particles even far ahead of the primary flame are exposed and heated by the radiation emanated from the primary flame enough to make them multiple ignition kernels capable to ignite the surrounding gas-air mixture. The multiple radiation-induced ignitions of many ignition kernels in a large area ahead of the primary flame increase the total flame area, resulting in a strong increase of the effective combustion speed, defined as the rate of reactant consumption of a given volume. The extent, to which the rate of combustion and overpressures can increase, depends on the particle size and parameters of the turbulent flow produced by the pressure waves pushed by the accelerating flame. For a strong radiative clearing effect the radiation-induced multi-point ignitions can produce a high rate of combustion and overpressures of the order required to account for the observed level of damages in unconfined dust explosions.

Brief Biography:

Michael (Mikhail) Liberman is a professor of theoretical physics at the Nordic Institute for Theoretical Physics (NORDITA) KTH and Stockholm University and emeritus professor of the Uppsala University, Sweden. His scientific interests span from plasma physics to quantum coherence, Bose-Einstein condensation of excitons, combustion theory and astrophysics. After having received his master degree from Moscow State University in 1966, he received his Ph.D. in 1970 at Lebedev's Institute of General Physics, Moscow: “Symmetry groups in quantum mechanics” and Doctor of Physical and Mathematical Sciences degree in 1981 at A. Budker Institute of Nuclear Physics: “Nonlinear phenomena and shock waves in plasma”. From 1971 Liberman was invited to the P. Kapitza Institute for Physical Problems, Moscow, where he worked at the Landau Theoretical Department till 2003. His many years association with Ya. B. Zeldovich was of particular importance. In 1993 Liberman became a professor of Theoretical Physics at Uppsala University, Sweden. He is currently a professor at NORDITA, Professor Emeritus at the Uppsala University and honorary professor of Moscow Institute of Physics and Technology, Russia. He was elected a fellow of American Physical Society: “For outstanding contributions ranging from laboratory plasma experiments to astrophysical phenomena, particularly in the areas of shock waves, Z-pinches, flame stability, and laser produced plasmas.” Liberman has authored/co-authored the books: Physics of Shock Waves in Gases and Plasmas, Springer-Verlag, 1985 (with A. Velikovich), Physics of High-Density Z-pinch Plasmas, Springer-Verlag, 1998 (with J.DeGroot, A.Toor, R.Spielman), Introduction to Physics and Chemistry of Combustion, Springer-Verlag, 2008. He has authored/co-authored over 300 peer-reviewed papers. He has advised over 45 Ph.D. students in the fields of plasma physics, quantum theory, shock wave physics and combustion. He has been a principal investigator on many projects for the Swedish National Foundation Research Council, Swedish Energy Agency, Swedish Royal Academy of Sciences, and a scientific consultant of various national laboratories at the US and private industry.

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