Effects of the Particle Size and Agglomeration on the Minimum Explosible Concentration and Flame Propagation Velocity in
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Effects of the Particle Size and Agglomeration on the Minimum Explosible Concentration and Flame Propagation Velocity in Dust Clouds K. Ichinosea , T. Mogia , and R. Dobashia
UDC 536.46
Published in Fizika Goreniya i Vzryva, Vol. 56, No. 4, pp. 56–62, July–August, 2020. Original article submitted January 9, 2020; revision submitted February 19, 2020; accepted for publication February 19, 2020.
Abstract: The flame propagation behavior and the effect of particle agglomeration are examined by changing the size of PMMA particles in laboratory-scale experiments. PMMA particles having a very narrow size distribution are used. We show that the minimum explosible concentration increases as the particle size decreases. On the other hand, the flame propagation velocity also increases as the particle size decreases. Therefore, the minimum explosible concentration and the flame propagation velocity show the opposite dependences on the particle size. It is considered that the minimum explosible concentration is strongly affected by the interparticle distance; meanwhile, the flame propagation velocity strongly depends on the specific surface area. It has to be emphasized that the severity of the explosion can be serious for very fine particles, although the minimum explosible concentration is fairly high. Keywords: dust explosion, particle size, agglomeration, flame propagation. DOI: 10.1134/S001050822004005X
INTRODUCTION A dust explosion occurs when sufficient ignition energy (e.g., static electricity) is introduced to a flammable particle cloud dispersed in air. During flame propagation, the pressure rises significantly, and serious damages to both humans and infrastructure can be caused. A dust explosion is a complex phenomenon of flame propagation in a heterogeneous medium, where particles undergo heating, vaporization, pyrolysis, mixing of volatiles with the oxidizer, ignition, burning, and flame extinction. As the particle size becomes smaller, the potential risk of the dust explosion is expected to increase because an increase in the specific surface area increases the reactivity of the particle cloud [1]. As a result, the ignitability becomes higher, the pressure ina
The University of Tokyo, Bunkyo-ku, Tokyo, Japan; k [email protected]
creases more rapidly, and, therefore, the risk of the dust explosion also increases [2]. However, as the particle size decreases to a few tens of micrometers, agglomeration occurs more easily and the dispersion condition changes [3]. To appropriately evaluate the risk of the explosion of fine dust particles, it is necessary to study the relationship between the flame propagation behavior and the particle characteristics, such as the particle size and agglomeration. In the previous study [4], flame propagation through the dust cloud of 1-octadecanol particles was mainly supported by combustion of small particles. It was suggested that the explosion hazard was determined by the surface median diameter [5]. It was proved that the dust particle size had the greatest influence on flame propagation
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