Visualization of aluminum dust flame propagation in a square-section tube: comparison of schlieren, shadowgraphy and dir
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R E G UL A R P A P E R
Clement Chanut
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Frederic Heymes • Pierre Lauret • Zacaria Essaidi • Pierre Slangen
Visualization of aluminum dust flame propagation in a square-section tube: comparison of schlieren, shadowgraphy and direct visualization techniques Received: 25 March 2019 / Revised: 8 April 2020 / Accepted: 7 May 2020 The Visualization Society of Japan 2020
Abstract This paper presents the results of aluminum dust flame propagation inside a vertical prototype of 700 mm height and 150 9 150 mm square cross section. The study considers three visualization techniques. At first, direct visualization is employed to record the flame light with high speed camera. Special attention is given to collect images without saturation. This is especially important with aluminum flames as they are very luminous. To ensure that the exact delimitation of the flame is well defined, two additional optical techniques have been implemented: schlieren and shadowgraphy. For each explosion test, these three techniques were used simultaneously to compare the flame propagation and the burning velocity. The first one corresponds to the flame speed in the laboratory referential, determined from the obtained images, while the burning velocity corresponds to the consumption rate of the reactants by the flame front. The method used for the determination of burning velocity from the images obtained is exposed. A pulsating behavior of the light emitted by the flame is observed with the direct visualization technique. This behavior confused the determination of the flame front. This contour is easier to define with shadowgraphy images. Nevertheless, results of flame front propagation velocity are close for each technique. Burning velocity is then determined only from direct visualization and shadowgraphy images, to avoid uncertainties due to flame contour detection from schlieren images. Again, results of burning velocity are fairly close for both techniques. Keywords Flame propagation Dust explosion Shadowgraphy Schlieren High speed imaging Burning velocity
1 Introduction Dust explosion is a major hazard in industries dealing with powders and dusts. All flammable dusts, if fine enough, can cause an explosion when dispersed. Three main categories of combustible powders can be defined: natural organic compounds (corn, carbon, sugar…), synthetic organic compounds (plastics, pigments…) and metallic compounds (aluminum, magnesium…). As a consequence, a lot of industries can be threatened by this hazard, and have to predict the consequences of potential explosions such as thermal effects, overpressure and even projectiles. Models used for gas explosions are sometimes used to predict dust explosion consequences. Although these models seem adapted for organic dusts, they are not accurate enough for metallic ones (Khalili 2012). For this reason, experimental studies are necessary to understand the mechanisms of flame propagation for such explosions. The tricky point of dust explosions experimental investigation is to control the dust
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