Experimental Study On The Ignition Of Combustible Bulk Materials By A Hot Metal Particle

Welding process,firework display,industrial cutting,clashing of high-voltage lines and other human activities and industrial processes,often produce hot metal particles easily.The surrounding materials may be ignited and a fire initiates,which threatens the safety of industrial activities.The fire risk of hot particles is mainly reflected by the ability to ignite surrounding materials.Thus,it is necessary to study the ignition of combustible bulk materials by a hot metal particle.In this work,the SDT-Q600 simultaneous thermal analyzer was utilized firstly to study the pyrolysis characteristics of wood powder,carbon powder and hydroxypropyl methyl cellulose(HPMC),which provided reliable references for the ignition experimental analysis.Secondly,a series of experimental studies on the ignition of combustible bulk materials by a hot metal particle with different powers and diameters were conducted and the conclusions are as follows.(1)Generally,for a certain material,the critical ignition powers of three materials increase with the increasing of the particle diameter.Among these three materials,the critical ignition powers of wood powder and carbon powder changes more significantly than that of HPMC.Among different materials,the ignition behavior is affected by the material properties,especially the structure of char-layer.With a unconsolidated char-layer,the unreacted material will fill the depletion region surrounding the hot particle and thus the hot particle keeps a good contact with unreacted material and heat transfer process undergoes smoothly.While a consolidated char-layer will hinder the unreacted material from supplementing the depletion region,a void will be formed after the material near hot particle burns out and the conduction heat transfer from the hot particle will turn to radiative heat transfer.(2)Compared with the numerical results of critical ignition powers of Brinley et al.,the variation trend of experimental results coincides well with numerical results.However,the result of two critical ignition powers predicted by the numerical results is not found in the experiments.Finally,a simplified numerical simulation was conducted to analyze the effect of hot particle diameter,heating power and the activation energy of materials on the ignition behavior qualitatively.