Abstract
The aim of the presented work was to study the dust lifting process from a layer of dust behind a propagating shock wave. The experiments were conducted with the use of a shock tube and a specially constructed, five-channel laser optical device enabling measurements at five positions located in one vertical plane along the height of the tube. The system enabled measurements of the delay in lifting up of the dust from the layer, and the vertical velocity of the dust cloud was calculated from the dust concentration measurements. The research was carried out for various initial conditions and for three fractions of black coal dust. In the presented tests, three shock wave velocities: 450, 490 and 518 m/s and three dust layer thicknesses, equal to 1.0, 1.5 and 2.0 mm, were taken into consideration. On the grounds of the obtained experimental results, it was assumed that the vertical component of the lifted dust velocity is a function of the dust particle diameter, the velocity of the air flow in the channel, the layer thickness and the dust bulk density. It appeared, however, that lifting up of the dust from the thick layers, thicker than 1 mm, is a more complex process than that from thin layers and still requires further research. A possible explanation is that the shock wave action upon the thick layer results in its aggregation in the first stage of the dispersing process, which suppresses the dust lifting process.
Highlights
The experimental research presented in this paper was aimed at investigation of the process of dust lifting from a layer by the flow behind a propagating shock wave
The results obtained with use of the system were compared with those obtained from the analysis of the framing pictures of the process recorded with use of the high-speed digital camera working with the schlieren system and with streak pictures of the dust lifting process
– The beginning of dust lifting from the layer is always observed just behind the propagating shock wave
Summary
The experimental research presented in this paper was aimed at investigation of the process of dust lifting from a layer by the flow behind a propagating shock wave. In various industrial facilities and factory buildings, dust layers cover floors, walls, ceilings and various installations. The deposited dust can be quite lifted up and dispersed by pressure waves generated by weak explosions, or as a result of damage of compressed gas systems. If the dusts are combustible, an explosive dust–air mixture can be generated, and if it is accidentally ignited, a devastating explosion may occur. Dust mixture explosions constitute one of the major hazards in coal mines that have a high risk of methane explosion, or in other industrial facilities where combustible dusts are present. The first experimental investigations into the dust lifting process were performed by Gerrard [1]. The process of dust lifting was studied experimentally and theoretically by Boiko [2], Fedorow [3,4], Klemens and Zydak [5,6,7,8]
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