Experimental investigation on explosion flame propagation of wood dust in a semi-closed tube

In order to explore flame propagation characteristics during wood dust explosions in a semi-closed tube, a high-speed camera, a thermal infrared imaging device and a pressure sensor were used in the study. Poplar dusts with different particle size distributions (0-50, 50-96 and 96-180 mu m) were respectively placed in a Hartmann tube to mimic dust cloud explosions, and flame propagation behaviors such as flame propagation velocity, flame temperature and explosion pressure were detected and analyzed. According to the changes of flame shapes, flame propagations in wood dust explosions were divided into three stages including ignition, vertical propagation and free diffusion. Flame propagations for the two smaller particles were dominated by homogeneous combustion, while flame propagation for the largest particles was controlled by heterogeneous combustion, which had been confirmed by individual Damkohler number. All flame propagation velocities for different groups of wood particles in dust explosions were increased at first and then decreased with the augmentation of mass concentration. Flame temperatures and explosion pressures were almost similarly changed. Dust explosions in 50-96 mu m wood particles were more intense than in the other two particles, of which the most severe explosion appeared at a mass concentration of 750 g/m(3). Meanwhile, flame propagation velocity, flame propagation temperature and explosion pressure reached to the maximum values of 10.45 m/s, 1373 degrees C and 0.41 MPa. In addition, sensitive concentrations corresponding to the three groups of particles from small to large were 500, 750 and 1000 g/m(3), separately, indicating that sensitive concentration in dust explosions of wood particles was elevated with the increase of particle size. Taken together, the finding demonstrated that particle size and mass concentration of wood dusts affected the occurrence and severity of dust explosions, which could provide guidance and reference for the identification, assessment and industrial safety management of wood dust explosions.