AN EXPERIMENTAL-STUDY OF DEFLAGRATION TO DETONATION TRANSITION SUPPORTED BY DUST LAYERS

The roles which dust layers play in severe dust explosions were invest igated in a 70-m-long and 30-cm-diameter horizontal Flame Acceleration Tube (FAT) with one end closed and the other end open to the atmosphe re. A variety of dusts such as corn dust, cornstarch, Mira Gel starch, wheat dust, and wood flour were layered on the bottom half of the FAT . Flame and detonation propagation parameters were closely monitored a t different locations along the FAT. The study demonstrated that the m oisture content of the dust, the exposed area of the dust layers to th e convective flow, and the physical characteristics of the dust are th e factors that most determine the severity of layered dust explosions, indicating that prelayered dust combustion is dominated by the dust/a ir mixing process. While the dust explosion rate constant K-st can be used to characterize dust explosibility in predispersed dust in consta nt volume enclosures, it does not appear to characterize the behavior of layered dust explosions. Qualitative measurements of the variation of dust concentration during a layered dust explosion were obtained. T he measurements indicated that the dust concentration at the time of f lame arrival is highly nonuniform. The maximum pressure rise (P-max - P-0) within the FAT during a layered dust explosion was found to vary linearly with the flame velocity V-f when V-f is subsonic. As V-f reac hes supersonic values the maximum pressure increase was found to vary with the V-f(2), the square of the flame velocity. This result was fou nd to be independent of dust type and concentration.