Abstract
There are at least two main requirements for repeatable and reliable measurements of flammability and explosibility parameters of dusts: a uniform dispersion of solid particles inside the test vessel and a homogeneous degree of turbulence. Measurements of these parameters are performed in spherical vessels (20 L sphere or 1 m3 sphere). In several literature works, it has been shown that, in the standard 20 L sphere, the dust injection system generates a non-uniform dust cloud, while high gradients characterize the turbulent flow field. In our recent work, CFD simulations of flow field and dust concentration distribution in the 1 m3 spherical vessel were carried out and the results compared to the data previously obtained for the 20 L. It has been found that in the 1 m3 vessel, the spatial distribution of the turbulent kinetic energy is lower and much more uniform. Concerning the dust distribution, as in the case of the 20 L, dust is mainly concentrated at the outer zones of the vortices generated inside the vessel. In this work we use the previously validated CFD model to simulate the dust dispersion inside the 1 m3 vessel at different dust diameters. Results show that on increasing the dust diameter, the dust paths are different from those of the fluid flow until the sedimentation effect prevails and the turbulence field becomes similar to the dust-free air case. Since the spatial distribution of the turbulent kinetic energy is lower and much more uniform than in the 20 L sphere, the 1 m3 vessel is less susceptible to variations in the dust intrinsic properties, making parameter measurements more reliable and repeatable.
