Numerical study on porosity distribution and analysis of ignition instability in packed beds of spheres.

Porosity distribution is an important factor that affects premixed flame stability in packed beds. In this paper, the discrete element method is used to simulate the sphere packing in cylindrical, conical, and pyramidal packed beds. The anisotropic characteristics of porosity and ignition temperature distributions in packed beds are calculated and analyzed. The results show that the distance of the oscillation period of the packed bed filled with spheres of the same diameter is approximately equal to the sphere diameter. The oscillation amplitude of radial and axial porosity curves can be reduced by filling with mixed spheres of different diameters in cylindrical packed beds. The influence factors on the oscillation period distance of the radial and axial porosity curves include the diameter difference of the spheres and the mixing ratio of the number of spheres. In the cylindrical double‐layer packed beds, the interfacial porosity can be decreased by the increase of the diameter difference among the spheres. Increasing the divergent angle of the conical packed beds can weaken the influence of wall effect on the radial and axial porosities, which makes the uniformity of the porosity in the conical packed beds better than that of the cylindrical and the pyramidal beds. The inhomogeneity of tangential porosity distribution in the packed beds is inherent. In the packed beds, the ignition temperature of premixed gas is negatively correlated with porosity, sphere diameter, equivalent ratio of mixed gas, and divergent angle of conical packed beds, and it is positively correlated with superficial velocity. [ABSTRACT FROM AUTHOR]