DISTINCT ELEMENT SIMULATION OF INTERSTITIAL AIR EFFECTS IN AXIALLY-SYMMETRICAL GRANULAR FLOWS HOPPERS

Two-phase flow of interstitial air in a moving packed bed of granular solids is modelled using a distinct element (DE) technique which consi ders the Newtonian dynamics of particle motion passing through a radia l flow field of air in a mass flow hopper. The air flow is assumed to be incompressible and the mass flux of air at any height within the ho pper is assumed to be constant. These assumptions allow the simulation of air-retarded and air-assisted hows in mass flow hoppers without th e need for an extensive development of the momentum balance calculatio ns on an Eulerian fixed grid. The particle-particle and particle-hoppe r wall interactions are modelled using a Hertzian interaction law and a contact friction algorithm of the Mindlin analytic form (Langston er al., 1995, Chem. Engng Sci. 50, 967). Predictions of discharge rates in both air-retarded and air-assisted flows are compared with the cont inuum mechanics calculations based on the steady-state flow assumption . The DE simulation results indicate certain transient and oscillatory features of the flow fields which have not hitherto been demonstrated by the continuum theories. Furthermore, it is shown that air-assisted flow leads to increased wall stresses which reduce the bulk solids di scharge rate for discharge through small orifices.