Sizing the outlet for the required discharge rate is
straightforward, provided the bulk material is both coarse
and free-flowing (4). A material is considered coarse if the
majority of its particles are larger than 1/8 in. or 3 mm. A
free-flowing material is one that does not experience arching
or ratholing flow problems. Assuming that the bulk material
is both coarse and free-flowing, such as plastic pellets, the
following equation can be used to approximate the maximum
discharge rate from a converging hopper: