The influence of the orifice height of a cylindrical, flat-bottomed hopper on the mass flow rate of the free-flowable size fractions of sodium chloride and boric acid was investigated. It was observed that a zone of sudden acceleration of the mass flow under gravity occurred when a critical orifice height had been achieved.
The orifice height should be taken into consideration as an important parameter of a cylindrical test hopper in order to obtain a reproducible and comparable mass flow as the single-point characteristic of powder flowability.