Effect of Orifice Geometry on Particle Discharge Rate for a Flat-Bottomed, Cylindrical Hopper

In this work, the influence of the geometry of a cylindrical flat-bottomed hopper orifice on the mass discharge rate of six free-flowable powder excipients with the size fraction 0.050-0.063 cm was investigated. Sixteen combinations of the orifice diameter and the height were used. The influence of the orifice diameter was described by the flow equation. However, the discharge rate was also affected by the orifice height. The influence of the orifice geometry on the powder discharge rate was indirectly studied by the parameters of the Beverloo equation. The value of the coefficient of determination and the precision of the discharge rate prediction were the basic criteria. The mean relative differences between the actual discharge rate at the combination of the orifice diameter and its height and the average discharge rate allowed a direct study of the effect of the orifice geometry. The complex nature of the orifice height impact on the powder discharge rate through the hopper opening has been determined. Based on the results, the orifice diameter of 0.8 cm with the height less than 0.8 cm is recommended. The method of powder flow evaluation proposed here can be used in testing of other powder fractions in future.