Cooling as a possible method for increasing the flowability of certain pharmaceutical and other powders

Measurements have been made of the rates of flow under gravity of powdered sugars and of fatty acids through circular orifices at temperatures between -25 and 110 degrees C. The flow rates decrease considerably as the powders are heated; conversely they increase as the powders are cooled from a high ambient temperature of 40 to -25 degrees C. The results are ascribed to changes in the cohesiveness of the powders caused by softening and plastic deformation of particles at elevated temperatures. Lactose, paracetamol and griseofulvin granule formations have been reported to show similar effects and the possibility is discussed of using cooling to increase the flowability of particular powders in pharmaceutical production. The rates of flow of the powders are given by the expression(formula: see text)where W is the flow rate in g min-1, Do is the orifice diameter in cm, rho is the particle density in g cm-3, g is the gravitational constant, and A and n are numerical terms which depend on temperature and particle size.