Effect of an upstream grid on the fluidization of pharmaceutical carrier powders.

The influence of grid generated mixing on the fluidization of pharmaceutical carrier powders is studied in a channel-flow experiment using direct high-speed imaging and particle image velocimetry (PIV). Four different lactose powders with mass median diameters that range between 61 µm and 121 µm are used. The degree of powder mixing in the flow as a function of grid position relative to the powder bed and grid area blockage ratios (ranging from ~25% to ~40%) is studied for a range of flow-rates. The study presents comprehensive mappings of how pharmaceutical powders are fluidised under the influence of mixing, by examining powder bed morphology, powder emptying rate, and the local flow-field surrounding the pocket. The use of a grid results in higher evacuation percentages (void fraction) and a faster evacuation rate but is associated with randomized evacuation behaviour as observed from the powder bed morphology. Use of a grid can enable evacuation of powder at lower overall flow-rates, which may have important implications on respiratory drug delivery. PIV results show the trend of mean velocities with the mass median powder diameter and demonstrates how a grid with lower blockage ratio can increase the degree of mixing of the evacuating powder and make the evacuation process more rapid. This study contributes towards a better understanding of fluidization processes as relevant to dry powder inhaler devices and sheds light on how simple design alterations, such as adding an upstream grid, can be incorporated to optimise device effectiveness.