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

Abstract

The influence of grid generated mixing on the fluidization of pharmaceutical carrier powders 15 is studied in a channel-flow experiment using direct high-speed imaging and particle image 16 velocimetry (PIV). Four different lactose powders with mass median diameters that range 17 between 61μm to 121μm are used. The degree of powder mixing in the flow as a function of 18 grid position relative to the powder bed and grid area blockage ratios (ranging from ~25% to 19 ~40%) is studied for a range of flow-rates. The study presents comprehensive mappings of how 20 pharmaceutical powders are fluidised under the influence of mixing, by examining powder bed 21 morphology, powder emptying rate, and the local flow-field surrounding the pocket. The use 22 of a grid results in higher evacuation percentages (void fraction) and a faster evacuation rate 23 but is associated with randomized evacuation behaviour as observed from the powder bed 24 morphology. Use of a grid can enable evacuation of powder at lower overall flow-rates, which 25 may have important implications on respiratory drug delivery. PIV results show the trend of 26 mean velocities with the mass median powder diameter and demonstrates how a grid with 27 lower blockage ratio can increase the degree of mixing of the evacuating powder and make the 28 evacuation process more rapid. This study contributes towards a better understanding of 29 fluidization processes as relevant to dry powder inhaler devices and sheds light on how simple 30 design alterations, such as adding an upstream grid, can be incorporated to optimise device 31 effectiveness.