Fluidization and break-up of powder particle aggregates during constant and pulsating flow in converging nozzles

Abstract

Deagglomeration of lactose particles during fluidization by air and the subsequent flow through converging nozzles was evaluated experimentally for constant (Q=5–30dm3/min) and pulsating airflows (Q=10/20dm3/min, f=1.6/4.3Hz). Discussion of observed effects was supported by results of CFD simulations of airflow pattern in the tested systems and calculations of the strain rate distribution. It was demonstrated that the increase of flow acceleration due to nozzle constriction leads to powder disaggregation (particle median size reduction from 5.6 to 3.2μm in the best case) on the cost of higher energy dissipation. The median size of aerosol particles obtained in the analyzed systems was correlated with the logarithm of the pressure drop. It was demonstrated that observed effect of particles deagglomeration relies on the focusing of aerodynamic stresses in the region of aerosol ejection to a stagnant fluid. Airflow pulsations were shown to enhance the break-up of powder aggregates but only in the systems of a low pressure drop. This effect is explained by amplification of particle–fluid interactions by flow unsteadiness. The results of the study were discussed in the perspective of possible application of proposed concepts to improve the performance of passive and active dry powder inhalers (DPIs).