Use this URL to cite or link to this record in EThOS:
Title: Modelling dry powder inhaler operation with the discrete element method
Author: Tuley, Robert James
ISNI:       0000 0001 3537 6401
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2008
Availability of Full Text:
Access from EThOS:
Access from Institution:
Dry powder inhalers (DPI) are a common asthma treatment. Despite the number of commercial devices available, little is known about their internal operation: the process of fluidising a powder dose into an inhalation airflow. This PhD aims to investigate this process, and demonstrate that it can be modelled computationally. . Experimental work is described to record high speed video of the dose fluidisation from simplified DPls. Typical DPI powders such as lactose are tested, along with cohesionless glass spheres and aluminium flakes. Two distinct dose fluidisation mechanisms are identified, labelled 'fracture' and 'erosion'. Lactose exhibits a fracture mechanism -- large agglomerates are produced as the powder bed cracks along lines of weakness. Glass or aluminium particles exhibit an erosion mechanism: powder is entrained into the flow as individual particles from the bed surface. The recorded video is quantitatively analysed to determine fluidisation timescales and pressures. Shear cell test results show that predicting the mechanism of fluidisation is not possible using averaged bulk powder properties. This suggests any DPI model must include the fundamental particle interactions. The discrete element method (OEM) is introduced as a computational technique capable of predicting DPI behaviour from individual particle properties. The numerical accuracy of the method is assessed, showing that time integration is limited to a maximum of 2nd order accuracy due to discontinuities in particle contact forces. A sensitivity analysis shows inter-particle cohesion is the dominant factor affecting OEM predictions. OEM is used to create a simple model of the dose fluidisation that occurs within a DPI. The results are compared with real powder behaviour. OEM is shown to capture the realistic fluidisation of both lactose and glass powder doses. It is concluded that OEM is a promising technique to predict DPI behaviour, although further work is required to quantify inter--particle cohesive parameters
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available