An investigation into the factors affecting the metered atomisation of
superheated liquids has been carried out. The investigation was aimed primarily
at developing an understanding of the factors which affect the performance of.
respiratory drug delivery systems (Suspension Pressurised Metered Dose
Initial investigations used a semi-empirical sizing technique, representing
the human airways, to identify the major variables (formulation and geometric)
which affect the performance of the MDI system.
Computer models were developed to describe both continuous and
metered discharge from a superheated-liquid aerosol generator. These models
were based on the concept of thermal and dynamic equilibrium, but they were
improved and extended, to describe metered discharge, by including empirical
corrections obtained from continuous discharge experiments. Experimental
investigations using 'instrumented inhalers' were used to confirm the validity of
the computer model. The experimental investigations encompassed the use of
conventional CFC's and the new non-chlorinated propellants 134A and 227. The computer models and droplet correlation function developed
during these investigations represent powerful tools for use in the design of both
current and future HFC/HFA powered metered dose inhaler delivery systems.
Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.