This research was concerned with the experimental and theoretical investigation of the spray issued from a pressurised metered-dose inhaler (pMDI) and has been motivated by the urgent need to find suitable replacements to the environmentally destructive Cf'Csbased propellants currently used and to extend the working knowledge of the device. The majority of the experimental work was conducted using phase-Doppler anemometry (PDA), a single particle light scattering technique which provides the simultaneous measurement of drop size, velocity and concentration, yielding the most detailed temporal and spatial analysis of the pMDI spray to date. The PDA analysis was complemented by a visual investigation of the near-orifice flow field in an attempt to obtain information on the primary atomization process. The theoretical investigation of the pMDI spray consisted of constructing a model of the fluid flow through the pMDI during a single actuation that was based on a quasi-steadystate separated flow analysis and included a qualitative and quantitative description of the primary atomization process. The construction of a model of the resultant spray was based on the solution of the multiphase transport equations using computational fluid dynamics (eFD) techniques, with the theoretical results being validated against the experimental data. The spray issued from a pMDI was found to be an unsteady, transient, threedimensional, multiphase fluid flow, generally characterised by high initial drop velocities with steep axial velocity radial gradients, small drop sizes, high levels of turbulence and a mean spray cone angle of approximately eleven degrees. The visualisation of the near-orifice flow field suggested that flash evaporation was the primary atomization mechanism, producing a finely pre-atomized spray. The pMDI spray was affected by attitude, it having been observed that the patternation of the spray was biased in the downward direction and this was a consequence of the asymmetric geometry of the actuator nozzle. The results predicted at the near-orifice measurement locations by the theoretical spray model suggested that the theoretical actuator flow model successfully simulated the fluid flow through the pMDI and the primary atomization process during a single actuation for a placebo hydrofluoroalkane formulation. However, the resultsproduced by the theoretical spray model could only be considered as preliminary until further numerical analysis is conducted.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:587518 |
| Date | January 1996 |
| Creators | Dunbar, C. A. |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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