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Title: A fundamental study of the primary atomisation mechanism and aerosol plume development of the pressurised metered dose inhaler
Author: Myatt, Benjamin J.
ISNI:       0000 0004 7970 9791
Awarding Body: Loughborough University
Current Institution: Loughborough University
Date of Award: 2017
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The pressurised metered dose inhaler (pMDI) is the most popular device for delivery of inhaled therapeutic aerosols to the lungs for treatment of asthma and COPD. One significant weakness of the pMDI is the high level of oropharyngeal deposition leading to low drug delivery efficiency. With the increasing prevalence of respiratory diseases and desire to improve the efficacy of drug delivery a deeper fundamental understanding of the atomisation process and aerosol plume physics is required. This thesis reports the findings of experimental studies using optical diagnostic techniques to investigate the internal flow processes and to characterise the spray plume of pharmaceutically relevant formulations. A new experimental protocol for laboratory measurements of pMDIs has been developed. The effect of actuation delay time and the number of spray events surveyed on the plume velocity and droplet diameter have been defined. Experiments requiring data of multiple pMDI actuations must allow a one minute delay between actuations for consistent data. Schlieren images confirm sonic gas flow exiting the spray orifice. A liquid annulus prevails through the event, suggesting an aerodynamic atomisation mechanism. Fluid in the spray orifice is superheated sufficiently that flash evaporation and rapid growth of bubbles in the liquid phase exiting the orifice is likely. Near orifice images show the spray is highly atomised within one orifice diameter of exit. Internal flow visualisations revealed a marked change of flow structure in the actuator sump, from a vapour core surrounded by a liquid annulus to a bubbly flow structure with inclusion and increasing concentration of ethanol in the formulation. The axial velocity of HFA134/ethanol formulations was broadly constant both in time and space. However, the arithmetic mean droplet size was found to increase with ethanol concentration. With no significant difference in saturation vapour pressure of the formulations surveyed this suggests that surface tension and/or viscosity must play a more significant role in governing the droplet sizes than previously acknowledged. Large fluctuations of Sauter mean diameter of HFA134, HFA227 and HFA134/2% ethanol plumes through time were linked to the erratic nature of the vapour core in the sump. Liquid slug flow in the orifice and ligament stripping from a liquid pool around its periphery produces large droplets. With higher ethanol concentration the plume is more stable due to the bubbly flow in the sump. Droplet sizes measured by PDA indicate that the log-normal distribution is an accurate description of the size distribution of the pMDI - important validation for analysis of ACI data With the likely replacement of HFA134 and HFA227 with more environmentally friendly propellants on the horizon the findings in this thesis may prove useful in the transition process. However, flow visualisation and plume characterisation studies of the nature carried out in this project of new formulations would provide valuable information in the quest to deliver new products to a highly competitive market in a timely manner.
Supervisor: Not available Sponsor: Chiesi Farmaceutici SpA
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Mechanical Engineering not elsewhere classified ; Pressurised Metered Dose Inhaler ; pMDI ; Metered Dose Inhaler ; Inhaler ; Phase Doppler Anomometry ; PDA ; Particle Image Velocimetry ; PIV ; Atomisation ; Atomization ; Atomisation mechanism ; Atomization mechanism ; Aerosol plume development ; HFA134 ; HFA227 ; HFA134-ethanol ; HFA134/ethanol ; Asthma ; COPD ; Optical diagnostics ; Optical diagnostic techniques ; Flow visualisation ; Internal flow visualisation ; External flow visualisation ; Schlieren ; Schlieren imaging ; Spray plume ; Aerosol ; Aerosol plume ; High speed imaging ; Plume characterisation ; Spray characterisation ; Droplet size ; Velocity ; Speed