Experimental and numerical research on pharmaceutical aerosols

Abstract

With the background of health issues regarding the consumption of tobacco, the widespread availability of safer nicotine products and a harm reduction policy is encouraged. A cigarette alternative is designed to deliver a dose of medicinal nicotine within a timeframe comparable to that of a cigarette, and gives much of what smokers expect from a cigarette without the risks of smoking tobacco. The general purpose of this Ph.D. project is to study the process of flashing atomization and dispersion, with a view to supporting the development of a cigarette replacement device. In order to test the effectiveness of the nicotine formulations, the analysis is carried out sizing the droplets of the aerosols at the position where human oropharynx locates, to support the further research on the deposition of droplets in the human respiratory tract. A mechanical lung has been assembled and programmed to trigger the ‘cigarette-like’ devices with different inhalation profiles, and a dual laser system has been designed to measure the global actuation flow characteristics (e.g. spray velocity and opacity). In order to efficiently acquire sufficient droplet information (e.g. diameter and aspect ratio) from images of in and out of focus droplets, a multi-threshold algorithm is developed and successfully implemented in the automatic particle/droplet image analysis (PDIA) system. It increases the depth of field (DoF) of small particles with diameters smaller than 50?m, and it performs more efficiently than the dual threshold methods which are widely used in the commercial software. A numerical multi-component two-phase actuation flow model has been developed, in order to test different formulations within various flow domains of the cigarette replacement devices. The simulated results of the numerical model have been validated with the experimental measurements and the results of previous researchers. In order to acquire an aerosol with relatively low and steady mass flow rate of nicotine, it is recommended that the mass fraction of propellant (HFA 134a) should be kept around 75%~90% to avoid the sharp temperature drop causing the sensation of freezing. The actuator nozzle diameter should be 0.2mm~0.3mm to produce a flow with relatively low mass flow rate. Furthermore the numerical model is capable of predicting the residual mass median diameter (MMD) of the spray, by using evaporation model of multicomponent liquid droplets, to quantify the sprays. Two different formulations with 95% and 98% mass fraction of HFA 134a, and two prototype cigarette alternatives with different expansion chamber volumes, have been analyzed by the numerical model and compared with the dual laser measurements. In addition, it considers the spray character by high speed imaging, with the special interest in the flashing phenomena and droplet sizes. It concludes that a larger expansion chamber volume enhances the propellant evaporation, recirculation, bubble generation and growth inside the chamber, and it made a significant improvement to produce finer sprays. Although the formulation with 98% of HFA 134a can generate smaller droplets, the formulation with 95% of HFA 134a produces more steady puffs with relatively low mass flow rate.

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