Analysis of the droplet size reduction in a pMDI to the addition of a turbulence generating nozzle

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Title: Analysis of the droplet size reduction in a pMDI to the addition of a turbulence generating nozzle
Author: Medlar, Michael
Abstract: Pharmaceutical inhalation aerosol technology has become an important therapy for the treatment of both respiratory and non-respiratory illness. Targeting therapeutic aerosols to the small airways of the lung can effectively treat many of these diseases. Delivery of the therapeutic agent directly to the site of action, for cases involving respiratory diseases, ensures an adequate therapeutic level of the drug is reached, without leading to side effects due to high systemic concentrations. For non-respiratory diseases, the periphery of the lung offers enormous surface area (approximately 100m2) for rapid absorption into circulation. In either case, the appropriate spray characteristics (0.5 um<MMAD<5 um and a low velocity) are vital to targeting the lung periphery. In inhalation technology, specifically pressurized metered dose inhalers (pMDI), many factors lead to the break-up or atomization of the formulation. These could include the nozzle geometry, volatilization of the propellant (cavitation), and turbulence in the nozzle. The purpose of this study was to design and analyze turbulence generating nozzles for the improvement of existing pressurized metered dose inhaler therapy. The existence of turbulence within the inhaler nozzle is one mechanism that leads to the production of the aerosol in this device. The current inhaler internal flow passage was analyzed on a turbulence basis and a baseline median representative droplet size was predicted using the Huh atomization model. The analysis of this atomization model led to the conclusion that changing the turbulence exit conditions in the inhaler through the addition of a nozzle could lead to a reduced median secondary droplet size. To investigate this, simple nozzles were designed to produce a turbulent flow condition on exit from the orifice. The flow condition was analyzed using computational fluid dynamics software (CFD). The average turbulent kinetic energy (kavg) and turbulent kinetic energy dissipation rate (savg) on exit from the orifice were related to a representative secondary droplet size distribution using the Huh atomization model. The nozzle with the largest potential (i.e. lowest median secondary drop size) was optimized in 3D and a resulting median secondary drop size was predicted. Development of the proper turbulence characteristics with this add-on nozzle led to a 15.5% improvement of the representative secondary median droplet size based on turbulence effects alone.
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Date: 2002-11

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