| Summary: | 博士 === 國立成功大學 === 航空太空工程學系碩博士班 === 97 === This dissertation investigates the atomization mechanisms and performance of twin-fluid micro atomizers. It produces micron-sized droplets sprays for the applications of inhaled drug delivery. The micro-atomizers were fabricated via MEMS bulk machining processes. The breakup mechanisms of the micro jet were examined experimentally using photographic technique. All tests were performed at room temperature and atmospheric pressure. The two types of the twin-fluid micro-atomizers were designed in the research program. One is the air-assist type micro-atomizer (AMA type) with three micro channels for the liquid and gas flows. The other one is the manifold type micro-atomizer (MMA type) with four micro channels. The orifice hydraulic diameters of the micro atomizers are less than 100µm. The aspect ratios of orifice are ranged from 9 to 23 for the AMA and MMA atomizers. This dissertation also describes the effects of liquid properties, liquid flow rate, and atomizing air pressure on drop sizes produced by disintegration of the micro-jet. The liquids employed in this study are water, ethyl alcohol, 0.45%NaCl solution, and a glycerin-water mixture. Liquid injection pressure is from 0 to 8bar and liquid flow rate ranging from 0.1 to 4mL/min is supplied with syringe pump. Atomizing gas pressure is varied from 1 to 6bar with volume flow rate less than 1L/min. A nonintrusive Malvern INSITEC RT-Sizer was used to measure drop size distribution of the spray and IDT/PIV system was used to measure the spray velocity. Flow visualization technique was also performed by the IDT high speed camera system. Observations of the breakup mechanisms in the near-field of the atomizer show that the breakup regimes can be described by the mechanisms involving the laminar jet disintegration, aerodynamic disintegration and turbulent mode based on the atomizing gas pressure, the injection pressure and Weber number. A new phenomenon of flow branching of the liquid jet emanating from the atomizer was also observed. Moreover, the ratio of liquid to gas flow rate determines the spreading angle and droplets size of the two-pronged liquid jets. It is also found that the flow focusing mechanism results in the mono-dispersed droplets stream.
Results also show that for AMA with hydraulic diameter 46µm the mean droplet size reduces from 14.1µm to 5.3µm as gas-to-liquid ratio (GLR) ranging from 1.3 to 2.9 and the mean droplet size (SMD) ranging 5 to 6µm can also be achieved by AMA with hydraulic diameter of 78µm under liquid flow rate less than 2mL/min and gas pressure ranging from 3 bar to 5bar. Moreover, for MMA with hydraulic diameter of 44µm the mean droplet size is further reduced from 3µm to 6µm with lower gas-to-liquid ratio ranging from 0.13 to 0.38 under the same pressure range. The axial velocity profile of the micro spray measured by using PIV instrument is essentially a jet flow structure. The mean axial velocity of spray droplets is below10m/s at Z=20mm downstream from the atomizer and reduced to 1m/s downstream Z=100mm. In order to evaluate the feasibility of drug delivery to lung with AMA, the mouthpiece, ball baffle, and micro-atomizer were connected in series and drop size of water spray was measured near the exit of mouthpiece. Results indicate that the finer micro spray with Sauter mean diameter (SMD) of 2.3µm under the test conditions of the air pressure greater than 2bar and the liquid flow rate ranging from 0.8 to 2mL/min can be achieved as the ball baffle and mouthpiece was installed. Dv50 less than 5µm are also obtained and the respirable percentage (< 5µm) of 68% can be achieved by the AMA nebulizing system with bending mouthpiece and baffle.
For in vitro experiments with the mouthpiece and the USP2000 throat model, the AMA nebulizing system with bending mouthpiece is also the best choice because the spray jet travels two bends to measurement region. The respirable percentage of 50% for aerosol measured in measurement region of USP can be achieved under gas pressure of 2bar, suction air of 18L/min, and QL=1mL/min. It turns out that the design of prefilming type micro atomizers can enhance the atomization performance in this research. As installing baffle and mouthpiece, the droplets size and slow velocity is further suitable for the application of drug inhalation to treat asthma, COPD, CF, and respiratory care.
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