Atomization performance of twin-fluid micro-injectors with micro-mixing mechanisms

This paper describes the development of two types of the twin-fluid micro-injectors. One is the air-assist type micro-atomizer (AMA type) with three micro channels for the liquid and gas flows. The other is the manifold type micro-atomizer (MMA type) with four micro channels. Two of them are used to supply the atomization gas and the others supply the liquid matter. The orifice hydraulic diameters (d_H) of the micro atomizers are 45μm. The aspect ratios of orifice were 20.8 and 15.8 for the AMA and MMA atomizers, respectively. The Malvern Insitec RT-Sizer is used to measure the particle size and the IDT/PIV system is used to measure the particle velocity. Flow visualization through a microscope shows that the atomizing mechanisms are related to the breakup processes due to the liquid column instability and the impinging oscillation mode for the AMA and MMA atomizers, respectively. Results also show that the dependence of the particle size on the gas-to-liquid ratio is quite different from the cases we know from the conventional atomizers. For example, the mean droplet size reduces from 14.1μm to 5.3μm with gas-to-liquid ratio ranging from 3.1 to 4.7 when the gas pressure increases from 2.0bar to 5.0bar. On the contrast, the mean droplet size was further reduced from 3.0μm to 6.0μm with lower gas-to-liquid ratio ranging from 0.13 to 0.38 under the same pressure range. This phenomenon is due to the fact that the effects of surface tension are more significant in the micro-atomization processes. It is also found that the atomization with impinging oscillation mode is more efficient as far as the design of the micro-atomizer is concerned. Moreover, the mean axial velocity of spray droplets is below 6.6m/s at a distance 20mm from the atomizer. The ultra-fine sprays with slow moving behavior can be used to the applications of the inhaled drug delivery for respiratory care.