| Summary: | 碩士 === 國立成功大學 === 航空太空工程學系碩博士班 === 91 === This research is to investigate the atomization performance of micro-nozzle and the effects of side blow on the droplet distribution of a single stream spray from micro-nozzle. All experiments are performed under room temperature and atmosphere pressure. Working pressure is 5atm to 11atm. The orifice aspect ratios of the micro nozzles are 2.0 , 5.0 and 10.0 with hydraulic diameter 53.33μm、66.67μm and 72.73μm respectively. The side blow is located at Z=10mm below the nozzle exit. The particle size distribution of the spray is measured by INSITEC RT-Sizer particle analyzer. Results show that the mass flow rate as low as 0.003g/sec-atm is achieved with this micro nozzle with aspect ratio 1:2. Results show that better atomization performance is achieved as the orifice aspect ratio increases. It seems that the different strain rate in the length and width directions, enhances the instability of the fluid and hence its atomization performance. Using the nozzle with orifice AR=10.0, Pt=9atm, Z=10mm and side blow at C=10mm, the volume of the smaller droplets (<100μm) is 5.19% of the spray without side blow. When the side blow increases to Vb =5m/s, the volume of the smaller droplets (<100μm) reduces to 0.44% of the spray, a value which is only 8.48% of the case without side blow. However, the standard deviation of the particle distribution remains unchanged. When the side blow velocity further increases to Vb =20m/s, the relative Weber number (Weij) associated with the particle collision is higher than 20, hence the volume of the smaller droplets increases because more small droplets are produced through the mechanisms of stretching separation and reflexive separation. The smaller droplets can be found at the radial away from r=0 due to side blow. Hence the SMD of the spray with side blow tends to increase in the downstream as comparing to the case without side blow. The distribution of spray particles becomes wider as the orifice aspect ratio increases. The particle collisions are mainly related to stretching separation and reflexive separation process in the core region because the particle velocities are high enough and St >> 1. This in turn results in the production of small particles. However, the particle collisions are mainly related to the collision coalescence process in the outer region because of the lower particle velocity. Hence the bigger particles due to coalescence are measured.
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