| Summary: | 碩士 === 國立成功大學 === 航空太空工程學系碩博士班 === 91 === The effects of different atomization mechanisms on the atomization performance of an air-assist atomizer are investigated in this research program. The atomizers with straight, contraction and expansion configurations are designated by CK5-S, CK5-C and CK5-E, respectively. Nozzles with side jets and multiple orifices are also characterized. The particle size of the spray is measured by Malvern RT-Sizer. The measurement is based on the diffraction pattern scattered by the spray droplets.
Results show that the singularity configuration of the contraction type nozzle enhanced the atomization processes. Hence reduction of the mean particle size (SMD) and size ratio (SR) of spray is achieved. As a typical example, SMD=33.20μm and SR=8.87 for CK5-S atomizer under Pw=5.2kg/cm2 and Pa=6kg/cm2, while SMD=15.72μm and SR=3.41 for CK5-C atomizer, respectively. Obviously, the CK5-C nozzle has better atomization performance. If the side jet is applied CK5-C atomizer, the quality of spray is further improved. For example, when a side jet with 9LPM airflow is injected into CK5-C atomizer, the particle size and size ratio are further reduced to SMD=13.29μm, SR=2.74, respectively. It turns out that the air-to-liquid mass ratio is 0.618. This indicates that the advantages of the spray from the nozzle with side jet are fine droplets and narrow particle size distribution. Simultaneously, the lower air-to-liquid mass ratio also reduces the operation cost. Results also show that a small amount of side jet can enhance the atomization effect substantially. According to the investigation of multiple orifices nozzle, the atomization performance of the contraction nozzle is better than that of the straight one. Comparison of CK5-C atomizer with single orifice and those contraction nozzles with multiple orifices shows that the water flow rate of the later ones is higher than that of CK5-C atomizer. In addition, the SMD and SR associated with CK5-C atomizer and those with multiple orifices are similar. Hence the contraction nozzle with multiple orifices can be regarded as a better atomization mechanism to produce a large amount of spray with good quality.
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