Abstract
The objective of this study is to design and fabricate the micro-atomizers assisted with the air swirler. By combining the pressure-swirl type atomizer and the air swirler, the swirling air makes great impact on the liquid swirl of spray. Double-swirl interaction is active to enhance the ability of disintegration between air and liquid, achieving the goal of fine atomization. MEMS technique is applied to fabricate the micro-atomizer characterized by high-aspect ratio structure which scales down the size of geometry and subsequently reduces the mean droplet size. In experiments, the performance test of the micro-atomizer and flow visualization have been carried out. Through measuring the flow rate of injection, performance of the micro-atomizer is evaluated via flow number and discharge coefficient. For analyzing the structure and the development of flow field, the spray is visualized by laser sheet illumination and high-speed camera recording; particle imaging velocimetry (PIV) is also manipulated to study the velocity field. The results show that the flow field caused variation in spray angle and hollow cone structure before and after the swirling air acts on spray. Spray angle expanded with increasing the air velocity. Also, vortex core was observed in the center of flow field and the vorticity increased with increasing the air velocity. It means that the strength of liquid swirl and the relative velocity between liquid and air increased and, therefore, are beneficial to atomize liquid. In addition, the velocity field across spray on the vertical face has “w” profile distribution, and the peak value occurs on the boundary layer. Accelerating the air velocity raises the axial velocity of spray as well; the vector plot of flow field indicates that the flow reversal occurred, indicating that the tangential velocity of spray is between 1.7 to 3.4 m/s. The experimental results show that the air swirler indeed has great effects on liquid atomization, and it proves the design concept of combining the pressure-swirl atomizer and the air swirler for better quality of atomization.