Atomization Performance of Pressure Type Micro Atomizers with Resonant Effects

• Main Authors: Yung-Wei Hsueh, 薛勇瑋
• Other Authors: Muh-Rong Wang
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/04490067353205754069

碩士 === 國立成功大學 === 航空太空工程學系碩博士班 === 94 === Abstract Atomization performance of pressure type micro-atomizers with resonant effects is investigated in this research program. The evolution of the micro-jet during the transient break-up processes was studied using IDT-high speed video camera. The particle size distribution was measured by Malvern RT-Sizer. Results showed that the liquid first formed a meniscus around the outlet of the orifice because of the higher surface tension effects associated the micro-injector. The meniscus was transformed to the spherical shape when the inertia force was increased with time. The spherical shape was then stretched to a column as the inertia force was further increased. Finally, the liquid jet became quite unstable and formed a conical shape near the orifice, a cylindrical column as the neck and a spherical head in the down stream. The above unsteady processes were preceded in a short time as the diameter of the nozzle was increased due to the increased inertia of the liquid column. Results also showed that the intact-length of the micro-jet increased with Reynolds number as Re＜ 392. However, the intact length reached a maximum and then began to decrease as Reynolds number was further increased. The instability modes of the liquid jet changed from the axi-symmetric mode to helical mode as Reynolds number reached 392. The helical instability was transformed to the sinusoidal motion as Reynolds number was further increased (i.e., Re＞635). It was also found that the diameter of the orifice was the control parameter of the spray production rate and the particle size. The spray production rate increased with the orifice diameter to the second power. The particle size of the spray also increased with the orifice diameter. For example, under the injection pressure of 125bar, the spray production rates were 3.95 kg/hr, 8.4 kg/hr, and 12.33 kg/hr and mean particle sizes were 6.65μm, 9.42μm, and 11.53μm for the cases of orifice diameters of 100μm, 150μm, and 200μm, respectively. The spray production rate was further increased with the multiple-orifice design. For example, under the liquid infection pressure of 125bar and the orifice diameter of 100μm, the spray production rate increased from 3.95kg/hr to 6.91 kg/hr as the number of orifice was doubled. However, the particle size of the spray was insensitive to the change of the number of orifice. Hence one may control the spray production rate by increasing the number of orifice without degrading the quality of the spray. The pitch of the multiple orifice design also affected the atomization performance. Ultra-fine spray could be obtained as the ratio of the pitch to orifice diameter was more than 10. It turned out that the interaction between the spray jets with the multi-injection design could be used to enhance the atomization processes of the micro-jet.