摘要
本研究探討氣助式超音波霧化器在空心管共振腔及對衝噴流共振腔中之噴霧特性。研究所採用之霧化器是以哈特曼聲音產生器產生超音波之高頻率震動，利用此震動的能量來對液體產生霧化作用，噴霧粒度以INSITEC粒徑分析儀量測。由流場觀測結果顯示，在適當的共振腔高度下，則噴霧錐角小於180 o，不會形成逆噴之噴霧，為穩定之操作條件，反之，若共振腔高度太小，則會形成逆噴之噴霧，落入不穩定之操作範圍。這是因為反向氣體動量與正向氣體及液體之正向動量產生不平衡，故會產生噴霧逆噴之不穩定情形。研究結果亦顯示，空心管型共振腔能改善噴霧平均粒徑，若共振腔再加上對衝噴流更能進一步改善其霧化特性，包括降低噴霧平均粒徑、Dv90、Dv10、噴霧粒度比(SR)。例如，CK-5型氣助式超音波霧化器配合A型共振腔，在共振腔高度為4mm，水壓5kg/cm2，氣壓6 kg/cm2下，所量測得之噴霧平均粒徑為27.78μm，而加了空心管型共振腔之後其噴霧平均粒徑則降為22.16μm，故其霧化效果顯著提昇。若再加上對衝噴流，其噴霧平均粒徑更進一步降到20.4μm。比較以上空心管型共振腔及對衝噴流共振腔所產生噴霧之Dv90、Dv10、噴霧粒度比(SR)顯示，對衝噴流共振腔噴霧之Dv90=51.03μm比空心管型共振腔噴霧之Dv90=64.9μm來的細小、對衝噴流共振腔噴霧之Dv10=10.73μm，比空心管型共振腔噴霧之Dv10=11.34μm更細，對衝噴流共振腔的噴霧粒度比為4.75，比空心管型共振腔的噴霧粒度比5.72還小，代表粒子範圍更窄。另外，研究結果亦顯示對衝噴流亦為氣液質量比之控制機制，若氣液質量比從0.84增加至1.09，其噴霧錐角會變小，霧化效果則大幅提昇，即其噴霧平均粒徑從20.40μm降低至13.65μm，Dv10及Dv90也分別降為8.14μm到32.87μm，噴霧粒度比則進一步降至4.04，故知對衝噴流具有效控制噴霧細微化之作用，對粒度分布範圍之窄化亦具有顯著之效果，
故為甚佳之霧化控制機構。

Abstract

Atomization performance of a Hartmann ultrasonic atomizer with hollow pipe resonator and impinging jet resonator is investigated in this research program. The high frequency vibration in the resonator provides energy for atomization of the liquid spray. The particle size of the spray is measured by INSITEC particle analyzer. Observation of the flow field shows that the spray cone angles are less than 180° with the proper resonator height. However, the spray cone angles may be larger than 180° when the resonator height is too low, a condition called the unstable operation. The unstable operation happens when the momentum of the reversal flow in the resonator can not be balanced by the momentum of the incoming air and liquid flow. SMD of the spray is found to be improved by hollow pipe resonator. Further improvement of the spray characteristics is also found in the case of impinging jet resonator. As a typical example, the mean particle size is SMD=27.78μm for CK-5 type ultrasonic atomizer with A-type resonator under h=4mm、Pw=5kg/cm2 and Pa=6kg/cm2 ,while SMD=22.16μm if the hollow pipe resonator is used. If the impinging jet resonator is used, particle size is further reduced to SMD=20.4μm. Comparison of Dv90、Dv10 and size ratio(SR) for the case of hollow pipe resonator and the impinging jet resonator shows the same trend. Dv90=51.03μm and 64.9μm for the impinging jet resonator and hollow pipe resonator, respectively. Dv10=10.73μm and 11.34μm for the impinging jet resonator and hollow pipe resonator, respectively. It turns out that the size ratio reduced to SR=4.75 of the impinging jet resonator, while the size ratio SR=5.72 in the case of the hollow pipe resonator. This implies that the impinging jet resonator has better atomization performance than other cases. Furthermore, the air to liquid mass ratio, ALR, is easily to adjust in the impinging jet case. Result shows that the particle reduces from SMD=20.4μm to 13.65μm as ALR increases from 0.84 to 1.09. The size ratio drops to SR=4.04 as well. Hence eighty percent of the particles are collected within 3 folds of particle size range. It is concluded that the impinging jet can be regarded as the useful mechanism to control the fine particle atomization and it can be used to narrow down the range of the
particle size distribution.

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