摘 要
本研究探討單流體微型噴嘴之霧化機制及其霧化特性，微型噴頭孔口直徑為100 μm，共振腔高度為400 μm，共振腔直徑為3000 μm，工作流體為純水。研究項目包括多孔噴頭微液柱之暫態演變過程及其穩態破裂過程，並探討微液柱在高壓下，空蝕共振效應對其霧化特性之影響。本研究以IDT高速攝影機拍攝微液膜及微液柱在共振效應下之演變過程，以Malvern RT-Sizer粒徑分析儀量測噴霧粒度及粒度分佈。研究結果顯示，多孔噴頭微液柱由於微流體表面張力之作用甚大，液體先在個別微噴嘴出口處形成半月型之液膜，此等液膜隨時間逐漸成長，從半月型之液膜演變為球狀體，由於液體表面張力與慣性力之平衡，個別球狀體亦逐漸成長，乃至與鄰近之球狀體相互結合，進一步成為錐狀體。當液體慣性力持續增加，錐狀體逐漸形成個別分立之不穩定噴射液柱，並在下游處相互纏繞，形成鎖鍊形噴流。在相同液體壓力下，當噴頭之孔數增加，由於鄰近噴流間之交互作用，會增強噴流之不穩定能量，故液柱暫態演變過程變長。研究結果亦顯示，微管流之液柱動態特性隨液體雷諾數而變。當雷諾數Re < 152時，雙孔噴頭之液柱為雙股之鎖鏈型態，單孔噴頭之液柱則呈現穩定的模態；當雷諾數Re > 152時，單孔及雙孔噴頭之液柱均為穩定模態；當液體雷諾數為Re = 230時，單孔與雙孔的液柱，皆呈現軸對稱不穩定模態。當雷諾數Re > 230時，雙孔噴頭的液柱會因交互作用，開始出現螺旋不穩定模態，單孔噴頭則在雷諾數Re > 275時才開始出現螺旋不穩定模態，並與軸對稱不穩定模態同時存在。當雷諾數Re > 350時，雙孔噴頭之液柱為螺旋不穩定模態所主導，單孔噴頭之液柱則在雷諾數Re > 617時液柱才會為螺旋不穩定模態所主導。顯然多孔噴頭液柱間之交互作用具有激發不穩定模態之效應。研究結果亦顯示，隨噴頭孔數及液體出口雷諾數之變化，空蝕數皆在0.5以下。根據文獻顯示，當空蝕數在0.94以下時，在腔體中會產生空蝕現象，顯示在本研究之實驗條件下，腔體中有空蝕現象之產生。實驗結果發現噴霧平均粒度與噴嘴霧化效率會隨空蝕數降低而減小，當噴頭孔徑為100 μm時，噴射壓力從50bar 遞增至125 bar，則噴霧平均粒徑從11.06 μm遞減至6.29 μm。當噴射壓力為125 bar時，若噴頭孔數為雙孔、四孔及六孔時，噴霧平均粒徑分別為7.22 μm、8.49 μm、9.27 μm，顯示多孔噴霧間因為粒子碰撞結合現象，呈現噴霧粒徑隨噴頭孔數而遞增之現象。噴霧產生量則隨噴頭孔數之遞增而線性增加，當噴射壓力為125 bar時，噴頭孔數為單孔、雙孔、四孔及六孔之噴霧產生率分別為3.72 kg/hr、7.33 kg/hr、15.73 kg/hr、及24.08 kg/hr，顯示單流體微噴嘴可以產生10微米級之大流量噴霧，可以因應產業上大流量細微噴霧粒子之需求。

Abstract
Enhancement of atomization performance of pressure atomizer with resonance effects in a multi-apertured nozzle are investigated in this research. The nozzle is installed with disposable orifice plates for different applications. The orifice plates are designed with single and multiple orifices having diameter and pitch of 100 μm and 2000 μm, respectively. The diameter and height of the resonator are 3000 μm and 400 μm, respectively. The particle size of the spray is measured by Malven RT-sizer. The evolution of the multi-apertured micro-jet during the transient break-up processes was studied using IDT-high speed video camera. Results show that the liquids first formed a meniscus around the outlet of the orifice because of the strong effects of the surface tension associated the micro-jet. The meniscus was transformed to the spherical shape as the inertia of the liquid was increased with time. The spherical shape further grew up based on the balance between inertia force and surface tension and became a conical shape near the orifices. The liquid jets were quite unsteady and finally became a chain of liquid jet in the downstream. The interactions between the liquid jets were observed as the number of the orifice was increased. The liquids from different orifices were merged together during the transient processes. However, they were separated each other as the inertia of the liquid jets were further increased. Results also showed the evolution of the instability modes of the liquid jets as the Reynolds number increased. In the case of the nozzle with double orifices, the liquid jets became a series of chain modes due to the interaction between jets as Re<152. It became relatively steady as Re>152.The instability modes of the both liquid jets further changed to the axi-symmetric mode as Re= 230. Both of the axi-symmetric and helical modes appeared as Re>230. The instability of liquid jets was further transformed to the helical mode as Re>350. As comparison, for the nozzle with single orifice, both of the axi-symmetric and helical modes appeared as Re>275. It transformed to pure helical mode as Re>617. It is concluded that the interactions between adjacent jets enhanced the unsteadiness of the multi-apertured liquid jets. It is also found that the cavitation numbers of the flow under the test conditions employed in this research were all under 0.5. As reported in the literature, the cavitation phenomenon appeared in the flow as the Cavitation number was less than 0.94. Hence it is expected that cavitation occurred in the nozzles with various orifice plates. Results showed that the particle size and the atomization efficiency were decreased as the Cavitation number was reduced. It was also found that the mean particle size of the spray decreased from 11.06 μm to 6.29 μm as the injection pressure was increased from 50 bar to 125 bar in a test using a single orifice plate. The particle size was further increased as the number of the orifices was increased. It turns out that the mean particle size and spray production rate increased from 7.22 μm to 9.27 μm and 3.72 kg/hr to 24.08 kg/hr, respectively, as the number of orifice was increased from two to six. It indicates that the new atomizer performs better as comparing to the traditional diesel-type atomizers.

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