本研究主要使用非侵入式、高解析度之平面雷射激發螢光技術(PLIF technique)觀察同質雙衝擊噴流之二維霧化液滴質量與混合分布；實驗使用內徑為0.3mm之噴孔(L/D=5)產生兩股高速液柱以60° (+30°/-30°)為衝擊角相互撞擊，且以液柱衝擊動量比等於1為設定前提，於完全發展模式(Fully developed state)下探討總動量通量改變對衝擊噴流混合特性之影響；本研究主要使用純水、10vol%丙酮水溶液與20wt%甘油水溶液為工作流體進行實驗觀察。於分析方面以穿透百分率(Penetration percentage, P.P.) 作為噴流混合狀態之參考指標；以實驗設定條件而言，理想上噴流之穿透百分率應為50%，但實驗結果顯示於不同之動量通量操作狀態下，穿透百分率皆大於50%。此外隨動量通量增加，穿透百分率則呈現一先上升、後下降，而再緩緩上升之三階段特徵趨勢變化；且當穿透百分率接近50%時，衝擊噴流則具有最佳的混合狀態。為了解此特殊三階段穿透百分率之形成原因，本研究進一步以高速攝影機進行實驗觀察，結果顯示衝擊噴流之液柱表面具有不穩定之波動產生，主要可區分為葫蘆狀之軸對稱曲張波(Axisymmetric varicose wave)與非對稱螺旋波(Asymmetric helical wave)。而不穩定表面波的形成使得液柱於撞擊瞬間會引起噴流的不穩定擾動，而其擾動強度與擾動模式會直接影響噴流穿透百分率(混合)的大小；軸對稱曲張波易因表面波本身之相位角差異使得液柱碰撞瞬間引起不穩定之動量通量擾動(Momentum flux fluctuation)，而非對稱螺旋波易使得衝擊噴流於衝擊點產生歪斜碰撞(Skew impingement)現象。此外，本研究亦使用具不同物理性質之丙酮水與甘油水進行衝擊噴流混合現象的觀察；結果顯示丙酮水與甘油水之衝擊噴流隨動量通量的增加，其穿透百分率亦有相似之三階段特徵趨勢變化；但其進入完全發展模式狀態的起始點與其穿透百分率變化的強度會有個別之差異；此結果證明流體物理性質的不同會改變衝擊噴流完全發展模式的時機與液柱不穩定表面波之擾動振幅與波形發展，亦進一步影響整體衝擊噴流的混合狀態。

This research utilizes the planar laser-induced fluorescence (PLIF) technique and high-speed photography to determine the mixing characteristics of equal-momentum like-doublet impinging jet sprays in fully developed conditions of three test liquids (water, 10 vol% acetone-water, and 20 wt% glycerol-water) with different physical properties. The injector composes of two 0.3mm diameter orifices at 60° (+30°/-30°) impinging angle. The penetration percentage (P.P.) of droplets passing through the center plane of the sprays from either jet is identified to characterize the mixing phenomena. In this experimental setup, the mixing ideally occurs at P.P. of 50%, indicating that the effects of convection and diffusion on liquid mixing are fully relaxed. However, all the penetration percentages (P.P.) observed in this study are over 50%. The analyses show that the state of the jets at the impinging point has crucial effects on P.P. The high-speed photography shows that the growth and the propagation of the instability waves on the surface of liquid jets are the controlling factors. The three-stage P.P. variations with momentum flux in fully developed conditions are induced by jet momentum flux fluctuation at impingement resulted from the onset of axisymmetric varicose waves on the free jets, and by the skew impingement resulted from the growth of asymmetric helical waves on the jets at impinging point. Besides water, both acetone-water solution and glycerol-water solution of different physical properties are also used to verify the three-stage P.P. variation observed in water spray. The similar three-stage P.P. variations are also observed in the acetone-water and glycerol-water sprays; however, the onset of the fully developed state and the points where the stages change occur at different momentum fluxes, and their corresponding P.P. values in each stage also vary. The results show that changes in physical properties of liquids influence the development of spray pattern for impinging jet spray and the fluctuation intensity and development of the instability surface waves of free liquid jet, which significantly influence the state of mixing in impinging jet sprays.

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