本研究以自由液滴法研究兩顆液滴在一對流環境下，流線向之相互影響性。實驗參數分別為：液滴直徑(di)、液滴初始間距(Si = s/di)、冷流場環境與熱流場環境(vg)，s為兩顆液滴之中心距離，使用流體為水與十二烷。本研究主要分為水液滴在冷流場環境與熱流場環境下，流線向之相互作用，以及十二烷液滴在熱流場環境下，流線向之相互作用兩部分。
實驗結果顯示，當兩顆液滴在落下飛行的過程中，後方液滴會受到前方液滴的尾流影響，因此後方液滴的速度(v)會略大於前方液滴，並且由於阻力係數(CD)較低的因素，進而發生後方液滴追撞前方液滴的現象。此液滴追撞行為可分為同軸碰撞與非同軸碰撞，其碰撞行為模式只有碰撞黏合一種，但在熱流場環境下，有機率會觀察到液滴在黏合過程有氣泡膨脹之現象。此外，增加液滴初始間距(Si)或減少兩顆液滴雷諾數(Re)可發現液滴碰撞點(xc)位置會有延後發生的現象，但液滴初始間距(Si)的影響性比雷諾數(Re)大。
兩顆十二烷液滴在熱流場環境下，由於會有蒸發與燃燒的現象發生，因此液滴之間的相互作用與水液滴完全不同。十二烷液滴在落下飛行的過程中，沒有觀察到液滴碰撞的現象發生。這是由於液滴的火焰會使得局部環境溫度與流場對流產生變化，進而影響兩顆液滴在飛行過程的縱向與側向間距變化，以及火焰型態的轉換模式。
研究結果指出，液滴直徑(di)和液滴初始間距(Si)皆會影響到兩液滴之間的相互作用強度，但初始間距(Si)的影響性比液滴直徑(di)大。液滴的火焰轉換過程可歸納成四種模式，而液滴蒸發速率則是受到直徑、間距與火焰結構的不同而有所變化。

The interaction of two drops in the direction of the stream is studied experimentally using a free-falling drop apparatus which provides different gaseous flows, cold flow (vg = 0 - 0.5 m/s) and a hot flow (vg = 2.5 m/s). Both water and dodecane were used in the experiments, and thus there are two main parts to discuss.
Two aligned water drops moved downward in the same direction of cold and hot flow. It was found that the travelling velocity of the trailing drop was higher than that of the leading drop due to the wake effect. The merging collision process was found to the same for three different flows. However, the position of the merging collision of the drops shifted downstream of the flow with a greater initial drop spacing and higher initial gas velocity, and this weakened the wake effect. It was found that the initial drop spacing was more dominated than the initial gas velocity in this experiment.
Two aligned dodecane drops moved downward only in hot flow. The two dodecane drops were affected by the interactions among the thermal expansion, convective effect caused by the different flame structures in the combustion chamber, and exhibited four main flame transition modes. It was found that the interaction of two drops was dominated by the initial drop spacing (Si), with the initial drop diameter (di) also having an effect. The different flame structure and Reynolds number would affect the vaporization rate (k) of a leading drop or a trailing drop.

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