本研究以自由液滴落下方式探討兩顆液滴群、三顆液滴群與液滴串在不同環境初始氣體流速的條件下，分別觀察液滴的速度、雷諾數、阻力係數與液滴之間的相互影響性。同時探討液滴串在不同直徑下液滴間的相互影響性。實驗參數分別為：液滴初始直徑(di)、液滴初始間距(Si = S/di)、環境初始氣體流速(vg)，其中S為兩液滴間中心距離，使用液滴流體為水。
實驗結果顯示，液滴速度會受重力影響並會隨著落下距離的增加而增加，而在液滴落下過程中，後方液滴會受到前方液滴尾流影響而有追撞黏合現象的發生。依照不同的實驗條件會有第一次碰撞黏合或第二次碰撞黏合發生，在液滴串的條件下更有第三次碰撞黏合的發生，而碰撞黏合模式又可以分為同軸碰撞與非同軸碰撞。在此之間的變化過程，其液滴受到尾流的影響性則是會隨著雷諾數或是液滴尺寸的變化而改變。
由不同的實驗條件結果可知，環境初始氣體流速(vg)、液滴初始直徑(di)與液滴初始間距(Si = S/di)的增加會使得碰撞點延後並降低碰撞次數。此外，在固定液滴初始直徑(di)和環境初始氣體流速(vg)的條件下，增加液滴數目亦會使碰撞點延後並降低碰撞次數。而在碰撞過程中，第一次碰撞黏合趨勢與第二次碰撞黏合趨勢或第三次碰撞黏合趨勢會有所不同。

In this study, the interaction of a stream of water drops aligned in a vertical direction was examined experimentally using a free-falling drop apparatus, which provided different gaseous flows, namely, no flow (quiescent air, vg = 0 m/s), convective air flow (vg = 0.3 m/s and 0.5 m/s) and hot flow (vg = 2.5 m/s). The initial drop diameter (di) was kept at 900 μm. In addition, there were three different numbers of drops to consider in the study, two drops, three drops and a drop stream, and three initial dimensionless drop spacings, Si ≈ 2.5, 5 and 10, were selected in the experiment. In the second part, two different initial drop diameters were considered, 900 μm and 1100 μm.
The results showed that the merged collision of drops is controlled by the wake effect, which depends on the initial drop spacing (Si), Reynolds number (Re), initial drop diameter (di), and number of drops. The initial drop spacing has a dominant influence in comparison with the others. In the downward moving process of drops with given values of Si and di, the initial merged collision of the first two drops was observed, after which they merged into a large drop; thereafter, this large drop was caught by the rear drop to achieve the second merged collision. The first merged collision occurred either along the same axis or in an off-center situation, but the second merged collision occurred only in the off-center situation. The results showed that the merged collision position shifted to the downstream region with increases in vg, Si, di or the number of drops under fixed di and vg.

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