本研究以水為工作流體，主要實驗參數為初始液滴直徑(di)、液滴韋伯數(We)、液滴撞擊時間(△t)、平板粗糙度以及平板傾斜角度(ɸ)。本研究的液滴撞擊時間(△t)分為六個條件: △t為單顆液滴撞擊， △t1到△t5為不同時間差的兩顆液滴碰撞。△t1為第二顆液滴在第一顆液滴開始擴展的時間撞擊； △t2為第二顆液滴在第一顆液滴達到最大擴展直徑的時間撞擊；△t3為第二顆液滴在第一顆液滴直徑開始回縮向上的時間撞擊；△t4為第二顆液滴在第一顆液滴直徑達到回縮高點的時間撞擊；△t5為第二顆液滴在第一顆液滴直徑回縮後穩定的時間撞擊。
在單顆液滴撞擊平板的研究結果顯示，液滴撞擊在高粗糙度的平板時，並沒有回彈的現象產生，但液滴撞擊在低粗糙度的平板(疏水性表面)，會有回彈的現象發生；對比液滴韋伯數We = 50和60，可發現撞擊現象相似。兩顆沿流線向液滴撞擊在高粗糙度的平板時，也沒有發生回彈的現象，但在△t2的條件下，可發現液滴在收縮的過程，會有最大高度的現象產生。當兩顆沿流線向液滴撞擊在低粗糙度的平板(疏水性表面)時， △t1與△t2的條件可觀察到液滴收縮之後的回彈與斷裂現象，但△t3到△t5的條件，由於增加兩顆液滴撞擊的時間差，因此第一顆液滴會在收縮與回彈的過程與第二顆液滴進行碰撞；此時會由於第二顆液滴向下的動量與第一顆液滴回彈向上的動量相互抵銷，因此沒有產生兩顆液滴撞擊之後的回彈與斷裂現象。

The Investigation of the dynamic effect of the water drop on the flat plate was performed. The drops were generated using the free-falling drop technique with the drop generator and the drop severance device. While performing the experiment water at 25°C (room temperature) was used as the working fluid and the drop impact velocity on the hydrophobic glass plate was 2 m/s. In our experiment we have specifically focused on the effect of the initial drop diameter (di) and oblique angle (ɸ) of the hydrophobic glass surface on the impact phenomena.
The investigation considers six different impingement conditions differentiated by the different time intervals (△t), namely Case 1: single drop impingement; Case 2: △t =△t1 (the leading drop starts to spread); Case 3: △t =△t2 (the leading drop spreads to maximum); Case 4: △t =△t3 (the leading drop starts to retract and form peak); Case 5: △t =△t4 (the leading drop retracts to from a dome shape); Case 6: △t =△t5 (the leading drop starts to stabilize). Notably, all of the cases correspond to the approximate same initial drop diameter.
For the case of the single drop impingement on the different roughness surfaces the surface with high roughness don’t allow the drop to retract back much and the low surface roughness makes the drop rebound-off the surface. The comparison of the 50 and 60 Weber number the impact characteristics were found similar. However, the two-stream wise drop impacting the low roughness surface hydrophobic glass surfaces will rebound-off the surface after spreading but if the time interval between the two drop increases the air gets trapped so the drop stays on the surface even after spreading. For the oblique angle hydrophobic glass surface the two-stream wise drop impacting spreads less and rebounds - off the surface and takes relative long time in comparison with the flat surface to strike back to the surface.
However, the two streamwise drops impacting on the low roughness surface hydrophobic glass surface will rebound-off the surface after spreading for the cases of △t1 and △t2. The results of △t3 to △t5 shows the merged drop stays on the surface even after spreading.

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