不同歐氏數之高速雙液滴碰撞

Abstract

本次的實驗中，利用不同歐氏數的工作流體進行雙液滴碰撞的實驗，此次實驗皆為正向對撞也就是碰撞參數為零下的碰撞。實驗主要的目的在觀察液滴碰撞後產生的現象及探討其物理機制。此外，實驗中嘗試發展有別於利用氣壓缸噴出液柱並利用轉動圓盤截斷液柱產生高速液滴的設備，使用較為簡單的構想，利用高速的氣體帶動液滴，使液滴跟隨高速氣體流動進而達到高速的目的。 實驗重點為拍攝清楚的液滴碰撞現象，無論是低韋伯數區或是高韋伯數區。實驗能達到的韋伯數大約為5100，另一方面討論不同的歐氏數對於液滴碰撞的影響。 在高速液滴的碰撞下，會有破裂的情況發生，利用歐氏數，韋伯數及W(此無因次參數定義為產生破裂盤寬直徑除以液滴直徑)描繪出破裂盤寬趨勢線，破裂現象邊界趨勢線及飛濺現象邊界趨勢線。

關鍵字：液滴碰撞，高速液滴，碰撞參數，歐氏數，韋伯數。

In this study, we investigate the phenomena of droplet-droplet collision with different Ohnesorge number in a head-on collision condition, i.e., the impact number is zero. It aims at observing the phenomena of droplet collision and discussing the physical phenomena of that under a head-on situation. In addition, we try to find a different way from the original one to generate high-speed droplets. Instead of using a compressor to inject a liquid jet and then cutting it off into several droplets by a rotating disk, we simply let the accelerating air move through a tube and carry the droplets into high speed. One of the main goals of this experiment is to take clear photographs whether in lower Weber number or in higher one. The other is to achieve a relative high Weber number about 5100. On the other hand, we discuss how Ohnesorge number influences the droplet collision. Break-up phenomenon is observed in high-speed droplet collision. The Z-We and We-W figures which illustrate the trends of break-up diameter, break-up boundary, and splattering boundary are also obtained in this thesis, where Z indicates the Ohnesorge number and W is the non-dimensional parameter of the diameter of droplet with respect to the break-up diameter.

Keywords: droplet collision, high-speed droplet, impact number, Ohnesorge number, Webber number