液滴撞擊旋轉表面研究

Liquid Droplet Impact on a Rotating Surface

李克威(Ke-Wei Li)

指導教授 ： 周復初

國立中央大學/工學院/機械工程學系/碩士(2006年)

摘要

本研究目的在於討論液滴撞擊在旋轉表面時，所發生的各種現象。實驗中液滴產生器由針筒和補液系統所組成，進而運用不同的掉落高度來產生不同的撞擊速度；為比較不同表面張力的影響，實驗所使用的液體為純水和酒精；撞擊表面為一個十二吋的矽晶圓，而旋轉的速度由控制器所操作，實驗過程中，表面切線速度由旋轉半徑以及轉速所決定。所有的實驗結果由影像的方式，使用高速攝影機拍攝，以千分之ㄧ秒的時間尺度量測影像中的液滴撞擊速度與液滴直徑。實驗中最重要之參數為韋伯數（Ｗｅ）和表面切線速度，隨著這兩個變數探討現象的變化。由實驗結果得知當表面切線速度為零時，隨著韋伯數的增加，水液滴撞擊會由附著現象轉變成手指不穩定性的現象，而酒精液滴撞擊會由附著現象變成飛濺。當表面切線速度隨著韋伯數改變，在水液滴撞擊實驗中顯示六個形變特徵：附著、手指不穩定性、尖端質量累積、手指擴散、平滑表面飛濺，以及手指狀表面飛濺。而酒精液滴實驗結果顯示，除了附著、尖端質量累積、平滑表面飛濺，以及手指狀表面飛濺四種特徵與其相似，另有:飛濺、前端薄膜飛濺，和水液滴撞擊有顯著的不同。實驗得知，當表面切線速度足夠大時，空氣膜就會影響液滴撞擊後的變化。

關鍵字

液滴 ； 旋轉表面 ； 韋伯數

並列摘要

An experimental study is presented for liquid droplet impingement on a rotating smooth wafer. The liquids used to obtain different surface tension are water and alcohol with given properties. Tangential velocities of the surface are given by the rotational radiuses and rotating speeds. A single droplet released from a needle is falling onto the wafer due to gravity. The impact process is recorded by two high speed CCD cameras providing vertical and lateral views. As the wafer is static, the evolution of water droplet impact with increasing Weber number varies from deposition (We < 115) to fingering (We > 132). As to alcohol droplet impact, the evolution is from deposition (We < 184) to splashing (We > 214). Statistically, regimes of features: (a) deposition, (b) fingering, (c) tip accumulation, (d) finger spreading, (e) air-cut film with smooth front, and (f) air-cut film with fingering are observed in water droplet impact under different Weber numbers and tangential velocities. And regimes: (a), (c), (e), (f), (g) splashing, and (h) front sheet are also found in alcohol droplet impact. Experimentally, the effect of air layer during impact is not negligible as the tangential velocity is large sufficiently.

並列關鍵字

Droplet ； Rotating Surface ； Weber Number

參考文獻

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