液滴撞擊液體引致不同型態氣泡之聲學與溶氧研究

Acoustics and Dissolved Oxygen Induced by Bubbles during Drop Impact

洪維聰(Wei-Tsung Hung)

指導教授 ： 王安邦

國立臺灣大學/工學院/應用力學研究所/碩士(2007年)

https://doi.org/10.6342/NTU.2007.02749

摘要

本文以實驗探討液滴撞擊液體過程所產生不同特徵型態氣泡，及其所引致的水下聲音與溶氧特性。本文之實驗結果分為四大部分並簡述如下：
第一部分對單顆液滴撞擊液體過程在水面下所產生之不同特徵型態氣泡實驗，除了完整的印證前人於液滴撞擊速度對液滴粒徑圖(簡稱v-d圖)之特徵型態外，另外也發現了兩個新的特徵區域：「新馬斯勒區」與「穿透型漂浮氣泡區」。另外，由不同撞擊型態過程之影像數位定量分析，發現在無因次時間0.4-1.4間，所有撞擊過程所產生的水漥寬深比(W/D)均為2，意即在此段時間水漥以半球型擴展。
第二部分對單顆液滴撞擊液體在水面上產生漂浮氣泡之實驗，本文首度發現水面上所產生漂浮氣泡並非如過去文獻所得之機率結論：即撞擊速度超過3m/s有50%機率會產生漂浮氣泡；而是決定於液滴撞擊液面前一瞬間之形狀參數與液滴撞擊速度。要產生水面上漂浮之氣泡，形狀參數愈高，所需之撞擊速度愈低。
第三部分對單顆液滴不同撞擊型態在水面下所產生不同之聲音實驗分析中，本文除在文獻中首度圖示比較不同撞擊型態所引致之聲壓模型外，並發現不同撞擊型態中以「穿透型漂浮氣泡」撞擊會產生最大聲壓，而「規則型」撞擊所產生之聲音頻率最高(約10-15k)。
第四部分對複數顆液滴不同速度、液滴粒徑與液滴撞擊頻率下所產生水中溶氧變化之實驗，本文得到一重大發現：即有效利用單顆液滴不同撞擊型態之知識為基礎，不需以大液滴、高速、高撞擊頻率亦可產生高的水中溶氧。此結果除可開啟液滴撞擊研究的一連串新領域外，此結論並有助於發展水產養殖業大量節省用水與用電的新方向。

關鍵字

液滴撞擊型態 ； 捲入氣泡 ； 液滴振盪 ； 漂浮氣泡 ； 水下聲學 ； 溶氧

並列摘要

The impact of a droplet on a liquid surface can result in different fantastic phenomena. In our experiment, we use high-speed camera, hydrophone, and DO meter to catch the impact phenomenon, sound signals and the magnitude of dissolved oxygen, respectively.
Many investigations have been conducted since decades; however, very few have been studied for the floating bubble induced by the impacting droplet since Worthington (1908). In the present study, floating bubble induced by the droplet impact has been experimentally studied and analyzed. Effects of impact velocity, drop size, oscillation parameter and depth of target liquid have been investigated and discussed. The oscillation parameter, sharpness ratio e, of free-falling droplet, defined as the ratio of maximum length of droplet in the vertical to the horizontal direction before impact has been found to be one of the most important controlling parameters in the present study.
The phenomena of free falling drop impacting into the deep water and their corresponding mechanism to generate sound under water have been experimentally investigated in this paper. Comparing with previous studies by Pumphery and Elmore (1990), new characteristic mode “Penetrated Floating Bubbles” and new Mesler regimes in the v (impact velocity)—d(diameter of droplet) map have been discovered by using hydrophone and high-speed carmera for the sound and image analysis.
The maginitude of dissolved oxygen is measured for different impact modes. Some characteristic initial conditions will lead oxygen dissolved most instead of those with larger impact velocity, larger drop size and higher frequency of drop generation. Include DO, the two above mentioned paragraphs are the main three sections in our results and discussion.

並列關鍵字

drop impact ； bubble entrainment ； drop oscillation ； floating bubble ； underwater acoustics

參考文獻

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