本文主旨係以實驗方法探討二氧化碳氣泡衰減特性，藉由影像量測技術，以高速攝影機拍攝水中氣泡變化，進一步影像處理分析，可計算出氣泡之粒徑，同時利用水下麥克風收集氣泡噪音，經由快速傅立葉轉換分析後，由理論推導的氣泡大小。本實驗在成功大學水利及海洋工程學系光纖感測及聲學實驗室玻璃實驗水槽進行兩項實驗:實驗一為用針頭釋出二氧化碳單一氣泡，以影像法計算氣泡粒徑衰減程度；實驗二為用可變孔徑氣幕帶釋出氣泡幕，以影像及水下麥克風同步量測訊號，將結果加以比對探討。實驗結果發現，二氧化碳氣泡之粒徑在水中衰減程度除了從影像法得到明顯的衰減外，在溫度及壓力相近的環境下，氣泡粒徑衰減率會隨著氣泡粒徑越大衰減率則越小，甚至氣泡的衰減率會有負值之結果。另外，聲音訊號與影像資料經比對結果，在氣泡群中由於氣泡會互相撞擊、結合及分裂，所以無法在頻域圖中得到水中實際整體氣泡大小與數量。本研究以影像法及聲學法同時進行觀測，以影像來輔助聲學法判別氣泡大小，使其更具有說服力。本研究除了瞭解二氧化碳衰減特性，未來可以應用於軍事上船艦用氣幕帶之替代氣體等議題。

A series of images of bubbles were taken by a high-speed camera with the image process method to estimate the size reduction of carbon dioxide bubbles in water. An acoustic technique (passive method) with a hydrophone was simultaneously employed to measure the bubble signal spectrum by Fast Fourier Transform (FFT). Experiments were carried out in a glass water tank in the Department of Hydraulic and Ocean Engineering, NCKU. The first experiment is to release a single CO2 bubble with the needle at the bottom of the tank, and the reduction of the bubble size was measured with the photographic method during its rising process. In the second experiment, a bubble screen belt with the same orifice (0.3 mm in diameter) was used to generate the CO2 bubble cloud which was synchronously measured by both photographic and acoustic methods to estimate the bubble population. The result of the first experiment demonstrates that the CO2 bubble became to shrink when it rises to the water surface. This result is not agree with previous investigations to verify the carbon dioxide is soluble in the liquid. In addition, the acoustic method seems difficult to calculate the magnitude of bubble cloud since bubbles will crash coalesce, and divide when they rise to the water surface. However, the bubble signal spectrum measured by the acoustic method indicates the bubble sizes in the tank and they were also confirmed by the photographic method.

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