本實驗研究旨在探討平行板間單顆上升氣泡引起的流場特性。本研究透過高速攝影機拍攝，可視範圍(Field of View, FOV)使用質點影像測速法(Particle Image Velocimetry, PIV)配合多時間間距速度計算法來量測液體相之流場，為了模擬污泥流變特性，實驗除了在清水中進行，另在兩種不同黏度羧甲基纖維素(carboxymethyl cellulose, CMC)溶液下進行，兩組CMC分別為0.05%、0.15%，實驗中於水槽底部注入一體積3毫升的氣泡，探討相同氣泡體積在不黏度溶液下其引起的流場特性。
　　試驗初期由流場可視化觀察到氣泡通過後之尾跡流場十分紊亂，因此所有試驗條件均重覆進行30次PIV流場量測，而為了確保每次進氣條件一致，本實驗自製一組簡單但精準的進氣系統，確保相同體積的氣體注入不同黏度溶液水槽中，並對氣泡的幾何形狀分析，單顆氣泡的形狀再現性高。
　　PIV使用高速攝影機搭配105 mm鏡頭、設定PIV相關參數，分別拍攝XZ平面(FOV = 50 mm x 34 mm)，YZ平面(FOV = 6 mm x 15 mm)，在極微小的觀測面，能有效分析其速度場，再由速度場獲得剪切速率場(shear rate)，並透過流變儀量測溶液以及使用Sisko模式擬和溶液黏度與剪切速率關係計算其剪應力場。
　　在氣泡前方流場從時序列分析可發現，流場再現性相當高也十分穩定，不同次拍攝的流場變化幾乎一致，流體最大速度近乎氣泡浮昇速度，三者溶液相比結果差不多；在氣泡尾部流場，同一溶液每次拍攝在微觀氣泡形狀上有些許不同以及液體黏度不同以致，低黏度流場發展紊亂，高黏度流場發展相對穩定；在時序列、速度剖面分析也發現，氣泡下方的流場速度逐漸大於氣泡本體上升的速度，原因來自於兩側向下的流體因渦旋的產生，將部分能量傳回水槽中間區域，使得中間區域的流速逐漸大於氣泡本體速度，隨後流場遞緩。
　　在清水、0.05% CMC、0.15% CMC，相同氣泡條件3毫升氣泡所引起的流場，儘管清水的剪切速率較大，剪切速率較低的0.15% CMC溶液流場對壁面會產生較大的剪應力最大可達1.4 Pa左右，0.05% CMC最大剪應力約可達0.8 Pa，而清水最大剪應力約可達0.6 Pa。

This study aims to investigate the characteristics of the flow field caused by a single rising bubble between parallel walls (i.e., the virtual geometry in flat-sheet membrane bioreactor). Particle Image Velocimetry (PIV) and multi-time interval velocity calculation method were conducted to measure the flow field caused by a 3 ml bubble. To simulate the rheological behavior of sludge , a transparent rheological fluid, carboxymethyl cellulose (CMC), was prepared in various level (0% - 0.15%) for PIV measurement. The time-series analysis result showed that the velocity increased exponentially followed by achieving bubble buoyancy velocity with high reproducibility among 30 times repeated tests for each case when the rising bubble closing to the measuring point from bottom. However, the following flow field varied a lot after bubble passing through the point among three tested CMC solutions. Briefly, maximum rising velocity could be 1.4 – 2.0 times higher than bubble buoyancy velocity both in long side and short side of rectangular tank, and wake developed with high turbulence in clean water while the velocity dropped down quickly with less turbulence in 0.15% CMC solution. Considering the shear stress near the wall, the maximum shear stress was found about 1.4 Pa for 0.15% CMC, 0.8 Pa for 0.05% CMC, and only 0.6 Pa for clean water according to Sisko model for non-Newtonian fluid, even though both velocity and corresponded shear rate were higher in clean water rather than in high viscosity CMC solution.

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