添加界面活性劑對U形微流道內排水效率與氣泡傳動之研究

Surfactant Effect on Drainage Efficiency and Bubble Transport in a U-shape Microchannel

馮啟棠(Chi-Tang Feng)

指導教授 ： 潘國隆

國立臺灣大學/工學院/機械工程學研究所/碩士(2013年)

https://doi.org/10.6342/NTU.2013.01639

摘要

本研究設計三種U形微流道並使用不同界面活性劑降低表面張力來分析氣泡產生的穩定、長度、頻率、分布、傳輸及排水傳輸效率，其中A、B、C-type主流道對U形及排水區域的寬度比分別為1:2:2及 1:1:2。由實驗結果知道在相同表面張力及型態下，添加不同界面活性劑會對氣泡產生有不同的結果。在C-type上可以利用 圖來區分氣泡型態以及氣泡的產生情形，並發現在Ca=0.005附近時為非濕潤性氣泡與濕潤性氣泡的過渡期，而濕潤性氣泡的氣泡產生頻率會比非濕潤性氣泡來的高；當流體的黏度越來越高以及表面張力越來越小時，不同的流量比會導致氣泡長度變化越來越大；對濕潤性氣泡而言，當排水傳輸越好時，氣泡上下游傳輸速度比率可以越高。最後，由以上分析知道C-type且濕潤性氣泡型態能在微流道中達到最好的排水效率。在氫氧燃料電池應用上，適合以C-type、低流量比且濕潤性氣泡型態；直接甲醇燃料電池應用上，適合以C-type、高流量比且濕潤性氣泡型態，且兩者的排水效率最高能達到90%，並遠高於傳統式機械鑽孔的排水效率；層流燃料電池應用上，在本實驗中吾人可以藉由水中添加界面活性劑，使氣泡產生頻率增加且使氣泡長度變短，而提升層流燃料電池效率。

關鍵字

微流體 ； 界面活性劑 ； 兩相流 ； 微流道 ； 氣泡

並列摘要

In this study, three kinds of U-shape micro-channels and different surfactants were applied to analyze the stability, length, frequency, distribution, transportation and the drainage efficiency of bubbles. The width ratio of the U area to the drainage region between A, B, C-type main channel is 1:2:2 and 1:1:2 respectively. The experimental results show that different phenomena will occur with different surfactants. In the results of C-type, we use a Ca-We diagram to categorize bubble generation patterns. The diagram shows that the transition boundary between non-wetting bubbles and wetting bubbles occurs at about Ca=0.005. The wetting bubbles have higher bubble generation frequency, compared to non-wetting bubbles. When the fluid viscosity is higher and the surface tension is smaller, different flow ratio causes the air bubble length to change more significantly. For a wetting bubble, the ratio of transportation rate in upstream to that in downstream is higher when the draining rate of water is larger. From the analysis, the C-type with wetting bubble patterns in the micro- channel can achieve the best drainage efficiency. For the hydrogen fuel cells, therefore, C-type is with the better choice regarding the low ratio of flow rate and wetting air bubble patterns. For direct methanol fuel cells, requiring high flow rate ratio and the wetting bubble patterns, C-type is the adequate one. The highest drainage efficiency of both types can reach 90%, and it’s much higher than traditional mechanical drilling drainage efficiency. This experiment used surfactant in water to increase the bubble generation frequency and shorten the bubble length, which can elevate the efficiency of laminar flow-based fuel cells.

並列關鍵字

Micro-fluidics ； surfactants ； flow ； micro-channel ； bubble

參考文獻

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