臺灣國際科展

毛細管內液體流速之探討及黏度測量方法之創新

科展類別
臺灣國際科展
屆次
2003年
科別
物理科
學校名稱
臺北市立麗山高級中學
指導老師
陳聲台
作者
鄭雨軒
備註
美國第五十四屆國際科技展覽會

摘要或動機

有一次上實驗課時看到鄰桌的同學正以實驗室的毛細管吸吮一瓶\r
葡萄汁,每當他吞嚥時,毛細管內殘餘的葡萄汁竟然以近似等速的狀\r
態降回果汁瓶裡,這似乎違背了重力加速度的常理,是毛細管的影響\r
嗎?還是葡萄汁特有的現象?這與毛細管插入葡萄汁的深度有關嗎?\r
這一連串的問題皆因升學壓力而無暇深究。\r
升上高中的那年暑假,我參加了學校舉辦的資優科學營,在物理\r
實驗課中恰好遇到了以毛細管測量液體黏度的實驗,使我有機會深入\r
思索毛細管內液體流速的問題。這個實驗很不好做,要調整兩個定高\r
容器,使水平毛細管兩端產生固定的壓差,讓流經管內的液體為等速\r
的流動。大家手忙腳亂地操作了近三小時,測出來的黏度不僅和老師\r
公布的答案差距甚大,而且各組同學所測得之結果也大相逕庭,不過\r
我們都體驗到了液體黏度對流速的影響。\r
實驗的誤差為什麼那麼大?扣除人為操作誤差後儀器本身還有多\r
大改進空間?有否更精簡的方法測量黏度?毛細管中液體的流速真\r
是固定的嗎?把毛細管斜置或是垂直架置,流速還會固定嗎?重力不\r
會影響流速嗎?若流速真為固定的,如何控制或改變流速呢?是否可\r
以利用流速來測出液體黏度?\r
由於我對這個實驗的專注,在學校選修的專題課程中即以此為題\r
目做長期的研究,在老師的指導下,我和同組同學不停地查閱有關書\r
籍及整理資料,漸漸研究清楚原理後定出實驗計畫,並開始購買材料\r
與工具,長期地動手實驗及改進,兩年來我們利用毛細管中液體的等\r
速及不等速流動的特性,發展出了兩種既精簡又準確的液體黏度測量\r
法,以下就是整個研究及創作的過程。\r
\r
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The viscosity is one of the most important parameters of the fluids. In conventional viscosity experiments, capillary-based viscometers are widely adopted because of their user-ready devices and moderate prices. However, to accurately measure the viscosity, the fluid velocity must be kept constant; otherwise, the fluctuation may cause the serious deviation. Besides, traditional capillary viscometers often require a long time to make the measurement. This research aims at exploring the capillary fluid mechanics and developing accurate and rapid methods to measure the viscosity. In this study, we developed two creative viscosity-measuring methods, the gravity sloping helical structure and the gradational liquid-level difference, and constructed two cost-effective capillary viscometer prototypes accordingly. The gravity sloping helical structure employs a long helical capillary as the flow channel and utilizes the gravity force to keep the fluid velocity extremely constant. The highlight of this method is that we can see the fluid flow through the capillary directly. On the other hand, the gradational liquid-level difference method uses the pressure sensors to precisely monitor the liquid-level difference, which drives the flow in the capillary, and allows automatic measurement of viscosity. Compared with computer simulation, the experimental results agreed well with the theoretical values. The gravity sloping helical and gradational liquid-level difference methods achieve 0.5% and 0.8% accuracy respectively. In addition, the automation of viscosity sensing also greatly facilitates the viscosity measurement. Furthermore, these two methods are both valuable for incorporating into educational purpose and industrial application.


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