臺灣博碩士論文加值系統

本研究利用數值模擬與實驗的方式觀察微管道中之流體行為，並藉由設計ㄧ具有阻塊之突擴管以探討管道中渦流生成之機制，藉由量測管道中之不同流向之壓力差，提出一微流體整流器之應用。
本研究主要分為三個部分：第一，分析阻塊與突擴處距離分別為100~1100 μm時之渦流生成行為，並探討渦流生成至達到完全發展(Fully developed)時，其面積與阻塊距突擴管肩部距離之關係。由該部分研究結果顯示，當阻塊距離突擴處為1000 μm時，其渦流發展開始呈現穩定狀態，意即渦流面積不再隨阻塊距離而變化。第二，本研究並觀察固定阻塊距離下渦流成長行為隨流速之關係，研究結果發現，渦流之生成會有四個階段。首先會在管道突擴處產生第一渦流，接著再於阻塊後方產生第二渦流，當流速(雷諾數)持續增加時，阻塊兩側會產生面積較小的第三渦流，最後第二及第三渦流會結合成一較大渦流。此時，僅於管道突擴處與阻塊後方出現兩對渦流，因此得知渦流的產生並非昔知的兩對，而是漸進式的發展。並隨著Re增加至555時，渦流之中心處會產生不規則震盪，而此現象是受到流體之慣性作用變大而造成渦流剝離(Vortex shedding)所致。第三，本研究並針對管道之順逆向流場於不同流速下之壓力降及流場分析，以探討本研究所設計之結構於流體整流之效能。結果顯示，當逆向流體進入突縮管時，阻塊後方亦會有渦流產生，且渦流會因管道突縮之影響，而有束流現象發生。且當雷諾數增加至Re = 416時，會在束流與管壁側產生成對漩渦。此外，由順逆向流之壓力量測結果顯示，逆向流在較高流速時由於渦流擠壓所形成的虛擬閥門(Virtual valve)作用，因此所測得之壓力會大於順向流。本研究利用一評估流體整流器效能的因子Diodicity (Di) 進行不同流速下之整流效能分析。研究顯示，當Re = 172時，經由三維模擬之數值結果顯示，其最大效能為1.76，且該條件下之實驗結果亦可高達1.5，此效能比起一般需要以複雜管道設計及製程技術之微流體整流器之效能還要更好。本研究之結果對微流體之基本行為及元件設計，有更清楚的瞭解與貢獻。

This study investigates the flow behaviors of the microflow in a sudden expansion microfluidic channel with a rectangular block structure. 2D and 3D numerical simulations are used to predict the vortex formation behavior and experimental approaches are adopted to confirm the simulated results. A novel microfluidic rectifier is proposed by operating the designed microfluidic device under opposite flow conditions. The performance of the flow rectifier is also evaluated under difference flow velocities.
There are three parts finished in this thesis. Firstly, the vortex formation behavior is investigated for the microchannel with the block at different distances downstream the sudden expansion channel. The size of the fully developed vortices is measured and analyzed. Results show that the size of the vortex reaches stable while the distance between the block and sudden expansion channel is longer than 1000 μm. Secondly, this study also investigates the sequence of the vortex formation under different flow velocity (Reynolds number). Results indicate that there are four stages for the vortex formation in the microfluidic channel. Vortices are formed firstly at the sudden expansion channel and then behind the block. Two small vortices are then formed once beside the block and then merge with the two big vortices behind the block under increasing velocity conditions. The flow becomes instable once the Reynolds number higher than 555, two symmetrical shedding flows are observed behind the block structure. This flow behavior is rarely observed in a microfluidic channel due to the big viscous force of the flow in the microchannel. Thirdly, this study measures the pressure drops for the forward and backward flows under different flow speeds. Results show that the vortex formation behavior in backward flow is different from it is in forward conditions. Two symmetric vortexes are formed beside the channel while the Reynolds number higher than 416. The squeezed vortices form a virtual valve structure and increase the flow resistance of the microflow, resulting in a high performance valve structure. The calculated results indicate that the diodicity (Di) of the designed microchannel is as high as 1.76 and 1.5 for the numerical result and experimental result, respectively. The rectifying performance of the developed microchip device is higher than the reported devices fabricated using delicate processes and designed. The results of this research will give valuable knowledge for the flow behavior in a microchannel and the design of microfluidic chips.

目錄 I
圖目錄 IV
表目錄 IX
符號表 X
簡寫表 XIII
中文摘要 XIV
英文摘要 XVI
第1章 緒論 1
1.1前言 1
1.2微管道中流場行為分析 2
1.3渦流於管道中的發展 8
1.3.1管道形狀設計 9
1.3.2管道內增加阻塊 13
1.3.3外力作用 16
1.3.4 渦流於突擴管道之生成分析 18
1.4渦流於微管道中之應用 21
1.5研究動機與目的 30
1.6論文架構 32
第2章 基本理論與數值分析 34
2.1基本假設 34
2.2模擬軟體簡介 34
2.2.1 GAMBIT-前處理 35
2.2.2 Fluent-中處理 36
2.2.3 Tecplot-後處理 39
2.3 模擬步驟 39
第3章 晶片製作與實驗方法 42
3.1管道設計 42
3.2晶片製作 43
3.3實驗系統架設 46
3.4實驗方法 47
第4章 結果與討論 48
4.1阻塊距離與渦流生成關係探討 48
4.2渦流成長 54
4.3壓力量測整合微流體整流器及微閥門 58
第5章 結論與未來展望 67
5.1結論 67
5.2未來展望 69

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