新式被動閥式微幫浦之開發及其流場量測

Abstract

本研究藉由簡易的微機電技術開發新式的微型幫浦，為了因應現代的研究趨勢，即整合微型元件為具實用性之微系統概念下，因此新式微幫浦的開發將比過去具備更多考量，本論文的新式微幫浦之設計概念包含: (1)簡易製作及高整合性;(2)低功耗與高效能;(3)提供良好的流量品質。在此設計概念下及歸納過去相關文獻，本研究設計之微幫浦共有兩種形式，分別為單腔體與雙腔體，腔體的功能主要產生形變以提供流體緩衝的區域，使流體於幫浦內發生流動之行為。為能提高淨流量輸出效率及考量設計製作上的簡易性，因此新式微幫浦搭配的整流元件為被動式平面閥門，藉由腔體週期性震動所產生的往復流場，推動閥門的動件進行開關的動作。由於閥門運動與流場特性，皆源自於腔體之規則往復振動，因此藉由橋式整流電路的概念，將兩個獨立腔體並聯操作，預期反相位的模式下，可在出口端達到近似穩態流場的結果。 本論文之第一章主要介紹歸納了近三十年來微幫浦的研究發展，並對於往復式微幫浦的結構進行介紹與分類，歸納過去的相關文獻及上述的設計概念，論文在第二章提出了新式微幫浦的設計架構，即以壓電片為驅動源，並以被動式平面閥進行整流。雖然本研究主要以幫浦實驗分析為重點，在進行實驗前，亦於第三章中針對此微幫浦進行初步的理論分析工作，本研究之主要重點則是流場行為及流體與閥門間的耦合效應。第四章則為本論文之實驗方法與步驟，為了進一步獲得幫浦內部的相關資訊，本實驗亦利用微粒子影像測速儀(micro-particle-image-velocimetry，簡稱micro-PIV)搭配外部觸發技術(externally triggered technique)對於幫浦內的暫態流場進行完整分析，以進一步了解幫浦的特性。 第五章則針對所得之相關實驗結果進行討論，實驗結果顯示，無論單腔體或雙腔體之微幫浦，都可在低於10V的電壓下驅動，然而所產生之流量亦相對偏低，為了能夠清楚觀察幫浦的運作，因此實驗所給之電壓為10-30V，在體積流率的測試中，可觀察在固定電壓與低頻的操作範圍下，流量隨頻率呈線性增加的關係，以單腔體微幫浦而言，其線性區的範圍為0.1-0.8kHz，而雙腔體微幫浦的之線性段，在同相位操作下為0.1-0.4kHz;而反向位則為0.1-0.5kHz，關於此線性關係，在過往的文獻中並無提出相關論述，因此微幫浦經過數次的測試後，利用了線性度(linearity)與重複性(repeatability)兩種指標進一步量化其效能，這項線性的特性對於實際整合此幫浦於微流系統中具有相當大的助益，除了可有效精確提供所需之流量外，亦可簡化為系統中的操控模組。 在單腔體微幫浦的流場拍攝中，除了可以量到暫態的流場行為外，亦可獲得閥門動件的運動行為，將此兩項結果進行整合比對，可發現閥門動件的運動，主要受到流體運動行為的影響，藉由往復流體動能的傳遞，閥門動件才能產生規律性的位移，實驗證實流體的速度變化在相位上領先閥門動件的位移變化，且頻率愈高，相位領先的幅度就愈大;另一方面，電壓增加時則有助於彼此間相位差的縮減，此外，實驗結果亦發現閥門動件的速度主要與電壓有關，同一電壓不同操作頻率下，動件的運動速度則接近定值，故頻率增加時，動件的運動速度相對於流體則逐漸偏低，故導致導流效率的下降。 雙腔體的微幫浦流場拍攝中則根據同相位與反向位兩種操作模式進行測量，實驗結果顯示同相位的模式下，其流場行為與單腔體微幫浦相似，而在反向位的操作下，此雙腔體微幫浦則具備整流轉換的功能，將原本的往復流場於出口端轉換為速度在一週期內皆為正向脈衝的流體，當頻率愈高時，出口端的流體連續性愈佳，也愈接近穩態的流場，因此反相位下所操作之雙腔體微幫浦的操作，有效提升微流體系統中之流量輸出品質，使所有的元件均可在穩定的流場下進行工作，以減少微型檢測系統在測量過程中所面臨之干擾等問題。 整體結論則歸納於第六章中，除了包含現階段的實驗結論外，最終亦針對現有之微幫浦於未來發展提供改進與最佳化的建議，未來，此類微型幫浦將則藉由流場測量的技術進行效能最佳化的工作，其中包含整體導流效率與流體轉換的效率，期望於未來對於微生醫檢測或其他微流體系統提供更進ㄧ步之實質貢獻。

In this study, a novel micropump has been successfully developed by simple MEMS fabrication technique. Based on the concept of micro-TAS or Lab-on-a-chip, more considerations are taken into account when designing a new micropump. The design guidelines for the present micropump include (1) easy fabrication and high integration capability, (2) low power consumption and high pumping performance, and (3) high quality of the output flow. According to the present design guideline and the summary of previous literatures, two types of planar micropumps, single-chamber and double-chamber, were proposed and tested in the experiments. The periodic volumetric change of the pumping chamber provided a dramatic pressure gradient to drive the flow in oscillatory form. The planar passive valves were then actuated by the oscillatory flows. Based on the concept of electronic bridge converter, two single-chamber micropumps in parallel arrangement can transform an oscillatory flow into a steady-like flow at the outlet. In chapter 1, numerous researches of micropump in the past 30 years are introduced. The pumping principles and the elements of the earlier micropumps are also classified. Based on the previous studies and the design guidelines described in previous paragraph, the new patterns of the present micropumps and their pumping principles are given in chapter 2. The fundamental analyses including (1) the coupling effects between the chamber diaphragm and the fluids, and (2) the oscillatory flow behaviors and their effects on the valve motions are discussed in chapter 3. The transient flow behaviors in the micropumps were measured by externally- triggered micro-particle-image-velocimetry (micro-PIV) system. The measurement results provided very useful information of the flow fields and the valve motions in the micropump. The detailed experimental methods and procedures are given chapter 4. The results in chapter 5 indicated that either a single-chamber micropump or a double-chamber one could be activated at an excitation voltage lower than 10 V. At the driving voltages from 10 to 30V, the results revealed that there were uniquely linear relationships existed between the flow rates and driving frequencies for both micropumps. The linear regime of single-chamber micropump was at 0.1-0.8 kHz. Moreover, the linear regimes of double-chamber micropump were at 0.1-0.4 kHz and 0.1-0.5 kHz for in-phase and anti-phase operations, respectively. The linearity and repeatability were used to further characterize those linear regimes. The reliable linear regimes of those micropumps were favorable for the integration of micro-systems. The measurement results of transient flow behaviors and the valve motions clearly exhibited that the variation of the oscillatory flow had a phase leading with respect to that of the moving part. This phase difference increased with an increasing frequency, but reduced with an increasing voltage. The larger phase difference would lead to more leakage so that the flow-rectifying capability and the pumping performance were thus reduced. Moreover, the switch-off time of the valve was found to be mainly depended on the excitation voltage, i.e. shorter switch-off time could be obtained by using higher excitation voltage. The flow measurements of the double-chamber micropump in in-phase and anti-phase modes clearly revealed different flow behaviors at the outlet. In the in-phase mode, the phase-dependent flow velocities presented similar results to those of single-chamber micropump. On the other hand, the flow measurements using micro-PIV clearly demonstrated the process of how oscillatory flows were converted into smoothly continuous flows in anti-phase mode operation. In addition, the flow became steady-like continuous when at higher frequencies and better output flow quality was thus obtained in this experiment. The conclusions are given in the last chapter and indicate the major contribution of the current study. Some further studies such as the optimization of the flow-rectifying capability and the pump performance are also proposed. Moreover, a high-quality flow at the outlet of a reciprocating micropump, i.e. a nearly steady flow, can also be effectively obtained by this microfluidic device.