進出口設計對無閥式微幫浦效能影響之實驗探討

A Experimental Study on the design of Inlet and Outlet in the Valveless Micropump

蔡文惠(Wen-Hui Tsai)

指導教授 ： 王安邦

國立臺灣大學/工學院/應用力學研究所/碩士(2010年)

https://doi.org/10.6342/NTU.2010.01903

摘要

目前微流體系統除了考慮各個微流元件本身的性能之外，也開始嘗試將各單一元件相互整合，因此各元件的介面端(interface)與如何有效系統化儼然成為微流領域中一重要的課題。對微幫浦而言，進出口是與其他微流元件相互連接之處，但回顧過往相關的文獻中，卻未發現有任何研究對此有所著墨發表。因此，吾人將首先針對進出口進行系統性研究與探討，因此本文藉由改變進出口的幾何尺寸與構型設計，來瞭解流阻變化對微幫浦性能的影響；更進一步透過流場可視化系統來了解微幫浦內流場的變化情形，以對無閥式微幫浦之作動機制得到更清楚的了解。
首先，吾人以可拆裝重組之概念為基礎，研製可拆卸式微幫浦，在壓電片與半成品微幫浦之間以螺絲固定，藉由可重組(reassemble)之特性可重複使用同一壓電片，以避免因微流道與壓電片在製程上些許的差異，而造成微幫浦效能量測分析上有不可預期的因素影響。並以原型微幫浦測試流量與背壓之關係，實驗結果顯示兩者工作曲線趨勢相似，當流量越大時，其所可承受的背壓相對也比較大，兩者呈現正相關；而最佳幫浦效率也出現在共振頻時，幫浦效率隨著操作頻率變化的趨勢也跟流量與背壓一致。
吾人改變微幫浦之進出口尺寸(R)，當R大於振動腔半徑(Rch)的0.64倍時，微幫浦有兩段可操作頻率區:第一流量區(10Hz~50Hz)和第二流量區(50Hz~600Hz)，且第二流量區為第一流量區的十數倍，此一現象為無閥式微幫浦研究文獻之首次發現。藉由流場可視化的分析，吾人探討進出口和腔體之渦漩對互相影響的關係。吾人發現當進出口渦漩對和腔體之出口端渦漩對最大時，其幫浦效率最好。實驗結果發現進出口尺寸有一最佳化設計尺寸(R /Rch =1.2倍)，過小或過大之進出口皆會造成微幫浦效率降低，所以微幫浦的設計除了考慮進出口幾何的因素外，吾人發現進出口的幾何形狀與尺寸大小對流場的發展也是需要被列入考量的重要因素。
接著，改以在微幫浦的結構前後加入一個到數個不等的緩衝區，探討緩衝區的個數與位置對微幫浦效率的影響，發現加入緩衝區的微幫浦對流量的提升亦有明顯的改善(尤以在振動腔體前後各置一緩衝區效果最好)。在相同的流道幾何結構之下，當緩衝區個數呈現反對稱時，其流量曲線相似且最大流量值亦近似相同，此說明緩衝區置於振動腔之前後，對幫浦效率無明顯的差異；而緩衝區串接的數量增加，可得到一越接近高原型的工作曲線，提供設計或使用者在高流量區有較寬廣的頻率選擇。改變進出口尺寸或是增加緩衝區至微幫浦之流道中，兩者皆可減小流阻與提供微幫浦腔體內之渦漩對有更好的發展空間，以提升微幫浦的性能。在設計微幫浦的幾何結構時，因實際的效能提升並非是兩者單獨效應線性疊加(linear superposition)，故應考慮兩者耦合(couple)的效應。最後，吾人以設計進出口與振動腔體尺寸相同的微幫浦，以進出口中心為原點，分別在對稱和不對稱上移動進出口的接管位置，發現接管位置在對稱軸上移動對流量無明顯影響，若接管位置在不對稱軸上移動對流量卻有顯著的影響。

關鍵字

可拆卸式壓電無閥微幫浦 ； 進出口尺寸 ； 緩衝區 ； 渦漩對 ； 接管位置

並列摘要

Nowadays, optimizing the performance of microfluidic elements has been gradually mature. Some researchers started to focus on the integration of microfluidic units .The concept of “systemization” has been greatly emphasized in the recent years.
For a micropump, the inlet and outlet are quietly essential since they build the bridge of a actuating source (micropump) to other functional kits. But there were few studies on the design of inlet and outlet..Therefore, by varying the geometrical design of the inlet and outlet , the pumping performance was firstly systematically analyzed. Furthermore, by the establishment of flow visualization system, the flow patterns inside the valveless micropump were clearly discovered in order to have more detailed explanation of the flow mechanism.
First, the concept of “reassembly” was applied to the fabrication of the micropump. In order to reduce the variance resulted from combination of the different PZT actuators and the substrates of micro-channel, the same piece of PZT actuator was fixed by a screw-fixing design in each experiments. Also, the relationship between the flow rate and the back pressure were conducted. The results showed that the flow rate was in positive correlation with the back pressure. Besides, the trends of the flow rate and the back pressure coincided with the developing trend of pumping efficiency. And, the best pumping efficiency also occurred at the resonance frequency.
The several designs of radius (R) of inlet and outlet were varied to analyze the pumping efficiency. The results showed that when the ratio of tinlet and outlet radius to the vibrating chamber radius (R/Rch)≧0.64, there were two operating frequency regions: the first region(located in 10Hz~50Hz)and the second region(located in 50Hz~600Hz), and the maximum flow rate of the second region is up to 10 times greater than that in the first region. This phenomenon has never been discovered in the previous literatures of valveless micropumps. The results showed that the optimal radiusfor the inlet and outlet was 1.2 times of the chamber. And for a smaller or bigger radius, the pumping efficiency would decrease. In addition, the flow visualization analysis showed that the best pumping efficiency happened as the vortex pairs of inlet and outlet region and the vortex pair in the vibrating chamber near the outlet diffuser reached maximum. Therefore, when designing the size and geometry of inlet and outlet, both the flow resistance and the development of vortex pairs should be considered.
Next, one to several buffers were serially connected to the micropump in order to discuss its influence on the pumping efficiency The design of buffers can really enhance the performance of micropump (especially, the design of each buffer serially connecting on the both sides of the chamber is optimal. ). In the same channel, when the number of buffers are anti-symmetrical, the flow rate curve and maximum flow rate were quietly similar; in other words, the position of buffers had no influence in this case. When the number of serial buffers increased, the shape of flow rate curve became trapezoid-liked. The frequency of the high flow rate region can be chosen widely.
Consequently, “varying the size of inlet and outlet” and “buffers serially connecting to a vibrating chamber” both could decrease the flow resistance and provided enough space to make the vortex inside chamber develop well. Hence, the micropump performance was obviously enhanced. So, when the two ways of enhancing performance were put together, the coupling effect should be considered carefully due to its property of non-linear superposition. Finally, moving the tube position of micropump along the symmetric axe made no difference in pumping efficiency.

並列關鍵字

reassemble PZT valveless micropump ； size of inlet and outlet buffer ； vortex pair ； tube position

參考文獻

23. 謝明哲, 無閥式微幫浦之腔體設計與作動機制研究. 國立台灣大學應用力學研究所, 2009.

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