壓力螢光感測分子於突縮擴微流道流場的探討及應用

The Application of Pressure Sensitive Paints for Investigation of Constricted Microchannel Flows

陳瑩璇(Ying-Hsuan Chen)

指導教授 ： 黃智永

國立清華大學/工學院/動力機械工程學系/碩士(2013年)

https://doi.org/10.6843/NTHU.2013.00321

摘要

本研究主要是將壓力螢光感測技術應用在突縮擴微流道內部流場的量測，並成功量測到因流體偏移效應引起的二維非對稱流場。因傳統壓力感測器以微機電製程佈置於微流道附近，難以密集地排列於突縮擴區域，並僅可提供一維沿流道軸向的壓力資料，無法討論流場偏移現象，故近年來探討突縮擴微流道內部流場非對稱的現象多以數值模擬方式進行。而壓力螢光感測技術因採取光化學方式進行量測，選取適當的螢光分子搭配光學系統擷取影像後，可獲得微流道內全域(二維)的壓力分佈，故使用此技術應用在突縮擴微流道內部流場的研究。
本文首先以套裝軟體ANSYS模擬微流道內的流場現象，模擬結果發現當緊縮比為5：1時，突縮擴結構後方有流場偏移的現象，壓力不對稱的差距約為2 kPa。而壓力螢光分子除了直接受壓力影響螢光亮度，量測表面的溫度也會造成螢光強度的變化，因此針對緊縮比為5：1的突縮擴微流道量測其內部溫度場，結果顯示於最大流量條件Re=121時，流體經過緊縮段因加速而導致溫度下降3.5 ℃。以本研究所使用的壓力螢光感測配方PtTFPP/PDMS而言，此溫度變化並不會造成壓力量測上的誤差，於是仍可真實呈現突縮擴微流道內的流體現象。
為了提高實驗量測的空間解析度，以及解決激發光源由流道上方斜射所造成的陰影，故以螢光顯微鏡搭配4X及10X顯微物鏡擷取螢光訊號影像，並利用即地校正及逐點影像校正修正傳統單點影像校正的不足。在深寬比(流道深度/流道寬度)為1且緊縮比(流道寬度：緊縮段寬度)為5：1的突縮擴微流道，在Re=279時，壓力分佈於緊縮段後即出現不對稱的現象，其流場偏移的情況約為2.5 kPa；當Re=107時，其流場偏移的情況則約為1.2 kPa。而本研究利用螢光分子感測技術，成功以二維壓力場顯示突縮擴微流道之流場偏移現象，並提供突縮擴微流道內部流場的實驗資料，將有助於微型混合器的設計與開發。

關鍵字

流場偏移 ； 突縮擴微流道 ； 壓力螢光感測技術

並列摘要

This study aims to apply pressure sensitive paint (PSP) technique in constricted microchannel flow. The asymmetric flow with two-dimensional and global flow fields has been measured successfully. The constricted microchannel flow has been studied by using micro pressure sensor fabricated with the conventional MEMS technique. Due to the arrangement of micro pressure sensor, only one-dimensional pressure distribution was acquired and pressure drop around constriction was detected. Asymmetric flow behavior was not observed using conventional MEMS pressure sensors. Thus, the study of the global pressure profile in constricted microchannel flow was almost executed by the numerical simulations. PSP is a technique using optical chemical reaction of luminescent molecules to provide the pressure/temperature data in experiments. Additionally, it can provide global flow field with detailed pressure and temperature data.
ANSYS CFX has been used to simulate the flow field in microchannel. While the constricted ratio (CR) greater than 5, the asymmetrical flow can be observed in simulation results. The pressure difference at lateral locations is 2 kPa due to the flow separation. Before applying PSP sensor in current study, the temperature dependence of PSP sensor has been examined. The intensity of PSP sensor not only changes with pressure, but also temperature. The temperature distribution inside a constricted microchannel (CR=5) has been measured. The result shows that the temperature difference through the ribs is around 3.5℃ at Re=121. The response of PSP sensor (PtTFPP/PDMS) does not change much in such temperature difference. Thus, PSP technique still can reveal the flow fields inside the constricted microchannel in current study.
In order to increase the spatial resolution of experimental data and eliminate the shadow effect caused by inclined light source, a microscope with a 4X and a 10X objective lens is used to collect the luminescent signals. Pixel-by-pixel calibration and in-situ calibration have been used to improve the accuracy of PSP sensor measurements. The constricted microchannel flow with higher CR ratio (CR=5), the pressure difference between lateral locations (±0.15 W) is 2.5 kPa at Re=279 and 1.2 kPa at Re=107. Overall, with the understanding of constricted microchannel flow provided by the PSP technique, the application of the constricted microchannel can be further extended to the design of MEMS devices like micro mixers.

並列關鍵字

Asymmetric flow ； Constricted microchannel ； Pressure sensitive paints(PSP)

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