微粒子影像測速法及溫度螢光感測技術應用於微流體90度彎管之流場與熱傳分析

The investigation of flow field and heat transfer in 90° bend microchannels using micro particle image velocimetry and temperature sensitive paint

林智仁(Jhih-Ren Lin)

指導教授 ： 黃智永 ； 劉通敏

國立清華大學/工學院/動力機械工程學系/碩士(2014年)

https://doi.org/10.6843/NTHU.2014.00214

摘要

本研究主要是利用「微粒子影像測速法(Micro-PIV)」以及「溫度螢光分子感測技術(TSP)」量測定熱通量加熱條件下PDMS微矩形90度彎管中流場以及流體與壁面溫度場分佈情形，並將流場與溫度場的量測結果相互比對以探討其熱傳特性，最後將實驗量測結果與數值模擬進行比對，驗證量測技術的準確性。其中為了更仔細探討90度彎管中二次流的現象，轉彎區域的幾何形狀部分又細分了以尖角轉彎及圓弧轉彎兩種方式。
本研究先以「電流觀測法」量測常用之TSP水溶液(包含Rubpy、Rhodamine B、Pyronin B以及Pyronin Y)的Zeta-potential並計算其電雙層厚度，最後以流道水力直徑與電雙層厚度之比值討論電雙層影響程度。
在流場分析中，Micro-PIV技術中顯微鏡影像對焦平面與螢光粒子相關深度的多寡會影速度分析的深度範圍，故實驗前會先量測本研究使用之螢光粒子搭配顯微鏡的相關深度，以判斷其對於速度量測結果的影響。實驗時會使用中位數帶通濾波的影像處理來協助計算轉彎區域之速度場，並進行定性及定量的分析，最後再量測不同深度的速度分佈分析出二次流情形。
在熱傳分析中，以自製的微型加熱器做為加熱裝置並放置在PDMS流道內來降低熱損，同時也將加熱基底的厚度降低，以避免軸向熱傳現象影響實驗結果。以TSP技術量測彎管全域之流體及壁面溫度場時，會搭配5×5中位數濾波的影像處理降低雜訊。將量測之液體與壁面溫度分佈計算從流道入口經轉彎處到出口的紐索數分佈，可得知兩種彎管之軸向平均紐索數皆會隨著雷諾數的增加而提升，其中又以尖角轉彎略高一點。
將模擬結果之入出口壓力差進行幫浦耗能(Pumping power)的計算，發現幫浦耗能會隨著雷諾數的增加而提升，且也以尖角轉彎的值較大，再進一步計算平均紐索數與幫浦耗能之比值，並利用其相對關係判斷其熱傳增益的效益。最終可歸納出兩種轉彎方式對於熱傳的表現，論增益以尖角轉彎較佳；論效益則圓弧轉彎較佳。

關鍵字

微粒子影像測速法 ； 溫度螢光感測技術 ； 微流體90度彎管

並列摘要

This study aims to investigate the characteristics of heat transfer in a 90-degree bend PDMS microchannel under one side constant wall heat flux thermal boundary condition with acquired velocity, fluid temperature and wall temperature distributions. The velocity profiles in the microchannel were obtained by Micro Particle Image Velocimetry (Micro-PIV), and the temperature distributions were measured by Temperature Sensitive Paint (TSP). The experimental results are compared with simulation data to verify the accuracy of measurement technique. In order to discuss the secondary flow in the 90-degree bend microchannel, two kinds of turn, sharp turn and round turn, are designed in this study.
Due to the concern that electrical double layer effect may affect the flow field and heat transfer in microchannel flow, the current monitoring technique is used to measure the zeta-potential of common TSP solutions, including Rubpy, Rhodamine B, Pyronin B and Pyronin Y. The thicknesses of electrical double layer are also calculated to find the ratio between hydraulic diameter and it. After carefully considering this ratio, the extent of electrical double layer effect could be determined.
In the flow field analysis using micro-PIV technique, the depth of correlation will change the acquired velocity profiles if using different depth range during velocity. Therefore, the depth of correlation based on the fluorescent particles and microscope system used in current experiment is first calculated to determine the influence to the results of velocity measurement. The median band-pass filter is performed in the measurement of turning region velocity during image process. Therefore, the secondary flow is observed by measuring velocity distribution at different depth in the microchannel flow.
In the heat transfer analysis, a micro-heater is fabricated as the heating device for the experiment to reduce the heat loss and avoid the axial heat conduction effect. The image process of 5×5 median filter is performed to reduce the noise in the fluid and wall temperature using TSP technique. From Nusselt number distribution calculated by fluid and wall temperature, it can be noticed that the mean Nusselt numbers along the microchannels with two different 90-degree bend designs, a sharp turn and a round turn, are increasing with increasing Reynolds number, and the Nusselt number in the sharp turn are larger than the round turn.
The pumping powers to drive the flow in the microchnanel device are calculated by using the pressure difference between inlet and outlet from simulation results, and they increase with increasing of Reynolds number. The sharp turn requires higher pumping power than the round turn. After calculating the ratio between mean Nusselt number and pumping power and considering the relative magnitude of ratio, the overall performance of heat transfer effect between sharp turn and round turn can be concluded. The sharp turn design shows higher heat transfer enhancement, but the round turn design has better performance if considering the pumping power.

並列關鍵字

Micro particle image velocimetry ； Temperature sensitive paint ； 90° bend microchannels

參考文獻

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