本研究旨在以實驗方法量測側壁加熱條件下之微流道溫度場，並藉由數值方法更進一步針對不同流道高度下之共軛熱傳行為進行探討。研究中將溫度螢光感測塗料(Temperature sensitive paint, TSP)實驗技術應用於微尺度熱傳領域，以液態金屬做為加熱器置於微流道側面以產生沿跨向的溫度梯度，並藉由TSP技術觀測全域溫度場的特性，量測截面尺寸500 μm(W) × 100 μm(H)的PDMS矩形微流道於側壁加熱條件下之局部壁面溫度、流體溫度以及熱通量，並計算沿軸向之紐賽數(Nusselt number, Nu)分布，最後將其與數值方法的結果比對以此驗證實驗結果之正確性。由於微流道的特徵長度較小，壁面對於熱傳行為的影響不可忽略，從熱通量與無因次化流體溫度沿軸向之分布皆可看到因軸向熱傳所造成的影響；而當雷諾數或流道高度提高時，由於流體的熱對流能力提升，軸向熱傳所造成的影響將隨之下降。
本研究透過套裝軟體ANSYS Fluent以數值方法分析不同流道高度對於共軛熱傳現象之影響。結果顯示，當流道深寬比為0.2時，從各面傳入流道的熱量比例接近，和理論的解析解相比，流道整體的紐賽數界於單面加熱與三面加熱之間。隨著流道高度的增加，共軛熱傳所造成的影響逐漸減少，從其餘三面傳入流道的熱量比例逐漸下降；當深寬比為2時，流體獲得之總熱量有81 %是由最靠近加熱器的面傳入，此時流道整體的紐賽數與解析解僅有不到1 %的差距，因此可將此高度下之加熱方式視為理想條件中單面加熱、三面絕熱的熱邊界條件。此外，還可從模擬結果中看到距離加熱器最遠的面在低雷諾數的條件下會發生熱傳方向由壁面往流體改變為穿過流體往壁面加熱的現象，在雷諾數10，深寬比為0.2、1、2的流道中，發生此現象之位置分別為x/L = 0.85、x/L = 0.53、x/L = 0.41，有隨著高度提高而提前發生的趨勢。

The objective of this study is to investigate the conjugate heat transfer in microchannel with different heights under side-wall heated experimentally and numerically. Temperature sensitive paint (TSP) technique was applied to the flow field of micro-scale conjugate heat transfer in rectangular PDMS microchannels. In order to generate temperature gradient along the spanwise direction, a liquid metal was used as heater and positioned next to the microchannel. The local wall temperature, fluid temperature and heat flux in a rectangular PDMS microchannel with a cross-section of 500 μm (W) × 100 μm (H) under side-wall heated condition can be measured due to the capability of measuring global temperature field with TSP. Nusselt number distribution along the streamwise direction has been calculated with the measured data and compared with the results obtained by the numerical method using ANSYS Fluent. Due to the small characteristic length of the microchannel, the effect on heat transfer behavior through by walls around the microchannel was not negligible. The influence of axial heat conduction has been identified from the heat flux distribution and dimensionless fluid temperature along the streamwise direction. In addition, increasing Reynolds number and increasing the height of microchannel can both reduce the influence caused by axial heat conduction.
In order to understand the difference among the heat transfer behavior of different microchannel heights, the effect of conjugate heat transfer was investigated numerically with the commercial software ANSYS Fluent. The heat transfer behavior can be determined by calculating the percentage of heat transfer through the four walls of the microchannel. The result showed that the heat transfer percentages of four walls were all contributed with considerable amount when the aspect ratio was 0.2. As the height of the microchannel increased, the influence of conjugate heat transfer diminished, and the heat transfer behavior was gradually dominated by the wall near to the heater. In the case of the aspect ratio of 2, more than 80 % of the total heat received by the fluid was transferred into the microchannel flow through the wall next to the heater. At this time, the Nusselt number of the microchannel was close to that obtained by analytical solution. There was less than 1 % difference between the estimated and theoretical values. Therefore, the behavior of this case can be considered as ideal one-wall heating of thermal boundary condition. Moreover, the result also showed that the heat transfer on the wall, which was away from the heater, changed so the heat passing through the fluid and coming to the wall at the downstream of the microchannel at low Reynolds number of 10. When the aspect ratio was 0.2, 1, 2, the phenomenon occurred at the locations x/L = 0.85, x/L = 0.53 and x/L = 0.41, respectively.

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