單相流體於仿生式楔形微流道中熱流行為之研究

A Study on the Thermo-Fluidic Behavior of Single-Phase Fluid in Bionics Wedge-Shaped Microchannels

連奕輔(Yi-Fu Lian)

指導教授 ： 鄧治東

中原大學/工學院/機械工程研究所/碩士(2012年)

https://doi.org/10.6840/cycu201200797

摘要

本研究係以實驗與數值模擬方式，針對單相流體於仿生式楔型微流道具不同階層數與深寬比之幾何參數，於固定散熱面積為前提進行探討。內容包括對流場與溫度場之模擬分析、設計實驗與建立設備，驗證結果並整理出經驗關係式，最後依性能效益進行評估。數值分析使用ESI-CFD-ACE+計算流體力學軟體進行模擬，其誤差範圍為0.2%~32.2%，平均誤差為9.7%。實驗試片之矽晶圓採用半導體製程進行製作，且工作介質為去離子水，其雷諾數範圍介於92到1835之間。結果顯示壓降與熱傳值於不同參數下與雷諾數皆有合理的趨勢與對應關係，而楔形結構將產生二次流行為且進入過渡流區，並使溫度均勻性提升，帶來更好的熱傳性能。
對於楔型結構而言，其楔型階層數越高、深寬比越小(短邊除以長邊)其熱傳性能越高，且圓弧轉角相對於直角能夠降低壓降值並提升效能。整體而言在階層2之圓角楔型性能曲線最高，相對於直管於深寬比為1且在雷諾數為1477時效能可提升至179.7%、深寬比為0.5且在雷諾數為737時效能可提升至174.9%、深寬比為0.333且在雷諾數為727時效能可提升至161.7%，而相同階層數下亦得到於深寬比越小則性能值越高之結果。
此外，對微型樹狀類結構提出線段積分法，深入考慮分支結構對於流體所產生之變化與入口效應長度之不可忽略性，其摩擦因子與紐賽數應不再只透過出入口溫度與壓力值進行古典理論計算。研究顯示此法能考慮整體內部流場變化，其發展流之文獻值和實驗值較為吻合，平均誤差僅在14.6%，優於古典理論於微尺度下產生較大之誤差達60.7% 之多，並佐證此類微型結構於理論上需被提出探討與修正。

關鍵字

性能係數 ； 二次流行為 ； 仿生式楔型 ； 理論分析 ； 計算流體力學

並列摘要

In this study, the single phase flow fluid characteristics in the bionics wedge-shaped microchannel with different aspect ratios and branching levels were investigated under constant heat transfer surface. The distributions of velocity and temperature fields inside the microchannel were simulated and analyzed. Then an experiment was designed and set up to verify the simulation. The experimental results were compared with the simulated results and the empirical correlations were determined to acquire the coefficient of performance (COP). The software of ESI-CFD-ACE+ was used for numerical simulations. The errors between the results obtained from the experiments and those obtained from the simulations were in the range of 0.2%-32.2% with an average error of 9.7%. The silicon wafers used in the experiments were fabricated by semiconductor manufacturing process, and the working fluid was de-ionized water flowing at the Reynolds number ranging from 92 to 1835. The experimental results showed that the curves of corresponding trends of pressure drop and heat transfer versus the Reynolds number were reasonable. The wedge-shaped structure helped to generate secondary flows and make the fluid flowing into the developing regime. The resulting temperature distributions were more uniform within the microchannel and the performance of heat transfer for wedged-shaped microchannel was enhanced.
For wedge-shaped structure, the effect of aspect ratios on the performance of heat transfer is more than that of the branching level. The higher the branching level and the smaller the aspect ratio, the better the performance of the heat transfer. Moreover, compared with the rectangular bend, the rounded bend can decrease the pressure drop, which also helps to improve the performance. Through the integrated crossover comparison, it was found that for the rounded bend wedge-shaped microchannels, when the branching level was 2, the COP curve was the best among all configurations studied. Compared with the straight microchannels, the COP could increase to 179.7% at Reynolds number of 1447 with the channel respect ratio of 1. And at Reynolds number of 737 with the channel respect ratio of 0.5, the COP could increase to 174.9%. While for the channel respect ratio of 0.33, the COP could increase to 161.7% at Reynolds number of 727. For the same branching level, the compared results show that the COP curve was better for the microchannel structural configurations with small aspect ratios.
The sectional integral method was used in this study to account for the specific structures of wedge-shaped microchannels. Since such kind of microchannel structures induced the flow to change its situation along the branching part of the channel, the effects brought about by the entrance length in the developing flow could not be ignored under such a situation. Therefore, the friction factor and Nusselt number should not be calculated by the classical theory involved only the entrance and exit parameters of pressure and temperature. The research done in this study showed that the results, verified by the experimental data, obtained from this improved method helped incorporate the variation of flow field along the length of the channel. The average error for the COP curve was 14.6%, better than that of 60.7% obtained from the classical theory in micro-scale, which demonstrated that accounting for the entrance effect resulting from the developing flow by using the sectional integral method was essential to describe the behavior of flow and heat transfer for bionics wedge-shaped microchannels.

並列關鍵字

Secondary flow ； Bionics wedge-shaped ； Computational Fluid Dynamics ； Coefficient of performance ； Experimental study ； Numerical simulation

參考文獻

[1] Status of the MEMS Industry, Yole Développement, 2009.

[2] Microfluidics Technology, BCC Research, 2009.

[6] J. Ku, “Overview of capillary pumped loop technology,” Heat Pipes and Capillary Pumped Loop, HTD-Vol. 236, pp. 1-17, 1993.

[8] D. Khrustaber and A. Faghri, “Coupled liquid and vapor flow in miniature passages with micro grooves,” HTD-Vol. 361-3/PID-Vol.3, Proceedings of the ASME Heat Transfer Division - Vol. 3, pp. 203-209, 1998.

[9] G.P. Peterson, L.W. Swanson, and F.M. Gerner, “Micro heat pipes,” Advances in Heat Transfer, Vol. 25, pp. 295-337, 1995.