臺灣博碩士論文加值系統

本研究擬以數值方法模擬兩種情況下之毫米矩形微流道內共軛對流冷卻特性，第一種為氧化鋁-水奈米流體於毫米矩形流道內探討有/無浮力之對流熱傳遞效益;第二種為純水於毫米矩形流道內，改變毫米微流道熱沉設計，將毫米微流道熱沉頂板材料替換成相變化微膠囊(MEPCM)，在毫米微流道熱沉底部脈衝熱載方式加熱，探討相變化微膠囊在頂板的情形。本研究探討之物理尺寸皆以無因次參數轉換為有因次參數進行模擬，其無因次化尺寸為流道截面高寬比為0.25、上蓋固體區厚度與流道寬比為0.5、流道基底固體區厚度與流道寬比0.5、流道側壁固體區厚度與流道寬比0.5、加熱段流道長為0.02。數值模擬所探討之相關參數及範圍為: 入口溫度34°C；氧化鋁-水奈米流體體積分率為5%、10%；矩形流道內流量為26.3-105 (雷諾數500-2000)；底部熱通量為7.1-19.4 。毫米矩形流道內三維流場之模擬採用擬渦漩法建構數學模式，並以並以有限體積法離散數值模式，成功解析出毫米矩形流道內三維強制對流速度場與溫度場，並與文獻中完全發展流之近似解進行結果比較。
本研究所得數值模擬結果顯示:奈米流體在高流量、高濃度下流經毫米微流道，可抑制壁溫及提升熱傳係數，當考慮浮力效應時其效果更加明顯，當濃度越高流道內壓降亦大量提升，熱傳增益幅度不及壓降上升幅度，故使其效能指標FOM皆小於1。當頂板材料替換成相變化微膠囊時，能有效減緩頂板溫度起伏，且加熱功率脈衝震幅越大其效果越好，當停止加熱相變化微膠囊反而有保溫作用使溫度下降不易。

In this study, we use numerical simulation method to discuss the conjugation cooling characteristics of Al2O3 nanofluid flow in a rectangular mini-channel. The aim of the present study is to discuss the results of two cases; the first case is to investigate the influence of buoyancy to the temperature and velocity in the mini-channel with/without thermal buoyancy effect. The second one is to investigate the effect of impeding the dramatic change in temperature under sudden pulsed power load with ceiling embedded with/without Micro-Encapsulated Phase Change Material (MEPCM). The geometries of the mini-channel are 4.016 mm in width, 1.004 mm in height, and 74.2 mm in length with the fin thickness of 2.008 mm. In order to describe the three dimensional heat transfer and fluid flows of the water-based suspensions in a single mini-channel, pseudo vorticity velocity formulation and energy equation are coupled to solve the temperature and velocity profile in the mini-channel. Numerical simulations for the laminar forced convection in mini-channel have been performed with parameters in the following ranges: the volumetric fraction of Al2O3 nanofluid, and ; the volumetric flow rate entering mini-channel, (equivalently, ); and the heat flux imposed on the bottom surface of the rectangular mini-channel . The diameter of the particle in Al2O3 nanofluid is 20 nm. The mini-channel is iso-flux heated with heat flux of and on the bottom, and the heat flux of the rectangular mini-channel is . The numerical results obtained for the channel with ARch = 0.25, ARbw =0.5, ARcw = 0.5, and Wsw = 0.5 clearly reveal that using the Al2O3 nanofluid to replace the pure water as the coolant in the rectangular mini-channel can reduce the bulk mean temperature in the fluid, enhance the averaged heat transfer coefficient, and reduce the overall resistance in the rectangular mini-channel, respectively. Al2O3 nanofluid has greater thermal conductivity than pure water and the thermal conductivity increases with increasing concentration. With the thermal buoyancy effect, the bulk mean temperature of the fluid is 1°C lower than that without the effect and the averaged heat transfer coefficient is enhanced about 5.2%. Furthermore, the thermal buoyancy effect reduces overall thermal resistance in the rectangular mini-channel about 3.5%. Plus, lower Reynolds number leads to greater difference in temperature and heat transfer coefficient.With sudden pulsed power load, the ceiling temperature with MEPCM is 2°C lower than that without MEPCM; however, the bulk mean temperature of the fluid reduces only 0.2°C.

摘要 I
Abstract II
誌謝 VIII
目錄 IX
表目錄 XII
圖目錄 XIV
符號表 XX
第一章 緒論 1
1-1 前言 1
1-2 文獻回顧 2
1-3 研究動機與目的 3
1-4 論文架構 4
第二章 毫米流道內奈米流體穩態共軛對流熱質傳遞現象模擬分析 5
2-1 物理模型 5
2-2 數學模型 6
2-2-1 基本假設 6
2-2-2 統御方程式 6
2-2-3 邊界條件 9
2-2-4 無因次化統御方程式與邊界條件 14
2-2-5 流體熱物理性質 22
2-2-6 熱質傳遞相關物理參數定義 25
2-2-7 數值方法 33
2-2-8 解題流程 34
2-2-9 網格測試 35
2-2-10 程式驗證 36
2-3 純水模擬結果分析 37
2-3-1 流場、溫度場分析 37
2-3-2 軸向熱傳分析 38
2-3-3 熱傳效果、流道延伸壁面散熱效率 38
2-3-4 流道平均熱阻 39
2-4 毫米流道內奈米流體視為均勻混合物之模擬結果分析 39
2-4-1 流場、溫度場分析 40
2-4-2 熱傳效果、流道延伸壁面散熱效率 42
2-4-3 效能指標、流道平均熱阻 44
第三章 具充填相變化材料微膠囊層頂板毫米流道離散加熱段功率脈衝下暫態共軛強制對流熱散逸性能模擬分析 106
3-1 物理模型 106
3-2 數學模型 107
3-2-1 基本假設 107
3-2-2 統御方程式 108
3-2-3 初始與邊界條件 109
3-2-4 無因次化統御方程式與邊界條件 114
3-2-5 相變化微膠囊層熱物理性質 120
3-2-6 數值方法 121
3-2-7 解題流程 122
3-3 相變化材料微膠囊層頂板對流道內奈米流體暫態共軛強制對流熱散逸特性之影響 122
3-3-1 流道溫度場分析 123
3-3-2 流道頂板相變化材料微膠囊層熔解率與熱傳遞特性 124
3-3-3 流道加熱段功率脈衝振幅的影響 124
第四章 總結與未來研究方向 155
4-1 結論 155
4-2 未來研究與展望 157
參考文獻 158
附錄 161

[1] D. B. Tuckerman and R. Pease, High-performance heat sinking for VLSI, Elec-tron Device Letters, IEEE, vol. 2, pp. 126-129, 1981.
[2] W. Qu and I. Mudawar, Analysis of three-dimensional heat transfer in mi-cro-channel heat sinks, International Journal of Heat and Mass Transfer, vol. 45, pp. 3973-3985, 2002.
[3] P.-S. Lee, S. V. Garimella, and D. Liu, Investigation of heat transfer in rectangular microchannels, International Journal of Heat and Mass Transfer, vol. 48, pp. 1688-1704, 2005.
[4] P.-S. Lee and S. V. Garimella, Thermally developing flow and heat transfer in rectangular microchannels of different aspect ratios, international journal of heat and mass transfer, vol. 49, pp. 3060-3067, 2006.
[5] 鄭偉成, 毫米流道熱沉孔內奈米微粒/相變化微膠囊懸浮液之強制對流特性研究, 成功大學機械工程學系學位論文,2000.
[6]S. Choi, Enhancing thermal conductivity of fluids with nanoparticles, ASME-Publications-Fed, vol. 231, pp. 99-106, 1995.
[7] Lee, J., Mudawar, I., Assessment of the Effectiveness of Nanofluids for Sin-gle-Phase and Two-phase Heat Transfer in Micro-channels, International Journalog Heat and Mass Transfer,Vol.50,pp.452-463,2007.
[8] 郭育惟, 毫米流道熱沉內相變化材料奈米膠囊/奈米微粒懸浮液強制對流熱散逸特性之數值模擬, 成功大學機械工程學系學位論文, pp. 1-112, 2014.
[9] P. Keblinski, S. Phillpot, S. Choi, and J. Eastman, Mechanisms of heat flow in suspensions of nano-sized particles (nanofluids), International journal of heat and mass transfer, vol. 45, pp. 855-863, 2002.
[10] J. A. Eastman, S. Phillpot, S. Choi, and P. Keblinski, Thermal transport in nanofluids 1, Annu. Rev. Mater. Res., vol. 34, pp. 219-246, 2004.
[11] J. C. Maxwell, A treatise on electricity and magnetism vol. 1: Clarendon press, 1881.
[12] R. Hamilton and O. Crosser, Thermal conductivity of heterogeneous two-component systems, Industrial ＆ Engineering chemistry fundamentals, vol. 1, pp. 187-191, 1962.
[13] K. Khanafer and K. Vafai, A critical synthesis of thermophysical characteristics of nanofluids, International Jornal of Heat and Mass Trans-fer,vol.54,pp.4410-4428,2011
[14] 魏連晉, 微流道熱沉內奈米流體之強制對流熱傳實驗研究,碩士論文,機械工程所,國立成功大學,1997.
[15] Xuan, Y., Li, Q ., Investigation on Convective Heat Transfer and Flow Features of Nanofluids, ASME J. Heat Transfer,Vol.125,pp.151-155,2003.
[16]Setoh, G., Tan, F.L. and Fork,S.C., Experimental studies on the use of a phase change material for cooling mobile phones,International Communications in Heat and Mass Transfer,Vol.37,pp.1403-1410,2010.
[17]Ceron, I., Neila, J. and Khayet, M., Experimental title with phase change mate-rials(PCM) for building use, Energy and buildings, Vol.36,pp.572-578,2011.
[18]Wu, S., Fang, G. and Liu, X., Dynamic discharging characteristics simulation on solar heat storage system with spherical capsules using paraffin as heat storage mate-rial, Renewable Energy,Vol.36,pp.1190-1195,2011
[19]C.J Ho, A continuum model for transport phenomena in convective flow of sol-id-liquid phase change material suspensions, Applied mathematical model-ing,vol.29,pp.805-817,2005.
[20] M. Harhira, S. K. Roy, and S. Sengupta, Natural convective heat transfer from a vertical flat plate with phase change material suspensions, Journal of Enhanced Heat Transfer,vol.4,1997.
[21]C. J. Ho and F. J. Tu, Visualization and prediction of natural convection of water near its density maximum in a tall rectangular enclosure at high rayleigh numbers, Journal of Heat Transfer,vol.123,p.84,2001.
[22]C. J. Ho and F. Lin, Numerical simulation of three-dimensional incompressible flow by a new formulation, International Jonrnal for Numerical Methods in Fluids, vol.23,pp.1073-1084,1996.
[23]C. Popiel and J. Wojtkowiak Simple formulas for thermophysical properties of liquid water for heat transfer caculations(from 0C to 150C),Heat Transfer Engineer-ing,vol.19,pp.87-101,1998.
[24]C. Ho, A continuum model for transport phenomena in convective flow of sol-id–liquid phase change material suspensions, Applied mathematical modelling, vol. 29, pp. 805-817, 2005.
[25]C.-J. Ho, J. Lin, and S. Chiu, Heat transfer of solid–liquid phase-change material suspensions in circular pipes: effects of wall conduction, Numerical Heat Transfer, Part A, vol. 45, pp. 171-190, 2004.