本文針對等熱通量圓管內水層流強制對流熱傳逸系統，藉內置入一較小管徑同心圓管構成內管/外環雙流道結構之替代對流熱傳逸模型，採實驗量測與數值模擬互補方式，探討利用固-液相變化奈米乳液取代流經外環流道之水為熱傳遞流體，及在固定雙管流道總流量條件下，調控內管/外環流道內工作流體流量比，所致相關對流熱傳遞特性及增益。本文所建構強制對流熱傳遞實驗迴路中所用同心圓雙流管為銅管，外管長度1250mm，內外徑為9.1mm與10mm內管長度2060mm，內外徑為5.35mm與6mm；在測試段外管壁面加熱段部分纏繞鎳鉻電阻線以達等熱通量的加熱條件。本文強制對流熱傳遞實驗所設定相關條件為：內/外管內工作流體進口溫度設為33℃，相變化奈米乳液的質量分率為2%、5%、10%，控制總流量為304.83cm^3/min、465.98cm^3/min，外管壁面加熱段加熱功率為70W、110W、130W、150W，調控內/外管流量比為0.33、0.51、0.7、1.0、1.63、2.0、2.8、4.0等。實驗結果顯示在適合的內/外管流量比及加熱功率下，外環流道以相變化奈米乳液取代水可有效降低加熱管壁溫度，並提升以同心圓雙流道以取代單圓管所致強制對流熱傳遞增益；相較於純水，其最大局部熱傳遞增益及平均熱傳遞增益可達36%，惟在同加熱壁熱點壓抑效益則僅有4%。此外，本文藉對應於實驗量測條件之數值模擬分析，進一步探討外環流道工作流體為奈米乳液時，其內含相變化微粒融解情形及內管對流熱傳遞特徵。此外，相較於與相對應原之純水單管對流模型之數值模擬結果，發現在相同總流量、加熱功率下，同心雙圓管對流結構的局部及平均熱傳遞增益可分別達75%及73%，且加熱段管壁溫壓抑之增益達14.94%。

In this study, the efficacy of enhancing the forced convection heat transfer of laminar water flow in an iso-flux heated circular tube by inserting a concentric smaller tube and controling the concurrent flow rates of water/Nano-PCM emulsion and water, respectively, through the outer annulus and the inner tube has been examined experimentally and numerically. The internal forced convection experiments have been performed in a two-tube duct configuration featuring a radius ratio between the outer and inner tube, ro = 1.7, under the pertinent variables/parameters as follows: the total volumetric flow rate, = 304,83 and 465.98 cm3/min; the heating power, qh = 70, 130, 110, and 150W ; the relative flow ratio of the outer annulus to that of the inner tube, = 0.33, 0.51, 0.7, 1.0, 1.63, 2.0, 2.8, and 4.0; the mass fraction of the Nano-PCM emulsion, pcmp = 2.13%, 3.04%, and 7.11%; the inlet fluid temperature, Tin = 33C. Results obtained from the forced convection heat transfer experiments performed for the two-tube duct configuration considered are presented focusing on first (a) the effectiveness of replacing the pure water by Nano-PCM emulsion as the working fluid in the outer annulus of the two-tube duct configuration; and then (b) the effectiveness of adopting the two-tube duct configuration for upgrading the heat dissipation performance of the parent single-tube duct configuration. Experimental results clearly demonstrated that in comparison with its parent single-tube configuration, the iso-flux heated wall temperature appears suppressed effectively and thus the local and averaged heat transfer coefficients over the iso-flux heated section become increasingly uplifted with the relative flow ratio between the outer annulus and the inner tube. Increasing the relative flow ratio between the outer annulus and inner tube up to 4.0 can result in the enhancements of 75% and 73%, respectively, for the local and average heat transfer coefficients of the two-tube duct using the pure water as the working fluid over those of the single-tube duct. Furthermore, using the Nano-PCM emulsion formulated instead of the pure water, as the working fluid in the outer annulus appears somewhat downgrading the average heat transfer effectiveness of the two-tube duct over the parent single-tube duct, which mainly is due to the fact that there exists a critical relative flow ratio for the Nano-PCM emulsion in the outer annulus to have sufficient residence time over the heated section whereby the latent heat absorption effect associated with the on-going melting process the Nano-PCM particles can in effect a role in upgrading the heat transfer effectiveness.

[1] S. U. S. Chol and J. A. Estman.,"Enhancing thermal conductivity of fluids with nanoparticles." , ASME-Publications-Fed, Vol.231, pp. 99-106, 1995
[2] K. E. Kasza and M. M. Chen ,”Improvement of the performance of solar energy or waste heat utilization systems by using phase-change slurry as an enhanced heat-transfer storage fluid.”, Journal of Solar Energy Engineering, Vol.107.3, pp. 229-236, 1985
[3] I. Sole, C. Solans, A. Maestro, C. Gonzalez and J. M. Gutierrez, ”Study of nano-emulsion formation by dilution of microemulsions.”, Journal of Colloid and Interface Science, Vol. 376, pp. 133-139, 2012.
[4] P. Fernandez, V. Andre, J. Rieger and A. Kuhnle, "Nano-emulsion formation by emulsion phase inversion", Colloids and Surfaces a-Physicochemical and Engineering Aspects, Vol. 251, pp. 53-58, 2004.
[5] T. Kawanami, K. Togashi, K. Fumoto, S. Hirano, P. Zhang, K. Shirai and S. Hirasawa,
“Thermophysical properties and thermal characteristics of phase change emulsion for thermal energy storage media”, Energy , Vol. 117, pp. 562-568, 2016
[6] C. Qian and D. J. McClements, "Formation of nanoemulsions stabilized by model food-grade emulsifiers using high-pressure homogenization: Factors affecting particle size", Food Hydrocolloids, Vol. 25, pp. 1000-1008, 2011.
[7] G. Gutiérrez, J.M. Benito, J. Coca, C. Pazos,"Evaporation of aqueous dispersed systems and concentrated emulsions formulated with non-ionic surfactants.", International Journal of Heat and Mass Transfer, Vol. 69, pp. 117-128, 2014.
[8] A.Ye, X. Zhu and H. Singh, "Oil-in-water emulsion system stabilized by protein-coated nanoemulsion droplets", Langmuir, Vol. 29, pp. 14403-14410, 2013.
[9] K. H. Persson, I. A. Blute, I. C. Mira and J. Gustafsson,” Creation of well-defined particle stabilized oil-in-water nanoemulsions”, Physicochemical and Engineering Aspects, Vol. 459, pp.48-57, 2014
[10] 王景宏,”相變化材料次微米膠囊製備與相關物性之研究”,國立成功大學機械工程研究所碩士論文, pp.1-88, 2000
[11] K. Resch-Fauster, M. Feuchter,” Thermo-physical characteristics, mechanical performance and long-term stability of high temperature latent heat storages based on paraffin-polymer compounds”, Thermochimica Acta, Vol. 663, pp 34-45, 2018
[12] M. Takashi, K. Hiroyuki,”Flow and heat transfer characteristics of phase change emulsions in a circular tube: Part 1. Laminar flow”, International Journal of Heat and Mass Transfer, Vol. 117, pp. 887-895, 2018
[13] J. Xu, B. Yang and B. Hammouda, "Thermal conductivity and viscosity of self-assembled alcohol/polyalphaolefin nanoemulsion fluids", Nanoscale Research Letters, Vol. 6, pp. 274-281, 2011.
[14] Z. H. Han, F. Y. Cao, and B. Yang, "Synthesis and thermal characterization of phase-changeable indium/polyalphaolefin nanofluids" Applied Physics Letters ,Vol. 92, 2018
[15] C.Selvam , T.Balaji , D.Mohan Lal , S. Harishb ,” Convective heat transfer coefficient and pressure drop of water-ethylene glycol mixture with graphene nanoplatelets”, Experimental Thermal and Fluid Science,Vol. 80, pp. 67-76, 2017
[16] T. Morimoto, K. Togashi, H. Kumano and H. Hong,”Thermophysical properties of phase change emulsions prepared by D-phase emulsification.” Energy Conversion and Management, Vol.122 , pp. 215-222, 2016
[17] J. Thomas, P.V.S.S. Srivatsab , S. R. Krishnan, R. Baby, “Thermal Performance Evaluation of a Phase Change Material Based Heat Sink: A Numerical Study.”, Procedia Technology, Vol. 25, pp.1182-1190, 2016
[18] X. Wang, J. Niu, Y. Li, X. Wang, B. Chen, R. Zeng and Y. Zhang,“Flow and heat transfer behaviors of phase change material slurries in a horizontal circular tube.” International Journal of Heat and Mass Transfer, Vol. 50 , pp. 2480-2491, 2007
[19] S. Saarinen, S. Puupponen, A. Meriläinen, A. Joneidi, A. Seppälä, K. Saari and T. Ala-Nissila,“Turbulent heat transfer characteristics in a circular tube and thermal properties of n-decane-in-water nanoemulsion fluids and micelles-in-water fluids.” International Journal of Heat and Mass Transfer , Vol.81 , pp. 246–251, 2015
[20] S. Mossaz, J. A. Gruss, S. Ferrouillat, J. Skrzypski, D. Getto, O. Poncelet and P. Berne,“Experimental study on the influence of nanoparticle PCM slurry for high temperature on convective heat transfer and energetic performance in a circular tube under imposed heat flux.” ,Applied Thermal Engineering,Vol. 81, pp. 388-398., 2015
[21] P.Charunyakorn, S. Sengupta and S. K.Roy,"Forced-convection heat-transfer in microencapsulated phase-change material slurries - flow in circular ducts," International Journal of Heat and Mass Transfer, Vol. 34, pp. 819-833, 1991.
[22] M. Goel, S. K. Roy and S. Sengupta, "Laminar forced-convection heat-transfer in microcapsulated phase-change material suspensions", International Journal of Heat and Mass Transfer, Vol. 37, pp. 593-604, 1994.
[23] Y. W. Zhang and A. Faghri, "Analysis of forced-convection heat-transfer in microencapsulated phase-change material suspensions," Journal of Thermophysics and Heat Transfer,Vol. 9, pp. 727-732, 1995.
[24] C.J. Ho, J. F. Lin and S. Y. 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
[25] J.F. Lin and C.J. Ho. “Thermally developing forced convection for PCM suspensions in a circular duct.”, Journal of Chinese Society of Mechanical Engineers,Vol. 26 ,pp. 45-53,2005
[26] R. L. Zeng, X. Wang, B. J. Chen, Y. P. Zhang, J. L. Niu, X. C. Wang,"Heat transfer characteristics of microencapsulated phase change material slurry in laminar flow under constant heat flux", Applied Energy, Vol. 86, pp. 2661-2670, 2009.
[27] 李政逸,”水基底奈米相變化乳液於水平圓管內強制對流熱傳遞特性之實驗研究”,國立成功大學機械工程研究所碩士論文, pp.1-77, 2012
[28] 劉匡育,”奈米相變化材料/石墨烯-水之混合型奈米流體於圓管內層流強制對流熱傳遞特性研究”,國立成功大學機械工程研究所碩士論文, pp.1-110, 2016
[29] Guangyao Lu and Jing Wang,” Experimental investigation on heat transfer characteristics of water flow in a narrow annulus”, Applied Thermal Engineering, Vol.28, pp. 8–13, 2008
[30] C.D. Ho, J.W. Tu, S.C. Yeng, J.J. Guo,”Heat-transfer efficiency improvement of Double-pass concentric circular heat exchanger under uniform wall fluxs”,International Communications in Heat and Mass Transfer, Vol.35, pp. 828-832, 2008
[31] J. Dirker and J.P. Meyer, “Heat transfer coefficients in concentric annuli”, Journal of Heat Transfer, Vol.124 , pp.1200–1203, 2002
[32] K. Vafai, C.P. Desai, S.V. Iyer and M.P. Dyko, “Buoyancy induced convection in a narrow open-ended annulus”, Journal of Heat Transfer, Vol.119 , pp.483–494 , 1997
[33] C. Yang,W. Li and A. Nakayama,“Convective heat transfer of nanofluids in a concentric annulus.” International Journal of Thermal Sciences,Vol.71, pp. 249-257, 2013
[34] C.D. Ho and W.Y. Yang. “An analytical study of heat-transfer effciency in laminar counterflow concentric circular tubes with external refuxes.”, Chemical Engineering Science,Vol. 58 , pp.1235-1250 , 2003
[35] C.D. Ho and S.C. Yeh ,“Improvement in device performance on laminar counterflow concentric circular heat exchangers with uniform wall fluxes.”, International Journal of Heat and Mass Transfer,Vol. 49, pp.2020–2032 , 2006
[36] 顏榮毅,” 奈米相變化乳液/奈米流體分別流於外壁加熱同心圓環道/內管共軛強制對流熱傳遞增益特性模擬研究”, 國立成功大學機械工程研究所碩士論文,pp.1-142,2016
[37] M. Harhira, S. K. Roy and S. Sengupta,“Natural Convection Heat Transfer from A Vertical Flat Plate with Phase Change Material Suspensions.” ,Journal of Enhanced Heat Transfer,Vol. 4, pp.17-34, 1997
[38] 黃俊博,” 一水平圓管內PCM微粒/奈米微粒懸浮流體之熱發展強制對流熱傳特性研究”, 國立成功大學機械工程研究所碩士論文, pp.1-105, 2007
[39] 張智揚,” 氧化鋁-水奈米流體進口溫度及隨溫度變化熱物性質對圓管內層流對流熱傳遞性能之效應”,國立成功大學機械工程研究所碩士論文, pp.1-127, 2011