隨著科技的日新月異以及對於環境保護的概念越來越重要的前題下，降低能源的浪費或是效率的提升方面一直是大家都在努力的方向。提升整體熱傳遞的效率減少廢熱的產生已成為一門重要的研究課題，尤其是在高科技產業及發電安全領域等應用方面極為廣泛。比較傳統熱傳效率以及改良熱交換器的熱交換效率為本文之研究重點。
本研究以一款交叉橢圓管熱交換器為探討對象，其內管為交叉橢圓之熱流管，外管為圓形絕熱冷流管。冷熱流體之間由內壁傳遞熱能，藉由改變內外管之雷諾數可模擬流場並估算其對於熱傳效率的差異，從而深入探討紐塞數摩擦因子，綜合性能指標以及當量熱阻以作為比較的依據。
本文了應用控制體積法數值求解紊流之橢圓、耦合及穩態條件之三維統御偏微分方程。再使用SST-"k-ω" 紊流模型以作細部求解。
經由場協同理論與耗散原理所推導出的速度場協同方程式完成管內流場之優化模擬，發現在內管內截面上產生8個渦流能強化管內縱向流動使管壁面處的溫度梯度增加，使得熱傳遞量提升，而在外管內截面則會產生4個渦流。
從數值模擬結果得知紐塞數隨著雷諾數增加而成長，綜合性能指標的趨勢大於1，說明了此強化管的熱表現良好。且強化管的場協同角比起圓管來得小，解釋了強化管之紐塞數比起圓管來得高的現象。相較於傳統圓管，交叉橢圓可以達到熱傳效率有效提升之結果。

Heat exchangers are one of the most commonly used heat transfer devices in many industries or daily life equipment. Among all the heat exchangers，double pipe heat exchangers have specific role and are widely used in oil refinements or chemical industries. Due to the low cost of manufacturing and easy to cooperate with other engineering design. The performance improvement has been a matter of interest for engineers.
Numerical simulations of air/water forced convection in an alternating horizontal or vertical oval pipe as inner section double-piped heat exchangers are investigated. In comparison with double circular pipe heat exchangers, the goal is to enhance the total heat transfer efficiency in turbulent flow. Next，we compare the difference between parallel flow and counter flow. Staggered oval tube constructs 8 vortexes in radial directions. The influences of these secondary flow are explained by the field synergy principle，the entransy dissipation rate 、 thermal resistance and performance evaluation criteria are also calculated to evaluate the overall heat transfer ability.
The average Nusselt number and the friction factor both increase with increasing Reynolds number. The thermal resistance of oval pipe is lower than circular pipe，but the difference and the performance evaluation criteria both decrease as Reynolds number increases. Furthermore，the results show that counter flow is more efficient than parallel flow.

[1] B.S. Petukhov, V.N. Popov, Theoretical calculation of heat exchange and frictional resistance in turbulent flow in tubes of an incompressible fluid with variable physical properties, High Temperature Institute, Vol.1 pp. 69–83.1963
[2] R.L. Webb, in: Principles of Enhanced Heat Transfer, John Wiley and Sons Inc, New York, p. 89. 1994
[3] W.Q. Tao, Z.Y. Guo, B.X. Wang, Field synergy principle for enhancing convective heat transfer––its extension and numerical verifications, International Journal of Heat Mass Transfer‚ Vol.45 pp.3849–3856. 2002
[4] A.E. Bergles, Advanced enhancement-third generation heat transfer technology. Experimental Thermal and Fluid Science, Vol.26 pp.335-344. 2002
[5] A.E. Bergles, ExHFT for fourth generation heat transfer technology. Experimental Thermal and Fluid Science, Vol.26 pp.335-344. 2002
[6] R.L. Webb, Bergles A E. Heat transfer enhancement: second generation technology. Mechanical Engineering, Vol.115(6) pp.60-67. 1983.
[7] A.E. Bergles, Some perspectives on enhanced heat transfer second Generation heat transfer technology. ASME Journal of Heat Transfer, Vol.110 pp.1082-1096. 1988.
[8] B. Timité, C. Castelain, H. Peerhossaini, Mass transfer and mixing by pulsatile three-dimensional chaotic flow in alternating curved pipes, International Journal of Heat Mass Transfer. Vol.54 pp.3933-3950. 2011
[9] M.Y. Wen, Flow structures and heat transfer of swirling jet impinging on
a flat surface with micro-vibrations, International Journal of Heat Mass Transfer‚ Vol.48 (3) pp. 545–560. 2005
[10] Y. Yan, H. Zhang, J. Hull, Numerical modeling of electrohydrodynamic (EHD)effect on natural convection in an enclosure, Numerical Heat Transfer‚ Part A: Appl. Vol.46 (5) pp. 453–471. 2004
[11] N. Kasayapanand, Electrohydrodynamic enhancement of heat transfer in
vertical fin array using computational fluid dynamics technique, International Communications in Heat and Mass Transfer‚ Vol.35 (6) pp.762–770. 2008
[12] T.Inagaki, K.Komori, Experiment study of heat transfer enhancement in turbulent natural convection along a vertical flow plate-part I: the effect of injection or sunction. Heat Transfer Japanese Research, Vol.22 pp.387-397. 1993.
[13] A.E. Bergles, Advanced enhancement-third generation heat transfer technology, or the “final frontier”. Chemical Engineering Research and Design, Vol.79. pp.437-444. 2001.
[14] C.A. Balaras. A review of augmentation technigues for heat transfer in single-phase heat exchanger. Energy, 15(10) pp.899-906 1990.
[15] J.P. O’Connor, S.M. You, A painting technique to enhance pool boiling heat transfer in saturated FC-72. ASME Journal of Heat Transfer, Vol.117 pp.387-393. 1995.
[16] S.J. Eckels, T.M. Doerr, M.B. Pate, heat transfer and pressure drop of R-164a and ester lubricant mixtures in a smooth and a micro-fin tube: part I-evaporation. ASHRAE Transactions, Vol.100(2) pp.265-281. 1994.
[17] S.J. Eckels, T.M. Doerr, M.G. Pate, In-tube heat transfer and pressure drop of R-134a and ester lubricant mixtures in a smooth and a micro-fin tube: part II-condensation. ASHRAE Transactions, Vol.100(2) pp.283-294. 1994.
[18] M.E. Taslim, T Li, S.D. Spring, Measurements of heat transfer coefficients and friction factors in passages rib-roughened in all walls. Journal of Turbomachinery, Transactions of the ASME, Vol.120(3) pp.564-570. 1998.
[19] M. Fiebig , M.A. Sanchez‚Enhancement of heat transfer and pressure loss by winglet vortex generators in a fin-tube element. Compact Heat Exchangers for Power and Precess Industries, HTD-n201, The American Society of Engineers, New York, 7-14. 1992.
[20] R.M. Eason, B.Y. Miade , A. Enhancement of heat transfer in square helical ducts. International Journal of Heat Mass Transfer, Vol. 37 pp.2077-2087. 1994.
[21] S. Liu, M. Sakr, A comprehensive review on passive heat transfer enhancements in pipe exchangers, Renew, Sustain, Energy Revolution, Vol.199. pp. 64-81. 2013
[22] M. Omidi , M. Farhadi , M. Jafari, A comprehensive review on double pipe heat exchangers. Applied Thermal Engineering‚ Vol.110. pp.1075–1090. 2017
[23] M. Heyhat, F. Kowsary, A. Rashidi, M. Momenpour, A. Amrollahi, Experimental investigation of laminar convective heat transfer and pressure drop of waterbased Al2O3 nanofluids in fully developed flow regime, Experimental Thermal and Fluid Science‚ Vol.44. pp.483–489. 2013
[24] D. Ashtiani, M. Akhavan-Behabadi, M.F. Pakdaman, An experimental
investigation on heat transfer characteristics of multi-walled CNT-heat
transfer oil nanofluid flow inside flattened tubes under uniform wall
temperature condition, International Communications in Heat and Mass Transfer‚ Vol.39 (9) pp.1404–1409. 2012
[25] A.E. Bergles, Handbook of heat transfer applications. New York: McGraw-Hill, 1985.
[26] R.L. Webb‚ Principle of Enhanced Heat Transfer. John Wiley & Sons, New York, ISBN 0-471-57778-2 , 1994.
[27] H. Haken‚ Synergetics, An Introduction: Nonequilibrium Phase Transitions and Self-Organization in Physics, Chemistry, and Biology, 3rd rev. enl. ed. New York: Springer-Verlag, 1983.
[28] Z.Y. Guo, A Brief Introduction to A Novel Heat-transfer Enhancement Heat Exchanger, Internal Report, Department of EMEMKLEHTEC, Tsinghua University, Beijing, China, 2003
[29] W.L. Chen, Z. Guo, C.K. Chen, A numerical study on the flow over a novel tube for heat-transfer enhancement with a linear eddy-viscosity model, International Journal of Heat and Mass Transfer‚ Vol.45. pp.3431-3439. 2004
[30] W.L. Chen, K.L. Wong, K.-D. Wong, A parametric study on the laminar flow in an alternating horizontal or vertical oval cross-section pipe with computational fluid dynamics, International Journal of Heat and Mass Transfer, Vol.49. pp. 287-296. 2006
[31] W.L. Chen, A numerical study on the heat-transfer characteristics of an array of alternating horizontal or vertical oval cross-section pipes placed in a cross stream, International Journal of Refrigeration, Vol.30 (3) pp. 454–463. 2007
[32] W.L.Chen,W-C Dung. Numerical study on heat transfer characteristics of double tube heat exchangers with alternating horizontal or vertical oval cross section pipes as inner tubes. Energy Conversion and Management, Vol.49. pp.1574–1583. 2008
[33] S. Vaezi, S. Karbalaee, P. Hanafizadeh , Effect of aspect ratio on heat transfer enhancement in alternating oval double pipe heat exchangers. Applied Thermal Engineering, Vol. 125. pp.1164-1172. 2017
[34] Z.Y. Guo, D.Y. Li, B.X. Wang, A novel concept for convective heat transfer enhancement, International Journal of Heat and Mass Transfer, Vo. 41, Issue 14, pp. 2221–2225. 1998.
[35] 劉偉,劉志春,馬雷,多場協同原理在管内對流強化傳熱性能評價中的應用.科學通報,57(10):867-876,2012
[36] A.Bejan , Study of entropy generation in fundamental convective heat transfer, J. Heat Transfer – Trans. ASME, Vol. 101 (4), pp. 718–725. 1979
[37] R.K. Shah, T. Skiepko, Entropy generation extrema and their relationship with heat exchanger effectiveness – number of transfer unit behavior for complex flow arrangements, Journal of Heat Transfer – Transaction of The. ASME, Vol. 126 (6) , pp. 994–1002. 2004
[38] Z.Y. Guo, H.Y. Zhu, X.G Liang., “Entransy – a physical quantity describing heat transfer ability, International Journal of Heat and Mass Transfer, Vol. 50, pp. 2545–2556. 2007
[39] Z.Y. Guo, X.G. Cheng, Z.Z. Xia, Least dissipation in principle of heat transport potential capacity and its application in heat conduction optimization, Chinese Science Bulletin Vol.48. pp.406-410. 2003
[40] Q.Chen , M.Wang , N. Pan et al. Optimization principles for convective heat transfer, Energy, Vol. 34 (9), pp. 1199–1206. 2009.
[41] J.F. Guo, M.T. Xu, The application of entransy dissipation theory in optimization design of heat exchanger. Applied Thermal Engineering, 36. 227-235. 2012
[42] 孟繼安.基於場協同理論的縱向渦強化換熱技術及其應用。博士論文。北京:清華大學,2001.
[43] 陳群.對流換熱過程的不可逆性及其優化。博士論文。北京:清華大學,2008.
[44] R.L. Webb‚E.R.G.Eckert, Application of rough surfaces to heat exchanger design, International Journal of Heat and Mass Transfer, Vol.15(9), pp. 1647–1658. 1972.
[45] F.R. Menter‚ Two-Equation Eddy-Viscosity Turbulence Models for Engineering Applications‚ The American Institute of Aeronautics and Astronautics Journal, Vol.32(8). pp.1598–1605. 1994.
[46] S.V. Patankar, Numerical Heat Transfer and Fluid Flow, McGraw-Hill, New York, 1980.
[47] S.V. Patankar, D.B. Spalding, A calculation process for heat, mass and momentum transfer in three-dimension parabolic flows, International Journal of Heat and Mass Transfer, vol. 15, pp. 1787-1806. 1972.