本文研究非牛頓流體於交叉橢圓套管紊流強制對流熱傳遞之數值模擬，其內管為交叉橢圓管且為熱流管，外管為圓形絕熱冷流管，流道配置為逆流型，透過管壁傳遞熱能達到冷、熱流體的熱交換，首先以參考文獻中純水於交叉橢圓套管之模擬、實驗數據作驗證，結果相當吻合，其最大誤差在5%以內，接著進一步延伸至非牛頓流體。
比較不同流變特性流體熱傳效率的差異，從而探討紐塞數、摩擦因子、熱性能以及當量熱阻以作為比較的依據。本文應用控制體積法數值求解紊流非牛頓流體之橢圓、耦合及穩態條件之三維統御偏微分方程。再使用 紊流模型作細部求解。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。
文中比較交叉橢圓管與圓管兩種結構的性能差異，模擬結果顯示，與圓管相比，流體流經交叉橢圓管時產生二次流、漩渦，在內管截面上產生8個渦流，外管截面則產生4個渦流，造成熱傳性能增強，但同時交叉橢圓管引起的擾動也會增加壓降。在研究範圍內，發現Power-law(n < 1)冪律型非牛頓流體具有的流變特性相較純水具有更好的熱傳性能，此外以場協同理論解釋二次流對於熱傳的影響，並計算橢圓扭曲管中的耗散率。結果顯示在交叉橢圓管中，扭曲的壁面使速度與溫度梯度有更好的協同性，因此可提高熱傳。
從數值模擬結果可知Power-law(n < 1)冪律型非牛頓流體紐賽數大於純水，且具有更好的場協同角，其熱阻不僅相較純水低也隨雷諾數增加而下降，皆說明了Power-law(n < 1)冪律型非牛頓流體的優良表現，場協同佳與熱阻低也解釋了Power-law(n < 1)冪律型非牛頓流體之紐賽數比起純水高的現象，此外更說明了在本文研究中流體的流變特性為影響熱傳性能最重要的因素。
關鍵字: 冪律型非牛頓流體流變特性、交叉橢圓管、耗散理論、場協同原理。

Numerical simulations of power law fluid/water forced convection in double pipe heat exchangers with staggered oval inner sections are investigated. In comparison with double circular pipe heat exchangers. This study compares the differences in heat transfer efficiency of fluids with different rheological properties. Use power law fluid the goal is to enhance the total heat transfer efficiency in turbulent flow. In addition, we compare the difference between parallel flow and counter flow. The simulation results show that the counter flow model has better performance than the parallel flow.
Heat exchangers with staggered oval inner sections create 8 vortexes in radial directions. The effects of these secondary flow are explained by the entransy dissipation rate 、the field synergy principle and thermal resistance to evaluate the overall heat transfer capability.
The average Nusselt number and the pressure drop both increase with the increasing Reynolds number. We found that the Nusselt number of power law fluid(n<1) is larger than water and has a better field synergy angle. Besides, the thermal resistance of power law fluid(n<1) is lower than water. Hence, the use of power law fluid can achieve the effect of improving heat transfer efficiency.

Keywords: Power law fluids, Staggered oval tubes, Entransy dissipation, Field synergy principle

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