本文採用數值模擬與實驗並行探討在等熱通量下流體通入同心雙圓管之強制對流層流中的熱傳遞現象與增益，在數值模擬的部分會先輸入入口溫度、總流量、流量比與加熱功率等參數後進行模擬並針對熱阻的結果進行分析，其中發現同心雙管的熱傳機制主要由外環流體帶走熱能，故設計以下實驗參數比較討論：改變加熱功率120W、160W和200W及總雷諾數800、1300和1700，並調控六個流量比為：0.1、0.286、0.454、1.0、1.6、2.38。此外，也藉由改變工作流體之熱物理性質，實現降低整體軸向與徑向熱阻值，進而增加熱傳增益，例如：外環以擁有高熱傳係數之 及 奈米流體代替純水，內管則以 奈米乳液代替純水，藉由其相變化過程增加熱散逸及降低壁溫。同心雙管之材料與尺寸如下：外管管材為無氧紅銅管，外管外徑為6mm，外管內徑為5.4mm，總長為1250mm；內管管材為不銹鋼管，內管外徑為4.6mm，內管內徑為4.2mm，總長為2060mm。
在同心雙管實驗結果可得外環為 奈米流體內管為純水因熱物理性質與散熱機制的關係並無明顯的增益，但當外環奈米流體濃度提升至 後，其平均熱傳增益在總雷諾樹為1700、加熱功率為200W且流量比在2.38時有12.63%的增益，而外環為 奈米流體內管為 奈米乳液則因內管流體潛熱的發揮提升了整體熱傳對流效果使其擁有最大平均熱傳增益16.5%，且與單管比較也有最大熱傳增益27.7%，而在壓降增幅的結果來看不論是改變工作流體還是流道從單管轉變成同心雙管的架構所增加的壓降都過大，以至於效能指標都偏低，不過單從熱傳增益的部分機能性流體除了外環為 奈米流體內管為純水外，都有不錯的收穫。

This paper uses numerical simulation and experiments to discuss the heat transfer phenomenon and enhance efficacy in forced convection laminar flow. The fluid passes through the concentric double circular tube under equal heat flux. In the part of numerical simulation, the results of thermal resistance are going to be analyzed after input the initial parameters, such as the inlet temperature, the total flow rate, the ratio of flow rate, and the heater power. It is found that the heat transfer mechanism of the concentric double-tube duct is mainly taken away by the fluid in outer tube. The following experimental conditions including the heater power (120W, 160W, 200W), the total Reynolds numbers( 800, 1300, and 1700), and the flow rate ratio of outer tube over inner tube (0.1, 0.286, 0.454, 1.0, 1.6, 2.38) are used to explore and discuss. In addition, improving the thermophysical properties of the working fluid not only reduces the overall axial and radial thermal resistance but also increases the heat transfer effect.
Therefore, choosing nanofluid of volume concentration of 0.5 percent or 1.0 percent and a weight concentration of 4.63 percent nano-emulsion as working fluids can improve high heat transfer conductivity and the latent heat mechanism, thus increase the heat transfer effectivity. The heat exchanger was made of concentric tubes with the following dimensions: inner and outer diameters of stainless-steel tube were 4.2mm and 4.6mm, respectively； inner and outer diameters of the oxygen-free copper tube were 5.4mm and 6mm, respectively. The total length of the inner and outer tubes was 2060mm and 1250mm.
Based on the experimental results, the working fluid combination of 0.5% nanofluid and the pure water in the outer annulus, as well as the inner tube, does not have a significant gain because of the thermophysical properties and the heat dissipation mechanism. For the specified condition of total Reynolds is 1700, the heating power is 200W, and the ratio of flow rate is 2.38, nanofluid of the concentration increases to 1.0 percent in the outer annulus, the average heat transfer has 12.63% improvement. Further, using 4.63% nano-emulsion to replace the pure water in the inner tube show that the maximum average heat transfer improvement compared with the pure water and the single pipe were 16.5% and 27.7%, respectively. However, the figure of merit (FOM) is low because the viscosity of the functional fluid and the flow channel structure cause the pressure drop dramatically increases as well as the increment of the heat transfer is relatively low. Although concentric double tube will cause a significant loss of pressure drop, using functional fluid or modifying the flow channel structure still has good harvests for heat transfer efficiency.

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