本文採用數值模擬與實驗並行方式，在數值模擬部分藉由改變進口溫度、流量和加熱功率且固定加熱段長度lh+/(di+Pef,0)=0.1所定義的無因次進口溫度參數範圍in=1.04~16.51並針對其對流場、熱傳遞及熵生成量的影響進行研究，結果顯示當in=1.04時，在考慮可變物性與固定物性下結果的比值，壓降與熵生成量有最小值；對流熱傳係數有最大值。實驗上針對氧化鋁奈米流體進行粒徑、黏度和熱傳導係數上的確認，所測得在水中懸浮粒徑為109.6 nm，並將其應用在等熱通量加熱水平圓管內的層流強制對流熱傳實驗；所用的圓管分為兩種:外徑分別為4 mm與6.3 mm，內徑分別為3.4 mm與6 mm，無因次管壁厚度tw=0.17和0.05，實驗相關條件參數：氧化鋁-水奈米流體濃度為ω_np^ =2~10 wt.%；進口溫度Tin = 25℃和50℃；Ref,0 =186~2095；外管壁等效熱通量q_(eff,o)^'=1066~7362 W/m2，實驗結果在進口溫度為50℃時，氧化鋁-水奈米流體與水的平均對流熱傳效益比值最大達1.18。本文研究中，局部壁溫與局部對流熱傳係數在數值模擬與實驗比對大致相符。

關鍵字: 奈米流體、可變物性、層流強制對流

In the present study, the laminar forced convection heat transfer characteristics of a horizontal tube partially heated with constant heat flux have been investigated experimentally and numerically. In numerical simulation, dimensionless inlet temperature parameter, θ_in^ , defined by inlet temperature, flow rate and heating power and dimensionless heating length lh+/(di+Pef,0) was fixed to 0.1, ranges from 1.04 to 16.51.
Under the consideration of the ratio of variable thermal physical property and constant thermal physical property, convection heat transfer coefficient and minimum value in the pressure drop and entropy generation. In thermal physical properties verification, Al2O3-water nanofluid was conducted for particle size test, about 109.6 nm in suspension fluid, viscosity and thermal conductivity. On the other hand, experiments have been performed using two copper tube of inner and outer radii, one is 3.4 mm and 4 mm, the other is 6 mm and 6.3 mm, for the relevant parameters in the following ranges: the mass fraction of nanoparticles, np = 2 ~ 10 wt.%; the Reynolds number, Ref,0 = 186 ~ 2095; the inlet temperature, Tin = 25℃ and 50℃, and the imposed heat flux, qo" = 1069 ~ 7362W/m2 . The laminar cooling effectiveness of the nanofluid flow can be enhanced up to 1.18 at inlet temperature 50℃. The experimental results clearly exhibit a good agreement with the corresponding numerical simulations.

Key words: nanofluid, variable property, laminar forced convection.

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