本研究以數值方法模擬加鰭片水平管的鰭片不均溫性對自然對流熱傳的影響，在固定0.5 mm鰭片厚度下透過改變鰭片外徑、管徑、鰭片間距、及鰭片材料來探討鰭片不均溫性與鰭片各項參數的相互影響。模擬結果顯示，當鰭片較為均溫(鋁鰭片)時，隨著管徑越小，總散熱量越大；當鰭片較為不均溫(不鏽鋼鰭片)時，隨著管徑越大，鰭片散熱通量增加使得總散熱量越大。鰭片不均溫性及管徑也會對最佳鰭片間距造成影響，若將現有最佳間距經驗式套用在大管徑及不均溫的加鰭片水平管會有顯著誤差。在自然對流的浮力熱流作用下，鰭片上的溫度與熱對流係數皆呈非軸對稱分布，當採用不鏽鋼鰭片時，隨著鰭片外徑增大，不鏽鋼鰭片的溫度及熱對流係數的不均勻性均較鋁鰭片劇烈，在管上方的鰭片區域甚至可發生負值的局部熱對流係數。因此，當採用現有加鰭片水平管之鰭片效率的軸對稱理論方法來估算高不均溫性的不鏽鋼鰭片時，會產生顯著的誤差，但使用簡易的面積修正法可將誤差縮小。本研究顯示鰭片的不均溫性與管徑大小均對加鰭片水平管的自然對流熱傳有顯著影響。

This study numerically investigates the thermal performance of non-isothermal finned horizontal tube under natural convection. The parameters considered include fin diameter, fin spacing, fin material and tube diameter, with fin thickness fixed at 0.5 mm. The effect of the temperature uniformity is found to affect the total heat output of the finned tube. The computational results show that when the fin temperature is relatively uniform (aluminum fins), the total heat output becomes greater for a smaller tube diameter; on the contrary, when the fin temperature is non-uniform (stainless-steel fins), the total heat output becomes greater for a larger tube diameter. The uniformity of fin temperature, and tube diameter as well, would affect the optimum fin spacing. Consequently, applying the empirical optimum-spacing formula available in the literature leads to notable discrepancies for the cases with non-isothermal fins or large tube diameters. Under natural convection, the distributions of temperature and heat transfer coefficient on the fins deviate from being axisymmetric due to the buoyancy flow. For stainless-steel fins, the non-uniformities of fin temperature and heat transfer coefficient are far more serious than for aluminum fins. On the non-uniform fins, the region above the tube could be distributed with negative local heat transfer coefficients. In calculating the fin efficiencies of highly non-uniform fins, the axisymmetric theoretical methods in the literature may yield significant errors. The present results indicate that both temperature uniformity and tube diameter are highly influential to the thermal performance of finned horizontal tube.

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