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題名 | 介面剪應力對垂直圓管內薄膜冷凝之影響 |
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作者 | 柯明村; 陳希立; | 書刊名 | 力學 |
卷期 | 7:2 1991.06[民80.06] |
頁次 | 頁129-139 |
分類號 | 440.137 |
關鍵詞 | 介面; 冷凝; 垂直; 剪應力; 圓管; 薄膜; |
語文 | 中文(Chinese) |
中文摘要 | 本篇主要是研究介面剪應力對垂直圓管內強制對流冷凝的影響。垂直冷凝管入口 為紊狀之飽和蒸汽,隨冷凝過程之持續此冷凝薄膜將由層流過渡成紊流薄膜。在冷膜內介面 剪應力與重力、壓力及黏滯力相互平衡,基於冷凝膜厚度相對於圓管半徑非常小之假設,吾 人應用局部相似性( local similarity )來簡化紊流蒸汽之統御方程式,同時亦提出一種 渦漩黏滯度模型,沿徑向將液汽區分為冷凝膜靠近壁面之內部區、包含液膜及蒸汽之介面區 和蒸汽核心之外部區。數值計算結果指出隨冷凝進行液汽介面剪應力有下降之趨勢,熱傳係 數漸漸遞減,而壓力降逐漸上升;當冷凝膜由層流變成紊流時汽相壓力有變成正壓降的趨勢 ,而且熱傳係數在薄膜過渡後陡增,然後再隨冷凝進行而減少。液汽介面剪應力會使冷膜的 臨界薄膜雷諾數降低而使紊狀膜提早發生,並且以本理論模式估測飽和氣體的冷凝與文獻之 實驗結果比對時相當吻合。 |
英文摘要 | An analytical study of interfacial shear effect on forced convective film condensation inside vertical tubes is presented. We proposed a unified procedure for predicting the condensation heat transfer coefficient and pressure gradient with turbulent vapor flow associated with laminar or turbulent film. The analysis for the vapor flow is performed under the condition that the velocity field is locally selfsimilar. The laminar and turbulent film models equate the gravity, pressure, and viscous forces and consider the effect of interfacial shear. The transition from laminar to turbulent film depends not only on the liquid Reynolds number but also on the interfacial shear stress. In this work we also proposed a new eddy viscosity model which is divided into three regions. They are the inner region in liquid condensate near the wall, the interface region including both liquid and vapor, and the outer region for the vapor core. Comparisons of present theory with some experimental data reported in the literature showed good agreement. |
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