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題名 | Superheated Mixed Convection Film Condensation in the Forward Stagnation Region of a Cylinder or Sphere=過熱蒸汽流經圓柱或圓球區域之混合對流膜狀凝結 |
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作者 | 楊勝安; 許昭和; | 書刊名 | 中國機械工程學刊 |
卷期 | 18:1 1997.02[民86.02] |
頁次 | 頁85-93 |
分類號 | 440.137 |
關鍵詞 | 蒸汽過熱效應; 混合對流; 膜狀凝結; Superheat; Condensation heat transfer; Filmwise; Laminar; |
語文 | 英文(English) |
中文摘要 | 本文係探討自然與強迫對流混合條件下,過熱蒸汽於圓柱或圓球上的膜狀層流凝 結之理論解析。基於位勢流理論與賽門所建議等效擴散模型,本文建立一套普遍性簡潔模型 ,可研究在同時考慮蒸汽過熱與壓力梯度之合併效應下的混合對流型的膜狀凝結熱傳,並完 成因壓力梯度效應所造成的凝結液分離角度之計算。此外,亦探討圓柱或圓球上由自然對流 演變至強迫對流中過渡區域下流動與熱傳的特性。本文結果顯示:對自然對流為主的膜狀凝 結而言,其蒸汽過熱效應 Sp=1.0 時,相對於蒸汽飽和 Sp=0 時,分別造成圓柱與圓球上平 均熱傳係數有 13.83% 與 13.76% 的增加。至於強迫對流為主的膜狀凝結,在壓力梯度效應 P=2.0 下, 蒸汽過熱效應 Sp=1.0 則又分別給圓柱與圓球產生 14.63% 與 8.6% 的平均 Nusselt 參數,NuRe,的增加。 |
英文摘要 | Analytical studies have been made of laminar film condensation on a cylinder or sphere in a superheated vapor under conditions of free and forced convection. The present treatment, based on potential flow theory and the penetration model proposed by Sideman, develops a general simple approach for mixed-convection film condensation heat transfer that incor-porates the major effects of both vapor superheating and the pressure gradient. The evaluation of the separation angle of the condensate film due to the pressure gradient effect is achieved. The characteristics of flow dynamics and heat transfer regarding the transition zone from free convection to forced convection film condensation on a cylinder or sphere have been also investigated here. For free convection dominated film condensation, the vapor superheating effect, Sp=1.0 ( superheat parameter ) results in an increase of 13.83% for a cylinder and 13.76% for a sphere in the mean heat transfer coefficient, compared with Sp=0; while, for forced convection dominated film condensation, Sp ( =1.0 ) provides 14.63% for a cylinder and 8.6% for a sphere increases in the mean Nusselt number, NuRe, under the effect of pressure gradient, P=2.0. |
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