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標題: Heat transfer enhancement of circular tube inserted with spring coil
作者: 陳誠安
Cheng-An Chen
關鍵字: heat transfer enhancement
wire coil
Nusselt number
friction factor
performance index
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摘要: Heat transfer and pressure drop data in smooth tubes inserted with various wire coils were measured respectively. Water and air were individually considered as working fluid. The wire diameter (e) and pitch (p) of the wire coils were in the range 1 - 1.8 mm and 18 - 32 mm respectively. For tightness between the wire coil and tube wall, three tubes with different inner diameters (12.8, 13.4 and 13.8 mm) were adopted. This work not only established correlations of Nu and f, but also examined performance indexes (r 1 , r 2 and r 3 ) of the test tubes. The r 1 represents the ratio of Nu values between a test tube and a smooth tube; the r 2 denotes the ratio of Nu/f values; the r 3 stands for the ratio of heat transfer rates based on per unit of consumed mechanical power. For air, the correlation of Nu value was found to be Nu = 0.00585(Re)m [(e / d )2 -0.0042]-0.24 ( p / d )-0.22 where m1= 0.51 + 6.16( e / d )-23.15( e / d ) 2 . For water, Nu = 2.55(Re)0.57 ( e / d )α3 ( p / d )-1.13= -0.17( p / d ) + 0.65 . For both air and water, a common f correlationwhere α 3 was acquired as follows: f = 36.13Re −0.36 (e / d )[ln( p / d )]−0.52 . The Nu and r 1 values increase with the e/d value, but increase with a decrease of the p/d value. As the e/d value decreases or the p/d values increases, the r 2 and r 3 values tend to increase. For air, the r 2 and r 3 values moderately increase with the Re value. For water, the r 2 and r 3 values decrease with an increase of the Re value. Keywords: heat transfer enhancement;wire coil;Nusselt number;friction factor;performance index
本實驗探討光滑圓管內部插入彈簧線圈後對工作流體與管壁間之熱傳 增強與壓力降之影響,工作流體分為空氣與水等兩種,所採用彈簧線圈之線徑(e)分為 1 mm、1.4 mm 及 1.8 mm 等三種,節徑(p)則分為 18 mm、24 mm及 32 mm 等三種,並依照彈簧線圈與管壁間之緊密程度,配置所需之圓管,因此測試管之內徑(d)分為 12.8 mm、13.4 mm 及 13.8 mm 等三種。此研究不僅探討 Nu 值與 f 值之相關性,同時也進行測試管之三種性能係數(r1 、r2 及r 3 )之比較,其中 r 1 值代表插入彈簧線圈之測試管與光滑圓管間 Nu 值之比值,r 2 值為兩者間 Nu/f 值之比值,而 r 3 則表示兩者間消耗每單位機械摩損功所獲得的熱傳量之比值。對工作流體為空氣而言,量測所得之 Nu 值經由相關性分析後,可得一組經驗公式為 Nu = 0.00585(Re)m [(e / d )2 -0.0042]-0.24 ( p / d )-0.22 ,1m1其中= 0.51 + 6.16( e / d )-23.15( e / d ) 2 ;對水而言,所獲得之熱傳相關性公式為 Nu = 2.55(Re)0.57 (e / d )α ( p / d )-1.13 ,其中 α 3 = -0.17( p / d ) + 0.65 ;而無論工作流體為水或空氣,摩擦因子(f)之經驗公式為 f = 36.13Re −0.36 (e / d )[ln( p / d )]−0.52 。熱傳(空氣與水)量測之結果顯示,Nu 值與 r 1 值均會隨著 p/d 值之增加而減少,但兩者皆會隨著 e/d 值的增加而增大,因此若要得到較大的熱傳效果,須採用較小 p/d 值與較大 e/d 值之彈簧線圈。而在 e/d 值越小與 p/d 值越大之情形下,r 2 值與 r 3 值均會越大。對空氣而言,r 2 與 r 3 值會隨著 Re 值之增加而略微增大;對水而言,此 r 2 與 r 3 值會隨著 Re 值之增加而減小。 關鍵字:熱傳增強;彈簧線圈;紐塞數;摩擦因子;性能指數
文章公開時間: 2018-07-15
Appears in Collections:機械工程學系所



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