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標題: 圓管內部突出環節之圓弧尺寸大小對熱傳增強之影響
Effect of Arc Size of Internal Ring-Type Protrusions on the Heat Transfer Enhancement of a Circular Tube
作者: 陳俊忠
關鍵字: heat transfer enhancement;熱傳增強;internal ring-type protrusion;Nusselt number;friction coefficient;內部突出環節;紐塞數;摩擦係數
出版社: 機械工程學系
圓管中內部突出之環節會破壞管內流體流動時之穩定性,而造成管內迴流與紊流之產生,因而可視為紊流增強之裝置,本研究主要針對此圓管內部突出環節之圓弧大小對熱傳增強之影響而加以探討。研究中將圓型銅管進行滾輪加工製程,使其內部產生不同圓弧之突出環節。測試管經量測熱傳性能後,並藉與不同圓弧突出環節之熱傳性能作比較,來探討節徑-內徑比(p/d)突出環節深度-內徑比(e/d) 與圓弧-內徑比(ra/d)對熱傳效果之影響,同時找出較佳p/d及e/d值之範圍,以利於熱傳之提昇及壓力差之降低。實驗中主要量測所用之測試管共計15支,可區分為五組,同組中之三支測試管乃具有相同之p/d與e/d值,但具有不同之ra/d值,所採用之p/d值為0.75、1.43及4.29等三種,e/d值為0.015、0.04、0.07、0.075及0.143等五種,ra/d值為0.0725、0.145及0.217等三種;另外並針對先前製作之11支環節銅管與一支光滑圓管重新進行量測,此11支環節銅管之ra/d值為0.0725。研究中考慮等溫管壁之操作狀態,並以空氣通過每一支測試管,以進行Nu值及摩擦阻力壓力降(f)值之量測。研究結果顯示,ra/d值之大小對Nu值之影響甚小,而在p/d值較小與同時e/d值較大的條件下,f值會隨著ra/d值之增加而減少。研究之結果亦顯示,此具環節之圓管在ra/d值等於0.217時,e/d值應小於0.07,而p/d值應小於1.43,此時方會有較佳之熱傳效率。

Ring-type protrusions in circular tube would destruct flow stability and result in flow recirculation and turbulence. Thus this arrangement can be viewed as a device for turbulence enhancement. This work mainly investigates the effect of arc-to-diameter ratio (ra/d) on the heat transfer characteristics of tubes with the protrusions. Test tubes with various arc-to-diameter ratios, pitch-to-diameter ratios (p/d) and protrusion's height-to-diameter ratios (e/d) were manufactured by a rolling process. The effects of p/d, e/d and ra/d on the heat transfer characteristics were experimentally determined. It intended to find an optimum range of the p/d value and e/d value for a large heat transfer coefficient and a small pressure drop. Totally 15 tubes in five categories were considered. In each category, three tubes with the same e/d value and p/d value, but with different ra/d values, were arranged. The three adopted p/d values individually are 0.75, 1.43 and 4.29;the five e/d values are 0.015, 0.04, 0.07, 0.075 and 0.143;the three ra/d values are 0.0725, 0.145 and 0.217. Another eleven previously made surface-roughened tubes, plus one smooth tube were also measured. These eleven tubes are with a ra/d value of 0.0725. In the measurement, an isothermal surface temperature condition was arranged. By passing air through every individual tube, the corresponding Nu value and f value were obtained. The result reveals that the effect of ra/d on the Nu is insignificant. For tubes with small p/d value and large e/d value, the f value would increase with a decrease of the ra/d value. The result also shows that, for the tubes with the ra/d value of 0.217, if e/d < 0.07 and p/d <1.43, an effective and efficient heat transfer can be achieved.
Appears in Collections:機械工程學系所

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