微小圓管的層流及熱傳數值模擬; Numerical laminar flow and heat transfer in microtubes

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题名:	微小圓管的層流及熱傳數值模擬;Numerical laminar flow and heat transfer in microtubes
作者:	曹聿男;Yu-Nan Tsao
贡献者:	機械工程研究所
关键词:	層流;微小管道流;數值模擬;熱傳特性;heat transfer characteristics;laminar flow;Numerical simulation;microtubes flow
日期:	2002-07-09
上传时间:	2009-09-21 11:40:56 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	本文以模擬軟體FIDAP對小圓管（直徑 0.502<D<1.10 mm）及微小圓管（直徑 63.5<D<254μm），進行層流的熱流模擬。比較楊建裕等人 (2000) 的實驗結果，發現壓力梯度及摩擦因子與數值解相近，摩擦因子也與理論值接近，顯示管徑介於0.502<D<1.10 mm的範圍，小圓管流場現象與傳統理論預測相符。但比較Mala及Li (1999) 的實驗數據，發現壓力梯度及摩擦因子與數值預測有差異，表示微小圓管流場現象 (直徑63.5<D<254μm) 與傳統理論結果有出入，且實驗值的中心軸向速度較數值解大，此因微小圓管的壓降較一般管徑值大上103倍。進一步分析發現，不銹鋼材之微小管的相對粗糙度介於0.007~0.028，而傳統鍛造不銹鋼管的相對粗糙度為 ~ ，可見粗糙度對微小圓管壓降影響之巨。比較楊建裕等人 (2001) 的熱傳量測，發現在中低雷諾數的數值解之溫度剖面與壁溫及平均溫度分布大致遵守傳統熱傳理論的結果，但在高雷諾數 (Re=1687) 的局部及平均Nu值的實驗值皆高於數值預測值，依據楊建裕等人所定義的過渡區範圍 (Re=1,500~3,000)，導致本文的模擬熱傳特性已受到紊流影響。 This study use the FIDAP software to simulate the laminar thermal-flow characteristics of the small tubes (where the diameter range: 0.502<D<1.10 mm) and the microtubes (where the diameter range: 63.5<D<254μm). Compared with experimental results of Yang et al. (2000), numerical solutions are in good agreement with the experimental results of pressure gradient (dp/dx) and friction factors (f) In addition, the simulated f’s value agree well with the theoretical value. It shows that the numerical solution of flow phenomenon in the small tube range (0.502<D<1.10 mm) is generally obeys the theory of conventional laminar flow. However, large difference in the values of dp/dx and f are obtained when the numerical solution compared with experimental data of Mala and Li (1999), the predicting deviations of numerical results compared with pressure gradient and friction factors. This indicates the flow characteristics in the microtube range (63.5<D<254μm) are different from the classical theory of laminar flow. Besides, experimental analysis shows higher axial velocity in the tube center than that of numerical solution. Such discrepancy is believed due to the huge ratio (about 103) of pressure gradient of the microtubes to the small tube. Further analysis shows that the relative roughness ( /D) of the microtube made of stainless steel is about 0.007~0.028, where the value of /D of the conventional forged stainless steel tubes are between 0.45x10-4 ~ 0.15x10-3. Thus, the roughness effect has significant influence on the pressure gradient of the microtubes. Compared with heat transfer measurement of Yang et al. (2001), numerical solutions of temperature profile, wall temperature and mean temperature distribution agree well with conventional heat transfer theory in low and moderate Re flow regime. But in higher Re conditions (Re =1687), experimental results of local and mean Nu are higher than predicted results. Based on Yang’s classification, the transition range is between Re=1,500~3,000. Thus, accuracy of present numerical solutions of laminar heat transfer is affected by turbulence effect in real flow condition.
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