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Effect of Channel Spacing on the Heat Transfer of a Radial Flow in a Spiral Heat Exchanger
|關鍵字:||spiral heat exchanger|
exergy recovery index
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|摘要:||本研究採用一維穩態之熱傳模式對一個螺旋式熱交換器進行模擬分析，並測試一個此類型熱交換器模型之熱傳性能。於模擬分析中，管內流體考慮為混合之狀態，其流動方式為螺旋式，管外流體為不混合之狀態，流動方式為由熱交換器之中心以輻射狀向外流出，研究中利用電腦模擬分析計算管內流體出口之無因次溫度，將其代入公式後，即可獲得此熱交換器之有效功回收指數(ηII)。分析之結果顯示，於一個固定之熱傳單位數(Ntu)下，在整體熱容率比值(Ct*)接近1.0時，有效功回收指數會出現一個最大值。實驗乃針對一個具五圈管道之螺旋式熱交換器模型，於四種不同管道間隙下(0.5 mm、0.8 mm、 1.2 mm、1.6 mm)，進行氣體側(管外)之摩擦因子(f)與熱對流係數(h)之量測，所考慮之雷諾數(Re)範圍為307至2547，此研究對實驗進行不準確度分析，並將所得之數據加以迴歸分析，分別歸納出摩擦因子(f)與紐塞數(Nu)之相關性公式，此摩擦因子(f)迴歸分析之平均誤差為3.60%，而紐塞數(Nu)之平均誤差則為4.00%。|
The heat transfer performance of a spiral heat exchanger was numerically and experimentally investigated. A one-dimensional steady-state heat transfer model was adopted. The flow inside the tube is considered to be mixed and it flows spirally from the inlet to the exit. The flow outside the tube is considered to be unmixed and it flows radially from the center of the heat exchanger toward the environment. The dimensionless temperature at the outlet of the tube flow was evaluated and it yielded an exergy recovery index (ηII). The result shows that, for a fixed Ntu value, there is a maximum ηII. This maximum ηII occurs at the ratio of flow heat capacity rates (Ct*) nears 1.0. In the experiment, the gas-side (outside the tube) Darcy friction factor (f) and convective heat transfer coefficient (h) of a five-lap spiral heat exchanger were measured. Four different channel spacings (0.5, 0.8, 1.2 and 1.6 mm) were individually considerded. The Reynolds numbers were in the range 307-2547. An uncertaintyanalysis for the measurement was performed. Two correlations, one for the Darcy friction factor and the other for the Nusselt number, were proposed. The average correlation error of the former is 3.60% and that of the latter is 4.00%.
|Appears in Collections:||機械工程學系所|
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