鰭管式熱交換器的熱傳與摩擦特性

Heat Transfer and Friction Characteristics of Fin-And-Tube Heat Exchangers

The airside performance of fin-and-tube heat exchangers having plain or slit fin geometry is experimentally investigatedin this study. A total of 14 samples were tested and compared. Effects of fin pitch, tube diameters, and the number of tube row were examined. The test results indicated that the heat transfer performance decreases with an increase of the number of tube row whereas the friction factors are independent of the number of tube row for plain fin-and-tube heat exchangers. More heat transfer rate are obtained for heat exchangers with slit fins than those with plain fins, but the effect of fin pattern on the pressure drop is reversed. In addition, it shows that the Colburn j and Fanning friction factors are higher for larger tubes. Finally, heat transfer and friction correlations were proposed to describe the performance of the tested heat exchanger. The correlations of j factors give a mean deviation of 10% for plain fins and 9.1% for slit fins, while the f factors show a mean deviation of 8.3% for plain fins and 7.2% for slit fins. 本文針對平板型鰭片及裂口型鰭片之鰭管式熱交換器，在吸入型開放式風洞測試系統中，進行乾盤管測試。總共實驗比較十四種不同之測試組，並討論鰭片間距、管排數、管徑尺寸及鰭片型式對鰭管式熱交換器的影響。，測試結果得知平板型鰭片熱交換器的熱傳性能隨著管排數的增加而減少，然而管排數對摩擦因子的影響並不大。在鰭片型式比較方面，裂口型鰭片比平板型鰭片熱傳性能好，但壓降也高於平板型鰭片。另外，實驗結果發現管子直徑愈大者，熱傳因子及摩擦因子皆愈大，平板型鰭片及裂口型鰭片之熱交換器鰭片間距越小，j值和f值均會增加。最後，本研究提出平板型鰭片及裂口型鰭片的設計經驗方程式。對於熱傳j因子而言，此經驗方程式的平均偏差分別為平板型鰭片10%，裂口型鰭片則為9.1%；而對於摩擦因子，此經驗方程式的平均偏差分別為平板型鰭片8.3%，裂口型鰭片則為7.2%。