漸擴管應用於合成噴流之平板衝擊熱傳研究

Abstract

本實驗透過改變不同孔口結構來研究其對於合成噴流的影響，主要以漸擴孔口為主軸去探討其孔口結構、不同開口角度以及孔口厚度所造成的影響。實驗中藉由固定壓電片的作用功率並改變其激發頻率及衝擊高度發現，當衝擊高度比為2時，漸擴孔口不論在流速及熱傳方面都有明顯的提升，其中開口角60度的漸擴孔口更是相較圓孔提升了20%至30%左右的熱傳效果。而隨著衝擊高度比越高，孔口結構所產生的效應便不再那麼顯著。實驗同時也比較了開口角角度的效應，其中比對開口角60度與90度發現，角度並非越大越好，其擴孔角度越大時在流場方面易造成壁面迴流進而影響噴氣時的流速。而從實驗數據斷定其開口角度有其最佳值存在。在此次實驗的限制下，發現孔口厚度的變化似乎並不顯著，若要再仔細探討其厚度效應，則噴口直徑與厚度比的比例建議差異大為佳。

Effect of using diffuser holes as orifice on synthetic jet heat transfer is studied. The synthetic jet is produced by the high frequency oscillating motion (400-800Hz) of a piezoelectric actuator. The power of actuator is 0.9Watt at different frequencies. The hydraulic diameter of all the orifices is 3mm and the jet-to surface spacing (Z/d) ranged from 2-25. Results showed that heat transfer enhancement and flow velocity in diffuser holes was dramatically improved compared to the round holes. Especially at the jet-to surface spacing of 2(Z/d=2), the heat transfer enhancement with diffuser holes were 30% higher than round holes. As the jet-to surface spacing increased, the effect caused by diffuser diminished. The opening angles in diffuser holes had an optimal value and the 60 degree of opening angle in diffuser hole is the best in our research.