本研究之目的為探討在低風速下之熱邊界層變化，據以設計應用於該條件下之斷續型鰭片及百葉窗型鰭片。在固定鰭片節距為1.2 mm時，改變兩種葉片長度分別為0.7 mm和1 mm，於風速範圍0.5 m/s至2.5 m/s，且加熱量為30W的條件下，討論影響性能之主要參數，與鰭片內部的流動狀態。並與風扇結合，探討風扇選用對於熱傳增強鰭片之重要性。 由壓降實驗結果可知，在斷續型鰭片時，縮小葉片長度，因剪應力較大，會使壓降上升；而百葉窗型鰭片，縮小葉片長度，可使通道流動的阻力下降，進而降低壓降。而熱傳方面，在風速小於1m/s時，本研究的斷續型和百葉窗型鰭片，氣流皆已完全發展；而在風速大於1m/s時，相同型式的鰭片受葉片長度的影響極低。 此外，若壓降大的熱傳增強鰭片，與平板鰭片使用相同之風扇，流量會下降許多，而使鰭片熱傳性能下降。因此，需根據各鰭片的壓降，選擇匹配之風扇，方可發揮鰭片原有的性能。 The purpose of research is to discuss how the thermal boundary layer changes its thickness in lower air velocity. With very low air velocity executed in the experiment, we have designed two types of fins, which are the louver fin and the offset strip fin to perform experiment with the following parameters. Under the given air velocity at 0.5 m/s to 2.5 m/s and heat addition in 30 Watt, we fix the fin pitch in length of 1.2mm and vary two different louver length with two types of fins at 0.7 mm and 1 mm respectively to observe the main factor to affect the performance of our system. In addition, we also combine fan into our system so as to discuss if the selection of fans could better the heat transfer enhancement significantly. From the result of pressure drops, the shear stress will become larger when reduced the louver length and the increase of the pressure drop in the offset strip fin. However, in the louver fin, the pressure drop is decreased with reducing the louver length. It is because the flow resistance also decreased with the louver length. According to our experimental study, the flow structure of both the two types of fin in air velocity below 1 m/s have been fully developed. When the air velocity increase upper than 1 m/s, the changing of louver length have nothing to do with the performance. If the same fan used in different type of fin , the volume flow rate will be different with the pressure drop. So we have to choose the fan that fitting the individual fin hoping the heat transfer performance is good as we designed.
