半凹窩型渦流產生器於鰭管式熱交換器之應用

Abstract

本文探討一種新世代，可應用於鰭管式熱交換器(Fin-and-Tube Heat Exchangers)的鰭片，即是將渦流產生器(Vortex Generators，VG)應用於鰭片上。渦流產生器據信是一種，僅僅小幅地增加壓降，但卻能大幅提高熱傳的方法。 本文以理論設計，決定以一”半凹窩型”(half-dimple)渦流產生器，作為本實驗的渦流產生器種類。接著再以數值模擬，試圖找出擺放最佳的位置，以及排列的方法。模擬的結果顯示：以V型排列，不但能有效提升熱傳效果，更能利用通過前方VG的渦流，有效地減小壓降，故採用此種設計。 在實驗時，一共探討的變數有：兩種鰭片間距(1.6mm、2.0mm)、三種管排數(1、2、4排)、以及三種鰭片種類(平板、渦流產生器、百葉窗)，共十八種測試物；再配合0.5、1、1.5、2、3、4、5米等共七個風速。結果顯示：在多數的情況下，百葉窗型鰭片(louver)仍然有較好的熱傳表現。但是，當鰭片間距由1.6mm增至2.0mm，百葉窗鰭片的熱傳性能下降，但對於VG型鰭片而言，影響卻不大，甚至在低風速時，其效率會勝過百葉窗型鰭片。

This study develops a new style fin having vortex generator configuration which is used in fin-and-tube heat exchangers. Vortex generators were commonly used in aircraft to reduce separation. There are many style vortex generators. In this study, we develop a new style having a “half-dimple” configuration. In the design stage, CFD is employed to locate the best position and the arrangement. The result is deployed in a “V” arrangement for the purpose of decreasing the pressure drop. The simulation results are then used to develop the prototype of actual fin-and-tube heat exchangers. In the experiment, the effect of fin pitches ((1.6mm, 2.0mm), and the number of tube row (1, 2, 4rows) for three kinds of fin style (plain, vortex generators, louver) are examined. The frontal velocity ranges from 0.5 to 5 m/s. The results show that louver fin outperforms other fin patterns in most cases. However, when the fin pitch is increased from 1.6 mm to 2.0 mm, the heat transfer coefficient of louver fin will decrease considerably. But for the vortex generators case, the influence is quite small. Even in the low velocity, the efficiency of vortex generator will be better than the louver fin