Effect of Helix Length on the Performance of a Swirl Flow Tube

In this paper, we use CFD to investigate the performance of a swirl flow tube (SFT) in terms of its heat transfer enhancement and pressure drop to obtain an optimal compromise between the uniformity in temperature distribution and the gain in pressure drop. The results show that the longer the helix is, the larger the pressure drop is. The pressure drop is appropriately proportional to the helix length. The temperature uniformity index is significantly improved using an SFT despite the penalty of higher pressure loss, as compared with using a bare tube. The improvement in temperature uniformity index is enhanced by increasing helix length. However, when the helix length is greater than 40 times pipe diameter (d), the temperature uniformity indices for different helix lengths nearly coincide. There is no need to use a helix length greater than 40d from the viewpoint of temperature uniformity as the temperature uniformity is not improved further but the pressure drop still increases. A helix length of 40d is an optimal compromise between the temperature uniformity and the pressure drop gain.