Alenezi Abdulrahman, Almutairi Abdulrahman, Alhajeri Hamad, Almekmesh Saad F, Alzuwayer Bashar B
Department of Mechanical Power and Refrigeration, College of Technological Studies, P.AA.E.T., Kuwait City 70654, Kuwait.
Department of Automotive and Marine Engineering Technology, College of Technological Studies, P.A.A.E.T., Kuwait City 70654, Kuwait.
Entropy (Basel). 2022 May 8;24(5):661. doi: 10.3390/e24050661.
In this paper, a numerical investigation was performed of an air jet incident that normally occurs on a horizontal heated plane. Analysis of flow physics and entropy generation due to heat and friction is included using a simple easy-to-manufacture, surface roughening element: a circular rib concentric with the air jet. This study shows how varying the locations and dimensions of the rib can deliver a favorable trade-off between entropy generation and flow parameters, such as vortex generation and heat transfer. The performance of the roughness element was tested at three different radii; R/D = 1, 1.5 and 2, where D was the jet hydraulic diameter and R was the radial distance from the geometric center. At each location, the normalized rib height (e/D) was increased from 0.019 to 0.074 based on an increment of (e/D) = 0.019. The jet-to-target distance was H/D = 6 and the jet Reynolds number (Re) ranged from 10,000 to 50,000 Re, which was obtained from the jet hydraulic diameter (D), and the jet exit velocity (U). All results are presented in the form of entropy generation due to friction and heat exchange, as well as the total entropy generated. A detailed comparison of flow physics is presented for all ribs and compared with the baseline case of a smooth surface. The results show that at higher Reynolds numbers, adding a rib of a suitable height reduced the total entropy (St) by 31% compared to the no rib case. In addition, with ribs of heights 0.019, 0.037 and 0.054, respectively, the entropy generated by friction (Sf) was greater than that due to heat exchange (Sh) by about 42%, 26% and 4%, respectively. The rib of height e/D = 0.074 produced the minimum at R/D = 1. As for varying R/D, varying rib location and Re values had a noticeable impact on Sh, Sf and (St). Placing the rib at R/D = 1 gave the highest total entropy generation (St) followed by R/D = 1.5 for all Re. Finally, the Bejan number increased as both rib height and rib location increased.
本文对通常发生在水平加热平面上的空气射流事件进行了数值研究。使用一种简单且易于制造的表面粗糙化元件（与空气射流同心的圆形肋条）对流动物理特性以及因热和摩擦产生的熵进行了分析。本研究展示了改变肋条的位置和尺寸如何能在熵产生与流动参数（如涡旋产生和传热）之间实现有利的权衡。在三个不同半径处测试了粗糙元件的性能；R/D = 1、1.5 和 2，其中 D 为射流水力直径，R 为距几何中心的径向距离。在每个位置，基于 (e/D) = 0.019 的增量，将归一化肋条高度 (e/D) 从 0.019 增加到 0.074。射流与目标的距离为 H/D = 6，射流雷诺数 (Re) 范围为 10,000 至 50,000 Re，该雷诺数由射流水力直径 (D) 和射流出口速度 (U) 得出。所有结果均以因摩擦和热交换产生的熵以及总熵的形式呈现。针对所有肋条给出了流动物理特性的详细比较，并与光滑表面的基线情况进行了对比。结果表明，在较高雷诺数下，添加合适高度的肋条与无肋条情况相比，可使总熵 (St) 降低 31%。此外，对于高度分别为 0.019、0.037 和 0.054 的肋条，因摩擦产生的熵 (Sf) 分别比因热交换产生的熵 (Sh) 大 42%、26% 和 4%。高度为 e/D = 0.074 的肋条在 R/D = 1 时产生的熵最小。至于改变 R/D，改变肋条位置和 Re 值对 Sh、Sf 和 (St) 有显著影响。对于所有 Re，将肋条置于 R/D = 1 时产生的总熵 (St) 最高，其次是 R/D = 1.5。最后，随着肋条高度和肋条位置的增加，贝扬数增加。
