Impact of Surface Roughness on Flow Physics and Entropy Generation in Jet Impingement Applications

Entropy

Bashar B. Alzuwayer¹  Abdulrahman Alenezi²  Abdulrahman Almutairi²  Hamad Alhajeri²  Saad F. Almekmesh² 

[1] Department of Automotive and Marine Engineering Technology, College of Technological Studies, P.A.A.E.T., Kuwait City 70654, Kuwait;Department of Mechanical Power and Refrigeration, College of Technological Studies, P.AA.E.T., Kuwait City 70654, Kuwait;

关键词: entropy;    heat transfer;    CFD;    jet impingement;    rib;   

DOI  :  10.3390/e24050661

来源: DOAJ

【 摘 要 】

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 ($S_t$) 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 ($S_f$) was greater than that due to heat exchange ($S_h$) by about 42%, 26% and 4%, respectively. The rib of height e/D = 0.074 produced the minimum S_t at R/D = 1. As for varying R/D, varying rib location and Re values had a noticeable impact on $S_h$, $S_f$ and ($S_t$). Placing the rib at R/D = 1 gave the highest total entropy generation ($S_t$) followed by R/D = 1.5 for all Re. Finally, the Bejan number increased as both rib height and rib location increased.

【 授权许可】

Unknown