Experimental investigations on the heat transfer performance of square air jets impinging on surfaces with various topologies

This experimental study narrates the heat transfer results pertaining to the effect of topography modifications on target surface impinged by square jet of air. Towards this, seven surfaces with dissimilar topography are deployed. Those surfaces include: (i) three rough surfaces (having unlike roughness height), (ii) three with longitudinal micro-fins (having distinct fin heights), and (iii) one with concentric grooves. The performance of these surfaces is compared with a baseline smooth surface, over jet Reynolds numbers of 2000 to 10000, that is, limiting to lower turbulent region. It is noticed that by varying the surface topography, the jet flow structure in both stagnation and wall-jet regions is altered, in-contrast-to the smooth surface, which impacted the heat transfer too. It is seen that the effect of surface roughness on Nusselt number is minimal, for the roughness height range considered. Whereas, by adopting the micro-fins, Nusselt number is boosted significantly and for the surface with tall-fins, it is about 15.3% higher than the smooth surface. Further, a comparison is made between the surfaces with tall-fins and concentric grooves, by ensuring that both are having same surface area. From this, it is testified that the surface with concentric grooves outperformed (about 6.4%), asserting that the orientation of surface modifications on the impingement surface significantly affect the Nusselt number. Finally, a comparison among all the surfaces is made and found that the surface with concentric grooves is the best choice, with an enhancement in Nusselt number of 22.8% compared to the smooth surface.