Heat Transfer Enhancement by Mitigating the Adverse Effects of Crossflow in a Multi-Jet Impingement Cooling System in Hexagonal Configuration by Coaxial Cylindrical Protrusion--[PERSON] [PERSON]  
[PERSON]  
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development and cooling performance. Enhanced heat transfer studies focus on increasing the average HTC, improving HTC uniformity, and elevating the system performance evaluation criterion (\(PEC\)), which is the ratio of proportional enhancement in heat transfer rate (\(\dot{Q}\)) to the proportional increase in fluid pumping power (\(\dot{W}\)). In the literature, the effects of various geometric or configuration changes, such as the shape and arrangement of the jets, the roughened jet or target surface, the number, location, shape, and orientation of the discharge ports interspersed on the jet or target plate or placed around the system, are investigated. For instance, the effects of corrugated jet plates, immersed nozzle lengths, variable diameter jet orifices, various crossflow schemes, target plate roughness, film hole shapes and orientations, etc. are explored. By interacting with, deflecting, reducing normal momentum of, and deforming and spreading the jets, respectively, crossflow increases fluid pressure drop, shortens the necessary distance between the jet inlet and the target surface for effective cooling, decreases cooling performance, and deteriorates cooling uniformity in the stagnation zones. Nozzles [15; 16; 17], protrusions [18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33], cavities, and discharge ports [29; 33; 34; 35; 36; 37] in various shapes, topologies, and configurations have been proposed for laminar or turbulent, liquid or gas multi-jet impingement cooling systems (MJISCs). Multiple jet nozzles or orifices and target surface protrusions may be arranged in an in-line, staggered, or hexagonal configuration [38; 39; 40; 41]. Single-phase impinging jet array cooling may be enhanced by constructing macro- or microscale structures such as conical or prismatic pin fins with a triangular, rectangular, pentahedral, circular, elliptical, or hydrofoil base, or their combinations [18; 19; 20; 21; 22; 23; 24; 42]; continuous or interrupted, monolithic or slotted ribs of various forms and inclinations [25; 26; 27; 28; 29; 30] as protrusions; and/or circular, elliptical, rectangular dimple, or spiral indentations [31; 32; 33], or a metal porous foam [30] on the target surface. Therefore, turbulent convective heat transfer to fluid is augmented due to increased heat transfer area, interruption of boundary layer growth, elevation of turbulence intensity (\(I\)), and flow mixing. In systems having fountains rising from the target surface after the impingement of jets, if the crossflow \(Re\) number is high, the cooling performance can be improved by placing vortex-forming delta-shaped winglet pairs on the target surface to control boundary layers and increase the jets' impact velocities and turbulence intensities [43; 44; 45; 46]. Impingement cooling of a target surface by multiple, immersed, or single-phase jets in a confined space can be studied by experimental [18; 19; 20; 21; 22; 23; 24; 25; 28; 29; 30; 31; 33; 36; 37; 43; 45; 46; 47; 48], computational [15; 49; 50; 51; 52], or both methods [26; 27; 32; 38]. Experimental and computational studies on enhancing the performance of MJISCs using pin fins also exist in the literature. In an experimental and computational study, the highest \(\dot{Q}\) and the average Nusselt (\(\overline{Nu}\)) number are obtained in the minimum crossflow scheme for both flat and micro cubic pin fin roughened target plates [48]. For minimum and maximum crossflow schemes compared with a flat plate, the \(\overline{Nu}\) number on the roughened plate decreases by 10% and 6%, respectively, the \(\dot{Q}\) increases by 35% and 42%, while the pressure drop penalty is 8% and 14%.