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    Assessment of Convective Heat Transfer Characteristics for Elliptical-Shaped Pin-Roughened Surface for the Jet Impingement Cooling
    (Asme, 2023) Yalcinkaya, Orhan; Durmaz, Ufuk; Tepe, Ahmet Umit; Uysal, Unal; Ozel, Mehmet Berkant
    In a jet impingement cooling (JIC) system, the layout of the target surface and length of the jet holes can change both the flow field and the heat transfer characteristics. Elliptical-shaped pins (ESPs) with different heights and layouts on the target surface of the extended jet hole configurations were examined numerically in a jet impingement system. The ESPs were arranged in a staggered and circular form. Normalized nozzle length (G(j)/D-j = 1.0, 2.0, 6.0) and normalized pin height (H-p/D-j = 0, 0.167, 0.417, 0.667) were investigated as geometric parameters. Also, the effect of different pin layouts (R-1, R-2, R-3) on heat transfer dissipation was studied by changing the number of pin rows in particular configurations. A numerical model was developed and verified with experimental and numerical data from the literature. Numerical analyses were conducted with the shear stress transport (SST) k-omega turbulence model taking the boundary conditions into account under turbulent flow conditions (16,250 <= Re <= 32,500). Nusselt (Nu) numbers, pressure drop, and the thermo-hydraulic performance of the physical model were quantitatively researched to elucidate the underlying mechanisms of enhanced heat transfer by the ESPs. Results were compared with the orifice surface (H-p/D-j = 0 and G(j)/D-j = 6.0). Results showed that area-averaged Nu number on the target wall increased up to 35.82% for Re = 16,250 by R-2_G(j)/D-j = 1.0 and H-p/D-j = 0.167 compared to the conventional JIC system. The performance evaluation criterion (PEC) was used to analyze the thermo-hydraulic performance of the examined physical models. According to the PEC values, the most feasible parameters for all Re numbers were R-3_G(j)/D-j = 1.0 and H-p/D-j = 0.167. Furthermore, increasing the number of pin rows in the channel also increased the uniformity of the local heat transfer distribution according to Nu contours.
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    Colorless distributed combustion characteristics of hydrogen/air mixtures in a micro combustor
    (Elsevier Sci Ltd, 2023) Yilmaz, Harun; Karyeyen, Serhat; Tepe, Ahmet Umit; Bruggemann, Dieter
    Colorless distributed combustion technique enables less pollutants emissions for a fuel/oxidizer mixture to be combusted. In this study, colorless distributed combustion characteristics (CDC) of hydrogen/air mixtures were numerically investigated in a micro combustor to overcome the difficulties associated with micro combustion and to obtain a more uniform temperature profile on the outer wall. To that end, hydrogen/air combustion was simulated by using ANSYS/Fluent CFD code at a constant equivalence ratio (1.0) and thermal input (100 W) and different mixture inlet temperatures of 300 K, 600 K and 1000 K to seek colorless distributed combustion. CDC conditions were tried to be achieved by decreasing the oxygen concentration from 21 % to 9 % at an interval of 3 %. In conclusion, colorless distributed combustion conditions could be achieved at different O2 concentrations, irrespective of the mixture inlet temperature. At 300 and 600 K, such conditions did not make any positive contribution to the power output of the micro combustor. Nevertheless, at 1000 K and 9 % O2 concentration, all combustion and emission performance metrics were improved in a manner that could increase the power output of the micro power generator.
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    Heat and Flow Characteristics of Aerofoil-Shaped Fins on a Curved Target Surface in a Confined Channel for an Impinging Jet Array
    (Mdpi, 2024) Yalcinkaya, Orhan; Durmaz, Ufuk; Tepe, Ahmet Umit; Benim, Ali Cemal; Uysal, Unal
    The main purpose of this investigation was to explore the heat transfer and flow characteristics of aero-foil-shaped fins combined with extended jet holes, specifically focusing on their feasibility in cooling turbine blades. In this study, a comprehensive investigation was carried out by applying impinging jet array cooling (IJAC) on a semi-circular curved surface, which was roughened using aerofoil-shaped fins. Numerical computations were conducted under three different Reynolds numbers (Re) ranging from 5000 to 25,000, while nozzle-to-target surface spacings (S/d) ranged from 0.5 to 8.0. Furthermore, an assessment was made of the impact of different fin arrangements, single-row (L1), double-row (L2), and triple-row (L3), on convective heat transfer. Detailed examinations were performed on area-averaged and local Nusselt (Nu) numbers, flow properties, and the thermal performance criterion (TPC) on finned and smooth target surfaces. The study's results revealed that the use of aerofoil-shaped fins and the reduction in S/d, along with surface roughening, led to significant increases in the local and area-averaged Nu numbers compared to the conventional IJAC scheme. The most notable heat transfer enhancement was observed at S/d = 0.5 utilizing extended jets and the surface design incorporating aerofoil-shaped fins. Under these specific conditions, the maximum heat transfer enhancement reached 52.81%. Moreover, the investigation also demonstrated that the highest TPC on the finned surface was achieved when S/d = 2.0 for L2 at Re = 25,000, resulting in a TPC value of 1.12. Furthermore, reducing S/d and mounting aerofoil-shaped fins on the surface yielded a more uniform heat transfer distribution on the relevant surface than IJAC with a smooth surface, ensuring a relatively more uniform heat transfer distribution to minimize the risk of localized overheating.
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    Numerical Analysis of Roughened Target Surface for Enhancing Jet Impingement Cooling
    (Springer International Publishing Ag, 2024) Yalcinkaya, Orhan; Durmaz, Ufuk; Tepe, Ahmet Umit; Benim, Ali Cemal; Uysal, Unal
    Roughening on a surface is crucial in heat transfer, primarily enhanced by the increased interaction between the fluid and the surface. Considering this, a thorough study was conducted to explore impinging jet array cooling (IJAC) applied to a semicircular curved surface, enhanced with aerofoil-shaped fins. Analyses were conducted under different Reynolds numbers (Re), fin arrangements, and nozzle-to-target surface spacings (S/d). Extensive analyses were conducted for both roughened and smooth target surfaces. The roughened surface and extending the nozzles to the surface increased the Nu numbers relative to the conventional IJAC scheme. The obtained heat transfer improvement was about 52.81%. In addition, the heat transfer distribution on the surface has become more homogeneous. The results of the study showed that a roughened target surface with elongated jets has significant potential for internal cooling.
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    Thermal performance of elliptical pins on a semicircular concave surface in the staggered array jet impingement cooling
    (Pergamon-Elsevier Science Ltd, 2023) Yalcinkaya, Orhan; Durmaz, Ufuk; Tepe, Ahmet Umit; Uysal, Unal; Ozel, Mehmet Berkant
    In a jet impingement cooling, decreasing heat transfer on the last jet's region due to the strong crossflow significantly increases thermal stress on the material. Thus, the main objectives of this study are to achieve relatively more uniform heat transfer distribution and enhance heat transfer on the surface compared to conventional jet impingement cooling (CJIC) configuration by mounting elliptical pins on the impingement regions. From this point of view, we have investigated the thermal performance of elliptical pins mounted on the impingement region of a staggered array jet impingement cooling (SJIC) on the semicircular concave surface. Numerical analyses were performed under various Reynolds numbers (Re = 5000, 15000, and 25000), jet nozzleto-target surface spacing (0.5 & LE; G/d & LE; 8.0), and dimensionless orifice plate-target surface gaps (H/d = 4.0 and 8.0). Average Nusselt (Nu) numbers, local Nu contours, flow properties, and Thermal Performance Factor (TPF) on pinned and smooth target surfaces were studied in detail. Results showed that the local and area-averaged Nu numbers increased with reducing G/d and roughening of the surface with elliptical pins compared to conventional SJIC. Maximum heat transfer enhancement was obtained as 55.68% at H/d = 8.0 with extended jets (G/d = 0.5) and elliptical pin roughening surface design. Besides, the highest TPF on the pinned surface is achieved as 1.10 by G/d = 2.0 and H/d = 8.0 at Re = 25000. Furthermore, mounting elliptical pins on the surface provided more uniform heat transfer distribution on the surface compared to flat surface by means of significantly enhancing heat transfer on the last jet region.
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    Thermohydraulic performance assessment of new alternative methods for anti-icing application against current application in an aircraft
    (Sage Publications Ltd, 2023) Pazarlioglu, Hayati Kadir; Tepe, Ahmet Umit; Arslan, Kamil
    In this study, anti-icing problems, which are mostly industrial problems in aerospace companies, have been numerically investigated. Herein, to enhance anti-icing performance of NACA0015, different jet-to-surface distances (H/d), jet angles (& alpha;), and slot jet designs with different aspect ratios (ARs) have also been investigated. ANSYS Fluent 2020R2 commercial program has been utilized for all numerical calculations. In addition, the SST k-& omega; with low-Re correction wall treatment turbulence model has been used for solving turbulence equation. Furthermore, the average Nusselt number (Nu) on the NACA0015's surface, pressure drop, and performance evaluation criteria (PEC) which define the anti-icing performance of novel proposed system have been presented section by section. As a result of the investigation, it has been obtained that the use of AR = 4 increases the Nu by 85.52% compared to circular jet for the H/d = 4 at & alpha; = 90 & DEG;. The pressure drop value dramatically increases using AR = 4 around 307.85% compared to circular jet for H/d = 4 at & alpha; = 90 & DEG;. Despite this drastic increment in pressure drop, the PEC value is kept as 1.14 using AR = 4, H/d = 4, and & alpha; = 90 & DEG;. Finally, empirical correlations developed from existing findings have been presented with an error rate of lower than 5%.