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    Constructal design of heat sources with different heat generation rates for the hot spot mitigation
    (Pergamon-Elsevier Science Ltd, 2020) Birinci, Soner; Saglam, Mehmet; Sarper, Bugra; Aydin, Orhan
    This work aims to determine the optimum heat generation ratio among discrete heat sources generating different amounts of heat in order to mitigate the hot spot. Six different heat generation ratios are considered by following the constructal design method. For comparison, the average and total heat sources' heat generation rates are kept equal for every examined cases. Meanwhile, Reynolds number ranges from 792 to 3962. All the three heat transfer mechanisms are taken into account with an integrated approach to calculate precisely the dimensionless global conductance of the IC pack. Three dimensional simulations are done with ANSYS Fluent while measuring surface temperatures in experiments. The output parameters of the study are the surface and hot spot temperatures, Nusselt number and dimensionless global conductance change with Reynolds number and heat generation ratio. It is disclosed that relative decreasing heat generation rates are convenient for hot spot mitigation. (C) 2020 Elsevier Ltd. All rights reserved.
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    Constructal enhancement of cooling performance of local heating elements with different heat generation rates under free and mixed convection regimes
    (Pergamon-Elsevier Science Ltd, 2022) Sarper, Bugra; Birinci, Soner; Saglam, Mehmet; Aydin, Orhan
    This study aims to obtain the optimum heat generation rate of local heating elements with different heat generation rates in a vertical duct. Covering free and mixed convection regimes, experimental and numerical studies are conducted. Various values of the modified Grashof and Reynolds numbers are taken into account. The influence of the heat generation rates of local heating elements on temperature of the hot spot, local temperatures, system's global conductance and Nusselt number are presented. It is shown that the heating elements with coheat generation rates cause a rise in the temperature of the hot spot and reduce the global conductance, and the gradual decrease in the heat generation rates of heating elements improves the system's cooling performance.
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    Effect of heaters' clearance on mixed convection cooling performance in a dicretely heated horizontal duct
    (Elsevier France-Editions Scientifiques Medicales Elsevier, 2021) Birinci, Soner; Saglam, Mehmet; Sarper, Bugra; Aydin, Orhan
    In this paper, effect of the heaters' clearance on mixed convective cooling performance in a discretely heated horizontal duct is examined. Tests are carried out for a constant value of the modified Grashof number (Gr*(Dh) = 1.15 x 10(7)), and for Reynolds numbers (Re-Dh) between 792 and 3,962. In the analysis, surface to surface radiation and wall conduction are coupled with convective heat transfer. Experiments involve measurements of surface temperatures and air velocity while ANSYS Fluent is used to conduct numerical simulations. Variations of the local surface temperatures, hot spot temperature, global conductance (C) and effective Nusselt number (Nu(eff)) with Reynolds number (Re-Dh) are presented. Finally, it is disclosed that up to 10.77% reduction in the hot spot temperature and an improvement of up to 20.84% in the system's global conductance can be achieved with an increase in the clearance.
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    EFFECT OF SURFACE RADIATION ON JET IMPINGEMENT COOLING OF A CONCAVE SURFACE
    (Begell House, Inc, 2022) Albayrak, Melisa; Sarper, Bugra; Birinci, Soner; Saglam, Mehmet; Aydin, Orhan
    This study aims to numerically investigate the influence of surface radiation on jet impingement cooling of a two-dimensional concave surface with a slot nozzle. For a constant value of the aspect ratio (h/2W=4.0), varying values of Reynolds number (Re=1185, 2370, 3555 and 4740) and surface emissivity (epsilon=0.05, 0.45 and 0.90) are tested. The cases with or without radiation are comparatively examined. The results are presented as the local temperature variations as well as the variations of the convective and radiative Nusselt numbers, Nusselt number ratio and total Nusselt number. It is disclosed that the increase in surface emissivity improves the overall cooling performance.
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    The role of jet-to-crossflow velocity ratio on convective heat transfer enhancement in the cooling of discrete heating modules
    (Elsevier, 2023) Albayrak, Melisa; Sarper, Bugra; Saglam, Mehmet; Birinci, Soner; Aydin, Orhan
    This study aims to investigate the role of jet-to-cross flow velocity ratio on convective heat transfer and flow characteristics in a channel with discrete heating modules simulating electronic components. Three-dimensional numerical simulations are performed using the finite volume method. The findings obtained for different velocity ratios of the jet-to-crossflow are compared with the reference case (crossflow solely). While keeping the crossflow velocity and the crossflow Reynolds number (Rec = 5000) constant, numerical calculations are performed for six different velocity ratios (Ur = 1.0, 2.0, 4.0, 6.0, 8.0 and 10.0). The focus is on the role of the velocity ratio (Ur) on the mean Nusselt number (Num) on the modules' surfaces, the Nusselt number ratio (Nur), the friction coefficient ratio (fr) obtained throughout the channel and the thermal enhancement factor (TEF). As a result of the study, it is revealed that the momentum of jet flow becomes dominant over crossflow, the influence of jet flow on convective heat transfer increases, and the thermal enhancement factor increases depending on the increase in jet-to-cross flow velocity ratio.
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    Thermal cycling performance of a Shell-and-tube latent heat thermal energy storage system with paraffin/graphite matrix composite
    (Elsevier, 2024) Saglam, Mehmet; Ceboglu, Esen; Birinci, Soner; Sarper, Bugra; Aydin, Orhan
    In this paper, thermal cycling behavior of paraffin/graphite matrix (PGM) composite in shell-and-tube configuration is investigated experimentally. It is aimed to investigate the effects of various graphite matrix bulk densities (50 g/L and 75 g/L) and compaction speeds (12 mm/min, 90 mm/min, 120 mm/min) on the leakage characteristics, dimensional changes, structural distortions, and thermal performance (specifically, meltingsolidification durations). A total of 120 cycles of charge-discharge experiments are conducted, during which the aforementioned parameters are continuously monitored and recorded. The findings indicate that PGM composites exhibit no notable leakage. However, when comparing different scenarios, it is seen that a compaction speed of 120 mm/min leads to a greater leakage of PCM compared to the others. The dimensional changes of all samples are attributed to the thermal expansion and contraction of paraffin. Following the initial cycles, the samples shrink 2.5 % in diameter. The extent of structural deformation is influenced by two factors: the bulk density of the graphite matrix and the cycle count. For a bulk density of 50 g/L, the surface exhibits obvious cracks after 48 cycles, which progressively expand as the cycle number increases. However, when the bulk density reaches 75 g/L, no evidence of cracking is observed after 120 cycles. The results indicate that the composite with a bulk density of 75 g/L is less affected by cycling due to its higher thermal conductivity in comparison to the composite with a bulk density of 50 g/L. Additionally, the temperature distribution in the radial direction is more uniform in the former composite. While certain samples exhibit structural deformations, it is important to note that the thermal performance and structural integrity are preserved among all the samples tested.