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Öğe 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, OrhanThis 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.Öğe 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, OrhanThis 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.Öğe 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, OrhanIn 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.Öğe 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, OrhanThis 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.Öğe EFFECTS OF COMPLETE AND PARTIAL CYLINDRICAL FIN CONFIGURATIONS ON THERMOHYDRAULIC PERFORMANCE OF A MINICHANNEL HEAT SINK(2023) Sarper, Bugra; Nur Türk, Dondü; Dagıdır, Kayhan; Aydın, OrhanIn this numerical investigation, the impacts of complete and partial cylindrical fin configurations on the thermohydraulic performance of a minichannel heatsink are studied. ANSYS Fluent software is used to conduct numerical analyses for four distinct mass flow rates ranging from 0.00265 kg/s to 0.0045 kg/s and three distinct fin positions. The effects of various configurations on velocity and temperature fields, average Nusselt number, Nusselt number ratio, friction coefficient, and performance evaluation coefficient are analyzed. According to the study’s findings, using partial cylindrical fins has a substantial impact on both heat transfer and pressure drop. When evaluating heat transfer, MCHS-R2a produces the greatest results, but this configuration greatly raises flow resistance. MCHS-R2c was found to have substantial potential when evaluated in terms of thermohydraulic performance.Öğe Influence of Buoyancy and Inter-Surface Radiation on Confined Jet Impingement Cooling of a Semi-Cylindrical Concave Plate(Asme, 2024) Sarper, BugraIn this article, the confined jet impingement cooling of a semicylindrical concave plate is analyzed numerically. The finite volume approach is applied to two-dimensional numerical simulations in the transient regime. Air is employed as the working fluid and is regarded as nonparticipant for radiation. The investigation is done for different jet Reynolds numbers ( Re j) ranging from 100 to 1000, as the Richardson number ( Ri) corresponding to this interval ranges between 0.1 and 10. For any Richardson number, the modified Grashof number ( Gr *) is fixed at 105. When analyzing the impact of intersurface radiation between the target plate and confined surfaces on the overall cooling performance, three emissivity values ( epsilon = 0.05, 0.5, and 0.95) are taken into consideration. Additionally, simulations are done for the pure convective heat transfer, ignoring intersurface radiation ( epsilon = 0.0). The influence of surface emissivity and the Richardson number on velocity, temperature, and pressure distribution in the flow domain, local dimensionless temperature ( theta) alterations on the target plate and confined walls, alterations in convective ( Nu c ), radiative ( Nu r ), overall Nusselt numbers ( Nu ovr ), pressure coefficient ( C p), and ratio of radiative Nusselt number to overall Nusselt number ( Nu r / Nu ovr) on the target plate are highlighted. The findings demonstrate that surface emissivity has a significant influence on thermal and hydrodynamic boundary layer formation, buoyancy induced flow and heat transfer, and the proportion of intersurface radiation in overall heat transfer rises as the Richardson number and surface emissivity increase. At low Richardson numbers, the pressure in the stagnation region is greater than the atmospheric pressure. However, as the buoyancy effect increases, the pressure in the stagnation region falls below the atmospheric pressure and rises toward the exit.Öğe Sıralı Tip Boru Demetinde Gözenekli Malzeme Gözenek Yoğunluğu ve Kalınlığının Isı Transferi ve Basınç Düşümüne Etkilerinin Sayısal Olarak İncelenmesi(2022) Dagıdır, Kayhan; Sarper, Bugra; Erdinç, Mehmet TahirBu çalışmada, sıralı tip boru demetinde borular etrafında bulunan gözenekli malzemenin gözenek yoğunluğunun ve malzeme kalınlığının ısı transferi ve basınç düşümüne olan etkileri sayısal olarak incelenmiştir. Sayısal hesaplamalar iki boyutlu olarak, laminer ve kararlı akış koşullarında gerçekleştirilmiştir. Çalışmada, etrafı çevresel olarak tamamen gözenekli malzeme kaplı borular dikkate alınarak, gözenekli malzemenin gözenek yoğunluğu () 10, 20 ve 40 PPI ve her bir gözenek yoğunluğu için gözenekli malzeme kalınlığı (tp) 1, 2, 3 ve 4 mm olacak şekilde analizler gerçekleştirilmiştir. Gözenekli malzeme kalınlığı ve gözenek yoğunluğunun, ısı transferi ve basınç düşümüne etkileri değerlendirilmiş olup; ısı transferi, basınç düşümü, ısı transferinin fan gücüne oranı ve hız-sıcaklık konturları sunulmuştur. Analizler sonucunda, en yüksek ısı transferinin 20 PPI gözenek yoğunluğunda ve 4 mm metal köpük kalınlığında, en yüksek basınç düşümünün 40 PPI gözenek yoğunluğunda ve 4 mm gözenekli malzeme kalınlığında elde edildiği belirlenmiştir. Isı transferinin fan gücüne oranı değerlendirildiğinde 20 PPI gözenek yoğunluğu ve 1 mm kalınlığındaki metal köpüğün ısı transferi ve basınç düşümü açısından optimum olduğu belirlenmiştir. Anahtar Kelimeler: Sıralı tip boru demeti, Gözenekli malzeme, Isı transferi, Basınç düşümüÖğe The Impact of Nozzle Position on Cooling Performance in Electronic Components Cooling with Twin Slot Jets(Gazi Univ, 2024) Sarper, Bugra; Kirisci, Nida Emin; Albayrak, MelisaIn this study, the impact of nozzle position on flow structure and characteristics of convective heat transfer in electronic components cooling with twin jet nozzles are investigated numerically. Assuming that nozzle widths and jet Reynolds numbers are equal, numerical calculations are performed in the laminar regime between the Reynolds number range of 100 and 500 for different nozzle positions (JP 1-2, JP 1-3, JP 1-4 and JP 1-5). Numerical calculations are realized via the ANSYS Fluent software, and velocity and temperature contours, local and mean Nusselt number variation on the heat sources' surfaces and the overall mean Nusselt number variation are investigated for different nozzle positions and Reynolds numbers. As a result of the study, it is disclosed that the flow structure and characteristics of convective heat transfer are considerably influenced by nozzle position, the overall rate of convective heat transfer in JP 1-2 is higher than in the other cases, and it decreases with the displacement of the second jet towards the outlet.Öğe 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, OrhanThis 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.Öğe The role of nozzle position and channel aspect ratio in thermal management of electronic modules(Elsevier B.V., 2023) Albayrak, Melisa; Sarper, Bugra; Erdinc, Mehmet Tahir; Aydin, OrhanIn this paper, cooling of electronic modules by a series of impinging jets is studied numerically and experimentally. The study investigates the effects of nozzle position (sj/b = 0 − 0.25 − 0.5) and channel aspect ratio (H/Dj = 3 − 4 − 5) on surface temperatures, local and average heat transfer characteristics and flow dynamics. The numerical analyses are conducted using the ANSYS Fluent software, and the numerical results are verified using experimental measurements. The study's findings indicate that the displacement of the nozzles has a notable impact on the location and sizes of the vortex cells around the modules. This alteration influences the rate of convection heat transfer from the modules’ surfaces. It is concluded that increasing the channel aspect ratio leads to a reduction in convective heat transfer. The highest cooling performance is achieved in the scenario where the aspect ratio (H/Dj) is 3 and the dimensionless nozzle position (sj/b) is 0.5. However, in terms of temperature uniformity, this is H/Dj = 3 with sj/b = 0. © 2023 The AuthorsÖğe The utilization of novel jet extension designs in multi-jet impingement for crossflow mitigation and thermal efficiency enhancement(Elsevier France-Editions Scientifiques Medicales Elsevier, 2024) Sarper, BugraThe aim of this study is to mitigate the distorting effect of crossflow on jet flow and to enhance heat transfer performance in multi-jet impingement heat transfer. To accomplish this objective, novel jet extension designs are proposed: a design with uniform jet extension, a design with linear jet extension in the streamwise direction, a design featuring an initial increase followed by a decrease, a design featuring an initial decrease followed by an increase, and a design where the last five jets exhibit a uniform extension inside the region mostly influenced by crossflow. The effects of various novel jet extension designs on flow and heat transfer are analyzed numerically in this study, focusing on the following: velocity contours, streamlines and velocity vectors, Local Nusselt number variations, variations of the average Nusselt number, friction coefficient, and thermal enhancement factor with Reynolds number. The study findings indicate that the investigated nozzle extension designs yield a notable enhancement of 13.26% in heat transfer. However, it is important to note that these designs may also lead to a substantial rise of 39% in the friction coefficient. In relation to thermohydraulic performance, it is found that all extension designs exhibit better results when compared to the reference state. Notably, the uniform extension design with dimensionless nozzle length of 2 demonstrates a higher degree of thermohydraulic performance.Öğe 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, OrhanIn 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.
