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Öğe An optimization study on thermo-hydraulic performance arrays of circular and diamond shaped cross-sections in periodic flow(Pergamon-Elsevier Science Ltd, 2021) Erdinc, Mehmet Tahir; Aktas, Arif Emre; Kuru, Muhammet Nasif; Bilgili, Mehmet; Aydin, OrhanIn this study, thermo-hydraulic characteristics of arrays of circular and diamond shaped cross-sections in periodic flow are investigated numerically. The main purpose of this study is to configure diamond shaped cross-sections in order to obtain better thermal performance compared to circular shaped cross-section. The optimization frameworks are constructed by using multi-objective genetic algorithm (MOGA) for both circular and diamond shaped cross-sections to obtain maximum heat transfer and minimum pressure drop while keeping the mass flow rate constant. The study can be divided into two parts: Firstly, an optimization study is carried out to achieve an optimum design for the circular type. Later, a new optimization scheme is constructed where the optimum design of circular type's heat transfer and pressure drop values are given as constraints. Thus, the optimization algorithm seeks better thermal performances with respect to the circular one. Moreover, optimum designs are illustrated graphically and given in the tabular form. Compared to circular geometries, it is found that the average Nusselt number of diamond shaped geometry can be increased by 10.11%, while pressure drop and volume of diamond shaped geometries are reduced by 11.90% and 52.76%, respectively.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 Optimizing the tube geometry to enhance thermohydraulic performance of tube bank heat exchanger(Elsevier France-Editions Scientifiques Medicales Elsevier, 2023) Aktas, Arif Emre; Kuru, Muhammet Nasif; Erdinc, Mehmet Tahir; Aydin, Orhan; Bilgili, MehmetIn this study, optimum design parameters of circular, diamond and enhanced shaped geometries for staggered tube banks are explored utilizing a multi-objective genetic algorithm (MOGA-II). For given three geometries, two step optimization studies are compared: (1) circular and diamond shaped geometries, (2) diamond and enhanced shaped geometries. Steady, incompressible, and turbulent flow around three-dimensional numerical models is solved using finite volume method. Initially, using literature experimental data numerical results are validated for circular and diamond geometries. In the optimization studies, maximization of heat transfer and minimization of required pumping power are preferred as objective functions. The results of optimization studies are demonstrated graphically. Furthermore, velocity and temperature distribution for the optimum cases are illustrated. The results of first step optimization studies exhibited that diamond shaped tube bank shows higher heat transfer rate than circular one for the same given volume (156%). Besides, as a result of second step optimization studies, optimal enhanced shaped geometry showed 0.59% higher heat transfer rate, 21.73% lower pumping power requirement and 9.65% lower total tube bank volume than optimal diamond shaped one.Öğe Performance improvement potential of a PV/T integrated dual-source heat pump unit with a pressure booster ejector(Elsevier, 2023) Erdinc, M. Tahir; Kutlu, Cagri; Unal, Saban; Aydin, Orhan; Su, Yuehong; Riffat, SaffaDual-source heat pump unit can utilize the evaporation of the refrigerant at two different pressures. By adopting an ejector, high-pressure refrigerant stream can be used to lift compressor inlet pressure which results in a higher coefficient of performance (COP). This study proposes a renewable energy sourced and high-efficiency heat pump system which can be easily building integrated to offer a renewable heating solution. The system is devised on the complementation of dual thermal sources; one is air and the other one is solar, to maximize the utilization of ambient energy for highly efficient operation of heat pump. Using the advantage of the relatively lower operating temperature in the solar collector line, the thermal efficiency of the collector would be sufficient in winter. Adaptation of photovoltaics in the collector as a PV/T unit, will benefit the system from the produced electricity for further reduction of the demand from the grid. Along with the use of PV/T collector, the system can be potentially carbon neutral for larger collector areas. In this study, the performance improvement potential of a dual-sourced heat pump unit with an ejector as a booster is investigated for different locations in Turkey which presents different solar and weather profiles. The optimum collector evaporation temperatures are determined, and COP improvement potentials are discussed for different conditions. For a heating supply of 5 kW, the COP of the system can be improved by 22.6 % under 400 W/m2 and 10 degrees C ambient using 15 m2 PV/T collector. Including the electricity generated from the PV, reduction of the electricity demand from the grid can reach to 75 % for the same conditions.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 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.Öğe Thermal Management and Entropy Minimization of Plain and Modified Shaped Plate Fin Heat Sinks Using Multi-Objective Genetic Algorithm(Asme, 2024) Kuru, Muhammet Nasif; Unal, Saban; Efe, Metin; Duman, Necdet; Karasu, Ilyas; Erdinc, Mehmet Tahir; Aydin, OrhanIn this study, an optimization methodology is followed in order to explore better form of heat sinks which improve thermal performances. Optimum designs of plate fin heat sinks (PFHSs) and modified shaped plate fin heat sinks (MS-PFHSs) are numerically investigated. The objective functions are minimizations of base plate temperature, entropy generation and mass. For both PFHSs and MS-PFHSs, optimization variables include inlet velocity (V-in), fin height (H-fin), and number of fins (N-L). Plate fin form is adjusted for MS-PFHSs by adding two optimization variables: the rib height (H-rib) and the number of patterns in the flow direction (W-p). For the multi-objective optimization problems, the maximum base plate temperature limit (T-base<70 degrees C) is used. The multi-objective genetic algorithm (MOGA) is used to solve optimization problems, and three-dimensional parametric models for numerical optimization work are examined using the finite volume approach. The flow is steady, incompressible, and turbulent, and heat transfer in the heat sink is represented by conjugate heat transfer (CHT). It is shown that MS-PFHSs outperform in terms of the analyzed objective functions. For the optimum designs, T-base values of MS-PFHS and PFHS are 60.23 degrees C and 65.25 degrees C, respectively, while the mass values are same. The results also indicate that T-base obtained in the optimum design of MS-PFHS is 7.69% lower than that obtained in the optimum design of PFHS.
