Yazar "Aksoy, I. Gokhan" seçeneğine göre listele

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    APPLICATION OF DIFFERENTIAL TRANSFORMATION METHOD FOR AN ANNULAR FIN WITH VARIABLE THERMAL CONDUCTIVITY
    (Vinca Inst Nuclear Sci, 2022) Aksoy, I. Gokhan
    The thermal analysis of the annular fin is performed by applying the differential transformation method. The thermal conductivity of the annular fin has been considered as a function of temperature. The effects of non-dimensional parameters, namely thermal conductivity and thereto geometric fin parameters on the fin efficiency and temperature distribution are determined. Obtained results from the differential transformation method are also compared with the exact analytical results and the results of the finite difference method in the constant thermal conductivity condition. It has been concluded that the differential transformation method provides accurate results in the solution of non-linear problems.
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    An Application of Explosive Metal Forming in Military Field: The Relationship Between Shaped Charge Jet Formation and Thickness Variation Along Liner Length of Conical Copper Liner
    (Springer Heidelberg, 2013) Sen, Sadri; Aksoy, I. Gokhan
    Shaped charges are very convenient in the formation of very intensive local forces required for penetration and demolition of high strength targets, important in military area. It is generally used to penetrate armored vehicles such as tanks and to demolish concrete fortifications, fuel vessels and bridge constructions, in mining and geophysics, e.g., petroleum research for hard rock penetration and cutting, also in welding and demolition works in industry. In this study, effects of wall thickness variation of the conical copper (CU-OFHC) liner in model group T1 and T2 are investigated. Wall thickness variation is taken into account from the center of the apex to the circular base edge in model group T1 and from the circular base edge to the center of apex in model group T2. In this sense, the relation between the variable thickness, and the geometry and pressure of the jet is investigated. Obtained results are evaluated to determine the stand-off distance between the shaped charge and target which is most important in jet performance. Thickness variation along the liner length changes the liner wall cross-sectional area and increases the liner total mass at both the model groups. Hence, the similar behavior is expected in the two model groups. Hence, the results do not show such a similar behavior between the two model groups. Consequently, It can be said that the dominant parameter is geometrical change, not increase in total mass. This also means that the mass distribution in the liner is determinative parameter in jet formation.
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    Experimental and numerical investigation on melting of phase change material in a disc-shaped container via hot air jet impinging
    (Pergamon-Elsevier Science Ltd, 2024) Kiyak, Burak; Oztop, Hakan F.; Aksoy, I. Gokhan
    Experimental and numerical analyses were performed to investigate the control parameters of a Phase Change Material (PCM) melting by impinging a hot air jet. A novel container was designed to store PCM. The RT25HC was chosen as the PCM, with a 22-26 degrees C melting temperature. Experiments were conducted under a constant air temperature (Tair) of 40 degrees C with two different Reynolds (Re) numbers, 2235 and 4470. The analysis was performed for three jet length-to-container diameter ratios (H/D): 0.4, 0.5, and 0.6. The Finite Volume Method (FVM) was used to solve three-dimensional and time-dependent governing equations. It was found that the optimum melting time was attained when the H/D = 0.5. The measurements, thermal camera images and the numerical results displayed good agreement. The influence of H/D on the melting time decreases as the Reynolds number increases, decreasing the difference between the maximum and minimum melting rates from 23.05 % at Re = 2235 to 7.67 % at Re = 4470. In the experimental comparison, when considering H/D = 0.5, which corresponds to the case with the maximum stored energy at both Reynolds numbers, the energy stored by the H/ D = 0.6 cases is 26.4 % lower at Re = 2235. In contrast, this difference reduces to 5.03 % at Re = 4470.
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    An intelligent approach to investigate the effects of container orientation for PCM melting based on an XGBoost regression model
    (Elsevier Sci Ltd, 2024) Kiyak, Burak; Oztop, Hakan F.; Ertam, Fatih; Aksoy, I. Gokhan
    The orientation of the container filled with phase change material (PCM) is a critical parameter that significantly effects the performance of thermal energy storage systems. In this study, the Computational Fluid Dynamics (CFD) method is utilised to analyse the effects of container position on the melting process of PCM. Unlike conventional methods, the melting process of PCM was conducted using the hot air jet impingement method. The study investigated the impact of two various Reynolds numbers (2235 and 4470) and three different H/D ratio (the ratio of the distance between the jet and the container to the container diameter) which were 0.4, 0.5, and 0.6, on the PCM melting process. In addition, regression analysis was executed using the Extreme Gradient Boosting algorithm (XGBoost). The outcomes unveiled that the artificial intelligence model attained a minimum accuracy of 97.89 % and reached a maximum accuracy of 99.35 % across the 12 datasets for comparing performance metrics. These results serve as a testament to the prowess of the XGBoost algorithm in providing precise predictions of the target variable within a notably extensive range of accuracy for the datasets under consideration.
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    A NUMERICAL STUDY FOR SOLID AND SERRATED ANNULAR FINNED TUBE BUNDLES
    (Vinca Inst Nuclear Sci, 2022) Tacgun, Ekrem; Aksoy, I. Gokhan
    Annular finned tube bundles are commonly used for heat recovery systems. Nowadays, heat recovery systems are important in the energy economy. Cross-flow heat exchangers, one of the heat exchanger types are suitable for waste heat recovery systems. Annular fins are utilized in cross-flow heat exchangers for a long time. In this study, two types of annular fin geometry, namely solid and serrated fins, were studied numerically in the cross-flow heat exchangers. All numerical analyses are performed in ANSYA-FLUENT program and the fin geometries are designed in 3-D geometry. Numerical results obtained for two different geometry fins are validated separately with the literature. It is seen that analysis results are found to be compatible with the literature. In numerical analyses, five different Reynolds Numbers and six different geometric parameters are studied. Effects of these parameters are investigated to determine the flow and thermal performance. According to analysis results, the thermal performance of the serrated annular fin geometry is about 8.2% higher than the solid fin geometry, while the flow performance decreases by 7.5%.
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    THERMAL AND FLOW ANALYSES OF PERFORATED SERRATED ANNULAR FINNED-TUBE BUNDLES IN A CROSS-FLOW HEAT EXCHANGER
    (Begell House Inc, 2023) Tacgun, Ekrem; Aksoy, I. Gokhan
    The thermal and flow analysis of a cross-flow heat exchanger is numerically investigated by experimental validation in this study. The cross-flow heat exchanger consists of a tube bundle with perforated serrated annular fins. Numerical analysis is performed in three dimensions by using the ANSYS Fluent program. Numerical studies are validated separately for thermal and flow characteristics. For the validation study, experiments are performed on a cross-flow heat exchanger experimental setup at five different Re numbers. The numerical results are found to be in agreement with these experiments using the appropriate turbulence model. Perforated serrated annular finned-tube bundles are compared with the existing tube bundles in the literature such as annular solid and serrated finned-tube bundles in terms of heat transfer and flow friction. As a result of the numerical analyses, heat transfer of the perforated serrated finned-tube bundle is 14.2% and 5.2% higher than that of solid and serrated finned-tube bundles, respectively. At the same time flow friction of the perforated serrated finned-tube bundle is also higher than that of solid and serrated finned-tube bundles. In addition, the segment height ratio is determined as a variable geometric parameter. This geometric parameter is examined for five Re numbers. The effects of this parameter on heat transfer and flow friction are investigated separately. As a result, it has been observed that drilling of circular holes on the segment section of the annular serrated finned-tube bundles increases heat transfer and flow friction.
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    Three dimensional analysis of melting performance of phase change materials in a disk-shaped container with partial circular heating
    (Taylor & Francis Inc, 2023) Kiyak, Burak; Oztop, Hakan F.; Aksoy, I. Gokhan
    Three dimensional analysis of melting performance of phase change materials in a disk-shaped container with partial circular heating has been studied. The phase change materials (PCMs) have succeeded in coming to the fore with their superior features in energy storage. However, the energy storage efficiency of these materials affected by many physical parameters, and determining the appropriate parameters is important for efficient energy storage. This study explores melting and energy storage performance of PCM-RT25 in a disk-shaped container with various partial circular heating cases and aspect ratios (AR). PCM melting analysis was performed with partial heating by selecting equal heating surface area on the disk. The effects of AR on melting performance were analyzed by observing the PCM melting behavior for different disk heights while keeping the disk diameter constant. Governing equations are solved by using finite volume method. Obtained results showed that the PCM melting time decreases as the AR increases in the case of full heating. In partial heating, the increase in AR not only extended the melting time, but also decreased the liquid fraction at the end of the melting. Parameters of AR = 4 and Delta T = 45 degrees C was provided the maximum liquid fraction in partial heating cases. Under these conditions, 90%, 94% and 96% liquid fractions were obtained at the end of melting for the cases that the heater is located in the center of the disk, in the middle near the inner part of the disk and in the middle near the outher part of the disk, respectively.