TR-Dizin İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/396
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Article Thermophysical Properties of Directionally Solidified the Zn-Mg Eutectic Alloy and the Effect of Growth Rates on Electrical Properties(2025-03-25) Bayram, ÜmitThe study aimed to investigate the effect of growth rates (V) on the electrical properties of a Zn–3.0 Mg–2.5 Al (wt.%) eutectic alloy. The alloy was directionally solidified at four different growth rates ranging from 8.28 to 164.12 μm/s. Directional solidification experiments were conducted using a Bridgman-type solidification furnace, which was employed for controlled solidification and minimizing undesirable casting defects, following the alloy's production and casting process. The electrical resistivity (ρ) of the samples, measured using the Four-Point Probe Method (FPPM) available in the laboratory, exhibited an increasing trend ranging from 72.80 to 96.20 (nΩm) with rising growth rates. In other words, the electrical conductivity of the Zn–Mg–Al eutectic alloy varies inversely with the growth rate. Additionally, the thermophysical properties of the eutectic alloy in the casting phase were determined using differential scanning calorimetry (DSC): ΔHf (the fusion enthalpy), ΔCp (the specific heat) and TM (the melting point) (26.69 J/g, 0.043 J/gK, 618.92 K, respectively). The results obtained for the Zn–Mg–Al eutectic alloy reveal that, when compared to Zn-Al-based alloys produced under similar experimental conditions, the elements comprising the alloy and mass proportions lead to microstructural changes, which in turn affect its electrical conductivity.Article Thermal Stresses in SOFC Stacks: The Role of Mismatch Among Thermal Conductivity of Adjacent Components(Tubitak Scientific & Technological Research Council Turkey, 2021-06-30) Aydin, Ozgur; Matsumoto, Go; Shiratori, YusukeGenerating power from renewable biogas in solid oxide fuel cells (SOFCs) is an environment-friendly, efficient, and promising energy conversion process. Biogas can be used in SOFCs via a reforming process for which dry reforming is more suitable as the reforming agent exists in the biogas mixture. Biogas can be directly reformed to H-2 -rich fuel stream in the anode chamber of a SOFC by the heat released during power generation. Exploiting the heat and water produced in the SOFC for internal reforming of biogas makes the energy conversion process very efficient; however, various challenges are reported. Thus, indirect internal reforming is opted for which a separate reforming domain is required. In an indirect internal reformer operating at usual conditions, dry reforming rate is quite high in the inlet and it decreases steeply toward the fuel outlet. Great temperature gradients develop over the reformer, since the dry reforming reaction is strongly endothermic. The abruptly varying rate of the reforming reaction affects the temperature fields in the adjacent components of SOFC and hence intolerable thermal stresses emerge on the SOFC components. In our preceding study, we graded the reforming domain, homogenized the temperature profile over the reforming domain, and executed performance and durability experiments. However, most of the experiments failed due to fracturing SOFC components hinting at existence of thermal stresses. In that study, we focused on minimizing the temperature gradients within the reforming domain; namely, we neglected the other processes. To eliminate the thermal stresses, we modeled the entire module of SOFC equipped with a reformer featuring a graded reforming domain. We found that the mismatch between the thermal conductivities of the adjacent module components is the major reason for the thermal stresses. When the mismatch is eliminated, thermal stresses disappear even if the reforming domain is not graded.Article Model Updating of a Euler-Bernoulli Beam Using the Response Method(2021-05-31) Oktav, Akın; İnan, Cevher YusufIn this study, the computational model is updated using an analytical model instead of an experimental one. Continuous and discrete parameter models of a Euler–Bernoulli beam are constructed analytically and computationally. To construct the computational models, Ansys™ software is employed, and 1-D beam elements are chosen to get the finite element model of a cantilever beam. To get analytical solutions for the continuous and discrete parameter models, a state-space representation is employed. In the first step, only mass and stiffness matrices are considered to model the beam. Eigenfrequencies and eigenvectors of the beam are calculated. The analytical and computational eigenfrequencies of continuous and discrete parameter models are compared. In the seconds step, non-proportional viscous damping and non-proportional structural damping matrices are introduced into the analytical discrete parameter model. Then, the frequency response functions of the model are generated. The damping matrices are identified using the generated frequency response functions. The damping matrices used in the analytical model, and the damping matrices identified using the frequency response functions are compared. It is observed that the assigned damping matrices and the identified damping matrices are identical, which shows that the computational model can be accurately updated provided the FRFs are available.Article Computational Fluid Dynamics (CFD) Analysis of 3D Printer Nozzle Designs(2024-12-31) Hajili, Rasul; Temirel, MikailAdditive manufacturing, particularly 3D printing, has gained significant attention recently due to its flexibility, precision, and sustainability. Among the various 3D printing technologies, Fused Deposition Modeling (FDM) stands out as one of the most popular due to its affordability, ease of use, and print quality. However, a major drawback of FDM-based 3D printers is their relatively low print resolution. One of the key factors influencing print quality is the nozzle design, especially its geometry. As a result, numerous studies in literature have focused on improving 3D printing performance by optimizing nozzle design. In this study, we investigated the effects of nozzle geometry from a Computational Fluid Dynamics (CFD) perspective, examining three aspects: die angle, outlet size, and outlet shape. The CFD analysis revealed that the die angle primarily influences the shear stress within the nozzle, while the outlet size has a significant impact on velocity and pressure difference. The outlet shape affects shear stress, velocity, and pressure difference to a lesser extent than the die angle and size.Article Citation - WoS: 2Citation - Scopus: 2Analysis of Optical Gyroscopes With Vertically Stacked Ring Resonators(Tubitak Scientific & Technological Research Council Turkey, 2021-05-31) Hah, DooyoungWithout any moving part, optical gyroscopes exhibit superior reliability and accuracy in comparison to mechanical sensors. Microring-resonator-based optical gyroscopes emerged as alternatives for bulky conventional Sagnac interferometer sensors, especially attractive for applications with limited footprints. Previously, it has been reported that planar incorporation of multiple resonators does not bring about improvement in sensitivity for a given area because the increase in Sagnac phase accumulation does not outrun the increase of area. Therefore, it was naturally suggested to consider vertical stacking of ring resonators because then, the resonators can share the same footprint. In this work, sensitivity performances of such configurations with vertically stacked microring resonators are analyzed and compared to that of a basic (single-resonator) configuration. Through comprehensive study, it is learned that the sensitivity performance of the devices with vertically-stacked resonators (either with a single bus waveguide or with two bus waveguides) does not exceed that of the basic sensor device (single resonator with one bus waveguide), i.e. the basic structure is yet to be remained as the most efficient configuration.