Person: KAYA, ALAATTİN METİN
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KAYA
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ALAATTİN METİN
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Publication Mesoscale morphologies of nafion-based blend membranes by dissipative particle dynamics(Mdpi, 2021-05-28) Şen, Ünal; Özdemir, Mehmet; Erkartal, Mustafa; Kaya, Alaattin Metin; Manda, Abdullah A.; Oveisi, Ali Reza; Ali Aboudzadeh, M.; Tokumasu, Takashi; KAYA, ALAATTİN METİN; Mühendislik Fakültesi; Makine Mühendisliği Bölümü; 0000-0002-1940-8749 ; AAC-4540-2020Polymer electrolyte membrane (PEM) composed of polymer or polymer blend is a vital element in PEM fuel cell that allows proton transport and serves as a barrier between fuel and oxygen. Understanding the microscopic phase behavior in polymer blends is very crucial to design alternative cost-effective proton-conducting materials. In this study, the mesoscale morphologies of Nafion/poly(1-vinyl-1,2,4-triazole) (Nafion-PVTri) and Nafion/poly(vinyl phosphonic acid) (Nafion-PVPA) blend membranes were studied by dissipative particle dynamics (DPD) simulation technique. Simulation results indicate that both blend membranes can form a phase-separated microstructure due to the different hydrophobic and hydrophilic character of different polymer chains and different segments in the same polymer chain. There is a strong, attractive interaction between the phosphonic acid and sulfonic acid groups and a very strong repulsive interaction between the fluorinated and phosphonic acid groups in the Nafion-PVPA blend membrane. By increasing the PVPA content in the blend membrane, the PVPA clusters' size gradually increases and forms a continuous phase. On the other hand, repulsive interaction between fluorinated and triazole units in the Nafion-PVTri blend is not very strong compared to the Nafion-PVPA blend, which results in different phase behavior in Nafion-PVTri blend membrane. This relatively lower repulsive interaction causes Nafion-PVTri blend membrane to have non-continuous phases regardless of the composition.Publication Examination of the performance effects of refrigerants in a multistage refrigeration cycle using advanced exergy analysis(Springer, 2022-05-07) Kaya, Alaattin; KAYA, ALAATTİN METİN; Mühendislik Fakültesi; Makina Mühendisliği Bölümü; 0000-0002-1940-8749; AAC-4540-2020A two-stage vapor compression refrigeration system was investigated using advanced-exergy-based analysis, which examines the effects of each component and their interactions with each other for system development. The advanced-exergy-based analysis guides how much improvement can be made on the parts of the system, examining exergy destruction in the form of endogenous/exogenous and avoidable/unavoidable parts. In addition, a parametric study was conducted and the performances of different refrigerants were evaluated to analyze the system under various operating conditions. The highest exergy destruction arises as 8.1 kW for R227ea. The total compressor works decrease 0.667 kW by changing the refrigerant from R227ea to R142b. R152a shows a preferable performance along with environmentally friendly characteristics. The condenser has the most critical improvement potential with 0.869 kW, and it accounts for 31% of the total irreversibility. It is followed by the evaporator 0.734 kW (26.2%). All exergy destruction in the evaporator falls into endogenous-part. The irreversibility of the evaporator is directly related to inner inefficiency. Coefficient of performance decreases by 40% for a condenser temperature variation from 30 to 50 degrees C. An increment in the evaporator temperature from - 15 to 0 degrees C increases coefficient of performance by 49.95%. The avoidable exergy-destruction rate can be minimized by 24.89% for that temperature variation.Publication Investigation of a cross-flow turbine under natural conditions(Springer India, 2022-03-01) Özdemir, Yavuz Hakan; Yigit, Kadri Süleyman; KAYA, ALAATTİN METİN; Mühendislik Fakültesi; Makina Mühendisliği Bölümü; 0000-0002-1940-8749; A-7950-2018; AAC-4540-2020In this study, the computational and experimental examination of the hydraulic cross-flow turbine (CFT) is presented. The experimental studies are conducted at the turbine laboratory of Gebze Technical University. The commercial Computational Fluid Dynamics (CFD) software, Star CCM+, is employed to calculate three-dimensional, incompressible, steady Reynolds-Averaged Navier-Stokes (RANS) equations for the flow inside the CFT. In the numerical model, the rotational motion of the blades is modeled by means of the moving reference frame approach. The correlation between the turbulent viscosity and the velocities is acquired using the standard k-e turbulence model. The computational results are obtained in terms of the torque, power, and efficiency of the turbine. The outcome of this research reveals that the CFD software used in this study can reliably be used to predict experiments since the numerical model can accurately estimate the experimental values of the torque, power, and efficiency of the CFT.Publication Thermodynamical study and taguchi optimization of a two-stage vapor compression refrigeration system(Vinca Inst Nuclear Sci, 2022-01-01) Kaya, Alaattin Metin; KAYA, ALAATTİN METİN; Makine Mühendisliği Bölümü; 0000-0002-1940-8749; AAC-4540-2020This study's primary purpose is to optimize the multistage refrigeration system with statistical methods. Taguchi optimization and ANOVA methods were applied to statistically determine the effects of components on system performance. The best operational conditions were defined for the maximum COP and exergy efficiency. Critical parameters have been determined to maximize the system's performance. The evaporator temperature was defined as the most vital parameter (46.32%), and it is followed by condenser temperature (32.65%) for the maximum COP. The most important two parameters are determined as evaporator temperature with 29.14% and condenser temperature with 20.34% for maximum exergetic performance. As a result of 27 tests, the highest COP of the system was calculated as 2.67 and exergy efficiency as 55.22%. By using the optimum levels determined by Taguchi, it was ensured that the system's COP was increased to 3.326 and its exergy efficiency to 71.23%. The ANOVA analyses indicate that the results' confidence level is relatively high, to be 99.9%. Another parameter examined in this study is the inter-stage level determination method and its effect on system performance. The method of determining the optimum inter-stage level may vary according to the objective function and system conditions.Publication Analysis of vapor compression refrigeration cycle using advanced exergetic approach with taguchi and anova optimization and refrigerant selection with enviroeconomic concerns by topsis analysis(Elsevier, 2022-03-24) Ustaoğlu, Abid; Kurşuncu, Bilal; Çalışkan, Hakan; Kaya, Alaattin Metin; KAYA, ALAATTİN METİN; Mühendislik Fakültesi; Makine Mühendisliği Bölümü; 0000-0002-1940-8749; AAC-4540-2020In this study, TOPSIS analysis was applied to decide the optimum refrigerants with cost, safety, environmental and enviroeconomic concerns along with thermophysical properties. A vapor compression refrigeration cycle performance was investigated with the statistical and thermodynamic approaches. COP, exergy efficiency, total, avoidable, and unavoidable exergy destruction rates were calculated for various experimental designs. According to the relative proximity to the ideal solution, the best refrigerants for the system were determined as R513a, R134a, and R448a, respectively. The optimum parameters for the greatest COP and exergetic performance were calculated as A(2)B(3)C(1)D(3)E(3)F(1). In the optimum case, the best COP and exergy efficiency of 2.65 and 10% and the lowest total exergy destruction of 0.34 kW were achieved for R134a. These are larger than all other 27 experimental patterns. The parameters having an impact on the COP, exergy efficiency, and total exergy destruction rate were found as T-EVA > T-CON > Refrigerant > eta(COM,H) > eta(COM,L) > P-in (B > C > A > E > D > F). The evaporator temperature is the most effective parameter on the performance with about 42.8% for the performance. It is followed by that of condenser and refrigerant to be 32.5% and 13.8%. The most effective parameters for the avoidable exergy destruction rate were high-and low-pressure compressors efficiencies, evaporator temperature, and condenser temperature, respectively.Publication Thermal and mechanical properties of a new insulation composite material(Gmbh, 2023-07-21) Koçyiğit, Fatih; Kaya, Alaattin Metin; KAYA, ALAATTİN METİN; Mühendislik Fakültesi; Makine Mühendisliği; 0000-0002-1940-8749; AAC-4540-2020The Taguchi optimization method was used to optimize waste and natural different components such as waste marble dust, expanded perlite, perlite aggregate size, cement, and molten tragacanth in the production of new insulation composite material. Compressive strength, thermal conductivity, abrasion loss, and water adsorption properties of the developed composite material were investigated. Taguchi's standard L18 array was chosen for optimization of these four components with different levels. Response plots were created using the Taguchi and the optimum test condition was determined. The insulation composite material with the best thermal and mechanical properties was obtained under the condition of waste marble dust (1), expanded perlite (1), perlite aggregate size (1) and molten tragacanth (1). In addition, using the anova (Analysis of Variance), percentage impacts on the mechanical and thermal properties of the test parameters were determined. Statistical values obtained from anova and mathematical models are developed by using multi-linear regression method. It was found that the mathematical model and the experimental results were quite compatible. The optimum test conditions detected were verified by confirmation experiments. Confirmation experiment results were obtained between 99.9 % confidence interval values.