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Öğe Influence of curved trapezoidal winglet vortex generators on thermalhydraulic performance in fin-and-tube heat exchangers(Kare Publishing, 2025) Alişan gönülFin-tube heat exchangers play a crucial role in various industrial and HVAC applications due to their high heat transfer efficiency. This study focuses on the numerical analysis of fin-tube heat exchangers integrated with curved trapezoidal winglet vortex generators. In the current work, the impact of three key factors on heat transfer and flow characteristics: inlet velocity (2–5 m/s), vortex generator position angle (45°–120°), and arc length (3.80–6.33 mm) is analyzed. To enhance the accuracy of output predictions, this research extends beyond conventional parametric studies by utilizing a structured design of experiments approach. The study determines the optimal configurations through Kriging response surface methodology analysis. Results indicate a potential 48.5% improvement in heat transfer and up to an 18.3% enhancement in thermo-hydraulic performance. Moreover, the study reveals that improper sizing and positioning of vortex generators may lead to a 5% decrease in thermo-hydraulic performance compared to the heat exchanger without vortex generators. This work aims to explore strategies for enhancing the thermal performance of fin-and-tube heat exchangers through novel vortex generator designs by considering their geometric dimensions and positioning.Öğe Prediction of photovoltaic panel cell temperatures: Application of empirical and machine learning models(Elsevier BV, 2025-05) Fatih BayrakIn this study, 25 different empirical models predicting the cell temperatures of PV panels were statistically analyzed and predictions were made using machine learning models. As a result of the correlation analysis, a strong positive correlation was found between the power output (Pm) of PV panels and solar radiation (Is) (PV1: r = 0.93, PV2: r = 0.94), indicating that photovoltaic energy conversion directly depends on solar radiation. In the analyses using error metrics (MAE and RMSE), the performances of wind speed dependent (MW) and independent (M) models were compared. However, since error metrics alone are not sufficient to assess the statistical significance and reliability of the models, t-test and confidence interval analyses were applied. The M5 model in the PV1 panel and the M1 model in the PV2 panel provided the closest predictions to the actual values. When MW models are analyzed, MW1 model for PV1 and MW13 model for PV2 produced the most accurate predictions. Within the scope of machine learning methods, different regression types such as Linear Regression, Non-Linear Regression, Decision Tree Regression and Support Vector Regression were evaluated and their prediction performances were compared. Among the Decision Tree based models, Extra Trees was one of the prominent models with R2 = 0.960 for PV1 and R2 = 0.974 for PV2 in the test phase.Öğe Discharge performance of side gates with different shapes(IWA Publishing, 2025-02-10) Veysi Kartal; M. Emin Emiroglu; M. Fatih YukselFlow measurement and water level control in open channels are vital to water management. Lateral intake structures are commonly used for different purposes in civil and environmental engineering applications. Flow characteristics of rectangular, triangular, and semi-circular shapes were experimentally investigated using 357 runs under subcritical flow conditions. Correlation analysis was conducted to determine the effect of various parameters on the discharge coefficient. Upstream Froude number (F1), the ratio of the gate opening to the upstream flow depth, and the gate length to flow depth ratio are influential for all side gates. However, the ratio of the gate opening to the gate length is also influential for triangular side gates. Discharge coefficient of the semi-circular side gate is relatively higher than that of the other tested gates within the range of 0.05Öğe A new hybrid CFD approach to study the impact of forced convection on radiant cooled wall with baseboard diffuser including various vane angles(Elsevier BV, 2025-07) Melek Caliskan Temiz; Aykut Bacak; Muhammet Camci; Yakup Karakoyun; Ozgen Acikgoz; Ahmet Selim DalkilicThe current work examines the effect of forced convection on thermal comfort in a space, including radiant wall cooling and an innovative floor-level diffuser system. It examines the impact of various vane angles on thermal comfort in room air conditioning at 15°, 30°, 45°, 60°, and 75°, and employs experimental data to confirm a hybrid 3D computational fluid dynamics (CFD) model. A new floor-level diffuser system delivers air at temperatures between 18 °C and 22 °C, with supply air velocities of 5 m/s and 10 m/s measured at the exit side of diffuser while the supply water temperature is kept constant at 14 °C. In the hybrid 3D solution, experimentally derived convective heat transfer coefficients (CHTCs) for forced airflow are utilized. This is accomplished by merging a k-ω model with a hydronic radiant panel system that incorporates forced convection. The analysis examines temperature and velocity distributions, CHTCs on the radiant-cooled wall, and the PMV-PPD components. Results indicate that at a supply air velocity of 5 m/s, thermal comfort parameters do not satisfy PMV and PPD indices, except in proximity to the diffuser. Nevertheless, elevating the supply air velocity to 10 m/s ensures thermal comfort across the space, with the exception of regions next to the cooled wall surfaces. The examination of several vane angles indicated that a 45° angle yields the most advantageous thermal comfort conditions, irrespective of air velocity. The CHTC adjacent to the radiant wall is roughly 6 W/m2K at a velocity of 5 m/s and rises to 8 W/m2K at 10 m/s. The temperature disparity between the head and ankle regions at 5 m/s adheres to the 3 °C tolerance established by international standards. The study determines that a 45° vane angle ensures best thermal comfort, and the devised numerical method yields significant insights for the construction of analogous indoor settings.Öğe Thermal annealing optimization for improved mechanical performance of PLA parts produced via 3D printing(Elsevier BV, 2025-03) Çağlar Kahya; Oğuz Tunçel; Onur Çavuşoğlu; Kenan TüfekciThis study employs an integrated approach using Taguchi, ANOVA, and Grey Relational Analysis to optimize the mechanical performance of PLA parts produced via Fused Filament Fabrication through controlled thermal annealing. The analysis examines the effects of annealing temperature and time on tensile, flexural, compressive, and impact strengths, aiming to identify optimal post-processing conditions for improved material properties. Annealing temperatures ranged from 70 °C to 110 °C, and durations varied between 40 and 200 min. Key findings indicate that the most influential parameters were achieved at 90 °C for 120 min, yielding notable enhancements in tensile strength, flexural strength, compressive strength, and impact resistance. The Taguchi method identified optimal conditions for each mechanical property, with temperature emerging as the most influential factor. ANOVA analysis further quantified the contribution ratio of temperature and time, validating the Taguchi results and confirming that temperature accounted for most of the variation in mechanical performance. Differential Scanning Calorimetry supported these findings, showing increased crystallinity in PLA, thus highlighting the significant impact of optimized thermal annealing on enhancing 3D-printed PLA parts.Öğe Biogas Production from Organic Waste: Recent Progress and Perspectives(Springer, 2018-12-14) M.R., Atelge; David, Krisa; Gopalakrishnan, Kumar; Cigdem, Eskicioglu; Dinh Duc, Nguyen; Soon Woong, Chang; A. E., Atabani; Alaa H., Al‑Muhtaseb; S., UnalanAnaerobic digestion (AD) from organic waste has gained worldwide attention in reducing greenhouse gas emissions, lowering fossil fuel combustion, and facilitating a sustainable renewable energy supply. Biogas mainly consists of methane (CH4) (50–75%), carbon dioxide (CO2) (25–50%), hydrogen sulphides (H2S), hydrogen (H2), ammonia (NH3) (1–2%) and traces of other gases such as oxygen (O2) and nitrogen (N2). Methane can replace fossil fuels in various applications such as heat and power generation and the transportation sector. The degradation of organic waste through an AD process o?ers many advantages, such as the decrease of pathogens and prevention of odour release. The digestate from anaerobic fermentation is a valuable fertilizer, however, the amount of organic materials currently available for biogas production is still limited. New substrates, as well as more e?ective conversion technologies, are needed to grow this industry globally. This paper reviewed the latest trends and progress in biogas production technologies including potential feedstock. Recycling of waste has recently become an important topic and has been explored in this paper.Öğe Optimisation of sepiolite clay with phosphoric acid treatment as support material for CoB catalyst and application to produce hydrogen from the NaBH4 hydrolysis(Elsevier-Hydrogen energy, 2019) Selvitepe, Nuran; Balbay, Asım; Saka, CaferHerein, the CoB catalyst supported on the sepiolite clay treated with phosphoric acid was utilized to produce hydrogen from the NaBH4 hydrolysis. In order to analyse the performance of the phosphoric acid treated sepiolite clay supported-CoB catalyst, the NaBH4 concentration effect, phosphoric acid concentration effect, phosphoric acid impregnation time effect, CoB catalyst percentage effect, and temperature effect were studied. In addition, XRD, XPS, SEM, TEM, BET, and FTIR analysis were performed for characterization of CoeB catalyst supported on the acid-treated sepiolite. The completion time of this hydrolysis reaction with CoeB (20%) catalyst supported on the sepiolite treated by 5 M phosphoric acid was approximately 80 min, whereas the completion time of this hydrolysis reaction with acid-free sepiolite-supported CoeB (20%) catalyst was approximately 260 min. There is a five-fold increase in the maximum production rate. The maximum hydrogen production rates of this hydrolysis reaction at 30 and 60 C were found as 1486 and 5025 ml min 1g 1 catalyst, respectively. Activation energy was found as 21.4 kJ/mol. This result indicates that the acid treatment on sepiolite is quite successful. The re-usability of NaBH4 hydrolysis reaction by CoB catalyst supported on sepiolite treated phosphoric acid for successive five cycles of NaBH4 at 30 C was investigated.Öğe Fast and effective hydrogen production from ethanolysis and hydrolysis reactions of potassium borohydride using phosphoric acid(Elsevier-Hydrogen Energy, 2018-10-25) Saka, Cafer; Balbay, AsımThe hydrogen production from potassium borohydride (KBH4) with the ethanolysis and hydrolysis reactions using the phosphoric acid as a catalyst is performed for the first time. KBH4 concentration, phosphoric acid concentration and temperature effects were investigated for the optimum hydrogen production from ethanolysis and hydrolysis reactions of KBH4. The maximum hydrogen production rates in the ethanolysis and hydrolysis reactions with 1 M phosphoric acid are 6423 and 4296 ml min 1g 1, respectively. At the same time, the ethanolysis and hydrolysis reactions with the 1 M acid concentration were completed within 7 and 9 s, respectively. The total conversions obtained for the volume ratio of KBH4/acid of (1:1) were 100%. The power law kinetic model is performed for the kinetic studies. The activation energies for the ethanolysis and hydrolysis reactions of KBH4 using phosphoric acid are found as 2.98 and 2.60 kJ mol 1.Öğe Semi-methanolysis reaction of potassium borohydride with phosphoric acid for effective hydrogen production(Elsevier-Hydrogen Energy, 2018-11-15) Balbay, Asım; Saka, CaferThe methanol and water solvents were used for the production of hydrogen from potassium borohydride. In addition, phosphoric acid was selected as the green catalyst so that this semi-methanolysis reaction would be more effective for the first time. The semimethanolysis of potassium borohydride is investigated depend on potassium borohydride, phosphoric acid concentrations and temperatures. The maximum normalized hydrogen production rate obtained from this semi-methanolysis reaction with 1 M phosphoric acid as a catalyst was 5779 ml min 1 g 1. In addition, this semi-methanolysis reaction was completed in 5 s. Kinetic studies have been carried out with the power law kinetic model. The activation energy obtained for this semi-methanolysis reaction is 1.45 kJ mol 1.Öğe Efficient hydrogen production with controlled hydrochloric acid addition using Ni-based catalyst synthesized in ethanol solvent(Taylor Francis-Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2019-04-03) Saka, Cafer; Balbay, AsımA Ni-based catalyst was synthesized in ethanol solvent by chemical reduction with sodium borohydride(NaBH4). This catalyst was used to catalyze the hydrolysis reaction of NaBH4 with hydrochloric acid (HCl) including different concentrations. Surface morphologies and characteristic properties of the Ni-based catalysts synthesized in the ethanol and water solvents were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), surface area measurements, and Fourier-transform infrared spectroscopy (FTIR) analyses, respectively. The maximum HGRs of the Ni-based (water) and Ni-based (ethanol) catalysts were 173 and 1054 ml g-1min-1, respectively. In addition, the HGR with 0.25 M HCl addition on the hydrolysis reaction using the Ni-based catalyst prepared in the ethanol solvent was about 1526 ml g-1min-1. Kinetic studies are performed according to the power law kinetic model. The activation energy (Ea) for the HG from the acidified hydrolysis reaction of NaBH4 using the Ni-based (ethanol) catalyst was found as 49 kJ mol-1.Öğe Influence of process parameters on enhanced hydrogen generation via semi-methanolysis and semi-ethanolysis reactions of sodium borohydride using phosphoric acid(Elsevier-Hydrogen Energy, 2019-10-16) Saka, Cafer; Balbay, AsımThe sodium borohydride(NaBH4) semi-methanolysis and semi-ethanolysis reactions to produce hydrogen are investigated using phosphoric acid(H3PO4) for the first time. The NaBH4 concentration, H3PO4 concentration, and temperature parameters on these semialcoholysis reactions are evaluated. The normalized hydrogen generation rates (HGRs) obtained from the NaBH4 semi-methanolysis and semi-ethanolysis acidified using 0.5 M H3PO4 are 11684 and 9981 ml min 1 g 1, respectively. Moreover, the completion times of these semi-methanolysis and semi-ethanolysis reactions with 0.5 M H3PO4 acid concentration are 0.10 and 0.116 min, respectively. Kinetic studies with the power-law model
