Sürdürülebilir Kalkınma Amaçları
Yayınlar
- MakaleAçık Erişim2026Scopus SJRQ2Examination of the thermal and metallographic characteristics at high temperatures of natural stones (andesite) extracted from different elevations
Işık, Erdem; Kahraman, Gökhan; Atalar, Aydın
This study examines the high‑temperature thermal response of andesite stones extracted from two different elevations of Mount Ağrı (Türkiye) in order to improve material selection strategies for engineering applications. Thermal conductivity and density values of the samples were first measured under laboratory conditions. The specimens were then heated to 850 °C and cooled by natural convection while surface temperatures were recorded at fixed time intervals using a thermal camera. Based on these measurements, convective heat transfer coefficients were determined, and the time‑dependent thermal diffusivity and Biot numbers were subsequently calculated using the first-term approximation of the Fourier series. Metallographic examinations were conducted to correlate the thermal behavior with microstructural characteristics. Results indicate a pronounced effect of elevation on thermal performance. The sample obtained from the higher elevation exhibited substantially greater thermal diffusivity, reaching 2.93 × 10⁻5 m2 s−1 at 360 s and decreasing to 8.96 × 10⁻6 m2 s−1 at 1300 s. In contrast, the lower‑elevation andesite showed lower diffusivity values (1.83 × 10⁻5 m2 s−1 at 360 s and 5.9 × 10⁻6 m2 s−1 at 1300 s). Conversely, Biot numbers were consistently higher for the lower‑elevation sample, decreasing from 0.60 to 0.29 during the cooling process, whereas the high‑elevation sample displayed values from 0.314 to 0.165. Metallographic analysis confirmed that variations in microstructure—linked to different geological formation conditions—directly influenced these thermophysical properties. Overall, the findings demonstrate that andesite sourced at higher elevations possesses superior thermal diffusivity and more favorable heat‑transfer characteristics at elevated temperatures. These results highlight the importance of geological origin in the design, assessment, and selection of natural stone materials for high‑temperature engineering applications.
- MakaleAçık Erişim2026Scopus SJRQ2Production and Thermal–Structural Characterization of Nano-Oxide-Doped Paraffin-Based Phase Change Composite Materials for Thermal Storage Applications
Yücel, Halit Lutfi; Özdemir, Osman; Kahraman, Gökhan
Paraffin-based composite phase change materials (PCMs) have been synthesized for thermal energy storage applications to enhance thermal conductivity and stability while maintaining latent heat storage capacity. In this study, RT42 paraffin was modified with inorganic nano-oxides (Al2O3, CuO, SiO2, and ZnO) in the presence of sodium dodecyl sulfate (SDS) as a surfactant. The incorporation of SDS improved nanoparticle dispersion and reduced agglomeration, resulting in enhanced phase-change behavior and improved structural homogeneity. Differential scanning calorimetry (DSC) analysis revealed slight variations in melting and crystallization temperatures, while the ZnO-doped composite retained up to 92% of the latent heat storage capacity of pure RT42. Among all the investigated composites, the Al2O3-doped sample exhibited the highest thermal conductivity and specific heat capacity. Thermogravimetric analysis (TGA) indicated an increase of approximately 15–20°C in the decomposition temperature, demonstrating enhanced thermal stability. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses confirmed the preservation of the crystalline structure and improved microstructural uniformity. The developed SDS-assisted nano-oxide/RT42 composites exhibit significant potential for passive thermal regulation in renewable energy and building applications.
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İncele - MakaleYalnız künye2026Scopus SJRQ2Experimental ınvestigation of hybrid passive cooling strategies for photovoltaic modules using nano-enhanced PCM and graphene-coated finned structures under hot climate conditions
Özdemir, Osman; Yücel, Halit Lutfi; Kahraman, Gökhan
This study experimentally investigates the use of several passive cooling techniques to enhance the electrical performance of photovoltaic (PV) modules under high ambient summer temperatures in Elazığ, Turkey. Throughout the trial period of July, August, and September, a system comprising four photovoltaic panels, one designated as a reference, was developed. The first passive cooling arrangement utilized a paraffin-based phase change material (PCM) RT42HC. In the second configuration, a nano-enhanced PCM (NePCM) composite was employed, prepared by dispersing 1 mass% of Al2O3 nanoparticles into the paraffin matrix and stabilizing them with 3 mass% of sodium dodecyl sulfate (SDS) to ensure homogeneous distribution. The third, hybrid configuration integrated 14 graphene-coated parabolic pin-tipped fins mounted externally onto the aluminum enclosure housing the NePCM composite. Experimental results demonstrated that the implemented passive cooling techniques markedly decreased the panel surface temperature, thereby enhancing electrical power output and photovoltaic efficiency. The hybrid graphene-coated fin-NePCM system demonstrated superior performance, achieving a maximum surface temperature reduction of 12.65 °C, a sustained electrical efficiency increase of 6–13%, and an average daily electrical energy gain of 26.23 Wh day−1 compared to the reference module. These findings demonstrate that the integrated hybrid design is an effective and reliable passive cooling method for sustaining photovoltaic system performance under hot climate conditions.
- MakaleAçık Erişim2025Hidroelektrik Santrallerde Türbin-Jeneratör Yatak Arızaları Sonucu Oluşan Mekanik Titreşimler ve Çözüm Yöntemleri
Kahraman, Gökhan
Günümüzde imal edilmekte olan hidrolik türbinlerin güçlerinin ve boyutlarının çok artmış olması ciddi bir mekanik titreşim ve şaft salınımı problemini de beraberinde getirmektedir. Bilinmektedir ki mekanik titreşime (vibrasyon olayı) maruz kalan bir makine devamlı olarak çekme, basma, eğme, burma, kesme gibi değişken mekanik baskılarla sürekli olarak zorlanmaktadır. Hidrolik türbinlerin bu tür titreşim ve salınımlara maruz kalmaları işletme güvenliğini ve işletmede kalma süresini önemli derecede azaltmaktadır. Bu çalışmada, bir hidroelektrik santrale ait Francis tipi tür-binde yatak boşluğunun müsaade edilen sınırları aşması neticesinde meydana gelen, mekanik titreşimler (vibrasyon olayı) ve şaft salınımları arızası incelenmiştir. Tür-bin – Jeneratör yataklarına tekrar ayar yapıldıktan sonra oluşan şaft salınımları, arıza durumunda oluşan şaft salınımları ile kıyaslanmıştır. Sonuç olarak arıza sonrası hidrolik türbin yataklarının ölçüleri kabul edilen standartlara getirildikten sonra mekanik titreşimler ve şaft salınımları normal seviyelere gelmiştir. Mekanik ti-tre-şimden kaynaklı arızalar ve aşırı şaft salınımı sonucu oluşacak yatak sürtmesi gibi büyük arızalar engellenmiştir.
- MakaleAçık Erişim2025Scopus SJRQ2Investigation of the effect of the metallographic properties of vertical and horizontal cylinders made of ferrochrome with different contents on heat transfer by natural convection
Kahraman, Gökhan; Taşgın, Yahya
In this study, ferrochrome materials containing elements with different content ratios were manufactured into six-cylinder specimens, 13 mm in diameter and 16 mm in length, and heated in a furnace up to 500 °C. The heated cylinders were removed and left to cool in vertical and horizontal positions in a 16 °C environment. The temperatures were recorded using thermal cameras at certain intervals while the materials cooled down. The six specimens, whose metallographic differences were identified using SEM and XRD analysis devices, were placed vertically and horizontally, and their heat transfer by natural conviction was noted. In the calculations, each specimen’s Nusselt and Rayleigh numbers were identified based on time and then compared. The fastest cooling among the specimens occurred in the ferrochromium material with 55.93% Cr, 31.11% Fe, 11.56% C, 0.48% Si, 0.83% O, and 0.09% Al compound ratios, both in vertical and horizontal positions. Additionally, since the Nusselt number of the horizontal cylinders remained below one based on their position, their natural convection flows were not initiated. The cooling in the horizontal cylinders occurred via conduction.
- MakaleYalnız künye2025Scopus SJRQ2Heat transfer and condensation analysis of the walls of a house built with natural andesite stone
Işik, Erdem; Kahraman, Gökhan; Atalar, Aydın
The use of natural stones in buildings is increasingly popular due to both their decorative appearance and their thermal performance. Proper use of these stones in buildings is crucial for energy conservation and preventing condensation within structural components. This study investigated heat transfer and condensation in the wall of a house made from natural andesite stone in Iğdır, Turkey, under steady-state conditions and different wall combinations. Samples were created from natural stones extracted from two different elevations in the foothills of Mount Ararat, with measured thermal conductivity values of 1.73 W/m·K (higher elevation– Haverage) and 1.31 W/m·K (lower elevation– Laverage). In the wall model using a 3-cm thick insulation board between two natural stones from the higher elevation, condensation occurred on the outer surface of the insulation layer. This can negatively impact the durability and thermal performance of the structure, and such design should be avoided. The highest heat flux of 18.27 W/m² was observed in the non-insulated wall made of higher elevation stones, while the lowest heat flux of 6.68 W/m² occurred in the model using a 3-cm insulation board between two lower elevation stones. No condensation risk was found in this configuration. The difference between the worst and best cases in terms of heat flux was approximately threefold, emphasizing the importance of proper material selection and insulation design. These findings provide guidance for energy-efficient building design using natural stone.
- MakaleYalnız künye2024Scopus SJRQ2Dynamic Analysis and Metallographic Examination of Linings with Different Composite Contents used in the Brakes of a Hydraulic Turbine
Işık, Erdem; Kahraman, Gökhan
The main aim of this study was to find ways to increase the performance and life of generator brake linings, which can lead to cost reduction and adequate downtime periods for hydroelectric power plants. First, the dynamic analysis of the linings used in hydraulic turbines was realized and their reactions were examined under different operating conditions. Second, two types of brake linings with different composite components produced in the market were examined metallographically and tested to determine both the stopping performance and durability time of the turbine-generator unit for a sufficient period of time in the vertical 150-megawatt Francis turbine with approximately 500 tons of rotary weight. As a result of these experiments, the lining with the boron component led to much better results than the other brake linings. It has been determined that the boron-containing lining makes 100 stops more than the other lining and stops 20 s earlier in one stop. Therefore, the use of a composite lining with boron content in the braking systems of hydroelectric power plants significantly reduces maintenance incidents and operation costs as it prolongs brake replacement periods in these plants. Graphical Abstract: (Figure presented.)
AtıfScopus1WoS1OpenAlex1İncele - MakaleYalnız künye2024Scopus SJRQ4How How Much Much CCondensation ondensation Occurs Occurs With With Various Various Insulation Insulation Thicknesses? Thicknesses?
Kahraman, Gökhan; Isik, Erdem
- MakaleYalnız künye2024Scopus SJRQ2Evaluating the metallographic properties and performance of heat transfer by natural convection of graphene-coated glass used for heating
Kahraman, Gökhan; Taşgın, Yahya
In this study, a decorative electric heater was manufactured to reduce carbon emissions related to residential and office heating, and this heater was metallographically evaluated. In addition, the heating performance of the manufactured plate was investigated by examining its heat transfer capacity by natural convection. For this purpose, the surface of the tempered glass plate was coated with graphene by spraying to improve its electrical and heat conduction properties. Copper strips were attached to both sides of the plate to allow for an electric current. The plate was connected to mains electricity, and its change in surface temperature over time was measured. Using the measured temperature values, the heat transfer rate by natural convection on the plate surface was calculated. As a result of the calculations, it was determined that the graphene-coated tempered glass plate reached a heating performance of 40 watts after 2400 s of electrical energy supply. This value can be increased by increasing the heat transfer surface area. This study, taking advantage of the excellent thermophysical properties of graphene, will contribute to other studies conducted in this field.
AtıfScopus2WoS2OpenAlex2İncele - MakaleAçık Erişim2023Application of a new dynamic analysis method to pid controlled speed governors in hydroelectric power plants
Işık, Erdem; Kahraman, Gökhan
Hydroelectric power plants are environmental-friendly as they are renewable energy sources and make great contributions to the economies. In addition, they are in the state of insurance of the electricity network, since they can respond to the power demands of the electricity network in a very short time. In this study, the effect of the speed governors dispense valve has been added to the classical control mechanism in order to accurately predict the reaction of hydroelectric power plants to the load requirement of the electrical network. As a result of the dynamic analysis, the data obtained in the simulation environment have been compared with the responses of the real hydraulic turbine. The results show that when the dynamic analysis of the speed governor dispense valve is added to the classical control mechanism, the power response behavior in the simulation environment becomes closer to the real hydraulic turbine behavior. These results will assist speed governor designers in predicting real-like behavior in hydroelectric power plants.
- MakaleAçık Erişim2023Theoretical and Practical Investigation of Stability Performance for Power Regulation in Hydroelectric Power Plants
Kahraman, Gökhan; Işık, Erdem
Hydroelectric power plants are the insurance of the interconnected system in order to provide fast energy to the system compared to other fossil fueled power plants. Hydroelectric power plants control the balance between the energy it supplies to the interconnected system and the pressurized water it uses with a system based on the fully automatic control principle. The quality of the energy supplied to the interconnected system depends entirely on this automatic control mechanism. In this study, mathematical models of the mechanisms that affect the automatic control system during the generation of energy in hydroelectric power plants are formed. Transfer functions of the obtained mathematical models are calculated by laplace transform. With the calculated transfer functions, the responses of the units of a hydroelectric power plant to the change of the amount of energy produced under different operating conditions are determined. The obtained data are compared with the actual conditions in a 1330 MW hydroelectric power plant with 8 Francis turbines. It is seen that the mathematical model and the turbine responses in real conditions are similar. In the calculations made at 115, 125, 135, 145 m. net head, the best stability conditions were obtained at 135 m. In addition, as a result of the calculations obtained under different operating conditions, ideal operating conditions are determined to minimize the fluctuations in energy production.
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İncele - MakaleYalnız künye2023Scopus SJRQ1Mathematical modeling of vibration failure caused by balancing effect in hydraulic turbines
Kahraman, Gökhan; Özdemir, Osman
This article discusses the causes of vibrations depending on unbalanced hydraulic forces in rotating and non-rotating equipment in hydraulic plants within the scope of vibration measurement standards. The radial and axial positions of the turbine shaft, normal operating conditions, the absolute vibration of the signal output velocity during startup and shutdown during unbalance condition of the turbine, the proximity probes have been measured by TMO 793 accelerometer sensor and TMO 793 velocity sensor. The results obtained from the monitoring are analyzed and the first discussion is over the comparison of the current operating levels and vibration standards. Secondly, the comparison is analyzed in order to examine the improvement in vibration level of the elimination of hydraulic imbalance more comprehensively, considering the stability of the hydro turbine-generator unit, a proportional row damping force, proportional-order oil-film force and a hydraulic force and by creating a new non-linear proportional-order mathematical model. Changes in vibration levels and spectral bands for failure types are stated as well. The solution of this integrated and accurate mathematical model shows that it is useful and concise in the diagnosis and prediction of faults in hydropower plants.
AtıfScopus13WoS13OpenAlex16İncele - MakaleAçık Erişim2022Failure-based maintenance planning using bayesian networks: a case study hydraulic turbine
Yucesan, Melih; Kahraman, Gökhan
The assessment of existing infrastructures in the energy sector is of great economic importance for the world. The extension of the power generation life of hydroelectric power plants depends on logical decisions regarding the maintenance and renewal of the equipment. For this purpose, a Bayesian network (BN) has been applied to evaluate the failures in the hydraulic turbine to calculate the failure of the turbine. Forty-six nodes have been identified that will affect the operation of the system. Preventive measures have been established for failures with the highest posterior probability. By creating four different cases, failure probabilities and the change of the main fault have been calculated. How much savings could be made in each case is determined with the maintenance. This proposed framework will be guided in determining the maintenance strategies for hydroelectric power plant operators.
AtıfOpenAlex1İncele - MakaleYalnız künye2021Scopus SJRQ1Crack failure in hydrodynamically lubricated bearings: A case study hydraulic turbine
Taşgın, Yahya; Kahraman, Gökhan
This study investigates the trunnion crack of a 50 MW hydraulic turbine in the generator guide bearing. The crack area has been examined metallographically and the fixing method for the the trunnion crack has been explained. Result of the study shows that the reason for the formation of the bearing trunnion crack can be the thermal stresses that occur during the mounting of the bearing trunnion to the turbine shaft and the material fatigue that occurs during the operation of the hydraulic turbine.
AtıfScopus9WoS7OpenAlex9İncele - MakaleYalnız künye2021Scopus SJRQ3Comparison of heat transfer and condensation on the walls of buildings constructed with iron profiles versus other classic models
Kahraman, Gökhan
This study aims to present the evaluation of the thermal performance and the amount of condensation on the walls of a building with iron profiles under steady-state conditions. Elazig, situated in the east part of Turkey, was chosen for fieldwork. In this region, minimum average temperature is around 1°C during winter. Calculations are made in a real wall model and three different wall model scenarios. Estimated advantages and disadvantages of these have been investigated. Heat transfer and condensation amount are taken as variables. In four different building component models, the required amount of energy during the heating period is calculated month by month. Calculations reveal the resistance of the wall without application of insulation material with iron profile is higher than of the other three wall types. The wall built with betopen and iron profile saves 37.5% more energy than the wall with bricks. When the iron-profiled wall model is compared with the insulated brick wall, it is observed that energy savings are similar, but calculations show condensation begins on the iron profile wall. Iron profile buildings become popular increasingly in rural areas. As a result of this study, it is observed that iron profile buildings are advantageous in terms of energy saving compared to other building component models. However, condensation is inevitable in wall components of iron profile buildings and so the damage in the buildings is more than just a disadvantage, it is an irreversible result.
AtıfScopus2WoS3OpenAlex3İncele - MakaleYalnız künye2020Holding of dam water levels at optimum with fuzzy linear programming when electricity is produced in serried dam lakes
Yucesan, Melih; Kahraman, Gökhan
In this study, the Euphrates river basin in a sequential manner established a scenario modeled after Turkey's three largest hydropower plant was established. In this scenario, according to the needs of the interconnected system, the lake levels of these three dams were kept at the highest possible level and energy was produced. In this way, the maximum level of water, which means energy, is kept and the turbine-generator units are operated at the highest possible efficiency and electricity is produced. The demand for electricity, the minimum and maximum water required in the dams, were handled as turbid. Then, for the determined scenario, the energy required by the interconnected system from these dams is determined from which dam and how many units will work for how long.
- MakaleAçık Erişim2020Faults Caused by Cavitation in Hydraulic Power Plants and Solution Methods
Kahraman, Gökhan; Özdemir, Osman
Hydraulic energy is one of the richest and most useful renewable energy sources in the world. For this reason, hydraulic turbines must be operated at optimum efficiency levels against multiple transient situations such as starting and stopping that shorten their useful life and cause fatigue damages in order to generate energy continuously. Pressure variations occur due to flow irregularities in Francis turbines operating at non-optimal partial loads. If the sepressure variations coincide with the natural frequency of a hydraulic, mechanical or structural component, they create high vibrations due to resonance, causing the turbine to operate in an unbalanced (balanced) manner. In this study, the high vibrations of the Francis turbine were monitored with the help of a continuous (online) vibration monitoring system via the cavitation sensor mounted on the turbine adjustment blade and the cavitation vibration effects of the operation in the case of unbalance and the cavitation vibration effect after the imbalance was eliminated. Vibration caused by the cavitation phenomenon in different operating conditions of hydraulic turbines has been shown graphically. In the the graphic given in the last part of the article, it is seen that vibration magnitude is reduced from 2 mm s-1 to 0.5 mm s-1 after the bearing failure is eliminated. This is an important consequence for the hydraulic turbines to be operated in the safe cavitation zone to avoid high vibration levels.
AtıfOpenAlex1TR Dizin1İncele - MakaleYalnız künye2020Scopus SJRQ3Application of Local Hard Fillet Weld to Repair Damage Caused by Cavitation in Hydroelectric Power Plant
Kahraman, Gökhan; Taşgin, Yahya
Hydroelectric power plants come into prominence worldwide day by day due to their low operating and maintenance costs, environment friendly structure and their use as renewable energy sources. In order to obtain maximum energy from such an important energy source, it is necessary to reduce downtime due to failures. One of the most important failures of hydroelectric power plants is the damage caused to the turbine wheel by cavitation. In this study, a sample with the same material as the turbine wheels of the hydroelectric power plants is provided. The effects of the hard fillet weld on the turbine wheel, which we have applied locally to this material, have been investigated both metallographically and physically. As a result of the research, it is observed that the main material and hard fillet weld are mostly compatible. The damages of the turbine wheel of the hydroelectric power plant have been repaired by applying the same method to the turbine wheel damaged by the cavitation. After 10,000 h of operation, the turbine wheel is inspected again. As a result, it has been determined that the hard fillet weld applied to the turbine wheel surface is resistant to the harmful effects of cavitation.
AtıfScopus2WoS2OpenAlex2İncele - MakaleYalnız künye2020Scopus SJRQ3Increasing the Power Generation by Raising the Capacity of the Thrust Bearing Oil Cooling System in Hydroelectric Power Plants
Kahraman, Gökhan
Cooling capacity decreases due to faults appearing over time in the thrust bearing oil cooling systems of hydroelectric power plants and cooling process cannot proceed sufficiently. For this reason, while the turbine-generator unit generates energy, the thrust bearing heats up. This temperature problem prevents the unit from operating at full capacity and therefore decreases in energy production. Producing deficient energy in hydroelectric power plants, which is a renewable energy source, causes long-term economic losses for countries. In this study, the thrust bearing cooling system of a vertical Francis turbine, which produces 150 MW of energy per hour, is investigated. The reduction in the cooling capacity over time in turbine thrust bearing cooling system is solved by using exchanger system with additional plate and the power produced by the turbine-generator unit is increased 15 MW/h. This improvement has greatly contributed to the national economy. The method of increasing the cooling capacity applied to the hydroelectric power plant thrust bearings can be applied to all hydraulic turbines. This method will increase the energy production amount of the unit by approximately 10% and it costs approximately 80% cheaper than completely replacing the existing cooling system.
AtıfScopus5WoS2OpenAlex5İncele - MakaleYalnız künye2020Scopus SJRQ3Investigation of the Effect of Operating Conditions Change on Water Hammer in Hydroelectric Power Plants
Kahraman, Gökhan
Renewable energy sources do not harm the environment, and they contribute greatly to national economies. Hydraulic energy is the leading renewable energy source. Hydraulic energy is used more widely than other renewable energy sources around the world. This situation of hydraulic energy makes it important to solve the faults in hydraulic turbine-generator units. In this study, water hammer impacts have been investigated. This issue is important and can be dangerous in hydroelectric power plants. As a result of the research, the optimum sudden shutdown time of the adjusting wings in the snail is determined by considering the different operating conditions of a hydroelectric power plant. When the turbine-generator units are operated according to the specified instantaneous shutdown time, they will be protected against the impact of the water hammer pressure and the turbine shaft overspeed. Thus, they will be operated with less risk.
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