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- Akkurt, Nevzat(24)
- Kahraman, Gökhan(17)
- Sabanci, Serdal(11)
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- Xu, Qian(8)
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- Gul, Muhammet(5)
- Aghakhani, S.(4)
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- Mahmoud, Mustafa Z.(4)
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- Younis, Obai(4)
- Yüzüak, E.(4)
- Yüzüak, G. Durak(4)
- Yüzüak, Gizem Durak(4)
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- Chen, Xingli(3)
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- Wang, Zhaoxiao(3)
- Yilmaz, Mehmet(3)
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- Zhang, Hui(3)
Yayınlar
- 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.
AtıfScopus9WoS8OpenAlex8
İncele - MakaleAçık Erişim2019Metallographic Aspects Investigation of Penstock Materials in Hydroelectric Power Plants and Penstock Maintenance Methods
Taşgın, Yahya; Kahraman, Gökhan
Hydroelectric power plants are renewable energy sources and have little impact on the environment.Therefore, it is one of the most preferred energy sources in the world. In parallel with this situation, it isvery important that the hydroelectric power plants are maintained, their failures are prevented orpermanently removed. One of the most important parts of hydroelectric power plants is penstock pipes.Along with the snail part of the power plant, the penstock supplies the pressurized water to the turbinewheel for energy production. In the power plants that have been producing energy for many years, themaintenance and material properties of penstock are very important. In this study, one of the most importantequipment of hydroelectric power plants, pressurized water pipes (penstock) and chemical componentshave been examined in macro and micro structure and their maintenance is investigated. In themetallographic study on the samples taken from two different regions of the penstock pipe; the perliticstructure, which has a homogeneous distribution into the ferritic structure forming the matrix, is determinedand supported by analyzes. This study will help to ensure that all hydroelectric power plants operatesmoothly in terms of penstock.
AtıfOpenAlex2
İncele - MakaleAçık Erişim2019Design and Analysis of a Water Pumping System with Photovoltaic Source and Switched Reluctance Motor
Omaç, Z.
Solar energy is a clean energy and it is increasingly being used all over the world. In this study, a centrifugal water pump system driven by switched reluctance motor (SRM) has been designed with powered by a photovoltaic (PV) energy source. The voltage of the PV source has been increased by using a boost converter. The mathematical model of the system has been composed in the Matlab/Simulink and simulation results have been obtained. Proportional–integral–derivative (PID) controller has been used to control output voltage of the boost converter at 50 kHz switching frequency. The boost converter is controlled by an eight-bit PIC16F877A microcontroller. The electrical energy obtained by PV panels has been stored in batteries. Battery charge testers have been used to control the battery charge level. The speed and current control of SRM has been done by using DS1103 Ace kit. The values of phases currents have been measured by using hall sensors and transferred to the digital signal processor (DSP) by analog to digital converter inputs. The accuracy of simulation results has been proved by experimental results.
AtıfOpenAlex3TR Dizin1İncele - MakaleAçık Erişim2019Hidroelektirik santrallerde generatör stator sargı arızaları ve çözüm yöntemleri
Taşgın, Yahya; Kahraman, Gökhan
Hidroelektrik santraller ile elektrik üretimi, dünyada toplam elektrik üretimine küçümsenmeyecek bir oranda katkıda bulunmaktadır. Hidroelektrik santralleri ile enerji üretimi için uygun coğrafi koşulların sağlanması gerekmektedir. Günümüz koşullarında kullanılabilir hidroelektrik kapasitenin büyük bir bölümü hali hazırda kullanılmaktadır. Türkiye hidrolik enerji bakımından dünyadaki birçok ülkeye göre avantajlı durumdadır. Özellikle Güney ve Doğu Anadolu bölgelerimizde hidroelektrik santraller sayesinde üretilen elektrik enerjisi küçümsenemez. Kurulması planlanan veya inşaatı süren birçok hidroelektrik santralleri, Türkiye'nin geleceğine damga vuracaktır. Hidroelektrik santralleri, diğer enerji üretim yöntemlerine göre doğaya en az düzeyde zarar verdikleri için temiz enerjikaynakları arasında değerlendirmek gerekir. Hidroelektrik santraller yenilenebilir bir enerji kaynağı olması ve enterkonnekte sistemin güvenliğinin sigortası olması açısından her zaman üretime hazır olmaları önemlidir. Hidroelektrik santrallerde arıza kaynaklı duruş sürelerini azaltmak için birçok ölçüm sistemleri, uzaktan izleme sistemleri geliştirilmiştir. Bu santrallerde en önemli ve giderilmesi uzun zaman alan arızalardan biride generatör stator sargı arızalarıdır. Bu çalışmada stator sargı arızalarının sebepleri, giderilme yöntemleri ve bu tip arızaları engellemek için yapılması gerekenler incelenmiştir. Bir hidroelektrik santralinde stator arızası örneği verilmiş arızanın oluşumu, tespiti, yapılan elektriksel testler,onarımı detaylı bir şekilde anlatılmıştır. Yapılan onarımın sonucunda sargı sıcaklıkları izlenmiş ve herhangi bir sorunun olmadığı görülmüştür. Hidroelektrik santrallerde işletme ve bakım şartlarında belirlenen önlemlerin alınması stator sargılarından kaynaklanan arızaları engelleyeceği gibi santralin elektrik arz güvenliğini en üst düzeyde tutacaktır. Ayrıca arızadan kaynaklanan işçilik vemalzeme maliyetlerini düşürecektir.
AtıfTR Dizin1İncele - MakaleAçık Erişim2019Scopus SJRQ1Identification of optimum working conditions in hydroelectric power plants for cavitation
Kahraman, Gökhan; Yücel, Halit Lütfi; Taşgin, Yahya
Turbine faults in hydroelectric power plants not only reduce the operation time of the plant, but also cause a serious loss of income. One of the most important turbine faults is the turbine wheel wear caused by the cavitation and accordingly the other machine equipment faults which cause excessive vibration. In this study, cavitation intensity that the turbines have been exposed in operating conditions has been investigated. As a result of the calculations, optimum working conditions of the units have been determined with graphs obtained in various operating conditions. The obtained data can be easily applied to all hydroelectric power plants exposed to cavitation, and safe operating conditions can be determined.
AtıfScopus11WoS10OpenAlex13İncele - MakaleYalnız künye2019Scopus SJRQ1Risk evaluation and prevention in hydropower plant operations: A model based on Pythagorean fuzzy AHP
Yucesan, Melih; Kahraman, Gökhan
Hydropower generation facilities are becoming increasingly popular in many parts of the world. One of the main reasons for this situation is that the resource reserves such as coal, petroleum and natural gas, which are called conventional energy sources, decrease day by day and their prices rise. So the efficient operation of hydroelectric power plants has become very important. When these plants are operated, it is possible to cause many hazards, including injury, illness, death, damage to the environment, property and equipment. In this study, it is aimed to perform risk assessment for hydroelectric power plants using Pythagorean fuzzy Analytical hierarchy process (PFAHP) method. The team of experts has identified twenty hazards and their results that could occur in the operation of the hydroelectric power plant. The weights of the hazards were determined by using linguistic expressions. Preventive measures have been taken for the three most important hazards. The results of this study are expected to contribute to the safety of hydropower plants and the prevention of financial losses.
AtıfScopus143WoS123OpenAlex147İncele - MakaleYalnız künye2019Scopus SJRQ1Research of thermal performance by metallographic investigation of stator winding solder region in hydroelectric power plants
Kahraman, Gökhan; Taşgın, Yahya
Hydroelectric power plants are the most widely used renewable energy sources all over the world. In these plants, many studies have been conducted in order to produce energy continuously and efficiently. Among these studies, predictive maintenance methods, efforts to increase power by improving cooling conditions, and improving efficiency by improving the turbine wheel. In this paper, soldering at the junctions of the stator windings in the central generators has been investigated. Traditional solder (Cu–Zn) materials and silver alloy solders (Ag-Cu-Zn) have been investigated in terms of thermal and metallographic. Silver alloy soldering has been found to have lower electrical conductivity than conventional soldering. The winding temperatures measured on the generating generator show that silver alloy soldering is more efficient. Reducing the stator winding temperature in hydroelectric power plants allows more energy production and also reduces costs by preventing winding failures.
AtıfScopus2WoS2OpenAlex2İncele - MakaleAçık Erişim2019Scopus SJRQ2Electrical characterization of solar sensitive zinc oxide doped-amorphous carbon photodiode
Koç, Mümin Mehmet; Aslan, Naim; Erkovan, Mustafa; Aksakal, Bünyamin; Uzun, Orhan; Farooq, W. Aslam; Yakuphanoğlu, Fahrettin
A new solar-sensitive zinc oxide doped-amorphous carbon diode was fabricated using the electrochemical deposition technique. The current-voltage characteristics of the fabricated Al/ZnO-a:C/p-Si/Al diode were investigated under dark and various lighting intensities using both I-V and C-V methods. The fabricated diode was characterized by XRD, SEM-EDS, FTIR and XPS analysis. Through the analysis, it was determined that the photocurrents increased with increasing intensity of incident light. The capacitance-voltage (C-V) characteristics revealed that the capacitance of the diode depended on voltage, frequency and illumination, indicating the existence of a continuous distribution of interface states. It was found that the capacitance changed drastically with changing frequency and separation was observed in different frequencies, as identified in the reverse bias region. The ideality factor obtained was found to be higher than unity, with the average barrier height and ideality factor of the diode were found to be 0.528 ± 0.0069 eV and 5.24 ± 0.39, respectively. The newly fabricated ZnO-doped amorphous carbon (Al/ZnO-a:C/p-Si/Al) photodiode exhibited good solar sensitivity. The overall results indicated that the fabricated Al/ZnO-a:C/p-Si can be used as a solar sensitive diode in optoelectronic device applications as an alternative to graphene-based materials.
AtıfScopus41OpenAlex46İncele - MakaleAçık Erişim2018Scopus SJRQ1Lightweight privacy-preserving data aggregation scheme for smart grid metering infrastructure protection
Baloglu, Ulas Baran; Demir, Yakup
The electric industry's planned shift to smart grid metering infrastructure raised several concerns especially about preserving the privacy. Various data perturbation and aggregation solutions are being developed to address these concerns. The drawback of these solutions is that a simple random noise scheme cannot protect privacy, and there is a need for more advanced perturbation techniques to increase hardware costs of smart metering devices. The proposed data aggregation scheme combines the power of perturbation techniques with crypto-systems in an efficient and lightweight way so that it becomes applicable for devices with limited hardware, such as smart meters. We investigated the privacy preserving capabilities of the proposed aggregation scheme with Holt-Winters and Seasonal Trend Decomposition using Loess prediction methods. The results indicate that the proposed scheme is resilient to both filtering and true value attacks.
AtıfScopus25WoS14OpenAlex25İncele - MakaleYalnız künye2017Scopus SJRQ1Performance analyses for evaporation of pomegranate juice in ohmic heating assisted vacuum system
Cokgezme, Omer Faruk; Sabanci, Serdal; Cevik, Mutlu; Yildiz, Hasan; Icier, Filiz
AtıfOpenAlex83İncele - BildiriAçık Erişim2017Economic Analysis of Hybrid Renewable Energy Systems with V2G Integration Considering Battery Life
Baloglu, Ulas Baran; Demir, Yakup; Caetano, N.S.; Faculty of Engineering University of Porto (FEUP), LEPABE, Rua Dr. Roberto Frias, Porto; Polytechnic Institute of Porto (IPP), CIETI, School of Engineering (ISEP), Rua Dr. Antonio Bernardino de Almeida 431, Porto; Felgueiras, M.C.; Forment, M.A.
Hybrid renewable energy systems considered as candidate solutions for environmental problems. Solar energy and wind energy are important components of these systems, but both of them cause fluctuations in the grid. Batteries of Electric Vehicles (EVs) can be connected to the grid to create an ancillary resource. These systems known as Vehicle to Grid (V2G) and they could be the most suitable solution to the fluctuation problems of renewable resources. In this paper, economic analysis of V2G is investigated from various perspectives. The findings of this study indicate that battery aging costs of a V2G system can be minimized with an intelligent energy management system, and these systems are both economically and environmentally better alternatives to fossil-fuelled generators.
AtıfScopus15WoS13OpenAlex16İncele - MakaleYalnız künye2017Scopus SJRQ2Effect of temperature and nitrogen concentration on the growth and lipid content of Spirulina platensis and biodiesel production
Seyhaneyildiz Can, Safak; Koru, Edis; Cirik, Semra
In this study, Spirulina platensis (Cyanophyceae) was cultured at five mediums with different amounts of sodium nitrate and three different temperatures. The study was conducted at 1600 lx light intensity and a pH value of 9. The influences of nitrate amounts and temperature on biomass growth and lipid amount were studied during 20 days. The best biomass growth (1.039 ± 0.668 g L−1 dry weight and 0.780 ± 0.501 optical density) for S. platensis was obtained from the group with the temperature value of 35 °C and 2.5 g L−1 of sodium nitrate. The highest lipid production (4.70 ± 0.067% dry weight) was in the nitrate-free medium at 15 °C. The best results for biomass growth and lipid production were obtained from the group at 35 °C and 1.25 g L−1 of sodium nitrate (P < 0.05). At the end of the study, it was determined that algal biomass increased with increasing the nitrate amount but the produced lipid by the algae decreased. Intensive production was performed in accordance with the culture conditions of the most productive groups and biodiesel was obtained from the algae. The density, viscosity, and flash point of the biodiesel were calculated as 0.78, 4.67, and 107 °C, respectively.
AtıfScopus34WoS27OpenAlex35İncele - MakaleYalnız künye2017Scopus SJRQ1Ohmic heating assisted vacuum evaporation of pomegranate juice: Electrical conductivity changes
Icier, Filiz; Yildiz, Hasan; Sabanci, Serdal; Cevik, Mutlu; Cokgezme, Omer Faruk
A novel electrical heating method, named as ohmic heating, was successfully integrated to vacuum evaporation system, and pomegranate juice was concentrated until its total soluble dry matter content reached to 40% by applying three different voltage gradients (7.5, 10, and 12.5 V/cm) at 180 mm Hg absolute pressure in this system. Total evaporation times were determined as 152, 78, and 53 min at the voltage gradients of 7.5, 10, and 12.5 V/cm, respectively. The concentration time of pomegranate juice was shortened about 56% by ohmic heating relative to conventional evaporation. The electrical conductivity values were increased up to reach 25% TSDM for 7.5 V/cm and at 35% TSDM for 10 V/cm, then showed a decreasing pattern. However, it was constant (0.55 ± 0.01 S/m) during evaporation process at 12.5 V/cm. It is recommended that the ohmic heating method could be successfully integrated to vacuum evaporation process to shorten the processing time significantly. Industrial relevance Ohmic heating has been utilized as alternative method for the purpose of heating, pasteurization, cooking etc., and relatively better products can be obtained by ohmic heating. Nowadays, energy efficient systems are needed in concentrated juice production. The integration of ohmic heating to the conventional vacuum systems could serve the production high quality juice concentrates with efficient use of energy. In present study, ohmic heating assisted vacuum evaporation of pomegranate juice was conducted, successfully. This method decreased the total process time for juice concentration, which is critically important for industrial scale productions. This novel method can be implemented to the fruit juice production lines by taking into account of design characteristics of ohmic systems such as electrical conductivity changes depending on both temperature and total soluble solids concentration. The effects of main process parameter, named as voltage gradient, on electrical conductivity changes during electrical heating assisted evaporation process has been also reported in the present study.
AtıfScopus93OpenAlex97İncele - MakaleYalnız künye2016Scopus SJRQ1Drying of sweet basil with solar air collectors
Gulcimen, Fevzi; Karakaya, Hakan; Durmus, Aydin
In this study, sweet basil was dried and its drying parameters were investigated experimentally and theoretically by using newly developed solar air collectors. Proper temperatures were chosen to dry sweet basil and experiments were carried out at different flow rates. At the end of drying experiments, it was determined that total mass of sweet basil decreased from 0.250 kg to 0.029 kg. In drying sweet basil, dimensionless moisture ratios were decreased rapidly to 300 min for 0.012 kg/s, 360 min for 0.026 kg/s, and 450 min for 0.033 kg/s. It was observed that the efficiency of collector was increased at the same rate with air flow changed between 29 and 63%. Among the models in the literature, Page Model was found to suit best for drying sweet basil. Furthermore, a novel mathematical model rendering more valid results for sweet basil and leafy products was developed. (C) 2016 Elsevier Ltd. All rights reserved.
AtıfWoS64OpenAlex80İncele - MakaleAçık Erişim2014Scopus SJRQ1Effect of Swirl Generator Inserted Into a Tube on Exergy Transfer: Decaying Flow
Kurtbas, I.; Guelcimen, F.; Kiliçarslan, A.; Kaya, M.
This study experimentally investigates the effect of conical injector type swirl generator inserts on heat and exergy transfer in a uniform heat flux tube for turbulence regime. One hundred twenty watts of heat are applied by coiling a flexible silicone heater on the tube (copper pipe) with an inside diameter of 62mm and length of 1,200mm. The conical injector type swirl generator has a conical shape, which is similar to a funnel, with angle (alpha) of 30 degrees, 45 degrees, and 60 degrees. Circular holes are drilled on the conical injector type swirl generator as three different cross-sectional areas (A(h)). The total areas (A(t) =N.A(h)) of the holes on the conical injector type swirl generator equal each other. Because of this, the three different holes numbers (N) are produced. Flow directors having three different angles (beta=30 degrees, 60 degrees, and 90 degrees) to radial direction are attached to every one of the holes. This study is a typical example for decaying flow. Reynolds number (Re) was varied from 10,000 to 35,000, so the flow was considered as only a turbulent regime. All experiments were conducted with air accordingly; Prandtl number was approximately fixed at 0.71. The local and average heat transfer Nusselt number (Nu(h)) and exergy transfer Nusselt number (Nu(e)) are calculated and discussed in this article. It is found that the Nu(h) increases with an increase in Reynolds number, director angle (beta), and director diameter (d) but with a decrease in the conical injector type swirl generator angle (alpha). However, Nu(e) decreases depending on the same independent parameters.
AtıfWoS12OpenAlex13İncele - MakaleAçık Erişim2009Scopus SJRQ1Heat transfer augmentation by swirl generators inserted into a tube with constant heat flux
Kurtbas, Irfan; Guelcimen, Fevzi; Akbulut, Abdullah; Buran, Dincer
A novel conical injector type swirl generator (CITSG) is devised in this study. Performances of heat transfer and pressure drop in a pipe with the CITSG are experimentally examined for the CITSGs' angle (alpha) of 30 degrees, 45 degrees and 60 degrees in Reynolds number (Re) range of 10,000-35,000. Moreover, circular holes with different numbers (N) and cross-section areas (A(h)) are drilled on the CITSG. In this way, total areas (A(t) = N . A(h)) of the holes on the CITSG are equaled each other. Besides, flow directors having three different angles (beta = 30 degrees, 60 degrees and 90 degrees) to radial direction are attached to every one of the holes. This study is a typical example for decaying flow. All experiments were conduced with air accordingly; Prandtl number was approximately fixed at 0.71. The local Nusselt number (Nu(x)), heat transfer enhancement ratio (Nu(ER)) and heat transfer performance ratio (Nu(PR)) are calculated and discussed in this paper. It is found that the Nu(ER) decreases with increase in Reynolds number, the director angle (beta), the director diameter (d), and with decrease in the CITSG angle (alpha). Likewise, variation of Nu(PR) and Nu(ER) is also essentially similar for the same independent parameters. (C) 2009 Elsevier Ltd. All rights reserved.
AtıfWoS32OpenAlex31İncele
