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Öğe N-type InP Schottky diodes with organic thin layer: Electrical and interfacial properties(Journal of Vacuum Science & Technology B, 2010-03) Güllü, Ömer; Turut, AbdulmecitThe rectifying junction characteristics of methyl red (MR) organic film on n-type InP substrate have been studied. It has been observed that MR-based structure shows an excellent rectifying behavior and that the MR film increases the effective barrier height by influencing the space charge region of the n-type InP. The barrier height and ideality factor values for this structure have been obtained as 0.75 eV and 1.93 from the forward bias current-voltage characteristics, respectively. By using capacitance-voltage characteristics at 1 MHz, the barrier height and the carrier concentration values have been calculated as 0.93 eV and 5.13×1015 cm−3, respectively. The energy distributions of the interface states and their relaxation times have been determined from the forward bias capacitance-frequency and conductance-frequency characteristics. Moreover, it was seen that both the interface-state density and the relaxation time of the interface states decreased with bias voltage from experimental results.Öğe Investigation of plasma arc cutting parameters with type-2 fuzzy set and system(De Gruyter, 2013-10) Çelik, Yahya Hışman; Özek, Cebeli; Bulut Özek, MüzeyyenThe objective of the present study was it to design a type-2 fuzzy set and system in order to predict surface roughness and hardness depending on the parameters (material thickness, cutting speed, arc voltage and current) of the plasma arc cutting process of S235JR sheet materials. Therefore, some experimental studies were conducted. The experimentally determined data were used to describe the type-2 fuzzy set and system. Type-2 fuzzy set and system was found to be usefull to predict surface roughnes and hardness. According to the obtained values, the best surface roughness and the values closest to the hardness of the raw material were obtained at 1500 mm/min cutting speed, 8 mm material thickness, 115 V arc voltage and 80 A current.Öğe Biodiesel production from inedible animal tallow and an experimental investigation of its use as alternative fuel in a direct injection diesel engine(Elsevier, 2009-02-15) Altun, Şehmus; Öner, CengizIn this study, a substitute fuel for diesel engines was produced from inedible animal tallow and its usability was investigated as pure biodiesel and its blends with petroleum diesel fuel in a diesel engine. Tallow methyl ester as biodiesel fuel was prepared by base-catalyzed transesterification of the fat with methanol in the presence of NaOH as catalyst. Fuel properties of methyl ester, diesel fuel and blends of them (5%, 20% and 50% by volume) were determined. Viscosity and density of fatty acid methyl ester have been found to meet ASTM D6751 and EN 14214 specifications. Viscosity and density of tallow methyl esters are found to be very close to that of diesel. The calorific value of biodiesel is found to be slightly lower than that of diesel. An experimental study was carried out in order to investigate of its usability as alternative fuel of tallow methyl ester in a direct injection diesel engine. It was observed that the addition of biodiesel to the diesel fuel decreases the effective efficiency of engine and increases the specific fuel consumption. This is due to the lower heating value of biodiesel compared to diesel fuel. However, the effective engine power was comparable by biodiesel compared with diesel fuel. Emissions of carbon monoxide (CO), oxides of nitrogen (NOx), sulphur dioxide (SO2) and smoke opacity were reduced around 15%, 38.5%, 72.7% and 56.8%, respectively, in case of tallow methyl esters (B100) compared to diesel fuel. Besides, the lowest CO, NOx emissions and the highest exhaust temperature were obtained for B20 among all other fuels. The reductions in exhaust emissions made tallow methyl esters and its blends, especially B20 a suitable alternative fuel for diesel and thus could help in controlling air pollution. Based on this study, animal tallow methyl esters and its blends with petroleum diesel fuel can be used a substitute for diesel in direct injection diesel engines without any engine modification.Öğe An exergy analysis of a concentric tube heat exchanger using hBN-water nanofluids(Inder Science Publishers, 2021) Budak Ziyadanoğulları, Neşe; Perçin, SüleymanThis study investigated the effects of using nanofluids prepared with hexagonal boron nitride (hBN) nanoparticles on the thermal performance and pressure drop of a concentric tube heat exchanger. Experiments were carried out with water-hBN nanofluids for stable, dispersed, 0.01%, 0.1% and 1% volume concentrations, at different flow rates and Reynolds numbers under parallel and counter-flow conditions. When the experimental results were examined, the exergy loss was higher in the parallel-flow heat exchanger compared to the counter-flow heat exchanger. The highest exergy loss value was obtained for distilled water at the highest Reynolds number (Re = 8,700) for parallel flow operation at 170 W. The exergy loss of water at the highest Reynolds number (Re = 8,700) for parallel flow operation increased by 15.7%, 24.8% and 49.8% for hBN-water concentrations of 0.01%, 0.1% and 1%, respectively. Exergy loss of water at the highest Reynold number (Re = 8,700) for counter flow operation increased by 11.3%, 17.3% and 29.2% for hBN-water concentrations of 0.01%, 0.1% and 1%, respectively. When evaluating the exergy analysis of the system, exergy losses due to pressure drops were negligible for both flows (parallel and counter).Öğe The effect of Plantago major Linnaeus on serum total sialic acid, lipid-bound sialic acid, some trace elements and minerals after administration of 7,12-dimethylbenz(a)anthracene in rats(SAGE, 2012-04) Oto, Gökhan; Ekin, Suat; Özdemir, Hülya; Levent, Abdulkadir; Berber, İsmetThe present study was designed to evaluate the effect of Plantago major Linnaeus (PM) extract on serum total sialic acid (TSA), lipid-bound sialic acid (LSA), some trace elements (copper (Cu), zinc (Zn) and iron) and mineral levels (magnesium, calcium and sodium) in Wistar albino rat administrated 7,12-dimethylbenz(a)anthracene (DMBA). Rats were divided into three equal groups (n = 6). Group I comprised the control group, group II was treated with DMBA (100 mg/kg, single dose) and group III was treated with DMBA (100 mg/kg single dose) and aqueous extract of PM 100 mg/kg/day for 60 days. After 60 days, statistical analyses showed that TSA and LSA levels in DMBA and DMBA + PM groups were significantly higher compared to the control group (TSA: p < 0.01, p < 0.05; LSA: p < 0.05, p < 0.05, respectively). Serum Zn levels were decreased in subjects treated with DMBA (p < 0.01) and DMBA + PM (p < 0.05) compared to the control group values. Serum Cu levels were increased in DMBA group and PM-treated group compared to the control group values. The results of this investigation showed that the levels of TSA and LSA changed significantly, which are sensitive markers for detecting the toxic effects of DMBA. On the other hand, observed decline in Zn levels in rats from DMBA + PM group might be due to decreased generation of free radicals and oxidative stress. Results from this study suggest that PM may be partially effective in preventing carcinogenesis initiated by environmental carcinogen DMBA.Öğe The comparison of engine performance and exhaust emission characteristics of sesame oil-diesel fuel mixture with diesel fuel in a direct injection diesel engine(Elsevier, 2008-01-09) Altun, Şehmus; Bulut, Hüsamettin; Öner, CengizThe use of vegetable oils as a fuel in diesel engines causes some problems due to their high viscosity compared with conventional diesel fuel. Various techniques and methods are used to solve the problems resulting from high viscosity. One of these techniques is fuel blending. In this study, a blend of 50% sesame oil and 50% diesel fuel was used as an alternative fuel in a direct injection diesel engine. Engine performance and exhaust emissions were investigated and compared with the ordinary diesel fuel in a diesel engine. The experimental results show that the engine power and torque of the mixture of sesame oil-diesel fuel are close to the values obtained from diesel fuel and the amounts of exhaust emissions are lower than those of diesel fuel. Hence, it is seen that blend of sesame oil and diesel fuel can be used as an alternative fuel successfully in a diesel engine without any modification and also it is an environmental friendly fuel in terms of emission parameters.Öğe Numerical and experimental investigation of solar chimney power plant system performance(Taylor & Francis, 2020-03-15) Karakaya, Hakan; Durmuş, Aydın; Avcı, Ali SerkanA prototype of a solar chimney power plant was performed by modeling in this study. The performed prototype was experimentally confirmed. Temperature, velocity, and radiation values were measured to actualize the confirmation. Experimental data that were obtained to determine the performance of solar chimney whose prototype was actualized by the help of measured values were computationally analyzed. The geometry of a solar chimney in the analysis was bidimensionally (2D) drawn on an axis of symmetry. The numerical simulation was analyzed with computational fluid dynamics (CFD) method. Since analysis results show that there is turbulent flow in system (RNG), k-ɛ turbulence model was used. Continuity, momentum, and energy equations were applied to the solar chimney system via the finite volume method. Moreover, DO (discrete ordinates) model was inserted in analysis to evaluate the radiation effect in the collector area. In addition to all these, correlation results between SPSS 17 statistics program and data obtained were evaluated. Finally, with reference to the comparison between numerical and experimental results, data obtained and numerical data are close to each other; the prototype is applicable to the real systems.Öğe Combustion, performance and emissions of a diesel power generator fueled with biodiesel-kerosene and biodiesel-kerosene-diesel blends(Elsevier, 2017-02-05) Bayındır, Hasan; Işık, Mehmet Zerrakki; Argunhan, Zeki; Yücel, Halit Lütfi; Aydın, HüseyinHigh percentages of biodiesel blends or neat biodiesel cannot be used in diesel engines due to high density and viscosity, and poor atomization properties that lead to some engine operational problems. Biodiesel was produced from canola oil by transesterification process. Test fuels were prepared by blending 80% of the biodiesel with 20% of kerosene (B80&K20) and 80% of the biodiesel with 10% of kerosene and 10% diesel fuel (B80&K10&D10). Fuels were used in a 4 cylinders diesel engine that was loaded with a generator. Combustion, performance and emission characteristics of the blend fuels and D2 in the diesel engine for certain loads of 3.6, 7.2 and 10.8 kW output power and 1500 rpm constant engine speed were experimented and deeply analyzed. It was found that kerosene contained blends had quite similar combustion characteristics with those of D2. Mass fuel consumption and Bscf were slightly increased for blend fuels. HC emissions slightly increased while NOx emissions considerably reduced for blends. It was resulted that high percentages of biodiesel can be a potential substitute for diesel fuel provided that it is used as blending fuel with certain amounts of kerosene.Öğe Investigation of low velocity impact behaviors of honeycomb sandwich composites(SpringerLink, 2018-08-09) Topkaya, Tolga; Solmaz, Murat YavuzHoneycomb sandwich composites are used as significant structural members in advanced engineering applications. Thus, it is critical to determine how they behave under impact loading, in addition to other loads. In this study, low velocity impact loading behaviors of honeycomb sandwich composites were experimentally investigated. Almost all of the design parameters of honeycomb sandwich composites were investigated. The results indicated that the core thickness of honeycomb had no effect on the strength of the composite, and the parameter influencing the impact behavior of the specimen the most was the face sheet thickness. When the face sheet thickness of the specimen was increased, the most apparent strength increase was observed in the models using carbon fiber-reinforced composite face sheets. For all face sheet types subject to impact energy of 10 Joules, the upper face sheets of 0.5 mm-thick specimens were perforatedÖğe Hardness and wear behaviours of al matrix composites and hybrid composites reinforced with B 4 C and SiC(Springer Nature, 2019-01-15) Çelik, Yahya Hışman; Kılıçkap, ErolThe conversion into the desired shape of the metal powders using Powder Metallurgy (PM) method enables economically mass productions. This case allows producing parts with complex and high dimensional accuracy with no machining. In this study the composites and hybrid composites with Al matrix were produced using PM method with different ratios B4C and SiC. Microhardness and wear experiments of the produced composites were investigated. Wear experiments were performed at a constant speed of 0.5 m/s, application loads of 5, 10 and 15 N and sliding distances of 250, 500, and 750 m. Then, SEM images of composites and hybrid composites were captured. The increase of the reinforcement ratio in the composites contributed to the increase of the hardness. The highest hardness value was computed as 58.7 HV from 16% B4C reinforced composite. In addition, the increase in the reinforcement ratio contributed to the increase of the wear resistance. The increase in the load and sliding distance also increased the wear. The minimum weight loss was calculated as 18 mg from 5 N load, 250 m sliding distance and 16% SiC reinforced composite.
