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Öğe Uniform nuclear heat density in the CANDU fuel bundle(2004) Şahin, Sümer; Yıldız, Kadir; Acır, Adem[No abstract available]Öğe Flow past an oscillating circular cylinder in a channel with an upstream splitter plate(American Institute Physics, 2008) Çelik, Bayram; Akdağ, Ünal; Güneş, Sibel; Beşkök, AliA transversely oscillating circular cylinder confined in a channel has the potential to promote mixing and heat transfer at moderate Reynolds number flows. In the present study, simulation results for flow past a circular cylinder subjected to forced cross-flow oscillations in a straight channel with an upstream splitter plate are presented in a wide range of cylinder oscillation frequencies, including the subharmonic, superharmonic, and primary lock-in regimes. Simulations are performed at Re=100, with cylinder oscillation amplitude of 0.4 diameters and a blockage ratio of 1/3. A spectral element algorithm based on the arbitrary Lagrangian Eulerian formulation is utilized. The numerical method exhibits spectral accuracy and allows large mesh deformation in the computational domain without mesh refinements. The main objective of this study is systematic investigations of the cylinder oscillation on the vortex shedding mechanism, downstream vortex patterns, and forces exerted on the cylinder. © 2008 American Institute of Physics.Öğe Cyclic behavior of high density polyethylene (HDPE)(American Institute Physics, 2010) Düşünceli, Necmi; Aydemir, Bülent; Terzi, Niyazi Uğur; DAmore, A; Acierno, D; Grassia, LThis article presents the mechanical behavior of high density polyethylene (HDPE). Samples were prepared by extracting extruded HDPE pipe. Cyclic and strain rate jump behavior of HDPE were studied under uniaxial tensile loading conditions. The strain jump tests indicated that mechanical behavior of HDPE has deformation memory. Further, it was found that increasing cycle number on cyclic loading test increased strain accumulation amount and HDPE exhibited ratcheting behavior at on loading-unloading-reloading at constant stress level.Öğe Comparing the energetic and exergetic performances of a building heated by solar energy and ground-source (geothermal) heat pump(Trans Tech Publications, 2012) Hepbaşli, Arif; Balta, Mustafa Tolga; Alsuhaibani, Zeyad; Pan, W; Ren, JX; Li, YGIn this study, we considered a building, which had a volume of 336 m(3) and a floor area of 120 m(2), with indoor and outdoor air temperatures of 20 degrees C and 0 degrees C, respectively. For heating this building, we selected two options, namely (i) a ground-source (geothermal) heat pump system (Case 1), and (ii) a solar collector heating system (Case 2). We employed both energy and exergy analysis methods to assess their performances and compare them through energy and exergy efficiencies and sustainability index. We also investigated energy and exergy flows for this building and illustrated from the primary energy transformation through the heat production system and a distribution system to a heating system, and from there, via the indoor air, across the building envelope to the surrounding air. We calculated that the total exergy efficiencies for Cases 1 and 2 were 4.7%, and 26.1% while sustainability index values for both cases were 1.049 and 1.353 at a reference (dead) state temperature of 0 degrees C, respectively.Öğe The effects of neutron energy-group structures and resonance treatment on integral parameters in a fusion breeder blanket fuelling with ThO2(2005) Şahin, Sümer; Şahin, Hacı Mehmet; Yıldız, Kadir; Acir, AdemThe purpose of this work is to investigate the effects of neutron energy-group structures and resonance treatments on the main integral neutronic parameters in a fusion-fission hybrid reactor, which has a fast and a thermal blanket fuelling with ThO2. As a neutron source, D-T fusion neutrons (14.1 MeV) are used and fissile zone is cooled (a) with light water for the moderated blanket and (b) with pressurized helium gas for the fast blanket. The neutronic parameters have been evaluated with and without a resonance treatment for the same blanket compositions for the sake of a consistent comparison. Neutron energy-group structures in the neutron libraries and description of fusion neutron source spectrum mainly affect the neutron reactions above a threshold energy in fast neutron groups such as 7Li(n, ?n')T and 232Th(n,f). These reactions are not affected to resonance treatment. Neutron reactions in the resonance and thermal energy groups are sensitive to resonance treatment, such as 6Li(n,?)T and 232Th(n,?), depending on the resonance structures.Öğe Unsteady flow over flexible wings at different low Reynolds numbers(E D P Sciences, 2016) Genç, Mustafa Serdar; Özden, Mustafa; Açıkel, Halil Hakan; Demir, Hacımurat; Isabekov, Iliasbek; Dancova, P; Vesely, MIn this study, unsteady flow around flexible membrane wing which had aspect ratio of 1 (AR=1) was investigated experimentally at various Reynolds numbers (Re = 25000 and Re = 50000). Smoke-wire technique for flow visualization over the flexible membrane wing was utilized in the experiments. Digital Image Correlation system (DIC) was used for measuring deformation of AR = 1 flexible membrane wing. Instantaneous deformation measurements of membrane wing were combined with the flow field measurements. In low aspect ratio flexible membrane wings, unsteadiness includes tip vortices and vortex shedding, and the combination of tip vortices. In these types of wings, complex unsteady deformations occurred due to vortex shedding. The results showed that the increasing angle of attack results in increase of membrane deformation. Moreover, it was concluded that analysis of the instantaneous deformation revealed chordwise and spanwise, modes which were due to the shedding of leading-edge vortices as well as tip vortices. Consequently, vibrational mode decreased and maximum standard deviation location approached to the trailing edge by reason of increasing angle of attack.Öğe Numerical investigation of flow on NACA4412 aerofoil with different aspect ratios(EDP Sciences, 2016) Demir, Hacı Murat; Özden, Mustafa; Genç, Mustafa Serdar; Çagdaş, Mücahit; Dancova, P; Vesely, MIn this study, the flow over NACA4412 was investigated both numerically and experimentally at a different Reynolds numbers. The experiments were carried out in a low speed wind tunnel with various angles of attack and different Reynolds numbers (25000 and 50000). Airfoil was manufactured using 3D printer with a various aspect ratios (AR = 1 and AR = 3). Smoke-wire and oil flow visualization methods were used to visualize the surface flow patterns. NACA4412 aerofoil was designed by using SOLIDWORKS. The structural grid of numerical model was constructed by ANSYS ICEM CFD meshing software. Furthermore, ANSYS FLUENTTM software was used to perform numerical calculations. The numerical results were compared with experimental results. Bubble formation was shown in CFD streamlines and smoke-wire experiments at z / c = 0.4. Furthermore, bubble shrunk at z / c = 0.2 by reason of the effects of tip vortices in both numerical and experimental studies. Consequently, it was seen that there was a good agreement between numerical and experimental results.Öğe The effect of porosity on performance of phosphoric acid doped polybenzimidazole polymer electrolyte membrane fuel cell(E D P Sciences, 2016) Çelik, Muhammet; Genç, Gamze; Elden, Gülşah; Yapıcı, Hüseyin; Dancova, P; Vesely, MA polybenzimidazole (PBI) based polymer electrolyte fuel cells, which called high temperature polymer electrolyte fuel cells (HT-PEMS), operate at higher temperatures (120-200 degrees C) than conventional PEM fuel cells. Although it is known that HT-PEMS have some of the significant advantages as non-humidification requirements for membrane and the lack of liquid water at high temperature in the fuel cell, the generated water as a result of oxygen reduction reaction causes in the degradation of these systems. The generated water absorbed into membrane side interacts with the hydrophilic PBI matrix and it can cause swelling of membrane, so water transport mechanism in a membrane electrode assembly (MEA) needs to be well understood and water balance must be calculated in MEA. Therefore, the water diffusion transport across the electrolyte should be determined. In this study, various porosity values of gas diffusion layers are considered in order to investigate the effects of porosity on the water management for two phase flow in fuel cell. Two-dimensional fuel cell with interdigitated flow-field is modelled using COMSOL Multiphysics 4.2a software. The operating temperature and doping level is selected as 160 degrees C and 6.75mol H3PO4/PBI, respectively.Öğe Hydrogen production potential and cost of wind-hydrogen hybrid energy system(Amer Soc Mechanical Engineers, 2013) Çelik, Muhammet; Genç, Gamze; Genç, M. Serdar; Yapıcı, HüseyinMain aim of this study is to investigate annual wind power output, annual hydrogen production quantity and hydrogen production cost of wind-hydrogen energy system in the Pinarba i-Kayseri region in Turkey which has remarkable wind potential in the central region of Turkey. Turkish State Meteorological Service (TSMS) measured the value of mean wind speed of Pmarba i. as 3.67 m/s above 10m ground between 2000 and 2006 years. In this study, three different hub heights (50m, 80m and 100m) were considered, and so the measured mean wind speed at 10m was extrapolated to considered heights and annual wind power output was calculated. Four different turbine rated powers (800kW, 900kW, 2000kW and 3000 kW) and two different electrolyser powers (120kW and 40kW) for hydrogen production were assumed. Levelised cost of electricity method was used in order to determine the cost analysis of wind energy and hydrogen production. The results of this study bring out clearly the variation of potential of hydrogen production and cost with wind speed, wind turbine hub height and wind turbine rated power and electrolyser power.
