Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 4Citation - Scopus: 4Adsorption Kinetics of Methane Reformer Off-Gases on Aluminum Based Metal-Organic Framework(Elsevier Ltd., 2020) Angı, Deniz; Çakıcıoğlu Özkan, Seher FehimeSolvothermal synthesis of aluminum based metal-organic frameworks (MIL-53(Al)s) were conducted by considering the effects of crystallization and activation temperatures, and the solvent at purification step. Adsorption kinetics of Steam Methane Reformer off gas components at 34, 70 and 100 °C temperatures was measured by using ZLC method. Henry constant decreases as diffusion coefficient of the gases increases with increasing temperature; It was determined that the CO gas has the highest activation energy. Adsorption kinetics of gases were controlled with electrostatic interaction. © 2020 Hydrogen Energy Publications LLCArticle Citation - WoS: 3Citation - Scopus: 2Adsorption of No in Clinoptilolite-Rich Zeolitic Mineral by Concentration Pulse Chromatography Method(Elsevier Ltd., 2016) Narin, Güler; Ülkü, SemraThe equilibrium and kinetic parameters for NO adsorption in a clinoptilolite-rich natural zeolitic material from Turkey were determined using the concentration pulse chromatography method. Under the experimental conditions (carrier gas velocities and adsorption temperatures) the micropore diffusion resistance was found to be the mass transfer controlling step. Matching the first moment of the response peaks to the mathematical model the Henry's Law constants and heat of adsorption at zero loading were determined. The axial dispersion, external film, macropore and micropore diffusion coefficients, and activation energy for diffusion of NO in the micropores were calculated from the analysis of the second moments of the response peaks. For successive NO pulses without regeneration between the pulses, the retention times of the response peaks decreased and peak areas increased with the injection number indicating irreversible adsorption. The reversibly adsorbed NO could be desorbed by purging with an inert gas at the adsorption pressure and temperature. Temperature programmed desorption profile obtained by heating the NO saturated adsorbent to 400 °C under inert flow revealed presence of multiple irreversibly adsorbed species in NZ with different thermal stabilities. Desorption of these species was not achieved during the heating up to 400 °C which makes the natural zeolitic materıal suitable for NO storage rather than for cyclic adsorptive separation processes.Article Citation - WoS: 24Citation - Scopus: 27Visualization of Diffusion and Convection Heat Transport in a Square Cavity With Natural Convection(Elsevier Ltd., 2010) Mobedi, Moghtada; Özkol, Ünver; Sunden, BengtIn this study, the total heatfunction equation which includes diffusion and convection transport is divided into the corresponding heatfunction equations. The superposition rule is used to obtain the mathematical definitions of diffusion and convection heatfunctions and corresponding boundary conditions. It is observed that the separate visualization of diffusion and convection heatlines provides significant information on understanding of the mechanism of heat transfer in a convective flow. The direction of the diffusion and convection heat transport as well as the strength of convection compared to the conduction in entire or in a portion of a domain can be visualized. The diffusion heatlines demonstrate a potential flow like behavior while convective heat flow rotates due to the source term of the convection heatfunction equation, similar to the rotation of fluid flow generated by fluid flow vorticity. The similarity between the streamfunction and the total heatfunction yields a concept of heat flow vorticity, Ωt. The obtained results show that the maximum absolute value of the convection heatfunction may be an appropriate parameter for determination of the convection strength. The diffusion and convection heatfunction equations for natural convection in a differentially heated square cavity for four different length of the heated surface on the right vertical wall as sp = L/4, L/2, 3L/4 and L and a fixed length of the cooled surface on the right vertical wall as L/4 are obtained and corresponding heatlines are drawn. The values of the conduction heatfunction are positive while the sign of convection heatfunction values is negative for the studied cases. Based on the distribution of total heatlines, two regions are detected in the cavity, an active region with the positive values of heatlines signifying dominant conduction heat transfer and a passive region with the negative heatfunction values in where convection heat flow is dominant and heat only rotates in a closed contour pattern. The variations of average Nusselt number, average of heat flow vorticity, maximum absolute values of convection heatfunction and streamfunction at different Rayleigh numbers and lengths of the heated surface are presented.Article Citation - WoS: 18Citation - Scopus: 21Predicting Emission Characteristics of Volatile Organic Compounds From Wet Surface Coatings(Elsevier Ltd., 2009) Alsoy Altınkaya, SacideA mathematical model is developed to describe the emission characteristics of VOCs from homogeneous wet coating materials deposited on impermeable substrates. The model considers mass transfer in the material and in air, boundary layer resistance and the change in the coating thickness with time due to emission of VOC. Key features of the model are incorporation of concentration dependent VOC diffusion coefficients predicted from a physical model and nonlinear equilibrium isotherm at the coating/air interface. The model is applied to predict emission characteristics of MMA from acrylic based surface coatings. In an attempt to investigate the influences of equilibrium isotherm type and diffusion formalism on the predictions, simulations are performed with either constant or concentration dependent diffusivities and linear or nonlinear equilibrium isotherms. The lowest MMA concentration in air is predicted by incorporating the concentration dependent diffusivity and nonlinear equilibrium isotherm. The results suggest that assuming the diffusivity of MMA constant or equilibrium isotherm linear may lead to wrong conclusions about the emission rates from wet coatings. The model is general, fully predictive and can be used to predict emission rates of different VOCs from different coating materials if diffusion and thermodynamic parameters are available.Article Citation - WoS: 17Citation - Scopus: 19Kinematic Wave Model for Transient Bed Profiles in Alluvial Channels Under Nonequilibrium Conditions(John Wiley and Sons Inc., 2007) Tayfur, Gökmen; Singh, Vijay P.Transient bed profiles in alluvial channels are generally modeled using diffusion (or dynamic) waves and assuming equilibrium between detachment and deposition rates. Equilibrium sediment transport can be considerably affected by an excess (or deficiency) of sediment supply due to mostly flows during flash floods or floods resulting from dam break or dike failure. In such situations the sediment transport process occurs under nonequilibrium conditions, and extensive changes in alluvial river morphology can take place over a relatively short period of time. Therefore the study and prediction of these changes are important for sustainable development and use of river water. This study hence developed a mathematical model based on the kinematic wave theory to model transient bed profiles in alluvial channels under nonequilibrium conditions. The kinematic wave theory employs a functional relation between sediment transport rate and concentration, the shear-stress approach for flow transport capacity, and a relation between flow velocity and depth. The model satisfactorily simulated transient bed forms observed in laboratory experiments.Article Citation - WoS: 24Citation - Scopus: 29Thermal Stability of the High-N Solid-Solution Layer on Stainless Steel(Elsevier Ltd., 2002) Öztürk, Orhan; Williamson, Don L.Low-energy, high-flux N ion implantation into austenitic stainless steel held at approximately 400 °C results in dramatic improvements in the tribological properties due to sufficiently large N layer thicknesses and high-N-content solid solution phase. γN. In this paper, post-ion beam processing via isothermal annealing of a low-energy (0.7 keV), high-flux (2.5 mA/cm2) N implanted fee 304 stainless steel held at 400 °C has been investigated by Mössbauer spectroscopy and X-ray diffraction (XRD). Post-implantation annealing at 400 °C demonstrated the metastability and showed that the magnetic γN produced at lower ion energies and higher fluxes transformed systematically to a paramagnetic γN phase with less N content and less lattice expansion, thereby destabilizing the magnetic state of γN. The isothermal annealing results in much thicker γN layers but with less N in solid solution due to the N diffusion into the substrate. Based on the XRD data, the N diffusivity under isothermal annealing conditions is found to be D = 2X10-13 cm2/s at 400 °C, consistent with a model which explains that the trapping by Cr atoms in the stainless steel becomes more effective when N contents are low relative to the Cr concentration ( ~ 19 at.% in 304 stainless steel).