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: 8Citation - Scopus: 7Cvd-Deposited Oxygen-Selective Fluorinated Siloxane Copolymers as Gas Diffusion Layers(American Chemical Society, 2022) Cihanoğlu, Gizem; Ebil, ÖzgençCopolymer thin films of 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (V4D4), 2-(perfluorohexylethylacrylate) (PFHEA), and 2-(perfluoroalkylethylmethacrylate) (PFEMA) were synthesized via initiated chemical vapor deposition (iCVD) as potential candidates for gas diffusion layers (GDLs) in gas diffusion electrodes (GDEs) for aqueous metal–air batteries. Thin-film GDLs exhibited an average water vapor transmission rate of 7.5 g m–2 day–1 and enhanced oxygen diffusion with oxygen permeabilities as high as 3.53 × 10–15 mol m m–2 s–1 Pa–1 (10.5 Barrer). The electrochemical performance of GDEs fabricated using commercial catalysts, current collectors, and synthesized GDLs was investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and potentiodynamic polarization measurements. The fabricated GDEs exhibited higher oxygen reduction current densities (228.2 mA cm–2) compared to commercial GDEs (132.7 mA cm–2). Copolymer GLDs exhibited an order of magnitude higher oxygen diffusion (39.5 × 10–8 cm2 s–1) in GDEs compared to commercial counterparts (1.84 × 10–8 cm2 s–1). Due to the high oxygen solubility of V4D4 and excellent hydrophobic behavior of PFHEA and PFEMA, their copolymers can effectively promote the diffusion of oxygen and restrict moisture intake, making them ideal materials for GDLs. Combining well-balanced properties of siloxane and fluorinated polymer chemistries, the iCVD process is an excellent low-cost method for the fabrication of GDLs for metal–air battery applications.Article Citation - WoS: 6Citation - Scopus: 6A Study on Numerical Determination of Permeability and Inetia Coefficient of Aluminum Foam Using X-Ray Microtomography Techniques: Focus on Inspection Methods for Reliability (permeability and Inertia Coefficient by Tomography)(Begell House, 2019) Mobedi, Moghtada; Nakayama, Akira; Özkol, Ünver; Çelik, HasanThe volume-averaged (i.e., macroscopic) transport properties such as permeability and inertia coefficient of two aluminum foams with 10 and 20 pores per inch (PPI) pore density are found using microtomography images. It is shown that a comparison between the numerical values and the experimental results may not be sufficient to prove the correctness of the obtained results. Hence, in addition to traditional validation methods such as grid independency and comparison with reported results in literature, further inspections such as (a) checking the development of flow, (b) inspection of Darcy and non-Darcy regions, (c) conservation of flow rate through the porous media, (d) sufficiency of number of voxels in the narrow throats, and (e) observation of transverse velocity gradients in pores for high and low Reynolds numbers can be performed to further validate the achieved results. These techniques have been discussed and explained in detail for the performed study. Moreover, the obtained permeability and inertia coefficient values are compared with 19 reported theoretical, numerical, and experimental studies. The maximum deviation between the present results and the reported studies for 10 PPI is below 25%, while for 20 PPI it is below 28%.Article Citation - Scopus: 7Transformation in a Housing-Design Story: Reading the Spatial Typologies of Apartment Projects in Hatay-Izmir(İstanbul Teknik Üniversitesi, 2018) Yaylalı Yıldız, Berna; Ek, Fatma İpek; Can, IşınThe politics of central government or incentives determine new design-systems of housing plots as well as housing units. Especially after the enactment of the law of urban regeneration for risky areas, regeneration of areas under disaster risk, there has been an acceleration in knocking down old buildings and constructing new ones in inner cities. Thus, this paper focuses on the changes in housing typologies in Hatay-Izmir, in terms of space syntax parameters through the time period 1960-2000, and interprets the final plan-solutions within the perspective of urban regeneration. By accelerating implementations of the urban transformation projects in Hatay region, alternative plan-typologies coming from the past have undergone the so-called “re-design and transformation” process; however, they have actually been substituted by the “never-changing” plan-templates of the apartment typology. We will examine these changes in plan typologies and spatial organisations of the mentioned apartment-projects on the same plots by utilizing the method of space syntax and visibility analysis (VGA). Transformations in spatial configuration in two periods are interpreted through their relationships to shifts in meaning of privacy and daily life represented by degree of permeability and connectivity of housing-unit-plans based on spatial analysis. © 2018, Istanbul Teknik Universitesi, Faculty of Architecture. All rights reserved.Article Citation - WoS: 100Citation - Scopus: 106Determination of Kozeny Constant Based on Porosity and Pore To Throat Size Ratio in Porous Medium With Rectangular Rods(Taylor and Francis Ltd., 2014) Özgümüş, Türküler; Mobedi, Moghtada; Özkol, ÜnverKozeny-Carman permeability equation is an important relation for the determination of permeability in porous media. In this study, the permeabilities of porous media that contains rectangular rods are determined, numerically. The applicability of Kozeny-Carman equation for the periodic porous media is investigated and the effects of porosity and pore to throat size ratio on Kozeny constant are studied. The continuity and Navier- Stokes equations are solved to determine the velocity and pressure fields in the voids between the rods. Based on the obtained flow field, the permeability values for different porosities from 0.2 to 0.9 and pore to throat size ratio values from 1.63 to 7.46 are computed. Then Kozeny constants for different porous media with various porosity and pore to throat size ratios are obtained and a relationship between Kozeny constant, porosity and pore to throat size ratio is constructed. The study reveals that the pore to throat size ratio is an important geometrical parameter that should be taken into account for deriving a correlation for permeability. The suggestion of a fixed value for Kozeny constant makes the application of Kozeny-Carman permeability equation too narrow for a very specific porous medium. However, it is possible to apply the Kozeny-Carman permeability equation for wide ranges of porous media with different geometrical parameters (various porosity, hydraulic diameter, particle size and aspect ratio) if Kozeny constant is a function of two parameters as porosity and pore to throat size ratios.Article Citation - WoS: 2Citation - Scopus: 3Effect of Voxel Size in Flow Direction on Permeability and Forchheimer Coefficients Determined by Using Micro-Tomography Images of a Porous Medium(Inderscience Enterprises Ltd., 2015) Uçar, Eren; Mobedi, Moghtada; Altıntaş, Gökhan; Glatt, ErikThe permeability and Forchheimer coefficients of a porous medium, volcanic rock, are determined using micro-tomography images. A cubic volume in the middle of the images is extracted as REV (representative volume). The voids in the REV are discretised into anisotropic voxels using the commercial program of GeoDict. Seven computational domains with different voxel size in flow direction are generated. The velocity and pressure fields in the voids are obtained for Reynolds numbers ranging from 0.01 to 10. The obtained fields are used to determine the permeability and the Forchheimer coefficients. The performed calculations show that the nominal pore size changes with the voxel size in flow direction, however permeability and the Forchheimer coefficient approaches to the constant values.Article Citation - Scopus: 1The Effect of Bio-Based Plasticizer on the Permanence and Water Vapour Transport Properties of Pvc Plastigels(Serbian Chemical Society, 2008) Okieimen, Felix Ebhodaghe; Egbuchunam, Theresa Obuajulu; Balköse, DevrimNovel formulations of PVC plastisols based on blends of bio-based and synthetic plasticizers were prepared and characterized. A traditional phthalate plasticizer, dioctylphthalate, was replaced in the plastisols studied by the epoxidized rubber seed oil (4.5 % oxirane content). The plastisols formed were processed into plastigels and characterized in terms of permanence properties using leaching and migration tests and water vapour barrier properties. It was found that the permanence properties of PVC/DOP plastigels were maintained in the presence of up to 50 % ERSO, and that blending with DOP did not impair the water barrier properties of PVC plastigels.Article Citation - WoS: 5Citation - Scopus: 9Consolidation of Elastic Porous Media Saturated by Two Immiscible Fluids(American Society of Civil Engineers (ASCE), 1996) Tuncay, Kağan; Çorapçıoğlu, M. YavuzA theory is presented to simulate the consolidation of elastic porous media saturated by two immiscible Newtonian fluids. The macroscopic equations, including mass and momentum balance equations and constitutive relations, are obtained by volume averaging the microscale equations. The theory is based on the small deformation assumption. In the microscale, the grains are assumed to be linearly elastic and the fluids are Newtonian. The bulk and shear moduli of the solid matrix are introduced to obtain the macroscopic constitutive equations. Momentum transfer terms are expressed in terms of intrinsic and relative permeabilities assuming the validity of Darcy's law. In one dimension, the governing equations reduce to two coupled diffusion equations in terms of the pore pressures of the fluid phases. An analytical solution is obtained for a column with a fixed impervious base and a free drainage surface. Results are presented for cases of practical interest, i.e., columns saturated by oil-water and air-water phases. Results indicate that the presence of a second fluid phase affects pore water pressure and total settlement.