Researcher: Şahin, İbrahim
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Şahin, İbrahim
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Publication Metadata only Investigation of the effect of gel properties on supercritical drying kinetics of ionotropic alginate gel particles(Elsevier, 2019) Uzunlar, Erdal; N/A; Department of Chemical and Biological Engineering; Şahin, İbrahim; Erkey, Can; PhD Student; Faculty Member; Department of Chemical and Biological Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 29633A series of spherical ionotropic alginate gel particles with different diameters ranging from 2.8mm to 5.0mm and porosities ranging from 0.899 to 0.976 were prepared by dripping a Na-alginate solution into a solution of salts of divalent cations (Ca2+, Mn2+, Ni2+, Co2+, Cu2+ and Zn2+). After solvent exchange with ethanol, kinetics of supercritical drying of these ionotropic alginate gel particles in a packed bed was investigated at 308-338 K and 100-120 bar. Experimental data were compared with predictions of a model which considers diffusive transport inside the pores and convection in the flowing fluid stream. The model predicted drying profiles by taking into account only the changes in porosity and diameter of the gel particles. A convective mass transfer coefficient correlation that was originally developed for supercritical drying of Ca-alginate gel particles was found to be suitable for M-alginate gel particles. (C) 2019 Elsevier B.V. All rights reserved.Publication Metadata only Investigation of kinetics of supercritical drying of alginate alcogel particles(Elsevier, 2019) Uzunlar, Erdal; N/A; Department of Chemical and Biological Engineering; Şahin, İbrahim; Erkey, Can; PhD Student; Faculty Member; Department of Chemical and Biological Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 29633Spherical calcium alginate gel particles were synthesized by dripping method. The effects of temperature, pressure, particle size and CO2 flow rate on kinetics of supercritical drying of alginate gel particles in a packed bed were investigated. Increase in CO2 flow rate, increase in temperature and decrease in particle size increased the drying rate and decreased the drying time. A mathematical model based on (i) the diffusion of the solvent inside the pores of gel particles, (ii) external mass transfer of the solvent from the surface of the gel particles into the flowing fluid stream, and (iii) convection and axial dispersion of the solvent in the flowing fluid stream was developed. A correlation for predicting external mass transfer coefficients for supercritical drying of alcogel particles was developed by fitting the model to experimental data. A good agreement between the experimental data and model results was achieved using the developed correlation.Publication Metadata only A new venue toward predicting the role of hydrogen embrittlement on metallic materials(Springer, 2016) N/A; N/A; Department of Chemical and Biological Engineering; Department of Mechanical Engineering; Bal, Burak; Şahin, İbrahim; Uzun, Alper; Canadinç, Demircan; PhD Student; PhD Student; Faculty Member; Faculty Member; Department of Chemical and Biological Engineering; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; N/A; N/A; 59917; 23433This paper presents a new crystal plasticity formulation to predict the role of hydrogen embrittlement on the mechanical behavior of metallic materials. Specifically, a series of experiments were carried out to monitor the role of hydrogen interstitial content on the uniaxial tensile deformation response of iron alloyed with hydrogen, and the classical Voce hardening scheme was modified to account for the shear stresses imposed on arrested dislocations due to the surrounding hydrogen interstitials. The proposed set of physically grounded crystal plasticity formulations successfully predicted the deformation response of iron in the presence of different degrees of hydrogen embrittlement. Moreover, the combined experimental and modeling effort presented herein opens a new venue for predicting the alterations in the performance of metallic materials, where the hydrogen embrittlement is unavoidable.Publication Metadata only Catalytic naphtha reforming(CRC Press, 2017) N/A; N/A; Department of Chemical and Biological Engineering; Balcı, Volkan; Şahin, İbrahim; Uzun, Alper; PhD Student; PhD Student; Faculty Member; Department of Chemical and Biological Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 59917Catalytic naphtha reforming (CNR) process was pioneered by UOP in the late 1940s to meet the burgeoning demand for high-octane motor fuels and has been a pivotal unit in petroleum refineries all over the world since its inception. The CNR process is specifically designed to convert naphtha to high-octane gasoline blending components called reformate. The low-octane components that usually have octane number in the range of 40–65 in naphtha, such as normal paraffins (n-paraffins), are converted into isoparaffins (i-paraffins) and naphthenes, and naphthenes are converted to aromatics in catalytic reformers to enhance the octane number of gasoline blends up to 90–105. In order to elaborate the dependency of octane number on chemical structure, numerous hydrocarbons are compared in Table 6.1 with respect to their research octane numbers. In general, aromatics possess the highest octane number, followed by naphthenes, olefins, and n-paraffins having the lowest octane number among other hydrocarbons listed. One of the essential characteristics of the CNR process is that it is the primary source of aromatics, such as benzene, toluene, and xylene (BTX) with more than 50 vol.% of production volume on worldwide basis. Moreover, it produces hydrogen as a by-product (also called net gas as a mixture of hydrogen, methane, ethane, and trace propanes), which can be utilized in hydrogen-consuming processes (i.e., hydrocracking, hydrotreating, hydrogenation, etc.) refinery-wide.Publication Open Access Kinetics of supercritical drying of gels(Multidisciplinary Digital Publishing Institute (MDPI), 2018) Ülker, Zeynep; Department of Chemical and Biological Engineering; Şahin, İbrahim; Özbakır, Yaprak; İnönü, Zeynep; Erkey, Can; PhD Student; Faculty Member; Department of Chemical and Biological Engineering; Graduate School of Sciences and Engineering; N/A; N/A; N/A; 29633Supercritical drying of gels is considered as the most important step of aerogel production since it enables preservation of the three-dimensional pore structure which lead to unique material properties such as high porosity, low density, and large surface area. An understanding of the kinetics of supercritical drying is necessary to provide insight into material development, scale-up, and optimization of the aerogel manufacturing process. Thus, investigation of supercritical drying is gaining increased attention in recent years. This review paper covers the experimental considerations and techniques to study the kinetics of supercritical drying, fundamental mass transfer mechanisms during the drying process and modeling efforts to predict the drying kinetics for varying operating conditions and gel properties. Transport phenomena involving diffusion, convection, spillage by volume expansion, and axial dispersion are discussed by providing the fundamental equations and empirical correlations to predict transfer coefficients. A detailed review of literature covering experimental and theoretical studies on kinetics of supercritical drying is presented.