Chemical Engineering / Kimya Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/14
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Article Citation - WoS: 23Citation - Scopus: 24Investigation of Kinetics of Supercritical Drying of Alginate Alcogel Particles(Elsevier Ltd., 2019) Şahin, İbrahim; Uzunlar, Erdal; Erkey, CanSpherical 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.Article Citation - WoS: 23Citation - Scopus: 25A Dimensionless Analysis of Heat and Mass Transport in an Adsorber With Thin Fins; Uniform Pressure Approach(Elsevier Ltd., 2011) Gediz İliş, Gamze; Mobedi, Moghtada; Ülkü, SemraA numerical study on heat and mass transfer in an annular adsorbent bed assisted with radial fins for an isobaric adsorption process is performed. A uniform pressure approach is employed to determine the changes of temperature and adsorbate concentration profiles in the adsorbent bed. The governing equations which are heat transfer equation for the adsorbent bed, mass balance equation for the adsorbent particle, and conduction heat transfer equation for the thin fin are non-dimensionalized in order to reduce number of governing parameters. The number of governing parameters is reduced to four as Kutateladze number, thermal diffusivity ratio, dimensionless fin coefficient and dimensionless parameter of Γ which compares mass diffusion in the adsorbent particle to heat transfer through the adsorbent bed. Temperature and adsorbate concentration contours are plotted for different values of defined dimensionless parameters to discuss heat and mass transfer rate in the bed. The average dimensionless temperature and average adsorbate concentration throughout the adsorption process are also presented to compare heat and mass transfer rate of different cases. The values of dimensionless fin coefficient, Γ number and thermal diffusivity ratio are changed from 0.01 to 100, 1 to 10 -5 and 0.01 to 100, respectively; while the values of Kutateladze number are 1 and 100. The obtained results revealed that heat transfer rate in an adsorbent bed can be enhanced by the fin when the values of thermal diffusivity ratio and fin coefficient are low (i.e., α -=0.01, δ=0.01). Furthermore, the use of fin in an adsorbent bed with low values of γ number (i.e. γ=10 -5) does not increase heat transfer rate, significantly.Article Citation - Scopus: 5Effect of Isotherm Shape on Mass Transfer in an Adsorbent Particle; an Isothermal Adsorption Process(Bentham Science Publishers B.V., 2011) Yıldırım, Zeynep Elvan; Gediz İliş, Gamze; Mobedi, Moghtada; Ülkü, SemraThe mass diffusion equation and corresponding initial and boundary conditions were non-dimensionalized for a spherical adsorbent particle in an infinite adsorptive medium to reduce number of independent governing parameters into two as mass transfer Biot number and dimensionless isotherm. The changes in local and average adsorbate concentration throughout the adsorption process were calculated and plotted for different values of mass transfer Biot numbers (ranging from 0.5 to 750) and for five different isotherm shapes. The obtained results indicated that the isotherm shape influences dimensionless period of adsorption, if the external mass transfer resistance is significant in the process. For those cases, the total dimensionless adsorption period for a convex shape isotherm is shorter than a concave one.Article Citation - WoS: 12Citation - Scopus: 11A Parametric Study on Isobaric Adsorption Process in a Closed Adsorbent Bed(Elsevier Ltd., 2010) Gediz İliş, Gamze; Mobedi, Moghtada; Ülkü, SemraA numerical study on heat and mass transfer in an annular adsorbent bed filled with adsorbent granules for an isobaric adsorption process is performed. In order to reduce the number of independent parameters that influences heat and mass transfer in the bed, the governing equations and related initial and boundary conditions for the problem are non-dimensionalized and this yields two dimensionless parameters as G and Γ. The G dimensionless parameter is the ratio of heat of adsorption to sensible heat stored by adsorbent particle and Γ parameter compares mass diffusion within the adsorbent particle and heat diffusion in the radial direction of the adsorbent bed. The obtained results show that the total dimensionless time for an adsorption process can be reduced by increasing of Γ value. The total dimensionless time is independent from G for low values of Γ (i.e. Γ=105). The results also show that the instantaneous equilibrium model can provide accurate results only for an adsorbent bed with a low value of Γ (i.e. Γ=105). The present study is performed for Γ values from 105 to 1 and G value from 1 to 100. © 2010 Elsevier Ltd.Article Citation - WoS: 9Citation - Scopus: 11Modeling of Hemodialysis Operation(Springer Verlag, 2010) Abacı, Hasan Erbil; Alsoy Altınkaya, SacideIn this study, a theoretical model was developed to predict the solute concentrations in patients' blood and optimize the efficiency of the hemodialysis operation. The model takes into account simultaneous mass and momentum transfer on the blood side both in radial and axial directions. A key component of the model is the incorporation of the protein adsorption on the inner surface of the membrane. The validity of the model was confirmed with the experimental data available in the literature for two different types of hemodiafilter. To illustrate the importance of including the radial concentration gradients and protein adsorption kinetics in the model, the experimental data were predicted with and without consideration of these effects. The results have shown that assuming uniform concentration in the radial direction or neglecting protein adsorption on the inner surface of the membrane leads to higher error in predicting the experimental data. In addition, significant error can be introduced in the calculation of the dialysis time if protein adsorption is not considered. © 2010 Biomedical Engineering Society.Article Citation - WoS: 2Citation - Scopus: 1Errors Associated With Swelling in the Analysis of Polymer-Solvent Diffusion Measurements(Elsevier Ltd., 2005) Alsoy Altınkaya, SacideSorption curves are generated from a mathematical model which includes the influence of the polymer swelling for unsteady-state sorption of a vapor or liquid by a polymer. To investigate the simultaneous effects of the specific volumes of the polymer-penetrant pair and the difference between the final and initial equilibrium concentrations on the sorption curves, statistical experimental design approach is used. Simulation results obtained from the numerical solution of model equations are utilized to estimate the error that would occur if one simply evaluates the diffusion coefficient using the traditional formulas derived from the analytical solution of the sorption equation. An empirical expression is developed that describes the effects of the difference between the final and initial equilibrium concentrations and the specific volumes of the polymer and the penetrant on the magnitude of error in diffusivity associated with the use of one of these traditional formulas so called the initial slope method. The predictive ability of the regression model is tested by performing additional simulations not used in the regression analysis.Article Citation - WoS: 24Citation - Scopus: 25Processing of Polymers With Supercritical Fluids(John Wiley and Sons Inc., 1999) Alsoy Altınkaya, Sacide; Duda, John LarryThe removal of impurities, such as residual solvents, unreacted monomers, catalysts, and side-reaction products from polymers represents an important step in polymer processing. Conventional devolatilization techniques for the purification of polymers have limited effectiveness. Devolatilization with supercritical fluids, however, can enhance impurity removal by increasing the thermodynamic driving force and molecular diffusivity.