Chemical Engineering / Kimya Mühendisliği

Permanent URI for this collectionhttps://hdl.handle.net/11147/14

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End date: 2009Publisher: search.filters.publisher.SAGE Publications Inc.

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  • Article
    Citation - WoS: 3
    Citation - Scopus: 5
    Adsorption Characteristics of Lead-, Barium- and Hydrogen-Rich Clinoptilolite Mineral
    (SAGE Publications Inc., 2003) Çakıcıoğlu Özkan, Seher Fehime; Ülkü, Semra
    The carbon dioxide and water vapour adsorption properties of local clinoptilolite-rich material, both as the original and as lead-, barium- and hydrogen-rich forms, were examined. The lead- and barium-rich forms were prepared by treatment of the original clinoptilolite with Pb(NO3)2 and BaCl2 respectively, while the hydrogen-rich form was prepared by NH4Cl and heat treatment. Water and CO2 adsorption experiments were conducted in a volumetric system under static conditions, with low-pressure adsorption data being used for the characterization of the natural, Pb-rich, Ba-rich and H-rich clinoptilolite samples. Although the existence of barium-exchange was not noted, an appreciable decrease in CO2 adsorption was observed with the Pb-rich and H-rich forms due to a decrease in the electrostatic interaction between the surface and the adsorbate. Application of the Dubinin-Astakhov equation to the water adsorption data established the existence of micropores of different sizes that exhibited different adsorption mechanisms.
  • Article
    Citation - WoS: 15
    Citation - Scopus: 18
    Modeling of Diffusion in Closed Cell Polymeric Foams
    (SAGE Publications Inc., 1999) Alsoy Altınkaya, Sacide
    Closed-cell foams made of polymers have the lowest thermal conductivity of any currently available insulation material other than vacuum insulation systems. The increase of foam conductivity with age occurs as air diffuses into the foam while the blowing agent diffuses out, thus modifying the cell gas composition. Also, the change in cell gas composition influences the dimensional stability of the foams. To predict the long term aging behavior and dimensional stability of these foams, the diffusion characteristics of the different components need to be known. Several models exist in the literature which describe diffusion in foams. The most popular of these models are reviewed, and effective diffusivities predicted from one model are compared with experimental data. An unsteady state model is then proposed and solved numerically using a finite difference scheme. The numerical solution algorithm is developed to efficiently solve the large number of coupled equations resulting from this model. The uptake curves predicted from both the unsteady-state model and a discrete model (Bart and Du Cauze De Nazelle, 1993) are compared with available experimental data for the polystyrene-nitrogen system. From the analysis of uptake curves generated for different numbers of cells, the effective diffusivity of the PS/N2 system is predicted. Also, the effect of initial cell gas composition and cell size on both the long term aging profile and dimensional stability of polyurethane foam is considered. The proposed model can easily be extended to include the influence of blowing agent concentration on diffusivity in the polymer phase and the isotherm describing the distribution of blowing agent between the gas and polymer phases.