Chemical Engineering / Kimya Mühendisliği

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

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Now showing 1 - 20 of 657

Citation - WoS: 10
Citation - Scopus: 11
Use of Clinoptilolite in Ethanol Dehydration
(Taylor and Francis Ltd., 1996) Tıhmınlıoğlu, Funda; Ülkü, Semra
Clinoptilolite-type natural zeolite, which exists in various regions of Turkey, has been experimentally studied. For the ethanol-water-local clinoptilolite system, uptake and breakthrough curves were determined under a nitrogen gas atmosphere. In adsorption kinetics and adsorption equilibrium studies, the effects of particle size, temperature and, amount of zeolite on the uptake rate have been investigated. The breakthrough curves for four different flow rates of ethanol and three different bed heights were determined in dynamic column studies. The results of the experiments show that intraparticle diffusion is the main resistance. The local clinoptilolite is a promising adsorbent for water adsorption from aqueous ethanol.
Citation - WoS: 19
Flexible Poly(vinyl Chloride)-Zeolite Composites for Dye Adsorption From Aqueous Solutions
(Taylor and Francis Ltd., 1996) Balköse, Devrim; Ulutan, Sevgi; Çakıcıoğlu Özkan, Seher Fehime; Ülkü, Semra; Köktürk, Uğur
Flexible poly(vinyl chloride) (PVC) composites having natural zeolite clinoptillolite were prepared by plastisol-plastigel technology. Adsoption of methylene blue on each raw material and on composites was studied both from an equilibrium and a rate approach. It was observed that the adsorption capacity of zeolite decreased when it was embedded in composites. The equilibrium uptake of methylene blue increased with an increasing zeolite fraction in composites. Methylene blue was adsorbed from a 0.02 g·cm-3 aqueous solution slowly, but was nearly adsorbed completely with a composite having a 0.3 volume fraction of zeolite. The effective diffusion coefficient of methylene blue in composites was of the order of 10-13 m2·s-1 and decreased with increasing filler fraction.
Citation - WoS: 68
Dry Deposition Fluxes and Mass Size Distributions of Pb, Cu, and Zn Measured in Southern Lake Michigan During Aeolos
(American Chemical Society, 1998) Paode, Rajendra D.; Sofuoğlu, Sait Cemil; Sivadechathep, Jakkris; Noll, Kenneth E.; Holsen, Thomas M.; Keeler, Gerald J.
As part of the Atmospheric Exchange Over Lakes and Oceans Study (AEOLOS) the dry deposition fluxes and atmospheric size distributions (ASDs) of anthropogenic metals were measured over the southern basin of Lake Michigan. The measurements were made during winter, summer, and fall, concurrently, in Chicago, IL; over Lake Michigan onboard the U.S. EPA RV Lake Guardian; and in South Haven, MI. The flux of Pb, Cu, and Zn was substantially higher in Chicago than in either South Haven or over Lake Michigan. The average measured Pb, Cu, and Zn fluxes were 0.07, 0.06, and 0.20 mg m-2 day-1 in Chicago; 0.003, 0.01, and 0.01 mg m-2 day-1 over Lake Michigan; and 0.004, 0.007, and 0.004 mg m-2 day-1 in South Haven. When the wind was from Chicago over the lake, the fluxes and concentrations measured over the lake were higher than when the wind was from other directions. In general, these anthropogenic metals had higher concentrations in the fine particle mode than in the coarse particle mode. Modeled and measured fluxes were in reasonable agreement. Coarse particles were found to be responsible for the majority of the flux at all locations.
Citation - WoS: 20
Dry Deposition Fluxes and Atmospheric Size Distributions of Mass, Al, and Mg Measured in Southern Lake Michigan During Aeolos
(Taylor and Francis Ltd., 1998) Sofuoğlu, Sait Cemil; Paode, Rajendra D.; Sivadechathep, Jakkris; Noll, Kenneth E.; Holsen, Thomas M.; Keeler, Gerald J.
In this study, which was a part of the Atmospheric Exchange Over Lakes and Oceans Study (AEOLOS) investigation, the dry deposition fluxes and atmospheric size distributions (ASDs) of mass and crustal metals (aluminum and magnesium) were measured over the southern basin of Lake Michigan (in Chicago, over Lake Michigan, and in South Haven, Michigan). Airborne crustal metals arise primarily from fugitive dust emissions and are associated with the coarse fraction of atmospheric aerosol. Consequently, they can serve as fingerprints for the atmospheric behavior of fugitive dust. The flux of these metals were substantially higher in Chicago than in either South Haven or over Lake Michigan. The measured average mass, aluminum, and magnesium fluxes were 138, 2.23, and 5.32 mg/m2-day in Chicago, 47.8, 0.24, and 0.28 mg/m2-day over Lake Michigan, and 37.4, 0.17, and 0.12 mg/m2-day in South Haven, respectively. The ASDs of crustal metals measured in Chicago had higher concentrations of coarse particles than ASDs measured over Lake Michigan and in South Haven. The calculated flux of metals using a multistep model and dry deposition velocities obtained from the Sehmel-Hodgson model were in general agreement with measured fluxes of crustal metals. Particles >10 μm were found to be responsible for the majority of the flux.
Citation - WoS: 11
Citation - Scopus: 14
A Study of Adsorption of Water Vapour on Wool Under Static and Dynamic Conditions
(Springer Verlag, 1998-01) Ülkü, Semra; Balköse, Devrim; Çağa, Tayfun; Özkan, Fehime; Ulutan, Sevgi
Adsorption of water vapour on wool provides not only textile comfort, but also convenience in transportation due to increase in its bulk density. The adsorption and desorption isotherms of water vapour for wool were determined by both volumetric technique using a Coulter Omnisorp 100CX instrument and gravimetric method employing a Cahn 2000 electronic microbalance. Adsorption isotherm fitting to B.E.T. model and hysteresis on desorption was observed. The average effective diffusion coefficient of water in wool was found to be 8.4 × 10-14 m2 s-1 at 25°C from gravimetric data. The effects of packing height and air velocity on the breakthrough curves were also investigated in the wool packed columns. For pseudo first order model, k values changing between 0.33 × 10-6 -69 × 10-6 s-1 was obtained for 2.2-6.4 cm s-1 air velocity and 0.05-0.20 m packing height ranges.
Citation - WoS: 12
Citation - Scopus: 17
Dynamics of Water Vapor Adsorption on Humidity-Indicating Silica Gel
(Elsevier Ltd., 1998-09) Balköse, Devrim; Ulutan, Sevgi; Çakıcıoğlu Özkan, Seher Fehime; Çelebi, Sedat; Ülkü, Semra
Well-defined CoCl2-containing silica gels were prepared by impregnation of the aqueous solution of the salt to silica hydrogel, drying and aging methods. Silica gels having 392-437 m2 g-1 surface area and 0.21-0.37 cm3 g-1 pore volume and having an average particle size of 3 mm were obtained. Aging in CoCl2 solutions decreased the surface area of silica gels from 540 cm2 g-1 to 392-430 m2 g-1 and pore volume from 0.27 to 0.21-0.23 cm3 g-1 for CoCl2 concentration smaller than 0.28 mol dm-3 in silica gel. Adsorbed water desorbed from the gels absorbing 1917-2555 J g-1 energy as determined by differential scanning calorimetry. The CoCl2-containing gels were successfully used in dynamic column experiments, with linear relation between velocities of inlet air and movement of blue to pink boundary. The colour change also makes the detection of the defects in column filling which causes air channelling
Citation - WoS: 18
Citation - Scopus: 22
Application of Inverse Gas Chromatography To the Measurement of Diffusion and Phase Equilibria in Polyacrylate-Solvent Systems
(Elsevier Ltd., 1999) Tıhmınlıoğlu, Funda; Danner, Ronald P.
The inverse gas chromatography technique (IGC) was used to determine the partition and diffusion coefficients of ethyl acetate and 2-ethylhexyl acrylate in polyacrylate for both infinite dilution and finite concentrations of solvent. Experiments were performed over a temperature range of 60 to 100°C, more than 100°C above the glass transition temperature of the polymer. The capillary column IGC model previously developed for determining partition and diffusion coefficients of infinitely dilute solvent has been modified to account for the concentration of the solvent in the polymer phase. Thermodynamic data obtained from retention theory and the modified capillary column IGC model are compared
Citation - WoS: 14
Citation - Scopus: 16
Modeling of Diffusion in Closed Cell Polymeric Foams
(SAGE Publications Inc., 1999-05) 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.
Citation - WoS: 23
Citation - Scopus: 24
Processing of Polymers With Supercritical Fluids
(John Wiley and Sons Inc., 1999-11) Alsoy Altınkaya, Sacide; Duda, John Larry
The 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.
Solunabilir Tozun Su Spreyleri Kullanılarak Bastırılmasında Son Gelişmeler
(2000) Polat, Hürriyet; Polat, Mehmet; Gürgen, Sabit
Türkiye'de görülen meslek hastalıklarının çoğunu tozun solunmasından kaynaklanan pnömokonyoz oluşturmaktadır. Bu yazının amacı, yeraltı ocaklarında işçi sağlığı açısından sakıncalı olan havada asılı tozların, su spreyleri kullanılarak bastırılması konusunda gelinen aşamayı sunmaktır. Bu amaçla, havada asılı toz ve su damlalarıyla yapılan detaylı çalışmalar ışığında, sprey suyuna katılan yüzey aktif maddelerin istenen verim artışını sağlayamama nedenleri ele alınmakta ve su spreylerinin Türkiye'deki maden ocaklarında kullanım olanakları tartışılmaktadır.
Effect of Some Physical, and Chemical Variables on Flocculation and Sediment Behaviour
(A.A. Balkema Publishers, 2000) Polat, Hürriyet; Polat, Mehmet; İpekoğlu, Üner
Effect of some chemical and physical variables on the settling rate, final sediment height, sediment viscosity and supernatant turbidity of a clay sample was studied using various polyacrylamide type flocculants. Increasing flocculant concentration significantly increased both the settling rate and sediment viscosity. More importantly, changes in the final sediment, height, hence the packing density, was minimal for all the conditions tested once the sediment was allowed to consolidate. Also, the mode of addition of the polymer, at once or continuous, did not seem to affect any of the parameters measured. Conditioning time seemed to alter the settling rate at low polymer concentrations, but had no effect at high polymer concentrations. However, increasing the conditioning time caused a decrease in the sediment viscosity. Different types of the polyacrylimides generated different settling rates at a given concentration, but the final sediment height was nearly independent of polymer type.
Predicting Drying in Solvent-Coated Polymeric Films
(American Chemical Society, 2000) Alsoy Altınkaya, Sacide; Duda, John Larry
[No abstract available]
Citation - WoS: 30
Citation - Scopus: 30
The Effect of Sb Substitution of Cu in Bi1.7pb0.3sr2ca2cu 3-Xsbxoy Superconductors
(John Wiley and Sons Inc., 2000-02) Kocabaş, Kemal; Çiftçioğlu, Muhsin
The effect of partial substitution of Cu in Bi1.7Pb0.3Sr2Ca2Cu 3-xSbxOy at x = 0.0, 0.05, 0.1, 0.15, and 0.2 levels on the electrical and structural properties was investigated in this work. X-ray diffraction analysis shows that these materials have a multiphase structure. Two different types of particles with different morphologies were observed in scanning electron micrographs. The Tc values decreased from 103.5 to 87 K for x = 0.1 Sb substitution level with a subsequent increase to 101 K at x = 0.2.
Citation - WoS: 17
Citation - Scopus: 18
Solvent Diffusion in Amorphous Polymers: Polystyrene-Solvent Systems
(John Wiley and Sons Inc., 2000-08) Tıhmınlıoğlu, Funda; Danner, Ronald P.
The inverse gas chromatography (IGC) technique was used to obtain the partition and diffusion coefficients of solvents in polystyrene over a wide range of temperatures. Infinite dilution experiments were performed with three solvents: toluene, benzene, and hexane. Finite concentration data were measured for the polystyrene-toluene system at various concentrations from 110 to 180 °C. For the finite concentration region, the modified capillary column model used by Tihminlioglu and Danner (J Chromatogr A 1999, 845, 93-101) was used to calculate diffusion and thermodynamic data. Finite concentration thermodynamic data were also calculated with the retention theory approach and compared with the capillary column model. The experimental IGC results are in good agreement with data from other experimental techniques.
Citation - WoS: 19
Citation - Scopus: 20
Solvent Diffusion in Amorphous Polymers: Polyvinyl Acetate-Toluene System
(John Wiley and Sons Inc., 2000-09) Tıhmınlıoğlu, Funda; Danner, Ronald P.; Lützow, Norbert; Duda, John Larry
In a previous publication (Tihminlioglu et al., J Polym Sci Part B: Polym Phys 1997, 35, 1279), we presented an extensive analysis of the polyvinyl acetate-toluene system. The inverse gas chromatography (IGC) technique was used to measure phase equilibria and diffusion coefficients above and near the glass-transition temperature of a polymer. At temperatures above the glass transition, the capillary column model developed by Pawlisch et al. (Macromolecules 1987, 20, 1564) was used. For the finite concentration region, the modified model of Tihminlioglu and Danner (J Chromatogr A 1999, 845, 93) was applied. Data obtained with the IGC method were in agreement with data measured with the gravimetric and piezoelectric sorption techniques. In this work, we revisit the partition coefficient issue and provide some new data at lower temperatures. At temperatures near the glass-transition temperature, the modification of the capillary column model proposed by Vrentas et al. (Macromolecules 1993, 26, 6670) was used for the infinite dilution region. The diffusion data correlated well with the Vrentas-Duda free-volume model.
Citation - WoS: 65
Overall Elemental Dry Deposition Velocities Measured Around Lake Michigan
(Elsevier Ltd., 2001) Yi, Seung-Muk; Shahin, Usama; Sivadechathep, Jakkris; Sofuoğlu, Sait Cemil; Holsen, Thomas M.
Overall dry deposition velocities of several elements were determined by dividing measured fluxes by measured airborne concentrations in different particle size ranges. The dry deposition measurements were made with a smooth surrogate surface on an automated dry deposition sampler (Eagle II) and the ambient particle concentrations were measured with a dichotomous sampler. These long-term measurements were made in Chicago, IL, South Haven, MI, and Sleeping Bear Dunes, MI, from December 1993 through October 1995 as part of the Lake Michigan Mass Balance Study. In general, the dry deposition fluxes of elements were highly correlated with coarse particle concentrations, slightly less well correlated with total particle concentrations, and least well correlated with fine particle concentrations. The calculated overall dry deposition velocities obtained using coarse particle concentrations varied from approximately 12 cm s−1 for Mg in Chicago to 0.2 cm s−1 for some primarily anthropogenic metals at the more remote sites. The velocities calculated using total particle concentrations were slightly lower. The crustal elements (Mg, Al, and Mn) had higher deposition velocities than anthropogenic elements (V, Cr, Cu, Zn, Mo, Ba and Pb). For crustal elements, overall dry deposition velocities were higher in Chicago than at the other sites.
Kompozit aluminyum köpük malzemesinin hazırlanması ve mekanik özelliklerinin karakterizasyonu
(TÜBİTAK - Türkiye Bilimsel ve Teknolojik Araştırma Kurumu, 2001) Yılmaz, Selahattin; Güden, Mustafa; Elbir, Semih
Bu projede SiC tozları (SiCt), Sic viskerları (SiCv kıl kristal) ve granule Al2O3 tozları (Al2O3g) ayrı ayrı Alüminyum ile karşılaştırılarak metal matriks kompozit (MMK) köpükler hazırlanmıştır. Matriks malzemesi olarak Alüminyum seçilmiştir. TiH2 tozları şişirici ajan olarak kullanılmışlardır.MMK köpükler toz metallurji tekniği ile hazırlanmıştır. Matriks, şişirici alan (%0.5%)ve takviye malzemesi (SiCt veya SiCv veya Al2O3g) iyice karıştırıldıktan sonra, sıcak preste 450circ C ve 200 MPa basınç altında sıkıştırılmaktadır. (%99 Relative yoğunluk) Burda yarı mamül olarak tanımlayabileceğimiz tabletler elde edilmketedir. Yarı mamül matriks malzemesinin erime sıcaklığının üstünde bir sıcaklığa (750 - 850circ C) kadar ısıtılmış bir fırına konmaktadır. Bu sıcaklıklarda, TiH2 bozunması ile açığa çıkan H2 gazları metal içerisinde genleşmekte ve metalin içinde gaz hücrelerinin oluşmasını (köpükleşme) sağlamaktadır. Köpükleşen malzeme fırından çıkarılarak hızlıca soğutulmaktadır. Bu yöntem izlenerek MMK köpükler üretilmiştir. Fırın sıcaklığı ve fırında kalma süresi parametre olarak çalışılmıştır. MMK köpükler malzemeler darbe enerjisini emme için kullanılabilirler. Sonuç olarak Aluminyum köpüklerden daha yüksek enerji emme kapasitesine sahip MMK köpükler hazırlanmıştır.
Citation - WoS: 23
Citation - Scopus: 25
Mass Transfer Coefficients for Polycyclic Aromatic Hydrocarbons (pahs) To the Water Surface Sampler: Comparison To Modeled Results
(Elsevier Ltd., 2001-03) Odabaşı, Mustafa; Sofuoğlu, Aysun; Holsen, Thomas M.
A sampling program was conducted between June and October 1995 in Chicago, IL using a modified water surface sampler (WSS) and dry deposition plates to measure the particulate dry deposition and gas exchange of PAHs. Oxygen transfer experiments were also conducted to evaluate the collection properties of the WSS for gas-phase compounds. Gas-phase fluxes were determined by subtracting the dry deposition plate fluxes (particulate) from WSS fluxes (particulate+gas). These fluxes were divided by concurrently measured ambient concentrations to obtain overall gas phase mass transfer coefficients. Two different two-film models, one developed based on experiments performed with the WSS and, one previously published, were compared to these results. Experimentally determined average gas phase overall mass transfer coefficient (Kg) for seven PAHs was 0.74±0.52cms-1. Experimental Kg values agreed well with those predicted by the model developed for WSS. The values predicted by previously proposed models were within a factor of 3 of the experimental ones.
Citation - WoS: 19
Citation - Scopus: 18
Predicting Drying in Multiple-Zone Ovens
(American Chemical Society, 2001-07) Alsoy Altınkaya, Sacide
In the coating industry, the drying of solvent-coated polymeric films takes place in convected heated dryers, which usually consist of a series of zones. The operating conditions of airflow, solvent partial pressure(s), and temperature at the entrance of each zone are chosen to minimize the drying time while maintaining an acceptable product quality. In this work, the drying behavior of polymer solutions in such oven configurations is predicted from binary and multicomponent drying models. Both models involve coupled heat- and mass-transfer equations that describe the changes in the concentration of each solvent, the temperature, and the thickness of the film throughout the drying. The model equations become highly nonlinear because of the strong and complicated concentration and temperature dependencies of the thermodynamic and transport properties of polymer solutions. These nonlinear equations are solved numerically using the finite difference approximation. The solutions show that multiple-zone ovens can be used to eliminate bubble formation and to minimize the residual solvent content by controlling the operating conditions individually or simultaneously.
Citation - WoS: 22
Citation - Scopus: 22
Onsager consistency checks for multicomponent diffusion models
(John Wiley and Sons Inc., 2001-07) Zielinski, John M.; Alsoy Altınkaya, Sacide
The Onsager reciprocity relations are applied to several recently proposed multicomponent diffusion models in an attempt to gauge their validity and ascertain their applicability. Each of these friction-based diffusion models stems from the more general Bearman formalism through various assumptions regarding the individual friction coefficients. By assessing the compliance of the Bearman model with respect to the Onsager relations, we ascertain the validity of the simplifications introduced to each diffusion model and suggest which postulates lead to results consistent with the Onsager relations. Although some models are not consistent with the Onsager relations, each model predicts the multicomponent drying of polymer films reasonably well. The necessity for consistency with the Onsager development is, therefore, revisited.

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