Mechanical Engineering / Makina Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4129
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Research Project Kompozit aluminyum köpük malzemesinin hazırlanması ve mekanik özelliklerinin karakterizasyonu(TÜBİTAK - Türkiye Bilimsel ve Teknolojik Araştırma Kurumu, 2001) Yılmaz, Selahattin; Güden, Mustafa; Elbir, SemihBu 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.Article Citation - WoS: 3Validation on of Local Thermal Equilibrium and Uniform Pressure Assumptions for an Isobaric Adsorption Process in an Adsorbent Bed(Türk Isı Bilimi ve Tekniği Derneği, 2016) Gediz İliş, Gamze; Mobedi, Moghtada; Ülkü, SemraBu çalışmanın amacı, adsorbent yatakta ısı ve kütle transferini analiz etmek için kullanılan yerel ısıl denge ve sabit basınç yaklaşımı varsayımların geçerliliğini araştırmaktır. İçerisinde silika jel partikülleri içeren bir yatak ile su kabı olan bir deney düzeneği tasarlanmış ve adsorpsiyon sürecinde yatağın içinde farklı yerlerde yerel sıcaklık ve basınç ölçülmüştür. Ayrıca, sabit basınç yaklaşımı ve yerel ısıl denge varsayımlara dayalı ısı ve kütle transferi denklemleri çözülmüştür. Sayısal sonuçlar, ilgili deneysel sonuçlarla karşılaştırılmış ve aralarında oldukça iyi bir uyum tespit edilmiştir. Gerçekleştirilen karşılaştırmaya dayanarak, incelenen yatak için iki önemli sonuç şu şekildedir: a) katı madde ve su buharı arasında yerel ısıl denge bulunmaktadır, b) bir yatak içinde parçacıklar arası kütle transferi direnci ihmal edilebilir düzeyde olup konsantrasyonunun ve sıcaklığın belirlenmesi için sabit basınç yaklaşımı geçerlidir. Ayrıca, bu çalışmada sunulan deneysel sonuçlar diğer araştırmacıların sayısal çalışmalarının geçerliliğini doğtulamak için değerli veriler sağlayacaktır.Article Citation - WoS: 25Citation - Scopus: 26Lowering the Sintering Temperature of Solid Oxide Fuel Cell Electrolytes by Infiltration(Elsevier Ltd., 2019) Sındıraç, Can; Çakırlar, Seda; Büyükaksoy, Aligül; Akkurt, SedatA dense electrolyte with a relative density of over 95% is vital to prevent gas leakage and thus the achievement of high open circuit voltage in solid oxide fuel cells (SOFCs). The densification process of ceria based electrolyte requires high temperatures heat treatment (i.e. 1400-1500 degrees C). Thus, the minimum co-sintering temperatures of the anode-electrode bilayers are fixed at these values, resulting in coarse anode microstructures and consequently poor performance. The main purpose of this study is to densify gadolinia doped ceria (GDC), a common SOFC electrolyte, at temperatures lower than 1400 degrees C. By this aim, an approach involving the infiltration of polymeric precursors into porous electrolyte scaffolds, a method commonly used for composite SOFC electrodes, is proposed. By infiltrating polymeric precursors of GDC into porous GDC scaffolds, a reduction in the sintering temperature by at least 200 degrees C is achieved with no additives that might affect the electrical properties. Energy dispersive x-ray spectroscopy line scan analyses performed on porous GDC scaffolds infiltrated by a marker solution (polymeric FeOx precursor in this case) reveals a homogeneous infiltrated phase distribution, demonstrating the effectiveness of polymeric precursors.Article Citation - WoS: 55Citation - Scopus: 60Effect of Regeneration Temperature on Adsorption Equilibria and Mass Diffusivity of Zeolite 13x-Water Pair(Elsevier Ltd., 2016) Sayılgan, Şefika Çağla; Mobedi, Moghtada; Ülkü, SemraThe adsorption equilibrium and mass diffusivity of zeolite 13X-water pair for different adsorption and regeneration temperatures were determined by a homemade volumetric system. The isotherms of the zeolite 13X-water pair were obtained by collecting pressure versus time data and applying ideal gas law. The effective diffusivity of the pair was calculated by using long term analytical solution of mass diffusivity based on Fick's law. The experimental study showed that the adsorption capacity of zeolite 13X-water pair was 23% (kg/kg), 21% (kg/kg) and 19% (kg/kg) when the adsorption temperature was 35, 45 and 60 °C respectively for the desorption temperature of 90 °C. Furthermore, the adsorption capacity increased from 22% (kg/kg) to 24% (kg/kg) when the desorption temperature was increased from 90 °C to 150 °C. It was observed that the present adsorption equilibrium results were compatible with the reported results in the literature. The mass diffusivity of the pair was found in the range of 4 × 10-9-6 × 10-8 m2/s for the long time period when the initial adsorptive pressure was 2000 Pa. The effective mass diffusivity depends on concentration and it was decreased with increasing adsorbate concentration.Book International Porous and Powder Materials Symposium and Exhibition Ppm 2015, 15-18 September 2015, Izmir-Turkey(Organizing Committee of the International Porous and Powder Materials Symposium and Exhibition, 2015) Polat, Mehmet; Tanoğlu, Metin; Kılıç Özdemir, Sevgi; Polat, Mehmet; Tanoğlu, MetinWe welcome you to the International Porous and Powder Materials Symposium and Exhibition, PPM 2015. The foreword of the proceedings and the abstracts books of the previous symposium, PPM 2013 which was the first of its series, started with the following sentence: ‘Idea of organizing a symposium on porous and powder materials owes its germination to the curiosity about the “other side of the fence”.’ It was a very fitting and almost a prophetic statement because 700 participants from 50 countries hosted by PPM 2013 belonged to an incredibly wide spectrum of science and technology, who one way or another dealt with porous and powder materials. It was both a fascinating and engaging sight to have people from the cement industry sitting in the sessions related to Biological and Medical Aspects since they realized that a characterization technique used in this field may actually answer some questions in theirs. Do we not deal with the same basic questions when we truly try to understand a material no matter where it originates from or how it is being put into application?Book International Porous and Powder Materials Symposium and Exhibition Ppm 2013, 3-6 September 2013, Çeşme Izmir-Turkey(Organizing Committee of the International Porous and Powder Materials Symposium and Exhibition, 2013) Özdemir, Sevgi Kılıç; Polat, Mehmet; Tanoğlu, Metin; Kılıç Özdemir, Sevgi; Polat, Mehmet; Tanoğlu, MetinWe welcome you to the first of the International Porous and Powder Materials Symposium and Exhibition, PPM 2013. The idea of organizing a symposium on porous and powder materials owes its germination to the curiosity about the ‘other side of the fence’. We are all familiar of the mild surprise when we come accross with a research paper from a totaly unrelated field written in a completely different terminology but describing something pleasantly familiar. Just imagine the elation of a PhD student in ceramics who is trying to optimize the stability and plasticity of the green body reading about the double layer around a protein, of an environmental engineer who is attempting to flocculate a nasty sludge coming accross with the concept of aggregation of micellar structures or of a researcher in chemical engineering who is looking for the perfect catalyst seeing the SEM pictures of porous nanoparticles developed for drug delivery. The list could be extended with much better examples by the readers of this book. But the best set of words to describe these feelings is an awareness of wholeness and solidarity.Article Citation - WoS: 11Citation - Scopus: 11Comparison of Uniform and Non-Uniform Pressure Approaches Used To Analyze an Adsorption Process in a Closed Type Adsorbent Bed(Springer Verlag, 2013) Gediz İliş, Gamze; Mobedi, Moghtada; Ülkü, SemraHeat and mass transfer in an annular adsorbent bed filled with silica gel particles is numerically analyzed by uniform and non-uniform pressure approaches. The study is performed for silica gel-water pair, particle radius from 0.025 to 1 mm and two bed radii of 10 and 40 mm. For uniform pressure approach, the energy equation for the bed and the mass transfer equation for the particle are solved. For non-uniform pressure approach, the continuity and Darcy equations due to the motion of water vapor in the bed are added, and four coupled partial differential equations are solved. The changes of the adsorbate concentration, pressure, and temperature in the bed throughout the adsorption process for both approaches are obtained and compared. The obtained results showed that the particle size plays an important role on the validity of uniform pressure approach. Due to the interparticle mass transfer resistance, there is a considerable difference between the results of the uniform pressure and non-uniform pressure approaches for the beds with small size of particles such as 0.025 mm.Article Citation - WoS: 4Citation - Scopus: 4Effects of Catalyst Precursor Type and Preparation Conditions, and Solvent Type on Activity and Selectivity of Pt/Sio2 Catalyst in Citral Hydrogenation(Walter de Gruyter GmbH, 2011) Depboylu, Can Okan; Yılmaz, Selahattin; Akkurt, SedatIn this study, citral hydrogenation reaction in liquid phase over silica gel supported Pt catalysts was investigated. It was desired to hydrogenate carbonyl group selectively to produce valuable unsaturated alcohols, namely geraniol and nerol. Pt/SiO2 catalysts were prepared by impregnation method. The effects of parameters investigated in the present study included Pt precursor type (hexachloroplatinic acid (HCLPA), platinum II acetylacetonate (PAA)), catalyst activation temperature (350°C and 450°C), catalyst activation without calcination, catalyst washing with 0.1 M NaOH and solvent type (ethanol, 2-pentanol). The catalysts activities and selectivities were affected by the type of precursor and activation temperature. The maximum citral conversion (89.50 percent) was achieved at lower activation temperature (350°C) with PAA precursor based catalyst. It was observed that higher activation temperature provided lower citral conversion but higher selectivity to unsaturated alcohols; increasing the activation temperature to 450°C decreased citral conversion to 26.10 percent. But selectivity to unsaturated alcohols, geraniol and nerol, increased from 7.06 to 54.60 percent. Catalyst washing and 2-pentanol prevented acetal formation. Catalyst activation without calcination gave lower citral conversion (20.84 percent) and selectivity to unsaturated alcohols (30.00 percent). Copyright © 2011 The Berkeley Electronic Press. All rights reserved.Article Citation - WoS: 23Citation - Scopus: 25Microcalorimetric Investigation of Water Vapor Adsorption on Silica Gel(Springer Verlag, 2011) Demir, Hasan; Mobedi, Moghtada; Ülkü, SemraWater vapor adsorption on silica gel was investigated using Tian-Calvet-type microcalorimetry. Differential heat of adsorption data was obtained. The setup of microcalorimetry was used volumetric system to determine adsorption isotherms of water vapor-silica gel. The Langmuir model was used in the interpretation of the adsorption data. The Clausius-Clapeyron diagram was also given. Effective mass diffusivity of water vapor in the silica gel particle as a function of temperature was also determined. The silica gel, which was degassed under vacuum at 10 -7 mbar and 120 °C for 18 h, was found to adsorb 0.6, 0.98, 1.1, 1.4, 2, 3.5, 11, 13, and 14 wt% water vapor at 120, 110, 100, 90, 75, 60, 40, 35, and 30 °C, respectively. The diffusivities of water vapor inside the silica gel for short- and long-range periods were described using kinetics data as a function of temperature in the Arrhenius form.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.