Yüzeyi Fonksiyonelize Edilmiş Nanoparçacıklar ile Kararlı Nanoakışkan Hazırlanması ve Isıl İletkenlik Değişiminin Belirlenmesi

TÜBİTAK MAG Proje01.04.2019Çok çesitli uygulama alanına sahip olan nanoakıskanlar, ısı transferi sistemlerinde, kullanılanakıskanların ısıl iletkenlik katsayısını arttırmak amacıyla baz akıskanın içerisine, ısıl iletkenligiyüksek nano boyutlarda parçacıklar katılmasıyla üretilirler. Nanoakıskanların hazırlanması,hazırlanan nanoakıskanın ısıl iletkenliginin arttırılması her ne kadar basit görünse de çokkarmasık bir sistemdir. Nanoakıskanların ısıl iletkenliginin artması ve ısı transferiuygulamalarında kullanılabilirligi, hazırlanan nanoakıskanın kararlılıgından, viskozitesinekadar birçok önemli parametre ile baglantılıdır. Isıl iletim katsayısı ne kadar artmıs olursaolsun, kararlı olmayan nanoakıskanların kısa sürede çökmesi ve viskozitesinin baz akıskanagöre fazlaca artıs göstermesi, ısı transferi sistemlerinde basınç düsüsüne, korozyona vetıkanıklıklara neden olmaktadır. Tüm bunlar göz önüne alındıgında, hazırlanannanoakıskanların pratikte kullanımı için bu parametrelerin incelenmesi ve birbiri ile olanbaglantılarının ortaya konulması gerekmektedir. Bu projede kararlı nanoakıskanlarınhazırlanması ve ısıl iletkenliklerinin belirlenmesinin yanı sıra bu parametrelerin birbiri ilebaglantısının aydınlatılması hedeflenmistir.Baz akıskan olarak su, etilen glikol (EG) ve kompresör yagı kullanılan bu projede,nanoparçacık olarak farklı yüzey alanlarına sahip grafen nanoplateletler (GNP) ve tek duvarlıkarbon nanotüpler (SWCNT) kullanılmıstır. Nanoakıskan kararlılıgının saglanması amacıyla,polietilen glikol türevi polihedral oligomerik silseskuokzan (PEG-POSS) nanoakıskanlarda ilkkez yüzey aktif madde olarak bu projede kullanılmıstır. Ayrıca hazırlanan akıskanlarınkararlılıgının artması için pH ayarlaması yapılmıstır. SWCNT içeren su bazlı nanoakıskanlarınhazırlanmasında 50 dk ve 100 dk olmak üzere iki farklı ultrasonikasyon süresi kullanılarak ısıliletkenlige etkisi incelenmistir. Kararlılık degerlendirmesi için UV-Vis Spektrofotometrisi veZeta Potansiyeli ölçümleri yapılmıstır. Bu projede örneklerin santrifüj edilmesi gibi farklıislemler sayesinde nanoparçacık konsantrasyonunun zeta potansiyeline etkisi basarıylaincelenmistir. Isıl iletkenlik ölçümleri 3-omega yöntemiyle gerçeklestirilmistir. Ayrıca farklıyüzey alanlarına sahip nanoparçacıkların kullanılması, farklı konsantrasyonlarda yüzey aktifmadde kullanımı ve farklı baz akıskanlarla çalısılması; bu örneklerin reolojik davranısı, ısıliletkenlik ve yüzey gerilimi ile temas açısı gibi ısı transferi sistemlerinde önem tasıyanözelliklerinin belirlenmesi ve bu özellikleri etkileyen parametrelerin incelenmesi, bu projeyi çokyönlü ve basarılı bir çalısma haline getirmistir.Nanofluids, which have a wide range of applications, are produced by the addition of nanosizedparticles having high thermal conductivity to the base fluid to increase the thermalconductivity of the fluids used in heat transfer systems. Preparing the nanofluids andincreasing the thermal conductivity of the nanofluid are very complex process. The increase ofthermal conductivity of nanofluids and its usage in heat transfer applications are related withmany important parameters from the stability of the nanofluids to their viscosity. No matter howmuch the thermal conductivity is increased, the rapid sedimentation of unstable nanofluids andthe increase in viscosity of nanofluids over that of the base fluid lead to pressure drop,corrosion, and clogging in heat transfer systems. Considering all these, it is necessary toexamine these parameters and to make connections with each other for the practical use ofprepared nanofluids. In this project, it is aimed to prepare stable nanofluids and determine theirthermal conductivity and to clarify the connection of these parameters.Distilled water, ethylene glycol (EG), and compressor oil were used as base fluid. Graphenenanoplatelets (GNP) with different surface areas and single walled carbon nanotubes(SWCNT) were used as nanoparticles. Polyethylene glycol-derived polyhedral oligomericsilsesquioxane (PEG-POSS) was used for the first time in literature, as a surface active agentin nanofluids in order to ensure their stability. In addition, pH value was adjusted to increasethe stability of the nanofluids. In the preparation of water-based nanofluids containing SWCNT,the effect of two different ultrasonication times, 50 min and 100 min, on thermal conductivitywas investigated. UV-Vis Spectrophotometry and Zeta Potential analyses were performed forstability assessment. In this project, the effect of nanoparticle concentration on zeta potentialhas been studied successfully through different processes such as centrifugation and dilutionof samples. Thermal conductivity measurements were carried out by 3ω method. In additionto the usage of different carbon based nanoparticles, various concentrations of surface activeagent, and 3 different base fluids; studying the other factors (e.g. pH, ultrasonication time etc.)affecting the thermal, rheological, and surface properties of nanofluids in heat transfer systemhas made this project a multi-faceted and successful work.Key Words: GNP, SWCNT, nanofluids, 3ω thermal conductivity, viscosity

Preparation and Performance Testing of SBS Modified Bitumens Reinforced with Halloysite and Sepiolite Nanoclays

In this study, halloysite and sepiolite nanoclays were used to reinforce SBS modified bitumens. The nanoclays used are different from the materials in the literature and have properties such as easy to find, economical and available from local sources. The mixing parameters were determined before production process. The polymer additive SBS was added into base bitumen at 3% and 5%, while the nanoclay additives were added into polymer modified bitumen at 2% and 4% ratios. The morphological structures were investigated under fluorescence microscope. Physical and rheological properties of the samples were compared. The phase separation cases were investigated by storage stability test. Furthermore, rutting performance of samples was measured with zero shear viscosity (ZSV) and multi stress creep recovery (MSCR) test methods.&nbsp;</p

Use of (pet-g) material in mini-scale unmanned surface vehicle (usv) for additive manufacturing

Thisstudy aims to determine the material performance of additive manufacturingmethods, which enable flexible designs against rapidly changing market needswith a high benefit/cost ratio to meet the increasing defense needs ofcountries. In addition, the design of an unmanned surface vehicle (UVS)resistant to sea conditions has been realized and produced by additivemanufacturing. Advantages such as freedom of design, on-site manufacturing, andlow cost in low-volume production have made additive manufacturing methods thefocus of today's production method and research topic. Among the additivemanufacturing methods, Fused Filament Fabrication (FFF) is the mostcost-effective and widely used method. In today's small craft sector, boatsmade of thermoplastic material are replacing metal hulls and thermosettingmatrix composite hull boats day by day. Although composite boats withthermoplastic or thermosetting matrix have limitations in terms of size, it canbe said that they are ideal for small USV. In this study, resistance analysisof the forms of 3 different boats was made with finite element and empiricalmethods. The hull form, which exhibits the lowest resistance value, wasproduced using the FFF method using PETG co-polymer developed fromenvironmentally friendly PET material. Cruise and field tests were carried out.Material performances were determined to be used in the production ofsmall-scale USVs with the FFF method, and the mini-scale USV was produced usingthe PETG material with the FFF method. The suitability of PETG material formarine uses was emphasized.</p

Preparation and Performance Testing of SBS Modified Bitumens Reinforced with Halloysite and Sepiolite Nanoclays

In this study, halloysite and sepiolite nanoclays were used to reinforce SBS modified bitumens. The nanoclays used are different from the materials in the literature and have properties such as easy to find, economical and available from local sources. The mixing parameters were determined before production process. The polymer additive SBS was added into base bitumen at 3% and 5%, while the nanoclay additives were added into polymer modified bitumen at 2% and 4% ratios. The morphological structures were investigated under fluorescence microscope. Physical and rheological properties of the samples were compared. The phase separation cases were investigated by storage stability test. Furthermore, rutting performance of samples was measured with zero shear viscosity (ZSV) and multi stress creep recovery (MSCR) test methods.&nbsp;</p

Melt processing of PHBV for functional fibres: effect of additives on process parameters

The objective of this study is to understand the effects of organic and inorganic additives on melt processing of biodegradable poly(3-hydroxybutyrate-co-valerate) (PHBV) polymer. For this purpose, PHBV compounds including different proportions of titanium dioxide (TiO2) and alpha-cellulose (0.5, 1 and 2%) (w/w) as additive were produced by melt-extrusion. The effect of additives on morphological, thermal and rheological properties was investigated using fluorescence microscopy, scanning electron microscopy, differential scanning calorimetry, thermogravimetric analysis and rheometry. X-ray diffraction and Raman spectroscopy were used to analyse crystal structure changes. Thermal characterization results suggest that the crystallization temperature and the degree of crystallinity increased with increasing additive content which may improve the processability of fibres and increase the tensile properties. The melting point of compounds shifted to higher temperatures and thermal stability slightly enhanced with the insertion of additives. TiO2 reduced the moisture content which can prevent the hydrolysis during extrusion. The morphological analyses revealed the presence of additives and well dispersion of cellulose. The flow behaviour of compounds improved in the presence of additives. As a conclusion, the improved properties of biodegradable polymer compounds are expected to ease the melt-spinning of PHBV fibres

The Use of Stirring Methods for the Production of SiC-Reinforced Aluminum Matrix Composite and Validation Via Simulation Studies

The aim of this study was to investigate the effect of different stirring methods on the mechanical properties of aluminum matrix composites in association with applied and computer-aided simulations. Four kilograms of A356 aluminum alloy was used as the matrix material, and 1wt% silicon carbide (SiC) with an average particle size of 50-56m was used as the additive material. Mechanical, ultrasonic and hybrid (both mechanical and ultrasonic) stirring methods were applied. Mechanical properties were determined by uniaxial tensile testing, and the quality index (QI) was calculated. Compared to the reference sample, QI was increased nearly 34% by using hybrid stirring. In accordance with computational fluid dynamics results, the effectiveness of hybrid stirring was confirmed where SiC particle distribution and dispersion were found to be uniform (homogeneity as 75%). After these detailed investigations, it was found that the optimum properties were obtained by using the hybrid stirring method