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Öğe A numerical study of mixed convection heat transfer in a lid-driven cavity using $Al_2O_3$-water nanofluid(2020) Çakmak, Neşe Keklikcioğlu; Durmazuçar, Hasan Hüseyin; Yapıcı, KerimThis study aims a numerical investigation of steady, laminar mixed convection heat transfer in a two-dimensional cavity by employing a finite volume method with a fourth-order approximation of convective terms, when nanoparticles are present. With the aim of solving two-dimensional momentum and energy conservation equations, a finite volume method on a non-uniform staggered grid is utilized. Second-order central differences are utilized to approximate diffusion terms in momentum and energy equations, while the development of a non-uniform four-point fourth-order interpolation (FPFOI) scheme is performed for the convective terms. Continuity and momentum equations are solved using the SIMPLE (SemiImplicit Method for Pressure-Linked Equation) algorithm. In order to evaluate heat transfer enhancement, various viscosity and thermal conductivity models were employed. Numerical solution results were obtained in different models in cases where Gr number is between $10^3 and 10^5$ , Re number is 10-100-1000 and nanoparticle volumetric fraction is 0-5%.Öğe A numerical study of the natural convection of Al2O3-EG nanofluid in a square enclosure and impacts and a comparison of various viscosity and thermal conductivity models(2021) Çakmak, Neşe Keklikcioğlu; Durmazuçar, Hasan Hüseyin; Yapıcı, KerimIn the current study, heat transfer enhancement in an enclosure was investigated by utilizing Al2O3-EG nanofluid. In the numerical solutions, the solid-liquid mixture equations were applied for theenclosure that composed alumina-ethylene glycol nanofluid, in terms of the two-dimensionalbuoyancy-driven convection. Various viscosity and thermal conductivity models were utilized forthe purpose of assessing heat transfer improvement. The purpose of this study was to reveal theimpacts caused by uncertainties in the viscosity and thermal conductivity of the nanofluid onlaminar natural convection heat transfer occurring in a square enclosure. The temperatures of theright and left vertical walls of the enclosure were kept constant as Tc and Th, respectively, whereasthe thermal insulation of the other walls was performed. The discretization of the governingequations was performed by utilizing the finite volume method and the SIMPLE algorithm.Calculations were made for the Rayleigh number (103-106) and the volume fraction of aluminananoparticles, ?= 0-5%. In this study, many parameters affecting heat transfer by naturalconvection were investigated in the enclosure containing Al2O3-EG nanofluid, and it was foundthat nanofluid viscosity was the most efficient factor for heat transfer rate.Öğe Cytotoxic activity of zinc oxide/titanium dioxide nanoparticles on prostate cancer cells(2019) Taş, Ayça; Çakmak, Neşe Keklikcioğlu; Agbektas, Tugba; Siliğ, YavuzProstate cancer is caused by uncontrolled growth of cells in the prostate gland. The aim of this study was to determine the cytotoxic activity of titanium dioxide (TiO2) and zinc oxide (ZnO) nanoparticles (NPs) and TiO2 + ZnO nanocomposite (NC) in human prostate cancer cell line (DU-145) and healthy mouse fibroblast cell line (L-929). In the study, TiO2 and ZnO NPs and TiO2 + ZnO NC were synthesized. Cytotoxic activities of NC and NPs was then analyzed in human prostate cancer cell line (DU-145) and healthy mouse fibroblast cell lines (L-929) using the MTT method. TiO2, ZnO and TiO2 + ZnO IC50 values were determined in DU-145 and L-929 cell cells (n = 6). TiO2 + ZnO NC in the Du-145 cell line was found as the most active, having statistically significant (***p < 0.0001, **p ? 0.001 and **p ? 0.01).Öğe Does dietary intake of acrylamide affect hydroxyproline levels? an animal study(2022) Agbektas, Tugba; Pazarcı, Özhan; Taş, Ayça; Çakmak, Neşe Keklikcioğlu; Kılınç, Seyran; Siliğ, YavuzAcrylamide is a chemical that occurs due to high temperatures during cooking. It consists of an amino acid found in foods and sugars. Studies have shown that cancer formation occurs within the scope of oxidant reagents and DNA damage due to exposure to acrylamide. Our study aims to examine the effects of dietary acrylamide intake on plasma hydroxyproline levels in rats. In this study, 4 groups were formed with 8 rats in each group (total number=32). Blood samples were collected on days 14 and 28. Acrylamide solution was applied to each rat in the treatment group by gastric gavage process at 5 mg/kg three times a week. Hydroxyproline levels in rats’ plasma samples were measured. The median (IQR) hydroxyproline levels were 7.40(2.45) ?g/L in group 1 (14. days control group) and 7.98(3.34) ?g/L in group 2 (14. days acrylamide applied) who received acrylamide. The mean hydroxyproline levels were 7.25(1.96) ?g/L in group 3 (28. days control group) and 9.76(2.64) ?g/L in group 4 (28. days acryl- amide applied) who received acrylamide. No difference was observed between the groups. Dietary acrylamide intake did not have a significant effect on hydroxyproline levels at the application dose and duration in our study.Öğe Removal of Acid Orange 74 from wastewater with TiO2 nanoparticle(2019) Canbaz, Gamze Topal; Çakmak, Neşe Keklikcioğlu; Eroğlu, Atakan; Açıkel, ÜnsalThe use of nanomaterials in wastewater treatment has gained importance. Nano-structuredadsorbents have good adsorption potential due to their properties such as large surface area. In thisstudy, removal of AO74 (Acid Orange 74) from the waters with TiO2 nanoparticles wereinvestigated. TiO2 nanoparticles were synthesized by sol–gel method. The X-ray diffraction(XRD), Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy(FTIR) and Ultraviolet–visible spectroscopy (UV–VIS) spectrometer techniques were used tocharacterize the synthesized products. Stability analysis was performed by zeta potential analysis.The anatase phase of the TiO2 nanoparticles was confirmed by XRD analysis. The SEMmicrographs revealed the spherical-like morphology with average diameter of about 32 nm whichagrees with XRD results. FTIR spectra show the vibrational mode of TiO2 around 600 cm-1.Absorption peak in the UV region at 320 nm are observed. This peak is characteristics of nanosized TiO2nanoparticles. If the measured zeta potential absolute value is greater than 35 mV, it canbe said that the produced nanofluid is stable. The zeta potential value greater than 35 mV in allmeasurements in this study, so that the synthesized TiO2 nanoparticle is stable in the fluidmedium. pH (2-5), contact time (10-120 min) and initial dye concentration (20-100 mg / L) wereinvestigated to determine the adsorption potential of TiO2 nanoparticles. The optimum parametersfor adsorption of AO74 were determined as pH and contact time, respectively: 5 and 75 minutes.The adsorption system is compatible with Langmuir and Freundlich isotherms. As a result, TiO2nanoparticles were identified as suitable adsorbent for removal of AO74.Öğe SYNTHESIS AND CHARACTERIZATION OF ETHYLENE PROPYLENE DIENE MONOMER (EPDM) RUBBER MIXTURE(2019) Çakmak, Neşe Keklikcioğlu; Engin, YahyaRubbers have a wide range of usage in polymeric materials since materials with a wide variety of mechanicalproperties can be obtained by varying the type or addition rates of the materials contained in the rubber inaddition to the important properties such as high elasticity, good abrasion resistance, and low deformation. Highperformance properties of the material are provided by cross-linking (vulcanization). Raw rubbers do not containcross-links. In this study, it was aimed to examine the changes that may occur in the mechanical properties of thenewly prepared EPDM rubber by changing the composition of the available Ethylene Propylene Diene Monomer(EPDM) rubber. For this purpose, a new rubber mixture, of which composition had been previously known andwhich was developed in this study, was prepared in two different Banbury mixers (tangential and intermeshingtypes), and both samples were subjected to mechanical and rheological analyses. The most important criteria inmechanical properties are tensile strength and elongation at break. As these properties increase, the final productbecomes more durable. When tensile strength and elongation at break of the EPDM rubber prepared according tothe new formulation were compared with the available EPDM rubber, a significant increase was observed inthese two values in the EPDM rubber sample prepared with the new formula. In conclusion, it was shown withthe characterization analyses that the newly developed modified EPDM rubber can be used in the rubberindustry.Öğe Synthesis and stability analysis of folic acid-graphene oxide nanoparticles for drug delivery and targeted cancer therapies(2019) Çakmak, Neşe Keklikcioğlu; Küçükyazıcı, Mustafa; Eroğlu, AtakanCancer is the growth and proliferation of damage-ending cells in an uncontrolled or abnormal way.Today, it takes place among the most important health problems around the world and in ourcountry. Surgery, radiotherapy, and chemotherapy are the main treatment methods in cancertreatment. The development of resistance to chemotherapeutic medicines has led scientists toinvestigate this issue as well as the drug’s ability to reach the targeted tumor site and destroyingcancer cells in addition to normal cells. The production of various nanostructures for anticancerdrug development has been one of the most important areas of nanomedicine. Thus, in the presentresearch, the improved Hummers’ method was employed for the synthesis of graphene oxidenanoparticle (NGO), and it was activated by the folic acid (FA) antibody to increase targetingability after attachment of the drug to the nanostructure systems. SEM, FTIR, XRD, UV/Visspectroscopy, and zeta potential analysis were performed for characterization of the products. Thehighest absorbance of the FA-NGO/DIW nanostructures produced at the concentration of 0.01mg/ml-0.05 mg/ml synthesized by the Hummers’ method and in the UV/Vis spectra, peaks at 232nm and 270 nm corresponds to NGO-DIW and FA-NGO/DIW, respectively. The zeta potentialvalue above 35 mV was obtained in all measurements, and the NGO-DIW and NGO-FA-DIWsamples maintained stability for days. These findings are consistent with the few studies in theliterature, and this study will guide future studies in which nanoparticle systems will be directedto the target by binding chemotherapeutic drugs.Öğe TiO2 Nanopartikülü ve TiO2/Aktif Çamur Sentezi ile Sulu Çözeltiden Cu (II) İyonlarının Adsorpsiyonu(2020) Çakmak, Neşe Keklikcioğlu; Canbaz, Gamze TopalSon zamanlarda sulardan ağır metal giderim çalışmaları önem kazanmıştır. Bu amaçla bu çalışmada sulu çözeltiden Cu(II) iyonlarının gideriminde kullanılmak üzere sol-jel yöntemi ile saf TiO2 nanopartikülleri ve TiO2/aktif çamur bileşimisentezlenmiştir. Sentezlenen materyallerin karakterizasyon analizleri; X ışını kırınım analizi (XRD), UV-Visabsorpsiyon spektroskopisi (UV-VIS), taramalı elektron mikroskobu (SEM), enerji dağılım X-ışınları spektroskopisi(EDS) ve Fourier Dönüşümlü Kızılötesi Spektroskopisi (FTIR) teknikleri kullanılarak gerçekleştirilmiştir. TiO2nanopartikülleri ve TiO2/aktif çamur bileşiminin Cu (II) giderim potansiyeli kesikli sistemde incelenmiştir. 25oC’desentezlenen TiO2/aktif çamur bileşimi bakır gideriminde en iyi adsorban olarak belirlenmiştir. Adsorpsiyon sistemininoptimum koşullarını belirlemek amacı ile pH, temas süresi, başlangıç metal iyon derişim gibi parametrelerin etkisiincelenmiştir. Sistemin Langmuir ve Freundlich adsorpsiyon izotermlerine uygunluğu araştırılmış, Langmuir izoterminedaha uygun olduğu belirlenmiş ve sistemin maksimum adsorpsiyon kapasitesi 47.61 mg/g olarak hesaplanmıştır. Enuygun kinetik modeli belirlemek için yapılan çalışmalarda ise adsorpsiyon prosesinin yalancı ikinci dereceden kinetikmodel ile uyum sağladığı gözlenmiştir. Gibbs serbest enerji ve entalpi değerleri ise sistemin kendiliğindengerçekleştiğini ve ekzotermik olduğunu göstermiştir.
