Organizational Unit: Mechanical Engineering
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ArticlePublication Metadata only Zinc(II) and cadmium(II) coordination polymers containing phenylenediacetate and 4,4′-azobis(pyridine) ligands: Syntheses, structures, dye adsorption properties and molecular dynamics simulations(Elsevier, 2017) Sezer, G. G.; Arıcı, M.; Fındıkçı, İlknur Eruçar; Yeşilel, O. Z.; Özel, H. U.; Gemici, B. T.; Erer, H.; Mechanical Engineering; FINDIKÇI, Ilknur EruçarTwo new coordination polymers (CPs) – [Zn(µ4-ppda)(µ-abpy)0.5]n(1) and [Cd(μ3-opda)(µ-abpy)0.5(H2O)]n(2) (o/ppda = 1,2/1,4-phenylenediacetate, abpy = 4,4′-azobis(pyridine)) – have been synthesized by using Zn(II)/Cd(II) salts in the presence of o- and p-phenylenediacetic acid and abpy under hydrothermal conditions. Their structures have been characterized by FT-IR spectroscopy, elemental analysis, X-ray powder diffraction and single crystal X-ray diffraction techniques. The structural diversities were observed depending on anionic ligands and metal centers in the synthesized complexes. Complex 1 consists of a 2-fold interpenetrated 3D+3D→3D framework with pcu topology while complex 2 has a 2D structure with sql topology. The adsorption of methylene blue (MB) was studied to examine the potential of the title CPs for removal of dyes from aqueous solution. Molecular dynamics (MD) simulations were also performed to examine diffusion of MB in 1 and 2. Thermal and optical properties of two complexes were also discussed.ArticlePublication Metadata only Subcooled flow boiling heat transfer of γ-Al2O3/water nanofluids in horizontal microtubes and the effect of surface characteristics and nanoparticle deposition(Elsevier, 2017) Karimzadehkhouei, M.; Sezen, M.; Şendur, K.; Mengüç, Mustafa Pınar; Koşar, A.; Mechanical Engineering; MENGÜÇ, Mustafa PınarIn this study, subcooled flow boiling heat transfer characteristics of nanofluids were investigated at micro scale. For this purpose, the effect of γ-Al2O3 (gamma-alumina) nanoparticles with an average solid diameter of 20 nm was considered. In the experiments, various mass fractions were considered in horizontal smooth stainless steel microtubes with inner and outer diameters of ∼502 µm and ∼717 µm, respectively, at mass fluxes of 1200 and 3400 kg m−2 s−1. Nanoparticles were added to distilled water (base fluid) at five mass fractions (low mass fractions 0.05 wt% and 0.2 wt%; high mass fractions 0.5 wt%, 1 wt% and 1.5 wt%). According to our results, subcooled flow boiling heat transfer coefficients for nanofluids with low mass fractions were nearly the same as those of the pure water. However, heat transfer deteriorated for nanofluids with high mass fractions. Observations of dynamic light scattering measurements for low and high mass fractions before and after the experiments revealed that agglomeration of nanoparticles is an important parameter in deterioration of heat transfer at higher concentrations. Besides, Scanning Electron Microscopy images of microtube inner surfaces showed that deposition of nanoparticles and agglomerated nanoparticles on the inner surface of the microtubes also contributed to the heat transfer deterioration at high mass fractions. Generally, the deterioration in heat transfer beyond a specific mass fraction value was linked to the disturbance in the stability of suspended nanoparticles and deposition of nanoparticles upon boiling.ArticlePublication Open Access Unlocking the effect of H2O on CO2 separation performance of promising MOFs using atomically detailed simulations(ACS Publications, 2020-02-19) Fındıkçı, İlknur Eruçar; Keskin, S.; Mechanical Engineering; FINDIKÇI, Ilknur EruçarMetal organic frameworks (MOFs) have been considered as potential adsorbents for adsorption-based CO2/CH4 and CO2/N-2 separations because of their high CO2 selectivities and high working capacities. H2O in flue gas and natural gas streams affects the gas uptake capacities of MOFs. However, the presence of H2O is commonly neglected in high-throughput computational screening studies while assessing the CO2 separation performances of MOFs. In this study, the impact of the presence of H2O on the CO2 separation performances of 13 MOFs that were previously identified as the best adsorbent candidates among several thousands of MOFs was examined. Molecular simulations were used to compute selectivity, working capacity, regenerability, and adsorbent performance score (APS) of MOFs considering separation of binary CO2/CH4, CO2/N-2, and ternary CO2/CH4/H2O and CO2/N-2/H2O mixtures. The results showed that introduction of H2O as the third component into binary CO2/CH4 and CO2/N-2 mixtures significantly affected the adsorbent evaluation metrics of MOFs that have strong affinity toward H2O because of the presence of specific functional groups and/or extra framework anions in the framework. Remarkable increases in CO2/N-2 selectivities of MOFs were observed in the presence of H2O. On the other hand, simulations performed using MOFs that are preloaded with H2O to mimic the exposure of MOFs to humidity prior to gas adsorption revealed drastic decreases in CO2 working capacities and APSs of MOFs both for CO2/CH4 and CO2/N-2 separations. These results will be useful for the design and development of efficient MOF adsorbents for CO2 capture under humid conditions.Conference ObjectPublication Metadata only Advanced slurry formulations for new generation chemical mechanical planarization (CMP) applications(Cambridge University Press, 2012-01) Başım, Gül Bahar; Karagöz, Ayşe; Özdemir, Zeynep; Mechanical Engineering; BAŞIM DOĞAN, Gül Bahar; Karagöz, Ayşe; Özdemir, ZeynepChemical Mechanical Planarization (CMP) is widely used to ensure planarity of metal and dielectric surfaces to enable photolithography and hence multilevel metallization in microelectronics manufacturing. The aim of this study is to establish a fundamental understanding on the dynamic growth of nano-scale protective oxide thin films during CMP to enable the selection of proper oxidizer concentrations for slurry formulations. Tungsten was selected as the model metal film to study the formation of these metal oxide films in various oxidizers and Atomic Force Microscope (AFM) was used to measure the surface roughness of the samples conditioned in the oxidizer environment before and after the CMP was conducted. The affect of surface roughness on wettability of the surfaces were also studied through contact angle measurements on the treated tungsten films. Fourier Transform Infrared Spectroscopy with Attenuated Total Reflectance FTIR/ATR technique in combination with the X-Ray Reflectivity (XRR) were utilized to determine the thicknesses of the oxidized nano films on the tungsten surface. The results were evaluated through the material removal responses reported in the literature for the W-CMP in addition to the comparison of the Pilling-Bedworth ratios of the oxidized nano films to determine the ability of the created oxide film as a self-protective oxide.ArticlePublication Open Access Analysis of sustainable materials for radiative cooling potential of building surfaces(MDPI AG, 2018) Family, Roxana; Mengüç, Mustafa Pınar; Mechanical Engineering; MENGÜÇ, Mustafa Pınar; Family, RoxanaThe main goal of this paper is to explore the radiative cooling and solar heating potential of several materials for the built environment, based on their spectrally-selective properties. A material for solar heating, should have high spectral emissivity/absorptivity in the solar radiation band (within the wavelength range of 0.2-2 m), and low emissivity/absorptivity at longer wavelengths. Radiative cooling applications require high spectral emissivity/absorptivity, within the atmospheric window band (8-13 m), and a low emissivity/absorptivity in other bands. UV-Vis spectrophotometer and FTIR spectroscopy, are used to measure, the spectral absorption/emission spectra of six different types of materials. To evaluate the radiative cooling potential of the samples, the power of cooling is calculated. Heat transfer through most materials is not just a surface phenomenon, but it also needs a volumetric analysis. Therefore, a coupled radiation and conduction heat transfer analysis is used. Results are discussed for the selection of the best materials, for different applications on building surfaces.Conference ObjectPublication Open Access An evaluation of energy efficiency measures in a Turkish campus building for thermal comfort and economic risk(International Building Performance Simulation Association, 2015) Wang, Q.; Öcal, M. Rıfat; Augenbroe, G.; Mengüç, Mustafa Pınar; Özuyar, Pınar Gökçin; Entrepreneurship; Mechanical Engineering; MENGÜÇ, Mustafa Pınar; ÖZUYAR, PinarAs new and retrofitted Turkish buildings adopt stateof-the-art energy efficiency measures, hidden risks associated with compromised thermal comfort and disappointing returns on investment could go unnoticed unless a building is subjected to an uncertainty and risk analysis. Standard deterministic predictions are not sufficient, as they do not capture the effects of uncertainty and variability with regard to local microclimate conditions, physical parameters, and discrepancies in the model formulations, also known as “model form uncertainties”. In this paper, we analyze the impact of uncertainty on the performance of a Turkish campus building. We examine the risk that an energy efficient design that is accepted because of the positive results of a conventional energy simulation, causes unacceptable discomfort and unsatisfactory returns on investment. The results of a comprehensive uncertainty analysis shows that these risks exist in certain areas and not in others. The predicted annual output of PV panels is relatively stable with only minor variability, which justifies the investment in Istanbul. Same with shading devices, which lead to a satisfactory internal rate of return under uncertainty. However, with regard to comfort we find that risks could be substantial. We find that relying completely on occupants opening and closing windows for fresh air with fan coil units maintaining the indoor temperature may lead to an insufficient supply of outdoor air for occupants and a substantial risk of overheating. Overall, the results of the analysis demonstrate that understanding risks is in some cases crucial to make an informed design decision regarding various energy saving design strategies.Conference ObjectPublication Metadata only Influence of warm rolling and aging on the microstructural evolution and mechanical behavior of AZ31 magnesium alloy(American Institute of Physics Inc., 2019) Mısırlı, Mustafa; Ghobadlou, Ali Hosseinzadeh; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Mısırlı, Mustafa; Ghobadlou, Ali HosseinzadehThe microstructural evolution and tensile properties of AZ31 after warm rolling and different aging methods and conditions were investigated. The warm rolling was conducted on the as-received AZ31 after homogenization at 400°C for 3h. The rolled slabs were artificially aged at different temperature of 120°C, 180°C and for various durations. As an alternative approach, stress aging was applied on the samples. The results of tensile tests illustrated that the ultimate tensile strength of the as- received AZ31 after 24h aging at 120°C increased up to 300 MPa with the expense of 5% reduction in elongation. While the ductility of the sample aged at 180°C and 48h increased to 14% with the UTS of 285MPa. Also, the stress aging at 120 °C for only 1h increased the yield strength of as-received sample to over 240 MPa. This points to almost 50% increase in strength thermo-mechanical processing. Microstructural observations revealed that the grain growth firstly decreased the strength of rolled samples while improving the ductility. This is followed by the nucleation of recrystallized grains during ageing enhanced the strength with decent ductility as compared to the rolled samples.Conference ObjectPublication Metadata only Thermal and optical performance of eco-friendly silk fibroin proteins as a cavity encapsulation over LED systems(ASME, 2015) Yuruker, Sevket Umut; Arık, Mehmet; Tamdoğan, Enes; Melikov, R.; Nizamoğlu, Sedat; Press, D. A.; Durak, Ilkem; Mechanical Engineering; ARIK, Mehmet; TAMDOĞAN, Enes; Yuruker, Sevket Umut; Durak, Ilkem; Tamdoğan, EnesThe demand for high power LEDs for illumination applications is increasing. LED package encapsulation is one of most critical materials that affect the optical path of the generated light by LEDs, and may result in lumen degradation. A typical encapsulation material is a mixture of phosphor and a polymer based binder such as silicone. After LED chips are placed at the base of a cavity, phosphor particles are mixed with silicone and carefully placed into the cavity. One of the important technical challenges is to ensure a better thermal conductivity than 0.2 W/m-K of current materials for most of the traditional polymers in SSL applications. In this study, we investigated an unconventional material of the silk fibroin proteins for LED applications, and showed that this biomaterial provides thermal advantages leading to an order of magnitude higher thermal performance than conventional silicones. Silk fibroin is a natural protein and directly extracted from silk cocoons produced by Bombyx mori silkworm. Therefore, it presents a “green” material for photonic applications with its superior properties of biocompatibility and high optical transparency with a minimal absorption. Combining these properties with high thermal performance makes this biomaterial promising for future LED applications. An experimental and computational study to understand the optical and thermal performance is performed. A computational fluid dynamics study with a commercial CFD software was performed and an experimental set-up was developed to validate the computational findings to determine the thermal conductivity of the proposed material.ArticlePublication Metadata only On the low-cycle fatigue behavior of a multi-phase high entropy alloy with enhanced plasticity(Elsevier, 2023-08) Radi, Amin; Sajadifar, S.; Seyedmohammadi, Seyedveghar; Krochmal, M.; Bolender, A.; Wegener, T.; Niendorf, T.; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Radi, Amin; Seyedmohammadi, SeyedvegharA multi-phase non-equiatomic FeCrNiMnCo high entropy alloy (HEA) was fabricated using vacuum induction melting. Thermo-mechanical treatments consisting of cold rolling and annealing at 750 °C and 850 °C were employed to improve the mechanical properties of the HEA in focus. Tensile experiments revealed that yield strength and ultimate tensile strength levels can be enhanced significantly after thermo-mechanical processing (TMP). At the same time, ductility remains at an adequate level. Strain-controlled low-cycle fatigue (LCF) experiments were carried out in order to assess the mechanical properties of this HEA under cyclic loading conditions. At the same strain amplitude, the stress levels of the processed samples were considerably higher than that of the as-received counterpart. Similarly, fatigue lives of the former could surpass the base condition at the strain amplitudes of 0.2% and 0.4%; however, at the higher strain amplitudes, cyclic softening was observed. Electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) results revealed that phase transformation from face-centered cubic (FCC) to body-centered cubic (BCC/B2) took place at a higher occurrence with increasing strain amplitude (0.2% to 0.6%). Furthermore, transmission electron microscopy (TEM) studies confirm that upon tensile deformation additional plasticity mechanisms, i.e., deformation twinning and phase transformation, contribute to the overall mechanical behavior of the multi-phase HEA.ArticlePublication Metadata only Multi-strategy Gaussian Harris hawks optimization for fatigue life of tapered roller bearings(Springer, 2022-12) Abbasi, Ahmad; Firoozi, Behnam; Şendur, Polat; Heidari, A. A.; Tiwari, R.; Mechanical Engineering; ŞENDUR, Polat; Abbasi, Ahmad; Firoozi, BehnamBearing is one of the most fundamental components of rotary machinery, and its fatigue life is a crucial factor in designing. The design optimization of tapered roller bearing (TRB) is a complex design problem because various arrays of designing parameters and functional requirements should be fulfilled. Since there are many design variables and nonlinear constraints, presenting an optimal design of TRBs poses some challenges for metaheuristic algorithms. The Harris hawks optimization (HHO) algorithm is a robust nature-inspired method with unique exploitation and exploration phases due to its time-varying structure. However, this metaheuristic algorithm may still converge to local optima for more challenging problems such as the design of TRBs. Therefore, this study aims to improve the accuracy and efficiency of the shortcomings of this algorithm. The performance of the proposed algorithm is first evaluated for the TRB optimization problem. The TRB optimization design has nine design variables and 26 constraints because of geometrical dimensions and strength conditions. The productivity of the proposed method is compared with diverse metaheuristic algorithms in the literature. The results demonstrate the significant development of dynamic load capacity in comparison to the standard value. Furthermore, the enhanced version of the HHO algorithm presented in this study is benchmarked with various well-known engineering problems. For supplementary materials regarding algorithms in this research, readers can refer to https://aliasgharheidari.com.