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This article presents an experimental study on the torsional behavior of composite tubes subjected to impact loadings. Four types of composite tubes with the winding angle of 30°, 45°, 60°, and 75° ([±30]FW, [±45]FW, [±60]FW, and [±75]FW) were produced with the filament winding method. Besides, a [0,90]PP composite tube was manufactured with the prepreg wrapping technique. After the composite tubes were impacted at 2.5 J, 5.0 J, and 7.5 J, non-impacted and impacted composite tubes were tested under torsional loading. Contact force–deformation curves of impacted tubes are presented. Torsional moment–twist angle relations for both impacted and non-impacted composite tubes were obtained. In addition, front view and side view of the impacted zone of composite tubes are given. The results showed that sample [±60]FW had the best impact performance with regard to absorbed energy. The impacted samples of [±60]FW and [±75]FW had the lowest torsional strength for each energy level.

In this study, mixed convection in a phase change material filled square cavity under the effect of a rotating cylinder was numerically investigated. The vertical walls are kept at constant temperatures while the horizontal walls are adiabatic. The effects of angular rotational speed of the cylinder (between −7.5 and 7.5), vertical location of the cylinder (between 0.25 and 0.75) and two different cylinder sizes (0.05 and 0.1) on the fluid flow and heat transfer were numerically investigated in detail. It was observed that rotating cylinder parameters can be used to control the heat transfer and melting process in the cavity. For angular rotational speed of cylinder at ( ω = 7.5 ) compared to motionless cylinder ( ω = 0 ), average heat transfer enhances by about 22.50 % . The highest value of the average heat transfer for different vertical locations of the cylinder depends on the angular rotational speed of the cylinder. The average Nusselt number increases 10 % when a large cylinder is used compared to smaller one for clockwise rotation of the cylinder and it is 19.8 % for the stationary cylinder configuration.

In the current study, magnetohydrodynamics mixed convective flow of Ag–MgO/water hybrid nanofluid in a triangular shaped partitioned cavity involving a porous layer is numerically investigated by using the finite element method. In the numerical simulation, various effects of pertinent parameters such as Richardson number (between 0.01 and 100), Hartmann number (between 0 and 60), magnetic field inclination angle (between 0 and 90), Darcy number (between $$10^{-4}$$ and $$5 \times 10^{-2}$$ ), location of the vertex of triangular porous region (between 0.2 and 0.8 H) and hybrid nanoparticle solid volume fraction ( $$\phi _1$$ between 0 and 0.01, $$\phi _2$$ between 0 and 0.01) on the fluid flow and convective heat transfer features are examined. It was observed that a large vortex is established below the main vortex near the upper wall for the lowest value Ri number. At the highest magnetic field strength, multi-recirculation flow pattern is seen in the right bottom corner. The average heat transfer enhances with higher values of permeability of the porous medium, magnetic field inclination angle, distance of the porous layer vertex from the hot wall and solid nanoparticle volume fraction of each particles in the hybrid nanofluid. The impact is reverse for higher values of Richardson number and Hartmann number. In the current work, significant changes in the average Nusselt number are obtained by varying the location of the porous medium. The triangular shaped porous compound can be used as an excellent tool for convective heat transfer control.

Purpose This paper aims to numerically examine the mixed convection of SiO2-water nanofluid flow in a three-dimensional (3D) cubic cavity with a conductive partition considering various shapes of the particles (spherical, cylindrical, blade, brick). The purpose is to analyze the effects of various pertinent parameters such as Richardson number (between 0.1 and 10), Hartmann number (between 0 and 10), solid nanoparticle volume fraction (between 0 and 0.04), particle shape (spherical, cylindrical, blade, brick) and different heights and lengths of the conductive partition on the fluid flow and heat transfer characteristics. Design/methodology/approach The numerical simulation was performed by using Galerkin-weighted residual finite element method for various values of Richardson number, Hartmann number, solid nanoparticle volume fraction, particle shape (spherical, cylindrical, blade, brick) and different heights and lengths of the conductive partition. Two models for the average Nusselt number were proposed for nanofluids with spherical and cylindrical particle by using multi-layer feed-forward neural networks. Findings It was observed that the average Nusselt number reduces for higher values of Richardson number and Hartmann number, while enhances for higher values of nanoparticle volume fraction. Among various types of particle shapes, blade ones perform the worst and cylindrical ones perform the best in terms of heat transfer enhancement, but this is not significant which is less than 3 per cent. The average Nusselt number deteriorates by about 6.53per cent for nanofluid at the highest volume fraction of spherical particle shapes, but it is 11.75per cent for the base fluid when Hartmann number is increased from 0 to 10. Conductive partition geometrical parameters (length and height) do not contribute to much to heat transfer process for the 3D cavity, except for the case when height of the partition reaches 0.8 times the height of the cubic cavity, the average Nusselt number value reduces by about 25per cent both for base fluid and for nanofluid when compared to case with cavity height which is 0.2 times the height of the cubic cavity. Originality/value Based on the literature survey, a 3D configuration for MHD mixed convection of nanofluid flow in a cavity with a conductive partition considering the effects of various particle shapes has never been studied in the literature. This study is a first attempt to use a conductive partition with nanofluid of various particle shapes to affect the fluid flow and heat transfer characteristics in a 3D cubic cavity under the influence of magnetic field. Partial or all findings of this study could be used for the design and optimization of realistic 3D thermal configurations that are encountered in practice and some of the applications were already mentioned above. In this study, thermal performance of the system was obtained in terms of average heat transfer coefficient along the hot surface, and it is modeled with multi-layer feed-forward neural networks.

Numerical study of natural convection and melting in a corrugated square cavity filled with CNT-water nanofluid under the influence of inclined magnetic field was performed. The left and right walls of the cavity are kept at constant temperatures while the horizontal wall is adiabatic. Galerkin weighted residual finite element was used. The effects of Hartmann number (between 0 and 40), magnetic inclination angle (between 0° and 90°), nanoparticle volume fraction (between 0 and 4%), number (between 1 and 20) and height (between 0.002 H and 0.16 H) of the corrugation on the convective heat transfer features and melting in the square cavity were examined. Magnetic field was found to dampen the fluid motion, and less movement of the melt front in the upper part of the cavity is observed. By using the CNT nanoparticles in the base fluid, significant enhancement in the heat transfer and faster propagation of the melt front is observed in the absence and presence of magnetic field. Average heat transfer enhancements are around 118% and 95% when nanofluid at the highest particle volume fraction is compared with water in the absence and presence of magnetic field. The heat transfer is reduced and melt front curve characteristics are affected when the number and height of corrugation waves are increased. © 2019, Akadémiai Kiadó, Budapest, Hungary.

Purpose The purpose of this study is to numerically analyze the convective heat transfer features for cooling of an isothermal surface with a cavity-like portion by using CuO-water nano jet. Jet impingement cooling of curved surfaces plays an important role in practical applications. As compared to flat surfaces, fluid flow and convective heat transfer features with jet impingement cooling of a curved surface becomes more complex with additional formation of the vortices and their interaction in the jet wall region. As flow separation and reattachment may appear in a wide range of thermal engineering applications such as electronic cooling, combustors and solar power, jet impingement cooling of a surface which has a geometry with potential separation regions is important from the practical point of view. Design/methodology/approach Numerical simulations were performed with a finite volume-based solver. The study was performed for various values of the Reynolds number (between 100 and 400), length of the cavity (between 5 w and 40 w), height of the cavity (between w and 5w) and solid nano-particle volume fraction (between 0 and 4 per cent). Artificial neural network modeling was used to obtain a correlation for the average Nusselt number, which can be used to obtain fast and accurate predictions. Findings It was observed that cavity geometrical parameters of the cooling surface can be adjusted to change the flow field and convective heat transfer features. When the cavity length is low, significant contribution of the inclined wall of the cavity on the average Nusselt number is achieved. As the cavity length and height increase, the average Nusselt number, respectively, reduce and slightly enhance. At the highest value of cavity height, significant changes in the convective flow features are obtained. By using nanofluids instead of water, enhancement of average heat transfer in the range of 35-46 per cent is obtained at the highest particle volume fraction. Originality/value In this study, jet impingement cooling of an isothermal surface which has a cavity-like portion was considered with nanofluids. Addition of this portion to the impingement surface has the potential to produce additional vortices which affects the fluid flow and convective features in the jet impingement heat transfer. This geometry has the forward-facing step for the wall jet region with flow separation reattachment in the region. Based on the above literature survey and to the best of the authors’ knowledge, jet impingement cooling for such a geometry has never been reported in the literature despite its importance in practical thermal engineering applications. The results of this study may be useful for design and optimization of such systems and to obtain best performance in terms of fluid flow and heat transfer characteristics.

Numerical study for the effects of an inner stationary cylinder having an elastic rod like extension on the mixed convection of CNT-water nanofluid in a three dimensional vented cavity was performed by using finite element method. Effects of various pertinent parameters such as Reynolds number (between 100 and 1000), elastic modulus of the flexible rod (between 10 5 and 10 8 ), size of the elastic rod (between 0.05H and 0.3H), size of the circular cylinder (between 0.025H and 0.25H), inclination angle of the left vertical surface of the cavity (between 0° and 30°) and CNT-nanoparticle solid volume fraction (between 0 and 4 % ) on the convective flow features in a 3D vented cavity were analyzed. It was observed that with the installation of the obstacle (cylinder + elastic rod) and changing its geometrical and other parameters (elasticity of the rod) affect the variations of established multiple re-circulation zones and isotherms with the three dimensional vented cavity. The average heat transfer rate for the left vertical surface deteriorated with higher inclination angle of the side surface of the cavity while the variations in the average heat transfer rate for the upper surface was found to be slight. Inclusion of the CNT nanoparticle results in average heat transfer enhancement which is about 60 % at the highest nanoparticle solid volume fraction and the rate of enhancement was found to be independent of obstacle geometrical parameters, elasticity of the flexible wall and side surface inclination angle of the cavity. A correlation for the average Nusselt number is obtained in polynomial form for the configurations in the presence and absence of obstacles.

In current text, we developed CVFEM code for nanomaterial hydrothermal management through a permeable compound cavity including two temperature model. Radiation and Lorentz source terms were added in formulations. Impacts of radiation parameter, Rayleigh, Hartmann number, interface heat transfer parameter and nanoparticles’ shape on nanofluid behavior were demonstrated. Contours indicate that convective mode becomes stronger with augment of buoyancy term. By increasing Nhs, conduction becomes more effective and Nusselt number reduces. As radiation term enhances, Nusselt number augments. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature.

International audience; The reactivity of water with Li-rich layered Li2RuO3 and partial exchange of Li2O with H2O within the structure is studied under aqueous (electro)chemical conditions. Upon slow delithiation in water over long time periods, micron-sized Li2RuO3 particles structurally transform from an O3 structure to an O1 structure with a corresponding loss of 1.25 Li ions per formula unit. The O1 stacking of the honeycomb Ru layers is imaged using high-resolution high-angle annular dark-field scanning transmission electron microscopy, and the resulting structure is solved by X-ray powder diffraction and electron diffraction. In situ X-ray absorption spectroscopy suggests that reversible oxidation/reduction of bulk Ru sites is realized on potential cycling between 0.4 and 1.25 VRHE in basic solutions. In addition to surface redox pseudocapacitance, the partially delithiated phase of Li2RuO3 shows high capacity, which can be attributed to bulk Ru redox in the structure. This work demonstrates that the interaction of aqueous electrolytes with Li-rich layered oxides can result in the formation of new phases with (electro)chemical properties that are distinct from the parent material. This understanding is important for the design of aqueous batteries, electrochemical capacitors, and chemically stable cathode materials for Li-ion batteries.

Inserting obstacles such as cylindrical pins in a micromixer has the potential to significantly enhance scalar transport and improve species mixing between two co-flowing streams. However, it remains unclear how the mixing efficiency in confined microchannel flows is affected by the positioning of the fluid interface and the cylindrical pin with respect to the wall or to each other. The present work investigates the mixing induced by a single cylindrical pin placed at different gap distances from the wall of a Y-type micromixer. Two fluid interface positions are considered by mixing the fluid streams at different ratios; one located at the channel centreline and one shifted towards one of the walls. Micro particle image velocimetry (μPIV) is applied to investigate the velocity fields and streamline patterns for the different pin locations, and micro laser-induced fluorescence (μLIF) to acquire the instantaneous concentration fields and assess the mixing performance, utilising the intensity of segregation technique. Prior to the onset of vortex-shedding and when the fluid interface coincides with the channel centreline, slightly offsetting the pin from the centreline is found to yield the best mixing performance compared to centreline or near wall pin locations. However, when vortex-shedding is present, a centreline pin location exhibits the best mixing performance. The present measurements indicate that single micropins can enhance mixing, even in the absence of vortex-shedding, and when vortex-shedding occurs, they are most efficient when the pin axis and fluid interface are aligned.

This study explores the preparation and mechanical behavior of free-standing polymer-dispersed liquid crystal (PDLC) film membranes. Polyurethane (PU) was used as a thermoplastic polymer matrix to form these free-standing film membranes. Cholesteryl oleyl carbonate (COC) and cholesteryl pelargonate were used as liquid crystals (LCs) with different molecular weights. PDLC membranes were produced by casting method after LCs and polymer were mixed in the tetrahydrofuran solvent at room temperature. These membranes were formed at different concentration ratios of polymer and LCs. The relationship among the phase separation, LCs and polymer contents as well as the LCs molecular weights was investigated. The morphological structures of these membranes were studied using scanning electron microscopy (SEM). SEM images exhibited that the shapes of LC droplets embedded in PU matrix were more uniform and smaller than those of the membranes which include LC with lower molecular weight. The mechanical properties of the PDLC membranes were determined by carrying out the tensile tests. It was found that the membranes which include COC LC were more flexible. Turkish Academy of Sciences (TUBA)Turkish Academy of Sciences The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This project was financially supported by the Turkish Academy of Sciences (TUBA).

An indium arsenide photovoltaic cell with gold front contacts is designed for use in a near-field thermophotovoltaic (NF-TPV) device consisting of millimeter-size surfaces separated by a nanosize vacuum gap. The device operates with a doped silicon radiator maintained at a temperature of 800 K. The architecture of the photovoltaic cell, including the emitter and base thicknesses, the doping level of the base, and the front contact grid parameters, are optimized for maximizing NF-TPV power output. This is accomplished by solving radiation and charge transport in the cell via fluctuational electrodynamics and the minority charge carrier continuity equations, in addition to accounting for the shading losses due to the front contacts and additional series resistance losses introduced by the front contacts and the substrate. The results reveal that these additional loss mechanisms negatively affect NF-TPV performance in a non-negligible manner, and that the maximum power output is a trade-off between shading losses and series resistance losses introduced by the front contacts. For instance, when the cell is optimized for a 1 x 1 mm2 device operating at a vacuum gap of 100 nm, the losses introduced by the front contacts reduce the maximum power output by a factor of ~ 2.5 compared to the idealized case when no front contact grid is present. If the optimized grid for the 1 x 1 mm2 device is scaled up for a 5 x 5 mm2 device, the maximum power output is only increased by a factor of ~ 1.08 with respect to the 1 x 1 mm2 case despite an increase of the surface area by a factor of 25. This work demonstrates that the photovoltaic cell in a NF-TPV device must be designed not only for a specific radiator temperature, but also for specific gap thickness and device surface area., 48 pages; 6 figures; 4 tables; 2 supplementary figures

Mixed convection of carbon-nanotube/water nanofluid in a vented cavity with an inner conductive T-shaped object was examined under pulsating flow conditions under magnetic field effects with finite element method. Effects of different parameters such as Richardson number (between 0.05 and 50), Hartmann number (between 0 and 30), cavity wall inclination (between 0 ∘ and 10 ∘ ), size (between 0.1 H and 0.4 H) and orientation (between −90 ∘ and 90 ∘ ) of the T-shaped object, and amplitude (between 0.5 and 0.9) and frequency (Strouhal number between 0.25 and 5) of pulsating flow on the convective flow features were studied. It was observed that the average Nusselt number enhanced with the rise of strength of magnetic field, solid nanoparticle volume fraction, and amplitude of the pulsation, while the effect was opposite for higher values of Ri number and cavity wall inclination angle. The presence of the T-shaped object and adjusting its size and orientation had significant impact on the main flow stream from inlet to outlet and recirculations around the T-shaped object and in the vicinity of hot wall of the cavity along with the magnetic field strength. Pulsating flow resulted in heat transfer enhancement as compared to steady flow case for all configurations. However, the amount of increment was different depending on the variation of the parameters of interest. Heat transfer enhancements were 41.85% and 20.81% when the size of the T-shaped object was increased from 0.1 H to 0.4 H. The T-shaped object can be utilized in the vented cavity as an excellent tool for convective heat transfer control. As highly conductive CNT particles were used in water, significant enhancements in the average Nusselt number between 97% and 108% were obtained both in steady flow and in pulsating flow cases when magnetic field was absent or present.

International audience; There is a crucial need for effective and easily dispersible colloidal microsensors able to detect local pH changes before irreversible damages caused by demineralization, corrosion, or biofilms occur. One class of such microsensors is based on molecular dyes encapsulated or dispersed either in polymer matrices or in liquid systems exhibiting different colors upon pH variations. They are efficient but often rely on sophisticated and costly syntheses, and present significant risks of leakage and photobleaching damages, which is detrimental for mainstream applications. Another approach consists in exploiting the distance-dependent plasmonic properties of metallic nanoparticles. Still, assembling nanoparticles into dispersible colloidal pH-sensitive sensors remains a challenge. Here, we show how to combine optically active plasmonic gold nanoparticles and pH-responsive thin shells into "plasmocapsules". Upon pH change, plasmocapsules swell or 2 shrink. Concomitantly, the distance between the gold nanoparticles embedded in the polymeric matrix varies, resulting in an unambiguous color change. Billions of micron-size sensors can thus be easily fabricated. They are non-intrusive, reusable, and sense local pH changes. Each plasmocapsule is an independent reversible microsensor over a large pH range. Finally, we demonstrate their potential use for the detection of bacterial growth, thus proving that plasmocapsules are a new class of sensing materials.

Forced convection of nanofluid in a vented cavity with elastic bottom wall is studied by using an inner conductive L-shaped object and magnetic field. Simulations are performed using the finite element method when the impacts of various pertinent parameters, such as Reynolds number (between 100 and 500), Hartmann number (between 0 and 40), elastic modulus of the flexible wall (between $$10^5$$ and $$10^9$$), solid nanoparticle volume fraction (between 0 and 0.04), size (between 0.1 and 0.4H), inclination (between − 90 and 90) and location ($$x_\mathrm{c}$$ between 0.25 and 0.75 H and $$y_\mathrm{c}$$ between 0.15 and 0.65H) of the L-shaped object on the fluid flow and heat transfer features, are investigated. It was observed that wall flexibility effects are influential for the configuration with strong convection and maximum of $$11\%$$ enhancement in the average heat transfer rate for the bottom wall is achieved. Suppression of the recirculations in the vented cavity and around the L-shaped object is observed with magnetic field. It is observed that impact of magnetic field on heat transfer enhancement is different for different segments of hot wall. When the cases with the highest magnetic field and in the absence of magnetic field are compared, the average heat transfer enhancement of $$5.5\%$$ is achieved for bottom elastic wall while $$24.5\%$$ of reduction in the average heat transfer is seen for upper hot wall. The overall Nusselt number reduces slightly when the magnetic field strength is increased. Significant impacts of the size, inclination and location of the of the L-shaped conductive object on the fluid flow such as branching of the main flow stream, size of the vortex below the inlet port and heat transfer are observed. $$31.6\%$$ rise of the average heat transfer for left vertical wall and $$34.6\%$$ reduction of average heat transfer for bottom wall are achieved when the minimum and maximum of the orientation angles are compared. The location of the L-shaped object has a significant impact on the flow and thermal pattern variations. The highest variation in the contribution to the overall heat transfer is seen for right vertical hot wall segment when the Nusselt numbers at the lowest and highest values of the horizontal and vertical locations of the object are compared. L-shaped object was found to be an efficient tool to control the heat transfer features of the vented cavity. Nanofluid inclusion resulted in heat transfer enhancement in the range of 8.5–16.5% while amount of enhancement is different for different hot wall segments either in the absence or in the presence of magnetic field effects. Finally, a polynomial-type correlation for the average Nusselt number of each hot wall segments of the vented cavity is proposed for water and for nanofluid at $$\phi =0.04$$.

In this study, the effects of long-term natural atmospheric ageing on the thermal properties of chicken feather fibre reinforced poly(lactic acid) biocomposite materials having chicken feather fibre mass content of 2, 5, and 10% were investigated. Chicken feather fibres, which are bio-based reinforcement material, and poly(lactic acid), which is bio-based matrix material, are compounded with a twin-screw extruder and injection-moulded; hence, the biocomposite material is produced. The effect of long-term natural atmospheric ageing on the thermal stability, crystallization, and melting behaviour of the biocomposite materials were analysed by thermogravimetric, derivative thermogravimetry, differential thermal, and differential scanning calorimetry analyses. In addition, the fracture surface of the samples was examined in depth by scanning electron microscopy analysis. The experimental results show that the long-term natural ageing process decreases the thermal stability values of the biocomposite materials and increases the glass transition temperatures and degree of crystallinities. © 2020, The Polymer Society, Taipei.

Magnetohydrodynamic free convection in a horizontal annulus formed by two isothermal surfaces and partially partitioned with a conductive ring was numerically studied by using finite element method. The numerical investigation was performed for various values of Rayleigh numbers (between 104 and 106), Hartmann number (between 0 and 40), magnetic inclination angle (between 0° and 90°), thermal conductivity ratio (between 0.01 and 100) and various locations of the conductive partition. Average Nusselt number enhances as the value of Rayleigh number, magnetic inclination angle and thermal conductivity ratio increases and as the value of Hartmann number decreases. The location of the partial conductive partition on the average Nusselt number becomes more effective for higher values of Rayleigh number and lower values of Hartmann number. Heat transfer process is effective when the partition is located on the bottom part of the hot wall. Heat transfer enhancement with location of the partition depends on the inclination angle of the magnetic field. Second law analysis of the system with entropy generation was also performed. It was observed that for higher values of magnetic field strength and lower values of magnetic inclination angle the entropy generation rate reduces, while the conductivity ratio increases the entropy generation rate. © 2019, Akadémiai Kiadó, Budapest, Hungary.

The purpose of this work is to check if additive manufacturing technologies are suitable for reproducing porous samples designed for sound absorption. The work is an inter-laboratory test, in which the production of samples and their acoustic measurements are carried out independently by different laboratories, sharing only the same geometry codes describing agreed periodic cellular designs. Different additive manufacturing technologies and equipment are used to make samples. Although most of the results obtained from measurements performed on samples with the same cellular design are very close, it is shown that some discrepancies are due to shape and surface imperfections, or microporosity, induced by the manufacturing process. The proposed periodic cellular designs can be easily reproduced and are suitable for further benchmarking of additive manufacturing techniques for rapid prototyping of acoustic materials and metamaterials. ispartof: Additive Manufacturing vol:36 status: Published online

Present research was devoted to modeling investigation of paraffin solidification within a wavy channel. Paraffin was mixed with CuO nano powders and creates NEPCM. Changing the surface of duct and working PCM is the main factors of this paper for improving the performance. The outer duct contains NEPCM and air within inner side can be warmer due to discharging process. The outputs indicate that wavy duct has better performance than the straight one due to its shorter solidification duration. Utilizing wavy duct and NEPCM can help the solidification and enhance the rate of process about 38%. Inclusion of nanomaterial leads to lower discharging time. © 2020 Elsevier B.V.

In this study, MHD conjugate free convection of a porous cavity having a curved shape conductive partition is numerically analyzed by using the Galerkin weighted residual finite element method. The numerical simulation is performed for different values of pertinent parameters: Rayleigh number (between 10 4 and 10 6), Hartmann number (between 0 and 60), Darcy number (between 5 × 10 - 4 and 0.05), porosity of the medium (between 0.25 and 0.75), curvature of the partition (minor axis radius of the horizontal ellipse, between 0.01H and 0.3H) and conductivity ratio (between 0.05 and 50). It was observed that the heat transfer rate enhances locally and in average for higher values of Rayleigh number, Darcy number, porosity of the medium and conductivity ratio, whereas the impact is opposite for higher values of Hartmann number. The amount of average Nusselt number reduction is obtained as 22 % when Hartmann number is changed from 0 to 60 at Rayleigh number of 10 5. Curvature and conductivity of the curved partition affect the variation in fluid flow and heat transfer characteristics. Maximum of 7 % variation in the average Nusselt number is achieved when the curvature of the conductive partition is varied but the effects of thermal conductivity ratio on heat transfer rate are higher. Long Short-Term Memory Networks are used for estimation of the velocity and temperatures in the computational domain for various values of pertinent input parameters variation in the system which includes conjugate heat transfer mechanism in a porous enclosure with complex-shaped conductive partition under the effects of magnetic field. © 2019, Akadémiai Kiadó, Budapest, Hungary.

To understand the impacts of adding twisted tape inside the tube with hybrid nanomaterial, the present paper has been examined with considering FVM. New testing fluid instead of water leads to lower exergy loss. Modeling outputs were carried out for different pitch ratio and Reynolds number. Decrement trend for secondary flow was reported when pitch ratio increases, and for this reason, convective flow reduces with rise of P which results in greater exergy drop. Turbulence intensity improves with augment of Re which provides stronger interaction of nanomaterial and tube wall. So, thinner boundary layer appears with rise of Re and exergy loss deteriorates. © 2020, Akadémiai Kiadó, Budapest, Hungary.

Numerical study for mixed convection of CNT-water nanofluid flow in a branching channel with annulus at the junction and a rotating surface was performed by using finite volume method. This geometry can be used in a variety of engineering applications such as in geothermal, gas pipelines, in pharmaceutical, fuel cells and many others. The numerical simulations are performed for various values of pertinent parameters such as Richardson number, angular rotational velocity of the inner surface at the annulus junction, solid nanoparticle volume fraction and diameter of the inner rotating. It was observed that the recirculation regions established within the annulus and separated fluid zones on the walls of the branching channel near the junction are strongly influenced by the by rotation of the inner surface at the annulus. The average Nusselt number enhancements up to 64% are obtained for the nanofluid containing the highest particle volume fraction for Ri = 0.01 and Ri = 1 when the inclination angle of the lower branching channel is 45°. Finally, ANFIS modeling technique with triangular-shaped membership function and 48 fuzzy rules are used to predict the average Nusselt numbers for the hot walls of the channel and annulus part. © 2018 Elsevier Ltd

Numerical study of double jet impingement cooling of an isothermal surface with Al2O3-water nanofluid under the influence of magnetic field was performed. Galerkin-weighted residual finite element method was utilized for the solution of the governing equations. The numerical simulations were performed for various values of Reynolds number (between 100 and 400), solid particle volume fraction (between 0 and 4%), and Hartmann number (between 0 and 2.5). The ratio of the slot-to-plate distance was varied between 4 and 16 whereas ratio of the distance between the slots to slot width was varied between 5 and 22.5. It was observed that magnetic field retarded the fluid flow and reduced the local and average heat transfer. At the highest value of the Hartmann number, the fluid cannot reach the stagnation point. Depending on the distance between the slots and slots to plate distance, average heat transfer enhances by about 46% and its value increases linearly with nanoparticle volume fraction. This study is particularly important where magnetic field is present and weakens the convective heat transfer characteristics in jet impingement cooling whereas it is possible to enhance its thermal performance by utilization of nanoparticles. © 2018, © 2018 Taylor & Francis Group, LLC.

In this study, the role of magnetic field and surface corrugation on the natural convective transfer characteristics in a three dimensional, CuO-water nanofluid filled trapezoidal cavity was numerically investigated with finite element method. Influence of various pertinent parameters such as Rayleigh number (between 104 and 106), Hartmann number (between 0 and 40), number (between 0 and 16) and height (between 0 and 0.5H) of triangular wave form and solid nanoparticle volume fraction (between 0 and 0.04) on the fluid flow and thermal characteristics were analyzed. It was observed that when corrugation height and number of corrugation waves enhance, local and average heat transfer reduce. The use of CuO nanoparticles is advantageous when heat transfer is effective and for the configurations without magnetic field. 26.86% increase in the average Nusselt number is obtained when magnetic field is imposed at Hartmann number of 30 whereas 40.72% of increment in the average heat transfer is attained in the absence of magnetic field when 4% of CuO nanoparticles are added to the water. A mathematical model based on proper orthogonal decomposition and polynomial interpolation among modal coefficients is developed that could be used to reconstruct the whole flow and thermal field and perform thermal predictions for the 3D corrugated cavity. © 2018 Elsevier Ltd

In this study, mixed convection in a lid driven trapezoidal cavity filled with Al2O3–water nanofluid under the effect of an inclined magnetic field was numerically investigated for various electrical conductivity models. The top and bottom wall of the trapezoidal cavity were maintained at constant cold and hot temperatures and the top wall is moving at a constant speed in positive x direction. The governing equations are solved with finite element method. Numerical simulations were performed for different values of Richardson numbers (between 0.01 and 25), strength and orientation of the uniform magnetic field (Hartmann number (between 0 and 40), magnetic inclination angle (between 0 o and 90 o )) and solid volume fraction of the nanofluid (between 0 and 0.03) for different electrical conductivity models. It was observed that as the value of the Richardson number, strength of the magnetic field and solid particle volume fractions enhance, discrepancy between the average Nusselt number increases for systems with different electrical conductivity models. Magnetic inclination angle for which the difference between average heat transfer rate is minimized for different electrical conductivity models depends on the side wall inclination angle of the trapezoidal cavity. After performing an optimization study, it was found that the optimum value of magnetic inclination angle is dependent on the electrical conductivity model.

In this study, a numerical and experimental study was carried out to determine the effects of variables such as curvature and foam properties on the natural frequencies of the sandwich panels. Sandwich panels consist of laminated E/glass epoxy face sheets with [0 degrees/90 degrees/-45 degrees/+45 degrees] stacking sequences and PVC foam cores with AIREX C70.55, C70.90, C70.200 and C70.250. A group of sandwich panels with radii of curvature ranging from 90 to 200 mm were analysed by ANSYS software. Vibration characteristics were obtained for clamped square sandwich panels. The results indicate that the natural frequencies increase with the increasing curvature and foam density. However, the increment in the natural frequency due to an increase in the magnitude of curvature decreases with increasing foam density. The highest increase in natural frequency due to increasing foam properties is seen in the flat panels. Also, it is found that in values beyond a specific curvature; increasing of the foam properties causes reduction in the natural frequencies. (C) 2017 Elsevier Ltd. All rights reserved.

Numerical study of mixed convection in a lid-driven 3D flexible walled trapezoidal cavity with nanofluids was performed by using Galerkin weighted residual finite element method. Effects of various pertinent parameters such as Richardson number (between 0.05 and 50), elastic modulus of the side surfaces (between 1000 and 10 5 ), side wall inclination angle (between 0° and 20°) and solid particle volume fraction (between 0 and 0.04) on the fluid flow and heat transfer characteristics in a 3D lid-driven-trapezoidal cavity were numerically examined. It was observed that these characteristics are influenced when the pertinent parameters change. Flexible side surface can be used as control element for heat transfer rate. Increment and reduction in the space which are provided by the flexible side walls result in heat transfer enhancement and deterioration for side wall inclination angle of 0° and 10°. Average Nusselt number enhances by about 9.80 % when the value of the elastic modulus is increased from 1000 to 10 5 for side wall inclination angles of θ = 0°. Adding nanoparticles to the base fluid results in linear increment of heat transfer and at the highest volume fraction, 25.30 % of heat transfer enhancement is obtained. A polynomial type correlation for the average Nusselt number along the hot wall was proposed and it has a fourth order polynomial dependence upon the Richardson number and first order dependence upon the solid particle volume fraction.

The effect of comonomer on structure and relaxation of flow-induced precursors was investigated in a series of isotactic polypropylene and random propylene–ethylene copolymers. The polymers were subjected to flow by fiber pulling and allowed to relax above their nominal melting temperature for specific times. The type of morphology developed after cooling revealed whether flow-induced precursors were still present or the melt had fully re-equilibrated. Precursors were long-lived and, at fixed temperature, decayed significantly faster with higher ethylene content. The critical time for precursor relaxation followed an Arrhenius-type dependence with temperature. The apparent energy of activation for precursor dissolution decreased with increasing comonomer content, indicating that the rate-limiting step of the relaxation process becomes less difficult with higher ethylene fraction. This effect is attributed to ethylene counits acting as disruptors of precursor structure and is discussed in terms of quasi-cr...

In this study, laminar forced convection of pulsating nanofluid flow over a backward-facing step with a corrugated bottom wall was numerically examined by using finite volume method. Part of the bottom wall downstream of the step was corrugated and kept at constant temperature. Effects of Reynolds number, length and height of the surface corrugation wave, nanoparticle volume fraction, amplitude and frequency of flow pulsation on the fluid flow and heat transfer were numerically investigated. It was observed that average Nusselt number enhances as the Reynolds number, length and height of the corrugation wave increase. Average Nusselt number versus Strouhal number shows a resonant type behavior and flow pulsation amplitude increment results in heat transfer enhancement. Average heat transfer rate increases with the inclusion of the nanoparticles but the rate of enhancement depends on the nanoparticle solid volume fraction interval. An efficient computational strategy for the thermal performance prediction of the system was developed by using proper orthogonal decomposition and artificial neural networks. © 2017 Elsevier Ltd

Heat transfer aspects of a typical flat-plate solar collector utilizing water-based nanofluids as the working fluid were analyzed numerically. Water-based nanofluids of various compositions containing metallic Al2O3 and Cu nanoparticles with volume fractions ranging from 1% to 5% were examined, and the effects of the nanofluids on the heat transfer were quantified. Relevant parameters such as the heat flux, Reynolds number, and the collector tilt angle were calculated and compared to each other at different boundary conditions. The flat-plate solar collector geometry was simplified, and only a fluid carrying pipe with an absorber surface was chosen as a numerical model with a particular at ention to symmetry, instead of taking the entire collector geometry. The numerical model was controlled and confirmed by applying it to similar studies existing in the pertinent literature. All numerical solutions were carried out by using a commercial finite volumes of ware package called ANSYS Fluent. The results show that the nanofluids increase the heat transfer rate ranging from 1% to 8%, when compared to water as a working fluid. © 2017 by Begell House, Inc.

In this study, mixed convection and entropy generation in a vented cavity with inlet and outlet ports are examined under the effects of an inclined magnetic field. Galerkin weighted finite element method was used for the solution of the governing equations. The numerical simulations are performed for various values of Reynolds numbers (between 100 and 500), Hartmann number (between 0 and 50) and solid particle volume fractions of CuO nanoparticles (between 0 and 4 % ). Different walls and domains of the computational model are considered for the heat transfer and entropy generation analysis. It was observed that at low Reynolds number number, magnetic field has the potential to enhance the heat transfer at the highest strength while the effect of magnetic field is to reduce the convection at higher Reynolds number. The contributions of different hot walls to the overall heat transfer change considerably with the change of Hartmann number while the effect of magnetic inclination angle is marginal. Inclusion of nanoparticle results in heat transfer enhancement in the absence and presence of magnetic field and the amount of enhancement is 25–27% at the highest value of solid nanoparticle volume fraction. Different parts of the cavity contribute differently to the overall entropy generation when Hartmann number varies while the overall entropy generation first decreases and then increases when the value of Hartmann number increases. The addition of nanoparticles increases the overall entropy generation rate. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature.

In this study, convective heat transfer performance of a nanofluids containing graphite is studied in an industrial microchannel. In the experiments, initially, to prepare nanofluids at the volume fraction values of 0.5, 1, 1.5, 2%, distilled water has been employed as the base liquid. To provide sedimentation and stabilization of nanofluids in distilled water, Cetyltrimethylammonium bromide (CTAB) is utilized as surfactant. Thermophysical properties of nanofluids such as thermal conductivity, dynamic viscosity, and specific heat are determined experimentally. Furthermore, by building an experimental setup, in the temperature range of 20–30 °C and with temperature intervals of 2 °C, performance experiments are carried out in a microchannel of which hydraulic diameter is 1.6 × 10-3 m. Additionally, experiments have been conducted using nanofluids at different volumetric rates from 1 to 7 l min-1, heat fluxes from 100 to 1100 W, and volume fractions from 0.5 to 2%. Measuring heat flux, temperature, and flow rate, outcomes such as convective heat transfer coefficient, Reynolds number, and Nusselt number are calculated. The validation process of the experimental results has been performed by plotting the figures of Nusselt numbers vs Reynolds ones, and heat transfer coefficient vs supplied heat considering distilled water and nanofluids having various volumetric proportions. Regarding with the performance of nanofluids against distilled water under similar operating conditions, some proportional positive increase are acquired. Using outcomes attained from experiments, new correlations for Nusselt number have been derived with the R2 values around 0.96, and afterward by means of those correlations experimental data have been compared with those in the literature. A large number of measured and calculated data are given in the paper for other researchers to validate their theoretical models. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature., Thailand Research Fund King Mongkut's University of Technology Thonburi Riordan Foundation, This study has been financially supported by Niğde Ömer Halisdemir University Scientific Research Projects Coordination Department, Project Number: FEB 2013/08-BAGEP. All authors also grateful for the Thailand Research Fund (TRF), the National Research University Project (NRU) and King Mongkut’s University of Technology Thonburi through the “KMUTT 55 th Anniversary Commemorative Fund”.

The photovoltaic panels are one of the most efficient energy systems that generate electricity by absorbing the solar radiation. Nevertheless, when the sun's rays are converted to electricity, a high amount of waste heat is generated. Therefore, the efficiency of photovoltaic (PV) panels needs to be studied to minimize the amount of waste heat. There is a non-linear relationship between the temperature, the current and the voltage values produced by the PV panels. In the present study, the performance of 75 W PV panels with polycrystalline cell structure under Elazig, Turkey climatic conditions were experimentally investigated. The system performances such as temperature, power and efficiencies were analyzed by applying different fin parameters (length, sequences) to PV panels. The aluminum fins were applied with 10 different configurations as given by A1-A10. The cell temperatures, output powers, power loss ratios and energy-exergy efficiencies were calculated based on measurements of the experimental study. It was observed that the temperature did not distributed homogeneously on the PV panel. In terms of the efficiency, the fins are designed as staggered array and the 7 cm × 20 cm dimensions showed the best results. The highest energy and exergy efficiencies values of the finned panels (A5) were calculated as 11.55%, and 10.91%, respectively.

Forced convection of pulsating nanofluid flow over corrugated parallel plate in the presence of inclined magnetic field is numerically studied by using Galerkin weighted residual finite element method. Impacts of Reynolds number (between 100 and 500), Hartmann number (between 0 and 15), magnetic inclination angle (between 0 o and 90 o ), number (between 1 and 12) of corrugation wave, height (between 0.05h and 0.35h) of the corrugation wave, solid particle volume fraction (between 0% and 4%), pulsation amplitude (between 0 and 0.9) and frequency (Strouhal number between 0.25 and 2) on the convective heat transfer features are analyzed. It is observed that increasing the Reynolds number, Hartmann number, magnetic inclination angle and solid particle volume fraction of the nanoparticle results in heat transfer enhancement while corrugation wave parameters have reverse impact on heat transfer enhancement in steady flow case. Various blocks of the heated plate contribute differently to the overall heat transfer rate and influence of block height on the distribution of the contributed effects is remarkable. Magnetic field redistribute the vortices between heated blocks of the corrugated plate and enhance the heat transfer both in steady flow and pulsating flow. Values for the spatial average Nusselt number are higher in pulsating flow as compared to steady case. At pulsation amplitude of 0.9, 40.30% and 34% heat transfer enhancement are obtained as compared to steady case in the absence and presence of magnetic field at Hartmann number of 15. Including nanoparticles in pulsating flow shifts the spatial average Nusselt number plots as compared to base fluid. The values at the highest particle volume fraction are higher 15–16% in pulsating flow as compared to base fluid and they are slightly different than the ones obtained in the steady flow.

In this study, convective heat transfer features of CNT-water nanofluid in a three dimensional cubic enclosure which is separated by a conductive partition and having an inner rotating adiabatic circular cylinder were examined. Numerical simulations were performed with Galerkin weighted residual finite element method. Various values of Richardson number of the left cavity (between 0.01 and 100), angular rotational speed of the inner cylinder (between −34724 and 34724), vertical (between 0.25 and 0.75) and horizontal (between 0.1 and 0.3) locations of the cylinder, thickness (between 0.01 and 0.2) and thermal conductivity ratio (between 0.1 and 100) of the conductive partition and nanoparticle volume fraction (between 0 and 0.03) on the fluid flow and heat transfer were analyzed. It was observed that the average heat transfer enhances for higher values of Richardson number, angular rotational speed of the cylinder (generally in both directions), solid particle volume fraction of nanofluid and thermal conductivity of the partition. The rate of enhancement are in the range of 11–14 % when configurations with the lowest and highest values of Richardson number are considered whereas 18 % of enhancement is attained at the highest rotational speed of the cylinder as compared to motionless cylinder configuration. The enhancements in the average Nusselt numbers with the inclusion of the CNT-nanoparticle at the highest solid volume fraction are in the range of 82 % and 90 % as compared to water. The average heat transfer coefficient is estimated by using POD and interpolation among POD modes and modal coefficients which is found to be computationally inexpensive and the method produces accurate results as compared to high fidelity three dimensional intensive computational fluid dynamics simulations.

Purpose The purpose of this study is to numerically examine the mixed convection of CuO-water nanofluid due to a rotating inner hot circular cylinder in a 3D cubic enclosure with phase change material (PCM) attached to its vertical surface. Heat transfer and fluid flow characteristics were examined for various values of pertinent parameters. Design/methodology/approach Finite element method was used in the numerical simulation. Influence of various pertinent parameters such as Rayleigh number (between 10$^5$ and 10$^6$), Hartmann number (between 0 and 100), angular rotational speed of the cylinder (between −50 and 50), solid nanoparticle volume fraction (between 0 and 0.04) and PCM parameters (height-between 0.2H and 0.8H, thermal conductivity ratio- between 0.1 and 10) on the convective heat transfer characteristics are numerically studied. Findings It was observed that local heat transfer variations along the hot surface differ significantly for the cases with and without magnetic field where three distinct hot spots of peak Nusselt number are established when magnetic field is imposed. The average Nusselt number enhancement with the nanofluid at the highest particle volume fraction is 52.85 per cent at Hartmann number of 100, whereas its value is 39.76 per cent for the case in the absence of magnetic field. When the inner cylinder rotates, flow and thermal fields are affected within the cavity. The local heat transfer variations spread over the hot surface with cylinder rotation and 16.43 per cent of reduction in the average heat transfer is obtained with counter-clockwise rotation at 100 rad/sec. An enhancement in the PCM height and a reduction in the thermal conductivity of the PCM result in average heat transfer deterioration for the 3D cavity. The amount of the reduction is 43 per cent when the PCM height is increased from 0.2H to 0.8H, whereas 19.10 per cent enhancement in the heat transfer is achieved when thermal conductivity ratio (PCM) to the base fluid is increased from 0.1 to 10. Originality/value Such configurations can be designed for convection control, and in our case, various methods are available. Some of the investigated methods can be used in applications where magnetic field already exists. Convection control study in 3D cavity gives more realistic results as compared to 2D configurations, and results of the current investigation may be used for the design, optimization and flow control of many thermal applications involving magnetic field effects.

In this study, free vibration responses of sandwich composite panels with different radius of curvature were presented numerically. The studies were carried out on square flat and curved sandwich panels made of E-glass/epoxy face sheets and polyvinyl chloride foam with three different radii of curvature. Experimental studies were used to verify the numerical results. Vibration tests were performed on flat and curved sandwich panels under free–free boundary conditions. The experimental data were then compared with finite element simulation, which was conducted by ANSYS finite element software and it was shown that the numerical analysis results agree well with the experimental ones. Effect of the curvature on natural frequencies under different boundary conditions (all edge free, simply supported, and fully clamped) was investigated numerically. Results indicated that the natural frequencies and corresponding mode shapes were affected by boundary conditions and curvature of the panel. For all boundary conditions, the variation of curvature had smaller effect on the natural frequency of the first mode than those of the other modes. © The Author(s) 2017.

International audience; Energy is vital to the profitable growth of every nation and to stimulate new research. Only natural resources can meet the growing energy demand in recent years, biodiesel has become very interested in the energy as well as environmental advantages that it can be combined with mineral diesel fuel in any quantity. The research focuses on the study of the replacement of diesel with a safflower methyl ester. The engine tests shall be performed using the safflower methyl ester as fuel in the DI diesel engine. The combustion, emission and performance characteristics were studied using alternative fuels and mixtures. SAfflower Methyl Ester 80% (SAME80) and SAME100 have high heat release rates. Nitrogen oxides were higher by about 50%, carbon monoxide decreased by 10%, unburnt hydrocarbon was slightly higher and the thermal efficiency was higher for the SAME than for diesel fuel.

This article contains the experimental investigations of different cooling methods used for photovoltaic (PV) panels. Phase change material (PCM), thermoelectric (TE) and aluminum fins were chosen as the cooling methods. The CaCl2·6H2O is chosen as one of the PCM which is widely used in the cooling of PVs and the other is the PCM with melting temperature above the surface temperature of the PV panel. By using TE material in different numbers (6, 8 and 12) and aluminum fins in different layouts, surface temperatures and output powers of PV panels were compared. It is observed that the PCM which is not chosen appropriately has insulation feature in the PV panel and enhances the temperature of the panel and decreases the output power. When the most successful cooling methods were tested under the same environmental conditions, PV with fin system produced the highest power generation of 47.88 W while PV with PCM and TEM produced the lowest power generation of 44.26 W. © 2020 Elsevier Ltd

Freeform surfaces are widely used in the design of complex parts to satisfy aesthetic and functional requirements, particularly in automotive, aeronautics, and die-mould industries. Traditional machining of freeform surfaces is gradual and involves significant manual interactions. Non-traditional machining processes such as electrochemical machining (ECM) enable to increase productivity and cost effectiveness when machining of freeform surfaces as well as hard to cut materials in large scale production. However, some manufacturing problems may be arisen during ECM process and the control mechanisms for preventing such problems (short circuiting, oxide layer and cavitation problems) are very critical for achieving correct form of freeform surfaces and a complete process without any faults in ECM process. This paper firstly investigates possible causes of the ECM drawbacks such as short-circuiting, cavitation, and oxide-layer formation while ECMing of freeform surfaces and then proposed solutions in order to prevent these drawbacks are discussed. A closed-loop control system was developed using a micro-controller board in order to control short-circuiting. Flow analysis was carried out using an ANSYS® Workbench and four different types of apparatus were designed for preventing the cavitation formation. The conducted experiments showed that the voltage feedback was alone insufficient to prevent short-circuiting during high feed rates. In addition, it was observed that the velocity distribution prevented the cavitation when the velocity was adequate within the gap domain. Additionally, it has been showed that the oxide-layer generation was associated with the amount of contamination in the electrolyte solution. © 2018 Elsevier B.V.

To enhance energy absorption of photovoltaics, several etching experiments with various parameters were performed. In addition, an Artificial Neural Network (ANN) simulation was utilized to predict chemical nano etching parameters such as masking and etching durations for Silicon (Si) solar cell applications to reach minimum surface reflectance in an optimum etching duration. Experiments were performed with different masking and etching durations to determine the characteristics of surface reflectance of micro textured n-type single crystalline Si wafers in 25mmx25mm width and 300 µm thickness to provide training data for ANN. For this purpose, solutions with identic properties including Ag nanoparticles were applied with different application durations on the surfaces of n-type single crystalline Si wafers to cover partially the Si surfaces with Ag nano-particles at masking step. After, partially masked Si surfaces were exposed to chemical nano etching to develop nano-sized porous structures under different etching durations in an identic acidic etching solution. For the etching of Si wafers, 32 masking and etching processes were performed. Reflectance measurements and SEM images were evaluated to determine the optimum etching duration resulting the best surface quality with minimum reflectance. In addition, reflectance values were utilized as input data for training, testing and validation steps of developed ANN. In the ANN simulation, 70% of reflectance values were used as training, 15% of reflectance values were used as validation and 15% of reflectance values were used to test data in the ANN. Consequently, surface reflectance values under different masking and etching durations were predicted with the new parameter set by using the trained ANN with a success level above 99%. © 2018 Elsevier B.V.

Implementation of a bypass laminar-to-turbulent transition is explored. We show that our method, by bypassing linear exponential growth, can induce high mixing capacity localized turbulence in a laminar channel flow at low $R\phantom{\rule{0}{0ex}}e$. An on-demand mixing enhancement in laminar channel flow is proposed.

International audience; Variations of the lattice parameter can significantly change the properties of a material, and, in particular, its electronic behaviour. In the case of graphene, however, variations of the lattice constant with respect to graphite have been limited to less than 2.5% due to its well-established high in-plane stiffness. Here, through systematic electronic and lattice structure studies, we report regions where the lattice constant of graphene monolayers grown on copper by chemical vapour deposition increases up to ~7.5% of its relaxed value. Density functional theory calculations confirm that this expanded phase is energetically metastable and driven by the enhanced interaction between the substrate and the graphene adlayer. We also prove that this phase possesses distinctive chemical and electronic properties. The inherent phase complexity of graphene grown on copper foils revealed in this study may inspire the investigation of possible metastable phases in other seemingly simple heterostructure systems.

In the present study, laminar forced convective nanofluid flow over a backward-facing step was numerically investigated. The bottom wall downstream of the step was flexible, and finite element method was used to solve the governing equations. The numerical simulation was performed for a range of Reynolds number (between 25 and 250), elastic modulus of the flexible wall (between 104 and 106), and solid particle volume fraction (between 0 and 0.035). It was observed that the flexibility of the bottom wall results in the variation of the fluid flow and heat transfer characteristics for the backward-facing step problem. As the value of Reynolds number and solid particle volume fraction enhances, local and average heat transfer rates increase. At the highest value of Reynolds number, heat transfer rate is higher for the case with the wall having lowest value of elastic modulus whereas the situation is reversed for other value of Reynolds number. Average Nusselt number reduces by about 9.21% and increases by about 6.1% for the flexible wall with the lowest elastic modulus as compared to a rigid bottom wall for Reynolds number of 25 and 250. Adding nano-additives to the base fluid results in higher heat transfer enhancements. Average heat transfer rates enhance by about 35.72% and 35.32% at the highest solid particle volume fraction as compared to nanofluid with solid volume fraction of 0.01 for the case with wall at the lowest and highest elastic modulus. A polynomial type correlation for the average Nusselt number along the flexible hot wall was proposed, which is dependent on the elastic modulus and solid particle volume fraction. The results of this study are useful for many thermal engineering problems where flow separation and reattachment coupled with heat transfer occur. Control of convective heat transfer for such configurations with wall flexibility and nanoparticle inclusion to the base fluid was aimed in this study to find the effects of various pertinent parameters for heat transfer enhancement.

In this study, mixed convection of nanofluids in a three dimensional cavity with two inner adiabatic rotating circular cylinders were analyzed by using finite element method. Vertical surfaces are kept at constant temperature while other walls and rotating cylinder surfaces were taken as adiabatic. The three dimensional cavity was filled with water and various types of nanoparticles (Cu, Al2O3 and TiO2). The water-Cu nanofluid provided the highest heat transfer rate and at the highest value of Rayleigh number, 4 % higher average heat transfer rate is obtained when compared to other particles. When cylinders rotate, depending on the rotational direction either enhancement or deterioration of average Nusselt number is observed. For the highest value of rotational speed of the cylinders, 8.5 % discrepancy between the average Nusselt number is observed for the nanofluid with Cu and Al2O3 nanoparticles. For Cu-water nanofluid at the highest volume fraction as compared to base fluid, 38.10 % of enhancement in the average heat transfer is obtained. A correlation for the average Nusselt number in polynomial form was developed which is a function of Rayleigh number and angular rotational speed of the cylinders.

Petroyag Lubricants;UCTEA Chamber of Mechanical Engineers, 9th International Conference on Tribology, Balkantrib 2017 -- 13 September 2017 through 15 September 2017 -- -- 135934, In this paper, the effects of cutting parameters on cutting forces and surface roughness based on Taguchi experimental design method are determined. Taguchi L9 orthogonal array is used to investigate the effects of machining parameters. Optimal cutting conditions are determined using the signal/noise (S/N) ratio which is calculated by average surface roughness and cutting force. Using results of analysis, effects of parameters on both average surface roughness and cutting forces are calculated on Minitab 17 using ANOVA method. The material that was investigated is Inconel 625 steel for two cases with heat treatment and without heat treatment. The predicted and calculated values with measurement are very close to each other. Confirmation test of results showed that the Taguchi method was very successful in the optimization of machining parameters for maximum surface roughness and cutting forces in the CNC turning process. © Published under licence by IOP Publishing Ltd.

In this paper, numerical study and thermal prediction for a nanofluid jet impingement cooling of an isothermal hot surface with an adiabatic rotating cylinder were performed. Finite volume method was used for the solution of resulting governing equations along with the boundary conditions. Influence of various pertinent parameters such as Reynolds number (between 100 and 400), angular rotational velocity of the cylinder (between −0.1 and 0.1), horizontal location of the cylinder (between 0 and 3.75w) and solid particle volume fraction (between 0 and 0.04) on the fluid flow thermal characteristics were examined. It was observed that cylinder rotation and its location affect the cooling performance of the hot surface. It can be used as control element for heat and fluid flow. At the highest angular rotational speed as compared to motionless cylinder case, average Nusselt number reduces by about 20.16 % for clockwise rotation. Solid particle addition to the base fluid affects the variation of first and secondary peaks in the Nusselt number along the hot wall. At the highest solid when the cylinder is away from the inlet slot and average Nusselt number enhancement is by about 8.08 % at the highest volume fraction. An efficient modeling strategy was developed based on proper orthogonal decomposition and radial basis neural networks for thermal predictions. Accurate and fast results were achieved as compared to high fidelity computational fluid dynamics simulation results.

In this study, laminar mixed convection of CuO–water nanofluid over a backward facing step with the presence of a triangular obstacle and under the effect of magnetic field was numerically investigated. Finite volume method was used to solve the governing equations for the range of parameters: Richardson number (between 0.01 and 100), Hartmann number (between 0 and 50), nanoparticle volume fraction (between 0 and 0.04), and horizontal location of the triangular obstacle (between 0.5H and 2H). It was observed that average heat transfer is a decreasing function of Richardson number and an increasing function of nanoparticle volume fraction. The dependence of average heat transfer on the magnetic field parameters shows a resonant-type behavior. The obstacle affects the local Nusselt number distribution near the step especially for lower values of Richardson number and Hartmann number. Artificial neural networks were used to develop models that can be used instead of high-fidelity computational fluid dynamics simulations for fast and accurate thermal performance predictions of the considered system. © 2018 by Begell House, Inc.

In this paper the effects of deformation modes on martensitic transformation for TRIP steels which are composed of Ferrite, Bainite and Retained austenite are investigated in the view of the microstructural level. For this porpose the simulations are run for a synthetically generated microstructure which have 55% Ferrit, 35% Bainite and 10% Retained austenite. In the simulations tensile, biaxial and shear type deformation modes are considered. The results reveal that biaxially loaded microstructure has the maximum amounts of martensite phases at the end of the given deformation and the less martensite is occurred in the shear type loading condition. © 2018 Brazilian Association of Computational Mechanics. All rights reserved.

Understanding the origins of intrinsic stress in Si nanowires (NWs) is crucial for their successful utilization as transducer building blocks in next-generation, miniaturized sensors based on nanoelectromechanical systems (NEMS). With their small size leading to ultrahigh-resonance frequencies and extreme surface-to-volume ratios, silicon NWs raise new opportunities regarding sensitivity, precision, and speed in both physical and biochemical sensing. With silicon optoelectromechanical properties strongly dependent on the level of NW intrinsic stress, various studies have been devoted to the measurement of such stresses generated, for example, as a result of harsh fabrication processes. However, due to enormous NW surface area, even the native oxide that is conventionally considered as a benign surface condition can cause significant stresses. To address this issue, a combination of nanomechanical characterization and atomistic simulation approaches is developed. Relying only on low-temperature processes, the fabrication approach yields monolithic NWs with optimum boundary conditions, where NWs and support architecture are etched within the same silicon crystal. Resulting NWs are characterized by transmission electron microscopy and micro-Raman spectroscopy. The interpretation of results is carried out through molecular dynamics simulations with ReaxFF potential facilitating the incorporation of humidity and temperature, thereby providing a close replica of the actual oxidation environment-in contrast to previous dry oxidation or self-limiting thermal oxidation studies. As a result, consensus on significant intrinsic tensile stresses on the order of 100 MPa to 1 GPa was achieved as a function of NW critical dimension and aspect ratio. The understanding developed herein regarding the role of native oxide played in the generation of NW intrinsic stresses is important for the design and development of silicon-based NEMS., Scientific and Technological Research Council of Turkey (TÜBİTAK)