Browsing by Author "Oztop, HF"

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    Experimental analysis and dynamic modeling of a photovoltaic module with porous fins
    Selimefendigil, F; Bayrak, F; Oztop, HF
    In this study, experimental analysis and performance predictions of solar photovoltaic (PV) module equipped with porous fins were performed. The experimental setup was tested in Technology Faculty of Firat University, Elazig of Turkey which is located at 36 and 42 North latitudes. The PV module was oriented facing south and tilted to an angle of 36 with respect to the horizontal in order to maximize the solar radiation incident on the glass cover. Experimental analysis was conducted for configurations where PV module is equipped with porous metal foams. A multi-input multi-output dynamic system based on artificial neural networks was obtained for the PV configuration with and without fin by using the measured data (ambient temperature, PV panels back surface temperatures, current, voltage, radiation and wind velocity) from the experimental test rig. It was observed that adding porous fins to the PV module results in performance enhancements. The developed mathematical model based on dynamic neural networks can be used for further development and performance predictions of these systems. (C) 2018 Elsevier Ltd. All rights reserved.
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    Effects of different fin parameters on temperature and efficiency for cooling of photovoltaic panels under natural convection
    Bayrak, F; Oztop, HF; Selimefendigil, F
    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 x 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.
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    Optimization assisted divide-combine approach to model cooling of a PV module equipped with TEG by using a trapezoidal shaped hybrid nano-enhanced cooling channel and performance estimation with generalized neural networks
    Selimefendigil, F; Oztop, HF
    Innovative cooling strategies and efficient thermal management techniques are needed to increase the efficiency of photovoltaic (PV) modules. In the current work, a novel cooling channel method and computational approach is utilized for thermal management of PV module combined with thermoelectric generator (TEG) unit. The method uses an optimization assisted divide-combine computational approach while a trapezoidal wavy cooling channel is utilized. Hybrid nanofluid is used in the cooling channel. Simulations for cooling channel and PV-TEG unit are conducted by using finite element method while COBYLA algorithm is considered for optimization of trapezoidal wavy channel. It is shown that the corrugation amplitude has the largest effect on a trapezoidal wavy channel's cooling effectiveness, while the inclination angle has the least effect. The range of average Nu improvements by adjusting the trapezoidal wavy channel's amplitude, wave number, and inclination are obtained as 36%-42%, 13.5%-15%, and 2.5%-3%. The average PV-cell temperature decreases by approximately 2.7oC to 3.4oC when the cooling channel is connected to the PV-TEG unit. It also decreases by approximately 1oC to 1.3oC when the wave number is changed. The optimum corrugation height (b/H) and inclination (0) for the best cooling performance are found as (b/H, 0)=(0.5, 36) when using 3 waves and (b/H, 0)=(0.5, 13.16) when using 11 waves. The PV-cell temperature drops with optimal channel configurations with wave numbers of 3 and 11 are obtained as 4.3oC and 6oC, respectively, in comparison to the reference cooling channel (flat channel employing only pure fluid). While the PV-TEG unit is coupled with parametric simulation of the cooling channel, generalized neural network models are used to successfully estimate the PV-cell temperature and TEG power. More complex channel assemblies and consideration of multiple PV-TEG combined units can be developed using the proposed optimization-assisted divide-combine methodology.
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    Effects of an adiabatic inclined fin on the mixed convection heat transfer in a square cavity
    Selimefendigil, F; Oztop, HF
    In this study, a square cavity with two ventilation ports in the presence of an adiabatic fin placed on the bottom wall of the cavity is numerically analysed for the mixed convection case for a range of Richardson numbers (Ri = 0.1,1, 10, 30) and at Reynolds number of 300. The top and bottom walls of the cavity are kept at constant temperature while the verticals walls are assumed to be adiabatic. The effect of the fin height, inclination angle and Richardson number on the fluid flow and heat characteristics is numerically analysed. The results are presented in terms of streamlines, isotherm plots and averaged Nusselt number plots. It is observed that length and inclination angle of the fin significantly alter the streamlines and isotherms and hence the thermal performance of the system. For the best performance at different fin lengths, optimum inclination angle changes.
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    Effects of Combined Utilization of Active Cooler/Heater and Blade-Shaped Nanoparticles in Base Fluid for Performance Improvement of Thermoelectric Generator Mounted in Between Vented Cavities
    Selimefendigil, F; Oztop, HF
    A wide range of technical applications, including solar power, waste heat recovery, electronics thermal management, and heat exchangers, employ thermoelectric generators. They can be mounted in between channels / cavities where hot and cold fluid streams exist. In this study, two novel methods of enhancing the power generation from thermoelectric generator device mounted in between vented cavities are proposed by combined utilization of active heater/cooler rectangular blocks and blade-shaped nanoparticles in base fluid. Finite element method investigation is conducted numerically for a range of hot and cold stream Reynolds numbers (250-1000), non-dimensional hot and cold block sizes (0.01-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$-$$\end{document}0.4), and heating/cooling increments (0-10), with nanoparticle loading limited to 0.03. Higher values of Reynolds number results in a rise in thermoelectric generator power. When comparing the cases of lowest and highest Reynolds number combinations, a 219%\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\%$$\end{document} increase in power is achieved. The thermoelectric generator power will rise by around 27.5%\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\%$$\end{document} when the object size reaches its maximum. However, for moderate object sizes, up to 31.6%\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\%$$\end{document} reduction in power generation can be realized. Greater temperature differences result in a linearly rising power generation, with an achievable power increase of up to 22%\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\%$$\end{document}. When nanoparticle loading in the base fluid for both cavities is raised to its maximum value, the resultant power increases by around 30%\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$30\%$$\end{document}. Thermoelectric generator power rises by 67.8%\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\%$$\end{document} when an active heater/cooler with nanofluid is used in vented cavities, as opposed to the reference scenario of employing no object and only water. The thermoelectric generator device's hot and cold interface temperatures are accurately estimated using the artificial neural network based method. The estimated temperature can be used as boundary condition for the solution of the governing equations in the thermoelectric generator device domain which will decrease the computational cost when dealing with very complex channel configurations.
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    A computational analysis on convective heat transfer for impinging slot nanojets onto a moving hot body
    Cosanay, H; Oztop, HF; Selimefendigil, F
    Purpose The purpose of this study is to perform computational analysis on the steady flow and heat transfer due to a slot nanojet impingement onto a heated moving body. The object is moving at constant speed and nanoparticle is included in the heat transfer fluid. The unsteady flow effects and interactions of multiple impinging jets are also considered. Design/methodology/approach The finite volume method was used as the solver in the numerical simulation. The movement of the hot body in the channel is also considered. Influence of various pertinent parameters such as Reynolds number, jet to target surface spacing and solid nanoparticle volume fraction on the convective heat transfer characteristics are numerically studied in the transient regime. Findings It is found that the flow field and heat transfer becomes very complicated due to the interaction of multiple impinging jets with the movement of the hot body in the channel. Higher heat transfer rates are achieved with higher values of Reynolds number while the inclusion of nanoparticles resulted in a small impact on flow friction. The middle jet was found to play an important role in the heat transfer behavior while jet and moving body temperatures become equal after t = 80. Originality/value Even though some studies exist for the application of jet impingement heat transfer for a moving plate, the configuration with a solid moving hot body on a moving belt under the impacts of unsteady flow effects and interactions of multiple impinging jets have never been considered. The results of the present study will be helpful in the design and optimization of various systems related to convective drying of products, metal processing industry, thermal management in electronic cooling and many other systems.
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    Mixed convection and entropy generation of nanofluid flow in a vented cavity under the influence of inclined magnetic field
    Selimefendigil, F; Oztop, HF
    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.
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    Cooling of double PV-TEG combined units by using a T-shaped branching channel equipped with an inclined elastic fin
    Selimefendigil, F; Oztop, HF
    Modern energy technology systems including batteries, hydrogen storage units, electronic equipments and photovoltaic (PV) modules require effective cooling methods and thermal management techniques for performance improvements and safety of operation. In this study, a novel thermal management system for double PV units is proposed by using combined effects of inclined elastic fin in the T-shaped branching cooling channel and thermoelectric generator (TEG) modules. The FEM based numerical analysis is carried out for different Reynolds numbers (between 200 to 1200), fin lengths (between 0 and H), fin tilt (between 10 and 45), and fin position (yf between-H and H) where both rigid or elastic fin configurations are considered. Cell temperature drops of 14 degrees C and 15.48 degrees C are seen in PV1 and PV2 when Reynolds number (Re) is raised from 200 to 1200 using a rigid fin while average temperatures become 2 degrees C and 0.5 degrees C higher at the highest Re when elastic finis used. Poor thermal transport is observed at the fin location of yf=-H. Fins and higher Re significantly lower the PV surface temperature of both PVs in double PV-TEG combined system. When elastic and rigid fins are used at the highest Re, the temperature of PV1 is lowered by about 14.5 degrees C and 16.7 degrees C compared to the reference configuration of the no-fin case at Re=200, while the temperature of PV2 is lowered by about 12 degrees C and 11.2 degrees C. PV's performance is estimated using artificial neural network model for different flow rates, fin lengths, and fin inclinations (both elastic and rigid scenarios).
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    MIXED CONVECTION AND ENTROPY GENERATION OF A NANOFLUID FILLED CAVITY WITH A CORNER PARTITION AND FLEXIBLEWALL
    Selimefendigil, F; Oztop, HF
    In this study, the effects of a conductive corner partition and flexible sidewall in a CuO-water nanofluid-filled lid-driven square enclosure on mixed convective heat transfer were numerically examined using the finite element method. The top wall of the square cavity is moving with constant speed and the bottom wall of the cavity is heated. The side wall is made flexible. The effects of the Richardson number (between 0.01 and 20), elastic modulus of the flexible wall (between 103 and 105), size of the corner partition (between 0 and 0.6), and solid particle volume fraction (between 0 and 0.05) on the fluid flow, heat transfer characteristics and entropy generation rate were numerically investigated. It was observed that local and average heat transfer enhances for higher values of the Richardson number, elastic modulus of the flexible wall and solid particle volume fraction of the nanoparticles. An average heat transfer enhancement of 38.34% was obtained when the elastic modulus of the flexible wall was reduced from 105 to 103, and 32.10% of the average Nusselt number enhancement was obtained for 5% nanoparticle addition to the base fluid. The presence of the conductive corner partition deteriorated the local and average heat transfer, and average heat transfer reduction for 23.78% of was observed for a partition size of 0.6. Entropy generation rates for the fluid domain and solid domain of the conductive partition were found to be affected by the variation of those parameters.
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    Combined effects of local curvature and elasticity of an isothermal wall for jet impingement cooling under magnetic field effects
    Selimefendigil, F; Çogan, M; Oztop, HF
    The aim of this study is to examine the effects of local curvature and elastic wall effects of an isothermal hot wall for the purpose of jet impingement cooling performance. Finite element method was used with ALE. Different important parametric effects such as Re number (between 100 and 700), Ha number (between 0 and 20), elasticity (between 10(4) and 10(9)), curvature of the surface (elliptic, radius ratio between 1 and 0.25) and nanoparticle volume fraction (between 0 and 0.05) on the cooling performance were investigated numerically. The results showed that the average Nu number enhances for higher Hartmann number, higher values of elastic modulus of partly flexible wall and higher nanoparticle volume fraction. When the magnetic field is imposed at the highest strength, there is an increase of 3.85% in the average Nu for the curved elastic wall whereas it is 89.22% for the hot part above it, which is due to the vortex suppression effects. Nanoparticle inclusion in the base fluid improves the heat transfer rate by about 27.6% in the absence of magnetic field whereas it is 20.5% under the effects of magnetic field at Ha=20. Curvature effects become important for higher Re numbers and at Re=700, there is 14.11% variation in the average Nu between the cases with the lowest and highest radius ratio. The elastic wall effects on the heat transfer are reduced with the increased curvature of the bottom wall.
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    MHD conjugate natural convection in a porous cavity involving a curved conductive partition and estimations by using Long Short-Term Memory Networks
    Selimefendigil, F; Akbulut, Y; Sengur, A; Oztop, HF
    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 104\ and 106 Hartmann number (between 0 and 60), Darcy number (between 5x10-4and 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 105Curvature 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.
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    EXERGETIC PERFORMANCE OF VAPOR-COMPRESSION REFRIGERATION SYSTEM WITH TiO2 NANOADDITIVE IN THE COMPRESSOR OIL
    Selimefendigil, F; Oztop, HF
    Exergy analysis of a vapor-compression refrigeration system with TiO2 nanoadditives in the compressor oil was performed. Two-step method was used for the preparation of nanooil for various solid particle volume fractions between 0% and 1%. Irreversibilities were determined by using the Second law of thermodynamics. It is found that a reduction in total irreversibility is achieved with nano-particle inclusion and it was significant for higher particle volume fraction.
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    EFFECTS OF AN ADIABATIC FIN ON THE MIXED CONVECTION HEAT TRANSFER IN A SQUARE CAVITY WITH TWO VENTILATION PORTS
    Selimefendigil, F; Oztop, HF
    In this study, a square cavity with two ventilation ports in the presence of an adiabatic fin of different lengths placed on the walls of the cavity is numerically analyzed for the mixed convection case for a range of Richardson numbers (Ri = 0.1, 1, 10, 100) and at Reynolds number of 300. The effect of the fin height, placement of the fin on each of the four walls of the cavity and Richardson number on the heat transfer and fluid flow characteristics is numerically analyzed. The results are presented in terms of streamlines, isotherm plots, and averaged Nusselt number plots. It is observed that for the convection dominated case, fin length and its position on the one of the four walls of the cavity do not alter the the performance whereas when the buoyancy effects become important thermal performance increases for high fin length.
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    Impacts of elasticity and porosity of the channels on the performance features of thermoelectric module mounted system and efficient computations with multi-proper orthogonal decomposition approach
    Selimefendigil, F; Oztop, HF; Doranehgard, MH
    Effects of wall elasticity and porosity of the channel on the performance characteristics of TEG module integrated system are explored numerically with finite element method. A porous layer in the lower channel is introduced with hybrid nanoparticles in the fluid. Effects of different values of elastic modulus of the top and bottom channel walls (5 & times;103 <= E1,& nbsp;E2 & nbsp;<=& nbsp;1010), Darcy number (5 & times;10 & minus;4 & nbsp;<=& nbsp;Da & nbsp;<=& nbsp;5 & times;10 & minus;1), porous layer height (0.2H & nbsp;<=& nbsp;py & nbsp;<=& nbsp;0.8H) and length in flow direction (0.25L & nbsp;<=& nbsp;px & nbsp;<=& nbsp;0.85L), Reynolds number (200 & nbsp;<=& nbsp;Re & nbsp;<=& nbsp;1000) and hybrid nanoparticle volume fraction (0 & nbsp;<=phi <=& nbsp;2%) on the convection and power generation are analyzed. The presence of elastic walls may affect the flow field in local regions but the overall impact on the power variation is slight while 2.8%& nbsp;variation is obtained. The presence of the porous layer altered the power generation features while increasing the permeability and height of the porous layer resulted in higher thermoelectric power generation. The increment amounts are 32%& nbsp;for the highest permeability and 17%& nbsp;for the highest porous layer height. The length of porous layer in the flow direction has slight impact on power generation features while introducing nano-sized particles further enhanced the power by about 15%& nbsp;at the highest & nbsp;phi. The computational cost of generated power is drastically reduced from 2.5 h for full coupled model to two minutes by using a multi-POD approach.& nbsp; (c) 2021 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
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    MHD Mixed Convection and Entropy Generation in a Lid-Driven Triangular Cavity for Various Electrical Conductivity Models
    Chamkha, AJ; Selimefendigil, F; Oztop, HF
    In this study, effects of different electrical conductivity models for magneto- hydrodynamic mixed convection of nanofluids in a lid-driven triangular cavity was numerically investigated with a finite element method. Effects of Richardson number and Hartmann number on the convective heat transfer characteristics were analyzed for various electrical conductivity models of nanofluids. Average Nusselt number decreases for higher Hartmann and Richardson numbers. Discrepancies in the local and average heat transfer exist between different electrical conductivity models, which is higher for higher values of Richardson number and Hartmann number. The total entropy generation rate was found reduced with higher values of Richardson number and Hartmann number while discrepancies exist between various electrical conductivity models. When the magnetic field is imposed, different behaviors of entropy generation rate versus solid particle volume fraction curve is obtained and it is dependent upon the range of solid particle volume fraction.
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    MHD mixed convection in a nanofluid filled vertical lid-driven cavity having a flexible fin attached to its upper wall
    Selimefendigil, F; Oztop, HF; Chamkha, AJ
    In this study, fluid flow and heat transfer in a vertical lid-driven CuO-water nanofluid filled square cavity with a flexible fin attached to its upper wall under the influence of an inclined magnetic field are numerically investigated. The left vertical wall of the cavity is colder than right vertical wall, and it moves in + y direction with constant speed. Horizontal walls of the cavity are insulated. The governing equations are solved with finite element method. The arbitrary Lagrangian-Eulerian method is used to describe the fluid motion within the cavity for the flexible fin in the fluid-structure interaction model. The influence of Richardson number (between 0.01 and 100), Hartmann number (between 0 and 50), inclination angle of the magnetic field (between 0 and 90%), nanoparticle volume fraction (between 0 and 0.05) and Young's modulus of flexible fin (between 250 and 5000) on the flow and heat transfer were numerically studied. It is observed that the presence of the elastic fin affects the flow field and thermal characteristics of the cavity. The local and average heat transfer enhance as the Richardson number, solid volume fraction of the nanoparticle increase whereas deteriorate as the value of the Hartmann number and inclination angle of the magnetic field increases due to the dampening of the fluid motion with Lorentz forces. The addition of the nanoparticles is more effective along the lower part of the right vertical wall where the heat transfer process is effective. The average heat transfer increases by 28.96% for solid volume fraction of 0.05% compared to base fluid when the flexible fin is attached to the upper wall. The average heat transfer deteriorates by 10.10% for cavity with and without fin at Hartmann number of 50 compared to the case without magnetic field. The average heat transfer enhances as the Young's modulus of the flexible fin decreases and the average Nusselt number increases by 13.24% for Young's modulus of 250 compared to configuration for the cavity having the Young's modulus of 5000.
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    Natural convection in a CuO-water nanofluid filled cavity under the effect of an inclined magnetic field and phase change material (PCM) attached to its vertical wall
    Selimefendigil, F; Oztop, HF; Chamkha, AJ
    In this study, natural convection of CuO-water nanofluid in a square cavity with a conductive partition and a phase change material (PCM) attached to its vertical wall is numerically analyzed under the effect of an uniform inclined magnetic field by using finite element method. Effects of various pertinent parameters such as Rayleigh number (between 105 and 106), Hartmann number (between 0 and 100), magnetic inclination angle (between 0 degrees and 90 degrees), PCM height (between 0.2H and 0.8H), PCM length (between 0.1H and 0.8H), thermal conductivity ratio (between 0.1 and 100) and solid nanoparticle volume fraction (between 0 and 0.04) on the fluid flow and thermal characteristics were numerically analyzed. It was observed that when magnetic field is imposed, more reduction in average Nusselt number for water is obtained as compared to nanofluid which is 31.81% for the nanofluid at the highest particle volume fraction. The average heat transfer augments with magnetic inclination angle, but it is less than 5%. When the height of the PCM is increased which is from 0.2H to 0.8H, local and average Nusselt number reduced which is 42.14% . However, the length of the PCM is not significant on the heat transfer enhancement. When the conductivity ratio of the PCM to the base fluid within the cavity is increased from 0.1 to 10, 29.5% of the average Nusselt number enhancement is achieved.
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    Thermal management and power generation characteristics in a bifurcating channel by using a piezo-embedded inclined elastic fin assembly during turbulent forced convection of ternary nanofluid
    Selimefendigil, F; Oztop, HF
    Numerous engineering systems use piezoelectric energy harvesters (PE-EHs), which have several benefits including low cost, simplicity, better power density, and ease of installation. They can be used in different applications for energy harvesting and different external sources such as wind and vortex induced vibrations due to fluid-structure interaction can be utilized. This study uses a unique elastic fin PE/EH assembly for power generation, thermal management, and flow control in a bifurcating channel. Performance of the system is improved by using ternary nanofluid in the channel cooling system. Galerkin weighted residual FEM with ALE is used as the solution method. The convective heat transfer performance and power generation by the EH device are investigated in relation to the varying following parameters: Reynolds number (Re between 10000 and 30000), PE-EH inclination (y between 0 and 60), fin horizontal location (xj j between -H and H), and nanoparticle loading in the base fluid (cent between 0 and 0.03). The vortex size and distribution near the junction are significantly influenced by the fin inclination and horizontal location of the fin assembly within the bifurcating channel. When varying other parameters of interest, using nanofluid at the highest loading results in significant deflection of the fin assembly and power generation within the PE-EH. Enhancement factors (EFs) for power generation becomes 15.6 and 39.8 when cases of lowest and highest Re are compared with pure fluid and nanofluid while they are 2.93 and 3.38 for thermal performance improvements. Fin inclination of y = 30 is found as the optimum inclination for achieving the highest power from the assembly. Higher inclination of elastic fin/PE-EH assembly results in cooling performance deterioration while average Nu reduces by a factor of 2.94 by varying inclination from y = 30 to y = 60 with nanofluid. For power generation, effects of using nanofluid with varying inclination is significant and EF becomes 252 from y = 0 to y = 30. There are opposing tendencies for the device's power generation and cooling performance enhancement when the fin's horizontal placement is changed. EF for average Nu is 7.25 for varying fin location. As the loading of nanoparticle inside the base fluid increases, the average Nu and generated power exhibit non-linear rising characteristics. Polynomial type correlations are provided for the average Nu and power from the device by varying elastic fin assembly inclination and nanoparticle solid volume fraction. Potential of using hybrid nanofluid in PE-EH embedded thermo-fluid system is shown. The design, development, and optimization of self-sufficient power production systems that may be used to various thermo-fluid systems, such as electronic cooling and thermal control in a range of heat transfer devices, may benefit from the findings.
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    A REVIEW ON COMPUTATIONAL FLUID DYNAMICS SIMULATION METHODS FOR DIFFERENT CONVECTIVE DRYING APPLICATIONS
    Coban, SO; Selimefendigil, F; Oztop, HF; Hepbasli, A
    This paper focuses on the CFD studies on one of the commonly used drying pro-cesses for different applications. First, a brief information about drying is given with determining important properties that effect drying characteristics. Next, ba-sic principles of CFD modelling are explained while capabilities of computational processing are presented. A detailed literature survey about CFD studies in con-vective drying process is then conducted. Finally, some sound concluding remarks are listed. It may be concluded that the CFD is a powerful and flexible tool that can be adopted to many different physical situations including complex scenarios, results of CFD simulations represent good predictions for fluid-flow, heat and mass transfer of various drying methods and those numerical studies can be used for validation and controlling of applicability of new drying systems.
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    Analysis of mixed convection and entropy generation of nanofluid filled triangular enclosure with a flexible sidewall under the influence of a rotating cylinder
    Selimefendigil, F; Oztop, HF; Chamkha, AJ
    In this study, mixed convection and entropy generation in a nanofluid filled triangular cavity under the influence of rotating cylinder and flexible sidewall were numerically analyzed with finite element method. The inclined sidewall was cooled while the left vertical wall is partially heated. Heat transfer rate enhances as the values of Rayleigh number, angular rotational velocity of the cylinder, elastic modulus of the flexible sidewall and solid nanoparticles volume fraction increase. Nusselt number enhances more in the counter-clockwise direction of the cylinder as compared to clockwise directional rotation and 13.55% of average heat transfer enhancement was achieved for =3000 when compared to motionless cylinder. Average Nusselt number increases by about 30.50% when the elastic modulus of the flexible wall is changed from 500 to 105. The changes in the velocity profiles are significant for the lower part of the triangular enclosure with respect to changes in angular rotational velocity and elastic modulus as compared to upper part of the cavity. Adding nanoparticles increases heat transfer especially for the lower part of the cavity and 49.63% of heat transfer enhancement was achieved for the highest volume fraction when compared to base fluid. Normalized total entropy generation rates enhance for higher values of elastic modulus of the flexible wall, angular rotational speed of the circular cylinder and nanoparticle volume fractions.